Effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate derived by chemical precipitation

This study focused on the effects of strontium substitution on the phase transformation and crystal structure of calcium phosphate. Chemical precipitation was used to prepare Sr-doped hydroxyapatite (HA) precursor powders. The phase transformation of the as-prepared samples during sintering was analyzed. The powders were characterized by X-ray diffraction, X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Quantitative analysis of the phase content and fine structure was performed by Rietveld refinement. Sr doping was found to facilitate the phase transformation from HA to beta-tricalcium phosphate (beta-TCP) at 1000 degrees C. The beta-TCP content increased with increasing Sr content, causing a decline in the ratio of HA to beta-TCP With Sr contents of <= 5 mol%, HA remained the major phase in the biphasic mixtures; in contrast, with Sr contents of >= 15 mol%, the mass fraction of beta-TCP exceeded 50%. The incorporation of Sr2+ into HA and beta-TCP caused the lattice parameters of both phases to increase. Additionally, Sr incorporation slightly enhanced the binding energy of Ca. The study confirmed that Sr doping could be used to modulate the phase fractions of HA and beta-TCP. The effective partial substitution of Sr in both HA and beta-TCP makes these materials promising for bone repair. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.