Corrosion Inhibition of Mild Steel by Citrus Sinensis (Orange) Leaves Extract in Hcl/H2SO4 Acid Medium

Mild steel is one of the most important alloys in existence and has a wild variety of industrial applications. However, it corrodes due to such factors as acidified moisture in the environment. Studies on mild steel surface reactions in acidified moisture has been the subject of investigation due to areas of applications of mild steel for durability in performance and in service (Cheng et al., 2007). Typical situations where inhibitors have been applied in other to mitigate corrosion are in the chemical process industries, textile wet processing plants, marine, oil and gas industries (Benabdellah et al., 2006; Bouklah et al., 2004). Many of synthesized organic compounds, such as amines (Fouda et al., 2005), triazoles (Bentiss et al., 1999), fatty acids (Loto et al., 2012), have been investigated as corrosion inhibitors for steel in acid media. However, plant extracts have continued to attract attention in research where in recent times, corrosion inhibition effect on metals by organic compound extracts from natural sources as plants otherwise called “green inhibitors” have been the focus of researchers. The plant extracts are primarily organic compounds composed of carbon, nitrogen, Abstract: In this work, citrus sinensis leaves extract was used as inhibitor in 1M HCl and 0.5M H2SO4 solution on mild steel. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were carried out on the inhibitor extract at 30°C. The mild steel was analyzed using Scanning Electron Microscopy (SEM). Density Functional Theory (DFT) – based quantum chemical computations involving EHOMO, ELUMO and ELUMO-HOMO were correlated to determine the interaction between the inhibitors and the corroding metals surfaces. Molecular dynamic stimulation of the reaction between the inhibitor molecules and the corroding metal surfaces were performed using Forcite quench molecular dynamics. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) showed that the extracts from citrus sinensis L. acts as bio-inhibitor in the acidic media. The results showed that increase in the concentration of the inhibitor up to 50 mg/L at 30°C, increased the efficiency of corrosion inhibition of mild steel. Polarization profiles for mild steel in 1 M HCl and 0.5 M H2SO4 in the absence and presence of citrus sinensis L. extracts showed that cathodic and anodic curves were very much polarized. Both the cathodic βc and anodic βa current values were retarded. This indicated that the citrus sinensis leaves extract influenced both the cathodic and anodic reaction and hence the addition of citrus sinensis leaves extract reduced the metal dissolution and rate of hydrogen evolution reaction on mild steel surface. Nyquist plots for mild steel in 1 M HCl and 0.5 M H2SO4 in the absence and presence of extracts from citrus sinensis L. , have shown that the two environments were significantly altered after the addition of extracts from citrus sinensis L. into the test solutions. The diameter of the capacitive loop increased with increase in inhibitor concentration which was significant in the acid solution containing citrus sinensis leaves extract. The inhibiting effect may be attributed to the presence of adsorbed organic compounds from the extract on the surface of the mild steel which formed a protective thin film on the surface of the mild steel.