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The effects of MgO, AlO and basicity on the heat capacity and enthalpy change of CaO-SiO-MgO-AlO slags at 1 673 K and 1 773 K as well as the thermal stability were investigated. The enthalpy change at 1 773 K increased with the addition of AlO and MgO, but decreased with increasing basicity. Thus, the higher basicity helped to reduce the heat consumption and fuel ratio of blast furnace. With increasing MgO content, the fluctuations of the temperature and viscosity caused by the reduction of the slag heat quantity decreased. Furthermore, the slag will have a better fluidity and thermal stability when MgO content is greater than 8 mass%. The increase of AlO content deteriorated the fluidity and thermal stability of the slag to some extent. When the reduction of the slag heat quantity was fixed, as the basicity increased, the slag temperature increased obviously and the viscosity significantly decreased. Also, the fluctuations of slag temperature and viscosity became less pronounced with increasing basicity. The increase of the basicity was favorable to improve the fluidity and thermal stability of the slag. For the slag system of this experiment, the suitable basicity was 1.10-1.15.

The effect of TiO and MnO on the viscous behavior and structure of CaO–SiO–MgO–AlO–TiO–MnO slags were studied using rotating cylinder method and FTIR spectroscopic analysis. Furthermore, the heat capacity and enthalpy change of the slag were calculated to clarify the influence of TiO and MnO on the heat quantity of the slag at elevated temperatures, and then the equilibrium temperatures and corresponding viscosities of the slag under various fixed heat quantities were also analyzed. The higher TiO and MnO contents resulted in lower viscosity. The FTIR results revealed that TiO and MnO depolymerized the slag by modifying the silicate network structure and breaking the linkage between the silicate and aluminate structure, while have little effect on aluminate structure of the slag. In the temperature range of interest, the enthalpy change of the slag increased with increasing TiO content, but remained basically unchanged with MnO additions. The fluctuations of the slag heat quantity had a significant influence on the slag temperature and viscosity. With the increase of TiO content, the equilibrium temperature of the slag at fixed heat quantity decreased and the corresponding viscosity increased. However, as the MnO content increased, the equilibrium temperature of the slag at fixed heat quantity was almost constant and the corresponding viscosity decreased.

A type of carbon composite brick was produced via the microporous technique using natural flack graphite, α-Al2O3 and high-quality bauxite chamotte (Al2O3≥87 mass%) as raw materials with fine silicon powder as additive. The composition and microstructure of the obtained carbon composite were characterized using chemical analysis, XRD and SEM with EDS. The high temperature properties of thermal conductivity, oxidization and corrosion by molten slag and hot metal of the composite were analyzed. Based on these, the type of carbon composite brick worked in a blast furnace hearth for six years was further sampled at different positions. The protective layer was found and its chemical composition and microscopic morphology were investigated. It is found that the carbon composite brick combines the good properties of both the conventional carbon block and ceramic cup refractory. The protective layer near the hot face consists of two separated sublayers, i.e. the slag layer and the carbon layer. A certain amount of slag phase is contained in the carbon layer, which is caused by the reaction of coke ash with the refractory. No obvious change in the chemical composition of the protective layer along the depth of the sidewall is found. This work provides a useful guidance for the extension of the lifetime of blast furnace hearths.