Test of a Thermodynamic Model Predicting Occupancy of Alkali Ions at Glass Surface Sites

摘要

Alkali surface concentrations as a function of pH for five different glass compositions were measured using SIMS and XPS, and were compared to those expected from thermochemical calculations. Agreement was generally lacking despite good agreement reported by others, but could be improved if the variation in acidity of surface silanol groups with the degree of neutralization was considered. Other complications included large differences in the surface concentrations of glass-forming agents from that of bulk glass, and sensitivity of only a very thin surface layer to changes in the solution pH rather than the complete hydrolyzed layer. Surface spectroscopies are considered superior to chemical etching methods for the purpose of this study.