Impurities in silicon nitride raw materials and correlation with mechanical strength of the hot-pressed body.

Abstract

Spark-source mass spectrometry was used in order to determine the impurity elements from Li to La in nine commercial samples of Si3N4 raw materials. Total contents of thirty three impurity elements detected from Si3N4 raw powders which were prepared by a reaction of Si and N2 were 1.0 to 2.2wt%. Otherwhile there were few kinds of impurities in samples which were prepared by reactions of pure SiCl4-NH3 and SiO2-C-N2, and total impurity contents was 0.07-0.14%. Three-point bending strength at 1200°C for the hot-pressed body from α-rich powder with 2wt% Al2O3 and 5wt% Y2O3 was decreased with the total impurity contents. Similar correlations were observed between the 1200°C-strengths and respective contents of Ca, Ti or Fe. However the room temperature strength was independent on the total impurity contents. Hot-pressed bodies from β-, α≅β- and amorphous powder showed lower strengths than those expected from the correlation curve for α-rich powder.