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39291 Publications

Antihypertensive drug classes, not blood pressure, are associated with cerebral perfusion. Results from the PREvention of Dementia by Intensive VAscular care (PREDIVA) study

van Dalen, J.; Mutsaerts, H.; Petr, J.; van Charante, M. E.; van Gool, W.; Nederveen, A.; Richard, E.

Background: Constant cerebral blood flow (CBF) is fundamental to cerebral function. With aging and chronic hypertension, arteriolar damage may disrupt the CBF autoregulatory capacity. This might cause CBF to fluctuate with blood pressure (BP) levels, low BP and antihypertensive medication (AHM), potentially evoking hypoperfusion. We investigated the cross-sectional and longitudinal relations of BP and AHM with cerebral perfusion using arterial spin labeling (ASL).
Methods: In 186 community-dwelling individuals with hypertension (77±3 years, 53% female), 125 (67%) with 3-year follow-up (Figure 1), we assessed grey matter (GM) and white matter (WM) CBF (ml/100g/min) and the spatial coefficient of variation (CoV; SD CBF/mean CBF). Cross-sectional associations were assessed combining baseline and follow-up data using mixed models, longitudinal associations using linear regression assessing change, adjusted for baseline. We additionally adjusted for age, sex, AHM, stroke and parenchymal fraction.
Results: Cross-sectionally, higher diastolic BP was associated with lower GM and WM CBF (Table 1). AHM were associated with lower GM CBF and higher spatial CoV. Since calcium channel blockers (CCB) and angiotensin receptor blockers (ARB) in our main study were specifically associated with lower dementia risk compared to other AHM, we assessed these separately. Other AHM were associated with lower GM and WM CBF, while CCBs and ARBs were not. There were no correlations between BP change and perfusion changes (Table 2). We observed no J-shaped relationships.
Discussion: We found no evidence for any direct relation between BP and cerebral perfusion. Possibly, higher diastolic BP was associated with lower CBF by being a marker of more severe long-standing hypertension evoking vascular damage. Our finding that ARBs and CCBs are relatively protective of CBF compared to other AHM is consistent with findings of a protective effect of these AHM classes on dementia incidence, and could influence future treatment.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28289

Cognitive complaints associated with spatial coefficient of cerebral blood flow in community-dwelling older people in the PREvention of Dementia by Intensive VAscular care (PREDIVA) study

van Dalen, J.; Mutsaerts, H.; Petr, J.; van Charante, M. E.; van Gool, W.; Nederveen, A.; Richard, E.

Background: Low cerebral perfusion is cross-sectionally associated with dementia and predicts accelerated dementia progression. Hypothetically, impaired cerebral autoregulation, associated with aging and hypertension, and consequent cerebral hypoperfusion may contribute to the development of old-age cognitive decline. We investigated the cross-sectional and longitudinal relation between cognition and cerebral perfusion in older people without dementia using arterial spin labeling (ASL).
Methods: We included 186 community-dwelling individuals with hypertension (77 ±3 years, 53% female), 125 (67%) with 3-year follow-up neuroimaging (Figure 1). Cognitive measures included the mini-mental state examination (MMSE), visual association test (VAT) and subjective memory complaints (SMC) assessed using one question. Perfusion measures included grey matter (GM) cerebral blood flow (CBF, ml/100g/min), white matter (WM) CBF and spatial coefficient of variation (CoV; SD CBF/mean CBF, a potential proxy of vascular insufficiency). Cross-sectional analyses combined baseline and follow-up data using mixed models. Longitudinal analyses comprised linear regression of follow-up values adjusted for baseline. We additionally adjusted for age, sex, antihypertensives, WM hyperintensity volume and brain parenchymal fraction.
Results: Participants with memory complaints had a significantly higher CoV (Table 1). Furthermore, participants with better VAT scores had lower CoV, although this was attenuated after adjustment. Cerebral perfusion did not predict change in cognition (Table 2) but increasing CoV was associated with declining MMSE and, to a lesser extent, VAT scores. There were no significant relations between CBF and cognition.
Discussion: Our results suggest that higher CoV is associated with worse cognitive function and CoV changes concordantly with cognitive function. Spatial CoV may be a more sensitive cerebral hemodynamic parameter related to cerebral function compared to CBF. None of the cerebral perfusion parameters predicted future cognitive decline, suggesting that low perfusion does not precede cognitive decline in non-demented older people or that the perfusion measures employed were insufficiently sensitive.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28288

ASL-vascular insufficiency parameters can differentiate healthy controls from Alzheimer’s and Parkinson’s diseases

Ingala, S.; Petr, J.; Pålhaugen, L.; Gajdos, M.; Fladby, T.; Selnes, P.; Barkhof, F.; Bjørnerud, A.; Rektorova, I.; Mutsaerts, H.

Decreased/Poor vascular health - e.g. increased vascular resistance, tortuosity - may lead to a delayed arrival of labelled blood to brain tissue causing vascular artefacts on arterial spin labeling (ASL) images [Figure 1]. Although these artefacts are traditionally treated as a nuisance, their presence can be quantified by the spatial coefficient of variance (CoV) parameter and used as an indication of vascular insufficiency. . Here, the goal was to investigate the ability of spatial CoV to assess the vascular health by comparing it between healthy controls and subjects with Alzheimer’s (AD) and Parkinson’s (PD) diseases.

Methods: We analyzed the MRI scans of 143 APGeM study participants, including healthy controls (HC, n=56) and subjects with AD- (n=41) or PD-related (n=46) mild cognitive impairment or dementia [Table]. We calculated CBF, spatial CoV, and WMH volume using ExploreASL [ref]. Pearson’s correlations of spatial CoV with age and WMH volume were investigated, as well as a t-test for the relation between spatial CoV and sex. A linear regression model was used to evaluate whether spatial CoV was able to discriminate HC vs. AD, HC vs. PD, and AD vs. PD after correction for age and sex.

Results: Spatial CoV measures showed a positive correlation with age (cor=0.35, p <0.001 and with WMH volume (cor=0.38, p <0.001 [Figure 2A], and differed between sexes (p <0.001). Differences in spatial CoV values were detected between HC and AD and between HC and PD subjects (p<0.05 in both cases) [Figure 2B]. With our model, spatial CoV was not able to discriminate between AD and PD.

Conclusions: These findings suggest that spatial CoV can provide insight in the vascular component of AD and PD pathologies. Validation of these results in larger cohorts and across a wider range of disorders might provide further insight in the relation between cerebrovascular health and neurodegeneration.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28287

Effects of intracranial stenosis on brain perfusion and cognitive performance in a memory clinic population

Hilal, S.; Mutsaerts, H.; Ferro, D.; Petr, J.; Kuijf, H.; Biessels, G.; Chen, C.

Background: Intracranial stenosis (ICS) contributes to cognitive dysfunction possibly via decreased cerebral blood flow (CBF). However, CBF measurements by Arterial Spin Labelling (ASL) are affected by vascular artefacts making it difficult to apply in elderly with large vessel disease. Recently, spatial coefficient of variance (CoV) is proposed as a robust estimate to quantify vascular artifacts and may be used as a proxy marker of large vessel insufficiency. We investigate the association of ICS with ASL measurements and its eventual effects on cognition in a memory clinic population.
Methods: We included 403 participants (mean age=72.3±7.9years, women=53.7%). ICS was graded as ≥50% stenosis in any intracranial vessel on 3D Time of Flight Magnetic Resonance Angiography. Gray matter spatial CoV and gray matter CBF were analyzed with ExploreASL from 2D EPI pseudo-continuous ASL images. Global cognition was assessed by a detailed neuropsychological test.
Results: ICS was present in 70 (17.4%) individuals. Persons with ICS had higher GM spatial CoV (mean difference (β)= 0.17, 95%CI: 0.07; 0.28, p=0.001) and lower CBF (β= -0.21, 95%CI: -0.33; -0.09), p=<0.001). This association persisted after partial volume correction of spatial CoV and CBF. The lateralization of spatial CoV and CBF (asymmetry index) (β for CoV: 0.23, 95%CI: 0.05; 0.40, p=0.013 and β for CBF: -0.22, 95%CI: -0.33; -0.11, p=<0.001) were correlated with ipsilateral stenosis. Spatial CoV was associated with worse cognition independent of CBF (β= -0.76, 95%CI: -1.09; -0.43, p=<0.001). Moreover, ICS was associated with global cognition, independent of gray matter CoV and CBF, although this effect attenuated in the presence of cortical microinfarcts (β= -0.23, 95%CI: -0.49; 0.02, p=0.072).
Conclusion: These findings suggest an association of ASL perfusion with ICS and cognition, which has a predominant component of large vessel insufficiency. Moreover, cortical microinfarcts mediate the link between ICS and cognition independent of large vessel insufficiency.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28286

Tissue inhibitor of proteinase-1 and cerebral blood flow in predementia

Pålhaugen, L.; Selnes, P.; Kirkeby, E.; Tecelao, S.; Ingala, S.; Petr, J.; Bjørnerud, A.; Mutsaerts, H.; Fladby, T.

Cerebrovascular disease (CVD) can increase the risk of dementia and is frequently seen in Alzheimer’s disease. Tissue inhibitor of proteinase-1 (TIMP-1) measured in cerebrospinal fluid (CBF) is considered a promising biomarker of subcortical small vessel disease (SSVD). In addition to inhibition of matrix metalloproteases, it occurs in several biological processes, such as protection of the blood brain barrier. This study explores how TIMP-1 is associated with CBF in amyloid and non-amyloid pre-dementia cases as well as in controls.

Cases and controls, aged 40-80, were included from the Norwegian multi-site study “DDI” (n=69, age=63.2 +/- SD, m/f=26/43). Participants underwent cognitive assessment, MRI and lumbar puncture. Cases were staged as Subjective Cognitive Decline (SCD) or Mild Cognitive Impairment (MCI). We stratified by A1-42 pathology (A+/-) using an amyloid-PET verified CSF cutoff. Cerebral blood flow (CBF) was measured with arterial spin labeling and analyzed using ExploreASL. Linear regression analysis was performed with TIMP-1 and CBF in total gray matter (GM), total white matter (WM) and several GM regions (frontal, temporal, insula, parietal, occipital, thalamus, putamen and caudate nucleus), adjusting for age and sex. CBF was log-transformed.

In the A- group (n=50, age=61.6, m/f=17/33, Controls/SCD/MCI=21/22/7) there was a significant positive relationship between TIMP-1 and CBF in total GM (=-0.46, p=0.001), total WM (=-0.44, p=0.002), frontal (=-0.41, p=0.004), temporal (=-0.45, p=0.001), insula (=-0.39, p=0.006), parietal (=-0.48, p<0.001), occipital (=-0.45, p=0.001), thalamus (=-0.53, p<0.001), putamen (=-0.41, p=0.004) and caudate nucleus (=-0.48, p=0.001) GM regions. There were no significant associations in the A+ group (n=19, age=67.4, m/f=9/10, Controls/SCD/MCI=2/7/10) or in the whole sample.

We found that TIMP-1 correlates positively with CBF in the A- group, whereas there were no significant association in the A+ group. Putatively, this may reflect different mechanisms for vascular pathology in the two groups.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Poster
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28285

Cortical microinfarcts in memory clinic patients are associated with reduced cerebral perfusion

Ferro, D.; Mutsaerts, H.; Hilal, S.; Kuijf, H.; Petersen, E.; Petr, J.; van Veluw, S.; Venketasubramanian, N.; Biessels, G.; Chen, C.

Background: Cerebral cortical microinfarcts (CMIs) are small ischemic lesions visible on autopsy and structural MRI. As CMIs occur/are observed more frequently in the cortical watershed areas, we hypothesize that hypoperfusion plays a role in their development. We investigated whether CMI presence is associated with decreased cerebral perfusion using arterial spin labeling (ASL).
Methods: We have analyzed 180 memory clinic patients (mean age 72 ± 9y, 51% male, 72% CMIs present ) with pCASL acquired at 3T MRI (PLD=xx ms, labeling duration=xx ms). Cerebral blood flow (CBF) was quantified (in ml/100g/min) and mean CBF and spatial coefficient of variation (CoV, quantitative proxy of transit time, expressed as SD of the CBF/mean CBF) was calculated in gray matter in each vascular territory. Vascular artefacts were observed in 33 patients due to prolonged transit time, and these were excluded from the CBF but not CoV analysis. CMIs were rated according to previously established criteria.
Results: In this cohort, CMIs presence was associated with a higher burden of cerebrovascular disease (Table 1). Patients with CMIs had lower CBF and a higher spatial CoV in the anterior circulatory territory, indicating a decreased perfusion and a delayed transit time (Table 1, Figure 1). The total number of CMIs was correlated to a lower CBF and a higher spatial CoV (p<.02). A sub-analysis in patients with unilateral CMI presence revealed no significant inter-hemisphere differences in CBF (n=27, .56 ±.7 ml/100g/min) or in CoV (n=36, .05 ±.25).
Conclusion: This is the first study to demonstrate that CMIs presence is associated with reduced global cerebral perfusion. Further research should identify at which level of the vascular tree the cause of hypoperfusion originates.

  • Contribution to proceedings
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China
  • Lecture (Conference)
    VasCog 2018 - The 9th International Conference of The International Society of Vascular Behavioural and Congnitive Disorders, 14.11.2018, Hong-Kong, China

Publ.-Id: 28284

µTRLFS: Spatially-resolved sorption studies of Eu(III) on Eibenstock granite with time-resolved laser fluorescence spectroscopy

Molodtsov, K.; Schymura, S.; Rothe, J.; Dardenne, K.; Krause, J.; Schmidt, M.

Finding a safe long-term repository for high-level nuclear waste is a highly relevant global issue. To that end, the interaction of radionuclides with mineral phases contained in possible host rocks and construction materials must be understood. On a time scale of up to one million years, especially the scenario of a water intrusion into the repository and thus dissolution of radionuclides has to be considered.

To investigate the sorption behaviour of actinides (e.g. Cm(III) and U(VI)O22+) and lanthanides (e.g. Eu(III)), time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method, because of its trace concentration sensitivity and capability to distinguish multiple species in complex systems. On the one hand this method gives the spectral information of the emitted fluorescence light, which allows determining the symmetry and the grade of complexation of the sorbed Ln/An. On the other hand the lifetimes of the excited electronic states provide information about the surrounding quenchers, mainly water. Typically, TRLFS investigations will focus on the interaction of an actinide with one relevant mineral phase. For a real rock formation, e.g. granite, sorption will however be a competitive process involving multiple mineral phases at the same time.

In this study a new method called µTRLFS is introduced, which will add a spatial dimension to TRLFS. By doing so, it is possible to separate the multi-phase system into discrete single-phase systems and therefore to make a step beyond model systems by investigating, for example whole natural granite rock with TRLFS. Because of its advantageous fluorescence properties, we use Eu(III) as an analogue for the trivalent actinides Am and Cm. Spatially resolved sorption experiments with Eu(III) on granite samples from Eibenstock, Germany are presented. These samples are excited by a focused laser beam at a wavelength of 394 nm, and scanned through the laser’s focal point by an XYZ-stage with a resolution of approximately 20 µm. Through this approach it becomes possible to characterize Eu(III) sorption on single grains of the complex material by mapping fluorescence intensity, F2/F1-band ratios, as well as fluorescence lifetimes.

A combination of spatially-resolved X-ray fluorescence spectroscopy (µXRF) and electron probe microanalysis (EPMA) is used to reveal the mineral phase composition in each point of measurement which can then be correlated to the µTRLFS maps. In addition, these methods provide impurity distributions of e.g. Fe or Mn as additional quenchers. By doing so, µTRLFS mapping of sorption capacity, complexation strength and surrounding quenchers can be correlated to phase distribution mappings and thus provide information about the sorption behaviour of each phase within the complete multi-phase system. The µTRLFS data can be directly compared to single phase TRLFS data of the main granite components quartz, feldspar, and mica. For verification, the Eu(III) distribution obtained from µTRLFS data will be compared to autoradiography images.

Keywords: µTRLFS; europium; sorption; granite

  • Poster
    10th International Conference on f-elements, 03.-06.09.2018, Lausanne, Schweiz
  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28283

µTRLFS: Spatially- and time-resolved laser fluorescence spectroscopy with Eu(III) as a fluorophore on Eibenstock granite

Molodtsov, K.; Schmidt, M.

Time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method to obtain information about the surrounding chemical environment of fluorophores with trace concentration sensitivity. This method allows determining the symmetry and grade of complexation of the fluorophore and provides information about the surrounding quenchers, mainly water as well. For highly heterogeneous systems however distinguishing and separating multiple binding species becomes an unsolvable problem. In this study a new method called µTRLFS is introduced, which will add a spatial dimension to TRLFS, giving the possibility to separate a multi-phase system into discrete single-phase systems. Because of its advantageous fluorescence properties we use europium as an analogue for Am(III) and Cm(III) to study the sorption behaviour of granite as a possible host rock for high-level nuclear waste repositories. Spatially resolved sorption experiments with Eu(III) on granite samples from Eibenstock, Germany are presented. These samples are excited by a focused and pulsed UV laser beam, and scanned with a resolution of 20 µm. Through this approach it becomes possible to characterize Eu(III) sorption on single grains of the complex material by mapping fluorescence intensity, band ratios, as well as lifetimes.

Keywords: µTRLFS; europium; sorption; granite

  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft Frühjahrstagung, 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 28282

The muon flux in the Felsenkeller shallow underground laboratory

Ludwig, F.; Wagner, L.; Al-Abdullah, T.; Barnaföldi, G. G.; Bemmerer, D.; Degering, D.; Surányi, G.; Zuber, K.

The muon intensity and angular distribution in the shallow-underground laboratory Felsenkeller in Dresden, Germany
have been studied using a portable muon detector based on the closed cathode chamber design. Data has been taken at
four positions in Felsenkeller tunnels VIII and IX, where a new 5 MV underground ion accelerator is being installed, and
in addition at four positions in Felsenkeller tunnel IV, which hosts a low-radioactivity counting facility. At each of the
eight positions studied, seven different orientations of the detector were used to compile a map of the upper hemisphere
with 0.85 ◦ angular resolution. The muon intensity is found to be suppressed by a factor of 40 due to the 45 m thick rock
overburden, corresponding to 140 meters water equivalent.
The angular data are matched by two different simulations taking into account the known geodetic features of the
terrain: First, simply by determining the cutoff energy using the projected slant depth in rock and the known muon
energy spectrum, and second, in a GEANT4 simulation propagating the muons through a column of rock equal to the
known slant depth. The present data are instrumental for studying muon-induced effects at these depths and also in the
planning of an active veto for accelerator-based underground nuclear astrophysics experiments.

Keywords: Muon intensity; Underground laboratories; GEANT4; nuclear astrophysics; wire chambers; muon tomography; muon radiography

Publ.-Id: 28281

Trivalent Actinide Incorporation into Zirconium(IV) oxide – Eu3+ and Cm3+ luminescence spectroscopic studies

Eibl, M.; Shaw, S.; Morris, K.; Hennig, C.; Stumpf, T.; Huittinen, N.

In a final repository for spent nuclear fuel (SNF), the mobilization of actinides from the UO2 matrix is a great concern for safety considerations. The SNF rods are surrounded by zircalloy cladding material, which, similarly to the UO2 waste matrix, has a very low solubility in aqueous solution. Despite the very good corrosion resistance of the cladding material, corrosion and dissolution are expected to occur together with the leaching of radionuclides from the SNF over geological timescales. Therefore, the dissolution of zircalloy and the formation of a corrosion layer mainly composed of zirconia (ZrO2) on the cladding surface may be accompanied by reactions with dissolved, long-lived radionuclides from the SNF matrix.
At ambient conditions zirconium oxide has a monoclinic (m) crystal structure. However, the incorporation of metal cations can stabilize the high-temperature zirconia phases, i.e. the tetragonal (t) and the cubic (c) phases, leading to the formation of stable structures at ambient conditions.[1] Such phase transformation may be expected when actinides from the SNF become incorporated and thus, immobilized within the zirconia corrosion layer.
In the present study the incorporation of aliovalent actinides in zirconia, and their stabilizing influence on the crystal structure, have been investigated. The crystallinity and structural properties of the resultant actinide-doped zirconia solids were investigated with powder x-ray diffraction (PXRD), while the local structure around the incorporated dopant was studied with laser-induced luminescence spectroscopy (TRLFS). Cm3+ and Eu3+ were taken as representatives for the trivalent actinides.
The PXRD results of calcined Eu3+ doped zirconia samples show that a systematic transformation of the monoclinic to the cubic phase via the tetragonal structure occurs as a function of increasing Eu3+ doping (Fig. 1, left) whilst the Eu3+ TRLFS results show a 7F1, 7F2 emission band splitting corresponding to a low symmetry environment despite the cubic bulk symmetry (Fig. 1, middle).

The Cm3+ co-doped luminescence spectra show strong red-shifts of the emission spectra in the cubic bulk system with a peak maximum of 643.9 nm (Fig. 1, right) which have been observed before.[2] Both spectroscopic methods point towards a strongly distorted local structure, caused by the effect of oxygen vacancies and lattice stress induced by the largely oversized dopant ions.

