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Surface Modification of Biomedical NiTi electronic structure of materials

Author: HuaYingJie
Tutor: YangDaZhiï¼›MengChangGong
School: Dalian University of Technology
Course: Materials Science
Keywords: discrete-variational Xa method compatibility Fermi energy level Density of State bond order surface electronic structure
CLC: TG174.4
Type: PhD thesis
Year: 2003
Downloads: 502
Quote: 5
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Abstract


The biocompatibility of an implant is closely related to its surface properties. Thus surface modification is one of effective methods for improving the biocompatibility of implants. In this study, the development status of biomedical materials has been summarized firstly, the biomedical application and biocompatibility of NiTi shape memory alloy have been reviewed. The method of surface oxidation and ion-implantation was used to modify NiTi alloy surface properties on a number of experiment researches. The surface morphology and structure were investigated by SEM and XPS, and the corrosion resistance of the samples were studied by electrochemical corrosive behavior and toxic ions releasing rate measurement in Simulated Body Fluid (SBF).. The discrete-variational Xa method (DVM-Jfa) in the frame of the Density Functional Theory was used to study the surface electronic structure. The consistency between theory and experiment was primarily evaluated.The theory research of competitive Ni and Ti oxidation on NiTi alloy surface was completed by discrete-variational X* method. Preferential oxidation of Ti on NiTi alloy surface has been observed and was consistent with the experimental result and the free energy of formation A G?(298K) of NiO, TiO, TiO2. Mulliken population and the partial density of state analysis showed that the interaction between Ti and O atoms was mainly donated by O 2p and Ti 4s orbital and O 2p and Ti 3d, 4s, 4p hybridization orbital. The electron structure in NiTi bulk material was not altered during 62 molecule adsorption process and the surface passivation oxide formation. Thus the mechanical properties and shape memory effect would not change after NiTi alloy surface oxidation. Stable microstructure demonstrates reliability of implant material.The even surface oxidation layer was formed on NiTi alloy surface by heating oxidation method. Then the surface oxidized sample was further implanted with nitrogen. The surface component analysis showed the titanium oxidation was formed on NiTi alloy surface after oxidation and ion implantation. The corrosion resistance, especially the pitting-corrosion resistance was greatly improved with more structural hydroxyl (-OH) on the surface of NiTi alloy after ion implantation.The rutile TiOi cluster model was used to simulate the local environment of C and N atom impurity. By use of the discrete variational Xa method, surface charge distribution, bond order and density of state were calculated. There was reaction between Ti and C (N) and the surface electronic structure was altered after C and N atom impurity in rutile TiO>2. The Fermi energy level decreased and surfaceCr,work function increased, so the corrosion resistance of NiTi alloy was improved.The nickel ion release rate was decreased about one order after NiTi alloy surface oxidation by atomic absorption spectrophotometry. The corrosion resistance was improved because of the surface oxidation film.The rutile TiC>2 and anatase TiC>2 cluster models were used to simulate the local environment of nickel ion release, respectively. The result showed the rutile TiC>2 structure would be more favorite for prevent nickel release than anatase TiC>2 structure.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Metal corrosion protection,metal surface treatment > Corrosion control and protection > Metal surface protection technology
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