Effect of Heat Treatment of Molten 6Bi2O3⋅SiO2 on the Phase Composition and Microstructure of Its Solidification Products

• Published in: Inorganic materials 2022-11, Vol.58 (11), p.1168-1178
• Main Authors: Bermeshev, T. V., Zhereb, V. P., Bundin, M. P., Yasinsky, A. S., Yushkova, O. V., Voroshilov, D. S., Samoilo, A. S., Mazurova, E. V., Zaloga, A. N., Yakivyuk, O. V., Yur’ev, P. O.
• Format: Article
• Language: English
• Subjects: Bismuth oxides; Bismuth silicon oxide; Bismuth trioxide; Chemistry; Chemistry and Materials Science; Cooling rate; Crystallization; Eutectoid decomposition; Heat treatment; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials Science; Metastable phases; Microstructure; Phase composition; Silicon dioxide; Solid solutions; Solidification
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168522110024

— We have studied the effect of heat treatment (isothermal holding in the temperature zone C , initial cooling temperature, and cooling rate) of a melt with the composition 85.7 mol % Bi 2 O 3 + 14.3 mol % SiO 2 (6 : 1) on the phase composition and microstructure of the forming crystals and found conditions for crystallization of a δ-Bi 2 O 3 -based metastable solid solution (δ*) at high melt cooling rates. The results demonstrate that low melt cooling rates lead to crystallization of the δ*-phase and an α-Bi 2 O 3 -based solid solution, followed by partial or complete eutectoid decomposition of dendritic δ*-phase crystals into a mixture of metastable phases, containing β*-Bi 2 O 3 and η-Bi 2 SiO 5 as well. Raising the melt cooling rate limits both the formation of secondary phases and eutectoid decomposition. The results we obtained make it possible to control the formation of polycrystalline Bi 12 SiO 20 and δ-Bi 2 O 3 upon 6Bi 2 O 3 ⋅SiO 2 melt solidification.