  • Lecture (Conference)
    4th International Workshop on Advanced Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28280

Pressure-tuning of the magnetic properties of the Heusler compound Mn2PtGa

Salazar Mejia, C.; Najak, A. K.; Felser, C.; Nicklas, M.

We report on the pressure-tuning of the magnetic properties of the Heusler alloy Mn2PtGa. At ambient pressure, Mn2PtGa orders ferrimagnetically below TC ≈ 222 K, followed by a first-order ferrimagnetic to antiferromagnetic transition around TFI-AF ≈ 102 K upon cooling. Magnetization measurements up to 1.2 GPa evidence a stabilization of the ferrimagnetic phase, i.e., TC increases while TFI-AF decreases upon application of pressure. The magnetic properties in the ferromagnetic phase are not altered upon increasing pressure. However, the fraction of the ferrimagnetic phase present in the inhomogeneous antiferromagnetic low-temperature phase increases with pressure.

Publ.-Id: 28279

Entwicklung einer alternativen Methode zur selektiven Laugung von Seltenen Erden aus Zirkonsilikaten

Balinski, A.; Scharf, C.

Zirkonsilikate spielen als Quelle für Seltene Erden trotz der geringen Belastung mit Uran und Thorium, des günstigeren Verhältnisses von schweren zu leichten Seltenen Erden und der Anwesenheit von wertvollen Begleitelementen immer noch eine untergeordnete Rolle. Eine industriell rentable Gewinnung von Seltenen Erden aus dieser Rohstoffgruppe hat sich trotz vieler initiierter Projekte bis auf eine Lagerstätte in Russland bisher nicht durchgesetzt. Der Grund dafür liegt in den geringen Konzentrationen der Zielelemente, der Kieselgelbildung während der Laugung und der Entstehung von komplexen Multielement-Laugungslösungen begründet. Die Arbeit beschäftigt sich mit der Entwicklung einer alternativen Methode zur Gewinnung von Seltenen Erden und der relevanten Begleitelemente unter Anwendung des unterschiedlichen Verhaltens der Sulfate der beiden Metallgruppen. Als Zwischenprodukte werden wässrige Phasen angereichert mit jeweils wertvollen Metallen beziehungsweise Seltenen Erden zur weiteren Raffination erzeugt.

  • Poster
    Jahrestreffen der Processnet-Fachgruppen Extraktion und Rohstoffe, 12.-13.03.2018, Frankfurt am Main, Deutschland

Publ.-Id: 28278

SE-FLECX-Projekt: alternative Ansätze zur Gewinnung von Seltenen Erden

Balinski, A.; Scharf, C.

Seltene Erden (Lanthanoide), eine Gruppe von 17 Elementen mit ähnlichen Eigenschaften, sind aus einer Vielzahl heutiger Produkte nicht mehr wegzudenken. Dazu gehören sowohl Gegenstände des täglichen Bedarfs wie z. B. LCD-Bildschirme oder Akkus für Laptops als auch hochspezifische Anwendungen wie z. B. Dauermagneten in Windkraftanlagen.
Um eine sichere Versorgung mit Seltenen Erden zu gewährleisten, müssen neue und innovative Methoden sowohl zur Aufbereitung von Erzen und Konzentraten als auch zur Verbesserung der weiteren Prozesskette durch Entwicklung von neuartigen Extraktionsmitteln gefunden werden. Das Forscherteam von „SE-FLECX“ nimmt die beiden Herausforderungen an, wobei drei Hauptziele im Fokus stehen: die Aufbereitung von unkonventionellen Rohstoffen, die Abtrennung der Actinoide und die selektive Auftrennung einzelner Seltenen Erden. Aufgrund der ähnlichen Eigenschaften der Elemente und der steigenden Komplexität der Erze ist die Bewältigung dieser Aufgaben entscheidend für die Erarbeitung von zukünftig durchsetzbaren Prozessen.

Keywords: Seltene Erden; Calixarene; unkonventionelle Rohstoffe; Flüssig-Flüssig-Extraktion

  • Lecture (Conference)
    r4-Clusterworkshop 2018, 10.-11.10.2018, Hannover, Deutschland

Publ.-Id: 28277

A Parallel Cellular Automata Lattice Boltzmann Method for Convection-Driven Solidification

Kao, A.; Krastins, I.; Alexandrakis, M.; Shevchenko, N.; Eckert, S.; Pericleous, K.

This paper presents a novel coupling of numerical techniques that enable 3D convection-driven microstructure simulations to be conducted on practical time scales appropriate for small size components or experiments. On the microstructure side, the cellular automata method is efficient for relatively large-scale simulations, while the lattice Boltzmann method provides one of the fastest transient hydrodynamic CFD solvers. Both of these methods have been parallelized and coupled in a single code, allowing resolution of large-scale convection-driven solidification problems. The numerical model is validated against benchmark cases, extended to capture solute plumes in directional solidification and finally used to model alloy solidification of an entire differentially heated cavity capturing both microstructural and meso/macro-scale phenomena.

Keywords: Lattice Boltzmann method; large-scale simulations; convection-driven solidification; fluid flow

Publ.-Id: 28276

SE-FLECX: Selektive Flüssig-Flüssig-Extraktion von Lanthanoiden und Actinoiden durch präorganisierte Calixarene

Balinski, A.; Scharf, C.

Zur Gewährleistung der sicheren Versorgung mit Seltenen Erden (Sc, Y und Lanthanoide) müssen innovative Methoden sowohl zur Aufbereitung von Rohstoffen als auch zur Verbesserung der weiteren Prozesskette durch Entwicklung von neuartigen Extraktionsmitteln gefunden werden. Im SE-FLECX-Projekt sollen diese Ziele durch die Anwendung der besonderen Eigenschaften von Calix[4]arenen und eine gezielte Aufbereitung der unkonventionellen Rohstoffquellen erreicht werden.
Die Entwicklung neuartiger Extraktionsmittel erfolgte durch die gezielte Substitution an makrocyclischen Calix[4]arenen. Zwei Typen von Liganden wurden für die effiziente Trennung der Actinoide (Typ A) und der Seltenen Erden (Typ B) synthetisiert, charakterisiert und erprobt.
Im Laufe des Projektes wurden zwei Vertreter gefunden, die aus einfach zusammengesetzten Systemen (Modelllösungen) sowohl Seltene Erden quantitativ in einer Stufe extrahieren (FG20) als auch U(VI) sehr effizient abtrennen können (AJ46).
Bei AJ46 wurde neben der Fähigkeit zur Uranabtrennung ebenso eine starke Affinität zu Schweren Seltenen Erden festgestellt. Sein industrieller Einsatz wurde jedoch aufgrund der hohen Synthesekosten als unwirtschaftlich bewertet. Diese konnten durch die Entwicklung einer alternativen Syntheseroute signifikant reduziert werden.

Keywords: Seltene Erden; Calixarene; Flüssig-Flüssig-Extraktion

  • Lecture (Conference)
    r4-Statuskonferenz, 31.01.-01.02.2018, Berlin, Deutschland
  • Poster
    r4-Statuskonferenz 2018, 31.01.-01.02.2018, Berlin, Deutschland
  • Poster
    24 Stunden für Ressourceneffizienz", Ressourceneffizienz-Kongress für Nachwuchsforscherinnen und Nachwuchsforscher, 14.-15.02.2017, Pforzheim, Deutschland

Publ.-Id: 28275

X-ray visualisation of melt flow effects on dendritic solidification

Shevchenko, N.; Keplinger, O.; Grenzer, J.; Rack, A.; Eckert, S.

X-ray radiography is an effective tool for investigating flow phenomena and solidification processes in opaque metallic alloys. This work is devoted to complex interaction between dendritic growth and melt flow during solidification of Ga-In alloys under natural and forced convection. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. The conventional X-ray radioscopic experiments with sufficient spatial resolution (5-10 µm) deliver simultaneous information of both the dendrite structure and the flow patterns ahead of the solidification front and especially near the mushy zone. Melt convection alters the solutal field near the solidification front leading to different microstructures or even to the formation of freckle defects. The coarsening stage of dendritic structure is characterized by transformation of the sidearm morphology present after growth. The direct investigation of dendritic sidearm evolution during coarsening appears to be rather complex and impose high requirements with respect to the spatial and temporal resolution and sensitivity of the detector. The synchrotron imaging experiments with solidifying Ga-In alloys were performed at the BM20 and ID19 beamlines (ESRF, France) at a spatial resolution of < 1 µm. The present measurements provide real-time in-situ data on three phenomena that are of major importance in coarsening of dendrites: sidearm retraction, pinch-off and coalescence of neighboring sidearms. Using an advanced image analysis of high temporal and spatial resolution experimental data allows us to verify existing microstructural models.

Keywords: X-ray radiography; dendritic growth; melt flow; sidearm evolution

  • Lecture (Conference)
    32nd International Congress on High Speed Imaging and Photonics, 09.-12.10.2018, Twente, The Netherlands

Publ.-Id: 28274

In-situ observation of dendritic growth under the influence of electromagnetically driven flow

Shevchenko, N.; Keplinger, O.; Eckert, S.

Many studies have demonstrated that the application of electromagnetic stirring enhances the area of equiaxed grains and reduces the mean grain size (see e.g. [1-2]). It is widely accepted that flow-induced grain refinement and the CET (columnar to equiaxed transition) in metallic alloys is triggered by the appearance of additional dendrite fragments originating from the columnar front. The mechanism for grain multiplication by melt convection is supposed to be complex and is not fully understood until now.
The X-ray radiography was used for an in-situ study of the effect of electromagnetic stirring during the solidification of a Ga-25wt%In alloy in a Hele-Shaw cell [3]. The experimental setup was extended by a magnetic wheel, which allowed for controlled excitation of a melt flow in the liquid phase. The forced flow induces different effects on dendrite morphology, such as the uneven growth of primary trunks or lateral branches, remelting of single dendrites and also of lager dendrite ensembles, freckle formation, changes the inclination angle of the dendrites and leads to an increasing arm spacing. These effects are primarily governed by the convective redistribution of solute. Figure 1 demonstrates an interesting effect of "repairing" of a segregation channel (see the right-hand side part of Fig. 1a) after switching off the magnetic wheel (Fig 1b). It can be seen that an area with equiaxed or fine dendrites was formed instead of a segregation channel. The appearance of small equiaxed grains in the undercooled melt in the segregation pools is triggered by quick redistribution of solute after stopping the magnetic pump.
1. B. Willers et al, Materials Science and Engineering A 402 (2005) 55-65
2. T. Campanella et al, Metallurgical and Materials Transactions A 35 (2004) 3201-3210
3. N. Shevchenko et al, Journal of Crystal Growth 417 (2015) 1-8

Keywords: Electromagnetic stirring; solidification; X-ray radiography; freckle formation; Ga-In alloy

  • Lecture (Conference)
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Awaji, Hyogo, Japan

Publ.-Id: 28273

Pd catalyzed cross-coupling of [11C]MeLi and its application in the synthesis and evaluation of a potential PET tracer for the vesicular acetylcholine transporter (VAChT)

Helbert, H.; Wenzel, B.; Deuther-Conrad, W.; Luurtsema, G.; Szymanskic, W.; Brust, P.; Feringa, B. L.; Dierckx, R. A. J. O.; Elsinga, P. H.

The short half-life of 11C (t1/2 = 20.33 min) requires ultra-fast reactivity in order to perform efficient labelling of PET tracers. A recently discovered cross-coupling methodology1 enables the coupling between aryl bromides and organolithium reagents within seconds and therefore can be an attractive strategy to access 11C-labelled compounds. In this work several clinically relevant structures were labelled via this method. The scope of the reaction was further explored and expanded, allowing radiolabelling of highly reactive compounds, such as aldehydes. Then we focused our attention on the development of a new potential tracer for vesicular acetylcholine transporter (VAChT) which was enabled by this novel cross-coupling of [ 11C]MeLi.

[11C]MeLi was prepared via lithium-halogen exchange by trapping [11C]MeI in a solution of n-BuLi. The prepared [11C]MeLi was further reacted in a Pd catalyzed cross-coupling reaction with aryl bromides at r.t. for 4 minutes. After quench and evaporation of the solvent, the mixture was directly purified by HPLC. A series of synthesized vesamicol derivatives were subjected to affinity studies.

Scheme 1: Relevant structures for PET labelled via cross-coupling of [11C]MeLi

Several clinically relevant structures with application in breast cancer imaging and early diagnosis of Alzheimer’s disease had been successfully labelled using this procedure (scheme 1). Employing this same methylation strategy, novel potential tracers for VAChT were synthesized and evaluated in vitro, identifying a compound with good selectivity for VAChT versus σ1 and σ2 and compared to established (-)FEOBV.

Table 1: In vitro affinities measured on rat VAChT (VAChT-PC12), n = 3; human σ1 (hS1-HEK293), n = 3; rat σ2 (rat liver), n = 2
Affinity (nM) (±)1-Me (±)2-Me (±)3-Me (-)3-Me (-)FEOBV
Ki(VAChT) 8.7 ± 0.1 7.2 ± 1.2 27 ± 18 28 ± 16 7 ± 2
Ki(σ1) 2.1 ± 0.5 5.3 ± 1.7 362 ± 36 382 ± 166 2275 ± 390
Ki(σ2) 373 ± 147 618 ± 257 1650 ± 650 >5000 2118 ± 1058
σ1/VAChT : σ2/VAChT 0.2 : 43 0.7 : 86 13 : 50 14 : >150 >300 : >300

A new labelling methodology was successfully applied to the synthesis of clinically interesting radiotracers, providing the purified target molecules in R.C.Y. ranging from 34% to 56% within 30 to 40 minutes (EOB). This procedure offers new opportunities in the development of novel tracers, illustrated by the synthesis of a novel VAChT tracer.

1Heijnen D, Tosi F, Vila C, Stuart M, Elsinga P, Szymanski W, Feringa B. Angew. Chem. Int. Ed. 2017, 56 (12), 3354-3359

  • Lecture (Conference)
    ISRS 2019, 26.05.-01.06.2019, Beijing, China
  • Lecture (Conference)
    Annual EANM congress 2019, 12.10.2019, Barcelona, Spanien

Publ.-Id: 28272

Characterization of Isostructural An(IV) Complexes with Hetero-donor Imine Ligands

Radoske, T.; Schöne, S.; Kaden, P.; Ikeda-Ohno, A.; Stumpf, T.

The coordination chemistry of actinides (An) serves as fundamental knowledge for chemical engineering and environmental science related to the nuclear industry.[1] However, as compared with other transition metals, the basic chemistry of An is far less explored. The chemistry of An is complicated by, e.g., various possible oxidation states ranging from II to VII for the early An. One possible approach to understand the chemical nature of the An series is the comparison of isostructural compounds containing different actinides with the same oxidation state.[2,3,4] With this approach, the relative changes observed among the An series could allow us to gain insight into their unique chemical nature, such as electronic properties originating from their f-electron orbitals. One major question remaining in the field of An chemistry is the degree of “covalency” across the An series.[5] In order to study the “covalency” across the An series, one would require to perform a systematic study on a wide series of An, including transuranium (TRU) elements. Nonetheless, precedent studies covering TRU elements are rather scarce. This background motivates us to perform the current study focusing on a systematic comparison of the isostructural An complexes (Th, U and Np).
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)), which is dominant particularly under anoxic environmental conditions.[1] Synthesis of their compounds and the experiments should be conducted under inert and water-free atmosphere. The ligands used in this study are a hetero-donor imine ligand of salen and its derivatives (Fig. 1). These ligands have a capability to coordinate to metal ions tetradentately and exhibit both the hard- (oxygen) and medium-donor (nitrogen) characters, which could be a simple analog of natural occurring organic molecules. The eightfold coordination, which is often preferred for An complexes, can be readily achieved with these ligands by coordination of two ligand molecules. Salen and its derivatives have also been employed as a framework for catalytic and extraction agents.[6,7]

  • Lecture (Conference)
    Plutonium Futures 2018, 11.09.2018, San Diego, Vereinigte Staaten von Amerika

Publ.-Id: 28271

Actinide Bonding – Comparative Study of Isostructural An(IV) Imine Complexes

Radoske, T.; Kaden, P.; Schöne, S.; Ikeda-Ohno, A.; Stumpf, T.

Because of their unique electronic properties originating from 5f-orbitals, the coordination chemistry of actinides (An) is still an attractive research field in terms not only of nuclear engineering but also of basic chemistry. In particular, the early An show profound complex chemistry due to a wide variety of possible oxidation states ranging from +II to +VII, which is in contrast to the dominant trivalent state for their chemical analog of lanthanides. The aim of our research activities is to gain knowledge about the interaction of An with a variety of hard- and soft-donor ligands, eventually providing a comprehensive understanding of the electronic nature of actinide compounds. The ligands used in this study possess both O- (i.e. hard) and N-donor (soft) containing functionalities (Fig.1) and could also be considered as a simplified model of naturally relevant organic O/N-donor ligands.
A series of single crystals of [AnIV(Lp)2] complexes were synthesized from the tetrachloride compounds of An = Th, U and Np. SC-XRD measurements on the obtained crystals reveal their crystal structures, all showing the eight-fold coordination of the metal centre with the ligands on their primary coordination sphere, forming a trigonal dodecahedral geometry around the metal centre.
1H-NMR spectra of the dissolved complexes [ThIV(Le)2], [UIV(Le)2], [CeIV(Le)2] and the pure ligand in solution were recorded. The observed shifts show unique features when comparing isostructural diamagnetic compounds of lanthanides and actinides, which can not be explained by charge density differences.

  • Lecture (Conference)
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 10.07.2018, Dresden, Deutschland

Publ.-Id: 28270

Atomic-level thermodynamics and kinetics in solids: Examples for Si, Ge, and SiC

Posselt, M.

In this talk examples of atomistic simulations on thermodynamics and kinetics in Si, Ge, and SiC are presented.

Keywords: Atomic-level simulations; thermodynamics; Si; Ge; SiC

Related publications

  • Lecture (others)
    Seminar "Topical Problems in Theoretical Physics", 28.11.2018, Chemnitz, Deutschland

Publ.-Id: 28269

Age and genesis of polymetallic veins in the Freiberg district, Erzgebirge, Germany: constraints from radiogenic isotopes

Ostendorf, J.; Henjes-Kunst, F.; Seifert, T.; Gutzmer, J.

The Freiberg mining district in the Erzgebirge hosts three principal types of polymetallic veins. These are (1) the quartz-bearing polymetallic sulfide type, (2) the carbonate-bearing polymetallic sulfide type, and (3) the barite-fluorite-sulfide type. We investigated the genesis of each vein-type using Rb-Sr sphalerite geochronology, Sm-Nd fluorite geochronology, and Pb, Sr, and Nd isotope systematics of ore and gangue minerals. Field relationships and the Rb-Sr and Pb isotope systematics of sulfides from quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins confirm their close genetic affiliation and yield a combined Rb-Sr errorchron age of 276 ± 16 Ma. The high mean squared weighted deviation (MSWD) value of 42 on the regression is considered to reflect initial isotopic heterogeneity, which is probably related to fluid-rock interaction during the hydrothermal mineralization process. Although some sphalerites from barite-fluorite-sulfide veins have strongly disturbed Rb-Sr isotope systematics, six sphalerites and one co-genetic fahlore yield a robust isochron age of 121.3 ± 4.2 Ma with an MSWD of 2.9. This age is supported by a fluorite Sm-Nd isochron age of 101 ± 18 Ma (MSWD = 1.3). The new ages and radiogenic isotope data place robust constraints on the long-held hypothesis that veins in the Freiberg district formed during two hydrothermal events. The Lower Permian age of first stage quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins coincides with post-Variscan crustal reorganization and Rotliegend volcanism. The Mid-Cretaceous age of second stage barite-fluorite-sulfide veins coincides with opening of the North Atlantic Ocean during the break-up of Pangea.

Keywords: Erzgebirge; Freiberg district; Pb isotopesRb-Sr sphalerite dating; Sm-Nd fluorite dating; Vein-type deposit

Publ.-Id: 28268

Cerebral perfusion changes in presymptomatic genetic frontotemporal dementia: a GENFI study

Mutsaerts, H. J. M. M.; Mirza, S. S.; Petr, J.; Thomas, D. L.; Cash, D. M.; Bocchetta, M.; de Vita, E.; Metcalfe, A. W.; Shirzadi, Z.; Robertson, A. D.; Carmela Tartaglia, M.; Mitchell, S. B.; Black, S. E.; Freedman, M.; Tang-Wai, D.; Keren, R.; Rogaeva, E.; van Swieten, J.; Laforce, R. J.; Tagliavini, F.; Borroni, B.; Galimberti, D.; Rowe, J. B.; Graff, C.; Frisoni, G. B.; Finger, E.; Sorbi, S.; de Mendonça, A.; Rohrer, J. D.; Macintosh, B. J.; Masellis, M.

