Engineering carbon into graphene on metals for corrosion resistance

Most conventional corrosion protection techniques, namely paints, organic coatings, anodization, metallic coatings and several others have been extensively employed for protection of metals and alloys against environmental degradation, but they are fraught with problems such as thickness, degradation and premature failures, as well as they can change properties of the metal underneath. The use of graphene coating has been explored in very limited research (2011-15) showing potential of graphene as a corrosion protective layer for short durations. Some of these studies show that graphene increases corrosion rather than preventing it for long exposure times because of its defects and poor surface coverage. It is proposed in this study that a possible solution to this problem of hampering corrosion protection ability of graphene due to defective single layer graphene can be overcome by applying multilayer graphene in place of single layer graphene as it is extremely difficult to get defect-free graphene with full surface coverage. A low vacuum CVD reactor for synthesis of graphene on copper and Cu-Ni (75/25) alloy using n-hexane as hydrocarbon source was designed and built in this PhD project. The characterisation of graphene was done using Raman spectroscopy to determine deposition of graphene on copper and Cu-Ni alloy. The performance of graphene coating on corrosion resistance of copper and Cu-Ni alloy in 0.1 M sodium chloride was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The potentiodynamic polarisation and electrochemical impedance spectroscopy showed ~5 times and ~10 times improvement in corrosion resistance of Cu and Cu-Ni alloy due to graphene coating, respectively. The systematic corrosion study using electrochemical impedance spectroscopy on graphene coated copper for different immersion times showed that graphene coating continued to provide improvement in corrosion resistance for long immersion periods (up to 386 h) in 0.1 M NaCl. The graphene coated Cu-Ni alloy also continued to show corrosion resistance for long durations (up to 336 h) of immersion in 0.1 M NaCl.