Interaction of sodium silicate with zirconia and its consequences for polysialation

In this study, the interaction of monomeric and polymeric sodium silicate with zirconia was investigated in an alkaline environment (pH=9–14) and the reaction mechanisms related to polysialation. Various adsorption and zeta potential measurements confirmed the initial adsorption of silicate to be dominated by hydrated cation sites and subsequent adsorption to be controlled by polycondensation reactions. The extent of polycondensation was shown to be controlled by the degree of polymerization of the silicate and amount of co-precipitation with sodium. The distribution of silicate species was described utilising a thermochemical model based on constants attained by Sjöberg et al. and Caullet et al. with the aid of 29Si Nuclear Magnetic Resonance (NMR) data. In addition, Scanning Electron Microscope (SEM) and X-ray Diffraction analyses confirmed that the morphology and elemental compositions of the polysialates were pH dependent, with a higher proportion of aluminium found in polysialates prepared at a higher pH. The formation of polysialates from sodium silicate and zirconia did not reveal a reaction exotherm through Differential Scanning Calorimetry (DSC) analysis. It is concluded that silicate and polysialate adsorption onto zirconia is greatest when monomeric species predominate at high pH, forming a network structure containing sodium, which is mostly amorphous in nature.