Calculation of Glass Transition Temperature of Na₂O-B₂O₃-GeO₂ Glass Based on the Sub-System Concept

Abstract

Assuming the structural units in Na₂O-B₂O₃-GeO₂ glass being composed of structural units of the Na₂O-B₂O₃ and Na₂O-GeO₂ systems (sub-systems), glass transition temperature T_g was estimated from the viscosity-temperature relationship based on the sub-system concept. The distribution of Na₂O component among the B₂O₃ and GeO₂ components is determined according to the assumption that Na₂O activity in the Na₂O-B₂O₃ system is equal to that in the Na₂O-GeO₂ system and the ratio of the Na₂O activity coefficients γ₁ in the Na₂O-B₂O₃ system over that γ₂ in the Na₂O-GeO₂ system is constant throughout the composition of the Na₂O-B₂O₃-GeO₂ system. The calculated and the observed T_g was in reasonable agreement within the experimental scatters.