The reaction of stoichiometric hydroxyapatite (HAp) with different crystallinity in Mg 2+ aqueous solution was investigated using X-ray absorption near edge structure (XANES). Crystallinity is one of important factors for the properties of HAp. Therefore, this study aimed to clarify the effect of crystallinity on the behavior of HAp in aqueous solutions. Stoichiometric HAp samples with different crystallinities were prepared using an aqueous solution precipitation method and subsequent calcination. The Mg-K XANES spectra of the HAp pellets after immersing in Mg(NO 3 ) 2 aqueous solution were classified into two groups: those of Mg-doped HAp and Mg(OH) 2 . This difference is caused by the solubility of the HAp pellets in water, owing to their crystallinity. This result provides insights into the reaction mechanism of HAp in the human body and facilitates selection of suitable biomaterials.
Stoichiometric hydroxyapatite (HAp) nanoparticles were prepared by the solution-precipitation method at 37 °C. During the 72-h maturation period, the Ca/P molar ratio first rapidly increased to >1.6, and then reached 1.67 relatively slowly. The crystallite sizes of the stoichiometric HAp nanoparticles were estimated to be 11.0(3) and 25.7(3) nm from 300 and 002 diffractions, respectively. The crystallite size in the [001] direction continued to increase after the 72-h maturation period at a constant Ca/P molar ratio of 1.67. The obtained stoichiometric HAp nanoparticles also exhibited higher thermal stability than commercially available HAP-100 and prevented grain growth during sintering. This material is suitable for use in various sintering methods.
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