The inhibitive action of Calendula officinalis flower heads extract for mild steel corrosion in 1 M HCl solution

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The present study provides a new application of the ethanolic extract of Calendula officinalis flower heads as a green inhibitor for corrosion of mild steel in acidic media. This corrosion inhibition activity was detected by using various methods including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, open-circuit potential (OCP) and weight loss. A concentration of 500 ppm of this extract protects efficiently mild steel by 94.88% from corrosion in 1 M HCl solution. This good anticorrosive mixture is mainly due to the presence of double bonds and hetero atoms in the components of this extract which were investigated using Fourier transform infrared (FTIR) analysis. Langmuir isotherm model is the most acceptable one to describe the extract adsorption on the surface of mild steel alloy. This adsorption is physical due to the decrease in inhibition percentage by rising temperature. The activation energy was increased as the extract concentration increased. According to the obtained polarization results, this extract works as mixed type corrosion inhibitor. The obtained EIS data confirms the inhibition behavior of this extract due to the elevation in the calculated values of the charge transfer resistance after addition of the extract to the corrosive medium. Finally, the inhibition effect of this flower extract was supported by the results of the morphology and composition analysis of the adsorbed film on the mild steel surface after immersion in the inhibited acidic solution. These results were obtained using FTIR, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX).