Multilayer CVD Graphene Coatings Developed with Suitable Geometrical Parameters for Improved Corrosion Resistance of Ni and a Ni-Cu Alloy in Chloride Environment.

Graphene layers on metals developed by chemical vapor deposition (CVD) possess characteristics of an ideal coating for durable corrosion resistance of industrial infrastructure, by a green approach. However, developing coatings of consistent quality is a challenge and its circumvention requires manipulation of CVD process parameters. The great variability (from remarkable to little) in graphene's ability as a corrosion barrier coating is attributed to the extent of defects/non-uniformity of graphene. Minimizing the defects by controlling a few CVD process parameters (chemistry, pressure, temperature, and flowrate of the precursor, and post-CVD cooling rate) has been demonstrated in earlier studies. This study investigates the role of the distance of the precursor delivery point (nozzle) with respect to the substrate as well as the role of substrate tilting in minimizing the defects in graphene coatings developed on Ni and a Ni-Cu alloy by CVD, and durable corrosion resistance due to graphene coatings thus developed. Electrochemical impedance spectroscopy is employed to monitor the corrosion behavior of the coated samples during a 1008 h immersion in a 0.1 m NaCl solution. The findings reveal a significant reduction in corrosion rate of ≈88% and 98% for graphene-coated Ni and Ni-Cu alloys, respectively, compared to their uncoated counterparts.