Aluminum nitride
Crystal structure | |||||||||||||||||||
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__ Al 3+ __ N 3− | |||||||||||||||||||
General | |||||||||||||||||||
Surname | Aluminum nitride | ||||||||||||||||||
Ratio formula | AlN | ||||||||||||||||||
Brief description |
white powdery solid |
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External identifiers / databases | |||||||||||||||||||
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properties | |||||||||||||||||||
Molar mass | 40.99 g mol −1 | ||||||||||||||||||
Physical state |
firmly |
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density |
3.26 g cm −3 |
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Melting point |
> 2400 ° C (decomposition) |
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solubility |
on contact with water gradual hydrolysis with formation of ammonia |
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safety instructions | |||||||||||||||||||
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Thermodynamic properties | |||||||||||||||||||
ΔH f 0 |
−318.0 kJ / mol |
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As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . |
Aluminum nitride , empirical formula AlN, is a chemical compound of aluminum and nitrogen . It belongs to the nitride class of materials and is a III-V compound semiconductor with a wide band gap . The band gap is at room temperature .
properties
Aluminum nitride is a white, flammable, but difficult to ignite, powdery solid with an ammonia-like odor that decomposes in water. It crystallizes in the wurtzite structure with the hexagonal space group P 6 3 mc (space group no.186) . The aluminum atoms form a tight packing of spheres on a hexagonal lattice, the N atoms occupy half of the tetrahedral gaps in this lattice. The lattice constants are a = 311.14 pm and c = 497.92 pm. The X-ray density of AlN is 3.26 g / cm³. Aluminum and nitrogen are predominantly covalently bonded, the proportion of ionic bonding is 45%. The relative molecular mass M r is 40.99 u. Under nitrogen atmosphere, it has a melting point of over 2200 ° C and a hardness on the Mohs scale of 9. From 2400 ° C decomposes the connection.
Aluminum nitride ceramic
Aluminum nitride is depressurized, usually at temperatures of about 1800 ° C sintered . With the help of suitable sintering additives, liquid phase sintering occurs. In practice, doping with calcium oxide and yttrium oxide has largely become the standard method.
AlN ceramic has a very high thermal conductivity of 180 W / (m · K). The use of AlN ceramics is therefore of interest where a lot of heat has to be dissipated, but the material must not be electrically conductive. AlN ceramic is mainly used as a substrate material in power electronics.
On an industrial scale, aluminum nitride is obtained as a thin film by physical deposition processes ( PVD ), sputtering or by organometallic chemical vapor deposition (MOCVD).
synthesis
Aluminum nitride powder can be produced from aluminum oxide , nitrogen or ammonia and carbon in excess at a temperature> 1600 ° C in a carbothermal reaction:
Another way is direct nitridation. With this type of synthesis, metallic aluminum or aluminum oxide powder is converted to AlN at temperatures> 900 ° C with N 2 or NH 3 :
Responsiveness
Aluminum nitride powder is very sensitive to hydrolysis . Incomplete splitting of aluminum nitride into aluminum hydroxide and ammonia can be observed in the water . Sintered ceramic is not sensitive to hydrolysis. In caustic soda , aluminum nitride decomposes both as a powder and as a sintered ceramic to form ammonia and an aluminate solution according to:
Web links
Individual evidence
- ↑ a b c d e f g h Entry on aluminum nitride in the GESTIS substance database of the IFA , accessed on January 8, 2020(JavaScript required) .
- ↑ Data sheet Aluminum nitride at Sigma-Aldrich , accessed on January 25, 2020 ( PDF ).
- ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, Standard Thermodynamic Properties of Chemical Substances, pp. 5-5.
- ↑ J. Li, KB Nam, ML Nakarmi, JY Lin, and HX Jiang: Band structure and fundamental optical transitions in wurtzite AlN . In: Applied Physics Letters . tape 83 , no. 25 , 2003, p. 5163-5165 , doi : 10.1063 / 1.1633965 .
- ↑ Martin Feneberg, Robert AR Menschen, Benjamin Neuschl, Klaus Thonke, and Matthias Bickermann: High-excitation and high-resolution photoluminescence spectra of bulk AlN . In: Physical Review B . tape 82 , no. 7 , 2010, p. 075208 , doi : 10.1103 / PhysRevB.82.075208 .