Aluminium nitride
White powdery solid
Fixed
3.26 g · cm -3
2150-2200 ° C
On contact with water hydrolysis gradual formation of ammonia
Attention
-318.0 KJ / mol
Template: Infobox chemical / molecular formula search is not possible
Aluminum nitride AlN empirical formula, is a chemical compound of aluminum and nitrogen. It belongs to the class of the nitrides and a III-V compound semiconductor.
Properties
Aluminum nitride is a colorless solid which crystallizes in the wurtzite structure with the hexagonal space group P63mc. The aluminum atoms form a densest packing of spheres on a hexagonal lattice, the N atoms occupy half of the tetrahedral voids of this grid. The lattice constants are a: 311.14 pm and c: 497.92 pm. X-ray density of AlN is 3.26 g / cm ³. Aluminum and nitrogen are predominantly covalently bonded to the fraction of the ionic binding is 45%. The relative molecular mass Mr is 40.99 and Under nitrogen atmosphere, it has a melting point of 2150-2200 ° C and a Mohs hardness of 9
Aluminum nitride
Aluminum nitride is usually sintered at atmospheric pressure at temperatures of about 1800 ° C. With the help of suitable sintering additives, another important factor for liquid phase sintering. In practice, the doping has largely prevailed with calcium and yttrium oxide as a standard procedure.
Since AlN ceramic has a very high thermal conductivity of 180 W / mK, it is mainly used in power electronics as a substrate material. Furthermore, the use of AlN ceramics is of interest where much heat must be removed, the materials should not be allowed to be electrically conductive.
Aluminum can also be by physical deposition ( PVD), so-called sputtering or by metal organic chemical vapor deposition ( MOCVD), win as a thin layer. It is weak piezoelectric.
Synthesis
Aluminum nitride can be represented > 1600 ° C in a carbothermic reaction of aluminum oxide, nitrogen or ammonia and carbon at a temperature in excess:
Another way is to Direktnitridierung. In this type of synthesis of metallic aluminum or aluminum oxide powder is reacted at temperatures of> 900 ° C and N2 or NH3 to AlN:
Responsiveness
Aluminum nitride powder has a high sensitivity to hydrolysis. In water, an incomplete cleavage of aluminum in aluminum hydroxide and ammonia can be observed. Sintered ceramic is not sensitive to hydrolysis. In aluminum hydroxide decomposes according to both as powder and as -sintered ceramic to ammonia and aluminate:
Other physical properties
The following properties apply to the AlN solid phase. The properties of AlN thin films are strongly dependent on the process, so that, for example, intrinsic mechanical stress occurs and AlN is characterized in thin layers by other mechanical and electrical properties.
- Breaking strength: 300-400 MPa (4- point bending test )
- Modulus of elasticity: 350 GPa
- Thermal expansion coefficient: 4.63 · 10-6 (RT to 1850 ° C)
- Specific heat: 0.738 J / gK
- Thermal conductivity: 180 to 220 W / mK