Mechanical and tribological properties of the tricalcium phosphate - magnesium oxide composites.

The mechanical of the tricalcium phosphate matrix sintered with different amounts of the magnesium oxide have been investigated. The tricalcium phosphate - magnesium oxide composites were characterized by using the mechanical properties such as rupture strength, Vickers hardness and elastic modulus. The effects of the sintering process on the structural changes of the composites were investigated. At 1300 °C, the highest performance was obtained for the tricalcium phosphate containing 5 wt% MgO. The maximum mechanical strength and Young's modulus of the composites reached 9 MPa and 38 GPa, respectively. The result can be explained by the formation of both, liquid phase, which helps to fill the pores in the microstructure, and a new phase relative to the calcium magnesium phosphate. At 1400 °C and beyond 5 wt% MgO, the performances of the composites are hindered by the intragranular porosity formation and by the exaggerated grain growth. The addition of the magnesium oxide to the tricalcium phosphate matrix promotes the reduction of the wear rate and the friction coefficient. The composites performances are close to the enamel.

Sintering and the mechanical properties of the tricalcium phosphate-titania composites.

The sintering of the tricalcium phosphate with different percentages of titania was investigated. The samples were characterized by differential thermal analysis, dilatometry analysis, X-Ray diffraction, infrared spectroscopy, magic angle scanning nuclear magnetic resonance and scanning electronic microscopy measurements. The samples were examined by using the mechanical properties such as rupture strength, Vickers hardness and elastic modulus. The sintering of the tricalcium phosphate-titania composites indicates the evolution of the microstructure, the densification and the mechanical properties. The performances of the composites increase with both the sintering temperature and the addition of the titania. The highest values of the composites of rupture strength (33 MPa), Vickers hardness (270 Hv), Young׳s modulus (33.1GPa) and shear modulus (15.7 GPa) were obtained after the sintering process with 40 wt% titania at 1200 °C. The increase of these performances is due to the formation of the liquid-phase which helps to fill the pores in the microstructure. Above 40 wt% TiO2, the mechanical properties of the composites are hindered by the exaggerated grain growth formation.

Sintering and mechanical properties of the alumina-tricalcium phosphate-titania composites.

The objective of this study was to determine the effect of the content of titania and the sintering process on the transformation phase, the densification, the rupture strength and the microstructures of the alumina-10 wt.% tricalcium phosphate composites. After the sintering process, the samples were examined by using (31)P and (27)Al magic angle scanning nuclear magnetic resonance, X-ray powder diffraction and scanning electron microscopy analysis. The Brazilian test was used to measure the rupture strength of the samples. The present results provide new information about solid-state reactivity in the ternary system α-alumina-ß-tricalcium phosphate-anatase-titania. The differential thermal analysis of the α-alumina-ß-tricalcium phosphate-titania composites shows two endothermic peaks, at 1360 °C and at 1405 °C, which are caused by the reactions between titania/alumina and titania/tricalcium phosphate, respectively. Thus, the presence of titania in the alumina-10 wt.% tricalcium phosphate leads to the formation of ß-Al2TiO5 at 1360 °C. At 1600 °C, the alumina-10 wt.% tricalcium phosphate-5 wt.% titania composites displayed the highest rupture strength (74 MPa), compared to the alumina-10 wt.% tricalcium phosphate composites (13.5 MPa). Accordingly, the increase of the rupture strength is due to the formation of the new ß-Al2TiO5 phase.

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 (31)P 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 beta tricalcium phosphate-33.16 wt% fluorapatite composites reached its maximum value (13.7 MPa) at 1400 ( composite function)C, whereas the optimum densification was obtained at 1350 ( composite function)C (93.2%). Above 1400 ( composite function)C, the densification and mechanical properties were hindered by the tricalcium phosphate allotropic transformation and the formation of both intragranular porosity and cracks. The (31)P 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.