Surface Chemistry of Calcium Aluminosilicate Glasses
The surface chemistry of synthetic calcium aluminosilicate glasses exposed to aqueous solutions of varying pH was described using zeta potential measurements and batch surface titrations. Element release and proton consumption were measured to characterize the reactions at the surface as a function of pH. It was found that proton-metal exchange or leaching was the dominant proton consumption process at low pH. The exchange reaction was observed to maintain charge balance, indicating that over the limited duration of the experiments no repolymerization of the silica-rich leached layer occurred. At high pH, dissolution and hydrolysis of aqueous ions controlled the proton mass balance, no evidence for the formation of leached layers was found. Silica-rich glasses were found to be more resistant to corrosion by either proton-metal exchange or dissolution than CaO-rich glasses. Glass basicity was found to be reflected in the establishment of a higher pH when immersing the glass in neutral aqueous solutions and in a reduced stability of the glass surface toward aqueous solutions. High pH, high surface charge and reduced glass network polymerization act together in enhancing the reaction of CaO-rich glasses with aqueous solutions.