Inhibition effect of Brugmansia suaveolens (BS) and Cassia roxburghii (CR) on mild carbon steel in 1.0 M HCl solution was studied. Inhibition efficiency of plant extracts were carried out by using chemical (weight loss method) and electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy). The effect of temperature on the corrosion behavior of mild carbon steel in 1.0 M HCl with addition of plant extracts was studied in the temperature range of 300-320 ± 1 K. Inhibition efficiencies up to 94.69 for BS and 93.22 for CR can be obtained. The adsorption mechanism of inhibition was supported by FT-IR, surface analysis (SEM-EDS), and adsorption isotherms. The thermodynamic parameter values of free energy of adsorption (DG ads ) reveal that inhibitor was adsorbed on the mild carbon steel surface via both physisorption and chemisorption mechanisms.

The influences of Polycarpaea corymbosa (PC) and Desmodium triflorum (DT) leaf extracts on the corrosion behavior of mild steel (MS) in 1.0 M HCl was investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements. The effect of temperature on the corrosion behavior of MS in 1.0 M HCl with the addition of plant extracts was studied in the temperature range of 300 K-320 ± 1 K. The results revealed that PC and DT were excellent green inhibitors and the inhibition efficiencies obtained from weight loss and electrochemical experiments were in good agreement. Inhibition efficiencies up to 91.78 % for PC and 92.99 % for DT were obtained. Potentiodynamic polarization studies revealed that both the inhibitors behaved as mixed-type inhibitors. Adsorption behavior of these green inhibitors on the MS surface was found to obey the Langmuir adsorption isotherm. The thermodynamic parameter values of free energy of adsorption (DG ads ) and enthalpy of adsorption (DH ads ) revealed that each inhibitor was adsorbed on the MS surface via both chemisorption and physisorption mechanisms. The adsorption mechanism of inhibition was supported by FT-IR, UV-Visible, WAXD and SEM-EDS.

The inhibitive action of Clematis gouriana (CG) on mild steel (MS) corrosion in 1.0 M HCl solution was studied. Inhibition efficiency of CG was carried out by using various weight loss methods, potentiodynamic polarisation, and electrochemical impedance spectroscopy. Inhibition efficiencies of up to 95.70% for CG can be obtained. Adsorption of CG on the MS surface was found to obey the Langmuir adsorption isotherm. Free energy of adsorption calculated from the temperature studies revealed the possibility of both chemisorptions and physisorption. The adsorbed film on the MS surface containing the CG inhibitor was also characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope and energy-dispersive spectrum. The possible active ingredient responsible for the anticorrosion effect is identified as aporphine alkaloid which is isolated and screened for the anticorrosion effect using electrochemical studies. The possible mode of corrosion inhibition of aporphine alkaloid is also derived using FTIR studies.

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