Nitrides formation from

Nickel, K., Riedel, R., and Petzow, G., Thermodynamic and Experimental Study of High-Purity Aluminum Nitride Formation from Aluminum Chloride by Chemical Vapor Deposition, /. Amer. Ceram. Soc., 72(10) 1804-1810 (1989)... 

Thermodynamic calculations (Table 2) indicate tl nitride formation from the elements is favorable, a indeed, many nitrides can be so prepared. For examp TiN, VN, and CrN can be made at 1 bar with me... 

Aluminum nitride from bauxite, carbon and nitrogen (17), and the formation of silica-aluminum-nitride mixtures from various clays at about 1500°C. and higher temperatures. 

Strategies for preparation are numerous and invoh widely differing starting metallic compounds, as we as different carbon and nitrogen sources. It is then fore instructive to consider the thermodynamics [2. of various kinds of transformations. The heats an free energies of formation from the elements at 2981 and 1000K are presented in Table 1 for carbides an Table 2 for nitrides. For illustration, different transfo mations to molybdenum carbide are presented at 2981 in Table 3 and at lOOOK in Table 4. 

Table 2. Heat and free energy of formation from the elements of transition metal nitrides (kJ mol-1) calculated from data in Ref. 22.

The product is described as a powder, white to dark red in colour according to the time of heating at 250° C. The density was 2-5. The nitride was tasteless, odourless, and chemically inactive at ordinary temperatures. The heat of formation (from white phosphorus) is given as +81-5 Cals, per mol.3 The molar heat of combustion was 474-7 Cals, (at constant pressure). The nitride dissociated into its elements in a vacuum at about 760° C.4 It was reduced to phosphorus and ammonia by hydrogen at a red heat, and burned when heated in oxygen or chlorine. It was hydrolysed by boiling water, thus... 

Combustion synthesis of boron nitride powder, BN, was reported in one of the earliest works on SHS (Merzhanov and Borovinskaya, 1972). The mechanisms of combustion and product structure formation from elements were later investigated (Mukasyan and Borovinskaya, 1992). More recently, finely dispersed hexagonal boron nitride powder has been obtained from reduction-type reactions (Borovinskaya et fl/., 1991). 

After the air is completely displaced from the apparatus by the NHg (air bubbles cease to emerge from the second Erlenmeyer flask), the Mg is heated at 800 to 850 C for four hours. The onset of nitride formation is recognized by incandescence of the Mg and the evolution of Hg. A high NHg flow must be maintained at the peak of the reaction to avoid sucking the absorption fluid into the reactor. Since the finished material always contains adsorbed NHg, heating in a Ng stream should be continued at the same temperature for 90 minutes. Because of the high moisture sensitivity of the material, bottling must be carried out with the usual precautions. 

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