SHS nitrides

The high temperatures present in the CS process make it possible to not only produce powders, but also to sinter materials and form net-shape articles in the combustion wave (Merzhanov, 1993a). Several types of SHS nitrides and their applications are presented in Table Vll. 

Dependence of SHS Nitride Composition and Structure on infiitration Combustion Mode... 

Table 7.2 Influence of nitrogen content on the phase composition of SHS-nitrided ferro-niobium.

Features of synthesis of nitrides of group III-VI elements and nitride-based composite materials by SHS nitriding of ferroalloys have been determined. 

Examples of products made by the SHS process include borides, carbides, chalcogenides, hydrides, intermelallic compounds, nitrides, silicides, carbonitrides, sulfides, cemented carbides (cermets), and various heterogeneous mixtures (microcomposiles). 

Nitrides such as TiN, AIN, ZrN, HfN, TaN, and Si3N4 and carbonitrides, such as TiCN, NbCN and ZrCN are among the important industrial products formed by the SHS process. Due to the high thermodynamic stability of titanium nitride and titanium carbide, their formation using the SHS method is highly favored even at relatively low pressures of nitrogen. 

The synthesis of transition metal nitrides by SHS was first mentioned by Merzhanov and Borovinskaya.6 The authors reported the crystal structure... 

These three ammonium salts, and the free acid, when heated may pass into thio-phosphoryl nitrile, and at a red-heat into phosphorus nitride. When diammonium nitrilodithiophosphate is heated, it loses ammonia, forming the monammonium salt —the free acid, nitrilodithiophosphoric acid, N P(SH)2, has not been made ... 

The synthesis of several hundred materials, by both the SHS and VCS modes, has been reported in the literature. The types of compounds produced include carbides, borides, intermetallics, silicides, aluminides, composites, nitrides, hydrides, and oxides. The purpose of this section is to provide a description of the synthesized compounds, as well as the materials (i.e., powders, poreless materials, and functionally graded materials) and articles produced. The practical applications of experimental and technological methods are also described. 

The industrial ceramics produced by conventional sintering of 8-phase Si3N4 powders synthesized by SHS (Petrovskii et al, 1981) can be used as high-temperature articles with attractive dielectric properties (tan6=4.4 10 at/= 10 Hz, and dielectric strength, Ea=9.2 kV/mm). Also, silicon nitride powders with a relatively high a-phase content ( 80%) have been used for the production of advanced structural ceramics with good mechanical properties ([Pg.109]

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). 

Some Properties of SHS Silicon Nitride-Based Ceramics"... 

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