Si_3N_4-SiC-Y_2O_3 複合材料の1000℃近傍における異常酸化

概要

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A composite with the composition of 58 mass%Si_3N_4-32 mass%SiC-10 mass%Y_2O_3 was oxidized at 900-1400℃ in dry and moist air atmospheres. The weight gain rate at 1400℃ in dry air was as low as 0.5 mg/cm^2 for 100h, revealing that the composite is highly oxidation-resistant. The weight gain in moist air was 3-7 times larger than that in dry air at all the temperatures tested. The weight gain at 1000℃ in moist air was almost the same as that at 1400℃ in moist air. The mechanism of the abnormal oxidation at 1000℃ is not the same but similar to that reported by Lange et air. At 1000℃, a protective SiO_2 layer which retards the diffusion of oxygen into the composite was not formed and the SiC fine particles in the grain boundary region of the composite were oxidized. It was assumed that the volume expansion of about 30% accompanying the conversion of SiC into SiO_2 generated cracks in the grain boundary region through which oxygen can penetrate toward the unoxidized composite. Four Si_3N_4-SiC composites with different compositions also showed large weight gain at 1000℃ in moist air. These results indicate that special care should be taken in handling Si_3N_4-SiC composite in moist atmospheres at high temperatures.
社団法人日本セラミックス協会の論文
1997-01-01