DEPOLYMERIZATION OF SOLUBLE SILICATE IN DILUTE AQUEOUS-SOLUTIONS

Experiments with diluted solutions of a customary water glass 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 NO3-, HCO3-, Cl-, SO42-, whereas HPO42- 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.