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.

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The removal of unexpanded materials from a commercial perlite product was studied using an air table. The air table has shaking motion similar to that of a wet table and a blast of air is driven through a perforated deck. The sample used was the perlite product containing 20% of unexpanded materials. The unexpanded materials and expanded perlites were almost the same in size and shape, however the density of unexpanded materials was slightly greater than that of expanded perlites. The authors tried to separate unexpanded materials on the basis of density difference using the air table. Several experiments were carried out to clarify the effect of frequency, slope angles of perforated deck and air flow on separation efficiency. The results indicated that the end slope angle of deck exerted a great influence on the removal of unexpanded materials.

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