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Corrosion inhibition behavior of crude alkaloids and flavonoids extracts of Ocimum tenuiflorum roots on the corrosion of high carbon steel in hydrogen chloride acid environment was studied using thermometric, electrochemical impedance spectroscopy and potentiodynamic polarization techniques. The phytocompounds showed excellent corrosion retardation ability on the high carbon steel metal in HCl acid environment. The alkaloids demonstrated a more reliable inhibition efficacy compared to flavonoids extracts with maximum inhibition efficiency of 98.1% and 93.6% respectively at a maximum concentration of 2.0 g/L. There was a noticeable increase in inhibition mitigation potential of the inhibitors with increasing concentration of extracts. A physical adsorption mechanism was recorded by the inhibitor and the Langmuir adsorption isotherm was well obeyed with correlation coefficient (R 2) at approximately 0.999. Results of electrochemical impedance spectroscopy and potentiodynamic polarization confirmed the strong adsorption of the inhibitors on the steel surface through the values of charge transfer resistance and corrosion current densities. The inhibitors proved to be stable ones on the metal and a spontaneous reaction process was recorded from the data derived from the Gibbs free energy of adsorption.

The corrosion and inhibition behavior of carbon steel in hydrogen tetraoxosulphate (IV) acid rich area in the presence of crude saponins and alkaloids extracts of Agrimonia eupatoria leaves have been studied using mass loss and potentiodynamic polarization techniques. The extracts presented good inhibition ability on the carbon steel metal in hydrogen tetraoxosulphate (IV) acid environment with the alkaloids inhibiting more compared to saponins with maximum inhibition efficiency of 97.6 % and 87.8 % respectively at 7.5 g/L concentration. There was a noticeable increase in inhibition mitigation potential of the inhibitors with increasing concentration of extracts. A physical adsorption mechanism was recorded by the inhibitor/carbon steel interface and the Langmuir adsorption isotherm was well obeyed with correlation coefficient at approximately unity. The inhibitors proved to be stable ones on the metal and a spontaneous reaction process was recorded from the data of the Gibbs free energy of adsorption.

The corrosion inhibition of Cu-Zn-Fe alloy in hydrochloric acid medium by crude ethanol extracts from roots-leaves synergy of Solanum melongena have been studied with chemical methods (mass loss and gasometric methods). At 3.0 grams per litre concentration of the roots-leaves synergy of Solanum melongena, it was observed that a 98.8 % inhibition efficiency was recorded as corrosion rate of alloy was decreasing with inhibitor increase. Temperature evaluation on the inhibitor showed 99.2 > 88.4 > 85.6 % as trial was conducted from 303-323 respectively, and in respect to increasing concentration, corrosion rate was found to be 1.718 > 0.013, 0.0192 and 0.247 at 303, 313 and 323 respectively. All these present a good result for the synergistic inhibitor and a proof of its efficiency in controlling the corrosion of Cu-Zn-Fe alloy in hydrochloric acid medium. Inhibition mechanism was deduced from the activation and thermodynamic parameters that govern the process. Adsorption of extract on the Cu-Zn-Fe alloy was found to obey the Langmuir adsorption isotherm. The phenomenon of physical adsorption is proposed from the obtained thermodynamic parameters.

The study on the action of Acetylcholine and Rivastigmine as Corrosion Inhibitors of Cu – Sn - Zn – Pb Alloy in Hydrochloric Acid Environment was carried out using density functional theory, electrochemical impedance spectroscopy, Potentiodynamic polarization, Scanning electron microscopy and weight loss. The result revealed that both Acetylcholine and Rivastigmine expired drugs were good inhibitors of Cu – Sn - Zn – Pb Alloy in Hydrochloric Acid Environment. This was confirmed from results of weight loss (99.1 % and 95.0 %), electrochemical impedance spectroscopy (EIS) (92.5 % and 91.8 %), and Potentiodynamic polarization (97.4 % and 87.1 %). Both inhibitors were able to increase the charge transfer resistance and corrosion current densities of the electrical solution and reduce the double layer capacitance of the metal – solution interface. Inhibition was as a result of adsorption of inhibitor molecules on the Cu – Sn - Zn – Pb surface. Thermodynamically, inhibitors showed greater stability on metal surface, spontaneous in the forward direction and reduction in level of disorderliness. Inhibitors demonstrated a mixed type inhibition while physical adsorption mechanism was proposed for the inhibitor – metal interaction. Langmuir adsorption isotherm was obeyed as data fitted adequately to the isotherm and regression coefficient was approximately unity. A monolayer adsorption was deduces.