The application of mullite in the metallurgical industry is mainly reflected in steel smelting. Mullite bricks prepared with mullite as the main raw material have the characteristics of small thermal expansion coefficient, low creep rate, high high temperature strength, good thermal shock resistance and strong chemical corrosion resistance. They can be used for blast furnaces, continuous casting, the dome of hot blast furnaces and the middle and upper parts of the combustion chamber, etc., and can also be used as bricks for ceramic burners. Amorphous refractory materials containing mullite also have good thermal shock resistance and mechanical properties, etc., and are used in blast furnaces, permanent linings of ladles, tundishes, ignition and insulation furnaces, molten iron desulfurization spray guns, etc.
1. Mullite-corundum refractory materials Mullite-corundum bricks have high density, low porosity, high strength and good resistance to erosion by molten iron and slag. They are ideal refractory materials for blast furnace ceramic linings, furnace walls, tuyere and furnace bottoms. Mullite-corundum castables can be used as lining materials for blast furnace hot blast furnaces and heating furnaces. The purity of mullite raw materials affects the performance of mullite-corundum refractory bricks. Corundum-mullite bricks prepared with high-purity sintered mullite as raw materials have excellent resistance to alkali vapor and CO erosion, and are suitable for use in high-temperature reducing atmosphere conditions such as hot blast furnaces. Compared with mullite-corundum castables prepared with fused mullite as aggregate, mullite-corundum castables prepared with microcrystalline mullite as aggregate have higher room temperature compressive strength, room temperature flexural strength, high temperature flexural strength, and better thermal shock resistance. Introducing other refractory raw materials on the basis of mullite and corundum can further improve the performance of mullite-corundum refractory materials. It was found that adding an appropriate amount of boron carbide to silica sol combined mullite-corundum castables can further improve the room temperature flexural strength, room temperature compressive strength, high temperature flexural strength and thermal shock resistance of the castable.
2. Mullite-cordierite refractory materials In order to meet the requirements of good thermal shock resistance, erosion resistance, high temperature resistance, erosion resistance, high load softening temperature and other requirements for ceramic burner refractory materials, Zhu Xinjun et al. used M70 sintered mullite, M70 fused mullite and cordierite as the main raw materials, and prepared mullite-cordierite ceramic burner composite bricks through casting-centrifugal molding process. The lining bricks of coke oven doors need to have good wear resistance, volume stability, carbon resistance and thermal shock resistance. Li Hongwei et al. used M70 sintered mullite and cordierite as the main raw materials and aluminate cement as the binder to prepare a mullite-cordierite precast brick with low linear expansion rate, low porosity and good thermal shock resistance. The precast brick was applied to the large coke oven door of Japan's Shin Nichia Chemical Co., Ltd. After one year of use, the surface of the precast brick was smooth and crack-free.
3. Mullite-alumina refractory materials Castables prepared with mullite and bauxite as the main raw materials use less water and show high mechanical strength in a wide temperature range. In order to further improve the wear resistance and thermal shock resistance of mullite-alumina-based castables, the authors used M60 mullite, bauxite and silicon carbide as the main raw materials and calcium aluminate cement as a binder to prepare a mullite-alumina-silicon carbide castable with excellent mechanical properties and wear resistance.
4. Mullite-magnesium aluminum spinel refractory materials Magnesium aluminum spinel has excellent thermal shock resistance, corrosion resistance and wear resistance. Khalil et al. found that the introduction of nano-magnesium aluminum spinel into mullite-based castables, due to the mismatch of thermal expansion coefficients between mullite and magnesium aluminum spinel, leads to tension ring stress around the spinel and microcracks in the matrix, which is conducive to strengthening the internal structure of the material, thereby limiting the expansion of cracks. Therefore, the prepared mullite-magnesium aluminum spinel castable has good thermal shock resistance.
5. Mullite-silicon carbide refractory silicon carbide has the properties of high strength, high thermal conductivity, wear resistance, etc., and can be combined with mullite to prepare a mullite-silicon carbide castable with excellent performance. Mullite-silicon carbide wet jetting castable. The wet jetting castable has good rheological properties, showing a pseudoplastic fluid with a small yield value and apparent viscosity. It is suitable for pumping pipeline transportation and can be used in kilns such as ladles, electric furnaces, blast furnaces, and torpedo tanks. pointed out that adding 6% (w) of zircon to the mullite-silicon carbide castable can further improve the wear resistance of the mullite-silicon carbide castable, making it suitable for lining parts with strict requirements on thermal shock resistance and wear resistance.
6. Mullite-bonded corundum-silicon carbide refractory materials In order to solve the problem of reduced high-temperature performance of corundum-silicon carbide castables bonded with common binders (such as calcium aluminate cement). used corundum and silicon carbide as aggregates, and M70 mullite powder, Al₂O₃ powder and SiO₂ powder as the bonding matrix to prepare a mullite-bonded corundum-silicon carbide cement-free castable. The introduction of mullite powder into the matrix can form a network structure of columnar mullite inside the castable after sintering, thereby improving the room-temperature flexural strength, room-temperature compressive strength, high-temperature flexural strength and thermal shock resistance of the corundum-silicon carbide castable.
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