Genetic forms of frontotemporal dementia are most commonly due to mutations in three genes, C9orf72, GRN or MAPT, with presymptomatic carriers from families representing those at risk. While cerebral blood flow shows differences between frontotemporal dementia and other forms of dementia, there is limited evidence of its utility in presymptomatic stages of frontotemporal dementia. This study aimed to delineate the cerebral blood flow signature of presymptomatic, genetic frontotemporal dementia using a voxel-based approach. In the multi-centre GENetic Frontotemporal dementia Initiative (GENFI) study, we investigated cross-sectional differences in arterial spin labeling MRI-based cerebral blood flow between presymptomatic C9orf72, GRN or MAPT mutation carriers (n=107) and non-carriers (n=113), using general linear mixed-effects models and voxel-based analyses. Cerebral blood flow within regions of interest derived from this model was then explored to identify differences between individual gene carrier groups and to estimate a timeframe for the expression of these differences. The voxel-based analysis revealed a significant inverse association between cerebral blood flow and the expected age of symptom onset in carriers, but not non-carriers. Regions included the bilateral insulae/orbitofrontal cortices, anterior cingulate/paracingulate gyri, and inferior parietal cortices, as well as the left middle temporal gyrus. For all bilateral regions, associations were greater on the right side. After correction for partial volume effects in a region of interest analysis, the results were found to be largely driven by the C9orf72 genetic subgroup. These cerebral blood flow differences first appeared approximately 15 years before the expected symptom onset determined on an individual basis. Cerebral blood flow was lower in presymptomatic mutation carriers closer to and beyond their expected age of symptom onset in key frontotemporal dementia signature regions. These results suggest that arterial spin labeling MRI may be a promising non-invasive imaging biomarker for the presymptomatic stages of genetic frontotemporal dementia.

Keywords: genetic frontotemporal dementia; arterial spin labeling; cerebral blood flow; presymptomatic biomarker

Publ.-Id: 28267

Sub-gap optical response in the Kitaev spin-liquid candidate α-RuCl3

Reschke, S.; Mayr, F.; Widmann, S.; Krug Von Nidda, H.-A.; Tsurkan, V.; Eremin, M. V.; Do, S.-H.; Choi, K.-Y.; Wang, Z.; Loidl, A.

We report detailed optical experiments on the layered compound α-RuCl3 focusing on the THz and sub-gap optical response across the structural phase transition from the monoclinic high-temperature to the rhombohedral low-temperature structure, where the stacking sequence of the molecular layers is changed. This type of phase transition is characteristic for a variety of tri-halides crystallizing in a layered honeycomb-type structure and so far is unique, as the low-temperature phase exhibits the higher symmetry. One motivation is to unravel the microscopic nature of THz and spin-orbital excitations via a study of temperature and symmetry-induced changes. The optical studies are complemented by thermal expansion experiments. We document a number of highly unusual findings: A characteristic two-step hysteresis of the structural phase transition, accompanied by a dramatic change of the reflectivity. A complex dielectric loss spectrum in the THz regime, which could indicate remnants of Kitaev physics. Orbital excitations, which cannot be explained based on recent models, and an electronic excitation, which appears in a narrow temperature range just across the structural phase transition. Despite significant symmetry changes across the monoclinic to rhombohedral phase transition and a change of the stacking sequence, phonon eigenfrequencies and the majority of spin-orbital excitations are not strongly influenced. Obviously, the symmetry of a single molecular layer determines the eigenfrequencies of most of these excitations. Only one mode at THz frequencies, which becomes suppressed in the high-temperature monoclinic phase and one phonon mode experience changes in symmetry and stacking. Finally, from this combined terahertz, far- and mid-infrared study we try to shed some light on the so far unsolved low energy (<1 eV) electronic structure of the ruthenium 4d5 electrons in α-RuCl3.


Publ.-Id: 28266

From curvilinear magnetism to shapeable magnetoelectronics

Makarov, D.

In this talk I will Review our activities on curvilinear magnetism and shapeable magnetoelectronics.

Keywords: curvilinear magnetism; shapeable magnetoelectronics

Related publications

  • Invited lecture (Conferences)
    Seminar at the Department of Physics, University of Konstanz, 22.01.2019, Konstanz, Germany

Publ.-Id: 28265

Highly compliant planar Hall effect sensor with sub 50 nT sensitivity

Granell, P. N.; Wang, G.; Cañon Bermudez, G. S.; Kosub, T.; Golmar, F.; Steren, L.; Fassbender, J.; Makarov, D.

Next generation of flexible appliances such as soft robots aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems, which typically include magnetic field sensors as key building blocks. Although there is a great progress in the field of shapeable magnetoelectronics [1], there is no technology available which can enable sensitivities to magnetic fields lower than 1 μT (below the geomagnetic field) in a mechanically compliant form factor. To address this challenging task we introduced a new fundamental effect towards magnetic field sensing --the planar Hall effect (PHE) [2-5]-- in the field of shapeable magnetoelectronics. We demonstrate that even when prepared on mechanically imperceptible 6-μm-thick polymeric foils, magnetic field sensors based on the planar Hall effect have a remarkable sensitivity of 0.86 V/T and are capable of detecting magnetic fields in the range of sub 50 nT. Furthermore, these sensors can be bent to a radius of 1 mm without any degradation of their electrical resistance and shows excellent cyclic bending performance with only 0.3% resistance variation after more than 150 bending cycles. The application potential of the device is showcased in two examples of an angle and proximity sensors. For the latter, we demonstrate that the compliant PHE sensor is able to detect small magnetic stray fields of magnetically functionalized objects as needed for conventional metrology as well as point of care diagnostics. High sensitivity of the prepared sensing devices combined with a remarkable simplicity of fabrication, is a step forward in the realization of cost efficient flexible magnetoelectronic devices, with possible application in soft robotics, interactive devices for virtual- and augmented reality [6,7] and point of care platforms for the detection of magnetic objects [8].
References: [1] D. Makarov, Applied Physics Reviews, Vol. 3, p.011101 (2016)
[2] F. G. West, Journal of Applied Physics, Vol. 34, p.1171 (1963)
[3] C. Goldberg, Physical Review, Vol. 94, p.1121 (1954)
[5] A. Schuhl, Applied Physics Letters, Vol. 66, p.2751 (1995)
[5] V. Mor, Journal of Applied Physics, Vol. 111 (2012)
[6] G. S. Cañón Bermúdez, Science Advances, Vol. 4 (2018)
[7] M. Melzer, Nature Communications, Vol. 6 (2015)
[8] G. Lin, Lab Chip, Vol. 14, p.4050 (2014)

Keywords: magnetic field sensors; flexible electronics

Related publications

  • Lecture (Conference)
    The 2019 Joint MMM-Intermag Conference, 14.-18.01.2019, Washington DC, USA

Publ.-Id: 28264

Droplet-based magnetofluidic platforms for detection and analytics

Makarov, D.

The development of next-generation biosensing technologies has picked up momentum in the past decade. Particularly, among a variety of biosensing principles, magnetic biosensing technologies based on magnetic particles and magnetic field sensors have attracted growing attention due to the unprecedented advantages brought by this unique sensing format.
Our contribution to this exciting field of research and technology includes the development of a compact droplet-based magnetofluidic platform encompassing integrated novel functionalities, e.g. analytics in a flow cytometry format [1-3], magnetic barcoding [4] and sorting of magnetically encoded emulsion droplets [5,6]. We put forth a novel high-capacity indexing scheme based on multiphase microfluidic networks for large-scale screening applications [5,6] and realized flexible microfluidic platform with integrated magnetoresistive sensorics [4]. The technology on how to integrate high-performance magnetic field sensors into multi-functional self-assembled tubular architectures [7-9] for lab-in-a-tube concept [10] will be discussed. These features are crucial to address the needs of modern medical research, e.g. drug discovery [11].
These developments will be outlined in my talk.

[1] G. Lin, D. Makarov et al., “Magnetoresistive emulsion analyzer”. Sci. Rep. 3, 2548 (2013).
[2] G. Lin, D. Makarov et al., “Magnetofluidic platform for multidimensional magnetic and optical barcoding of droplets”. Lab Chip 15, 216 (2015).
[3] D. Karnaushenko, D. Makarov et al., “Monitoring microbial metabolites using an inductively coupled resonance circuit”. Sci. Rep. 5, 12878 (2015).
[4] G. Lin, D. Makarov et al., “A highly flexible and compact magnetoresistive analytic device”. Lab Chip 14, 4050 (2014).
[5] G. Lin, D. Makarov et al., “Magnetic suspension array technology: Controlled synthesis and screening in microfluidic networks”. Small 12, 4553 (2016).
[6] W. Song, D. Makarov et al., “Encoding micro-reactors with droplet chains in microfluidics”. ACS Sensors 2, 1839 (2017).
[7] I. Mönch, D. Makarov et al., “Rolled-up magnetic sensor: Nanomembrane architecture for in-flow detection of magnetic objects”. ACS Nano 5, 7436 (2011).
[8] D. Karnaushenko, D. Makarov et al., “Self-assembled on-chip integrated giant magneto-impedance sensorics”. Adv. Mater. 27, 6582 (2015).
[9] T. Ueltzhöffer, D. Makarov et al., “Magnetically patterned rolled-up exchange bias tubes: A paternoster for superparamagnetic beads”. ACS Nano 10, 8491 (2016).
[10] E. J. Smith, D. Makarov et al., “Lab-in-a-tube: ultracompact components for on-chip capture and detection of individual micro-/nanoorganisms”. Lab Chip (Tutorial Review) 12, 1917 (2012).
[11] G. Lin, D. Makarov et al., “Magnetic sensing platform technologies for biomedical applications”. Lab Chip (Critical Review) 17, 1884 (2017).

Keywords: droplet Fluidics; millifluidics; magnetic field sensors

Related publications

  • Invited lecture (Conferences)
    The 2019 Joint MMM-Intermag Conference, 14.-18.01.2019, Washington DC, USA

Publ.-Id: 28263

Exchange-driven chiral effects in curvilinear magnetism: theoretical abstraction or experimental observable

Makarov, D.

In this talk I will Review our recent exterimental and theoretical activities on curvilinear nanomagnets.

Keywords: curved magnetic thin films; curvilinear magnetism

Related publications

  • Invited lecture (Conferences)
    Workshop „Topological Phenomena in Quantum Materials“, 04.-05.12.2018, Dresden, Germany

Publ.-Id: 28262

Shapeable magnetoelectronics with sensitivities to geomagnetic fields and below

Makarov, D.

The recent rapid advance and eagerness of portable consumer electronics stimulate the development of functional elements towards being lightweight, flexible, and wearable. Next generation flexible appliances aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems. Key building blocks of navigation and position tracking devices are magnetic field sensors.
Although there is a remarkable progress in the field of shapeable magnetoelectronics [1], there is no technology available which can enable sensitivities to geomagnetic fields of 50 µT and, ultimately, magnetic fields of smaller than 1 µT in a mechanically compliant form factor. If available, these devices would contribute greatly to the realization of high-performance on-skin interactive electronics [2,3] and point of care applications [4].
Here, I will review two technological platforms allowing to realize not only mechanically imperceptible electronic skins, which enable perception of the geomagnetic field (e-skin compasses) [4], but also enable sensitivities down to ultra-small fields of sub-50 nT [6]. We demonstrate that e-skin compasses allow humans to orient with respect to earth’s magnetic field ubiquitously. Furthermore, biomagnetic orientation enables novel interactive devices for virtual and augmented reality applications. We showcase this by realizing touchless control of virtual units in a game engine using omnidirectional magnetosensitive skins.

[1] D. Makarov et al., Applied Physics Reviews 3, 011101 (2016).
[2] G.S. Canon Bermudez, D. Makarov et al., Science Advances 4, eaao2623 (2018).
[3] M. Melzer, D. Makarov et al., Nature Communications 6, 6080 (2015).
[4] G. Lin, D. Makarov et al., Lab Chip 14, 4050 (2014).
[5] G.S. Canon Bermudez, D. Makarov et al., Nature Electronics, in press.
[6] P.N. Granell, D. Makarov et al., npj Flexible Electronics, in press.

Keywords: flexible electronics; magnetic field sensors

Related publications

  • Invited lecture (Conferences)
    2018 International Workshop on Nanomembrane Origami Technology, 10.-11.11.2018, Shanghai, China

Publ.-Id: 28261

Observation of charge density waves in free-standing 1T-TaSe2 monolayers by transmission electron microscopy

Börner, P. C.; Kinyanjui, M. K.; Björkman, T.; Lehnert, T.; Krasheninnikov, A. V.; Kaiser, U.

While bulk 1T-TaSe2 is characterized by a commensurate charge density wave (CCDW) state below 473K, the stability of the CCDW state in a 1T-TaSe2 monolayer, although theoretically predicted, has not been experimentally confirmed so far. As charge density waves and periodic lattice distortions (PLDs) always come together, we evaluate the PLD in a 1T-TaSe2 monolayer from low-voltage aberration-corrected high-resolution transmission electron microscopy experiments. To prevent fast degradation of 1T-TaSe2 during exposure to the electron-beam, a 1T-TaSe2/graphene heterostructure was prepared. We also perform the image simulations based on atom coordinates obtained using density functional theory calculations. From the agreement between the experimental and simulated images, we confirm the stability of the CCDW/PLD in a monolayer 1T-TaSe2/graphene heterostructure at room temperature in the form of a 13 13 superstructure. At the same time, we find that in comparison to multi-layer structures, the superstructure is less pronounced.

Keywords: 1T-TaSe2; graphene; TEM; first-principles calculations

Related publications


Publ.-Id: 28260

Reversible superdense ordering of lithium between two graphene sheets

Kühne, M.; Börrnert, F.; Fecher, S.; Ghorbani-Asl, M.; Biskupek, J.; Samuelis, D.; Krasheninnikov, A. V.; Kaiser, U.; Smet, J. H.

Many carbon allotropes can act as host materials for reversible lithium uptake1,2, thereby laying the foundations for existing and future electrochemical energy storage. However, insight into how lithium is arranged within these hosts is difficult to obtain from a working system. For example, the use of in situ transmission electron microscopy3–5 to probe light elements (especially lithium)6,7 is severely hampered by their low scattering cross-section for impinging electrons and their susceptibility to knock-on damage8. Here we study the reversible intercalation of lithium into bilayer graphene by in situ low-voltage transmission electron microscopy, using both spherical and chromatic aberration correction9 to enhance contrast and resolution to the required levels. The microscopy is supported by electron energy-loss spectroscopy and density functional theory calculations. On their remote insertion from an electrochemical cell covering one end of the long but narrow bilayer, we observe lithium atoms to assume multi-layered close-packed order between the two carbon sheets. The lithium storage capacity associated with this superdense phase far exceeds that expected from formation of LiC6, which is the densest configuration known under normal conditions for lithium intercalation within bulk graphitic carbon10. Our findings thus point to the possible existence of distinct storage arrangements of ions in two-dimensional layered materials as compared to their bulk parent compounds.

Keywords: Li storage; graphene; TEM; first-principles caclulations

Related publications


Publ.-Id: 28259

Epitaxial Mn5Ge3 (100) layer on Ge (100) substrates obtained by flash lamp annealing

Xie, Y.; Yuan, Y.; Wang, M.; Xu, C.; Hübner, R.; Grenzer, J.; Zeng, Y.; Helm, M.; Zhou, S.; Prucnal, S.

Mn5Ge3 thin films have been demonstrated as promising spin-injector materials for germanium-based spintronic devices. So far, Mn5Ge3 has been grown epitaxially only on Ge (111) substrates. In this letter, we present the growth of epitaxial Mn5Ge3 films on Ge (100) substrates. The Mn5Ge3 film is synthetized via sub-second solid-state reaction between Mn and Ge upon flash lamp annealing for 20 ms at the ambient pressure. The single crystalline Mn5Ge3 is ferromagnetic with a Curie temperature of 283 K. Both the c-axis of hexagonal Mn5Ge3 and the magnetic easy axis are parallel to the Ge (100) surface. The millisecond-range flash epitaxy provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with CMOS technology.

Keywords: Mn5Ge3; epitaxial thin film; ferromagnetism; spintronic devices

Related publications

Publ.-Id: 28258

First Series of Tetravalent Thorium-, Uranium- and Neptunium-Amidinate Complexes

Schöne, S.; Kaden, P.; Patzschke, M.; Roesky, P. W.; Stumpf, T.; März, J.

Actinides (An) can possess a variety of different oxidation states, which typically range from +III to +VI for the early actinides Th-Cm. They have unique electronic properties originating from the 5f-orbitals, what makes their coordination chemistry a fascinating area of research for both, the nuclear engineering but also for fundamental chemistry. Thorium (Th), uranium (U), neptunium (Np) and plutonium (Pu) can form highly charged cations with the oxidation state of four (An4+), which is the dominant one under reductive conditions. Furthermore, An(IV) are of particular interest for the coordination chemistry because of their strong interaction with ligands.
Hence, the overall aim of our investigations is a deep understanding of the interaction mechanisms between tetravalent An (An(IV)) and ligands bearing soft donor atoms, such as nitrogen (N). Thus, we focused on the synthesis and characterization of a series of An(IV) complexes with the N-donor ligand N,N’-Diisopropylbenzamidine (iPr2BA) both in solution and in solid state.
The structures of the synthesised complex series were determined by single-crystal X-ray diffraction (SC-XRD), showing the An(IV) coordinated by three iPr2BA molecules and one chloro ligand in a monocapped octahedral coordination geometry. This is the very first example of an An(IV) complex series including Np(IV) as a transuranium element with an amidinate ligand. The isostructural complexes allow a direct comparison of the binding situation of the An(IV) across the series. Quantum chemical calculation strongly supported the experimental results to to further study the electronic structure of the complexes.
NMR-spectroscopic investigations of the dissolved complexes in toluene-d8 showed significant chemical shifts due to considerable effects of the paramagnetic metal centres U(IV) and Np(IV) compared to the diamagnetic reference [Th(iPr2BA)3Cl].

Keywords: actinide; amidinate; coordination chemistry; thorium; uranium; neptunium; NMR; SC-XRD

  • Invited lecture (Conferences)
    10th International Conference on f-Elements (ICFE-10), 03.-07.09.2018, Lausanne, Schweiz

Publ.-Id: 28257

Coordination Chemistry of Tetravalent Actinides: Series & Trends

Schöne, S.; Radoske, T.; Kloditz, R.; Köhler, L.; Kaden, P.; Patzschke, M.; Roesky, P. W.; Stumpf, T.; März, J.

The coordination chemistry of actinides (An) using model ligands helps to deeply understand their bonding situation on a molecular level. However, the basic An chemistry is still little explored. Characteristic of An is a huge variety of possible oxidation states, typically ranging from II to VII for early An. A suitable approach to explore the fundamental phico-chemical properties of An is to study a series of isostructural An compounds in the same oxidation state. Observed changes in e.g. the binding situation or magnetic effects among the An series could deliver insight into their unique electronic properties mainly origination from the f-electrons. A question still remaining in An chemistry is the degree of "covalency". However, studies covering TRU elements are rather scarce. Against this background, we are strongly motivated to perform a systematic comparison of isostructural An complexes (Th, U and Np).
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)) for two major reasons: a) the series of An(IV) is the largest accessible one within the early actinides, and b) the tetravalent state is the dominant one particularly under anoxic conditions. The ligands used in this study range from hard- (oxygen) and medium- (nitrogen) to pure soft-donor (carbon) character, according to Pearsons's HSAB concept. Due to the expected changes in orbital overlap between the metal and ligand, the formed complexes could further provide us a deep insight into the electronic situation of the actinides.
The An(IV) complexes are characterised in solution by NMR-, IR- and UV-vis spectroscopy as well as in the solid-state by SC_XRD. The acquired experimental results are further supported by quantum chemical calculations with a focus on the electronic structure of the complexes.

Keywords: actinide; coordination chemistry; thorium; uranium; neptunium

  • Invited lecture (Conferences)
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 08.-13.07.2018, Dresden, Deutschland

Publ.-Id: 28256

Synthesis and Characterization of U(IV) Imidazol-2-ylidene Complexes

Köhler, L.; März, J.; Patzschke, M.; Kaden, P.; Monkowius, U.

In the field of actinide coordination chemistry, it is assumed that ligands bearing soft donor atoms, according to Pearson’s hard-soft-acid-base concept, such as sulphur, phosphorous or carbon lead to stable complexes. Furthermore, due to the expected strong orbital overlap between the metal and ligand, the formed complexes would provide us a deep insight into the electronic situation of the actinides. However, the majority of published actinide compounds still focusses on complexes with hard donor atoms such as oxygen.
A few examples of actinide-carbene complexes reported in the literature emphasise the remarkable strong σ donor properties of the carbon donor ligands, making the complexes e.g. excellent catalysts in organic synthesis1. Of particular interest are N-heterocyclic carbenes (NHCs) based on an imidazole-2-ylidene backbone, also known as “Arduengo carbenes”. For instance, the stability and electronic properties of these ligands can be easily tuned by synthetic introduction of suitable substituents at the nitrogen atoms.
The aim of this study is the synthesis of tetravalent actinide (An(IV)) complexes with soft-donor carbene ligands according to Figure 1 and the characterisation of the formed complexes in solution by NMR-, IR- and UV-vis spectroscopy as well as the solid-state characterisation with the help of single crystal X-ray diffraction. The acquired experimental results are further supported by quantum chemical calculations to further study the electronic structure of the complexes.

