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Natural extracts have been widely used to protect metal materials from corrosion. Mild steel (MS) corrosion inhibition in 0.5 M sulfuric acid was investigated in the absence and presence of Thyme leaf extracts as an economical corrosion inhibitor. The effects of various concentrations and different temperatures on inhibitor efficacy were investigated. Using electrochemical impedance spectroscopy and polarization curves, the corrosion resistance of the alloy was also estimated. The polarization technique indicated that the Thyme extract is a mixed‐type inhibitor for MS in 0.5 M H2SO4. The obtained results revealed an excellent inhibition efficiency of 98% at 200 ppm of Thyme concentration. The thermodynamic parameters calculated, the effects of temperature, and the adsorption mechanism were also investigated, that suggested formation of monolayer inhibitor molecules (i.e. the Langmuir adsorption isotherm) on the metal surface. The ∆Gadso value calculated from the Langmuir adsorption isotherm plots for inhibitor indicated that it was adsorbed on the alloy surface via a physisorption mechanism. Additional studies on plant extracts as corrosion inhibitors on metals are needed to produce solutions for industrial purposes.

The current study includes a systematic examination of copper corrosion initially in each of NaCl and Na2SO4 solutions separately and then in the mixture solution of Cl− and SO42− ions as aggressive ions. Electrochemical current noise (ECN) signals resulting from asymmetric (Asy) as well as symmetric (Sym) cells have been interpreted using wavelet transform (WT) along with statistical procedures. The signals have been detrended and the decomposition of every signal has been carried out into 8 crystals. Then the standard deviation of every crystal has been illustrated with the standard deviation of partial signal (SDPS) plots. The Asy electrodes increased the pitting detection on copper compared with the Sym ones, indicating higher efficiency of the Asy electrodes. Asymmetric-copper electrodes have been studied using SDPS plots at different temperatures (40, 60, as well as 80 °C). Finally, in order to partly understand the effect of Cl− and SO42− ions on the corrosion of copper, the stabilization of Cu2+ cations by Cl− and SO42− ions in aqueous solutions have been modeled by DFT calculations. The derived results are in accordance with the experimental data.

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