SYNTHESIS OF ALN-SIC COMPOSITES AND SOLID-SOLUTIONS BY FIELD-ACTIVATED SELF-PROPAGATING COMBUSTION

The synthesis of AlN-SiC composites and solid solutions was achieved t hrough the imposition of an electric field in self-propagating high-te mperature reactions. Despite its highly exothermic nature, the reactio n Si3N4 + 4 Al + 3C = 4 AlN + 3 SiC is not self-sustaining without the imposition of a threshold field (E) of 8 V cm(-1). At higher fields, the nature of the product depended on the value of the field. At E = 8 and 16.5 V cm(-1), the product is a composite of AlN-rich and SiC-ric h phases. The extent of solubility of each phase into the other increa sed with increasing field. When E = 25.0 V cm(-1), the product is a so lid solution with the 2H structure. The degree of randomness of the so lution increased with a further increase in the value of the imposed f ield. Compositional analyses of the product phases are in reasonable a greement with the reported tentative phase diagram for AlN and SiC. Th e work demonstrates the use of an electric field as a processing param eter in self-sustaining combustion synthesis of nitride composites and solid solutions. (C) 1997 Elsevier Science Limited.