Thermal study of the influence of chemical bond ionicity on the glass transformation in (Na2O, CaO, MgO)-Al2O3-SiO2 glasses

The relation between change of the specific heat (DeltaC(p)) accompanying the glass transformation and the chemical composition of glasses ( Na2O, CaO, MgO) - Al2O3 - SiO2 system has been studied. The exchange of modifiers in the glass structure causes the DeltaC(p) increase in the sequence Na> Ca> Mg. Change the glass network composition by introducing Al into it makes smaller increase of the DeltaC(p) values. It has been shown that degree of DeltaC(p) value changes is dependent on the iconicity/covalence of chemical bonds of cations with oxygen of glass structure network.