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discovered_02_2013

FOCUS// The HZDR Research Magazine WWW.Hzdr.DE 10 11 An initial proposal for compaction of the sawdust was submitted by the company GARBO. The compacted material has to be inductively heated and molten using high- frequency magnetic fields. Thereafter, it's important to collect the contaminants at the edge of the molten metal and separate them out. Due to differences as regards the electrical conductivity of silicon and silicon oxide or silicon carbide particles, an electromagnetic force acts on the dirt particles, which can be adjusted in such a way as to cause the contaminants to migrate towards the edge. At the same time, however, you have to make sure that the silicon flow, which is caused by the magnetic field, doesn't end up negating this separation effect through too intense mixing. In other words, you need a cunning combination of magnetic field parameters to bring about the desired results. "That is what we're working on right now. MULTIMAG, our magnetic multi-function facility at the HZDR, allows us to set up different flow forms and speeds and we're counting on getting the hang of it," says liquid metal expert Eckert. As soon as the HZDR scientists are successful at proving this using their model alloy - which is liquid at room temperature - they're planning on building a demonstrator to help them even better understand the different steps of the process using their own measuring technique. Numeric models designed by their London colleagues at Greenwich University will also help with a better understanding. But before they are transferred to the industrial setting, the worked-out steps of the process have to first be tested on silicon; after all, the metal won't melt until it has reached a temperature of 1,410 degrees C. Since scientists at Padua University are able to melt and process silicon, they will be able to build a demonstrator for use with the silicon in this process on the basis of insights from Dresden and London. The German company EAAT is planning and supplying the necessary power supply. The facility has to be able to drive different heating steps and set up different magnetic field frequencies. Unlike current heating processes, the EU project is using an induction process known from induction heating and its optimization, customized to the desired degree of particle segregation. The partners from both science and industry have a clear- cut goal: To use a single process in partly parallel steps to compact and melt the expensive silicon waste, separate out the inevitable dirt particles - and all this from an ecological and economical perspective. Only then, Sven Eckert is certain, can the energy yield of photovoltaic silicon be improved by a substantial factor even when considering that for compacting and melting the silicon chips energy has to be put in as is true for electromagnetic stirring and separation. Silicon – next steps Silicon is the material of choice on a rapidly growing solar market as it is comparatively efficient at converting energy from sunlight into electricity. In Germany, some 32 gigawatts of performance are currently installed in photovoltaic modules and the sector's plan is to ultimately increase that number to more than 200 gigawatts. Then as now, new concepts are needed for continuously improving efficiency. If, in the context of the SIKELOR project, it were possible to process the raw material which accumulates as dust during wafer production, this could mean the solar industry would be able to save on expenses. Currently, the cost of silicon on the World market is around 18 US dollars per kilogram - experts, however, are projecting that this price will go up significantly within the next several years - the SIKELOR partners are projecting a cost of a mere 10 US dollars per kilogram of recyclable material for their recycling process. Finally, even recycling worn-out solar modules could help continue to improve photovoltaics' energy balance. Sven Eckert and his HZDR colleagues are already thinking about whether or not - and, if so, then how - silicon waste might be recycled. Unlike during the manufacturing process, they would then be looking at large silicon wafer splinters and fragments. A novel but at the same time an exciting challenge. TORNADO INSIDE THE LAB: Magnetic fields produce flows inside a fluid-filled cylinder that can be examined with the help of ultrasound technology. Photo: Rainer Weisflog Contact _Institute of Fluid Dynamics at HZDR Dr. Sven Eckert s.eckert@hzdr.de

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