Preparation and corrosion behaviour of electroless Ni-P-CNT composite coating with various CNT contents

In the present study، Ni-P-CNT composite coatingswith different contents of carbon nanotube were successfully deposited on copper surface via electroless plating. The effect of CNTs concentration in the bath on its content in the composite coatings and corrosion behaviour of the coatings has been studied. Scanning electron microscopy (SEM) and EDS analysis were used to characterize the coatings. The SEM results showed that the thickness of the coatings was about 30µm and the deposited coatings had nodular features with a typical cauliflower-like structure. The corrosion behaviour of the coatings with different contents of CNTs was evaluated using Tafel polarization and electrochemical impedance spectroscopy (EIS) methods in 3. 5 wt. % NaCl aqueous solution. According to Tafel extrapolation results، the incorporation of CNTs into the Ni-P coatings is led to the formation of a better passive film. It was also concluded that with increasing the CNTs concentration in the bath، corrosion rate decreased at first and then increased. Furthermore، the EIS results indicated that the real impedance of the Ni-P coating is much smaller than that of the Ni-P-CNT coatings. In this context، as the concentration of CNTs in the bath increased، charge transfer resistance values were initially increased and then decreased. This behavior could be related to the role of the CNTs in the formation of low ionic conductivity surface passive film.