| 摘要 |
PURPOSE:To obtain the subject sintered silicon nitride at a low temperature in a short time by adding a specific amount of an iron component to the raw material powder to promote the growth of beta-prismatic crystal grains. CONSTITUTION:The objective sintered silicon nitride is composed of beta-Si3N4 prismatic crystals having an average minor axis diameter of 6-20mum averaged on five large-diameter prismatic crystals appearing on a cross-sectional area of 7,000mum<2>, has an iron content of 100ppm to 10,000ppm and a fracture toughness of >=8MPa.m<1/2>. The sintered material can be produced by using a powdery silicon nitride such as trisilicon tetranitride as a raw material preferably having high alpha-ratio and purity. The raw material is incorporated with pure iron powder, iron alloy powder, etc., in an amount to attain an iron concentration of 100-10,000ppm, the components are uniformly mixed and the obtained powdery mixture is formed and sintered in an atmosphere containing nitrogen. The alpha-type Si3N4 is dissolved in a sintering assistant in the course of heating in the sintering process and deposited in the form of a beta-prismatic crystal. The beta-prismatic crystal having a minor axis diameter falling within the above range is formed by controlling the deposition condition. |
