Pressure and temperature dependence of viscosity of glassforming and of geoscientifically relevant systems

The paper discusses a model of viscosity eta of glassforming melts in an attempt to predict the dependence of eta on temperature T and on pressure P. The equation, derived here, describes with excellent accuracy all existing experimental viscosity data including those of glassforming melts, igneous materials and polymers. It is demonstrated that the activation energy E(T-g) can be expressed through the glass transition temperature T-g as E(T-g)=epsilon RTg where epsilon R=260 +/- 10% in J/(mol K). The dependencies of the parameters of the viscosity equation are discussed for certain geoscientifically relevant systems. According to the model the relaxation time of the mantle is about 32000 years, a time suspiciously close to the period during which the direction of magnetic poles changes. (c) 2006 Elsevier B.V. All rights reserved.