Effects of Adding Fluid Boron Aids in the Normal Sintering of Alpha-SiC

The effect of boron dispersion on the sintering of SiC was studied by comparing the addition of soluble compounds (B2O3, B10H12C2 and NaBF4) in fluid form with that of amorphous boron powder. A large part of the boron in the fluid additions disappeared below 1550°C. The residual amount of boron was nearly constant up to the sintering temperature (2050°C). The density values for the residual boron contents were identical with that for powder boron addition. NaBF4 gave the low mechanical strength, because of the remaining sodium till high temperature. However, in B2O3 or B10H12C2, the mechanical strength was higher than 55kg/mm2 (room temperature strength for boron powder addition). B10H12C2 addition resulted in high strength (max. 82kg/mm2, mean 68kg/mm2, min 44kg/mm2: density 3.16g/cm3), even for a small amount of boron content (0.11wt%). The weak strength (40-50kg/mm2) was attributed to the large pore defects (0.05-0.2mm) which were considered to be formed in the initial stage of sintering by the rearrangement of SiC particles. In fluid addition, it may be assumed that the homogeneity of boron dispersion was improved, resulting in the suppressed particle rearrangement.