Keywords: actinide; coordination chemistry; carbene; uranium

  • Poster
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 08.-12.07.2018, Dresden, Deutschland

Publ.-Id: 28255

Coordination Chemistry of Uranium (U(IV) and -(VI)) with Bidentate N-donor Ligands

März, J.; Schöne, S.; Radoske, T.; Patzschke, M.; Stumpf, T.; Ikeda-Ohno, A.

The bidentate N-donor ligands 2,2’-bipyridine (bipy) and 1,10-phenanthroline (phen) have attracted considerable attention in the field of coordination chemistry over the last decades because of their remarkable stability towards a wide variety of transition metals1. The coordination chemistry of uranium (U) has been explored with these N-donor ligands as well with a primary focus on its hexavalent state (U(VI) as UO₂2+). To the contrary, much less attention has been paid for the lower oxidation states, such as a tetravalent state (U(IV)). Here we present a systematic study on the coordination chemistry of U(IV) and -(VI) with bipy and phen under different chemical conditions, such as different solvents and changing the metal / ligand ratio.

In this study we succeeded to obtain a series of U(IV) complexes with U:ligand ratios of 1:1 and 1:2, all of which show an eight-fold coordinated uranium centre. In addition to the ligand, chloro and methanolato ligands are coordinating to the metal centre for charge compensation. Interestingly, the complexation between U(IV) and the ligand does occur even in protic solvents, in which the ligand is expected to be protonated. We also obtained another series of U(VI) complexes with both bipy and phen, underlining the versatile coordination chemistry of uranyl (UO22+). That is, the coordination between uranyl and the ligand depends strongly on the pH of the solvent used. For instance, in media with lower pH mononuclear complexes are formed, showing the uranyl unit in an unusually bent geometry.3 On the other hand, dinuclear uranyl arrangements with hydroxo-brinding are dominated in the media with higher pH, as shown in the right of Fig. 1. As illustrated in Fig. 1, bipy and phen are forming isostructural complexes both with U(IV) and- (VI).

Keywords: uranium; coordination chemistry; N-donor ligand; bipyridine; phenanthroline

  • Lecture (Conference)
    RadChem 2018, 13.-18.05.2018, Mariánské Lázně, Tschechien

Publ.-Id: 28254

Recovery of gallium from wafer fabrication industry wastewaters by Desferrioxamine B and E using reversed-phase chromatography approach

Jain, R.; Fan, S.; Kaden, P.; Tsushima, S.; Foerstendorf, H.; Barthen, R.; Lehmann, F.; Pollmann, K.

Gallium (Ga) is a critical element in developing renewable energy generation and energy efficient systems. The supply of Ga is at risk and needed recycling technologies for its availability in future. This study demonstrated the recovery of Ga3+ from low gallium concentrated wafer fabrication industry wastewaters using the siderophores desferrioxamine B (DFOB) and desferrioxamine E (DFOE). The complexation of Ga3+ by DFOB and DFOE was through hydroxamate group as demonstrated by infrared spectroscopy, nuclear magnetic resonance and density functional theory calculations. The high selectivity of DFOB/E towards Ga3+ was observed due to the formation of highly stable complex. Indeed, due to the formation of such high stability complex, the DFOB and DFOE were able to successfully complex 100% Ga in the two different wastewater from wafer fabrication industry. For the recovery of the siderophores, a high rate of decomplexation of Ga (>90%) was achieved upon addition of 6 times excess of ethylenediaminetetraacetic acid (EDTA) at pH of 3.5. More than 95% of Ga-DFOB and Ga-DFOE complex were recovered with purity (% of Ga moles in comparison to total moles of metals) of 70.4 and 94.9%, respectively by application of a C18 reversed-phase chromatography column. A preliminary cost-calculation demonstrated that acetonitrile consumption and desferrioxamines are major cost input for the technology. This study, for the first time, demonstrated a technical solution to the recovery of Ga3+ from the low concentrated wastewater based on siderophores and reversed-phase chromatography. A German patent application had been filed for this technology.

Keywords: Metal recovery; recycling; resource efficiency; cost-benefit; wastewater

Publ.-Id: 28253

Pulsating dissolution of crystalline matter

Fischer, C.; Lüttge, A.

Fluid-solid reactions result in dissolution or precipitation reactions. The prediction of the related material flux
from or to the reacting surface, its variations and changes with time are of interest to a wide array of disciplines.
Reaction rate maps that are derived from sequences of topography maps illustrate the spatial distribution of
reaction rates across the crystal surface [1]. Here we present dissolution rate maps that reveal the existence
of rhythmic pulses of the material flux from the crystal surface. This observation leads to a change in our
understanding of the way crystalline matter dissolves. Rhythmic fluctuations of the reactive surface site density
and potentially concomitant oscillations in the fluid saturation imply spatial and temporal variability in surface
reaction rates. Knowledge of such variability could aid attempts to upscale microscopic rates and predict reactive
transport through changing porous media.
[1] Fischer, C., Luttge, A., 2017. Beyond the conventional understanding of water–rock reactivity. Earth and
Planetary Science Letters 457, 100-105.

  • Lecture (Conference)
    EGU 2018 - European Geosciences Union General Assembly 2018, 08.-13.04.2018, Wien, Österreich

Publ.-Id: 28252

Dissolution rate variability of sandstone calcite cement

Pedrosa, E. T.; Fischer, C.; Lüttge, A.

For a holistic understanding of the long-term usage and safety analysis of reservoir rocks it is crucial to understand the fundamental mineral reactions and its control mechanisms. Kinetic quantification of the processes involved with fluid-rock interactions are especially important for predicting the evolution of pore space in rocks subjected to fluid injection, such as in CO2-sequestration and hydrocarbon exploration techniques.
The calcite cement selected for this study belongs to a fluvial-aeolian Rotliegend succession exposed near Bebertal (Flechtinge High, Germany) that was deposited in the same conditions as those that form the prolific gas reservoirs of the Southern Permian Basin1,2. Optical microscopy, SEM-BSE images and Cathodoluminescence analysis of the unreacted samples showed that two types of cement were present, although the calcite cement patches were composed of single crystals. We hypothesized that these different types of cement would react differently to fluid input. We used polished thick-sections of plug samples for dissolution experiments in a flow-through cell using a 2 mmol Na2CO3 solution (pH = 8.6, T≈ 21°C), for 7 reaction intervals (3 to 32 hours). Before and after each experiment the sample’s topography changes were mapped using a vertical scanning interferometer (VSI). High-resolution surface maps are subsequently used to calculate surface dissolution rates3.
After experiments, VSI images revealed an increase of the surface roughness in the cement patches. Detailed analysis of the rate dissolution variability in between the calcite cement patches and the intravariability of each cement patch related to chemical composition variability in the samples will be presented.
1Fischer, C., Gaupp, R., Dimke, M., Sill, O., 2007. A 3D high resolution model of bounding surfaces in aelian-fluvial deposits: An outcrop analogue study from the Permian Rotliegend, Northern Germany. Journal of Petroleum Geology, 30(3), 257–273.
2Fischer, C.; Dunkl, I.; von Eynatten, H.; Wijbrans, J. R.; Gaupp, R., 2012. Products and timing of diagenetic processes in Upper Rotliegend sandstones from Bebertal (North German Basin, Parchim Formation, Flechtingen High, Germany). Geological Magazine, 149 (5), 827-840.
3Luttge, A., and Bolton, E., 1999. An interferometric study of the dissolution kinetics of anorthite : The role of reactive surface area. American Journal of Science, 299, 652–678.

  • Lecture (Conference)
    GeoBonn 2018, 02.-06.09.2018, Bonn, Deutschland

Publ.-Id: 28251

Precipitation and dissolution of cement minerals in sandstone: Opportunities and limitations of pore and plug scale flow analysis for reactive transport modelling approaches

Kulenkampff, J.; Karimzadeh, L.; Fischer, C.

Reservoir properties of sandstones are controlled by precipitation and dissolution reactions at the pore walls. Both, the formation and dissolution of cement minerals are responsible for the complex pattern formation of porosity and permeability in reservoir rocks.
At the scale of drilled core sections (plugs), experimental and analytical approaches utilize positron emission tomography (PET) with radiotracers (Kulenkampff et al. 2016). Resulting spatiotemporal concentration distributions provide quantitative insight into fluid flow and diffusion parameters. The sensitivity is in the picomolar range of the utilized radiotracers and the spatial resolution is about 1 mm. Thus, mechanistically-important surface features such as etch pits or growth hillocks and their evolution during reaction are not yet part of the direct analysis of the flow field.
Here, we present an approach based on existing information about the complex crystal surface morphology and rate evolution (Fischer& Luttge 2017). We utilize artificial materials that are produced by 3D printing capabilities. Such an approach using PET analysis of sequences of machined surfaces in flow-through experiments provides quantitative insight into the local stability vs. temporal heterogeneity of fluid flow close to reacting surfaces. The measured flow velocity data from PET are implemented into reactive transport models and compared to existing small-scale calculations. We discuss the resulting size and complexity of surface rate patterns.

Fischer, C. and A. Luttge (2017). Beyond the conventional understanding of water–rock reactivity. Earth and Planetary Science Letters, 457: 100-105
J. Kulenkampff, M. Gründig, A. Zakhnini and J. Lippmann-Pipke (2016): Geoscientific process monitoring with positron emission tomography (GeoPET). Solid Earth, 7: 1217-1231

  • Lecture (Conference)
    Interpore 2018, 14.-17.05.2018, New Orleans, USA

Publ.-Id: 28250

Surface-Functionalized Mesoporous Nanoparticles as Heterogeneous Supports To Transfer Bifunctional Catalysts into Organic Solvents for Tandem Catalysis

Zhang, N.; Hübner, R.; Wang, Y.; Zhang, E.; Zhou, Y.; Dong, S.; Wu, C.

The combination of chemo- and biocatalysts offers a powerful platform to address synthetic challenges in chemistry, particularly in synthetic cascades. However, transferring both catalysts into organic solvents remains technically difficult because of the enzyme inactivation and catalyst precipitation. Herein, we designed a facile approach using functionalized mesoporous silica nanoparticles (MSN) to transfer chemo- and biocatalysts into a variety of organic solvents. As a proof-of-concept, two distinct catalysts, palladium nanoparticles (Pd NPs) and Candida antarctica lipase B (CalB), were stepwise loaded into separate locations of the mesoporous structure, which not only provided catalysts with heterogeneous supports for the recycling but also avoided their mutual inactivation. Moreover, mesoporous particles were hydrophobized by surface alkylation, resulting in a tailor-made particle hydrophobicity, which allowed bifunctional catalysts to be dispersed in eight organic solvents. Eventually, these attractive material properties provided the MSN-based bifunctional catalysts with remarkable catalytic performance for cascade reaction synthesizing benzyl hexanoate in toluene. With a broader perspective, the success of this study opens new avenues in the field of multifunctional catalysts where a plethora of other chemo- and biocatalysts can be incorporated into surface-functionalized materials ranging from soft matters to porous networks for synthetic purposes in organic solvents.

Keywords: multifunctional biocatalyst; mesoporous silica nanoparticles (MSN); palladium nanoparticles; lipase CalB; cascade reaction

Related publications

Publ.-Id: 28249

Strong Variation Of Electronic Properties Of MoS2 And WS2 Nanotubes In Presence Of External Electric Fields

Zibouche, N.; Philipsen, P.; Kuc, A.

Transition-metal dichalcogenides attracted a huge international research focus from the point of two-dimensional materials. These materials exist also as nanotubes, how- ever, they have been mostly studied for their lubricant properties. Despite their inter- esting electronic properties, quite similar to their 2D counterparts, nanotubes remain much less explored. Like in 2D materials, electronic properties of nanotubes can be strongly modulated by external means, such as strain or electric field. Here, we report on the effect of external electric fields on the electronic properties of MoS2 and WS2 nanotubes, using density functional theory. We show that the electric field induces a strong polarization in these nanotubes, what results in a nearly linear decrease of the band gaps with the field strength and eventually in a semiconductor-metal transi- tion. In particular for large tube diameters, this transition can occur for field strengths between 1 - 2 V nm−1. This is an order of magnitude weaker than fields required to close the band gaps in the corresponding 2D mono- and bilayers of transition-metal dichalcogenides. We also observe splittings of the degenerate valence and conduction band states due to the Stark effect. Accordingly, such nanotubes could be used in na- noelectronics as logical switches, even at moderate field strengths that can be achieved experimentally, for example, by applying a gate voltage.


Publ.-Id: 28248

Trace element geochemistry of sphalerite in contrasting hydrothermal fluid systems of the Freiberg district, Germany: insights from LA-ICP-MS analysis, near-infrared light microthermometry of sphalerite-hosted fluid inclusions, and sulfur isotope geochemistry

Bauer, M. E.; Burisch, M.; Ostendorf, J.; Krause, J.; Frenzel, M.; Seifert, T.; Gutzmer, J.

The historic silver mining district of Freiberg (Germany) comprises hydrothermal vein-style mineralization of Permian and Cretaceous age. We compare sphalerite compositions with associated ore-forming fluids and constrain the behavior of critical metals such as In, Ge, and Ga in contrasting hydrothermal environments. Fluid inclusion studies reveal that the Permian veins formed due to boiling and cooling of a low-salinity (0 to 6% eq. w[NaCl]) magmatic-hydrothermal fluid at 350 to 230 °C. In contrast, Cretaceous veins formed by mixing of highly saline (17 to 24% eq. w[NaCl + CaCl2] and variable Na/(Na + Ca) ratios) brines at low temperatures (~ 120 °C). Sulfides of the Permian ore stage have a narrow range of δ34SVCDT from − 2.3 to + 0.9‰, while the sulfides of the Cretaceous stage have a large scatter and significantly more negative δ34SVCDT values (− 30.9 to − 5.5‰), supporting the different nature of the hydrothermal systems. Contrasting fluid systems and ore-forming mechanisms correspond to markedly different trace element systematics in sphalerite. Permian sphalerite is significantly enriched in In (up to 2500 μg/g In) relative to two sphalerite generations of Cretaceous veins. The latter have higher Ge (up to 2700 μg/g Ge) and Ga (up to 1000 μg/g Ga) concentrations. The observed trace element systematics of different sphalerite generations imply that In is enriched in high-temperature, low- to intermediate-salinity fluids with a significant magmatic-hydrothermal fluid component, while Ge and Ga are more concentrated in low-temperature, high-salinity crustal fluids with no obvious magmatic-hydrothermal affiliation.

Keywords: Sphalerite; Indium; Germanium; Gallium; Critical metals; EPMA; LA-ICP-MS; Fluid inclusions; Near-infrared light microthermometry; Sulfur isotopes; Geothermometer; Erzgebirge

Publ.-Id: 28247

Indium and selenium distribution in the Neves-Corvo deposit, Iberian Pyrite Belt, Portugal

Carvalho, J. R. S.; Relvas, J. M. R. S.; Pinto, A. M. M.; Frenzel, M.; Krause, J.; Gutzmer, J.; Pacheco, N.; Fonseca, R.; Santos, S.; Caetano, P.; Reis, T.; Goncalves, M.

High concentrations of indium (In) and selenium (Se) have been reported in the Neves-Corvo volcanic-hosted massive sulfide deposit, Portugal. The distribution of these ore metals in the deposit is complex as a result of the combined effects of early ore-forming processes and late tectonometamorphic remobilization. The In and Se contents are higher in Cu-rich ore types, and lower in Zn-rich ore types. At the deposit scale, both In and Se correlate positively with Cu, whereas their correlations with Zn are close to zero. This argues for a genetic connection between Cu, In and Se in terms of metal sourcing and precipitation. However, re-distribution and re-concentration of In and Se associated with tectonometamorphic deformation are also processes of major importance for the actual distribution of these metals throughout the whole deposit. Although minor roquesite and other In-bearing phases were recognized, it is clear that most In within the deposit is found incorporated within sphalerite and chalcopyrite. When chalcopyrite and sphalerite coexist, the In content in sphalerite (avg. 1400 ppm) is, on average, 2–3 times higher than in chalcopyrite (avg. 660 ppm). The In content in stannite (avg. 1.3 wt.%) is even higher than in sphalerite, but the overall abundance of stannite is subordinate to either sphalerite or chalcopyrite. Selenium is dispersed widely between many different ore minerals, but galena is the main Se-carrier. On average, the Se content in galena is ~50 times greater than in either chalcopyrite (avg. 610 ppm) or sphalerite (avg. 590 ppm). The copper concentrate produced at Neves-Corvo contains very significant In (+Se) content, well above economic values if the copper smelters recovered it. Moreover, the high In content of sphalerite from some Cu-Zn ores, or associated with shear structures, could possibly justify, in the future, a selective exploitation strategy for the production of an In-rich zinc concentrate.

Keywords: Neves-Corvo; indium; selenium


Publ.-Id: 28246

A spectroscopic study of trivalent cation (Cm3+ and Eu3+) sorption on monoclinic zirconia (ZrO2)

Eibl, M.; Virtanen, S.; Pischel, F.; Bok, F.; Lönnrot, S.; Shaw, S.; Huittinen, N.


Zirconia (ZrO2) formed by corrosion of zircalloy, can immobilize radioactive contaminants (e.g. actinides) in repositories for spent nuclear fuel (SNF). The presence of organic and inorganic carbon at the highly reactive ZrO2 surface impacts the adsorption of these metal ions and their surface speciation.
Sorption of Eu3+ and Cm3+ on zirconia was studied in batch-sorption experiments, and via laser spectroscopy (TRLFS). Two zirconia solids with varying carbon content were utilized. The influence of carbon impurities on the ZrO2 surface charge was investigated via zeta-potential measurements. Batch data was collected for various Eu3+ concentrations, while the pH-dependent Cm3+ surface speciation was studied with TRLFS. The spectroscopic sorption data was modeled using the Diffuse Double Layer (DDL) model.
The ZrO2 surface charge measurements yielded a pHIEP of 6 which was influenced by the presence of inorganic and organic carbon species. The pH-dependent sorption of Eu3+ showed a maximum sorption above pH 5.5, with no impact of the carbon concentration. The speciation of the trivalent metal, however, was different in the presence of intrinsic organic carbon in the sample, resulting in the formation of an organic Cm3+-complex on the surface. The sorption data was well described by our DDL model.

Keywords: Cm3+; Eu3+; zirconia (ZrO2); organic impurity; laser spectroscopy (TRLFS); sorption; surface complexation modeling


Publ.-Id: 28245

Bestimmung der Input Funktion für das kinetische Modelling von (+)-[18F]Flubatine

Patt, M.; Tiepolt, S.; Sattler, B.; Hoepping, A.; Smits, R.; Deuther-Conrad, W.; Becker, G. A.; Steinbach, J.; Brust, P.; Sabri, O.

Der Abstract wird nachgereicht.

  • Lecture (Conference)
    56. Jahrestagung der DGN, 18.-21.04.2018, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 56(2018), V10

Publ.-Id: 28244

C-11 Markierung von zwei neuen Liganden für den Alpha7-Subtyp des nikotinischen Acetylcholinrezeptor (nAChR)

Patt, J. T.; Deuther-Conrad, W.; Peters, D.; Barthel, H.; Brust, P.; Sabri, O.; Patt, M.

Abstract wird nachgereicht.

  • Lecture (Conference)
    56. Jahrestagung der DGN, 18.-21.04.2018, Bremen, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 56(2018), V24

Publ.-Id: 28243

On Development and Validation of subcooled nucleate models for OpenFOAM Foundation Release

Peltola, J.; Bainbridge, W.; Lehnigk, R.; Schlegel, F.; Pättikangas, T. J. H.

Subcooled nucleate boiling capability based on [1] was introduced to OpenFOAM 4.0 [2] within multiphase framework called reactingEulerFoam that supports two- and multiphase simulations. Since then the capability has been further refined and extended in subsequent releases 5.0 and 6. The present implementation - available in OpenFOAM Foundation development release [3] - includes the RPI wall boiling model [4] with run time selectable nucleation site density and bubble departure diameter and frequency models. Runtime selectable wall heat transfer models for distribution of wall heat flux between gas and liquid phases are also included for non-equilibrium phase change simulations. Interfacial heat transfer and phase change are calculated with two-resistance approach and interface temperature using user selectable heat transfer models and saturation temperature model. For turbulence modelling, single-phase models available in the release can be selected and there are also specialized k-ε and k-ω two-phase models available. For bubble diameter modelling algebraic [5], IATE [6] and inhomogeneous class method models are available [7, 8].

The present paper compares simulation results obtained with different model combinations to publicly available experimental data from DEBORA and other experiments. The implications of the choices of the models and model parameters on accuracy and performance are discussed and practical recommendations are given for those that intend to use this publicly available resource for further research.

