Viscosity behavior and mixed alkali effect of alkali aluminosilicate glass melts

Abstract

The viscosities of (25-x)Na2O·xK2O·yAl2O 3·(75-y)SiO2 glasses between 1400-1000°C and their transformation temperatures (Tg) were determined. In the case of mixed alkali glass melts with Al2O3/R2O=0 (R2O =Na2O + K2O) a viscosity minimum, so-called mixed alkali effect has been found against K2O/R2O. However, mixed alkali aluminosilicate glass melts show no minimum but a linearity. This indicates that the mixed alkali effect in viscosity becomes weaker or disappears with decreasing nonbridging oxygen content. On the other hand, although viscosity minima have been found at Tg curves, this mixed alkali effect in Tg showed an independence on Al2O3 content. The results of this experiment were compared with the previous work on the resistivity measurement in mixed alkali aluminosilicate melts and it has been concluded that the models for the mixed alkali effect in both properties (viscosity and electrical conductivity) have to be considered separately.