A comparison of the corrosion inhibition performance in sulfamic acid medium between refluxed and ultrasonic extracts of rapeseed meal.

Effective utilization of its by-product of rapeseed meal (RM) can improve its economic value and promote the development of rapeseed industry. Existing research has concerned the chemical composition of RM, failing to deeply explore the potential of these important constituents. In this paper, refluxed and ultrasonic RM extracts (RRME and URME) are developed as steel corrosion inhibitors due to their chemical components containing substantial important organic compounds. The inhibition performances of both RME inhibitors against cold-rolled steel (CRS) corrosion in sulfamic acid (SA) medium are evaluated by weight loss, electrochemical measurements, surface characterizations, as well as theoretical calculations and simulations. It is found that these two RME inhibitors can dramatically reduce the corrosion current density while increase the polarization resistance. Characterizations show a significant decrease in roughness and an increase in hydrophobicity of the inhibited CRS surface compared to the corroded sample. Comprehensive results confirm that RRME and URME can be regarded as hybrid inhibitors, which simultaneously inhibit the anodic and cathodic reactions, forming an organic film to prevent the movement of corrosive particles to CRS surface, achieving the highest inhibition efficiencies of 93.7 % and 95.4 % respectively at the same concentration of 100 mg/L. The adsorption behaviors of these two RME inhibitors are consistent with the Langmuir adsorption isotherm model, and RRME is a more excellent inhibitor due to its higher adsorption equilibrium constant (Kads), longer half-life time (t1/2), and performs better stability and durability with the extension of immersion time.