Patent ID: 6187706
Filing Date: 2001-02-13
Classification: C04B

Abstract:
A method of producing a silicon nitride sintered body by molding a starting material comprising sintering additives and a silicon nitride powder to form a molded article and subjecting the molded article to a primary sintering and a secondary sintering in a nitrogen atmosphere, wherein the primary sintering and the secondary sintering are carried out under the following conditions:a first temperature of said primary sintering being higher than a grain boundary temperature that a grain boundary phase is crystallized for said starting material and not more than 100.degree. C. higher than said grain boundary temperature;said primary sintering being up to 6 hours longer than a point in time at which a contraction has started as a dense .beta. silicon nitride is formed during said primary sintering;said primary sintering being at a pressure of 0.1 kgf/.cm.sup.2.about.3.0 kgf/cm.sup.2 ;a second temperature of said secondary sintering being higher than said grain boundary temperature at which the grain boundary phase is crystallized but lower than said first temperature of primary sintering for promoting the crystallinity of the grain boundary phase and preventing abnormal grain growth; andsaid secondary sintering being at a pressure of 100 kgf/cm.sup.2.about.2000 kgf/cm.sup.2 ;wherein said grain boundary temperature at which the grain boundary phase is crystallized is determined by selecting a temperature at which a crystallinity of said grain boundary phase is the highest among a plurality of molded articles prepared from the starting material and sintered at different temperatures; and said contraction starting point time as said dense .beta. silicon nitride is formed is determined from the relation between a progress time and a contraction ratio at the time of being heated at said primary sintering first temperature.