Study On The Carbon Composite Coating By Electro-deposition And Its Structure And Performance

With quantum size effect, small size effect, surface and interface effect,tunneling effect, nano-materials can showing a unique magnetic, mechanical, optical,electrical, electrochemical, catalytic properties. In the past years, nanotechnology hasdrawn increasing attention, nano science and technology played a key role inpromoting the development of materials science. Nano composite electro-depositiontechnology is the result of a combination of nanotechnology and compositeelectro-deposition technique, and an important research topic in the technologydevelopment process of the composite deposition. In this thesis, we studied thetechnique of electro deposition and the performance of the two functional compositecoatings.（1） with high wear resistance electrical contact coating--Ag/nano-diamondcomposite coatingsThe Ag/nano-diamond composite coating was plated on copper sheet substrateby the composite electro-deposition technique in the basic silver plating solution withadding some10-30nm nano-diamond powders which had been pre-processed. Theeffect of the plating conditions on the surface morphology, the composition and thestructure of the composite coating was studiedby scanning electron microscopy（SEM）, energy disperse spectroscopy （EDS） and X-ray diffraction （XRD）. As aresult,the best plating conditions are the cathodic current density8mA/cm², thestirring speed400r/min and the concentration of nano-diamond powderin the platingsolution10g/L. Diamond powders were uniformlydispersedin the composite coatingwith two phases structure. And the diamond content reaches the highest value9wt%.According to the micro-hardness and electric resistance tests, the micro-hardness andthe electrical resistivity of the composite coating rise observably with the diamondcontent increase. The corrosion resistance of the composite coating was researched bythe Tafel test in5.0wt%Na₂SO₄solution. The corrosion resistance of theAg/nano-diamond composite coating is superior to thesilver coating. （2）with self-lubrication corrosion resistance coating--Zn/graphite compositecoationgThe Zn/graphite composite coating was plated on carbon steel substrate by thecomposite electro-deposition technique in the zincate plating solution with some10²5micron graphite powders which had been pre-processed in the ultrasonic stir.The effect of the plating conditions on the surface morphology and the compositionof the composite coating was studiedby scanning electron microscopy and energydisperse spectroscopy.As a result,the best plating conditions are the cathodic currentdensity50mA/cm²and the concentration of graphite powder in the plating solution8g/L.With dark gray appearance, the composite coating isuniform. According to theabrasion test, the Zn/graphite composite coating has less friction coefficient and lessvolume loss than that of the pure zinc coating in the same condition test, so thecomposite coating is more abrasion resistance.The corrosion resistance of thecomposite coating was investigated by Tafel test and electrochemical impendencespectroscopy（EIS） test in3.5wt%NaCl solution andneutral salt spray acceleratedcorrosion test （NSS） in5.0wt%NaCl solution. The corrosion resistance of theZn/graphite composite coating with chromate passivation is better thanthat of the purezinc coating.