Synthesis, structural analysis and fabrication of coatings of the Cu2+ and Sr2+ co-substitutions in β-Ca3(PO4)2

Abstract

The combined substitutions of Sr2+ and Cu2+ in β-tricalcium phosphate [β-TCP, β-Ca3(PO4)2] have been achieved using an aqueous precipitation technique. Four different concentrations of either single or combined substitution of Sr2+ and Cu2+ in β-Ca3(PO4)2 have been investigated and the results were compared with those of pure β-Ca3(PO4)2 without any substituted ions of Cu2+ and Sr2+. Heat treatment at 1000 °C led to the formation of well crystalline β-Ca3(PO4)2 as well as Sr2+ and Cu2+ co-substituted β-Ca3(PO4)2. The Rietveld refinement technique using GSAS-EXPUGI was employed to generate complete structural information on the effect of Sr2+ and Cu2+ substitutions in the structure of β-Ca3(PO4)2. Substitution of Sr2+ and Cu2+ in β-Ca3(PO4)2 resulted in the formation of a well crystalline rhombohedral structure with a hexagonal setting (space group R3c). The Rietveld refinement results revealed a gradual decrease in the a-axis and c-axis lattice parameters with increasing concentration levels of Cu2+ and Sr2+ co-substitutions in the lattice of β-Ca3(PO4)2. Cu2+ prefers to occupy the sixfold coordinated Ca (5) site, whereas Sr2+ preferentially occupies the ninefold coordinated Ca (4) site of the β-Ca3(PO4)2 structure. The electrophoretic deposition (EPD) technique was employed to generate Sr2+ and Cu2+ co-substituted β-Ca3(PO4)2 coatings on a titanium alloy. A uniform deposition of β-Ca3(PO4)2 on a titanium alloy was generated using the EPD technique, and heat treatment up to 1000 °C has resulted in no phase changes in the coating being observed, which has also been confirmed by the Rietveld refinement technique.