A fine powder SiC was formed into SiC specimens of 5×5×30mm under 1500 kgf/cm2
and heated at temperatures from 1000 to 1500°C in air. At the heat treatment temperature (HTT) 1100°C, it was found that the weight of SiC specimens increased to a maximum but the density decreased to a minimum because of oxidation reaction occurred during heating. The SiC specimens heat-treated at 1300°C showed a bending strength of 200 MPa at density of 2.05 g/cm
3. This high strength was caused by the development of a thin SiO
2 phase formed by the oxidation of the surface of SiC specimens.
By the use of X-ray diffraction measurement, it was seen that SiO
2 in the oxidationphase was amorphous below HTT 1300°C and gradually crystallized with increasing HTT. Above HTT 1500°C, the oxidation phase came off from inside of SiC specimens accompanying self disintegration caused by the structural difference between surface and inside of SiC specimens.
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