Structural effects on glass stability and crystallization

Abstract

Herein, glass stability and crystallization activation energy (E_c) were evaluated in a pure devitrite glass (Na₂Ca₃Si₆O₁₆) and two other glasses (Dev, 4Ti, and 8Ti, respectively) in which 4 mol% and 8 mol% of devitrite glass was replaced with TiO₂. The results were in agreement with those of glass structure studies reported in the literature. Glass stability parameters were calculated from DSC experiments using the equations K₂ = T_x − T_g and K_M = (T_x − T_g)²/T_g. It was observed that for all equations, the glass stability values increased with the addition of TiO₂ contents. This behavior was due to the following two factors: a decrease in the glass modifier concentrations (Na⁺ and Ca²⁺) and Ti ions added on the glass network, acting as glass formers, in which Si–O–Si were replaced with Si–O–Ti⁴⁺ tetrahedrons. Isothermal heat treatments were carried out at 800 °C, and it was verified by scanning electron microscopy that TiO₂ did not act as a nucleating agent in Na₂Ca₃Si₆O₁₆ and surface crystallization was predominant for all glasses studied herein. The Kissinger equation was used to obtain the crystallization activation energy (E_c); it was observed that the E_c values decreased with the addition of TiO₂, and this behavior was explained regarding the bond energy dissociation (Si–O and Ti–O) and the calculated viscosity data.