In the iron and steel metallurgical industry, refractory materials are indispensable basic materials. Refractory materials generally refer to inorganic non-metallic materials or products with a refractoriness of not less than 1580℃. They are mainly used in blast furnaces, converters, coke ovens in the ironmaking industry, converters, secondary refining furnaces, continuous casting, etc. in the steelmaking industry, and are also used in cement kilns and kilns for glass and non-ferrous metals. In the process of steel smelting, refractory materials must not only play the role of containers for molten iron and molten steel to ensure production efficiency and service life, but also need to ensure stable quality and not pollute molten steel. In recent years, with the increasingly stringent requirements of aerospace technology and industries such as automobiles and microelectronics on the strength, toughness and processing properties of steel, the requirements for refractory materials used in the steel smelting process have also increased.
In the entire steel smelting process, refractory materials with excellent performance are needed to avoid the erosion of molten iron or molten steel, which causes the refractory materials to contaminate non-metallic inclusions or harmful elements O, P, S, N, and H in steel. At the same time, it is necessary to use environmentally friendly raw materials through reasonable optimization design to obtain pollution-free, superior performance, good economic benefits and long-life refractory materials, while improving production efficiency and economic benefits, meeting the requirements of green environmental protection.
Corundum (Al2O3) has superior performance and is non-toxic to the environment. It is widely used in refractory materials. Al2O3 is an amphoteric compound with a density of 3.94.0g/cm3, a melting point of 2050℃, a boiling point of 2980℃, and its hardness is second only to diamond; Al2O3 has a variety of crystal forms, α-Al2O3 is the most stable crystal form among all alumina crystal forms, and belongs to the corundum structure, the trigonal crystal system R-3C space group, and the unit cell is a pointed rhombohedron. The structure has a hexagonal most densely packed oxygen atom layer, and 2/3 of the octahedral voids of oxygen atoms are filled with metal aluminum atoms. Aluminum atoms are surrounded by six oxygen atoms to form an octahedral hexacoordinate type.
Corundum crystals are ionic crystals with relatively strong ionic bonds. Corundum has high hardness and good thermal conductivity, especially at low temperatures. It has a small dielectric constant and high insulation resistance. It has good light transmittance and is an excellent optical crystal material. Its chemical properties are stable, it is not corroded by acids and alkalis at room temperature, and it is insoluble in water. The degree of wetting of different metals on corundum varies greatly. The wetting angles of lead, zinc, aluminum, copper and some iron alloys are greater than 90°, and the wetting angles with iron-manganese alloys, iron-chromium alloys, and some titanium alloys are less than 90°. However, corundum can interact with oxides in materials such as slag, glass, and refractory materials to form compounds, so corundum materials are easily corroded by slag. Corundum also has disadvantages such as low fracture strength, poor thermal expansion resistance, and poor creep resistance, which limit its application.
In order to improve the shortcomings of Al2O3 refractory materials, people add binding phases or in-situ synthesize reinforcing phases in Al2O3 refractory materials to prepare corundum composite refractory materials. In the last century, a wide variety of oxide-reinforced corundum refractories were developed, including Al2O3-Cr2O3 refractories, Al2O3-MgO refractories, Al2O3-ZrO2 refractories and other oxide composite refractories. However, the oxide bonding phase has the disadvantages of large thermal expansion coefficient and poor corrosion resistance, which gradually cannot meet the growing industrial technology needs. C can improve the thermal shock stability and corrosion resistance of Al2O3 refractories. People add C to Al2O3 refractories to develop Al2O3-C refractories. Today, Al2O3-C refractories are widely used in the field of steel smelting. However, C is easily oxidized during use, and the use of carbon-containing materials will cause carbon increase in molten steel, which cannot meet the production requirements of modern clean steel technology. With the development of non-oxides such as Si3N4 and SiC in the field of ceramics, especially the emergence of AlON and SiAlON in Si-Al-O-N and Al-O-N systems in the 1970s, non-oxide combinations have been gradually applied to Al2O3 refractory materials, and Al2O3-Si3N4 refractory materials, Al2O3-SiC refractory materials, and Al2O3-SiAlON refractory materials have been developed.
With the emergence of metal ceramic technology, people have found that a small amount of metal in brittle inorganic ceramics or refractory materials can improve brittleness and microstructure. People add metal Al and Si to Al2O3 refractory materials, synthesize SiAlON reinforcement phase in situ through reaction sintering, and a small amount or trace of residual metal can improve the brittleness or oxidation resistance of the material, so a new type of metal-non-oxide-oxide refractory with excellent performance has been developed. Corundum refractory materials combined with metals and non-oxides will have great application potential. Ferrosilicon nitride contains Si3N4 and Fe-Si intermetallic compounds. Therefore, introducing ferrosilicon nitride into corundum refractory materials can prepare metal-non-oxide-oxide refractory materials, which has great theoretical and practical significance.
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