| 摘要 |
PURPOSE:To obtain a calcined compact, having a crystalline structure and grain boundaries consisting of an amorphous substance and excellent in stability, high-temperature strength and oxidation resistance by calcining a mixture of Si3N4 with a rare earth element oxide of a specific composition prepared by excessively adding SiO2 thereto at a low temperature and quenching the calcined mixture. CONSTITUTION:The above-mentioned calcined Si3N4 compact is a calcined compact of a composition system consisting of 77-90mol% Si3N4, 0.1-5mol% rare earth element oxide and <=25mol% excess oxygen at >2 to <=25 molar ratio of excess oxygen/rare earth oxide. The average grain diameter of the Si3N4 crystals is <=7mu and the grain boundary phase thereof is an amorphous substance composed of Si, rare earth element, O and N. The aforementioned calcined compact is produced by providing a gas-impermeable sealing on the surface of the compact consisting of the above-mentioned composition, calcining the compact at 1450-1800 deg.C in a high-pressure gas and then cooling the calcined compact at >=1000 deg.C/hr rate. |
