THE INFLUENCE OF THE CRUCIBLE AND THE COOLING RATE ON THE STRUCTURE OF GLASSES AND GLASS-CRYSTALLINE MATERIALS IN THE CaO-Na2O-P2O5-B2O3 SYSTEM

Abstract

Batches with composition 47.2B2O3-24.98Na2O-27.54CaO-0.27P2O5 (mol %) were melted in porcelain and corundum crucibles by melt quenching and normal cooling rate techniques. As a result, four different materials were obtained. Powder X-ray diffraction analysis showed that the sample melt in a corundum crucible and melt-quenched was almost fully amorphous, whereas its slowly cooled analogue exhibited near-complete crystallization. Samples prepared in porcelain crucibles, regardless of cooling technique, had predominantly amorphous structures, but two different crystalline phases appeared when the melts were slowly cooled. Scanning electron microscopy revealed distinct microstructural differences between the slowly cooled samples from porcelain and corundum crucibles. Fourier-transform infrared and Raman spectroscopy identified BO3 and BO4 units as the main structural units, likely
interconnected in pentaborate superstructural units. The influence of crucible material on crystallization behavior and phase formation was discussed.