Structural effects on glass stability and crystallization

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 K-2 = 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 degrees 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.