THE CRYSTALLIZATION OF POTASSIUM GERMANATE GLASS WITH HIGH CONTENT OF NIOBIUM OXIDE

Abstract

Potassium germanate glass with molar ratio [GeO2]/[K2O] = 1.2 and Nb2O5 content of 34 mol% have been synthesized by a melt-quenching method. The crystallization behavior under non-isothermal and isothermal crystallization conditions was investigated. The results showed that this glass exposed complex primary crystallization. In the temperature range 800 °C. K10Nb22Ge4O68 and metastable KNbO3 and K4Nb6O17 were formed as secondary phases. The crystallization commenced at T > 640 °C with high homogeneous nucleation rate and spherulite crystal growth morphology. DTA curves recorded for powder samples particle size 0.1 mm showed two exothermic peaks and two endothermic peaks within temperature range of T = 640-1020 °C. The analysis of the dominant crystallization mechanism of powder glass sample and kinetics of crystallization is presented