The Effect of Blackening Treatment on the Corrosion Behavior of Ni-P-CNT Nanocomposite Coatings

Introduction and objectives: In this research, carbon nanotubes (CNTs) were used to optimize the properties of Ni-P electroless coating in optical applications and the effect of CNT content on the corrosion behavior of Ni-P-CNT composite coating was investigated.Materials and methods: The coatings were blackened in nitric acid solution after electroless coating deposition. The morphology and elemental analysis of the coatings were examined using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), respectively. Also, the electrochemical tests such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were employed to investigate the corrosion behavior.Results: The results declared that increasing CNT in the plating bath from 0 to 2 g/l led to increase in CNT content in the composite coating, while the co-deposition of CNT was decreased in greater values. It was also found that the blackened composite coating containing 1.5 g/l CNT had the highest corrosion resistance among all the composite coatings. This behavior can be the result of the optimum co-deposition of carbon nanotubes in Ni-P matrix and subsequently lower amounts of defects after blackening process.Conclusions: In this research, the effect of co-deposition of carbon nanotubes on the corrosion behavior was studied. The results indicated that the corrosion resistance of blackened composite coating was improved in an optimum content ~1.5 g/l of carbon nanotube in the Ni-P matrix.