Depolymerization of soluble silicate in dilute aqueous solutions

Experiments with diluted solutions of a customary water glas show that the rate of depolymerization depends not only upon pH and the SiO₂ concentration, but also varies systematically as a function of the type and concentration of an additional electrolyte. Increasing cation activities of metal chlorides are causing a decrease of the rate constant in the order 1) Na⁺, K⁺, 2) Mn²⁺, Mg²⁺, Ca²⁺, Sr²⁺, 3) Zn²⁺, Ni²⁺, Ce³⁺, Cu²⁺. With respect to anions of sodium salts the rate constants are increasing with increasing activities in the order NO ₃ ^– , HCO ₃ ^– , Cl^–, SO ₄ ^2– , whereas HPO ₄ ^2– causes a decrease. The results permit to identify those components of water which are most responsible for a change of the depolymerization rate and may be used to evalute the properties of a water glass as a possible anticorrosive agent for water supply systems.