Study on the shear viscosity of several inorganic glasses

The viscosities of metaphosphate, pyrophosphate, molybdate, and fluorophosphate glasses were measured under the shear deformation mode using a sandwich method from room temperature up to the glass transition temperature T-g. An optical method was used to measure the deformation under constant load as a function of time, and the results were analyzed using a mechanical model of anelasticity plus viscosity. In glasses containing long molecular chains, two relaxations appeared at lower and higher temperatures, while only one relaxation existed at higher temperatures in glasses without the chain. Both these relaxations were of the thermal activation type. A correlation between the frequency factor and the activation energy was found for the high temperature relaxation, and the values of the frequency factor were very large. Another apparatus, a rotation disk viscometer, was also used to measure the shear viscosity above T-g. The data obtained by the two experimental methods related to each other well, and the viscosity value at T-g was of the order of 10(8) Pa s. The viscosity was in the hydrodynamic regime at temperatures sufficiently above T-g, and in the hopping regime below a temperature near: T-g. (C) 1998 American Institute of Physics.