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 Alkaloid and Non-alkaloid fractions of the ethanolic extracts from Costus afer (AECA and NAECA) were comparatively studied for their inhibitive properties on the corrosion of mild steel in 5 M HCl solution using Gravimetric and Gasometric techniques. The results revealed that both extracts inhibited the corrosion of mild steel in HCl solution following the order: NAECA > AECA. The maximum inhibition efficiencies obtained were 49.2 % for AECA and 86.4% for NAECA at an inhibitor concentration of 5 g/L. Inhibition efficiency was found to increase with increase in concentration and increase in temperature. The adsorption of both extracts on the mild steel was found to be consistent with Langmuir adsorption isotherm.Physical adsorption mechanism was proposed for the adsorption of the components of the extracts on the mild steel surface.

We present the evaluation of four Eco-friendly corrosion inhibitors for the corrosion mitigation of mild steel in acid media. The corrosion inhibition of mild steel by ethanol extracts from Viscum album (EEVA) and some of its isolated phytochemical components; phytates extract (PEVA), saponins extract (SEVA), and flavonoids extracts (FEVA) have been studied using gravimetric and gasometric techniques. The results of the study reveal that these ecofriendly and benign extracts function as good inhibitors for mild steel corrosion in sulphuric acid. Inhibition efficiency of the extracts increases with inhibitor concentration and temperature rise. The trend of inhibition efficiency in lower inhibitor concentration is EEVA > PEVA > SEVA > FEVA and at higher concentration, the order was SEVA > PEVA > EEVA > FEVA. The presence of the plant extracts decreases the corrosion activation energy in the solution which indicates chemical adsorption mechanism. The adsorption of the components of the extracts is consistent with Temkin isotherm. The interaction between the isolated extracts is synergistic at lower inhibitor concentration and antagonistic at higher concentrations. The K ads values for PEVA and SEVA are higher than those of EEVA and FEVA. This implies that PEVA and SEVA are more efficiently adsorbed on the mild steel surface.