Ceramics-Silikáty 50, (2) 78 - 82 (2006)

Viscosity, density, thermal expansion, glass transition temperature, refractive index, molar refraction, and chemical durability of 15M₂O.10CaO.xZrO₂.(75-x)SiO₂ (M = Na for NCZ glasses, and M = K for KCZ glasses; x = 1, 3, 5, and 7) glasses were measured. The effect of SiO₂/ZrO₂ equimolar substitution on measured physical and chemical properties was discussed. Increasing content of ZrO₂ significantly improves the chemical durability against water in both studied glass series. The ZrO₂/SiO₂ substitution strengthens the silicate network and therefore increases the values of glass transition temperature, and viscosity and decreases the value of the thermal expansion coefficient. Molar refractivity depends linearly on the ZrO₂ content. The slope of the regression line is the same for both studied glass series, whereas the higher intercept for potassium glasses reflects the greater polarizability of the potassium cation with respect to the Na⁺ cation. In comparison with the NCZ glasses both the viscosity and the viscous flow activation energy of KCZ glasses are higher and their dependence on the ZrO₂ content is steeper.