Rice husks are a by-product of rice production. When rice husks are burned in an appropriate manner, rice husk ash, which is mainly composed of amorphous silica, is produced. Currently, rice husk ash is expected to be a biomass resource. In this study, we aimed to synthesize water glass using rice husk ash in a low-process and low-cost manner. A porous geopolymer was fabricated by mixing water glass and metakaolin and adding additives such as Si powder. In addition, we evaluated the thermal conductivity and other physical properties of porous materials with different alkali concentrations at room and high temperatures, assuming their use as heat insulating materials. It was found that water glass could be synthesized by simply mixing rice husk ash with a potassium hydroxide solution and allowing the mixture to stand at room temperature. When the porous geopolymer was fired at 800°C, shrinkage occurred, and the rate of shrinkage was greater for samples with higher alkali concentrations. Furthermore, it was found that the heat conduction at high temperatures was suppressed in the sample with a smaller alkali concentration. © 2024 Society of Materials Science Japan. All rights reserved.
