Abstract
The economical production method of sintered body of nitride by using the volcanic ejecta "Shirasu" of particle size -5 mm was investigated. At first, two kinds of forming processes of the raw sample for getting the Shirasunitride powder were compared as follows: conventional disc-type sample by press-molding (A-process) and balltype sample by pelletizing (B-process). Furthermore, two kinds of nitride powders obtained by A and B-process were formed into disc-shape by press-molding and heat-treated to get sintered body of nitride. And the effect of forming process of A and B on the characteristics of the products were investigated. And following results were obtained.
1) In the case of conventional A-process, the difference of nitride substance between surface layer and inner part of the disc-type sample was observed. Much more β-Si3N4 was recognized in the inner part untill at 50: 50 mixing ratio of Shirasu and Al, however, in the surface layer at 40: 60 ratio.
2) In the case of B-process, nitriding reaction occurred uniformly from surface to inner part. Comparing to Aprocess, β-Si3N4 was increased but α-Al2O3 and 15R-A1N were decreased in B-process.
3) Sintered body made from nitride powder obtained by B-process shows the miximaum amount of β-Si3N4 at 1700°C, and the decreasing tendency of α-Al2O3 by higher temperature. Especially, about 10 times amount of 15-AIN comparing to the sintered body made from raw powder of A-process was generated at 50 : 50 ratio.
4) According to the characteristics of sintered bodys, it was clarified that, comparing to the raw material obtained by A-process, the raw material obtained by B-process gives the sintered body of nitoride with the 10 wt% less addition of Al as raw material, and by heat treatment at lower temperature and in shorter keeping time.
