Solid-state reactions in the system TALC-CaCO 3 doped with Ni(II) at high temperatures

Abstract

The system talc- xCaCO 3-0.2NiCl 2 · 6H 2O in the molar ratio 1 : x: 0.2 ( x =1, 2, 3 and 4) was studied at two different temperatures, viz., 1000 and 1200 ° C. The quenched, coloured reaction products at room temperature were identified using X-ray diffraction and absorption spectrum techniques. X-ray results revealed that the main constituent or constituents of the reaction products obtained after firing at 1000 ° C were (I) enstatite-diopside at x = 1, (II) enstatite-diopside and monticellite at x = 2 and (III) monticellite and akermanite at x = 3 and 4. At 1200 ° C the main phases identified at x = 1 and 4 were the same as in case of firing at 1000 ° C, whereas the phases enstatite-diopside and akermanite at x = 2 and akermanite at x = 3 were characterized. On the other hand, absorption spectra of the resulting Ni 2+-containing silicate phases after the firing process at the two working temperatures showed characteristic absorption bands of tetrahedrally as well as octahedrally coordinated Ni 2+, in confirmation with the formation of akermanite and enstatite-diopside, monticellite, which offer tetrahedral and octahedral lattice positions for Ni 2+, respectively. Generally, it was observed that the concentration of some resulting Ni 2+-containing phases increased or decreased with increasing firing temperature, depending on the formation tendency of other silicate phases at varying x.