Low-temperature Hydrothermal Reaction of Mullite in Sodium Hydroxide Solutions

Keqin LI*, Kaoru IGARASHI and Tadao SHIMIZU

Department of Industrial Chemistry, Chiba Institute of Technology; 2-17-1 Tsudanuma, Narashino-shi 275-0016 Japan

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·Al2O3·1.68SiO2·1.8H2O and Na14Al12Si13O51·6H2O in spherical grains. Successively, a small amount of Na3Al3Si3O12·2H2O was observed at the final stage. The ratio of Al2O3/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.

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