| Titanium alloy materials were widely used as human joint implantmaterials for their high specific strength, non-toxic, good corrosionresistance and biocompatibility. However, there are also some urgentproblems which should be settled. Titanium alloy materials can berapidly worn out in physiological environment conditions with certainapplied load for their low hardness. Wearing can produce a largenumber of black debris which contain Ti, Al and V elements. Thesedebris can cause the joints loose or even arthroplasty failure,accumulation of those debris tend to spread to other places. Thetechnique of self-assembly molelayer (SAM) which has been developedin the last30years provides an effective way to solve this problem.This research using carbon nanotubes (MWNTs) with high tensilestrength, good flexibility, and high friction load carrying capacity andrare earth (RE) with special physical and chemical properties ofelements, which act as medium connecting silane film with MWNTsfilm, obtained3-aminopropyl-triethoxysilane carbon nanotubes(APTES/MWNTs) self-assembly composite film of excellenttribological properties. This composite film aimed at resolving theproblem of inadequate wear resistance of titanium alloys. The studyshows that: this film acts as a self-lubricating layer between the frictionpairs, which greatly increased carrying capacity of the friction pairs,thus increased wear resistance of titanium alloy. The achievements ofthis research are listed below: Firstly, APTES/MWNTs composite film was successfully preparedon the surface of the hydroxylated titanium alloy substrate byself-assembling technique. By changing the kinetic factors ofassembling process and the concentration of the rare earth, the optimalpreparation parameters of APTES/MWNTs composite film wereobtained. Studies have shown that the rare earth concentration of0.6wt%of the rare earth modified carbon nanotube suspension with apH of5-6were the most suitable process for the preparation ofAPTES/MWNTs composite film.Secondly, the self-assembly mechanism of APTES/MWNTscomposite film was figured out. Atomic force microscope (AFM) wasapplied to measure the changes of surface roughness during theassembling process, contact angle measurement was used to evaluate thefilm surface energy, scanning electron microscopy (SEM) was ultilizedto observed the surface appearance of the composite film, and X-rayphotoelectron spectroscopy (XPS) was used to analyze the typicalelements in surface of titanium alloy substrate. Results show that therare earth elements can react with the phosphate group of the organicsilane surface forming ligand and adsorpt oxygen atom in the carboxylgroup of the carbon nanotube surface, so that carbon nanotubes can beclosely coupled on organosilane surface.Thirdly, we systematically investigated the friction and wearproperties of APTES/MWNTs composite film in macroscale byuniversal multifunction tribometer (UMT). The results show that:APTES/MWNTs composite film had a small surface coefficient offriction (COF), about0.11to0.14, and the wear resistance lifetime wasas long as12,000times of friction sliding.By means self-assembly technique, and by making good use of thestrong affinity to oxide of the lanthanum ion, this research successfullyprepared the self-assembled APTES/MWNTs composite film on thesurface of titanium alloy. Measured the changes of surface roughness of the film during the assembly process by AFM and revealed theassembling process of the film; investigated the valence states and theirchanges of the typical elements on the surface of film by XPS anddisclosed the chemical principle of the assembling process ofAPTES/MWNTs composite film; measured the contact angle ofAPTES/MWNTs composite film and further revealed the mechanism ofthe film assembly. Measured COF of the composite film with thevariation of parameters of the assembly process by UMT and obtainedthe wearing mechanism of APTES/MWNTs composite film. Theaccomplishment of this research broadened the field of carbonnanotubes and rare earth. |
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