Combustion Synthesis of Si_3N_4 from Si/NH_4CI at Low Nitrogen Pressure

摘要

Combustion synthesis (CS) of Si_3N_4 was accomplished by using as-milled Si/NH_4Cl as reactants at low nitrogen pressure. The additive of NH_4Cl decreased the combustion temperature and promoted the Si nitridation. Full nitridation of Si was achieved by burning Si in pressurized nitrogen with 10～25 wt. % NH_4Cl as additives while no Si_3N_4 diluent added. The maximum combustion temperature (T_c), the combustion velocity (u) together with the α-Si_3N_4 content and mean particle size (d_(50)) of the powder products were found to be great dependent on the NH_4Cl content added in the reactants. Fine Si_3N_4 powder products with α-phase content up to 85 wt. % were obtained via steady combustion mode. A mathematical approach named combustion wave velocity methods for the analysis of temperature profiles in CS was proposed and the reaction kinetics was discussed. The apparent activation energy calculated according to the temperature profile analysis method is 29.7 kJ/mol, which agrees well with the corresponding low temperature nitriding combustion of Si.