| 摘要 |
PURPOSE:To improve the transverse rupture strength at ambient and high temperatures by controlling the content of Si3N4 component in grain boundaries to a prescribed ratio in a silicon nitride-based sintered compact composed of an Si3N4 crystal phase and a grain boundary phase containing a group IIIa element. CONSTITUTION:Mixed powder composed of a group IIIa element oxide (hereinafter referred to as RE2O3, e.g. Dy2O3) and SiO2 is mixed with <=30mol% Si3N4 and the resultant mixture is then melted at 1600-2000 deg.C to prepare Si3N4-RE2O3-SiO2-based glass, which is subsequently pulverized to afford a sintering assistant. The obtained sintering assistant is then added to raw material powder of Si3N4 (e.g. alpha type Si3N4) having about 14 m<2>/g specific surface area and 1-2wt.% oxygen content so as to afford 1-5mol% RE2O3 content and 1-20mol% Si02 content expressed in terms of oxides at 0.7-9 molar ratio of SiO2/RE2O3 in the composition after sintering. After mixing, drying and granulating are then carried out and the obtained granulated mixture is formed to remove the binder in a vacuum. The prepared mixture is then sintered at 1600-2000 deg.C in a nitrogen-containing nonoxidizing atmosphere to provide the subject sintered compact having >=700 MPa transverse rupture strength at ambient temperature and >=500 MPa transverse rupture strength at 1400 deg.C. |
