Fast synthesis of La-substituted apatite by the dry mechanochemical method and analysis of its structure

Abstract

Compared to pure apatite, La-substituted apatites have improved thermal, mechanical and biological characteristics. In this article, a fast synthesis of La-substituted apatites by a dry mechanochemical method is presented. Structural studies by X-ray diffraction and Fourier transform infrared spectroscopy indicated the formation of a single-phase nanosized product after 30min of high-energy ball milling of the reaction mixtures. The dry mechanochemical method is technologically attractive for the preparation of La-substituted apatites, as it allows reducing the processing time down to half an hour and does not require prolonged high-temperature annealing normally used in the synthesis practice of the substituted apatite. As the mechanochemically synthesized samples are nanosized, it is difficult to determine the details of their crystal structure by the Rietveld refinement method. Therefore, a series of the mechanochemically synthesized samples with different concentrations of lanthanum were annealed at 1000 оС for 5h. It was found that the annealed powders are microcrystalline La-substituted apatites Ca10−xLax(PO4)6Ox(OH)2−x, where 0 ≤ x ≤2. In their structure, the Ca2+ ions are replaced by the La3+ ions localized near the Ca2 sites, and the ОН– groups are replaced by the О2– ions in the hexagonal channels.