Viscosity and thermal expansion of lithium aluminosilicate glasses

Viscosity and thermal expansion have been measured for 12 series of lithium aluminosilicate glasses. The compositional dependency of the viscosity, glass-transformation temperature, dilatometric-softening temperature, and refractive index all exhibit an abrupt change in slope at an aluminum-to-lithium ratio between 1.05 and 1.10. The thermal-expansion coefficients of these glasses were found to depend only on the lithium oxide content, i.e., to be independent of the aluminum-to-silicon ratio. These results suggest that the traditional structural model for these glasses must be modified slightly. A new model is proposed which allows some aluminum to act as a modifier in all alkali aluminosilicate glasses.