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Effect of spinel kinds on the properties of alumina—spinel castables was investigated. The results showed that the addition of various kinds of spinels has an effect on the physical and mechanical properties of these refractory castables. The reason is that the Al2O3‐rich spinel precipitated Al2O3 and MgO‐rich spinel solid solution and formed secondary spinel. In addition, stable spinel in castables during heat treatment process was found to be more effective for enhancing cold and hot strength.

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In order to overcome the shortcoming of the calcium aluminate cement (CAC) bonded castables, we prepared corundum‐spinel castables using silica sol as binder and tabular corundum, sintered magnesia‐alumina spinel, and reactive alumina as raw materials in this study. The effect of spinel grain size and solid content of silica sol on the flow value, sintering, mechanical strength and microstructure of the specimens treated at varying temperature of 400, 1000, 1500, and 1650°C for 5 hours in an air atmosphere were studied by SEM and EDS analyses. The results indicate that silica sol is suitable as a binder for corundum‐spinel systems. And silica sol with solid content of 25% bonded samples containing ≤90 μm spinel perform quite better than the others. At the same time, silica sol bonded samples had high strength in medium temperature. This is because that the closer proximity of silica sol and alumina powder and the high activity of nanometer SiO2 in silica sol are beneficial for the reaction of SiO2 and Al2O3 to generate mullite needed for reinforcement of castables matrix.

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An environmentally friendly tap-hole clay that contains almost no benzo [a]pyrene was developed using resin and pitch as binder. The effects of the pitch addition on the tap-hole clay were investigated through evaluating the physical and chemical properties together with the microstructure, phase compositions and thermal analysis. The plasticity of the tap-hole clay is significantly improved with increasing pitch addition. However, the bulk density of tap-hole clay decreases gradually with increasing pitch content after treatment at different temperatures, while the apparent porosity increases due to the evaporation of pitch components and relatively low solid components. Also, this phenomenon is the main reason for the poor volume stability of taphole clay after heat treatment at different temperatures, although mullite formation has negated some of the shrinkage. Mechanical-strength evolution of the tap-hole clay is closely related to the carbonization process of the resin and pitch at high temperatures. Oxidation resistance could be significantly improved with 2 wt % of the pitch, but there is almost no change with much more than 2 wt %. However, the higher pitch content corresponds to better slag resistance. In terms of the comprehensive performance of the tap-hole clay, 4 wt % of the pitch would be better.