Development of porous lightweight heat-insulators using gypsum

Abstract

Besides natural gypsum, byproduct gypsum is always discharged from the desulfurization process in power plants and the neutralization process in chemical industry. In this study, a porous lightweight material was studied in order to develop a fundamental technology for recycling byproduct gypsum. First of all, several kinds of byproduct gypsums were converted to hemihydrate type gypsums by heating at 150 °C overnight, and their bending strengths were tested. Then, as next step, using one of the hemihydrates, porous materials were prepared at ambient temperature by the aid of an organic foaming agent and water. Two types of lightweight materials were obtained through adjusting the amounts of water and the forming agent. One is ordinary porous monolith having 96–183 kg/m³ of bulk density and 0.043–0.069 W/m K of thermal conductivity. Another is granule, of which bulk density was 69–137 kg/m³ and thermal conductivity was 0.047–0.050 W/m K. Hence, it is concluded that even using byproduct gypsum, high-performance porous heat-insulators could be produced, if the counterpart nonporous monolith has over 3 MPa of bending strength.