Combustion synthesis of AlN-SIC solid solutions

AlN-SiC solid solutions were successfully prepared by combustion synthesis from a mixture of Al, Si and C under high-pressure nitrogen. The reaction mechanism for combustion synthesis of AlN-SiC solid solutions is as follows: Al and Si melt at the front of combustion wave; carbon black is mixed into the molten mixture; Al reacts with nitrogen to form AlN; both liquid Si and silicon vapor (from evaporation of Si powder due to the high exothermic heat of the reactions, or from the decomposition of intermediate Si₃N₄) react with C to form SiC. Simultaneously, Si and C (or SiC) diffuse into the AlN crystal lattice directly to form an AlN-rich solid solution, and Al (or AlN) diffuses into the SiC crystal lattice directly to form a SiC-rich solid solution. The strengthening of the atomic bonding within the basal planes of the AlN-SiC solid solution, and a weakening of the bonds between the basal planes due to interdiffusion of AlN and SiC hinders the nucleation on the 0001 planes and promotes the growth of the 0001 planes, with the result that AlN-SiC solid solution tends to grow in the form of platelets. The combustion synthesised AlN-SiC solid solution spinodally decomposes into AlN-rich and SiC-rich domains during cooling. Both the AlN-rich and the SiC-rich domains share the same <0002> zone axis and their reciprocal planes perpendicular to the <0002> zone axis are rotated 30° clockwise around it.