Study On Deposition Technology And Properties Of Carbon Nanotube Composite Coatings

Carbon nanotubes are widely used in industry for its excellent mechanical properties, electrical properties and unique tubular structure. Therefore combination the engineering material and carbon nanotubes to develop high performance composite materials with wear resisting and corrosion resisting has become a research hotspot in recent years. This topic adopts electro-deposition to prepare Ni/CNT composite coating with carbon nanotubes as second reinforcements. The main research contents are as follows:(1) Study the effect of different surfactants on the dispersion of carbon nanotubes and performance of composite coating. It found that adding appropriate amount of anionic surfactant is not conducive carbon nanotubes to deposit on cathode surface, but significantly increased the cohesive between carbon nanotubes and metal matrix. It can avoid defects to form compact structure, high hardness and good electrochemical performance composite coating. Carbon nanotubes also kept a good suspension state during electroplating process. After immersed in mixed acid, the carbon nanotubes have been shorted and there are some active groups on surface. Sedimentation experiments show that the dispersion of carbon nanotubes significantly improved after treatment. In this thesis, adopting acid treatment and anionic surfactant SDS to keep a stable dispersion state in solution and get a more superior performance of composite coating.(2) Study the effect of carbon nanotubes concentration in solution, cathode current density, deposition time, pH, temperature, stirring speed and dispersant concentration on carbon nanotubes percentage content and deposition rate of Ni/CNT composite coating. Determine the optimum technological condition by orthogonal optimized experiment and range analysis. The results show that the composite coatings have a compact surface and the carbon nanotubes uniformly distributed in the composite coating. EDS indicated that composite coating is composed of three elements Ni, C, O, so the carbon nanotubes and Ni achieve co-deposition.(3) Carbon nanotubes concentration in plating solution has great effect on surface morphology and composition of composite coating. The results show that with the carbon nanotubes concentration in plating solution improved, composite coating surface is rougher, and the C element content can be up to 11.21%. Hardness test of composite coating shows that the hardness reaches the maximum value when the carbon nanotubes concentration in plating solution is 2g/L. Tafel curve and electrochemical impedance spectroscopy were measured in 3.5%NaCl with electrochemical workstation. The corrosion potential of composite coating is greater than the nickel metal layer, and the corrosion current is less. This result shows that composite coating has higher corrosion resistance than pure Ni coating. AC impedance spectra is single capacitive arc, the decrease of capacitance and the increase of electric charge transfer resistance show that composite coatings have better corrosion resistance. This is consistent to the Tafel.