| 摘要 |
PURPOSE:To obtain a calcined compact having both a high strength at high temperatures and a high density without using steps for reheating treatment, etc., by adding specified amounts of a rare earth element, Mg and Zr to Si3N4, further adding a specific amount of SiC, forming the resultant mixture and calcining the formed compact. CONSTITUTION:A powder blend is prepared by adding compounds of a rare earth element, Mg and Zr in respective total amounts of 15-2 pts.wt., 15-0.5 pt.wt. and 13-0.5 pts.wt. expressed in terms of oxide weights and 0.3-5 pts.wt. SiC to 100 pts.wt. Si3N4 raw material powder. A forming assistant is then added thereto and the resultant mixture is mixed, formed and calcined. Thereby, the SiC is further added to the system containing the rare earth element, Mg and Zr mixed with Si3N4 and capable of readily crystallizing a grain boundary glass phase to remarkably increase the above-mentioned crystallization rate and crystallization of the complete grain boundary glass phase can be attained. If the amount of the added SiC is less than 0.3 pt.wt., part or all of the calcined compact is normally still in a noncrystallized state in a furnace. If the amount exceeds 5 pts.wt., deterioration in strength at ambient temperature is remarkable. |
