Corrosion Evaluation of 316L Stainless Steel Exposed to CNT-Water Nanofluid

CNTs-water nanofluids are new innovative materials that own extraordinary properties due to the presence of fine particles suspended in their base solutions. They have potential applications in many industrial sectors as they are expected to provide remarkable energy savings and emission reductions if used in cooling applications. Hence, it is important to study their corrosion behaviour to maintain equipment performance and ensure safety aspects. Three consequent corrosion tests were conducted on 316L stainless steel (SS) exposed to carbon nanotubes (CNTs) water-based nanofluids: open circuit test, polarization resistance test, and potentiodynamic scans. The electrochemical testing was performed at different CNTs loadings of 0.05, 0.1, 0.3 and 0.5 wt.% that were suspended in deionized water using the surfactant Gum Arabic (GA). Temperature effect was also examined with the same corrosion testing performed on the same SS exposed to 0.1 and 1.0 wt.% CNTs nanofluids at temperatures of 22, 40, 60 and 80°C. Different corrosion parameters were investigated, such as corrosion rate, corrosion potential, pitting potential, and anodic and cathodic Tafel slopes. Adsorption isotherm for CNTs adsorption on the surface of the metal and some thermodynamic properties of adsorption were found to help in proposing a mechanism for CNTs corrosion inhibition. It was observed that the SS tested in CNTs nanofluids presented low corrosion rates, which were comparable to those for tap water and lower than those for 3.5 wt.% NaCl solutions. CNTs had a blocking effect on increasing corrosion resistance as a black layer was physically adsorbed on the surface of the metal. A maximum inhibition of 61% was achieved in 0.1 wt.% CNTs nanofluid at room temperature. Further increase in the CNTs concentrations and in nanofluid’ temperature showed to decrease the corrosion performance.