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Investigation into the Inhibition of pitting corrosion in mild steel around heavy salt deposits by some selected secondary plant metabolites-alkaloid extract (AESML), saponin extract (SESML and flavonoid extract (FESML) of natural product origin-Strongylodon macrobotrys was successfully completed with the aid of electrochemical impedance spectroscopy, potentiody-namic polarization, gravimetric and gasometric experimentation. The research proved that the selected secondary plant metabolites were excellent in-hibitors of mild steel in the salt water environment as inhibition efficiency was recorded at 99.2%, 92.6% and 84.7% for AESML, SESML and FESML. The inhibitors showed higher inhibition at lower temperature due to frequent scale redeposition from agitation in temperature rise and loss in collision of the molecules. The potentiodynamic polarization result confirmed the reduction in the loss of electrons at the anode by the inhibitors that would have trigger oxidation reaction that causes the anode to corrode. Charge transfer resistance reflected the maximum inhibition efficiency obtained for mild steel at maximum concentration and the decrease in double layer capacitance is due to the decrease of the area where electrolyte is present due to the formation of inhibitor film. Thermodynamic investigation shows that the inhibitor has the potential of increasing the energy of the intermediate, reducing both the number of collisions, and number of particles that have enough energy to react and also number of corrosion reaction particles with the correct orientation. The adsorption isotherm consideration shows physical adsorption me-How to cite this paper: Ugi, B.U., Bassey,

Taraxacum officinale leaves were extracted of its phytochemical compounds (crude saponins, flavonoids and alkaloids) and used in the investigation of corrosion inhibitor of stainless steel in the presence of HCl acid solutions using methods ranging from weight loss, thermometric, potentiodynamic polarization and electrochemical impedance spectroscopy. The weight loss results revealed that the plant extracts are good corrosion inhibitors to the exposed metal. Electrochemical polarization data revealed a mixed mode of inhibition and the results of electrochemical impedance spectroscopy have shown that the change in the impedance parameter (charge transfer resistance and double layer capacitance) with the change in concentration of the inhibitors was due to the adsorption of active molecules leading to the formation of a protective layer on the surface of steel. A physical adsorption mechanism was revealed from the inhibitor /metal interface and the Langmuir adsorption isotherm was well obeyed (R 2 = 0.999). The thermodynamic parameter (ΔG ads) proved inhibitors to be stabled on the metal surface and a spontaneous reaction process was recorded also.