Non-isothermal devitrification of sodium germanate glasses

The devitrification behavior of sodium germanate glasses, examined by Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction is reported. The glass compositions are expressed by the general formula: xNa2O·(1−x)GeO2 with x=0.100; 0.125; 0.200; 0.250 and 0.333. The glass transition temperature values do not change linearly with the increase in Na2O content but go through a maximum at x=0.200. The phases crystallizing during DTA runs were identified and devitrification mechanisms proposed. The effect on devitrification processes of the specific surface area of the samples was also pointed out.