THERMAL-CONDUCTIVITY IN HOT-PRESSED SILICON-CARBIDE

Silicon carbide ceramics with equiaxed grain structure were obtained b y hot-pressing at 2000 degrees C in a vacuum with the aid of sufficien t amounts of Al2O3 and Y2O3 as sintering additives. The thermal conduc tivity of the SiC ceramics was investigated using a laser-flash techni que and a pure polycrystalline 6H-SiC prepared by Lely's method for bu lk crystal growth for comparison purposes. Experimental results reveal ed that the thermal conductivity of the SiC ceramics, consisting prima rily of 6H, 4H and 3C polytypes with various concentrations, appeared to exhibit a strong dependence upon the content as well as the polytyp e of the SiC at lower temperatures, the dependence, however, became le ss pronounced at elevated temperatures. Solid-solution and inhomogenei ty are assumed to play an important role in further reducing phonon me an free path of the ceramics. A considerable deviation in thermal resi stivity between the SiC ceramics and the pure 6H-SiC was observed. A d ifference in the temperature dependence of phonon mean free path compa red with the theoretical expectation was discussed. (C) 1996 Elsevier Science Limited and Techna S.r.l.