Study of the Substitution Process of Phosphate by Aluminate in the Hydroxyapatite Structure at Mechanochemical Synthesis and Annealing
M. V. CHAIKINA1, N. V. BULINA1, A. V. ISHCHENKO2,3, I. Yu. PROSANOV1
1Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
2Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia
3Novosibirsk State University, Novosibirsk, Russia
Keywords: механохимический синтез, алюминат-замещенный гидроксиапатит, mechanochemical synthesis, aluminate-substituted hydroxyapatite
Abstract
Samples of hydroxyapatite (HAP) were synthesized by the mechanochemical method with introducing into the reaction mixture from 0.1 to 1.5 mol of Al2O3 per 1 mol of HAP. The samples after mechanochemical synthesis and annealing were studied by X-ray phase (XPA) methods with the clarification of elementary cell parameters, crystallites size and calculation of phase concentration according to the Rietveld method, as well as by IR spectroscopy method and electron microscopy with energy-dispersive X-ray microanalysis. It was found that after mechanochemical synthesis, according to XPA data, single-phase nanocrystalline HAP without original and accompanying phases was formed. The cell parameters of mechanochemically synthesized HAP slightly change after the introduction of 0.1 mol of aluminum oxide, and then remain constant. After annealing of the samples, entering into the HAP structure to 0.5 mol of aluminium ions per 1.0 mol of HAP was found. Single-phase Al-substituted HAP was obtained when introducing into the reaction mixture up to 0.25 mol of aluminum oxide. When introducing 0.5 mol and more of HAP alongside with Al-substituted HAP, calcium aluminates of the composition of Ca3Al2O6 and Ca12Al14O33 are formed. It is not clear yet, in which form aluminum enters the HAP structure. The issue of the coordination environment of aluminate that enters the structure of Al-substituted HAP was considered. The octahedral environment of aluminum ions is characteristic for calcium aluminates; however, when substituting phosphate with other anions the cation of the complex anion usually has the tetrahedral environment. Based on data obtained by the IR spectroscopy method, it was suggested that with introducing aluminum oxide in the amount of 1.0 and 1.5 mol the appearance of absorption bands in the region of 745-900 cm-1 in IR spectra of the samples was conditioned by entering aluminate in the apatite structure as a group in the tetrahedral environment, as in Ca(AlO). Aluminium-substituted HAP can be of interest for coating medicinal corundum ceramic implants.
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