STRUCTURE AND NONISOTHERMAL CRYSTALLIZATION OF GLASSES IN THE BAO-B2O3SIO2 SYSTEM

The structure and devitrification behaviour of barium borosilicate gla sses, examined by Fourier transform infrared spectroscopy, x-ray diffr action and differential thermal analysis, are reported. Glass composit ions are expressed generally as: (50-x/2) BaO. (50-x/2) B2O3.xSiO(2) w ith x=4, 8 and 16. The progressive increase of SiO2 content in the gla ss composition produces a wider distribution of structural units, [BO3 ], [BO4] and [SiO4] groups, and a more polymerised glass network. The investigated glasses devitrify forming beta-BaB2O4 microcrystals. The surface crystallisation was found to be dominant for all glasses. The values of activation energy of crystal growth, evaluated using a Kissi nger type plot, were found to be 716, 841 and 540 kJ/mol for the glass es with x=4, 8 and 16 respectively.