Effect Of Y₂O₃ On Dynamics Of HA Synthesized By Pyrogenic Process

Synthetic hydroxyapatite(Ca10(PO4)6(OH)2,HA) has been studied extensively as a bone and teeth substitute. Mineral phases in human bone are composed of HA and a few of rare earth,carbonate ions, fluorinion,silicium ions, magnesium ions and so on. Accordingly,doped HA with the above mentioned ions may be closer to the natural bone than undoped ones. In this paper,HA was synthesized via sintering the mixture of dicalcium phosphate dehydrate (CaHPO4·2H2O) and calcium carbonate(CaCO3),with and/or without Y2O3 in addition. In order to investigate the effect of Y2O3 on the diffusion of Ca, two groups of powder diffusion couples,in which dicalcium phosphate dehydrate powders were surrounded by CaCO3 powders,were prepared. 2wt% Y2O3 powder was mixed into both powders of one group, while no other powder was mixed into the other one. The diffusion couples were sintered at 1000oC and 1150oC for 2 to 12 hours. Then they were characterised by XRD, SEM and EDX. According to Fick's Second Law, the Ca diffusion coefficients of different samples were calculated with error function solution. The effects of Y2O3 on the diffusion dynamics of Ca were researched.The following points were shown in this study:①The powders were pressed in canning powder diffusion couples. The contracting rate of CaCO3 is higher than that of CaHPO4·2H2O, thus the interface bonding strength was secured when well sintered samples resulted. It is possible to research the interface diffusion and bonding.②Y2O3 accelerated the reaction synthesis of HA. At the same temperature and holding time, the total integral area of the diffraction peaks of the doped samples were larger than those of the undoped ones.③When sintered at 1150oC, Y2O3 engaged in the solid phase reaction, and CaY2O4 and Ca9Y(PO4)7 were generated after 2 hours and 6 hours, respectively. However, Y2O3 did not engage in the reaction until holding for 12 hours when sintered at 1000oC, and the resulting phase was Ca3Y(PO4)3 .④When sintered at 1150oC, HA decomposed after it was synthesized. Y2O3 can delay and restrain the decomposition reaction. The decomposing product Ca4P2O9 appeared in the doped samples after holding for 4 hours, but it appeared in the undoped samples only sintered for 2 hours. As the holding time increased, the HA integral area sum of the diffraction peaks reduced whereas the integral area sum of the diffraction peaks of Ca4P2O9 increased. The integral area sum of Ca4P2O9 in the doped samples were larger than the undoped ones. There was no decomposition of HA at 1000oC.⑤The interface were analysed by SEM. As the holding time increased,the breadth of solid phase reaction zone increased. Under the same conditions,Y2O3 increased the breadth of solid phase reaction zone.⑥Based on the Ca concentration distribution in the samples sintered at 1000oC, the diffusion coefficients were calculated using Fick's second law. It was shown that Y2O3 increased the diffusion coefficient of Ca. The diffusion coefficients of the doped and undoped samples were 4.6×10-11 cm2/s and 1.8×10-12cm2/s, respectively. When sintering temperature was 1150oC,the diffusion model with fixed interface was not applicable.