Tween-40 as corrosion inhibitor for cold rolled steel in sulphuric acid: Weight loss study, electrochemical characterization, and AFM

Berberine was abstracted from coptis chinensis and its inhibition efficiency on corrosion of mild steel in 1 M H2SO4 was investigated through weight loss experiment, electrochemical techniques and scanning electronic microscope (SEM) with energy dispersespectrometer(EDS).Theweight loss resultsshowedthat berberineisanexcellentcorrosioninhibitor formild steelimmersed in1 MH2SO4.Potentiodynamiccurves suggestedthatberberinesuppressedbothcathodicandanodicprocesses for itsconcentrations higher than 1.0 10 4 M and mainly cathodic reaction was suppressed for lower concentrations. The Nyquist diagrams of impedance for mild steel in 1 M H2SO4 containing berberine with different concentrations showed one capacitive loop, and the polarization resistance increasedwiththe inhibitor concentration rising.Agood fit to Flory–Huggins isothermwasobtained between surface coverage degree and inhibitor concentration. The surface morphology andEDSanalysis for mild steel specimens in sulfuric acid in the absence and presence of the inhibitor also proved the results obtained by theweight loss and electrochemical experiments. The correlation of inhibition effect and molecular structure of berberine was then discussed by quantum chemistry study.