Phase transformation and thermal conductivity of hot-pressed p-Sic with A1203 and carbon additions were studied. Densification rate was a complex function of both A1203 and carbon. Simultaneous additions of A1203 and carbon accelerated the 3C +4Hphase transformation. Carbon additions lowered the thermal conductivity of the compact as did the high-temperature hot-pressing . The 3C +4H transformation and the thermal conductivity were deduced to be related to each other.ILICON CARBIDE is a promising material sas an engineering ceramic. Alumina is one of the important dopants for S i c because it is difficult to densify without an additive. The phase transformation of P-SiC doped with AI2O3 during sintering is very interesting because the properties of hot-pressed and of pressureless sintered Sic compacts are strongly dependent on the morphology of S i c grains formed during sintering.Early studies of 3C + 4H phase transformation of S i c doped with A1 or A1203 indicated that the stability of each polytype depends on both the hot-pressing temperature and the concentration of A1 or Al2O3.'.' It was shown by Boecker et al.that a-and p-Sic can be densified to near theoretical density with the addition of both A1 and ~a r b o n .~ But a closer examination of the effect of carbon on S i c polytypes has not yet been made.In the present work, the effect of both A1203 and carbon on the 3C-+4H phase transformation of the S i c compact was studied. The effect of carbon on the thermal conductivity was also studied. These effects were found to be related to each other.
ChemInform Abstract It is shown that addition of up to 2 wt.% Al2O3 has a strong effect on the densification of hot-pressed β-SiC. When the Al2O3 concentration is below 2 wt.%, carbon addition is also effective to improve densification. Simultaneous addition of Al2O3 and C accelerates the 3 C → 4 H phase transformation during hot-pressing (> 2 wt.% Al2O3). Carbon addition lowers the thermal conductivity of the compact. It is found that the 3 C → 4 H transformation and the thermal conductivity are related to each other.
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