Solid-state reactions of talc towards Co(II) at high temperatures

Abstract

Solid-state reactions in talc and talc- x COCl 2·6 H 2O systems (mole ratio 1: x, where x = 0.1, 0.2, 0.4, 0.6, 0.8 and 1.0) were carried out at two different temperatures, viz. 1000 and 1200°C. X-Ray diffraction and ligand-field absorption spectrum methods were applied to characterize the phases in the reaction products after rapid cooling to room temperature. DTA of talc was also carried out and showed an endothermic peak at 960°C (dehydration process) and a broad exothermic band between 1070 and ∼1300°C. The results of X-ray diffraction showed, generally, the presence of the three known proto, ortho and clinoenstatite forms in reaction products, together with the appearance of cristoballite SiO 2 at 1200°C. Moreover, the formation of Co 2SiO 4 was detected at higher concentrations of Co 2+. The spectra indicated, on the other hand, that the absorption bands within the system talc-Co(II) were characteristic of an octahedrally coordinated Co 2+ in different enstatite modifications, in confirmation with X-ray data. In general, it was observed that the concentration of phases whose formation was favoured at high temperature increased on increasing the firing temperature, whereas the degree of crystallinity appeared to decrease with increase of the Co concentration.