RES³T - Rossendorf Expert System for Surface and Sorption Thermodynamics

The interfacial properties of ZrO₂ and Fe₃O₄ inmersed in water were studied through measurements of electrophoretic mobilities and surface charge densities obtained by potentiometric titrations. The pH(pzc) values were also determined by the addition method. The results are critically compared with previous data from the literature, and interpreted through the model of Davis, James, and Leckie [J. Colloid Interface Sci. 63, 480 (1978); 67, 90 (1978); 74, 32 (1980)]. Values of the constants pK_a1^int, pK_a2^int, p*K_anion^int, and p*K_cation^int are derived for both oxides in KNO₃ solutions. The relative contribution of the two mechanisms (potential-determining ions exchange with solvent and complex pairs formation with swamping electrolyte) to charge development is very different in both cases. This behavior is discussed in terms of the DJL model.