| Hydroxyapatite (HA) with excellent biological compatibility, bioactivity and osteoconductive properties has been regarded as the most promising materials for bone repair and replacement. However, the poor mechanical properties of synthesized HA, especially low strength and brittle nature restrict its applications. Being a bio-inert material, Al2O3 exhibits excellent mechanical properties and wear resistance, which has been used in parts of the artificial teeth and artificial joints. In the past few years, nano-Al2O3 particles have been widely used as the reinforcing phase to improve the mechanical properties of the matrix. The Al2O3 reinforced HA composites have also been extensively studied. However, the commonly used method is ball milling mixture method, this method is time-consuming and is not good for the dispersion of nanosized particles dispersion. Moreover, the addition of Al2O3 will promote the decomposition of HA. Therefore, nano-Al2O3/HA composite powders were synthesized by chemical precipitation method, and the nano-Al2O3/HA composites were preparedby hot pressed sintering. The effects of the addition of Al2O3 and F doping on the structure and properties of nano-Al2O3/HA composites were studied.The main research contents are as follows:(1) Nano-Al2O3/HA composite powders were prepared by stepwise chemical precipitation method, and the effect of preparation conditions on the properties of the composite powders was studied. The results show that the grain sizeand crystallinity of the precursors progressively increased with increasing precipitation temperatures; the preparation of the precursor powder with good dispersion and uniform powder size could be prepared when the initial reactant concentration is 0.2mol/L; molecular weight of PEG had a great influence on the morphology of HA, HA particles with larger particle size can be prepared when the larger molecular weight of PEG was added; the crystallinity and the dispersionof the composite powders showed great improvement after calcination, the HA particles with 50nm in diameter were obtained after calcination at 900℃; in addition, the addition of Al2O3 had less effect on the functional groups of HA, and OH- could be replaced by F- in the F-doped composite.(2) Nano-Al2O3/HA composite ceramics were prepared by hot pressing. The research showed that the composite ceramic had the highest flexural strength and fracture toughness of 159.37MPa and 2.07MPa-0.5 when the sintering temperature was 1250℃, and HA decomposed to a-TCP when the sintering temperature was higher than 1250℃ and the phase of calcium aluminate with lamellar morphology were obtained in the composite. Addition of nano-Al2O3 can obviously improve the mechanical properties of HA. The composites containing 30wt% Al2O3 exhibited the maximum bending strengh and fracture toughness of 147.2MPa and 2.19MPa·m-0.5 after sintering at 1250℃. Moreover, mechanical properties of the Al2O3/HA composites could be improved by F doped, the bending strength and fracture toughness were 147.2MPa and 2.19 MPa·m-0.5 when the F content was 1 and the decomposition of HA could be inhibited with F addition. What’s more, the obtained AIF3 phase could promote the densification process of composite ceramics. In addition, toughening and strengthening of the composites relied on the addition of Al23 sintering at lower temperatures, while it was the results of the cooperative action of Al2O3 and calcium aluminate.(3) The in vitro bioactivity of Al2O3/HA composites were investigated by soaking in simulated body fluid. The resluts showed that bone-like apatite could be formed on the surfaces of the composite, indicating that the composite ceramics displaying good bioactivity. The contentand the diameter of bone-like apatite increased with the increase of immersion time.In addition, the addition of Al2O3 decreased the bioactivity of the composite ceramics, while F doping could improve the bioactivity of the composite ceramics, but the F content had little effect on the bioactivity of the composite ceramics. |
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