Basic knowledge of aluminum nitride
Overview of aluminum nitride
Aluminum nitride, a covalent bond compound, is an atomic crystal, belonging to diamond-like nitride, hexagonal crystal system, wurtzite type crystal structure, non-toxic, white or off-white.
Properties of aluminum nitride
AlN can be stabilized up to 2200℃. The room temperature strength is high, and the strength decreases slowly with the increase of temperature. It has good thermal conductivity and small thermal expansion coefficient, making it a good thermal shock material. It has strong resistance to molten metal corrosion and is an ideal crucible material for melting and casting pure iron, aluminum or aluminum alloy. Aluminum nitride is also an electrical insulator with good dielectric properties, and it is also promising as an electrical component. The aluminum nitride coating on the surface of gallium arsenide can protect it from ion implantation during annealing. Aluminum nitride is also a catalyst for the transformation from hexagonal boron nitride to cubic boron nitride. It reacts slowly with water at room temperature. It can be synthesized from aluminum powder at 800~1000℃ in ammonia or nitrogen atmosphere. The product is white to grayish blue powder. Or synthesized by Al2O3-C-N2 system at 1600~1750℃, the product is off-white powder. Or aluminum chloride and ammonia are made by gas phase reaction. The coating can be synthesized by vapor deposition method in AlCl3-NH3 system.
Storage method of aluminum nitride
Dispose of under dry protective gas and keep the container sealed. Put it in a tight container and store it in a cool, dry place.
The history of aluminum nitride
Aluminum nitride was first synthesized in 1877. By the 1980s, because aluminum nitride was a ceramic insulator (polycrystalline material was 70-210 W‧m−1‧K-1, and single crystal could be as high as 275 W‧m−1‧K−1), the nitrogen Aluminum has high heat transfer ability, so that aluminum nitride is widely used in microelectronics. Unlike beryllium oxide, aluminum nitride is non-toxic. Aluminum nitride is treated with metal, which can replace alumina and beryllium oxide in a large number of electronic instruments. Aluminum nitride can be prepared by the reduction of aluminum oxide and carbon or directly nitriding metal aluminum. Aluminum nitride is a substance connected by covalent bonds. It has a hexagonal crystal structure, which is the same shape as zinc sulfide and wurtzite. The space group of this structure is P63mc. Industrial-grade materials can only be manufactured by hot pressing and welding. The substance is very stable in an inert high temperature environment. In the air, when the temperature is higher than 700 ℃, the surface of the material will be oxidized. At room temperature, 5-10 nanometer thick oxide films can still be detected on the surface of the material. Up to 1370°C, the oxide film can still protect the substance. However, when the temperature is higher than 1370°C, a large amount of oxidation will occur. Up to 980°C, aluminum nitride is still quite stable in hydrogen and carbon dioxide. Mineral acids dissolve slowly by attacking the boundaries of granular substances, while strong bases dissolve them by attacking granular aluminum nitride. The substance will slowly hydrolyze in water. Aluminum nitride can resist the attack of most molten salts, including chloride and cryolite (ie, sodium hexafluoroaluminate).
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