GLASS-TRANSITION TEMPERATURE AND CRYSTALLIZATION OF GLASSES IN THE LI2O-CENTER-DOT-4GEO(2)-K2O-CENTER-DOT-4GEO(2) COMPOSITION RANGE

The effect of replacing Li2O by K2O on the glass transition temperatur e and on devitrification behaviour in a series of glasses in the lithi um tetragermanate-potassium tetragermanate composition range has been studied by differential thermal analysis, X-my diffraction and Fourier -transform infra-red spectra. All glasses studied exhibit internal cry stal nucleation. The progressive replacing of Li2O by K2O causes the v alue of the glass transition temperature to go through a minimum at mo lar ratio Li2O/K2O=1. The crystallising phases have been identified an d related to the devitrification mechanism. The effect of the specific surface of the glass samples on devitrification processes has also be en pointed out. (C) 1998 Published by Elsevier Science Limited.