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 t o express the temperature dependence of the viscosity of liquids. Both equa tions 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 incompatibili ty is a lack of good high viscosity measurements. We report new measurement s on a series of stabilized liquid silicates which allow us to fit both equ ations 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 i s comparable to the experimental precision of the data. The values of the a djustable 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 therm odynamic information. The nature of the glass transition and the significan ce of the Vogel temperature have been discussed. (C) 2001 Elsevier Science B.V. All rights reserved.