Viscosity and Thermal Expansion of Mixed‐Alkali Sodium‐Potassium Borate Glasses

Abstract

The transformation‐range viscosity and thermal expansion be‐havior of sodium‐potassium borate glasses were studied. The results indicate that negative deviations from additivity in the viscosity of these glasses are a function of the Na2O to K2O ratio and that the magnitude of these deviations increases with alkali oxide content. The thermal expansion coefficient exhibits a maximum deviation from additivity as a function of the Na2o to K2O ratio. The magnitude of this deviation increases with increasing total alkali oxide content. The results indicate that there is little, if any, interaction between the factors which lead to the mixed‐alkali effect and the changes in the structure of the vitreous network which occur as the alkali oxide content of the glasses increases.