Corrosion Inhibition of Mild Steel in Hydrochloric Acid Environments Containing Sonneratia caseolaris Leaf Extract

Sonneratia caseolaris leaf extract was characterized for its mitigation of the electrochemical corrosion of steel in naturally aerated hydrochloric acid environments by electrochemical methods and surface analysis. The presence of S. caseolaris leaf extract (SCLE) in the hydrochloric acid medium ameliorated the corrosion resistance of steel via the adsorption of SCLE species to form a barrier layer. The improved inhibition effectiveness was demonstrated to be independent of the SCLE concentration and the corrosive environment. The highest inhibition performance of approximately 98% was reached for steel in a 1 M HCl medium containing 2500 ppm SCLE. The performance significantly decreased with a decrease in the HCl concentration from 1.00 to 0.01 M with the same SCLE concentration. In addition, severe corrosion occurred on the uninhibited steel surface but was significantly reduced on the inhibited steel surface. The analyzed results also indicated the existence of electronegative functional groups in SCLE, which could promote the adsorption process for the self-formation of the barrier layer on the steel surface. The work reported herein suggested a powerful strategy to mitigate electrochemical corrosion by adding an effective new inhibitor to achieve a green inhibitor system.

Experimental and DFT studies on the ultrasonic energy-assisted extraction of the phytochemicals of Catharanthus roseus as green corrosion inhibitors for mild steel in NaCl medium

Catharanthus roseus (Apocynaceae family) extract is rich in organic phytochemicals such as alkaloids, polyphenolic compounds, and flavonoids. It contains several functional entities such as fused heterocycles, and hydroxyl and carbonyl groups, which could be useful for corrosion inhibition of mild steel in NaCl environments. In the present work, ultrasonic energy was used to obtain the ethanolic extracts of root and stem which were then tested as corrosion inhibitors for mild steel in the presence of 3.5% NaCl. The corrosion inhibition process was studied by UV-visible spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, weight loss, and electrochemical methods. After immersing in the corrosive medium, the microstructures of mild steel were investigated by scanning electron microscopy, X-ray diffraction, and ellipsometry. The extract of C. roseus showed excellent adsorption on mild steel surface as confirmed by DFT calculations. The results indicate that the extract of C. roseus acts as a mixed type corrosion inhibitor, where the stem extract is the most efficient inhibitor in 3.5% NaCl solution possibly due to the higher active area of stem phytochemicals.

C. roseus phytochemicals are physisorbed on the 111 Fe surface, and the oxygen non-bonding electron chemisorbed on the polarized state 111 Fe surface.