T.G. Kalinichenko, N.N. Bagmut, A.B. Brik, V.V. Radchuk. Electron Paramagnetic Resonance of Magnesium-Containing Hydroxylapatite

UDC 549.903 : 539.219.3
T.G. Kalinichenko 1, N.N. Bagmut 1, A.B. Brik 1, V.V. Radchuk 2
1 M.P. Semenenko Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine
34, Acad. Palladin Ave., 03142, Kyiv, Ukraine
E-mail: t_kalinichenko@yahoo.com
2 Institute of Telecommunications and Global Information Space of the NAS of Ukraine
13, Chokolovsky Blvd., 03186, Kyiv, Ukraine
Е-mail: valentyn.radchuk@gmail.com
Language: Russian
Mineralogical journal 2018, 40 (4): 45-52
Electron Paramagnetic Resonance of Magnesium-Containing Hydroxylapatite
Abstract: In the structure of apatite, both isovalent and heterovalent substitutions in cationic and anionic positions are possible. With such substitutions in the structure of apatite, local changes in symmetry occur and pre-center situations are created that contribute to the formation of different paramagnetic centers. The properties of these centers depend on the number of isomorphous and non-isomorphous substitutions, as well as on the temperature processing of synthesized materials, which significantly affects the stability and properties of synthesized samples. Information on paramagnetic centers and features of the structure of hydroxylapatite (HAp) is important for the synthesis of apatite bioceramics, the manufacture of implants based on synthetic HAp, as well as to solve the problems of retrospective dosimetry. The powdery HAp samples, in which calcium ions are replaced by magnesium ions in different concentrations, were studied by the electron paramagnetic resonance (EPR) method. Several years ago the HAp samples were synthesized and stabilized at 600 and 900 °C. The paramagnetic centers of NO32- are observed in the HAp samples which were heated at. 600 °C. These paramagnetic NO32- centers are converted to NO42- centers with increasing of the concentration of magnesium. The EPR spectra’s from the HAp samples, that were heated at 900 °С, are represented by PO32- and CO33- centers. The intensity of the EPR signals of these centers increases with increasing magnesium concentration in the samples, as well as their relaxation time. A remark was made on the mistaken attribution of some authors of the doublet EPR signal in phosphates with the splitting 50.1 mT to atomic hydrogen at room temperature. It was shown that in annealed synthetic HAp the doublet EPR signal with the splitting 50.1 mT and the effective factor of spectroscopic splitting geff = 2.016, is due to the paramagnetic PO32- center. It was shown that in synthetic HAp, magnesium, which isomorphous replaces calcium in the structure of apatite, significantly affects to the formation of paramagnetic centers, as well as to the radio spectroscopic parameters of these centers. In this case, the type and number of paramagnetic centers, as well as the relaxation characteristics of these centers, essentially depend on the features of thermal stabilization HAp.
Keywords: electron paramagnetic resonance, magnesium hydroxylapatite, paramagnetic centers.

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