Thermodynamic analysis of reactions of the celsian phase formation during the synthesis of thermal shock resistance ceramics based on eutectic glasses of the BaO–Al2O3–SiO2 system

Abstract

The search for effective ways of obtaining densely sintered celsian ceramics at low firing temperatures usually requires a large volume of experimental research. The object of our research is the reactions of the formation of the celsian phase with the participation of glass components of eutectic compositions of the BaO–Al2O3–SiO2 system under low-temperature firing conditions. In this case, thermodynamic analysis was used as a tool to assess the probability of chemical reactions. This paper reports the results of theoretical and experimental studies into the features of the course of chemical reactions with the participation of glass components of eutectic compositions of the BaO–Al2O3–SiO2 system. It was revealed that once the stoichiometric ratio is maintained, the final product of the interaction between the components of eutectic glasses E-4, E-5 and E-6 with crystalline fillers is the celsian phase. The most probable is the formation of celsian when the components of eutectic glasses interact with Al2O32SiO2, which is a product of kaolinite (Al2O32SiO22H2O) dehydration. It was found that barium orthosilicate, in comparison with other barium silicates, exhibits the highest activity when interacting with charging components in the direction of formation of the сelsian phase already at the temperature of 7500С. At the temperature of 9000C, such a composition is noted to have an active transition of hexagonal celsian to monoclinic celsian. As a result, the content of monoclinic celsian increases significantly. The determined patterns allow making a reasonable choice of glasses in the BaO–Al2O3–SiO2 system with the lowest melting temperatures for the subsequent production of low-temperature сelsian ceramics.