Viscosity of model barium crystal glasses

Abstract The viscosity temperature dependence of model barium crystal glasses was studied. The composition of fifteen studied glasses was derived from the composition of currently produced (RONA, a.s. Lednické Rovne) barium crystal glass (10.49 mol.% Na 2 O, 2.36 mol.% K 2 O, 9.06 mol.% CaO, 0.78 mol.% ZnO, 2.44 mol.% BaO, 0.85 mol.% Al 2 O 3 , 74.02 mol.% SiO 2 ) by increasing/decreasing the content of each particular oxide and retaining the same mutual relative amounts of the other oxides. The composition of the prepared glasses was determined by X-ray fluorescence spectrometry (XRF). Due to the uncontrolled volatility of alkali oxides, the composition does not fulfil the prescribed pseudo-binary character for samples with a changed amount of particular oxide. The temperature dependence of viscosity was measured by thermomechanical analysis (high viscosity / low temperature) and rotational viscometry (low viscosity / high temperature). The Vogel-Fulcher-Tammann-Hesse equation (VFT) was used for description of viscosity temperature dependence. The glass transition temperature (log η(T g )/dPa.s = 13) and kinetic fragility index (m) were evaluated from VFT parameters. The activation energy of viscous flow (E a ) was evaluated from the low temperature viscosity described by Andrade’s equation. The Shakhmatkin Vedishcheva thermodynamic model (SVTDM) was evaluated for each glass composition at the glass transition temperature. From 57 considered components of SVTDM, only 21 with non-negligible equilibrium amounts were found. From SVTDM, the Q-units distribution was evaluated. By multilinear regression analysis, the dependence of considered quantities (T g , E a , m, and VFT parameters) on molar amounts of various Q-units was evaluated. The obtained results confirmed that the Q-distribution obtained from SVTDM describes the compositional dependence of the considered properties with sufficient accuracy.