[1] Peltola, J., & Pättikangas, T.J.H. (2012). CFD4NRS-4, paper 59.
[2] OpenFOAM Foundation, OpenFOAM 4.0, (2016)
[3] OpenFOAM Foundation, OpenFOAM-dev, (2014-2018)
[4] N. Kurul and M.Z. Podowski, 27th National Heat Transfer Conference, Minneapolis, USA, July 28–31, 1991.
[5] Anglart, H., Nylund, O., Kurul, N., & Podowski, M. Z. (1997). Nuc. Engineering and Design, 177(1-3), 215-228.
[6] Ishii, M., Kim, S., & Kelly, J. (2005). Nuclear Engineering and Technology, 37(6), 525-536.
[7] Kumar, S., & Ramkrishna, D. (1996). Chemical Engineering Science, 51(8), 1311-1332.
[8] Liao, Y., Oertel, R., Kriebitzsch, S., Schlegel, F., & Lucas, D. (2018). Int. J. Num. Meth. Fluids, 87(4), 202-215

  • Lecture (Conference)
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, USA
  • Contribution to proceedings
    18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18), 18.-23.08.2019, Portland, USA
    Proceedings of NURETH-18

Publ.-Id: 28242

Compact high-brightness X-ray sources for ultrafast probing of explosively driven solid-density materials by Travelling-Wave Thomson-Scattering

Steiniger, K.; Bussmann, M.; Loeser, M.; Albach, D.; Debus, A.; Pausch, R.; Roeser, F.; Schramm, U.; Siebold, M.; Debus, A.

The Traveling-Wave Thomson-Scattering geometry is introduced and the possibility to realize optical free-electron lasers with it explained. An example setup for a TWTS OFEL providing 1 Angström radiation is shown and its application to the probing of the ion dynamics in a laser driven cryogenic hydrogen slab presented.

  • Lecture (Conference)
    EUCALL Joint Foresight Topical Workshop: Theory and Simulation of Photon-Matter Interaction, 02.-05.07.2018, Szeged, Hungary

Publ.-Id: 28241

Two-bubble class approach based on measured bubble size distribution for bubble columns with and without internals

Möller, F.; Kipping, R.; Lavetty, C.; Hampel, U.; Schubert, M.

The complex flow patterns in bubble columns can be phenomenologically described by the two-bubble class approach. For the first time, this approach is applied to bubble columns with dense internals. Internals of square and triangular pitch tube patterns of two tube sizes (8×10-3 and 13×10-3 m) with flat and U-tube bottom design and cross-sectional occupation of ~25% were inserted in a bubble column of 0.1 m diameter and 2 m height. Contrary to the well-known gas disengagement technique, dual-plane ultrafast X-ray computed tomography data have been used for the bubble class allocation. Experiments were performed at superficial gas velocities ranging from 0.02 m s-1 to 0.20 m s-1 to cover homogeneous and heterogeneous flow conditions. The contributions of small and large bubble classes on total holdup, flow structure and bubble rise velocities were determined. Furthermore, the regime transition onset was determined based on the two-bubble class approach. Eventually, new correlations for regime transition, small and large bubble rise velocity, large bubble holdup as well as total holdup are proposed based on sub-channel area, sub-channel hydraulic diameter and occlusion area.

Keywords: Bubble column; heat exchanger internals; two-bubble class approach; bubble size distribution; gas holdup; bubble rise velocity; ultrafast X-ray tomography


Publ.-Id: 28240

Compact, high-yield incoherent and coherent X-ray sources by Traveling-Wave Thomson-Scattering

Steiniger, K.; Loeser, M.; Albach, D.; Pausch, R.; Roeser, F.; Schramm, U.; Siebold, M.; Bussmann, M.; Debus, A.

In Traveling-Wave Thomson-Scattering pulse-front tilted, petawatt class laser pulses are scattered off relativistic electrons to realize compact optical free-electron lasers or brilliant incoherent X-ray sources with state-of-the-art electron accelerators and high-power laser systems. Example setups of TWTS OFELs providing ultraviolet radiation are presented together with an optical setup to compensate laser dispersion.

  • Invited lecture (Conferences)
    Visions on Future Laser-based X-ray Science and Technology, 19.-20.11.2018, Castelldefels, Spain

Publ.-Id: 28239

Irradiation tests at HZDR

Müller, S. E.; Ferrari, A.

Irradiation tests at HZDR in the framework of the MUSE project are presented

Related publications

  • Lecture (Conference)
    MUSE meeting, 22.10.2018, Fermilab, USA

Publ.-Id: 28238

FLUKA simulations for the Mu2e experiment

Müller, S. E.; Ferrari, A.

FLUKA simulations for the Mu2e experiment are presented

  • Lecture (Conference)
    MU2E collaboration meeting, 18.10.2018, 18.10.2018, Fermilab, USA

Publ.-Id: 28237

Laser-driven plasma pinching in e−e+ cascade

Efimenko, E. S.; Bashinov, A. V.; Gonoskov, A. A.; Bastrakov, S. I.; Muraviev, A. A.; Meyerov, I. B.; Kim, A. V.; Sergeev, A. M.

The cascaded production and dynamics of electron-positron plasma in ultimately focused laser fields of extreme intensity are studied by 3D particle-in-cell simulations with the account for the relevant processes of quantum electrodynamics (QED). We show that, if the laser facility provides a total power above 20 PW, it is possible to trigger not only a QED cascade but also pinching in the produced electron-positron plasma. The plasma self-compression in this case leads to an abrupt rise of the peak density and magnetic (electric) field up to at least 10^28 cm^−3 and 1/20 (1/40) of the Schwinger field, respectively. Determining the actual limits and physics of this process might require quantum treatment beyond the used standard semiclassical approach. The proposed setup can thus provide extreme conditions for probing and exploring fundamental physics of the matter and vacuum.

Publ.-Id: 28236

Unconventional trace elements in sphalerite – Clues to fluid origin?

Frenzel, M.; Slattery, A.; Wade, B.; Gilbert, S.; Ciobanu, C. C.; Cook, N. J.; Voudouris, P.

It is well known that the trace element content of sphalerite correlates with the conditions of ore formation (T, fS2). However, the suite of trace elements analysed in geological studies is generally restricted to the chalcophile and siderophile elements (Ag, As, Cd, Co, Fe, Ga, Ge, In, Mn, Sb, Se etc.). This may limit the inferences that can be made about the chemistry of the ore-forming fluids.

We used an integrated analytical approach consisting of electron probe micro-analysis, laser-ablationinductively coupled plasma-mass spectrometry, scanning electron microscopy and transmission electron microscopy to investigate the incorporation of the halogens Cl and Br, as well as the alkali metals Na and K into natural sphalerite from a range of deposits. This allowed us to study element distribution at length scales from >1 mm down to ~1 nm.

We found that Cl, Br, Na and K occur in measurable concentrations (100s to 1000s of ppm) in samples from several deposits. Chlorine occurs as either atomic substitutions in the sphalerite lattice or as a mixture of substitution and nano-inclusions. Unfortunately, analytical limitations mean that an investigation of the nanoscale distribution of Br, Na and K was not possible. However, concentrations of these elements (determined by LA-ICP-MS) correlate with Cl concentrations suggesting that they may be present together
with Cl in the sphalerite lattice.

The levels of trace elements present as atomic substitutions are generally related to the chemistry of the oreforming fluids. Therefore, our findings raise the possibility to measure Cl concentrations as well as Cl/Br ratios in natural sphalerite, and use these measurements to constrain fluid salinity and origin. However, more work will be required to constrain the relevant thermodynamic relationships and improve the detection limits of Cl and Br before such measurements can become a standard tool in economic geology.

  • Lecture (Conference)
    SEG 2018 conference, Keystone, 24.09.2018, Keystone, Colorado, United States of America

Publ.-Id: 28235

Criticality - What makes a raw material critical?

Frenzel, M.; Kullik, J.; Reuter, M. A.; Gutzmer, J.

A key to the current debate on the supply security of mineral raw materials is the concept of 'criticality'. This presentation provides a brief review of the criticality concept, as well as the methodologies used in its assessment, including a critical evaluation of their validity. Furthermore, it discusses several risks present in global raw materials markets that are not captured by most criticality assessments. The key result is that current assessments of raw material criticality are fundamentally flawed in several ways. This is mostly due to a lack of adherence to risk theory, and highly limits their applicability. Many of the raw materials generally identified as critical may not be critical, meaning that new assessments are urgently required.

While these are important results for policy makers, it is not necessarily clear what their implications are for geoscientific research on critical element deposits, the topic of this session. Therefore, this question will briefly be explored in the second part of the presentation.

  • Invited lecture (Conferences)
    GeoBonn, 05.09.2018, Bonn, Deutschland

Publ.-Id: 28233

Investigation of 18F-labelled pyrazolo[2,3-d]pyrimidines for molecular imaging of the adenosine A2A receptor with positron emission tomography (PET)

Lai, T. H.; Moldovan, R.-P.; Brust, P.

Objectives: The adenosine A2A receptor (A2AR) is a promising target for the development of PET radiotracers for molecular imaging of neurodegenerative diseases and cancer. Based on binding-affinities the 4 and 2-fluorobenzyl derivatives 1 (Ki(hA2A) = 5.3 nM) and 2 (Ki(hA2A) = 2.1 nM) were chosen for radiofluorination. Methods: Three different strategies for the synthesis of [18F]1 have been investigated. The first two are using [18F]fluorobenzaldehyde, which was applied either in a reductive amination or in a reduction followed by an Appel and benzylation reaction. The third strategy is based on a one-step radiolabelling starting from a boronic acid pinacol ester precursor employing [18F]TBAF and Cu(OTf)2(py)4 in n-BuOH/DMA. The specific binding of [18F]1 and [18F]2 on mice brain slices was evaluated by in vitro autoradiography. Results: The two- and four-step labelling strategies resulted in a radiochemical yield (RCY) of only 1.4% or 10% [18F]1 (non-isolated). Thus, [18F]1 and [18F]2 were prepared by a one-step procedure with a RCY of 52+7 or 9+1% (EOB), a molar activity of 135+64 or 132 GBq/µmol (EOS) and a radiochemical purity of >98%. In vitro autoradiography performed with [18F]2 demonstrated high binding to the striatum, a brain region with high density of A2AR, which could be blocked by selective A2A ligands. Conclusions: An efficient copper-mediated one-step radiolabelling procedure was established for two new highly affine A2A radiotracers. The first in vitro study with [18F]2 demonstrated excellent potential for the imaging of adenosine A2AR. Current work focuses on further in vitro and in vivo investigations.

Keywords: adenosine A2A; PET; radiotracer; 18F

  • Poster
    15th Research Festival Leipzig 2019, 18.01.2019, Leipzig, Deutschland

Publ.-Id: 28232

The geometallurgical assessment of by-products - Geochemical proxies for the complex mineralogical deportment of indium at Neves-Corvo, Portugal

Frenzel, M.; Bachmann, K.; Carvalho, J. R. S.; Relvas, J. M. R. S.; Pacheco, N.; Gutzmer, J.

Many by-productmetals are classified as critical.However, they are only ofmarginal interest tomanymining companies and are rarely part of detailed resource statements or geometallurgical assessments. As a result, there is a general lack of reliable quantitative data on the mineralogy and spatial distribution of these metals in ore deposits—hampering assessments of future availability.We propose here an innovative approach to integrate by-product metals into geometallurgical assessments. As an example, we use the distribution and deportment of indium at Neves-Corvo, a major European base-metal mine (Cu + Zn), and one of the largest and richest volcanichosted massive sulfide (VHMS) deposits in the world. Based on a combination of bulk-ore geochemistry and mineralogical and microanalytical data, this study is the first to develop a quantitativemodel of indium deportment inmassive sulfide ores, demonstrating how regularities in indium partitioning between different minerals can be used to predict its mineralogical deportment in individual drill-core samples. Bulk-ore assays of As, Cu, Fe, Pb, S, Sb, Sn, Zn, and In are found to be sufficient for reasonably accurate predictions. The movement of indium through the ore processing plants is fully explained by its mineralogical deportment, allowing for specific mine and process planning. The novel methodologies implemented in this contribution for (1) the assessment of analytical uncertainties, (2) the prediction of complex mineralogical deportments from bulk geochemical data, and (3) the modeling of byproduct recoveries from individual mining blocks, are of general applicability to the geometallurgical assessment of many other byproduct metals in polymetallic sulfide ores, including Ga, Ge, Mo, Re, Se, Te, as well as the noble metals.

Keywords: Geometallurgy; By-products; Trace elements; Automated mineralogy; Mineral balances; VMS deposits; VHMS deposits


Publ.-Id: 28231

Simulation-based exergy, thermo-economic and environmental footprint analysis of primary copper production

Abadías Llamas, A.; Reuter, M. A.; Valero Capilla, A.; Torres Cuadra, C.; Peltomäki, M.; Stelter, M.; Valero Delgado, A.; Roine, A.; Hultgren, M.

The transition from a Linear to Circular Economy has become a societal challenge to be tackled. However, the increasing complexity of materials and products increases also the sophistication of the circular economy systems required to deal with them. These systems are very resource consuming, therefore, a rigorous evaluation of the impact of every “actor” in circular economy must be done at design and operation stages to ensure the sustainability of the metal-production value chain.

A circular economy system implies, among others, low consumption of energy and material resources and low production of wastes or pollutant emissions. Its sustainability cannot therefore be evaluated just with one indicator. In this paper, we integrate indicators such as recovery rates, environmental impact indicators, as well as the quantities and qualities of the flows, losses and emissions, quantified through exergy. These must all be considered and evaluated simultaneously to perform a rigorous sustainability analysis.

The challenges of achieving a circular processing system and society are illustrated using a unique copper flowsheet that covers the complete processing chain from ore to refined metal including among others minor elements refining, scrap recycling, residue processing, steam utilization, sulphur capture and power generation in 129 unit operations linked by 289 streams and all the compositional and thermochemical detail. Using a simulation-based approach, two scenarios have been studied and compared: (i) a representative primary copper flowsheet and (ii) excluding all waste treatment processes. This unique simulated flowsheet permits a complete evaluation of various scenarios of all copper related processing options (while any additional unit operations can also be added) and also rigorously permits an allocation of impacts of all flows, products, residues etc. as a function of the complete mineral composition.

This approach to evaluating systems shows how to estimate the true losses from a system and will be a key approach to evaluate the true circularity of the circular economy system.

Keywords: Circular economy; Metallurgical process simulation; Thermoeconomics; Exergy; Copper production; Life Cycle Assessment (LCA); System design

Publ.-Id: 28230

Application of Layered Double Hydroxides for 99Tc remediation

Daniels, N.; Franzen, C.; Kvashnina, K.; Petrov, V.; Torapava, N.; Bukaemskiy, A.; Kowalski, P.; Hölzer, A.; Walther, C.

The present study investigates possible use of Layered Double Hydroxides (LDH) for Tc(VII) remediation. Mg/Al- and Mg/Fe-LDH were obtained by a hydrothermal route and thermally activated at 450°C, which was shown to significantly improve the Tc(VII) removal efficiency. Based on XRD investigation of Tc-LDH phases, the Tc(VII) uptake follows the restoring of an LDH structure. X-ray absorption spectroscopy demonstrates that Tc ions interact solely via the Tc-O bond, leaving no evidences of farther atomic interactions with, e.g., layers of LDH. The presence of competing anions, like NO3-, or CO32- in the solution decreases Tc(VII) uptake by LDH. Presently investigated thermally activated Mg0.67/Al0.33-LDH revealed a maximum uptake capacity of up to 1.27 mol/kg (or 20 wt.%), which is higher than that of the Mg0.75/Fe0.25-LDH (0.9 mol/kg). In agreement with these findings, theoretical simulations predicted incorporation energies for Mg0.67/Al0.33-LDH and Mg0.75/Fe0.25-LDH of -128 kJ/mol and -110 kJ/mol, respectively. Investigation of Tc-LDH in different leaching media demonstrated a rather high Tc(VII) stability in LDH in contact with diluted solutions containing Cl- and OH-, however, in a high saline solution, like Q-brine a rather fast release of TcO4- occurs due to anionic exchange with Cl-.

Keywords: Technetium; Layered Double Hydroxides; uptake; disposal

Related publications


Publ.-Id: 28229

Developments in the estimation of tensile strength by small punch testing

Holmström, S.; Simonovski, I.; Baraldi, D.; Bruchhausen, M.; Altstadt, E.; Delville, R.

The Small Punch (SP) test is a relatively simple test well suited for material ranking and material property estimation in situations where standard testing is not possible or considered too material consuming. The material tensile properties, e.g. the ultimate tensile strength (Rm) and proof strength (Rp02) are usually linearly correlated to the force-deflection behaviour of a SP test. However, if the test samples and test set-up dimensions are not according to standardized dimensions or the material ductility does not allow the SP sample to deform to the pre-defined displacements used in these correlations, the standard formulations can naturally not be used. Also, in cases where no supporting Rm data is available the applied correlation factors cannot be verified. In this paper a formulation is proposed that enables the estimation of Rm without supporting uniaxial tensile strength data for a range of materials, both for the soon to be standardized flat samples as well as for curved (tube section) samples. The proposed equations are based on the classical and recent SP and Small Punch Creep (SPC) formulations. It is claimed that the both equivalent stress in small punch creep and tensile strength can be robustly estimated with the same type of equations at least for ductile and semi-ductile ferritic/martensitic and austenitic steels. It is also shown that the same equations can be applied on non-standard test samples and test set-ups. The tensile strength of semi-ductile materials such as 46% cold worked 15-15Ti cladding steel tubes are successfully estimated by correcting the correlations for the curvature of the samples. The usability of the SP testing and assessment method for estimating tensile strength of engineering steels in general and for nuclear claddings in specific has been verified.

Keywords: small punch testing; tensile strength; models; fuel claddings

Publ.-Id: 28228

Dancing performance of organic droplets in aqueous surfactant solutions

Cejkova, J.; Schwarzenberger, K.; Eckert, K.; Tanaka, S.

Droplet systems remain the subject of a constant fascination in science and technology. Here we focus on organic droplets floating on the surface of aqueous surfactant solutions. These droplets can exhibit intriguing interactions. Recently we have found independently in two laboratories that we can observe almost the same complex collective behaviour in two different droplet systems. The aim of this paper is to compare both droplets systems, present their differences and show their similar oscillatory behaviour. The first system consists of decanol droplets floating on sodium decanoate solution. In the second one, the droplets consist of a mixture of ethyl salicylate and liquid paraffin and they are placed on the surface of aqueous sodium dodecyl sulphate solution. Although the mechanism of these spatio-temporal interactions of droplets is not fully understood yet, we believe that this behaviour is based on the same phenomena.

Publ.-Id: 28227

Materials research in high magnetic fields

Wosnitza, J.

  • Invited lecture (Conferences)
    12th Annual Matsurf Seminar, 05.11.2018, Turku, Finnland

Publ.-Id: 28226

FFLO states in organic superconductors − Modulated order parameter

Wosnitza, J.

  • Invited lecture (Conferences)
    Workshop on “Emergent Phenomena in Strongly Correlated Quantum Matter”, 26.-31.08.2018, Natal, Brasilien

Publ.-Id: 28225

"Superconductivity under Extreme Conditions” (Discussion Leader of this Session)

Wosnitza, J.

  • Invited lecture (Conferences)
    Gordon Research Conference on Conductivity and Magnetism in Molecular Materials, 12.-17.08.2018, Smithfield, USA

Publ.-Id: 28224

Spin-imbalanced superconductivity in layered organic superconductors

Wosnitza, J.

  • Invited lecture (Conferences)
    International Conference on Science and Technology of Synthetic Metals 2018 (ICSM 2018), 01.-06.07.2018, Busan, Korea

Publ.-Id: 28223

Frustrated and low-dimensional magnets in high magnetic fields

Wosnitza, J.

  • Invited lecture (Conferences)
    12th International Conference on Research in High Magnetic Fields (RHMF 2018), 24.-28.06.2018, Santa Fe, USA

Publ.-Id: 28222

Kinetic concepts for quantitative prediction of fluid-solid interactions

Lüttge, A.; Arvidson, R. S.; Fischer, C.; Kurganskaya, I.

