ZnCo-carbon nanotube composite coating with enhanced corrosion resistance behavior

The electrochemical behavior, surface morphology characteristics, phase constitution and microstructure of electrodeposited Zn-Co (similar to 5 wt%) coatings with five different volume fractions of multi-walled carbon nano-tubes (MWCNTs) are discussed. All the coatings contained a mixture of Zn and Zn10.63Co2.34 intermetallic phases the relative fraction of which was sensitive to the amount of the MWCNTs present in the coatings. For initial MWCNT addition, the morphology became smoother while higher MWCNTs addition lead to development of surface defects. It was observed that the addition of MWCNTs into the coating matrix produced compositional homogenization. The electrochemical measurements showed that the corrosion rate of the ZnCo-CNT composite coatings decreased for initial addition of MWCNTs to reach a minimum for an optimum MWCNTs concentration, after which it increased with further MWCNTs addition. The improved corrosion resistance for the composite coating with optimum MWCNTs addition was attributed essentially to its compact surface morphology and highest intermetallic (Zn10.63Co2.34) phase fraction.