On the Production and the Properties of “Perlite” from Shirasu

Abstract

Shirasu, which is widely distributed in Southern Kyushu, is mainly composed of the volcanic ash and the pumice. In order to utilize shirasu as the industrial materials, the Production of the Lightweight sand, i. e. perlite, was examined.Firstly, it was found out in the experiments using an electric furnace that shirasu (the particle size used was under 1.0mm) bloated at about 1000°C by the instantaneous heating, but it didn't bloat by the gradual heating from the room temperature to 1030°C.The effect of preheating for the bloating was very complex and changed with the particle size of shirasu and the preheating time and temperature.It was concluded from the following reasons that the main component of the bloating gas in shirasu would be water which was released over 100°C.1. The weight decrease curves of shirasu by the thermal balance were very analogous with those of the natural volcanic glass rock whose bloating gas was said to be consisted mainly of water.2. The weight decrease ratio by the thermal balance agreed well with the weight ratio of the water catched in absorbent.Shirasu enriched with volcanic glass which contained more water bloated better than shirasu enriched with crystals of feldspar, quarz and others.Nextly, the continuous production of shirasu perlite was performed with an experimental rotary kiln.Shirasu perlite A and B, which had open pores and closed pores respectively, could be produced arbitrarily by changing the heating speed.The methods were mainly divided into two of the instantaneous heating method and the heating method with a little preheating.The bulk densities and the coefficients of water absorption of these shirasu perlites elutriated by air were nearly equal with those of perlites which were sold on the market.These shirasu perlite-cement mortars showed low thermal conductivity.