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.