ESR study of 13C-enriched carbonated calciumapatites precipitated from aqueous solutions.

Abstract

The ESR spectrum of X-irradiated carbonated apatites precipitated from aqueous solutions was studied at carbonate contents ranging from approximately 5.4 up to 12.4 wt%. 12C- as well as 13C-enriched samples were prepared and examined with ESR after dying until constant weight at 25 degrees C and 400 degrees C. In these carbonated apatites, two CO3(3-) radicals were detected, one of which is derived from B-type carbonate situated at a phosphate lattice site. The other CO3(3-) most probably arises from CO3(2-) ions situated at OH- lattice sites. In contradistinction to the B-type contribution, the A-type contribution to the overall ESR signal decreases in absolute terms with increasing carbonate concentration. In addition, the line shape and the complete set of principal g-values of the A1-signal found in previous studies could be determined, corroborating the assignment of A1 to a surface O- ion.