Preparation And Behaviour Study On Porous Gradient HAP Bioceramic Artificial Bone

The structure of artificial bone was designed according to the long bone of people, the outer was compact layer, the inner was porous spongiosa layer.HAP powders were firstly prepared by auto-combustion method in this study. The calcium nitrate, ammonium hydrogen phosphate and citric acid were blended according that the mole ratio of Ca/P and Ca2+/(citric acid) were 1.67 and 1. Then the blender were heating at 80 to form gel after some hours. At last the gel was firing at 200 and calcined at 750 to get the HAP powders. The results showed that the sample was pure-phase HAP and the grain size was about 85 nm. Via TG-DTA and XRD testing on the nanosized hydroxyapatite (HAP) prepared by auto-combustion method, the course of HAP was analyzed, and the mechanism of reaction was discussed. The influence factors of this method such as, the quantity of water, PH value, temperature and the quantity of citric acid were studied. The results show that the mechanism of reaction is complex mechanism in the generating stage of sol-gel and then the oxidation-reduction combustion mechanism; The forming of HAP mostly experienced the phases of B-Ca2P2O7, y- Ca2P2O7, CaH2P2O7, C2Ca, CaCO3 and so on. The optimum technical parameters are that the n(H2O)/ n(Ca2+) is 30-35, the PH value is 2-3, the heating temperature is about 80, and the mole ratio of citric acid to Ca2+ is 1-2.The material was sintered at 1050 for three hours to get the porous artificial bone, that its apparent porosity was54%, its volume density was 1.28 g/cm3, and its bending strength was 13.25Mpa.The results showed that the sintering temperature was reduced by adding bioglass. Along with the rising of sintering temperature and the increasing of heat preservation time, the porosity and water absorption reduced, the density and bending strength increased, the bending strength was mostly estimated by the porosity.Through observing the interface of porosity HAP sintered at 1050, the gradient changing of pore size was observed that was like gradient structure of bone. In the compact layer there were a few about 50 y mpores and many about 5um micropores. In the porous layer there were many about 500um pores.