In a unique “perspectives” format that examines both past and future, we appraise the field of crystal dissolution kinetics, showing how the last century’s strong progress in experimental discovery has both driven, and been driven by, the tandem evolution of basic theory. To provide context for examining the current state-of-the-art in this critical field, we highlight the key milestones that have punctuated our progress in understanding the dynamics of crystalline surfaces. For crystal growth, these are the energy relations between kinks on stepped surfaces, and the phenomena of screw dislocations sustaining steady state growth at low thermodynamic overstep. For crystal dissolution, the corresponding recognition is the tie between defects, hollow cores, and macroscopic etch pits. These latter relationships have been more recently formalized in the stepwave model, incorporating etch pit nucleation, step generation, and global retreat of the crystal surface: the total dissolution rate. All these conceptual advances contain an assertion of a link, fundamental but often implicit, between mass action and kinetics, where chemical potential is the primary driver of rates of physical process. This link is inherent in many “classical” rate equations, whose parameterization is often the endgame of laboratory observations.
Today, this extant framework serves as the conceptual basis for organizing the data available from a sophisticated suite of analytical and experimental instrumentation. These resources permit ever-increasing resolution of reacting surfaces in breathtaking detail, often under in situ conditions. These direct observations are now further enhanced by powerful computer-driven simulation and numerical modeling, allowing the virtual exploration of complex reaction systems, ranging from isolated single crystals to porous, multiphase networks. Despite the exhilarating breadth and detail of these accomplishments, it is also becoming increasingly apparent that we are moving further, not closer, from the goal of predictive understanding, a goal that is an increasingly vital social responsibility of our science. A major source of this divergence reflects the fact that at key intersecting points of study, our prowess in technical observation has effectively outpaced our theoretical understanding. In confronting the daunting complexity of these systems, we must be careful to first identify major vacancies in theory. Until we resolve these deficits, more observations may be of only limited utility.
In assessing this problem, a major uncertainty is how to properly reconcile thermodynamics, by its very nature a macroscopic formalism, with our current focus on atomic scales of reaction. This may be a problem unique to crystalline materials and their interactions with phases whose components are otherwise mobile. Detailed balancing and related microscopic reversibility, the implicit link referred to above, is often used to form a mechanistic bridge between the macroscopic distribution of energy and microscopic heterogeneity of events in crystal surfaces, but its employment creates two problems: spatial and temporal. First, reaction mechanism is truly atomic in dimension, involving actual, nondegenerate collisions at crystal surface sites, whereas 〖∆G〗_r or ∆μ is macroscopic. Second, the rate at which a crystal surface dissolves reflects both the chemical composition of the ambient fluid and the distribution of surface energy. Reaction towards “equilibrium”, involving the typically slow redistribution of surface energy, may thus inherit topography inconsistent with the computed “driving force”. This reactivity mismatch yields surfaces that evolve over time, producing a heterogeneous distribution of rates. This distribution can be efficiently characterized by rate spectra: the span of non-steady-state rates reflecting diversity of reactive sites established under previous 〖∆G〗_r regimes. We use these spectra as a basic compact variable: a signal that encodes the complex link between site-specific surficial energy distributions, solution and surface chemistry, and the cumulative rate that results. Because this encoding is efficiently captured by numerous surface analytical microscopies (VSI, AFM), this approach permits the testing of hypotheses regarding the probabilistic nature of rate distributions, a process we hope the community will embrace, serving ultimately as a key step forward in establishing useful predictive approaches. We illustrate this potential with a series of case studies that target a range of composition, space, and time scales.

Publ.-Id: 28221

Compact millijoule Yb³⁺:CaF₂ with 162fs pulses

Löser, M.; Bernet, C.; Albach, D.; Zeil, K.; Schramm, U.; Siebold, M.

We report on a compact diode-pumped, chirped pulse regenerative amplifier system with a pulse duration of 162 fs and an output pulse energy of 1 mJ before as well as 910 µJ after compression optimized for the probing of ultrafast relativistic laser-plasma processes. A chirped volume Bragg grating (CVBG) acts as a combined pulse stretcher/compressor representing a robust solution for a CPA laser system in the millijoule range. Yb3+:CaF2 is used as gain medium to support a large bandwidth of 16 nm (FWHM) when spectral gain shaping is applied. Chirped mirrors compensate for any additional dispersion introduced to the system.

Keywords: ytterbium laser; laser amplifier; CVBG; CPA laser

Publ.-Id: 28220

Neutronic analyses of the FREYA experiments in support of the ALFRED LFR core design and licensing

Sarotto, M.; Firpo, G.; Kochetkov, A.; Krása, A.; Fridman, E.; Cetnar, J.; Domanska, G.

During the EURATOM FP7 project FREYA, a number of experiments was performed in a critical core assembled in the VENUS-F zero-power reactor able to reproduce the ALFRED lead-cooled fast reactor spectrum in a dedicated island. The experiments dealt with the measurements of integral and local neutronic parameters, such as: the core criticality, the control rod and the lead void reactivity worth, the axial distributions of fission rates for the nuclides of major interest in a fast spectrum, the spectral indices of important actinides (U238, Pu239, Np237) respect to U235. With the main aim to validate the neutronic codes adopted for the ALFRED core design, the VENUS-F core and its characterisation measurements were simulated with both deterministic (ERANOS) and stochastic (MCNP, SERPENT) codes, by adopting different nuclear data libraries (JEFF, ENDF/B, JENDL, TENDL). This paper summarises the main results obtained and points out a general agreement between measurements and simulations, with few discrepancies for some parameters that are here discussed. Additionally, a sensitivity and uncertainty analysis was performed with deterministic methods for the core reactivity: it clearly indicates that the calculation accuracy of the different codes/libraries resulted to be lower than the uncertainties due to nuclear data.

Keywords: FREYA EU FP7 project; ALFRED LFR, VENUS-F reactor; Measurements of neutronic parameters; ERANOS deterministic code; MNCP and SERPENT stochastic codes


Publ.-Id: 28219

Wasserstoffbrennen in der Sonne: Die 12C(p,γ)13N-Reaktion und die Radiofrequenz-Ionenquelle für den Felsenkeller-Beschleuniger

Reinicke, S.

Die Reaktion 12C(p,γ)13N bestimmt die Rate des Bethe-Weizsäcker-Zyklus in der anfänglichen Entwicklungsphase von Sternen und am äußeren Rand der Sonne. Eine genaue Kenntnis der Reaktionsrate ist somit für die Entwicklung von stellaren Modellen erforderlich. Über das Verhältnis der Raten von den Protoneneinfangreaktionen von 12C und 13C kann außerdem das entsprechende Isotopenverhältnis in Sternen bestimmt werden. Eine Revision der Rate von 12C(p,γ)13N könnte damit einen unerwartet hohen Isotopenanteil von 13C erklären, der in verschiedenen Meteoriteneinschlüssen gemessen wurde und mit den existierenden stellaren Modellen nicht hinreichend in Konsistenz gebracht werden kann.
Für den S-Faktor der Reaktion existieren im Energiebereich unterhalb von 190 keV nur Messdaten aus den 1950er Jahren. Bei der Untersuchung von ähnlichen Reaktionen des Wasserstoffbrennens wurden die mit der verwendeten Messtechnik erlangten Messdaten durch moderne Experimente teilweise um einen Faktor zwei oder höher revidiert.
Ziel der gegenwärtigen Arbeit war das Messen von S-Faktor-Werten in einem weiten Energiebereich von 130 keV bis 450 keV zur Überprüfung der alten Messdaten und um eine zukünftige präzisere Extrapolation zu astrophysikalisch relevanten Energien hin zu ermöglichen. Dabei wurde eine Messung in inverser Kinematik, eine Methode, für die bisher keine publizierten Daten zu der Reaktion existieren, am HZDR 3 MV Tandetron Beschleuniger durchgeführt mit TiH2-Proben, die mit 12C2+-Ionen bestrahlt wurden. Die Reaktion wurde mittels Gammaspektrometrie ausgewertet und die Proben durch die Methode der Nuklearen Resonanz-Reaktionsanalyse charakterisiert.
Die neuen Messdaten sind im Energiebereich von 130 keV bis 170 keV im Mittel etwa 20 % höher als die Werte eines existierenden Fits an die bestehenden Messdaten, im Rahmen der Messunsicherheiten aber mit diesen konsistent. Im Energiebereich der Resonanz oberhalb von 420 keV wurde eine Diskrepanz zu den alten Messwerten festgestellt. Die neuen Werte liegen in diesem Bereich systematisch bis zu 50 % unterhalb der alten Messwerte.
Als weiteres Ziel dieser Arbeit wurde mithilfe von ionenoptischen Simulationen mit SIMION 8.1 ein elektrostatischer Deflektor und eine Einzellinse für eine RadiofrequenzIonenquelle entwickelt, die im Inneren des Hochspannungsterminals des Felsenkeller Beschleunigers eingesetzt werden soll. Durch die Erkenntnisse der Simulationen konnte ein Deflektor gebaut und getestet werden, der unter den Bedingungen auf dem Beschleuniger-Terminal funktionsfähig ist und zusammen mit der Ionenquelle einen intensiven Strahl von Wasserstoff oder Helium in die Beschleunigungsstrecke umlenken kann. Die Simulationen sagen Strahlverluste von maximal 10 % für Wasserstoff und 1.5 % für Helium voraus, womit, basierend auf den Messungen an einem Vakuumteststand und den Angaben des Herstellers der Ionenquelle, Strahlströme von 80 µA für 4He+ und über 100 µA für Protonen nach Verlassen des Beschleunigers zu erwarten sind. Der Untertage-Beschleuniger am Felsenkeller und die Radiofrequenz-Ionenquelle können zu einer weiteren Messung der Reaktion 12C(p,γ)13N mit besserer Statistik und einem zu niedrigeren Energien erweiterten Messbereich verwendet werden.

The reaction 12C(p,γ)13N determines the rate of the Bethe-Weizsäcker cycle in the initial development phase of stars and near the surface of the Sun. An exact knowledge of the reaction rate is thus required for the development of precise stellar models. In addition, the ratio of the rates of the proton capture reactions of 12C and 13C is used to determine the corresponding isotopic ratio in stars. A revision of the rate of 12C(p,γ)13N might help to explain an unexpectedly high isotopic abundance of 13C, which was measured in presolar grains and cannot be sufficiently explained with the existing stellar models.
For the S-factor of 12C(p,γ)13N in an energy range below 190 keV, the only existing data were measured in the 1950s. For similar reactions of hydrogen burning, data obtained with these measuring techniques were revised by a factor of two or higher by modern experiments.
The aim of the present thesis was to measure S-factor data in a wide energy range from 130 keV to 450 keV in order to verify the old data and to allow a more precise extrapolation towards astrophysically relevant energies in the future. A measurement in inverse kinematics, a method for which no published data on the reaction exist, was performed at the HZDR 3 MV Tandetron accelerator with a 12C2+ ion beam and the use of TiH2 targets. Gamma spectroscopy was used to measure the yield and the targets were characterized with nuclear resonant reaction analysis (NRRA).
In the energy range from 130 keV to 170 keV, the new values are on average about 20 % higher than the values of a recent fit to the old data, but they are consistent within uncertainties. In the energy range of the resonance above 420 keV, a discrepancy to the old data was found. The new values in this region are up to 50 % lower than the values from previous measurements.
Another goal of this work was the development of an electrostatic deflector and an einzel lens for a radio frequency ion source inside the high voltage terminal of the Felsenkeller accelerator. For this purpose, ion-optics simulations with SIMION 8.1 were performed, which lead to a design choice for the deflector allowing the transmission of intensive beams through the accelerator. The simulation predicts beam losses of less than 10 % for hydrogen and less than 1.5 % for helium, which based on easurements with a vacuum test chamber leads to expected beam currents of 80 µA for 4He+ at the exit of the acceleration tube. According to the data sheet of the radio frequency ion source, proton beams of more than 100 µA are to be expected.
The Felsenkeller underground accelerator and its radio frequency ion source can be used to perform further measurements of the reaction 12C(p,γ)13N with improved statistical uncertainties and an extension of the energy region towards lower energies.

Related publications

  • Doctoral thesis
    TU Dresden, 2018
    Mentor: Prof. Dr. Kai Zuber, PD Dr. Daniel Bemmerer
    171 Seiten
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-095 2019
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 28218

Physical and electrical properties of nitrogen-doped hydrogenated amorphous carbon films

Fenker, M.; Julin, J.; Petrikowski, K.; Richter, A.

Nitrogen-doped hydrogenated amorphous carbon films (a-C:H:N) have been prepared by a plasma-activated chemical vapor deposition technique (PACVD) by using a plasma beam source (PBS). The properties of the a-C:H:N films were changed by varying the total pressure, the substrate temperature (100 °C, 300 °C) and nitrogen partial pressure p(N₂) by adding nitrogen to the precursor acetylene (C₂H₂). For the investigations, a-C:H:N films have been deposited onto glass slides and doped silicon wafers. The deposition rate decreased with increasing nitrogen content in the N₂/C₂H₂ gas mixture and with decreasing total pressure. The elemental composition of two sample series (300 °C) has been analyzed with Elastic Recoil Detection Analysis (ERDA). The highest N content and N/C ratio was estimated to be 16 at.% and 0.25 at the highest p(N₂), respectively. Microhardness measurements showed that the hardness decreased with increasing p(N₂). Electrical resistance of the a-C:H:N films was measured by 4-point probe. Electrically conductive coatings have been obtained by nitrogen-doped a-C:H films at higher substrate temperature (300 °C). The electrical resistance of the a-C:H:N films also decreases with ecreasing total pressure, with the lowest value being about 1 Ohm cm. The film density was determined by means of X-ray reflectometry (XRR).

Keywords: PACVD; DLC; carbon films; carbon nitride films; XRR; electrical conductivity

Related publications

Publ.-Id: 28217

Measurement of the prompt fission γ-ray spectrum of 242Pu

Urlass, S.; Beyer, R.; Junghans, A. R.; Kögler, T.; Schwengner, R.; Wagner, A.

The prompt γ-ray spectrum of fission fragments is important in understanding the dynamics of the fission process, as well as for nuclear engineering in terms of predicting the γ-ray heating in nuclear reactors. The γ-ray spectrum measured from the fission fragments of the spontaneous fission of 242Pu will be presented here. A fission chamber containing in total 37mg of 242Pu was used as active sample. The γ-quanta were detected with high time- and energy-resolution using LaBr3 and HPGe detectors, respectively, in coincidence with spontaneous fission events detected by the fission chamber.
The acquired γ-ray spectra were corrected for the detector response using the spectrum stripping method. About 70 million fission events were detected which results in a very low statistical uncertainty and a wider energy range covered compared to previous measurements. The prompt fission γ-ray spectrum measured with the HPGe detectors shows structures that allow conclusions about the nature of γ-ray transitions in the fission fragments. The average photon multiplicity of 8.2 and the average total energy release by prompt photons per fission event of about 6.8 MeV were determined for both detector types.

Keywords: nELBE; prompt fission; gamma-rays; plutonium; 242Pu; fission chamber

Related publications

Publ.-Id: 28216

Calcium molybdate, CaMoO₄: a promising target material for 99m-Tc and its potential applications in nuclear medicine and nuclear waste disposal

Johnstone, E. V.; Czerwinski, K. R.; Hartmann, T.; Poineau, F.; Bailey, D. J.; Hyatt, N. C.; Mayordomo, N.; Nuñez, A.; Tsang, F. Y.; Sattelberger, A. P.; German, K. E.; Mausolf, E. J.

Calcium molybdate (CaMoO₄ ) is a robust, inorganic material known for its favorable physicochemical properties making it ideal for a wide scope of applications concerning optics (i.e., phosphors, scintillators, laser hosts, etc.), nuclear waste encapsulation and disposal, corrosion inhibition, etc. Calcium molybdate occurs in nature as the mineral Powellite, and the compound adopts the scheelite (CaWO₄ ) structure-type with Mo fully oxidized in the +6-oxidation state. This Mo-containing ceramic phase exhibits limited insoluble in aqueous environments and relative thermal stability at elevated temperatures. In the laboratory, CaMoO₄ can be synthesized straightforward from the stoichiometric solid-state reaction MoO₃ with the respective calcium oxide or carbonate, e.g., CaO or CaCO₃, at elevated temperatures, or alternatively via co-precipitation, sol-gel, or mechanochemical methods. Depending on synthetic conditions, single phase nano-powders to monoliths can be generated and tailored for its successive application. Likewise, the scheelite structure type can incorporate different doping elements into the host lattice, such as Pb2+ or elements arising from the lanthanoid series, which are used for applications with phosphors. , ,
On the periodic table, Mo (Z = 42) is located on the 5th row within the transition metals and precedes the lightest, inherently radioactive element, technetium (Tc, Z = 43). Molybdenum is characterized by an assortment of naturally occurring isotopes (i.e., 92Mo 14.53%, 94Mo 9.16%, 95Mo 15.84%, 96Mo 16.67%, 97Mo 9.60%, 98Mo 24.39%, and 100Mo 9.82%) making it a suitable starting material for the transmutation to an array of different Tc isotopes depending on isotope enrichment, particle beam type (e.g., proton, deuteron, electron, neutron, photon, etc.), and beam energy. One of the most recognized Mo-Tc radionuclidic parent-daughter couples is 99Mo-99mTc, where the daughter isotope 99mTc has been notoriously branded as the workhorse of the nuclear diagnostic imaging industry used worldwide in 30 to 40 million procedures annually, i.e., ~ 9,000 6-day Ci at end of processing (EOP) per week. As the international geopolitical attitude towards using highly enriched uranium (HEU) for the production of 99Mo begins to shift, the use of non-fission sources for the production of 99mTc is becoming increasingly more vital, and new methods for production and separation are desperately being sought. For example, the United States of America currently has no domestic supply in place for the production of 99mTc, although it is responsible for half of the world’s usage.
When considering both, the isotopic and physicochemical composition and properties of Mo and CaMoO₄, strong arguments can be made to pursue the better understanding of CaMoO₄ and its relationship as a host material for direct transmutation of Mo → Tc and / or post-processing integration of Tc, specifically 99mTc at the atomistic level to weight percentages in its fundamental structure for applications such as nuclear waste disposal and radiopharmaceuticals. In this work, the synthesis and irradiation of CaMoO₄ using a modular, fusion-based neutron source and its successive characterizations are reported. Further discussions are presented considering these empirical data and their context with potential applications in the realms of nuclear medicine and materials.

Keywords: technetium; waste disposal encapsulation; molybdate; ceramics; post-irradiation

  • Contribution to proceedings
    10th Symposium on Technetium and Rhenium science and application, 03.-06.10.2018, Moscow, Russia
    10th Symposium on Technetium and Rhenium science and application, 978-5-9933-0132-7
  • Lecture (Conference)
    10th Symposium on Technetium and Rhenium science and application, 03.-06.10.2018, Moscow, Russia

Publ.-Id: 28215

Effects of gamma-alumina nanoparticles on strontium sorption in smectite: additive model approach

Mayordomo, N.; Alonso, U.; Missana, T.

Strontium sorption was analysed in binary mixtures of smectite and γ-alumina nanoparticles under different pH, ionic strength and Sr concentration. The aims were to verify if γ-alumina nanoparticles enhance Sr sorption in smectite and to analyse whether a component additive model satisfactorily described Sr sorption in the mixtures.
In smectite, Sr sorption mainly occurs by cation exchange but surface complexation was also accounted for. In both solids, surface complexation was described with a non-electrostatic model.
The addition of γ-Al₂O₃ nanoparticles to smectite improved Sr uptake under alkaline pH and high ionic strength, and the additive model successfully reproduced experimental data. In contrast, under acid pH and low ionic strength, no sorption improvement was observed upon adding the nanoparticles and the additive model overestimated Sr sorption. The competition of Al(III) ions, coming from γ-Al₂O₃ dissolution, partially explained the differences between data and model. Nevertheless, surface interactions between alumina particles and smectite layers may be shielding the charge, hindering contaminant access to exchangeable sites in smectite.

Keywords: Strontium; smectite; alumina; nanoparticles; sorption modelling; additive model

Publ.-Id: 28214

Is It Here/There Yet? - Real Life Experiences of Generating/Evaluating Extreme Data Sets Around the World

Juckeland, G.; Huebl, A.; Bussmann, M.

Large scale simulations easily produce vast amounts of data that cannot always be evaluated in-situ. At that point parallel file systems come into play, but their per node performance is essentially limited to about the speed of a USB 2.0 thumb drive (e.g. the Spider file system at OLCF provides over 1 TB/s write bandwidth, but with 18000+ nodes of Titan writing simultaneously, this number is reduced to about 50 MB/s per node). Making the most out of such a limited resource requires I/O libraries that actually scale. In addition such libraries also offer on the fly data transformations (e.g. compression) to better utilize the raw I/O bandwidth, albeit, opening a new can of worms by trading compression throughput with compression ratios for performance. We will present a detailed study of I/O performance and various compression techniques at OLCF and compare them against smaller local I/O installations, demonstrating the highest achieved I/O performance for real world applications at OLCF. Furthermore, we demonstrate that the best performing I/O setup can be determined prior to starting the job based on hardware characteristics.
Now that you have your data on disk the clock starts ticking and you are fighting against the deadline until your data will be purged, since most centers only offer the high performing storage spaces on a temporary basis. Extracting all valuable information out of a petabyte sized data set requires parallel processing as well and induces wait times until the resources are available and quite naturally a lot of trial-and-error for the evaluation. The time constraint for keeping the temporary data becomes even more troublesome when trying to compare multiple large simulations that naturally have a delay of multiple days until they are scheduled and write their results. And ideally analysis could embrace the data of multiple simulations of a quarterly accounted, yet year-long computing campaign. Another challenge for actually conducting scientific discoveries comes when utilizing multiple compute sites. This seems to be rather usual for research groups as they will use all the compute clock cycles they
can get wherever that may be. For comparative studies the data sets now need to be available at the same time for analysis, e.g. via archiving solutions or transfer to one location. The achievable transfer bandwidth between data centers is in our experience still much lower than expected. The talk will also present on the experiences of evaluating petabyte sized data sets in such a diverse environment.


