Synthesis and characterization of Ag-containing calcium phosphates with various Ca/P ratios

Ag-containing calcium phosphate (CaP) powders were synthesized by a precipitation method using aqueous solutions of calcium nitrate, silver nitrate, and ammonium phosphate. The powders were sintered at temperatures ranging from 1173 to 14731<. The charged atomic ratios of (Ca + Ag)/P and Ag/(Ca + Ag) in solution were varied from 133 to 1.67 and from 0 to 030, respectively. The Ag content in the as-precipitated CaP powders increased with the charged Ag/(Ca + Ag) atomic ratio in solution and was lower than the charged Ag/(Ca + Ag) value. The as-precipitated CaP powders consisted of hydroxyapatite (HA) as the main phase. Ag nanoparticles were observed on the as-precipitated HA particles under all conditions of Ag addition. After the sintering, HA,beta-TCP (tricalcium phosphate), alpha-TCP, and beta-CPP (calcium pyrophosphate) were mainly detected as CaPs on the basis of the Ca/P atomic ratio of the as-precipitated powders. The addition of Ag stabilized the beta-TCP phase, and the distribution of Ag in beta-TCP was homogeneous. A metallic Ag phase coexisted with HA. The solubility of Ag in HA was estimated to be 0.0019-0.0061 (Ag/(Ca + Ag)) atomic ratio, which was lower than that in beta-TCP (higher than 0.0536) and higher than that of beta-CPP (below the detection limit of analyses). (C) 2015 Elsevier B.V. All rights reserved.