Calculation of eutectics temperatures and compositions of multicomponent sections of the system (Mg, Ca, Sr, Ba)O—Al2O3—Cr2O3

Abstract

With change in the structure of metallurgical production in Ukraine, the range of used refractory materials is expanding: the share of unshaped highquality refractories is growing, since this eliminates the time-consuming and energy-consuming operation of firing piece products, and also simplifies the operation of creating a lining layer. To establish the maximum possible operating temperature of materials developed on the basis of compositions of the optimal regions of multicomponent oxide system (Mg, Ca, Sr, Ba)O— Al2O3—Cr2O3, it was necessary to calculate the temperatures and compositions of the eutectics of binary, ternary and four-component sections, which was the purpose of this study. For calculations in binary sections, the Epstein — Howland method is most acceptable, and in three- and four-component sections — the solution of nonlinear equations system. It was found that to obtain a refractory unshaped material based on calcium aluminium chromite cement with periclase as a filler, it is necessary to adjust the phase composition of the cement towards an increased CaCr2O4 content, and the total composition must contains at least 75 wt. % periclase or magnesium spinel. In addition, in the case of alumina hydrates formation as a result of cement hydration processes, magnesium spinel will be synthesized as part of a refractory unshaped material during service. To obtain refractory unshaped materials based on strontium aluminium chromite cement and periclase as filler, it is necessary to increase the SrAl2O4 content and minimize the Sr3Al2O6 content in the cement composition, while the filler content in the composition can vary within wide limits, since the melting temperature of such compositions will be more than 1700 °C. To create refractory unshaped materials based on barium aluminium chromite cements, it is necessary to increase the content of BaAl2O4 in the cement composition as the most hydraulically active and refractory component and the composition of the composite material should be low- or ultra-low-cement in order to increase the operating temperature. In addition, in the case of chromium hydroxides formation during the hydration of aluminium chromite cement, chromium spinel will be synthesized in the composition during service, increasing the refractoriness of resulting composition. Thus, by varying the type and phase composition of cement and the ratio of cement and aggregates in the concrete composition, it is possible to obtain unshaped materials with a wide operating temperature range for use in heat-stressed areas of high-temperature aggregates.