Research Article | Open Access
Cuminum cyminum Extracts as Eco-Friendly Corrosion Inhibitor for Mild Steel in Seawater
The inhibitive effect of Jeera (Cuminum cyminum) plant extracts on the corrosion of mild steel in an aqueous solution of seawater was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The stability of the inhibition efficiency of Jeera extracts was examined by weight-loss method. Potentiodynamic polarization curves indicated that the Jeera extract behaves as an anodic type inhibitor. EIS measurements showed that the dissolution process occurs under activation control. The corrosion rates of steel and the inhibition efficiencies of the extract obtained from impedance and polarization measurements were in good agreement. Inhibition was found to increase with an increasing concentration of the plant extract. The results obtained show that the Jeera extract could serve as an effective inhibitor for the corrosion of mild steel in seawater.
Recently, plant extracts have again become important as an environmentally acceptable, readily available, and renewable source for a wide range of needed inhibitors. Plant extracts are viewed as an incredibly rich source of naturally synthesized chemical compounds that can be extracted by simple procedures with low cost. However, synergistic (and antagonistic) effects are often expected with these mixtures of inhibitors that may affect their inhibition efficiency. Several investigations have been reported using such economic plant extracts. El Hosary et al.  studied the corrosion inhibition of aluminium and zinc in 2 N HCl using naturally occurring Hibiscus sabdariffa (Karkade) extract. The inhibition of corrosion of steel, aluminium, and copper in HCl, H2SO4, and citric acid by molasses was also studied , and 83% and 13% inhibition efficiencies were obtained for HCl and H2SO4 solutions, respectively, containing 0.75% molasses. Loto reported the inhibitive action of Vernonia amygdalina (bitter leaf) on the corrosion of mild steel in 0.5 M HCl at 28°C . Avwiri and Igho studied the inhibitive action of V. amygdalina on the corrosion of aluminium alloys in HCl and HNO3 at concentrations of 0.2 and 0.4 g/L at 29°C . They showed that the solution extract of the leaves serves as an excellent inhibitor. The inhibition effect of Zanthoxylum alatum plant extract on the corrosion of mild steel in 20%, 50%, and 88% aqueous orthophosphoric acid has been investigated by weight loss and electrochemical impedance spectroscopy (EIS). Plant extract was found to reduce the corrosion of steel more effectively in 88% than in 20% phosphoric acid . An inhibition efficiency of 75.11% was observed with the extract of the leaves of Nypa fruticans Wurmb  for the corrosion of mild steel in hydrochloric acid solutions. El-Etre et al. examined some naturally occurring substances as corrosion inhibitors for different metals in various environments [7–11].
The application of extracts of henna, thyme, bgugaine, and inriine was investigated for their anticorrosion activity [12–15]. The effect of addition of bgugaine on steel corrosion in HCl is patented . Saleh and El-Hosaray studied the peel of pomegranate  and beetroot [18, 19] as corrosion inhibitor for mild steel in acid media. Sanghvi et al. have investigated the anticorrosion activity of Emblica officinalis, Terminalia chebula, Terminalia bolivia , Sapindus trifoliatus, and Acacia concinna . Corrosion inhibition has also been studied for the extracts of Swertia angustifolia , Eucalyptus leaves , Eugenia jambolana , Pongamia glabra, Annona squamosa , Acacia arabica , Carica papaya , Azadirachta indica , and Vernonia amygdalina  for steel in acid media. The anticorrosion effect of Andrographis paniculata  and tea wastes  has been reported from our laboratories. Kliskic et al. analyzed aqueous extract of Rosmarinus officinalis  as corrosion inhibitor for aluminium alloy corrosion in chloride solution. Guar gum was analyzed for its anticorrosion activity by Abdallah . Martinez and Stern have studied the inhibitory mechanism of low carbon steel corrosion of mimosa tannin in H2SO4 media . Oguzie investigated the efficiency of Telfairia occidentalis extract as corrosion inhibitor in both HCl and H2SO4 media . The extracts of chamomile, halfabar, black cumin, and kidney bean were analyzed for their inhibitive action of corrosion of steel in acid media by Abdel-Gaber et al. . El-Hosary et al.  studied the corrosion inhibition of aluminium and zinc in HCl using Hibiscus sabdariffa extract. Rajendran et al. [38, 39] studied the corrosion inhibition of aluminium in rain water containing garlic extract. Aqueous extracts of rhizome powder , beet root extract , and Hibiscus rosa-sinensis have been used as corrosion inhibitors.
