Topological understanding of the influence of mixed alkali components on the structure and properties of aluminosilicate glass

Abstract

Herein, aluminosilicate (AS) glasses exhibit varying trends in Vickers hardness (HV), coefficient of thermal expansion, softening temperature (Ts) and glass transition temperature owing to the mixed alkali effect. To elucidate the mechanism of the mixed alkali effect, the glass structure was characterised using multiple methods. Employing temperature-dependent topological constraint theory, the variations in HV and Ts were investigated, and the constraint strengths of sodium (Na) and lithium (Li) in AS glasses were calculated. The findings indicated that an increase in alkali metal–ion content elevates the proportion of non-bridging oxygen, leading to a progressive decrease in constraint strength and the depolymerisation of the glass structure. For AS glasses with mixed alkali components, as the content of Li2O replacing Na2O increases, the constraint strength of the glass structure below the critical temperature (Tc) gradually rises, while above Tc, it undergoes unconventional changes. These alterations lead to non-linear variations in glass properties.