Adsorption Of Carbonate-Derived Molecules On The Surface Of Carbonate-Containing Apatites

Carbonated apatites synthesized at low temperatures were dried until constant weight at 25-degrees-C. Two 99% C-13-enriched samples were examined with EPR after X-irradiation. The observed spectra are interpreted in terms of five paramagnetic radicals, i.e. on O-, two CO3- and two CO2-radicals. As a result of the C-13 hyperfine coupling, practically no signals were found in the region around g = 2, where EPR signals originating from C-12-containing radicals (commonly called C-12 signals) are to be expected. Afterwards, the apatite powders were spread out in order to ensure a good contact of the apatite surface with the surrounding atmosphere. The samples were again X-irradiated and re-examined with EPR. Strong C-12 signals were detected and attributed to surface radicals. Two different paramagnetic species were tentatively identified as CO2- and CO- radicals adsorbed on the apatite surface. The g values for these radicals are g1 = 2.0030, g2 = 2.0015, g3 = 1.9973 for the CO2- radical and g1 = 2.0058, g2 = 2.0041, g3 = 2.0023 for the assumed CO- radical.