Ceramics-Silikáty 56, (1) 61 - 68 (2012) |
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THE CRYSTALLIZATION OF POTASSIUM GERMANATE GLASS WITH HIGH CONTENT OF NIOBIUM OXIDE
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Matijaševic Srđan D. 1, Tošić Mihajlo B. 1, Stojanović Jovica N. 1,
Grujić Snežana R. 2,
Živanović Vladimir D. 1,
Nikolić Jelena D. 1,
Đošić Marija S. 1
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1 Institute for Technology of Nuclear and О
2 Faculty of Technology and Metallurgy, University of Belgrade,
4 Karnegijeva St., 11000 Belgrade, Serbia
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Keywords: Germanate glass, Niobium oxide, Crystallization
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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
< 800oC primary phase is K3.8Nb5Ge3O20.4, while K6Nb6Ge4O26 appeared as primary phase at temperatures > 800oC.
K10Nb22Ge4O68 and metastable KNbO3 and K4Nb6O17 were formed as secondary phases. The crystallization commenced
at T > 640oC with high homogeneous nucleation rate and spherulite crystal growth morphology. DTA curves recorded
for powder samples particle size < 0.1 mm revealed three exothermic peaks and three endothermic peaks within temperature
range of T = 640-940oC, while the DTA curves recorded for powder samples particle size > 0.1 mm showed two exothermic
peaks and two endothermic peaks within temperature range of T = 640-1020oC. The analysis of the dominant crystallization
mechanism of powder glass sample and kinetics of crystallization is presented. |
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