Publ.-Id: 28213

Neutron flux and spectrum in the Dresden Felsenkeller underground facility studied by moderated He-3 counters

Grieger, M.; Hensel, T.; Agramunt, J.; Bemmerer, D.; Degering, D.; Dillmann, I.; Fraille, L. M.; Köster, U.; Marta, M.; Müller, S.; Taín, J. L.; Zuber, K.

Ambient neutrons may cause significant background for underground experiments. Therefore, it is necessary to investigate their flux and energy spectrum in order to devise a proper shielding. Here, two sets of altogether ten moderated ³He neutron counters are used for a detailed study of the ambient neutron background in tunnel IV of the Felsenkeller facility, underground below 45 meters of rock in Dresden/Germany. One of the moderators is lined with lead and thus sensitive to neutrons of energies higher than 10 MeV. For each ³He counter-moderator assembly, the energy dependent neutron sensitivity was calculated with the FLUKA code. The count rates of the ten detectors were then fitted with the MAXED and GRAVEL packages. As a result, both the neutron energy spectrum from 10⁻⁹ MeV to 300 MeV and the flux integrated over the same energy range were determined experimentally.
The data show that at a given depth, both the flux and the spectrum vary significantly depending on local conditions. Energy integrated fluxes of (0.61±0.05), (1.96±0.15), and (4.6±0.4)×10⁻⁴ cm⁻² s⁻¹, respectively, are measured for three sites within Felsenkeller tunnel IV which have similar muon flux but different shielding wall configurations.
The integrated neutron flux data and the obtained spectra for the three sites are matched reasonably well by FLUKA Monte Carlo calculations that are based on the known muon flux and composition of the measurement room walls.

Keywords: Underground; Felsenkeller; Neutron Flux; FLUKA


Publ.-Id: 28212

Cross section and neutron angular distribution measurements of neutron scattering on natural iron

Pirovano, E.; Beyer, R.; Dietz, M.; Junghans, A. R.; Müller, S. E.; Nolte, R.; Nyman, M.; Plompen, A. J. M.; Röder, M.; Szücs, T.; Takacs, M. P.

New measurements of the neutron scattering double differential cross section of iron were carried out at the neutron time-of-flight facilities GELINA and nELBE. A neutron spectrometer consisting of an array of up to 32 liquid organic scintillators was employed, which was designed to measure the scattering differential cross section at eight scattering angles and to simultaneously determine the integral cross section via numerical quadrature. The separation of elastic from inelastic scattering was achieved by analysing the time-of-flight dependent light-output distributions to determine the scattered neutron energy. The method was validated by studying elastic scattering on carbon and it was proved to work well for the determination of the elastic cross section. Here, the possibility to extend it to inelastic scattering was investigated too. For these experiments a sample of natural iron was used and the results cover the incident neutron energy range from 2 to 6~MeV. Both the differential and the integral elastic cross sections were produced for Fe, while for inelastic scattering, partial angular distributions for scattering from the first excited level of Fe could be determined.

Keywords: GELINA; nELBE; fast neutron scattering; cross section; angular distribution; iron

Related publications

Publ.-Id: 28211

Radiosynthesis and preliminary biological evaluation of a novel 18F-labeled MCT1/MCT4 inhibitor for tumor imaging by PET

Sadeghzadeh, M.; Moldovan, R.-P.; Wenzel, B.; Deuther-Conrad, W.; Toussaint, M.; Fischer, S.; Ludwig, F.-A.; Teodoro, R.; Kranz, M.; Spalholz, T.; Gurrapu, S.; Steinbach, J.; Drewes, L. R.; Brust, P.

Aim: Monocarboxylate transporters (MCTs) are integral plasma membrane proteins that bi-directionally transport lactate and ketone bodies and are highly expressed in non-hypoxic regions of human colon, brain, breast, lung and other tumors.[1] Transporter inhibition leads to intracellular lactate accumulation, acidosis and cell death especially in glioma cell lines.[2] Accordingly, MCT1/MCT4 inhibitors are regarded to be of potential clinical use. In the current study a new 18F-labeled MCT1/MCT4 inhibitor was developed for in vivo PET imaging of MCT1/MCT4-overexpressing brain tumors.

Methods: (E)-2-Cyano-3-{4-[(3-fluoropropyl)(propyl)amino]-2-methoxyphenyl}acrylic acid (CAPAA) was synthesized from m-anisidine in three consecutive steps with 50% overall yield. Similar strategy was carried out to synthesize the mesylated precursor for radiosynthesis. Radiosynthesis of [18F]CAPAA was achieved by a two-step reaction, starting with the nucleophilic substitution of fluorine-18 on the alkyl chain using [18F]TBAF followed by removal of the protecting group by TFA at room temperature. [18F]CAPAA was isolated by semi-preparative HPLC eluting with 46% CH3CN/aq. 20 mM NH4HCO2 (Reprosil-Pur C18-AQ column, 250 × 10 mm), purified via Sep-Pak® C18 light cartridge and formulated in 10% EtOH/saline solution. LogD was assessed by the shake-flask method. The average IC50 values for MCT1 and MCT4 were evaluated via [14C]lactate uptake assay on the rat brain cerebrovascular endothelial cell line RBE4. The apparent affinity of [18F]CAPAA (KD) was determined using brain homogenate obtained from female CD1 mouse. The radiotracer metabolism was investigated in female CD1 mice by radio-HPLC of plasma and brain samples obtained at 30 min p.i. Plasma obtained at 60 min p.i. was used to measure the in vivo plasma free fraction.

Results: During radiosynthesis, a radiolabeled intermediate was obtained by an optimized procedure (CH3CN, 50µl of TBAHCO3-, 2-5 GBq of K[18F]F, 100 ̊C, 15 min) with 55-70% yield (n=8, non-isolated) determined by radio-HPLC analysis. Deprotection of tert-Bu group was accomplished with TFA in acetonitrile at r.t. for 15 min with 65-73% yield (n=10, radio-HPLC, non-isolated). The radiotracer was obtained in 42-65% radiochemical yield (RCY) with >98% radiochemical purity (RCP). The radioligand was highly stable in saline and PBS (>95%) up to 60 min. LogD was determined as 0.42 which reveals the tracer has moderate lipophilicity. CAPAA showed high MCT1 and MCT4 inhibition activity (IC50 = 11 and 6.4 nM respectively). [18F]CAPAA binds with an apparent KD value of ~30 nM in a saturable manner to a binding site in the brain of healthy mice. In vivo studies showed >99% of intact tracer in plasma at 30 min p.i. and a free fraction in plasma of ~3% at 60 min p.i.

Conclusions: [18F]CAPAA was achieved in high RCY and RCP and showed considerable in vitro and in vivo stability. Accordingly, the newly developed MCT1/MCT4 radioligand is anticipated to be a useful agent for imaging of tumors by PET. Animal PET imaging on healthy and brain tumor-bearing mice is currently performed.

Keywords: Radiofluorination; MCT1; Tumor imaging

  • Contribution to proceedings
    26. Jahrestagung Arbeitsgemeinschaft Radiochemie und Radiopharmazie (AGRR2018), 20.-22.09.2018, Aachen, Deutschland

Publ.-Id: 28210

Paramagnetic NMR investigations of metal-organic complexes of soft donor ligands and the tetravalent actinides

Schöne, S.; Radoske, T.; Felsner, B.; Köhler, L.; Patzschke, M.; März, J.; Kaden, P.

NMR spectroscopy of metal-organic complexes of the f-element metal ions is often challenging due to additional chemical shifts and enhanced relaxation close to the paramagnetic metal center. These effects originate from electronic interactions between metal and ligand and often result in large additional NMR chemical shifts, compared to isostructural diamagnetic complexes, ob-served on the resonances of the ligands’ nuclei. The major two contributors to these paramag-netic chemical shifts are Fermi-contact shifts (FCS) and pseudo-contact shifts (PCS). FCS are due to delocalization of unpaired electron density in molecular orbitals involving both metal and ligand orbitals and thus report on the bond properties. PCS are originating from distance- and angle-dependent dipolar coupling of electron spins through space and are therefore bearing structural information.

The paramagnetic contributions can be mathematical separated provided that a suitable diamag-netic reference is available in order to subtract non-paramagnetic contributions. For the trivalent actinides no diamagnetic reference in the same series is available in milligram scale. Further-more, all available theories behind mathematical disentangling of contributions to the paramag-netic chemical shift, even for the lanthanide series, omit the influence of spin-orbit effects that might have a sizeable contribution as well. [1,2] Comparing studies of isostructural diamagnetic complexes of both f-element series of tetravalent metal ions (Ce(IV) and Th(IV)) allow for an es-timation of additional influences to the chemical shifts and the effect of contributions usually omitted by commonly used mathematical theories.

With Th(IV) as a diamagnetic reference in the same series, studying paramagnetic metal-organic complexes of the tetravalent actinides (An(IV)) allows to assess the chemical bonding situation via the influences on NMR chemical shifts (via FCS) and additionally allows to exploit the geo-metrical information which can be extracted from dipolar interactions (via PCS). These structural properties of the complexes as derived from PCS contributions can be compared to single crys-tal X-ray diffraction structures enabling a comparison of solution state and solid state structure of the metal-organic complexes under investigation. Herein we report the first results of investiga-tions of N- and N,O-donor ligand complexes of the An(IV) series (Th(IV), U(IV) and Np(IV)).

Keywords: NMR; actinides; paramagnetic; metal organic; Th; U; Np; Pu; Thorium; Uranium; Neptunium; Plutonium; diamagnetic

  • Lecture (Conference)
    ATAS - 4th International Workshop on Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28209

Development of the first 18F-labeled MCT1/MCT4 lactate transport inhibitor: Radiosynthesis and preliminary in vivo evaluation in mice

Sadeghzadeh, M.; Moldovan, R.-P.; Wenzel, B.; Kranz, M.; Deuther-Conrad, W.; Toussaint, M.; Fischer, S.; Ludwig, F.-A.; Teodoro, R.; Gurrapu, S.; Drewes, L. R.; Brust, P.

Objectives: Although, lactate is occasionally considered as a waste in physiological cell metabolism, it is also known as an important substrate that fuels the oxidative metabolism of oxygenated tumor cells. Therefore, tumor cells express a set of plasma membrane transporters for lactate. Those monocarboxylate transporters (MCTs) are regarded as functional biomarkers for the metabolic symbiosis between glycolytic and oxidative tumor cells [1]. Overexpression of MCT1 and MCT4 has been shown for a variety of human cancers (e.g. colon, brain, breast, and kidney) [2]. Experimentally, inhibition of MCT1/MCT4 resulted in intracellular lactate accumulation, acidosis and cell death. In the current study, the first 18F-labeled MCT1/MCT4 inhibitor was developed for potential in vivo imaging of MCT expression in cancer.
Methods: Fluorinated α-CHC derivatives (FACH and tert-Bu-FACH) were synthesized and the inhibitory activity of FACH towards MCT1 and MCT4 was estimated by [14C]lactate uptake assays using an immortalized rat brain endothelial cell line (RBE4). For the radiosynthesis of [18F]FACH, a protected mesylate precursor was developed to prevent any possible effect on the labeling reaction. [18F]FACH was produced via a two-step radiosynthesis approach, starting with the nucleophilic substitution on the alkyl chain using [18F]TBAF followed by removal of the protecting group by trifluoroacetic acid (TFA) at room temperature (Figure 1A).
Isolation of [18F]FACH was performed by semi-preparative HPLC (Reprosil-Pur C18-AQ column, 250 × 10 mm, 46% CH3CN/aq. 20 mM NH4HCO2, pH = 4-5, flow 3.5 mL/min). The tracer was finally purified via solid-phase extraction (Sep-Pak® C18 light cartridge) and formulated in 10% EtOH/saline solution. In vitro stability tests were performed in pig plasma, saline, PBS and n-octanol. The LogD value was assessed by the shake-flask method. The in vivo metabolism of the radiotracer was investigated in female CD-1 mice at 30 min p.i. The biodistribution of [18F]FACH and the inhibitory effects of FACH and α-CHC were investigated by dynamic PET imaging (60 min, nanoScan® PET/MRI, MEDISO, Budapest, Hungary) of female CD-1 mice (Figure 1B).
Results: FACH showed strong inhibition of MCT1 and MCT4 (IC50 = 11 and 6.4 nM respectively). The intermediate [18F]tert-Bu-FACH was obtained by an optimized procedure (CH3CN, 3.75 µmol of TBAHCO3, 2-5 GBq of K[18F]F, 100 ̊C, 15 min) with 55-85% radiochemical yield (n = 10, non-isolated). [18F]FACH was obtained after deprotection of [18F]tert-Bu-FACH with TFA in acetonitrile at room temperature for 15 min. After purification and formulation, the novel radiotracer could be achieved with a RCY of 39 ± 3% (n = 10, EOB), molar activity of 42-100 GBq/µmol (EOS), and RCP >98%. The measured logD value (0.42) reveals moderate lipophilicity of the radiotracer. [18F]FACH was highly stable in saline (>98%) up to 60 min. In vivo metabolite studies showed >98% of intact tracer in plasma, brain, liver and kidney at 30 min p.i. Beside [18F]FACH, a few polar metabolites were also found in urine after 30 min p.i. The organ distribution pattern of [18F]FACH in healthy mice corresponds to the specific expression of MCT1 and MCT4 in kidney, lung, pancreas and liver. In these tissues, a moderate to high reduction of uptake was observed after after pre-injection of FACH and α-CHC, respectively.
Conclusions: The high uptake of [18F]FACH in kidney and other peripheral MCT-expressing organs together with the strong inhibition by specific drugs provide evidence that the new MCT1/MCT4-targeting radiotracer could be proven in ongoing studies to be useful for imaging of solid tumors with PET.

Keywords: Monocarboxylate transporter; Radiofluorination; PET; [18F]FACH

  • Contribution to proceedings
    23rd International Symposium on Radiopharmaceutical Sciences (ISRS2019), 26.-31.05.2019, Beijing, China

Publ.-Id: 28208

The Unofficial "Green HPCG"

Huebl, A.

An unofficial list of HPC systems, compiled from the HPCG Benchmark and TOP500 in order to explore an alternative metric for the Green500.

Keywords: hpc; manycore; top500; computing; hardware; energy efficiency


Publ.-Id: 28207

FMR Linewidth Variation with Distance from Lateral Antiferromagnet/Ferromagnet Interfaces

Usami, T.; Bali, R.; Lindner, J.; Itoh, M.; Taniyama, T.

B2-ordered FeRh alloys show a fascinating first-order magnetic phase transition from the antiferromagnetic (AFM) to the ferromagnetic (FM) state at around 380 K[1]. Recently, the AFM/FM phase transition and its related phenomena have been extensively studied; the transition temperature can be manipulated by substituting ions[2], introducing disorder via ion irradiation[3], injecting a spin-polarized current[4], and applying an electric field[5]. These experimental demonstrations would provide a fundamental basis for the use of FeRh in practical novel spintronic applications such as magnetic recordings, AFM memory resistors, and magnonic devices. Also, we have shown a long-range propagation of spin waves in a ferromagnetic Fe60Rh40 thin wire, demonstrating that FeRh has its potential of an alternative material for magonics [6]. In this study, we report ferromagnetic resonance (FMR) in the proximity of lateral AFM/FM FeRh interfaces that are generated by Ne+ ion irradiation. From the FMR measurements, we find a unique dependence of linewidth of the FMR spectra as a function of distance between the rf-antenna and the AFM/FM interface.

Related publications

  • Poster
    Magnetics and Optics Research International Symposium 2018, 07.-10.01.2018, New York, United States of America

Publ.-Id: 28206

Measurement of Diamond Nucleation Rates from Hydrocarbons at Conditions Comparable to the Interiors of Icy Giant Planets

Schuster, A. K.; Hartley, N. J.; Vorberger, J.; Döppner, T.; van Driel, T.; Falcone, R. W.; Fletcher, L. B.; Frydrych, S.; Galtier, E.; Gamboa, E. J.; Gericke, D. O.; Glenzer, S. H.; Granados, E.; Macdonald, M. J.; Mackinnon, A. J.; Mcbride, E. E.; Nam, I.; Neumayer, P.; Pak, A.; Prencipe, I.; Rohatsch, K.; Saunders, A. M.; Sun, P.; Kraus, D.

We present measurements of the nucleation rate into a diamond lattice in dynamically compressed polystyrene obtained in a pump-probe experiment using a high energy laser system and in situ femtosecond X-ray diffraction. Different temperature-pressure conditions that occur in planetary interiors were probed. For a single shock reaching 70GPa and 3000K no diamond formation was observed while with a double shock driving polystyrene to pressures around 150GPa and temperatures around 5000K nucleation rates between 1029 m-3s-1 and 1034 m-3s-1 were recorded. These nucleation rates do not a agree with predictions of recent theoretical models for carbon-hydrogen mixtures by many orders of magnitude. Our data suggests that there is indeed significant diamond formation to be expected inside icy giant planets like Neptune and Uranus.

Publ.-Id: 28205

The role of fluid flow in heat and mass transport in Liquid Metal Batteries

Personnettaz, P.; Landgraf, S.; Nimtz, M.; Weber, N.; Weier, T.

Liquid metal batteries (LMBs) are suggested as a promising energy storage technology. An LMB is a three liquid layers concentration cell: two liquid metal electrodes are divided by a molten salt electrolyte. The relatively simple composition and geometry, the occurrence of multi-physics phenomena and the completely liquid nature of the active material have made the LMB an interesting candidate for continuum mechanics studies, ranging from magnetohydrodynamics to transport phenomena, such as Marangoni convection. The cell is in fact subject to a simultaneous transport of charge, heat, mass and momentum together with electrochemical reactions. The fluid flow can be beneficial if it is able to enhance the mixing at the electrolyte interfaces, thereby preventing the formation of intermetallic solid phases. However, a vigorous flow can also be detrimental to the safe operation of the battery, leading to short circuit induced by the rupture of the thin electrolyte layer. In our work the attention is focused on the role of fluid flow in heat and mass transport.
Thermally driven convection is investigated in a three layer Li||Bi LMB with an extended version of the VOF solver multiphaseInterFOAM. A relevant flow is discovered in the pure negative electrode, however it is too weak to deform the liquid interface. Moreover mass transfer is studied in the positive electrode with a single-phase CFD solver. The presence of solutal convection is numerically confirmed during the charge of the cell. The flow structures and the effects on cell efficiency are presented, the modeling limitations and the future developments are discussed.

Keywords: LMB; mass transport; heat transfer; openFoam; CFD

  • Poster
    MHD Days and GDRI Dynamo Meeting, 26.-28.11.2018, Dresden, Germany

Publ.-Id: 28204

Ion induced ferromagnetism combined with self-assembly for large area magnetic modulation of thin films

Krupinski, M.; Bali, R.; Mitin, D.; Sobieszczyk, P.; Gregor-Pawlowski, J.; Zarzycki, A.; Böttger, R.; Albrecht, M.; Potzger, K.; Marszałek, M.

A highly versatile and scalable path to obtain buried magnetic nanostructures within alloy thin films, while maintaining a flat topography, is described. A magnetic pattern of nanoscale periodicity is generated over ∼cm 2 areas by employing a B2 → A2 structural transition in the prototype Fe 60 Al 40 thin alloy films. The phase transition was induced in the confined regions via ion-irradiation through self-assembled nanosphere masks. In this way, large area patterns of a hexagonal symmetry of ferromagnetic nanostructures embedded within a paramagnetic Fe 60 Al 40 thin film are realized. The depth and lateral distribution of the induced magnetization was investigated by magnetometry and microscopy methods. Magnetic contrast imaging as well as simulations shows that the obtained magnetic structures are well defined, with the magnetic behavior tunable via the mask geometry.

Keywords: self-assembly; magnetic nanostructures; chemical disorder; magnetic patterning; ion irradiation

Related publications

Publ.-Id: 28203

Identical pion intensity interferometry in central Au+Au collisions at 1.23A GeV

Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, L.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kühn, W.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.

For the first time, identical pion HBT intensity interferometry is investigated for a large heavy ion collision system in the energy region of 1 GeV per nucleon. High-statistics π−π− and π+π+ data are presented for central Au+Au collisions at 1.23A GeV, measured with HADES at SIS18/GSI. The radius parameters, derived from the correlation function depending on relative momenta in the longitudinal-comoving system and parametrized as three-dimensional Gaussian distribution, are studied as function of transverse momentum. A substantial charge-sign difference of the source radii is found, particularly pronounced at low transverse momentum. The extracted Coulomb-corrected source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy. Our data would thus rather disfavour any strong energy dependence of the radius parameters in the low energy region.

Publ.-Id: 28202

High-field ESR in low-dimensional spin systems

Zvyagin, S.

