Synthesis Of Hydroxyapatite Whiskers And Preparation Of Hydroxyapatite Whiskers-Zirconia Composite

\Hydroxyapatite has been verified to be the predominant inorganic constituent of human hard tissues. Actually, in human dental enamel, hydroxyapatite has reached as high as 97%. Especially, hexagonal morphology of the HA has been found promising application in dental implants because the human tooth enamel has flattened hexagonal prisms of HA crystals. However, the single hydroxyapatite can not meet the mechanical propertites of human teeth. On the other side, ZrO₂ shows biocompatibility and high mechanical properties. In this thesis, we add nano zirconia to the hydroxyapatite whisker powders and prepare the composite, which will have potential value as biomimetic dental restorative materials in oral medicine.First, the dental enamel-like HA whiskers with high crystalline, uniform morphology were synthesized by the hydrothermal homogeneous precipitation method. Ca(NO₃)₂·4H₂O and (NH₄)₂HPO₄ were used as calcium and phosphorus sources, sorbitol as template and urea as the pH control agent. The composition, crystallinity and morphology of obtained products were characterized by XRD and SEM. From the results ,we analyzed the effects of urea and sorbitol on the morphology and composition of materials.It was revealed that the uniform,well crystallized enamel-like HA whiskers with the length 1²Î¼m, width 100²00nm were obtained at the condition of [urea]= 0.80mol·L^-1 and [sorbitol]=0.26 mol·L^-1. In the process of whiskers growth, the regulation mechanism of HA crystal growth along c-axis was proposed according to the strength of hydrogen bond between sorbitol and hydroyapatite. The hydrogen bond occurred on HA's (001) and (100) planes.Secondly, we prepare the hydroxyapatite whiskers/zirconia composite and study the phase of the composite. At different sintering temperature, the composites all consisits of t-ZrO₂ ,β-TCP and c-Ca_0.15Zr_0.85O_1.85. As the sintering temperature rises, the mount of m-ZrO₂ decreases and the HA decomposite toβ-TCP. The mount ofβ-TCP and c-Ca_0.15Zr_0.85O_1.85 increase with the increasing content of hydroxyapatite.The tests are performed for the composite sintering and mechanical properties. The results show that, the linear shrinkage rate increases and porosity decreases then hardness and fracture toughness increase first and then decreases as the sintering temperature rises. At the same sintering temperature, the porosity decreases and the sintering activation energy increases with the increasing content of zirconia. In addtion, the hardness and fracture toughness increased simotaniously. The hardness and toughness are about 7GPa and 2.3MPa.m^1/2 respectively for the sample with 40 mass% hydroxyapatite sintered at 1300°C, which is close to the hardness of enamel. It is shown that the composite we prepared have potential application as dental substitute materials.