A thermodynamic model of amorphous silicates

A thermodynamic model is proposed to provide a physical picture of the glass transition in amorphous silicates. Below the glass transition temperature Tg the model considers the phase to be a random network of oxide compounds which relaxes to provide local structural fluctuations as the temperature rises above Tg Thermally activated development of these fluctuations accounts for gradual transition between the "solid", as existing below Tg, and the liquid state appearing above the melting point T-fus The randomness of the structure and its fluctuation contribute both to the Gibbs energy as estimated near Tg. The model parameters of analytical expressions of Gibbs energy have been adjusted to fit the experimental information. The model has been developed for silicate glasses considered to a first approximation as ideal solution of single amorphous oxides. The relative enthalpy Delta H = H(T) - H(298K) has been calculated for a series of silicate glasses. The computational results agree quite satisfactory with experimental data. The constraints of the model are briefly discussed.