Low-temperature Hydrothermal Reaction of Mullite in Sodium Hydroxide Solutions

Abstract

Hydrous sodium aluminosilicate was formed when mullite powder of high purity prepared by alkoxide method was hydrothermally treated with sodium hydroxide aqueous solution. The hydrous sodium aluminosilicates were mainly composed of 1.08Na₂O Al₂O₂.1.68SiO₂.1.8H₂O and Na₁₄Al₁₂Si₁₃O₅₁.6H₂O in spherical grains. Successively, a small amount of Na₃Al₃Si₃O₁₂.2H₂O was obser ved at the final stage. The ratio of Al₂O₂/SiO₂ in the mullite had an influence on the kind of products besides treatment temperature and time. ICP (Induced coupling plasma) analyses indicated that more Al in the mullite was dissolved into the solution than Si. At the beginning of reaction, boemite was precipitated. The SiO₂ rich mullite was positively formed Na₆Al₆Si₁₀O₃₂.12H₂O instead of boemite.