Investigation of corrosion inhibition of medium carbon steel using palm kernel and grapeseed oils in 3.5 % NaCl solution

This research investigates the sustainable corrosion inhibition of medium carbon steel (MCS) in 3.5% NaCl solution, simulating seawater, using palm kernel oil (PKO), grapeseed oil (GS), and their 1:1 admixture (AD). Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), open circuit potential (OCP), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffractometry (XRD) were employed to elucidate inhibition mechanisms. Uninhibited MCS exhibited a high corrosion rate (0.007 mm/y) and low polarization resistance (442 Ω). The AD formulation demonstrated the most effective performance, achieving 94.79% inhibition efficiency at 1.5% concentration, lowering the corrosion rate to 0.00036 mm/y and enhancing polarization resistance to 8568 Ω. EIS confirmed AD’s superior behavior, with Rp reaching 458,700 Ω at 3.5%, indicating strong chemisorption and dense film formation. FTIR spectra revealed adsorption of O–H, C=O, and C–O functional groups, with AD showing the strongest bonding interactions. XRD analysis further supported AD’s protective effect, with crystallite size reduced to 295 Å, evidencing robust surface modification. While PKO and GS also inhibited corrosion (67.23% and 81.69% efficiency at 2% concentration, respectively), their protective films were less stable, with efficiency declining at higher concentrations due to film instability. OCP measurements indicated that GS at 3.5% approached a pseudo-passive state (–0.786 V). The study establishes AD as a highly effective, green corrosion inhibitor, outperforming its individual components through synergistic interactions. These findings highlight the potential of plant-derived oils as eco-friendly alternatives to toxic inhibitors, supporting sustainable corrosion protection strategies for steel in chloride-rich environments.