Self-Propagating High-Temperature Synthesis of Nitrides - Progress of SHS in SICCAS

Self-propagating high-temperature synthesis (SHS, or combustion synthesis) of nitrides has been investigated in Shanghai Institute of Ceramics (SICCAS) since 1989. Fruitful results have been benefited from this excellent technology that was proposed systematically by Russian Scientists. beta-Si3N4 powder and beta-Si3N4 rod crystals up to 20 mum in length with aspect ratio 5similar to10 are synthesized, AlN powder is fabricated both in laboratory and in industrial scale. By using SHS method the cost of these powders can be greatly reduced. More over dense ceramics have been made from these powders, fully dense Si3N4 ceramic has a strength 700MPa which is compatible with that of the Si3N4 ceramics made from conventional Si3N4 powders, AlN ceramic has a thermal conductivity of 170W/m(.)K at 25degreesC. We also propose a reaction mechanism for SHS of Si3N4 and compare it with that of the conventional nitridation of silicon. The dominate reaction in the combustion synthesis of Si3N4 is between Si vapor and N-2 on the surfaces of Si3N4 microcrystals which act as seeds. The whole combustion reaction process can be divided into the kinetic reaction stage and the diffusion-controlled reaction stage. That the newly formed Si3N4 does not adhere on the surfaces of silicon particles makes the SHS reaction rate fast than that of the conventional nitridation of silicon.