AlO1.5/SiO2 substitution effect on the viscosity of alkali silicate melts

Abstract

The effect of alumina addition on the viscosity of silicate melts is strongly related to the type of non-framework cations; however, the origin of these interactions is not well understood. In this study, we measured the viscosity change in selected alkali disilicate (R2O·2SiO2, R: Na or Li) melts by varying the AlO1.5/SiO2 molar ratio (AlO1.5 = 0–16.8 mol%) within the 1373–1823 K temperature range. We observed that as the molar ratio increased, sodium silicate viscosity increased, whereas lithium silicate viscosity was not affected. Aluminum-27 nuclear magnetic resonance spectra of the quenched glasses indicated that the aluminum cations in both types of alkali silicate melts were mostly present as AlO4 tetrahedra. In contrast to sodium-containing systems, the shear strain on the AlO4 tetrahedron was greater for lithium aluminosilicate glass. Our findings indicated that the degree of shear strain on AlO4 plays an essential role in controlling the viscosity of aluminosilicate systems.