Preparation and Evaluation of Inorganic Porous Material from Rice Husk Ash

Abstract

Rice husks are a by-product of rice production, and 2 million tons are emitted annually in Japan. However, its use is limited to low value-added methods, and effective utilization methods are not sufficiently studied. On the other hand, gramineous plants are silicic acid-accumulating plants that have the characteristic of selectively absorbing silica in soil and storing it in the body. Therefore, about 20% of the composition of rice husks is composed of silica. Since the rice husk ash obtained by burning the organic component of the rice husk contains a large amount of silica, it is expected to be used as a Si source. In this study, we succeeded in producing a cured product by a geopolymer reaction by synthesizing an alkaline aqueous solution of silicate using rice husk ash as raw material and adding metakaolin to it. In addition, a geopolymer porous body was obtained by adding Si powder as a foaming agent and introducing pores by hydrogen foaming reaction into the cured body. Furthermore, it was clarified that by adding a surfactant as a bubble stabilizer in addition to Si powder, defoaming of generated hydrogen bubbles can be suppressed and pores can be made fine and uniform. As a result of measuring the heat insulating performance of the geopolymer porous body, it was possible to introduce a large number of pores of 0.5 to 1, 5 to 100 µm by adjusting the amount of Si powder and surfactant added. Furthermore, it was clarified that the porous body with many fine pores shows better heat insulation performance.