Nano-crystallinite hydroxyapatite synthesized by neutralization with the assist of citric acid

Abstract Bioactive hydroxyapatite (HA) powders with nano-crystallinity were prepared by an economic way, i.e. the neutralized route, during which a supersaturated suspension of lime chelated with citric acid was titrated by orthophosphoric acid diluted with deionized water or ethanol. The crystal behaviors of HA powders were characterized by X-ray diffraction and Fourier transform infrared spectra. It was found that uncalcined powders were amorphous calcium phosphate, while the crystallinity increased significantly after calcined at 800 °C and their crystal sizes synthesized with aqueous and ethanol solutions were determined as 54.8 and 85.4 nm, respectively. The inhibition of crystal growth was attributed to the chelating reagent, resulting in the B-substituting CO32− ions to PO43− groups and causing a-axis shortened and c-axis lengthened in the crystal cell.