Thermochemical Modeling of Oxide Glasses

A modified associate species approach is used to model the liquid phase in oxide systems. The relatively simple technique treats oxide liquids as solutions of end-member and associate species. The model is extended to representing glasses by treating them as undercooled liquids. Equilibrium calculations using the model allow the determination of species activities, phase separation, precipitation of crystalline phases, and volatilization. In support of nuclear waste glass development, a model of the Na2O–Al2O3–B2O3–SiO2 system has been developed that accurately reproduces its phase equilibria. The technique has been applied to the CaO–SiO2 system, which is used to demonstrate how two immiscible liquids can be treated.