Synthesis of mullite powders by the geopolymer technique

Abstract

Geopolymer technique using alkaline silicate solutions as main source materials is preferrable for synthesing nm-sized silicate powders. Two kinds of sodiumu silicate were used in this study, Na20.SiO2 and Na20.2SiO2 solutions. Gel prepcipitates were obtained by dropwise of Al-nitrate solution. Caustic soda was used as pH regulation agent. Some gels obtained in alkaline region showed polymer character, when examined with MAS-NMR and DTA. The gels turned into crystalline after heating above 1000°C to form mulite and cristobalite. Chemical composition of a gel, for instance, showed 86% mullite and 13% crystobalite contents. Generally sodium contamination was less than 0.5 percent.