Aluminum nitrides

Aluminum nitride is used in manufacturing of steel and in semiconductors. 

White crystalline solid, hexagonal odor of ammonia in moist air suhhmes at 2000°C melts in N2 atmosphere over 2200°C density 3.26 g/cm decomposes in water, alkahes and acids 

Aluminum nitride may be prepared in the laboratory by heating powdered aluminum metal with nitrogen. 

Commercially, it is made by heating an aluminous mineral, such as, bauxite with coal in a stream of nitrogen. 

The nitride reacts with water forming aluminum hydroxide and ammonia. AIN 3H2O------------------ A1(0H)3 + NHs 

Aluminum nitride (AlN) has interesting properties, such as a high thermal conductivity (70-210 W m for the polycrystalline material, and up to 285 W m for single crystals), a high volume resistance, and moderate dielectric properties. The thermal expansion coefficient of AlN is close to that of silicon, and it is one of the most mechanically strong and thermally stable ceramics. These excellent attributes make AlN a useful material for many applications [160, 161]. 

The wurtzite phase of AlN (w-AlN) is a wide band gap (6.2 eV) semiconductor material, which provides a potential application for deep UV optoelectronics. The space group is and the coordination geometry is tetrahedral. 

The lack of a suitably volatile homoleptic hydride for aluminum (AIH3 is an involatile polymeric species) led to the application of aluminum halides and organometallic compounds as precursors. However, the advent of volatile hydride complexes, such as A1H3(NR3)2, offers the possibility of AIN films being grown from all hydride sources [172]. 

A summary of precursor combinations with their relevant deposition parameters is given in Table 5-11. 

Aluminum precursor Nitrogen source Carrier gas CVD method Deposition temp. rc] Growth rate [A min ] Comments Ref. 

A1Mc3 precracked NH3 (1747°C) Hj/He APCVD (LPCVD) 310-460 500-2000 N-Hand [181] AIN-N bonds detected by FTIR 

AlMej PrNH, H2 APCVD 500 - very high C [183] content, lowN 

After heat treatment, the microstracture is made up of aluminum nitride crystals and secondary phases of aliuninates at the grain boundaries and at the triple points. The degree of crystallization and the distribution vary with the nature of the additives used and the thermal cycle. As pure alitmintrm nitride is a very good conductor of heat and aluminates of heat insulators, the development of the microstmcture, in particular the location of the phases at the grain boundaries, have been the srrbject of extensive research. It transpires that yttrirrm-based additives (Y2O3, YF3) yield sintered alumimrm nitride substrates with the highest thermal conductivity (150-200 W/m h ). 

What explanation can you give for the action of potassium hydroxide in facilitating the change of the black to the red modification  

The very active metals are capable of combining directly with nitrogen to form nitrides. In the air the oxide is formed so much more readily, that nitride formation is likely to escape notice but if the metal is presented in powdered form in a thick mass the oxygen is all combined in the surface layer and only nitrogen penetrates to the interior where pure nitride is formed. 

Although aluminum is a very active metal, it enters into many reactions with extreme difficulty on account of a thin, tenacious coating of oxide, which keeps it physically separated from the reacting material. Aluminum powder alone cannot be made to bum in air, but when it is mixed with lampblack and any part is brought to the kindling temperature, which is very high, the combustion spreads throughout the mass. The function of the carbon is to react with this oxide layer. Carbon alone reacts with aluminum oxide to yield the carbide 

In the presence of nitrogen, however, the nitride instead of the carbide is produced. 

Materials finely powdered aluminum, 45 grams. The material sold for use as a pigment and often labeled aluminum bronze is nearly pure aluminum and is suitable for the purpose. The small amount of oil which it contains is no disadvantage, carbon, lampblack, 5 grams, magnesium ribbon, 4 inches. 

Reaction of tetrakis-diethylamino titanium (TDEAT) or tetrakis-dimethylamino titanium (TDMAT) with ammonia (NH3) at 300°C in a flow of helium. Possible carbon retention. 

Pyrolysis of tetrakis(dimethylamido)titanium (TDMAT) in nitrogen at 300°C. 

Decomposition of acetylacetonate, Fe(C5H702)3, at 400-500°C, or of the iron trifluoro-acetylacetonate, Fe(F3C5H4)3, at 300°C in oxygen. 

The preparation given here is based on chemistry first discovered by Wiberg. It provides a high-purity AIN powder at relatively low materials cost. The mechanism of the process has been studied.  

Within the glovebox, the reaction is carried out in a 500-mL, three-necked round-bottomed flask equipped with reflux condenser (gas outlet at the top) and silicone rubber septa. Teflon sleeves are used to avoid silicone grease contamination. A solution of (Et3Al)2 (85 mL, 0.62 mol Al) in 150 mL of n-hexane is placed in the flask and heated in a sandbath to 50°, with continuous stirring. A flow of N2 (25 mL/min) through a stainless-steel needle is bubbled into the solution to establish a positive flow and prevent back-diffusion of air ammonia gas (75 mL/min) is then added to this stream. A test of the effluent gas with wet litmus paper shows no ammonia present. 

After 12 h, a similar litmus test shows NH3 in the effluent. The ammonia and nitrogen are shut off. The resulting solution of (Et2AlNH2)3 is then cooled and the n-hexane removed under reduced pressure at ambient temperature. 

The liquid (Et2AlNH2)3 is transferred to a Schlenk tube fitted with a 19-cm air condenser. The tube is gradually heated to 145° so that a slow evolution of ethane gas occurs, then held at 145° for 12 h, yielding a solid of approximate composition (EtAlNH) . 

