Interdiffusion in SiC-AlN and AlN-Al2OC systems

AlN, Al2OC, and the 2H form of SiC are isostructural, Both SiC-AlN and AlN-Al2OC form homogeneous solid solutions above 2000 degrees and 1950 degrees C, respectively, The kinetics of phase separation in the two systems, however, are quite different, Interdiffusion in both SiC-AlN and AlN-Al2OC systems was examined in the solid-solution regime in an attempt to elucidate differences in the kinetics of phase separation that occur in the two systems when annealed at lower temperatures, Diffusion couples of (SiC)(0.3)(AlN)(0.7)/(SiC)(0.7)(AlN)(0.3) and (AlN)(0.7)(Al2OC)(0.3)/(AlN)(0.3)(Al2OC)(0.7) were fabricated by hot pressing and were annealed at high temperatures by encapsulating them in sealed SiC crucibles to suppress loss due to evaporation, Interdiffusion coefficients in (SiC)(0.3)(AlN)(0.7)/(SiC)(0.7)(AlN)(0.3)/ diffusion couples were measured at 2373, 2473, and 2573 K, and the corresponding activation energy was determined to be 632 kJ/mol, (AlN)(0.7)(Al2OC)(0.3)/(AlN)(0.3)(Al2OC)(0.7) samples were annealed at 2273 K, The interdiffusion coefficient measured in the AlN-Al2OC system was much larger than that in the SiC-AlN system.