The role of entropy on viscosity of silicates

The article compares different approaches describing shear viscosity of glassforming melts. It is demonstrated that they all could be derived from the original assumption of the Avramov and Milchev (AM) model that, due to the disorder, activation energy barriers of different heights appear. This leads to dependence of shear viscosity on the variance σ of the probability distribution function that the barrier of height E is present. All models are the result of the premise that (with different degrees of reliability) σ depends on temperature and/or on entropy.An approach is developed capable to describe, although with limited accuracy, the composition dependence of glass transition temperature.

► The equations describing viscosity are derived from one general assumption.
► The glass transition temperature is estimated within the model of Avramov and Milchev.
► The AM equation permits the prognostication of viscosity from the knowledge of composition.