Preparation of Ag-doped calcium phosphates

Ag-doped calcium phosphate (CaP) powders were prepared by a precipitation method to obtain antibacterial properties from aqueous solutions of calcium nitrate, silver nitrate, and ammonium phosphate. The atomic ratios of (Ca+Ag)/P and Ag/(Ca+Ag) were varied from 1.33 to 1.67 and from 0 to 0.10, respectively. The chemical compositions, phases, and morphologies of as-precipitated powders and sintered compacts were examined by ICP-AES, XRD, and TEM. The amount of Ag in the as-precipitated CaP powders was lower than the corresponding nominal value whereas the (Ca+Ag)/P ratios were enhanced. Only the hydroxyapatite (HA) phase was observed from as-precipitated powders under all investigated conditions. The shapes of HA particles changed from plate-like/needle-like to ellipsoidal with increasing Ag addition, and Ag nanoparticles were observed on HA particles. After sintering, tricalcium phosphate and HA phases were detected on the basis of an atomic ratio of (Ca+Ag)/P= 1.33, and further, the existence of HA, CaO, tetracalcium phosphate, and metallic Ag phases was inferred from the ratio (Ca+Ag)/P=1.67. Since the X-ray diffraction peaks of HA and tricalcium phosphate shifted upon Ag addition, this shift was taken as evidence of Ag doping in CaPs.