Ionic Equilibria in Liquid Silicates

Abstract

Liquid silicates, in common with phosphates and probably other oxygen‐containing inorganic polymers which are stable at high temperatures, contain in general a multitude of anionic species ranging in size and complexity from simple “monomeric” groupings such as SiO 4 4− and P0 4 3− to continuous, cross‐linked networks of infinite molecular weight. The average size and distribution of these species in binary systems may be inferred, at least approximately, from thermodynamic data in combination with polymer theory on the assumption that the activity coefficients of the constituents are arrayed in geometric series. This is equivalent to assuming ideal mixing of polymeric segments. As anticipated, deviations from the theory become significant at the gel point, which varies with the nature of the cation. The significance of these concepts in relation to the constitution of glasses is discussed. In particular, it is indicated that a glass may consist of sol and gel portions, the complexity and relative proportions of which vary with the nature of the cation and the silica content. In theory, the ion SiO 4 4− is the most abundant single species of discrete silicate ion at all silica contents.