Electrical double layer at zirconium oxide-solution interface

The double layer properties of zirconium oxide-solution interface have been investigated by measuring the equilibrium distribution of potential-determining ions (H+ and OH-) between the interface and the bulk solution, as a function of H and ionic strength. Potentiometric acid-base titration and electrophoretic mobility measurements have been used to determine the zero point of charge (ZPC) of zirconium oxide-solution interface. Na+ and Cl- ions are found to be indifferent towards uncharged zirconium oxide-solution interface. Quantitative data have been obtained on (i) zero point of charge, (ii) surface charge densities, (iii) differential capacities of the double layer, and (iv) the effect of surface charge density and ionic strength on the interfacial free energy (-Δγ). From a consideration of the solubility of different hydroxo-complex ionic species (both positively and negatively charged), it has been found that the zero point of charge of zirconium oxide surface coincides with the isoelectric point (i.e.p.) of the solution which is in equilibrium with solid zirconium oxide. (author)