Aluminum nitride production

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... 

The combination of toxic hazard and high price (itself in part due to the extra measures needed in production processes to ensure the workers safety) has been an effective brake on commercial development of beryllium chemistry. Where possible substitute, albeit less effective, materials are often used titanium as an alternate lightweight metal or carbon fiber composites, phosphor-bronzes in place of beryllium alloys, aluminum nitride in place of BeO (1). 

Fedotova, T. D., Glotov, O. G., and Zarko, V. E., Ghemical Analysis of Aluminum as a Propellant Ingredient and Determination of Aluminum and Aluminum Nitride in Gondensed Gombustion Products, Propellants, Explosives, Pyrotechnics, Vol. 25, 2000, pp. 325-332. 

A variety of other ceramics are prepared by pyrolysis of preceramic polymers.32,38 Some examples are silicon carbide, SC, tungsten carbide, WC, aluminum nitride, AIN, and titanium nitride, TiN. In some cases, these materials are obtained by simple pyrolysis in an inert atmosphere or under vacuum. In other cases a reactive atmosphere such as ammonia is needed to introduce some of the atoms required in the final product. Additional details are given in Chapter 9. 

Fibers of aluminum nitride have been produced by the melt-spinning of ethyl-alazanes derived from the reactions of triethylaluminum and ammonia.72 The spinnable products have compositions such as (I l AIN11 )c(Et2A INH2 )v(Et3 A1 ),] which probably consist of linked alazane rings and chain structures. Pyrolysis in ammonia gives aluminum nitride fibers. 

Carbides, (a) The aluminum nitride made in Preparation 13 contains a considerable amount of carbide AI4C3. Treat some of this product, or some commercial aluminum carbide, with 6 N NaOH in a test tube with a delivery tube. Collect some of the gas over water, which will dissolve all the ammonia. Test the combustibility of this gas and find that it bums with a nearly colorless flame. 

Alumtnum phosphide, hke aluminum nitride, reacts with moisture but in this case the gaseous product is phosphine, PH3, a very toxic gas. For this reason, AlP is used as a fumigant to control insects in stored products such as raw agricultural products, animal feeds, processed foods (for example, flour and sugar), tobacco, wood, paper, leather, hair, and feathers. It is also used for control of rodents such as rats, mice, squirrels, and gophers in and around mills, food processing plants, warehouses and silos, and in rail cars, ships, and shipping containers. 

Aluminum nitride is most commonly used for its high thermal conductivity. Recently, a poreless composite material, TiAl-TiB2-AlN, was obtained by reacting a Ti-F(0.7-0.95)A1+(0.05-0.50)8 mixture at 30- to 100-atm nitrogen pressure (Yamada, 1994). The use of high-pressure nitrogen gas was found to be effective for simultaneous synthesis and consolidation of nitride ceramics with dispersed intermetallic compounds (e.g., TiAl). Dense, crack-free products with uniform grains (approximately 10 mm in size) were obtained. 

Numerous ceramics are deposited via chemical vapor deposition. Oxide, carbide, nitride, and boride films can all be produced from gas phase precursors. This section gives details on the production-scale reactions for materials that are widely produced. In addition, a survey of the latest research including novel precursors and chemical reactions is provided. The discussion begins with the mature technologies of silicon dioxide, aluminum oxide, and silicon nitride CVD. Then the focus turns to the deposition of thin films having characteristics that are attractive for future applications in microelectronics, micromachinery, and hard coatings for tools and parts. These materials include aluminum nitride, boron nitride, titanium nitride, titanium dioxide, silicon carbide, and mixed-metal oxides such as those of the perovskite structure and those used as high To superconductors. 

The production of silicon nitride [16,17] and aluminum nitride [18-21] has been extensively studied plasma reactions [21-23] were also reported. Instead of ammonia nitrogen may be used [24,25]. Hydrocarbons and metal halides for the formation of carbides are worth mentioning [26,27]. 

Figure 8.13 SEM images of the combustion products of the (a) silicon, (b) boron, and (c) aluminum nitride powders.

The results of the grain-size analysis of the systems combusting products meant for obtaining of aluminum nitride are presented by Figures 8.22 and 8.23. By Figure 8.22, it is seen that the mean particle size is 50-150 nm. It is obvious that size of the particles basis mass is 0.6-1.0 pm (Figure 8.23). 

The plasma chemical method is relatively often used now for preparing many nanopowders for production of refractory compounds (nitrides, oxides, carboni-trides, and their compositions) [6]. The process of preparing aluminum nitride nanopowder by this technique is based on evaporation of aluminum in high temperature nitrogen flow, following chemical interaction, and subsequent condensation of reaction product. It means that this process could be considered as a kind of combustion synthesis. 

The plasma technique allows also production of nanosized nitride powder doped with sintering additives, for example, aluminum nitride doped with yttria. Such composite powders are characterized with high degree of homogeneity because the formation of powder particles occurs by simultaneous condensation from gaseous-vapor phase [13]. 

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