The influence of various zirconia contents on crystallite sizes, shrinkage, and physical and mechanical properties of hydroxyapatite-based nanobiocomposites

Carbonated hydroxyapatite (CHA)-based nanocomposite powders with different zirconia (ZrO2) contents, up to 8 wt.%, were prepared using high-energy ball mill.Phase composition of the resultant nanocomposites was investigated by X-ray diffraction (XRD) technique.Moreover, the crystal size, lattice strain and dislocation density were calculated.In order to measure shrinkage, physical and mechanical properties of these nanocomposites, their powders have been consolidated and sintered at 1000 °C.The results revealed that the gradual increase in ZrO2 contents caused increase in the lattice strain and dislocation density.On the opposite side, their crystal sizes decreased with increasing ZrO2 content.Moreover, the mechanical properties including microhardness, compressive strength, Young's modulus, elastic modulus, bulk modulus, shear modulus and Poisson's ratio of the sintered nanocomposites were greatly improved with increased ZrO2 contents until they reached 7 GPa, 165 MPa, 57 GPa, 70 GPa, 47.5 GPa, 22 GPa and 0.267, respectively for the sample containing the highest ZrO2 content.However, in spite of the great importance of ZrO2 contents on the mechanical properties, they caused noticeable increases in the porosity of the sintered samples.Additionally, increasing of ZrO2 contents, up to 8 wt.%, reduced the shrinkage percentages from 12.3% to 9.5%.