The oxide-solution interface

Abstract

We extend previous treatments of the gel model of the oxide-solution interface and solve exactly the most general soluble case, of such an oxide in the presence of a 1 : 2-2 : 1 electrolyte, for the distribution of charge and potential across the interface. We calculate values of the surface charge and zeta potential of the oxides TiO2, Fe2O3, SiO2 and M203 using reasonable values of adsorption potentials and dissociation constants taken from tables. We find, for the samples of such oxides for which high measured charges have been reported, that we can account quantitatively for all the data by characterizing the interface by a gel layer of thickness 20-40�. We infer that such comprehensive agreement, and the consistency in all cases of the high charge and low zeta potential with the theory, gives strong support to the view that a thin surface layer distorted by the penetration of water and all types of ions is a general feature of the oxide-solution interface.