Thermal behavior and the properties of BaO-B2O3-P2O5 glasses

Abstract

Borophosphate glasses of the BaO-B2O3-P2O5 ternary system were prepared and studied within the large glass-forming region of the system. Fourteen investigated glass samples of barium borophosphate glasses were discussed for a comparison of the compositional trends in their properties in four compositional series such as A: (100 - ) Ba(PO3)(2)-xB(2)O(3), B: 40BaO-yB(2)O(3)-(60 - y) P2O5, C: (50 - z) BaO-zB(2)O(3)-50P(2)O(5), and D: (60 - w) BaO-wB(2)O(3)-40P(2)O(5). Changes in glass density and molar volume primarily depend on the BaO content in the glasses. The thermal properties were studied with a differential thermal analysis, hot-stage microscopy, and dilatometry. Glass transition temperature increases with a rising B2O3 content most rapidly in the glass series A and B. It reaches its maximum in these series for the glasses containing 20-30 mol%, where the glass network represents a 3D structure interlinked with P-O-B, P-O-P, and B-O-B bridges. The thermal expansion coefficient decreases, in contrast, with the increasing B2O3 content in these ternary glasses as well as their chemical durability. The crystallization of these glasses, in the samples with a low B2O3 content, results in the formation of barium metaphosphate BaP2O6. Certain crystallized samples also contain a small amount of BPO4, and diffraction lines of ternary compounds BaBPO5 and Ba3B(PO4)(3) were revealed in a number of samples. A new compound of the composition Ba5B2P8O28 was identified in the crystallized glass 50BaO-10B(2)O(3)-40P(2)O(5).