Effect of Mixed Grinding of Kaolinite-Gibbsite Mixture on Formation of Mullite

Abstract

Effect of mixed grinding of a kaolinite-gibbsite mixture on formation of mullite has been investigated by the X-ray diffraction method, DTA, SEM and surface area determination of powders. The both structures of individual specimen and their mixture are transformed easily into an amorphous state within about 60 minutes grinding by a planetary ball mill under dry condition. The amount of amorphous phase in the ground specimen increases with increasing grinding time. Accordingly, there has been a rapid decrease in the density of the mixture in the beginning of grinding and a leveling off with the progress of grinding. The specific surface area of the mixture increases sharply at the initial stage of grinding, then decreases gradually with an increase in grinding time, because of the coagulation. The mixed grinding has resulted in the formation of mullite directly from spinel phase without formation of corundum and cristobalite phases during sintering at more than 1223K. The ratio of formation of mullite has increased with an increase of grinding time and sintering temperature.