In the glovebox, the white chunky solid is pulverized with a spatula and transferred to a molybdenum or tungsten boat. This is then placed in a fused-silica tube equipped with inlet and outlet valves (Fig. 1). The tube is inserted into a furnace and heated under flowing ammonia (10 mL/min) to 1000° over a period of 6 h, held at this temperature 8 h, then cooled. Overall yield is 17.8 g (70%). 

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Evans R, Smith I, Munz W D, Williams K J P and Yanwood J 1996 Raman microscopic studies of ceramic coatings based on titanium aluminum nitride ICORS 96 XVth Int. Conf. on Raman Spectroscopy ed S A Asher and P B Stein (New York Wiley) pp 596-7... 

ALUMDIUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - CALCINED, TABULAR, AND ALUMINATE CETffiNTS] (Vol 2) -aluminum nitride for [NITRIDES] (Vol 17)... 

Metal powder—glass powder—binder mixtures are used to apply conductive (or resistive) coatings to ceramics or metals, especially for printed circuits and electronics parts on ceramic substrates, such as multichip modules. Multiple layers of aluminum nitride [24304-00-5] AIN, or aluminay ceramic are fused with copper sheet and other metals in powdered form. The mixtures are appHed as a paste, paint, or slurry, then fired to fuse the metal and glass to the surface while burning off the binder. Copper, palladium, gold, silver, and many alloys are commonly used. 

The nitrides of Groups 4(IVB) and 5(VB) elements form at ca 1200°C. The nitrides of magnesium and aluminum form at 800°C. Aluminum nitride, obtained by beating aluminum powder in the presence of ammonia or nitrogen at 800—1000°C, is formed as a white to grayish blue powder. A grade of... 

Annual production of aluminum nitride is 50—100 t and it is sold for ca 40/kg. Extra high purity, ie, high heat conductive aluminum nitride, is sold... 

Materials used for substrates can be broadly classified into ceramics and metals. Gommonly used ceramics, ie, alumina, aluminum nitride, and beryUia, can be easily incorporated into a hermetic package, ie, a package permanently sealed by fusion or soldering to prevent the transmission of moisture, air, and other gases. 

Although beryllium oxide [1304-56-9] is in many ways superior to most commonly used alumina-based ceramics, the principal drawback of beryUia-based ceramics is their toxicity thus they should be handled with care. The thermal conductivity of beryUia is roughly about 10 times that of commonly used alumina-based materials (5). BeryUia [1304-56-9] has a lower dielectric constant, a lower coefficient of thermal expansion, and slightly less strength than alumina. Aluminum nitride materials have begun to appear as alternatives to beryUia. Aluminum nitride [24304-00-5] has a thermal conductivity comparable to that of beryUia, but deteriorates less with temperature the thermal conductivity of aluminum nitride can, theoreticaUy, be raised to over 300 W/(m-K) (6). The dielectric constant of aluminum nitride is comparable to that of alumina, but the coefficient of thermal expansion is lower. 

Magnesium reacts slowly at lower temperatures to give the amide, as do all active metals this reaction is catalyzed by transition metal ions. Aluminum nitride [24304-00-5] AIN, barium nitride [12047-79-9] Ba2N2, calcium nitride [12013-82-0] Ca2N2, strontium nitride [12033-82-8], Sr2N2, and titanium nitride [25583-20-4], TiN, may be formed by heating the corresponding amides. 

Table 3 summarizes the properties of the so-called nonmetallic hard materials, including diamond and the diamondlike carbides B C, SiC, and Be2C. Also iacluded ia this category are comadum, AI2O2, cubic boroa nitride, BN, aluminum nitride, AIN, siUcon nitride, Si N, and siUcon boride, SiB (12). 

Next to Cr C2, TiC is the principal component for heat and oxidation-resistant cemented carbides. TiC-based boats, containing aluminum nitride, AIN, boron nitride, BN, and titanium boride, TiB2, have been found satisfactory for the evaporation of metals (see Boron compounds, refractory boron compounds Nitrides). 

Vapor—sohd reactions (13—17) are also commonly used ia the synthesis of specialty ceramic powders. Carbothermic reduction of oxides, ia which carbon (qv) black mixed with the appropriate reactant oxide is heated ia nitrogen or an iaert atmosphere, is a popular means of produciag commercial SiC, Si N, aluminum nitride [24304-00-3], AIN, and sialon, ie, siUcon aluminum oxynitride, powders. 

There are several vacuum processes such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), sputtering, and anodic vacuum arc deposition. Materials other than metals, ie, tetraethylorthosiHcate, silane, and titanium aluminum nitride, can also be appHed. 

The measures of solid state reactivity to be described include experiments on solid-gas, solid-liquid, and solid-solid chemical reaction, solid-solid structural transitions, and hot pressing-sintering in the solid state. These conditions are achieved in catalytic activity measurements of rutile and zinc oxide, in studies of the dissolution of silicon nitride and rutile, the reaction of lead oxide and zirconia to form lead zirconate, the monoclinic to tetragonal transformation in zirconia, the theta-to-alpha transformation in alumina, and the hot pressing of aluminum nitride and aluminum oxide. 

Carr and his co-workers [86C01, 87C01] have shown that transmission electron microscopy is a powerful tool in characterizing linear and higher-order defect configurations and their densities on shock-modified rutile, alumina, aluminum nitride, and zirconia [84H02]. The principal impediment to detailed characterization of shock-formed defects is their very high concentrations, which prevent identification of specific deformation features except in... 

Aluminum nitride is a highly stable covalent compound with the unusual combination of high thermal conductivity (comparable to that of metals) and high electrical insulation (comparable to the... 

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