MODIFIED SILICON NITRIDE POWDER AND ITS PRODUCTION AND SILICON NITRIDE MIXTURE POWDER AND PRODUCTION OF SILICON NITRIDE SINTERED PRODUCT

摘要

PROBLEM TO BE SOLVED: To obtain modified silicon nitride powder improved in a sintering property and capable of giving a sintered product improved in a sintering density by subjecting silicon nitride powder to a hydrothermal treatment to form an amorphous silica glass phase. SOLUTION: Silicon nitride powder containing 0.5-10mol.% (based on a metal element) of at least one kind of compound selected from rare earth element compounds, alkaline earth element compounds and aluminum oxide is subjected to a hydrothermal treatment at 60-200 deg.C for several times to 100hr to produce the modified silicon nitride powder in which an amorphous silica glass phase is formed. The modified silicon nitride powder is mixed with a rare earth element oxide or a rare earth metal element compound capable of being calcined into the rare earth element oxide in an amount of 0.5-10mol.% based on the metal, molded and subsequently sintered at 1600-1900 deg.C in a non-oxidizing atmosphere at the atmospheric pressure to an elevated pressure to produce the silicon nitride sintered product free from a sintering auxiliary.