Synthesis And Characters Of Hydroxyapatite Coating By Electrochemical Methods

Every year, the number of the patient repairing and replacing the teeth and bones in our country gradually increases due to the illness and traffic accidents. The development of implants materials has become the Chinese important components of the national economy. However, the poor biological activity, pitting corrosion and releasing metal ions harmful to human, which leads to the failure of implant, restrictes the Ti6A14V alloy in implants clinical application. Therefore, the Ti6A14V alloy surface modification has become the main implants materials development trend. In this paper, the corrosion behaviors in Hank's solution, Ringer's solution and Tyrode's solution are tested, and HA coatings are prepared on Ti6A14V alloy by three kinds of electrochemical methods. Moreover, the biocompatibility and the electrochemical behaviors are researched.The results show that with the increase of temperature, the thermodynamics stabilities of Ti6A14V alloy decrease, the corrosion current densities increase, and the corrosion resistances reduce, gradually in the three kinds of simulated solution. The kinetic equation of pitting corrosion are iHank=1.0756·(t-1.1649)-1/2, iRinger= 1.0940·(t-1.4437)-1/2, iTyrode=2.0564(t-0.4568)-1/2. The pitting corrosion process is controlled by the dissolution of surface salt membrane. The activation energy Ea in Hank's solution, Ringer's solution and Tyrode's solution are 45.71KJ/mol,155.1 KJ/mol and 87.62 KJ/mol respectively, which under the chemical reaction.Based on the cathodic electrodeposition, the HA coatings are prepared on Ti6A14V alloy by sacrificial anode method. The HA coating is composed of flower-like crystal or, the Ca/P ratio is 1.41, and the thickness is about 15μm. The bonding strength is 10.02MPa. By the platelet adhension test, dynamic clotting time curves and hemolysis rate, the HA coating has good blood compatibility. The electrochemical behaviors show the HA coating has more anti-corrosion characters than Ti6A14V alloy.In order to improve the bonding strength of the HA coating, TiO2 coating is prepared by microarc oxidation on Ti6A14V alloy. Then, the HA coating is synthesized using cathodic electrodeposition. The surface of TiO2 coating has circular microporous, and the thichness of coating is about 6μm. The TiO2/HA coating is composed of piece-like crystal with thichkness of 7.5μm. The bonding strength of TiO2/HA coating is 14.04MPa. But the blood compatibility is 6.02% worse than the 4.64% of the sacrificial node method. The electrochemical characters test impresses the TiO2/HA coating decreases the corrosion tend of Ti6A14V alloy.Based on the above, the single-layer of TiO2 and HA composite coating is prepared by ac pulse electric synthesis on Ti6A14V alloy. The morphology and composition of coating are tested. The blood compatibility and electrochemical behaviors in three kinds of simulated solution are tested, too. The HA composite coating is distributed of flat crystal and the flower-like crystal. The flat crystal is composed of O,P, Ca and Ti, whose Ca/P ratio is 1.671. The flower-like crystal is comosed of O, P and Ca, whose Ca/P ratio is 1.668. The thichness of HA composite coating is 7μm. The bonding strength of HA composite coating is 18.29MPa, and the HA composite coating has excellent blood compatibility and electrochemical performance. The synthesis mechanism is analysised by SECM.