Investigations Of Viscous Flow In Glass During Phase Seperation

The isothermal viscosity of 2 borosilicate glasses, one of which a commercial glass widely used for chemical ware, shows a large increase (4 to 5 orders of magnitude) with heat-treatment time (up to 100,000 min) near the annealing point. The 2 glasses have similar compositions but differ greatly in their phase separation characteristics. Electron micrographs were used to analyse the development of the microstructure during phase separation. The structure of development was primarily responsible for the viscosity increase in both glasses. An analysis of the data and a theoretical interpretation are given.