engleski

An EPR study of Cd2+ incorporation in vaterite

13C-vaterite, the unstable calcium carbonate polymorph, doped with Cd2+ was g-irradiated and the stable paramagnetic centres were studied using electron paramagnetic resonance (EPR) spectroscopy. The 13C isotope has nuclear spin (I = 1/2) and as a consequence the hyperfine interaction with the unpaired electron occurs. This revealed all paramagnetic centres of carbonate origin, i.e. ˙CO3- and ˙CO2- free radicals. Two paramagnetic centres induced by cadmium doped to vaterite, one characterized by ga = 1.9939 and the other by gb = 1.9886, were not split by the 13C-hyperfine splitting. Therefore, these paramagnetic centres are most probably due to CdO-. The locations of these paramagnetic centres in vaterite are determined and the role of cadmium in the formation of calcite crystals in the vaterite-precipitating system is discussed.

calcium carbonate; vaterite; electron paramagnetic resonance (EPR) spectroscopy; cadmium

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