Is alumina a refractory?Alumina is a raw material for refractory products, which can be made into high alumina, corundum bricks, refractory castables and so on by calcination and artificial synthesis.
Alumina is one of the more well-studied oxides with high melting points. It has abundant raw material reserves, low price, and has many good properties. Therefore, alumina is a widely used oxide refractory material in refractory plants. Alumina has a hardness of 9 on the Mohs scale, which is lower than that of diamond and some refractory compounds. Alumina refractory material has high mechanical strength, the flexural strength at room temperature is 250MPa, there is still 150MPa at 1000, the compressive strength at room temperature can be as high as more than 2000MPa, and the compressive strength of some microcrystalline products can even reach 5000MPa. The refractory degree of alumina refractory is greater than 1900,0The starting point of 2MPa load softening is around 1850. It has a limited service temperature of 1950 and a common temperature of 1800. The flat expansion coefficient of alumina at 20-1000 is 86×10-6／℃。The thermal conductivity of alumina at room temperature is half that of metallic aluminum, and the thermal conductivity decreases as the temperature rises. The thermal shock stability of alumina refractory depends on its microstructure and the shape and size of the product. In short, alumina has high temperature resistance, high strength, high hardness, oxidation resistance, electrical insulation, corrosion resistance, good air tightness and other properties, so it is widely used as a special refractory material. The typical use is to use its high temperature resistance, corrosion resistance, high strength and other properties, as a sliding nozzle, immersion nozzle, metallurgical high-purity metal or crucible for growing single crystals, as well as structural parts (furnace walls, furnace tubes), heat-resistant and anti-oxidation coatings for various high-temperature furnaces. 
Alumina (corundum) special refractories have been widely used due to their good high-temperature performance and low price ratio. High-purity, high-density and high-performance corundum refractory bricks are widely used in large-scale blast furnaces and large-scale ladles in steel mills, and have achieved good results. It is used in the second-stage furnace and gasifier of large-scale ammonia synthesis plant, and in the cracking furnace of ethylene engineering, which is the best furnace lining material. High thermal stability corundum brick is a lining material for various furnaces such as firing furnace and molybdenum silicide electric furnace for special materials and products. High-quality corundum bricks are also used in hot blast stoves for ferrofluid power generation. Alumina hollow ball products and alumina fiber products are high-temperature and energy-saving products. Due to its small bulk density and low thermal conductivity, it is an ideal furnace lining material for energy saving and consumption reduction. Alumina is a neutral (amphoteric oxide) oxide material, which has good erosion resistance to acid, alkali and salt materials. It is chemically stable and suitable for use under oxidation, reduction, protective atmosphere and vacuum conditions. The varieties of alumina special refractory materials are: high-performance refractory brick products, ceramic products, lightweight thermal insulation products, fiber products and amorphous products, etc., and their main application scope is: (1) furnace lining structural materials for warm kilns;(2) Crucibles for smelting and purification of high-purity metals, high-temperature alloys, dilute metals, etc(3) High-temperature furnace tubes, thermocouple tubes, high-temperature insulation, etc(4) High-temperature resistant kiln furniture, gaskets, pressing rods and briquetting, etc.;(5) High-temperature resistant and anti-corrosion furnace lining materials for petrochemical industry;(6) Transparent alumina ceramics can be used as high-pressure sodium lamps, microwave covers, and high-temperature observation window glass(7) In the electronics industry, circuit substrates, electronic tube sockets, high-voltage ceramic tube shells, radomes, spark plugs, etc(8) Abrasives and abrasives, such as grinding wheels, cutting discs, drawing dies, drawing tower wheels, textile porcelain parts, sandblasting nozzles, high-temperature wear-resistant bearings and various cutting tools, etc(9) Piston pump parts, sealing rings, etc. for chemical industry(10) Metallurgical and non-ferrous industry metal melt transportation pipelines;(11) High-temperature, high-efficiency and energy-saving materials in various industrial sectors, such as alumina hollow balls, alumina whiskers, alumina fibers, etc. and their products. Alumina precision ceramics can be made into crucibles and negatives for smelting or purifying non-colored, rare and high-quality furnaces, thermocouple protection tubes and insulating porcelain tubes, laser tubes, rectifier tubes, transparent sodium lamps, radar radomes, microwave devices, sodium-sulfur battery shells, gas purifiers and spark plugs. Wear-resistant and corrosion-resistant refractories made of alumina ceramics, filters for metal liquids, high-temperature ceramics for physical and chemical analysis, parts of chemical and textile industry machinery, such as sealing rings, valves, piston pumps, catalyst carriers for petrochemical industry, etc.