Effect Of Yttria On Synthesis Of HA In Situ

Synthetic hydroxyapatite (HA) has good bio-compatibility due to its composition close to bones and teeth of vertebrate. When implanted into human body, synthetic HA can achieve tight bonding with bones, as a resullt of which, HA has been extensively studied as a bone substitute or coating for metallic implant. When being synthesized by dry process, HA bio-ceramics tends to be amorphous and easily loses hydroxyl. Due to that, the application of HA bio-ceramics has been much limited. So a new method of synthesizing HA is required. HA in human body is not a perfect one, containing different levels of carbonate ions, fluorinion, silicium ions, magnesiam ions, sodion and etc. Doping ions may make properties of synthesized HA closer to natural bones. In the paper, dry process of synthesizing HA in situ was employed, that is, a solid state reaction between calcium hudrogenphosphate (CaHPO4·2H2O) and calcium carbonate (CaCO3) , with various amounts of yttium oxide (Y2O3) added as agent, was carried out. The effects of Y2O3 on the synthesis of HA in situ were investigated. The changes of weight, enthalpy, phases and radicel of samples with different Y2O3 content were ditermined by analytical balance, Synchronous thermal analysis (STA), X-ray diffraction (XRD) and Fourier transform-infrared spectroscopy (FT-IR) respectively. The conclusions are detailed as below: ①Y-CHA, HA doped by CO 32 ? and Y3+, was synthesized, and for the first time, Y-CHA has been systematically studied. ②Y2O3 has an abvious effect on the conversion velocity of γ-Ca2P2O7 to β-Ca2P2O7. When W (Y2O3) = 0.5%, activation energy is at its lowest level while conversion velocity highest. Stability of β-Ca2P2O7 is improved with incremental Y2O3 content. ③With the increase of the amount of Y2O3, increasing Yttrium enters into the structure of β-Ca3(PO4)2 to form Ca9Y(PO4)7. Especially, when W (Y2O3) = 1.0%, the space group of synthetic β-Ca3(PO4)2 changes to R3m, a structure that can promote a higher level of OH-and CO 32? content in synthetic HA, which shows that the problem of HA easily losing OH-when synthesized by dry process has been solved. The addition of Y2O3 also improves the high temperature stability of OH-and CO 32? . ④Ca9Y(PO4)7, β-Ca3(PO4)2 doped by Yttrium, displays phase transfomation at 1250℃. With the increase of the amount of Y2O3, activation energy of phase transfomation will increase. When W (Y2O3) = 2.0%, activation energy is so high that the reaction can't occur. So the high temperature stability of Ca9Y(PO4)7 is improved with the incremental amount of Y2O3. ⑤Y2O3 has an influence on crystallization velocity of HA. The temperature of maxium conversion and activation energy of HA decreases. Especially, when W (Y2O3) = 1.0%, the lowest activation energy and strongest XRD intensity of HA was observed. In addition, Y2O3 has little effect on decomposability of HA.