Electron spin resonance (ESR) is traditionally recognized as one of the most sensitive tools for probing magnetic excitations in strongly-correlated spin systems. Among other exchange-coupled spin systems, low-dimensional magnets serve as almost ideal paradigmatic models in quantum magnetism, exhibiting highly unusual ground-state properties and spin dynamics. Here, I review results of our recent high-field ESR studies of some low-dimensional magnets, including quantum spin chains [1], quantum antiferromagnets on triangular lattice [2], Heisenberg spin ladders [3], and quasi-two-dimensional magnets on a honeycomb lattice [4]. In addition, I will give a brief introduction into the high-field ESR facilities at the Dresden High Magnetic Field Laboratory, which allows for multi-frequency ESR experiments in a very broad frequency range (ca 50 GHz - 9 THz) in magnetic fields up to 60 T and above.

  • Invited lecture (Conferences)
    Third Joint Conference of the Asia-Pacific EPR/ESR Society and The International EPR (ESR) Society (IES) Symposium, 23.-27.09.2018, Brisbane, Australia

Publ.-Id: 28200

TEM investigation of irradiation-induced defects in an ion-irradiated Fe-9Cr ODS steel

Vogel, K.; Duan, B.; Heintze, C.; Bergner, F.

Oxide dispersion strengthened (ODS) steels are promising candidate materials for structural components in nuclear power generators. Here we report on our preliminary results of TEM investigations of irradiation-induced defects in an ion-irradiated Fe-9Cr ODS steel. A cross-sectional TEM sample prepared by focused ion beam (FIB) was studied in a FEI Talos F200X transmission electron microscope by imaging under various diffraction conditions in bright- and dark-field mode. The TEM micrographs show a defect-rich band of about 400 nm width. The band is aligned parallel to the specimen surface and its position corresponds to the position of the peaks in the damage and/or injected interstitials profiles. Therefore we conclude that the defects within the band are caused by the ion irradiation. In higher magnified images of the band we observe a large number of defects, which appear as "black dots" showing a high contrast under kinematic bright-field conditions. We assume that these defects are interstitial loops, however this assumption has to be proved by further investigations. Additionally we observe some strongly curved dislocation segments, which will also be a subject of our further TEM studies.

Keywords: Transmission Electron Microscopy; Irradiation-induced defects

Related publications

  • Poster
    Microscopy of Radiation Damage 2018, 21.-23.03.2018, Oxford, United Kingdom

Publ.-Id: 28199

Effect of Tb for Gd substitution on magnetic and magnetocaloric properties of melt-spun (Gd1-xTbx)3Co alloys

Shishkin, D. A.; Volegov, A. S.; Ogloblichev, V. V.; Mikhalev, K. N.; Gerasimov, E. G.; Terentev, P. B.; Gaviko, V. S.; Gorbunov, D. I.; Baranov, N. V.

The melt-spun (Gd1-xTbx)3Co alloys (0≤x≤1) have been obtained and studied by X-ray diffraction, ac-susceptibility, magnetization in steady and pulse magnetic fields, and NMR measurements. A comparison of the results obtained on melt-spun alloys with their crystalline analogs has revealed a strong impact of amorphization on the magnetic state and magnetocaloric properties. The Gd-rich amorphous (Gd1-xTbx)3Co alloys (x≤0.1) exhibit increased magnetic ordering temperatures in comparison with the crystalline compounds, which is attributed to the appearance of a magnetic moment on Co atoms. The substitution of Tb for Gd results in the growth of the ratio of local anisotropy to exchange. The melt quenching of the (Gd1-xTbx)3Co alloys allows improving their magnetocaloric properties in the temperature range from 80 K up to 170 K.

Publ.-Id: 28198

Cm complexation with aqueous phosphates at elevated temperatures

Huittinen, N.; Jordan, N.; Demnitz, M.; Lösch, H.; Starke, S.; Brendler, V.

Orthophosphate ions (H2PO4-, HPO42-, and PO43-) are ubiquitous in the environment and may originate from the natural decomposition of rocks and minerals (e.g. monazite or apatite), agricultural runoff, or from wastewater treatment plants. Furthermore, the potential use of monazite (LnPO4) ceramics for the immobilization of specific actinide-containing waste streams may become an important source of phosphates in the future [1–2]. Among the inorganic ligands, phosphates are strong complexants and can be expected to influence the speciation of dissolved radioactive contaminants when present in solution. However, very little data is available on the complexation of especially actinides with aqueous phosphates, even though these complexation reactions precede any aqueous synthesis of monazite ceramics and are expected to occur in natural waters as well as in the proximity of monazite-containing high-level waste repositories. The existing data also suffers from an almost systematic absence of independent spectroscopic validation of the stoichiometry of the proposed complexes.
In the present work, time-resolved laser fluorescence spectroscopy (TRLFS) has been employed to study the complexation of the actinide Cm3+ (5×10-7 M) as a function of total phosphate concentration (0–0.5 M Σ(PO4)) in the temperature regime 25–80°C, using NaClO4 as a background electrolyte (0.5–2.1 M). The studies have been conducted in the acidic pH-range ( log[H+] = 1–2.5) to avoid precipitation of solid Cm rhabdophane (CmPO4×nH2O). Under these experimental conditions, the trivalent actinide cation was found to form a complex with the anionic H2PO4- species, i.e. CmH2PO42+ and Cm(H2PO4)2+, depending on the solution pH and the total phosphate concentration, Figure 1.
The complexation reaction occurs at lower total phosphate concentration when increasing the ionic strength or the temperature. Using specific ion interaction theory (SIT) and the Van’t Hoff equation, obtained conditional constants at varying ionic strengths and temperatures have been extrapolated to infinite dilution (logβ0) and values for the enthalpy ΔRH° (assumed constant between 25 to 80 °C) and entropy ΔRS° of reaction have been acquired. The results of the extrapolations are shown exemplarily for the CmH2PO42+ species in Figure 2.
The new thermodynamic data derived in this fundamental study will contribute to a fundamental process understanding necessary to critically assess the environmental fate of actinides in the environment.

  • Lecture (Conference)
    Radiation in the environment – scientific achievements and challenges for the society, 16.-17.04.2018, Helsinki, Finland

Publ.-Id: 28197

Spectroscopic investigations of Cm3+ incorporation in lanthanide orthophosphates

Huittinen, N.; Scheinost, A. C.; Ji, Y.; Kowalski, P. M.; Arinicheva, Y.; Neumeier, S.

Monazites (LnPO4) are envisioned as potential immobilization matrices for high-level radioactive wastes produced e.g. during the nuclear fuel cycle [1–2]. Hydrated rhabdophane (LnPO4×0.67H2O) is a precursor phase during monazite synthesis and a potential solubility-limiting solid phase under nuclear waste storage conditions [3–4]. Thus, for a reliable long-term safety assessment of nuclear waste repositories for conditioned radioactive waste, a fundamental understanding of the radionuclide incorporation process in both the pristine monazite ceramics and their alteration products is required.
In the present study [5] we have combined two spectroscopic methods, (1) time-resolved laser fluorescence spectroscopy (TRLFS) and (2) extended x-ray absorption fine structure spectroscopy (XAFS) with density functional theory-based ab initio calculations to investigate the incorporation of the actinide curium (Cm) in (La,Gd)PO4 monazite and rhabdophane solid phases. Spectroscopic methods allow for direct probing of the dopant and its local environment in host matrices, providing a better understanding of potential lattice defect formations, lattice strain or disordering phenomena, and site population deviances with regard to the composition of the host structure, which may occur in the solid phase upon introduction of the dopant. Ab initio calculations can further deliver descriptions and explanations for spectroscopic findings, thus, contributing to a better understanding of the incorporation processes on a molecular level.
The solid phases were synthesized by addition of phosphoric acid to a solution containing La3+ and Gd3+ in desired relative concentrations and a small amount of the actinide (248Cm), until a white precipitate of La1-xGdxPO4 rhabdophane doped with approximately 50 ppm Cm3+ was obtained. An aliquot of the obtained solid phase was thereafter sintered at 1450°C to acquire the crystalline monazite ceramic. Structural refinement of collected XRD data for both rhabdophane and monazite solids show a linear dependency of lattice parameters as a function of Gd3+ substitution according to Vegard’s law.
Our combined spectroscopic results show that Cm3+ is incorporated in the monazite end-members (LaPO4 and GdPO4) on one specific, highly ordered lattice site. In the intermediate solid solution compositions, an increasing disorder around the Cm3+ dopant can be seen as a result of a broader distribution of possible Cm∙∙∙O bond-lengths in comparison to the end-member compositions with very well-defined nearest neighbour distances. Despite this local structural disordering, homogenous solid solutions were obtained for all synthesized monazite compositions without the formation of dopant clusters that could potentially hamper the performance of the monazite ceramics for the immobilization of minor actinide containing wastes.
The hydrated rhabdophane lattice comprises two different site types that could accommodate the actinide dopant: a 9-coordinated “hydrated” site amounting to two thirds (2/3) of the total number of lanthanide sites in the solid structure, where one coordinating oxygen atom originates from a water molecule, and an 8-fold coordinated “non-hydrated” site (1/3 of available Ln sites) where all oxygen atoms are provided by phosphate groups [4]. Based on our laser spectroscopic investigations, curium incorporation on both site types can be confirmed, however, the site occupancy is not in agreement with the hydrated rhabdophane structure. In contrast, a preferential incorporation of curium on non-hydrated lattice sites can be seen, especially for the La-rich rhabdophane compositions, implying that structural substitution reactions cannot be predicted based on the structure of the host matrix only.

Related publications

  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 06.-09.11.2018, Nice, France

Publ.-Id: 28196

Inverted hysteresis and negative remanence in a homogeneous antiferromagnet

Opherden, L.; Billitewski, T.; Hornung, J.; Herrmannsdörfer, T.; Samartzis, A.; Islam, A. T. M. N.; Anand, V. K.; Lake, B.; Moessner, R.; Wosnitza, J.

Magnetic remanence—found in bar magnets or magnetic storage devices—is probably the oldest and most ubiquitous phenomenon underpinning the technological applications of magnetism. It is a macroscopic nonequilibrium phenomenon: A remanent magnetization appears when a magnetic field is applied to an initially unmagnetized ferromagnet, and then taken away. Here, we present an inverted magnetic hysteresis loop in the pyrochlore compound Nd2Hf2O7: The remanent magnetization points in a direction opposite to the applied field. This phenomenon is exquisitely tunable as a function of the protocol in field and temperature, and it is reproducible as in a quasiequilibrium setting.


Publ.-Id: 28195

Quantitative Modelling and Assessment for Circular Economy Systems

Bartie, N.; Fröhling, M.; Reuter, M. A.

Minerals and metals required to produce renewables and everyday electric and electronic technologies are extracted from both geological (primary) and urban (secondary, recycling) mines. Extraction and recycling process complexity is often neglected in impact assessments. Treatment of interconnected components in isolation is physically impossible, and should be reflected in impact assessments. Claims of completely closed loops neglect irreversible losses governed by the thermodynamics. Aggregation of complex processes into average “black boxes” reduces resolution, removing the ability to allocate impacts and optimise circular economy systems that are often geographically and temporally dispersed. We aim to expand and integrate existing frameworks, models and tools, including fundamental thermochemistry, process simulation, life cycle inventory and impact assessment, costing and thermoeconomics, and to utilise multi-criteria optimisation to conduct holistic assessments and optimisation of resource efficiency, losses and impacts of entire circular economies at high resolution. This will benefit stakeholders from operational through to policy-making levels.

Keywords: Life cycle; Recycling; Metals; Exergy; Thermodynamics; Holistic analysis

  • Poster
    Sustainable Minerals 2018, 14.-15.06.2018, Windhoek, Namibia

Publ.-Id: 28194

HILIC - A simple method to determine [18F]fluoride in plasma and tissue samples

Wenzel, B.; Moldovan, R.; Teodoro, R.; Deuther-Conrad, W.; Brust, P.

Objectives: The investigation of the metabolism of 18F-labeled radiotracers is a crucial step in the development process. Most often radio-defluorination as well as O- and N-dealkylation are observed resulting in the formation of very polar radiometabolites such as [18F]fluoride, [18F]fluoroethanol or [18F]fluoroacetic acid. Due to their high polarity these compounds are not easy to separate and analyze by the routinely used reversed phase HPLC. In a recent study we were faced with the problem of finding a high fraction of a very polar radiometabolite in brain samples of mice obtained after injection of a newly developed radiotracer, which seemed to be [18F]fluoride. However, as [18F]fluoride is not able to penetrate the blood-brain barrier to a considerable amount, we were interested to investigate the identity of this radiometabolite in the brain samples.

Methods: Hydrophilic interaction chromatography (HILIC) was selected as HPLC method since the elution order is more or less the reverse of the elution order in RP-HPLC. This is achieved by the use of a polar stationary phase and an aqueous mobile phase with a high content of organic solvent. In the present study, the retention and elution profile of [18F]fluoride was investigated by using a Nucleodur HILIC column (250 × 4.6 mm; Macherey-Nagel GmbH, Germany) and modifying the following parameters: i) organic solvent (e.g. CH3CN, CH3OH, THF), ii) pH value of the eluent, iii) concentration and nature of buffer additives (e.g. ammonium acetate, ammonium formate) and iv) isocratic and gradient mode. Typical investigated conditions comprised eluent compositions of 86-70% organic solvent/14-30% water, buffer concentrations ranging from 5 to 100 mM and acid concentrations of 0.05%.


The type of the organic solvent strongly influenced the retention of 18F]fluoride. Best results could be achieved with CH3CN, while with CH3OH almost no retention could be obtained. Also the pH value of the eluent played a crucial role. By using 0.05% trifluoroacetic acid (pH ~2) or formic acid (pH ~3) in the eluent, [18F]fluoride strongly retained on the stationary phase and eluted only at long retention times as very broad peak. The use of buffer systems at pH 6 to 8 improved the retention and the peak shape. Comparing ammonium formate and ammonium acetate the latter gave so far the best results. For example, under isocratic conditions at 74% CH3CN/20 mM NH4OAcaq, [18F]fluoride eluted at a retention time of 14 min while more lipophilic compounds such as typical 18F-labeled radiotracers elute close to the dead time of the column (A in Figure 1). Subsequently, this method was used to investigate homogenates of ex vivo brain samples of our newly developed P2Y1 receptor radiotracer [18F]1 (1-{2-[2-(tert-butyl)phenoxy]pyridin-3-yl}-3-[4-[18F.

Figure 1: A) HILIC radio-chromatogram of a mixture of [18F]1 and [18F]fluoride, B) HILIC radio-chromatogram of a mouse brain sample at 30 min p.i. of [18F]1; conditions: Nucleodur HILIC, 250 x 4.6 mm, 74% CH3CN/20 mM NH4OAcaq, flow 1.0 mL/min.


Hydrophilic interaction chromatography is a simple and useful method to determine [18F]fluoride in biological samples such as plasma and brain homogenates. Further investigation is ongoing to further improve the retention profile and to use this method also for other typical polar radiometabolites such as [18F]fluoroacetic acid and [18F]fluoroethanol.

References: [1] Moldovan et al. Eur. J. Med. Chem. (in revision) "Studies towards the development of a PET radiotracer for imaging of the P2Y1 receptors in the brain: synthesis, 18F labeling and preliminary biological evaluation".

  • Lecture (Conference)
    ISRS 2019, 26.05.-01.06.2019, Beijing, China

Publ.-Id: 28193

Association of Eu(III) and Cm(III) onto an extremely halophilic archaeon

Bader, M.; Moll, H.; Steudtner, R.; Lösch, H.; Drobot, B.; Stumpf, T.; Cherkouk, A.

Regarding the final storage of high-level radioactive waste in a deep geological repository next to geological, geochemical and geophysical also microbial aspects have to be taken into account. Rock salt is a potential host rock formation for the repository. One in rock salt common indigenous microorganism is the halophilic archaeon Halobacterium noricense DSM15987T, which was used in our study to investigate its interactions with the trivalent actinide curium and its inactive analogue europium as function of time and concentration. Time-resolved laser-induced fluorescence spectroscopy was applied to characterize formed species in the µM europium concentration range. An extended evaluation of the data with parallel factor analysis revealed the association of Eu(III) to a phosphate compound released by the cells (F2/F1 ratio: 2.50) and a solid species (F2/F1 ratio: 1.80). The association to an aqueous phosphate species and a solid species could be proven with the site-selective TRLFS. Experiments with Cm(III) in the nM concentration range showed a time- and pCH+-dependent species distribution. These species were characterized by red shifted emission maxima, 600 – 602 nm, in comparison to the free Cm(III) aqueous ion, 593.8 nm. After 24 h 40 % of the luminescence intensity was measured on the cells corresponding to 0.18 µg Cm(III)/gDBM. Our results demonstrate that Halobacterium noricense DSM15987T interacts with Eu(III) by the formation of phosphate species, whereas for Cm(III) also a complexation with carboxylic functional groups was observed.

Publ.-Id: 28192

Experimental investigation on the buoyancy-induced flow in a model of the Czochralski crystal growth process

Pal, J.; Franke, S.; Eckert, S.; Gerbeth, G.

Within this paper we present a model experiment focusing on investigations of the flow field in a Czochralski puller. Low melting point liquid metals as GaInSn are an important tool to investigate the flow structure for such industrial processes. The topology of the prevailing thermally-driven convection might be very complex and is mainly determined by the aspect ratio of the liquid volume and the strength of the convection described by the characteristic dimensionless Grashof number. The measurements of the fluid flow have been conducted by means of the ultrasound Doppler velocimetry (UDV) with and without the influence of external magnetic fields. Two kinds of sensor configurations were used to investigate the flow. Firstly, measurements of the radial velocity component by means of single UDV transducers were carried out shortly below the melt surface across the entire diameter of the cylindrical liquid column at various azimuthal angles. Secondly, a vertically arranged UDV array was applied at the side of the cylinder to obtain more detailed information about the radial velocities in the covered meridional plane. The results reveal the complex flow structure of natural convection in a Czochralski crucible which gains in complexity with applied external magnetic fields.

Keywords: Czochralski crystal growth process

Publ.-Id: 28191

The challenge of digitalising lead smelting with technology elements

Schalkwyk, R. F. Van; Reuter, M. A.; Stelter, M.

Technology elements (e.g. Te, Se, Ge) are crucial to the creation of complex products, e.g. photovoltaic cells, which also drive the circular economy. However, these elements introduce complexity when the waste materials (slags, flue dusts or electronic wastes) that contain them are treated in lead smelters. This strategy of treating wastes in lead smelters is followed to utilise existing infrastructure as far as possible. In order to address the complex metallurgy, a dynamic model of the furnaces that are operative in lead metallurgy is required. This project focuses on the laboratory measurements of thermodynamic and kinetic parameters that will be used to create a dynamic model of a Top Submerged Lance furnace.

Keywords: Top Submerged Lance furnace; Kinetics; Technology Elements; Modeling

  • Lecture (Conference)
    GDMB Lead Experts Meeting, 26.04.2018, Freiberg, Deutschland

Publ.-Id: 28190

Digitalizing the circular economy: Behaviour of technology elements during lead smelting

Schalkwyk, R. F. Van; Reuter, M. A.; Stelter, M.

Lead pyrometallurgical infrastructure plays an important role in the circular economy, due to the application of existing lead infrastructure and smelters for processing of secondary materials (e.g. electronics, flue dusts and waste slags). However, as the proportion of non-traditional secondary feed materials to smelters increases, so does the complexity. Better understanding is required of non-traditional and minor elements in lead metallurgy, e.g. Se.
During direct lead smelting, molten metal and slag phases form and minor elements are distributed amongst these. Se typically reports to the lead bullion and is removed from the bullion during refining stages. It is important to determine the metal/slag distribution in order to understand downstream process impacts and to avoid contamination of the final product.
Equilibration experiments are carried out in a laboratory furnace to determine slag/metal distributions of minor elements. At thermodynamic equilibrium, the distribution is affected by the temperature, slag composition, oxygen potential and interactions between elements in the melt. Results from equilibrium measurements and process implications will be discussed.

Keywords: Lead; Equilibrium; Selenium; Technology Elements; Circular Economy

  • Poster
    Sustainable Minerals, 14.-15.06.2018, Namibia, Namibia

Publ.-Id: 28189

Two-dimensional Pd3P2S8 Semiconductors as Photocatalysts for Solar Oxygen Evolution Reaction: A Theoretical Investigation

Jing, Y.; Heine, T.

On the basis of first principles calculations, we propose Pd3P2S8 monolayer and bilayer, two-dimensional semiconductors, whose layered bulk parent crystals are experimentally reported, as promising photocatalysts for the solar-driven oxygen evolution reaction. The monolayer is kinetically and thermodynamically stable and shows a small cleavage energy of 0.35 J m−2, suggesting that it can be prepared by exfoliation from its bulk material, and exhibits a direct band gap of 2.98 eV, which can be engineered by applying strain. The Pd3P2S8 bilayer is an indirect band gap semiconductor with a slightly smaller band gap of 2.83 eV. The photoexcited holes generate favorable driving forces for promoting the specific solar-driven O2 evolution reaction. The extraordinary electronic properties, pronounced light harvesting capability in the visible and ultraviolet regions and active surface sites render the Pd3P2S8 monolayer and bilayer as compelling 2D materials with interesting application potential for photocatalytic and photoelectrocatalytic water splitting.

Publ.-Id: 28188

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