The present work is to examine the aqueous Jeera extract as an inhibitor for corrosion of carbon steel in solution-containing seawater. Weight loss measurements, potentiodynamic polarization, fluorescence, and UV-spectroscopy are used to study surface film formed on the metal surface.
2.1. Preparation of Plant Extract of Jeera Extract
An aqueous plant extract was prepared by grinding 10 g of (Cuminum cyminum) extract, filtering, and making up to 100 using double distilled water.
2.2. Preparation of Specimens
Carbon steel specimens (0.0267% S, 0.06% P, 0.4% Mn, 0.1% C, and the rest iron) of dimensions 1.0 cm 4.0 cm 0.2 cm were polished to a mirror finish and degreased with trichloroethylene.
2.3. Weight Loss Method
Relevant data of seawater used in the study are given in Table 1.
Carbon steel specimens in triplicate were immersed in 100 mL of the solutions containing various concentrations of the inhibitor for one day. The weight of the specimens before and after immersion was determined using Shimadzu balance, model AY 62. The corrosion products were cleansed with Clarke’s solution . The inhibition efficiency (IE) was then calculated using where = corrosion rate in the absence of the inhibitor, and = corrosion rate in the presence of the inhibitor.
2.4. Surface Examination
The carbon steel specimens were immersed in various test solutions for a period of one day, taken out, and dried. The nature of the film formed on the surface of metal specimens was analyzed by FTIR spectroscopic study.
2.4.1. FTIR Spectra
FTIR spectra were recorded in a Perkin-Elmer 1600 spectrophotometer. The film was carefully removed and mixed thoroughly with KBr made in to pellets, and FTIR spectra were recorded.
The fluorescence spectra of the film formed on the CS samples recorded with a Hitachi F-4500 fluorescence spectrophotometer.
2.5. Potentiodynamic Polarization
A three-electrode cell consisting of mild steel as working electrode (WE), a platinum wire counter electrode (CE), and a saturated reference electrode was used for measurements. All the potential values reported here were VS SCE. The working electrode was mechanically polished on various grades of emery sheet, rinsed with double distilled water, and degreased with trichloroethylene. Potentiodynamic polarization curves were recorded using an H and CH electrochemical work station impedance analyzer model CHI 660A provided with iR compensation option. Polarization curve measurements were carried out at scan rate of 0.01 V s−1. The exposed area (1 cm2) was mechanically polished with a series of emery sheets of variable grades. The samples were washed thoroughly with double distilled water before insertion in the cell. During the polarization study, the scan rate was 0.01 V s−1, hold time at Ef was 0 s, and quiet time was 2 s.
2.6. Ac Impedance Measurements
The instrument used for polarization was used for AC impedance study also. The cell set-up was the same as that had been used for polarization measurements. The real part and imaginary part of the cell impedance were measured in ohms at various frequencies. The values of charge transfer resistance, , and the double layer capacitance, , were calculated. The equivalent electrical circuit diagram is shown in Figure 7.
