Zinc additions in calcium phosphate system. Phase behavior, microstructural and mechanical compatibility during sequential heat treatments

Abstract

The study investigates the structural and mechanical stability of the calcium phosphate - ZnO composites during sequential heat treatments. The composites were synthesized through a solution based co-precipitation technique by varying the precursor concentrations. The characterization results infer the Zn2+ insertion in calcium phosphate and moreover the isostructural phase of β-Ca3(PO4)2 → Ca19Zn2(PO4)14 is preserved until 1300 ℃. The upsurge in Zn2+ concentration ensure the presence of apatite trace at 1300 ℃. Zn2+ inclusion tends to the alter the calcium phosphate structure, mainly by delaying the allotropic β → α-Ca3(PO4)2 conversion until 1300 ℃. Zn2+ prefers to accommodate at Ca2+(4), and Ca2+(5) sites of Ca19Zn2(PO4)14 lattice, while the Zn2+ ions exceeding the saturation limit crystallize as ZnO. The structural distortion of PO4 bands due to the inclusion of Zn2+ concentration is verified from FTIR and Raman results. Zn2+ play a crucial role in the microstructural features and density of the resultant calcium phosphate system thus displaying the constant distribution of grains and resilient solidity in the system. Low ZnO content tends to boost the Youngs modulus and hardness while an inverse trend is noticed in case of high ZnO content.