Effects of Heating Rate on the Thermal and Mechanical Properties of the Bauxite-Based Low-Cement Refractory Castables
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JMEPEG https://doi.org/10.1007/s11665-020-05079-z
Effects of Heating Rate on the Thermal and Mechanical Properties of the Bauxite-Based Low-Cement Refractory Castables Hajar Ahmadi Moghadam and Seyed Mohammad Arab (Submitted March 12, 2020; in revised form August 16, 2020) This study was conducted to investigate the effects of sintering conditions on the phase composition, microstructure, and physico-mechanical properties of the bauxite-based low-cement refractory castables. For this purpose, the specimens were sintered at various temperatures (1350-1450 °C) and heating rates (310 °C/min). Results showed that the sintering conditions have a remarkable effect on the physico-mechanical properties of the refractory castables. The mechanical strength was considerably increased by increasing the heating rate from 3 to 10 °C/min which was attributed to lower amounts of porosity and higher amount of the platy crystals of CA6 phase. The lower porosity of the specimens sintered at lower temperature with 10 °C/min of heating rate also resulted in the higher mechanical strength. The results obtained in this study showed a negative linear relationship between the cold crushing strength and porosity of the specimens with a high degree of measurement conformity. Keywords
bauxite, heating rate, microstructure, physical and mechanical properties, refractory castables, sintering
1. Introduction The advantages of the refractory castables including appropriate green mechanical strength, high-temperature strength, high corrosion resistance, high thermal shock resistance, low cost, and non-toxicity have led to their applications in different fields (Ref 1-5). The refractory castables can be simply used for complex shapes and in the places with difficult accessibility (Ref 6, 7). They have a wide range of compositions, such as high-alumina refractory castables, silicon carbide-based refractory castables, and bauxite-based refractory castables (Ref 7). The latter one has been broadly used in high-temperature applications in the ceramic, metallurgical, and petrochemical industries (Ref 2, 8). They generally include the fine grains and refractory cement, as bonding and matrix phase, respectively, and coarse aggregates as the reinforcement phase (Ref 2, 9). Calcium aluminate cements (CACs) act as the hydraulic binders in the refractory castables. CACs lead to the high green strength in a short time. At high temperatures, CACs react with a fraction of alumina castables matrix and produce the C12A7, CA, CA2, and CA6 phases where C stands for CaO and A stands for Al2O3 as the intermediate phases of Al2O3-CaO system. Calcium hexaluminate (CA6:CaAl12O19) is the most thermodynamically stable phase that has the maximum alumina content (Ref 8, 10-13). Hajar Ahmadi Moghadam, Department of Materials Science and Engineering, Faculty of Engineering, Shahrekord University, Shahrekord, Iran; and Seyed Mohammad Arab, Department of Mechanical Engineering, University of Mohaghegh Ardabili, Ardabil, Iran. Contact e-mail: [email protected].
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