Effect of Heat Treatment of Molten Bi2O3 Containing 22 mol % SiO2 on the State of the Metastable δ*-Phase Forming during Solidification

We have studied the effect of isothermal holding of a melt containing 78 mol % Bi2O3 and 22 mol % SiO2 and various melt cooling schedules on the morphology, microstructure, and phase composition of crystals of a metastable solid solution based on the high-temperature delta-polymorph of Bi2O3 (delta*-phase). The results demonstrate that high-temperature holding is favorable for melt supercooling and crystallization of the delta*-phase in a wide range of cooling rates. We have investigated peritectoid decomposition of the delta*-phase at subsolidus temperatures. Its products are a silicon dioxide-deficient delta*-phase and crystalline polymorphs of metastable SiO2.

Automated summary

In this study, the effect of isothermal holding and various cooling rates on the morphology, microstructure, and phase composition of a metastable solid solution based on the high-temperature delta-polymorph of Bi2O3 was investigated. The results show that high-temperature holding promotes melt supercooling and crystallization of the delta*-phase. The study also reveals the peritectoid decomposition of the delta*-phase at subsolidus temperatures.