Alumina fiber (polycrystalline mullite fiber), compared with carbon fiber, silicon carbide fiber and other non-oxide fibers, alumina fiber not only has high strength, high modulus, high temperature resistance and other excellent properties, but also has very good properties. High temperature oxidation resistance, corrosion resistance and electrical insulation. Alumina fiber (polycrystalline mullite fiber) can be compounded with resin, metal or ceramic to prepare high-performance composite materials, which are widely used in aviation, aerospace, military and high-tech fields.

The production process of alumina fiber (polycrystalline mullite fiber) is relatively simple and does not require high production equipment and production conditions. Compared with carbon fiber, the cost of alumina fiber (polycrystalline mullite fiber) is much lower. Makes a large number of applications of alumina fiber possible. At present, many companies abroad have produced various types of high-performance alumina fibers.

　　 The American ICI Company uses the Bu Nemen method to produce alumina short fibers under the trade name Saffil, which can be used at temperatures up to 1200-1600°C, and have begun to be applied to the lining of industrial sintering furnaces.

　　 US 3M Company produces Nexte1 series alumina fiber (polycrystalline mullite fiber) through the sol method, and the more representative one is Nexte1312.

　　 Japan's Sumitomo Chemical Company uses the prepolymerization method to produce Altex alumina fiber, the composition of which is Al2O3, SiO2, B2O3.

　　U.S. DuPont company uses the siltation method to produce EP alumina fiber with an alumina content of 99.9%.

　　 Japan's Mitsui Mining Company also produced continuous alumina fibers with an alumina content of more than 95% through a slurry method.

In China, the earliest successful pilot test was Zhejiang Oushiman Crystal Fiber Co., Ltd., which won the bid in the national economic and trade season and built the first domestic alumina fiber continuous production line. It is currently the most representative production enterprise in China. Build the largest polycrystalline mullite fiber production base in China.

　　Alumina fiber (polycrystalline mullite fiber) is mainly used for high-temperature thermal insulation materials (short fibers) and reinforced composite refractory (long fibers), and can be woven into fiber products of various shapes such as non-woven fabrics, braided belts, and ropes.

　　In the field of industrial high temperature furnaces, the energy saving effect is remarkable

　　 Alumina short fiber has outstanding high-temperature resistance, and is mainly used as a heat-insulating refractory material, and as a heat-insulating material for body lining in metallurgical furnaces, ceramic sintering furnaces or other high-temperature furnaces. Because of its low density. With good thermal insulation and small heat capacity, it can not only reduce the quality of the furnace body, but also improve the temperature control accuracy, and the energy-saving effect is significant. The energy-saving effect of alumina fiber (polycrystalline mullite fiber) used in high-temperature furnaces is better than that of ordinary refractory bricks or high-temperature coatings. The energy saving is much greater than the heat loss. The reason is not only the reduction of heat loss, but also the main reason. The convective heat transfer of the furnace gas to the furnace wall is strengthened, so that the furnace wall can get more folded heat, which is then transferred to the material through the national emblem, thereby improving the heating speed and production capacity of the material.

　　Aerospace field mullite fiber has advantages

　　 Polycrystalline mullite fiber is the main type of alumina-based fiber, which mainly exists in the form of mullite microcrystalline phase in structure. Compared with general alumina-based fiber, polycrystalline mullite fiber has better high temperature resistance, and the service temperature is 1500-1600℃, especially the high temperature creep resistance and thermal shock resistance are greatly improved. The latest ultra-lightweight high-temperature heat-resistant fiber at home and abroad. As a heat-resistant material, mullite short fiber has been used in the aerospace industry. The US Space Shuttle has used aluminum silicate fibers to make insulation tiles and flexible insulation materials. The insulation board liner of the US "Columbia" space shuttle uses Saffil alumina fiber. When the space shuttle returns to the atmosphere, since the Saffil alumina fiber can withstand a high temperature of 1600°C, this liner will prevent heat from passing through the insulation. The gap between the hot plates enters the heat shield.

　　 The thermal expansion rate and thermal conductivity of the polycrystalline mullite fiber and the basic interface of the ceramic are very close. The addition of polycrystalline mullite fiber can improve the basic toughness of the ceramic and increase the impact strength, and it has developed rapidly in the development of heat-resistant composite materials. The continuous mullite fiber reinforced metal matrix and ceramic matrix composite material can be used in supersonic aircraft, and can also be used to manufacture nozzles and gaskets of liquid rocket engines, which can be used above 2200°C.

　　Environmental protection and recycling field application has bright spots

　　 Alumina fiber can be used in the fields of environmental protection and recycling technology due to its good chemical resistance. For example, the equipment for incineration of electronic waste, after years of operation, alumina fiber still shows its excellent corrosion resistance to various harmful substances in the furnace, and can be used as a ceramic lining on automobile exhaust equipment. Its characteristic is stable structure. Saffil alumina fiber can be used for aluminum alloy plugs. Its advantage is that it expands less when the temperature rises, which is about 25% less than pure alloy, so that the piston and cylinder are in good agreement and can save fuel.

　　Reinforced composite materials have obvious performance advantages

　　 Because the alumina fiber has good wettability with the metal matrix and the interface reaction is small, the mechanical properties, wear resistance and hardness of the composite material are improved, and the thermal expansion coefficient is reduced. Alumina fiber reinforced metal matrix composite materials have been used in automobile piston groove parts and rotary gas compressor blades. In addition, because the alumina fiber is well bonded to the resin matrix, it is more elastic than glass fiber and has higher compressive strength than carbon fiber. Therefore, alumina resin composite materials are gradually replacing glass fiber and carbon fiber in some areas. Especially in the field of cultural and sports goods, it can be made into high-strength fishing poles, golf balls, snowboards, tennis rackets, etc. of various colors.

Alumina long fiber reinforced metal matrix composite materials are mainly used in high-load mechanical parts, high-temperature and high-speed rotating parts, and high-functional components with lightweight requirements, such as automobile connecting rods, transmission rods, brake pads and other parts and helicopter transmission Devices, etc. Recently, some researchers have begun to use it for the lining of thermonuclear reactor cooling and heat exchange devices.

　　Alumina fiber is widely used in various fields due to its many excellent properties. my country's research and development of alumina fiber is of great significance in both the national defense industry and the industrial field.