Comparative study on Corrosion Inhibition of Vietnam Orange Peel Essential Oil with Urotropine and Insight of Corrosion Inhibition Mechanism for Mild Steel in Hydrochloric Solution

Abstract

The corrosion inhibiting mechanism of Vietnam orange peel essential oil (OPEO) for mild steel in 1 N HCl solution was investigated elaborately. Corrosion inhibition ability of OPEO was characterized by electrochemical polarization, electrochemical impedance spectroscopy (EIS), and weight loss method. In the corrosive solution, OPEO worked as a mixed inhibitor and the inhibition efficiency of OPEO increased with the increase of its concentration. High inhibition efficiencies over 90% were achieved for the concentration of 3 - 4 g/L OPEO, comparable to that of 3.5 g/L urotropine (URO), a commercial corrosion inhibitor for acid media used in industry. By using adsorption isotherm models (Langmuir, Temkin and Frumkin), thermodynamic parameters of adsorption were calculated. The obtained results indicated physical adsorption mechanism of OPEO on the steel surface. The components responsible for the corrosion inhibition activity of OPEO were not only D-limonene, but also other compounds, which contain C=O, C=C, O-H, C-O-C, -C=CH and C-H bonding groups in the molecules.

Fig. 1. Polarization curves of the mild steel in 1N HCl solution without and with different concentration (1÷4 g/L) of OPEO and 3.5 g/L URO

Fig. 2. The inhibition efficiency of OPEO and URO for the mild steel in the 1N HCl acid after different immersion times

Fig. 3. SEM images of the mild steel surface before and after 1h of exposure in 1N HCl acid at 25 °C: (A) before; (B) after corrosion in the blank solution; (C) after corrosion in the presence of 3 g/L OPEO; and (D) after corrosion in the presence of 3.5 g/L URO

Fig. 5. Dependence of surface coverage of the mild steel on the concentration of OPEO added in the test solutions.

Fig. 6. Isotherm adsorption of inhibitor on the surface of the mild steel in 1N HCl at different temperatures: (A) Langmuir isotherm; (B) Temkin isotherm and (C) Frumkin isotherm

Fig. 7. SEM images of the mild steel surface before and after 1h of exposure in acid 1N HCl with and without 3 g/L OPEO at 25°C: (A) pristine; (B) after corrosion in the blank solution; (C) and (D) after corrosion in the blank solution followed by rinsing; (E) after corrosion in the presence of OPEO; and (F) after corrosion in the presence of OPEO followed by rinsing

Fig. 8. FTIR spectrum in the region of 400-4000 cm^-1 of the film formed on the mild steel surface after 24 hour immersed in 1N HCl solution with 3 g/L OPEO at 25°C

Fig. 9. The adsorption model of OPEO on the mild steel surface

Fig. 4. (A) Nyquist plots of the mild steel in 1N HCl solutions in the absence and presence of OPEO with various concentrations (1÷4 g/L); (B) Relevant equivalent circuit model used for fitting measured impedance data. R_s is solution resistance; R_ct is charge transfer resistance; CPE is the constant phase element; R_L and L are inductive parameters

Table 1. The composition of OPEO analyzed by GCMS method

Table 2. Potentiodynamic polarization parameters for the mild steel in 1N HCl solution with and without inhibitors.

Table 3. EIS parameters for the mild steel in 1N HCl solution in the absence and presence of OPEO fitted by the equivalent circuit

Table 4. The adsorption-desorption equilibrium constant K (M^-1) and adsorption free energy ΔG_ads calculated Langmuir and Temkin models

Table 5. The compositions of the mild steel surface before and after corrosion in the test solutions in the absence andpresence of 3 g/L OPEO inhibitor.

Table 6. Data analysis of FTIR spectrum of the absorption film formed on the steel surface