低酸素濃度雰囲気で加熱されたSiCセラミックスの酸化挙動に及ぼす既成シリカ保護膜の影響

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  • Effect of Preformed Silica Protective Film on Oxidation Behavior of SiC Ceramics during Soaking in Oxygen-Deficient Atmosphere
  • Effect of Preformed Silica Protective F

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Effect of preformed silica protective film on the oxidation behavior of porous SiC ceramics at 1700K in Ar-O2 atmosphere with PO<sub>2</sub> in the active oxidation range was investigated and following results were obtained.<br>(1) when the inner pore surface of the ceramics was incompletely covered by the silica layer, CO evolution rate exhibited a peak indicative of the occurrence of the active oxidation soon after the dropping operation for PO<sub>2</sub> from 2 or 10kPa to 0.02kPa. This active oxidation accompanied the silica reduction.<br>(2) The sample oxidized for 10h at PO<sub>2</sub>=10kPa showed no peaking in the CO evolution rate after the PO<sub>2</sub> dropping operation. Thickness of the silica layer of this oxidized sample was about 0.2μm. This sample showed no weight change during the successive soaking for 10h at PO<sub>2</sub>=0.02kPa.<br>(3) As the scheme without the weight change during the soaking in the oxygen-deficient atmosphere, the following reaction was assumed, SiC+4/3O2→2/3SiO2+1/3SiO(g)+CO<br>This reaction forcing the volume increase in the reacting zone, was assumed to contribute to the preservation of the silica protective film.<br>(4) It was pointed out that, in the case of the well-passivated SiC ceramics, at least minor correction should be done in Gulbransen's theory which is known to be valid for the fresh ceramics.

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