New high viscosity data for 3D network liquids and new correlations between old parameters

The Adam-Gibbs and the Vogel-Tamman-Fulcher equations are very often used to express the temperature dependence of the viscosity of liquids. Both equations reproduce very well the same sets of viscosity measurements, but the adjustable constants in these equations, evaluated by fitting the equations to the same data, are always incompatible. The cause of this incompatibility is a lack of good high viscosity measurements. We report new measurements on a series of stabilized liquid silicates which allow us to fit both equations to sets of temperature-viscosity data for 10 different compositions in the temperature interval 700-2700 K, with viscosities ranging from 10(16) to 10 Pa s. The precision of the fits of the equations to the data sets is comparable to the experimental precision of the data. The values of the adjustable constants in both equations are in mutual agreement. Moreover the adjustable constants in the Adam-Gibbs equation are physically acceptable and in perfect harmony with already published experimentally obtained thermodynamic information. The nature of the glass transition and the significance of the Vogel temperature have been discussed. (C) 2001 Elsevier Science B.V. All rights reserved.