PHYSICOCHEMICAL AND THERMAL-PROPERTIES OF MECHANOCHEMICALLY ACTIVATED TALC

The progressive physicochemical and textural changes undergone by talc when submitted to mechanochemical treatment in a planetary mill are described. Crystallinity loss is observed together with particle agglomeration, while specific surface area increases in the early stages . of the treatment, diminishing afterwards. The distortion of the basal planes of the crystal structure is greater than that of the planes nonparallel to the (001) ones. Differential thermal analysis reveals the formation of a noncrystalline metastable phase which exothermically crystallizes to enstatite at 830-degrees-C; at the same time, the endothermic effect at 1060-degrees-C, corresponding to the decomposition of talc into enstatite and SiO2, disappears. The formation of enstatite at 830-degrees-C from noncrystalline precursors is also observed by thermal treatment of a stoichiometric mixture Mg(OH)2 - SiO2 gel.