Effects of kaolinite layer expansion and impurities on the solid-state reaction of kaolinite.

Expanded kaolinite without impurities was found to serve as a suitable raw material for the rapid formation of metastable CaAl 2 Si 2 O 8 with the suppression of byproduct formation. This was accomplished based on the solid-state reaction of the kaolinite with calcium carbonate promoted by mechanical grinding.