Synergism between walnut green husk extract and sodium dodecyl benzene sulfonate on cold rolled steel in 1.0 mol/L H2SO4 solution

Abstract

Walnut green husk extract (WGHE) was prepared by the reflux method using the agricultural residues of walnut green husk as raw materials. Its synergistic inhibition effect with an anionic surfactant of sodium dodecyl benzene sulfonate (SDBS) on the corrosion of cold rolled steel (CRS) in 1.0 mol/L H₂SO₄ solution at 20-50 ℃ was investigated using mass loss measurement, electrochemical techniques and surface analysis. Effective components for synergistic inhibition in WGHE were also explored in depth. The results show that individual WGHE or SDBS exhibits moderate inhibition, and the maximum inhibition efficiency of 100 mg/L is below 60%. However, the mixture of WGHE/SDBS has better inhibitive performance, and the maximum inhibition efficiency can reach as high as 95%. The corresponding synergism parameter is higher than 1, and the optimum concentration ratio is 1:1, but decreases at relatively higher temperatures. The adsorption of WGHE follows Freundlich isotherm, while SDBS and WGHE/SDBS obey Langmuir isotherm. Comparing with individual WGHE or SDBS, WGHE/SDBS inhibits both cathodic and anodic reactions simultaneously to more extent, and further increases charge transfer resistance for CRS corrosion. SEM and AFM microphotographs confirm that WGHE/SDBS exhibits greater inhibitive ability on CRS surface than individual inhibitor. XPS analysis confirms the adsorption of inhibitor molecules containing O and N atoms in WGHE on CRS surface. The synergistic inhibited CRS surface has superior hydrophobic properties with a larger obtuse contact angle. There is also a synergism between SDBS and the major components of rutin, quercetin and 1-methylnaphoqinone in WGHE, but their synergistic inhibition degree is a little weaker than WGHE/SDBS.