From agricultural waste to green corrosion inhibitors: High-performance rapeseed meal extracts for cold-rolled steel in acidic media

Abstract

Rapeseed meal, an agricultural by-product rich in heterocyclic and nitrogenous compounds, is a novel and environmentally friendly corrosion inhibitor for cold rolled steel (CRS) sheets in citric acid. The corrosion inhibition efficiencies of reflux and ultrasonic extracts (RMRE and RMUE) reached 90.88 % and 87.86 %, respectively, which is superior to many synthetic corrosion inhibitors. Both extracts follow the Langmuir isotherm and form a protective layer by mixing chemisorption and physisorption. RMRE and RMUE increased the charge transfer resistance by nearly 10-fold and reduced the corrosion current density by 90 % at 50 °C, while RMRE and RMUE significantly reduced the surface roughness, suggesting that they were effective in mitigating citric acid attack. XPS characterization showed that the protective inhibition layer formed on CRS originated from the polar functional groups in the RME molecule. Theoretical simulations show that the inhibition effect is due to electron-rich aromatic rings, N/O-heterocycles, and carbonyls, which are active sites adsorbed on the surface of Fe (0 0 1). The high efficiency, low cost, and biodegradability of RMRE and RMUE make them viable and green alternatives to toxic inhibitors.