Аbout the structure of a multicomponent system CaO-Fe2O3-Al2O3 -SiO2

Abstract

High-temperature refractory materials for metallurgy, energy and other industries are being developed based on compounds of the CaO-Fe₂O₃-Al₂O₃-SiO₂ oxide system. Since such materials are used at high operating temperatures, there is interest in studying the reactions in this system at operating temperatures up to 1500 °C. This oxide system also includes aluminosilicate fibre-basalt fibre compositions, which, due to their high thermal insulation properties, are promising for use in ferrous and non-ferrous metallurgy, mechanical engineering, energy and other industries. In this regard, a more detailed theoretical study of its subsolid structure is of interest. The paper presents the results of Gibbs free energy calculations for the conjugate reaction in the selected multicomponent system. Based on the thermodynamic calculations, the possibility of the conjugate reaction CaAl₂Si₂O₈ + 3CaAl₁₂O₁₉ + 17Fe₂O₃ = 2Ca₂Al₂SiO₇ + 17Fe₂Al₂O₆ has been established.  It was also shown that the reaction between the Ca₂Al₂SiO₇ and Fe₂Al₂O₆ phases does not occur in the temperature range of 300-1700 K. The existence of Ca₂Al₂SiO₇ – Fe₂Al₂O₆ conodes has been established, and the combination of phases CaAl₂Si₂O₈ + CaAl₁₂O₁₉ + Fe₂O₃ in the temperature range 300-1500 K forms an ‘empty’ triangle between them. The temperature ranges of coexistence of phase combinations are given and the region of the Ca₂Al₂SiO₇–FeAlO₃–CaAl₂Si₂O₈–CaAl₁₂O₁₉-Fe₂O₃ system is constructed. The results of theoretical studies have established that the multicomponent system under consideration breaks down into 25 elementary tetrahedra for which the temperatures and compositions of eutectics are given. A topological graph of the interrelationship of elementary tetrahedra has been constructed, which will subsequently make it possible to track changes in the phase composition of the compositions. The relative volume and temperature of melt appearance in elementary tetrahedra were estimated, and the minimum temperature of melt appearance was determined. The promising areas of the system are suitable for the manufacture of refractory thermal insulation materials. The research can be applied in the development and use of refractory materials, for example in mullite-silica fibre-basalt fibre systems, refractory slag and others.