NITRIDES solid phase synthesis

Detailed experimental studies on these gas-solid combustion reactions reveal the dependence of combustion and propagation characteristics, like front propagation velocity, combustion temperature and degree of conversion, on operating parameters like nitrogen pressure, particle size and morphology of the reactant metal and dilution of the gas and solid phases. From these studies the optimum synthesis conditions for a variety of nitrides are determined and information about the mechanisms of several gas-solid combustion reactions is obtained. With the aid of combustion theory, the apparent values of activation energy for several nitridation reactions are calculated from measured combustion characteristics. 

Cubic BC2N. Hetero-diamond B C—N compounds have recently received a great interest because of their possible applications as mechanical and optical devices. The similar properties and structures of carbon and boron nitrides (graphite and hexagonal BN, diamond, and cubic BN) suggested the possible synthesis of dense compounds with all the three elements. Such new materials are expected to combine the best properties of diamond (hardness) and of c-BN (thermal stability and chemical inertness). Several low-density hexagonal phases of B,C, and N have been synthesized [534] while with respect to the high-density phases, different authors report contradictory data [535-538], but the final products are probably solid mixtures of c-BN and dispersed diamonds [539]. 

A frequent reason for the dependence of catalyst structure on the chemical potential in the gas phase containing all the reactants is the incorporation of molecules or atoms from the reaction mixture into the catalyst phases. Formation of subphases, often only in the near-surface region of the solid, fails to create phases with individual reflections but modifies the reflections of the starting precatalyst phase notably (see previous sections). This complication presents a massive problem in the analysis of working catalysts when significant partial pressures of products are important to the phase formation and when the necessary conversions cannot be reached in the experimental cell. The investigation of ammonia synthesis catalysts when insufficient partial pressures of the product ammonia prevent the formation of the relevant nitride phases is a prominent example of this limitation (Herzog et al., 1996 Walker et al., 1989). 

Alkali metal nitride chemistry is effectively confined to that of lithium and sodium [2], and dominated by lithium nitride, Li3N, a compound that has long fascinated solid-state chemists since early reports of its synthesis and characterisation [3-5]. In the ternary phase system, Li-N-H, lithium also forms three stoichiometric ternary hydrogen-containing compounds, the imide, Li2NH, the amide, LiNH2, and the nitride hydride, Li4NH. The first... 

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