Si3N4-MgO-Al2O3セラミックスの諸性質に及ぼす焼純処理の影響

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The effects of annealing in N2 gas of 0.1 MPa at 1173-1673K on microstructures and room temperature transverse-rupture strength were investigated for Si3N4-10 mold%MgO-5.5 mol%Al2O3 ceramics which was cooled at the rate of 0.25-1Ks-1 after sintering in N2 gass of 0.1 MPa at 1973 K and was mainly composed of a-, β-Si3N4, MgAl2O4, Mg2SiO4 and glass phases. It was confirmed by the X-ray diffraction method that the glass phase became crystalline above about 1200 K in the case of isochronal annealing for 10.8 Ks; the MgSiO3 enstatite appeared by the annealing at about 1200-1500 K and the amount of MgAl2O4 spinet increased above about 1450 K. The appearance of MgSiO3 caused a sharp decrease in the strength of ceramics, while the increase in the amount of MgAl2O4 gave a little effect on the strength.
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