Effects of different potassium salts on the formation of mullite as the only crystal phase in kaolinite

The phase transition in kaolinite from 1050 degrees C to 1600 degrees C without and with different potassium salts (KF, KNO3 and K2SO4) as mineralizers and the changes of the composition and morphologies of mullite formed in kaolinite have been investigated. The adding of enough potassium has been found to inhibit the formation of cristobalite in kaolinite. The fluorine is found to be beneficial to increase the reaction activity of aluminium from metakaolinite and so the potassium fluoride has promoted more pseudotetragonal mullite formed at 1100 degrees C than the other two mineralizers. The influence of potassium salts on the composition and microstructure of mullite formed from kaolinite with increasing the heating temperature has been scrutinized in detail. The formation condition for the only crystal phase of mullite from kaolinite has been shown. (C) 2009 Elsevier Ltd. All rights reserved.