Potential of borage flowers aqueous extract, Borago officinalis L., against the corrosion of mild steel in phosphoric acid

Purpose - This paper aims to evaluate the inhibitive potential of borage flowers' aqueous extract (BFAE), Borago officinalis L., against the corrosion of mild steel in 1.0 M phosphoric acid. Design/methodology/approach - Evaluation was carried out by chemical hydrogen evolution (HE), mass loss (ML) and electrochemical potentiodynamic polarization (PDP) measurements. SEM-EDX analysis also was used to confirm the existence of the adsorbed film. Findings - It was found that the inhibition efficiency of BFAE increases with the increase in its concentration, but decreases with the increase in temperature. The potentiodynamic polarization curves indicated that BFAE acts as a mixed-type inhibitor with a predominantly anodic action. The adsorption of BFAE on mild steel surface was found to obey Langmuir and thermodynamic-kinetic adsorption isotherms by forming a thin film on the metal surface. SEM-EDX analysis confirms the corrosion inhibition ability of BFEA in 1.0 M H3PO4 by forming a thin film on mild steel surface. In this study, the inhibitive action of BFAE components is discussed on the basis of the physical adsorption mechanism. The same results were obtained for both the freshly prepared extract and the one that kept in a refrigerator for one year. Originality/value - This paper indicates that BFAE can act as a good inhibitor for the corrosion of mild steel in 1.0 M H3PO4 even after one year of preparation.