A STUDY ON TALC GROUND BY TUMBLING AND PLANETARY BALL MILLS

The size reduction and structural changes of talc induced by dry grinding with tumbling and planetary ball mills were investigated by means of particle size analysis, SEM observation, X-ray diffraction and TG-DTA. Size reduction of talc samples was observed to predominate in grinding using a moderate energy type tumbling ball mill. The resultant fine particles of ground talc were found to agglomerate with increasing grinding time. A morphological change of talc from the original platy shape to agglomerated spherical particles was clearly observed, although X-ray diffraction results show no intensive structural change within 684 ks grinding. In the case of energy-intensive dry grinding using a planetary mill, the talc changed its structure from a crystalline to an amorphous state. This change resulted in a decrease in density and an increase in strength of a single particle. The radial distribution function analysis of ground talc samples suggests the environmental change of magnesium from a parent octahedral to a tetrahedral coordination with increasing grinding time. A low temperature dehydroxylation reaction and a new exothermic peak at 1120 K for the ground talc samples were also detected in TG-DTA analysis. The variation in thermal behavior suggests a change in the hydroxyl component in the structure of ground talc samples.