Effect of fluorapatite additive on densification and mechanical properties of tricalcium phosphate

Tricalcium phosphate and synthesized fluorapatite powder were mixed in order to elaborate biphasic composites. The samples were characterized by X-ray diffraction, differential thermal analysis, infrared spectroscopy, scanning electron microscopy and by an analysis using 31P nuclear magnetic resonance. The sintering of tricalcium phosphate with different percentages of fluorapatite (13.26 wt%; 19.9 wt%; 33.16 wt% and 40 wt%) indicates the evolution of the microstructure, densification and mechanical properties. The Brazilian test was used to measure the rupture strength of the sintered biphasic composites. The mechanical properties increase with the sintering temperature and with the addition of fluorapatite additive. The mechanical resistance of ββ tricalcium phosphate–33.16 wt% fluorapatite composites reached its maximum value (13.7 MPa) at 1400 ∘C, whereas the optimum densification was obtained at 1350 ∘C (93.2%). Above 1400 ∘C, the densification and mechanical properties were hindered by the tricalcium phosphate allotropic transformation and the formation of both intragranular porosity and cracks. The 31P magic angle spinning nuclear magnetic resonance analysis of composites as sintered at various temperatures or with different percentages of fluorapatite reveals the presence of tetrahedral P sites.