Viscosity of oxide melts in the Doremus model

It is shown that a model recently proposed by R. H. Doremus for the viscosity of oxide melts correctly reproduces a two-exponential expression for viscosity, which is observed experimentally. For both low and high temperatures, the temperature dependence of viscosity is of the Arrhenius type. The viscosity activation energy at low temperatures is high and equal to the sum of enthalpies of defect formation and their motion. The temperature of transition from high to low viscosity-activation energies is determined by the enthalpy and entropy of defect formation and is not associated with configurational changes.