3. Result and Discussion
3.1. Analysis of Results from Weight Loss Method
Table 2 shows the values of corrosion rates and inhibition efficiencies obtained from weight loss measurements of different concentrations of Jeera extract. 4 mL of the Jeera extract offered 93% corrosion inhibition efficiency to carbon steel immersed in 100 ml solution containing seawater. When the concentration of Jeera extract was increased, the inhibition efficiency decreased, and the corrosion rate increased, and this is due to the fact that when higher concentrations of Jeera extract are added, the protective film (Fe2+-Cuminum cyminum complex) formed on the metal surface goes in to the solution and thus destroying the protective film. It may be considered that the protective film formed may go into transpassive state, where the film is broken .
3.2. Analysis of Polarization Curves
A polarization study has been used to detect the formation of protective film on the metal surface . When a protective film formed on the metal surface, the linear polarization resistance (LPR) increases, and the corrosion current decreases. The potentiodynamic polarization curves of carbon steel immersed in various test solution are shown in Figure 1. The corrosion parameters, namely, corrosion potential tafel slopes ( = cathodic; = anodic), linear polarization resistance (LPR), and the corrosion current are given in Table 3 when carbon steel is immersed in seawater. The corrosion potential of seawater is −926 mV VS SCE. The formulation consisting of 4 mL of Jeera extract in presence of seawater solution shifts the corrosion potential −883 mV VS SCE. This suggested that anodic reaction is controlled predominantly. The (LPR) value increases from 51.67 10−2 to 63.67 10−2 ohm cm2. This suggests that a protective film is formed on the metal surface. Further the corrosion current decreases from 7.963 10−6 to 6.295 10−6 Acm2 [45, 46].
3.3. Analysis of Ac Impedance Spectra
AC impedance spectra have been used to detect the formation of the film formed on the metal surface. If the protective film is formed, the charges transfer resistance increases, and double layer capacitance value decreases . The AC impedance spectra of carbon steel immersed in various solutions are shown in Figure 2 (Nyquist) and Figure 3 (impedance-Bode plots). The AC impedance parameter, namely, charge transfer resistance and double layer capacitance are given in Table 4.
When carbon steel is immersed in aqueous solution containing seawater, the value is 88 ohm cm2, and value is 1.027 10−7 F/cm2. When 4 ml of (Cuminum cyminum) extract is added, the value increases from 88 ohm cm2 to 116 ohm cm2, and value decreases from 1.027 10−7 F/cm2 to 0.7817 10−8. This suggest that a protective film is formed on the metal surface of the metal. Further there is increase in impedance log (Z/ohm), value from 2.02 to 2.12 (derived from Bode plot shown in Figure 3).
3.4. Fourier Transfer-Infrared Spectra
The Cuminum cyminum extract was evaporated to dryness to a solid mass. Its FTIR spectrum is shown in Figure 4(a). –C=C stretching frequency appeared at 2141 cm−1. The aromatic –CH stretching frequency appeared at 2927 cm−1. –C=O stretching frequency appeared at 1607 cm−1 [48, 49].
The FTIR spectrum of the protective film formed on the surface of the metal after immersion in the aqueous solution containing seawater and Seawater containing 4 mL of Jeera extract is shown in Figure 4(b). –OH stretching frequency appeared at 3402 cm−1 to 3435 cm−1. –C=C stretching frequency appeared at 2141 cm−1 to 2091 cm−1. The aromatic –CH stretching frequency appeared at 2927 cm−1 to 2923 cm−1. –C=O stretching frequency appeared at 1607 cm−1 to 1638 cm−1.
3.5. Fluorescence Spectra
The UV-visible adsorption spectrum of aqueous solution of Cuminum cyminum and Fe2+ is shown in Figure 5. Peaks appear at 228 nm, 268 nm. When the Fe2+ sis added to the aqueous solution of Cuminum cyminum, peak appears at 225 nm and 265 mm .
The fluorescence spectrum = 225 nm) of an aqueous solution of Fe2+-Cuminum cyminum is shown in Figure 6(a). A peak appears at 252 nm. This due to that Fe2+-active principle complex is formed in solution .
The fluorescence spectrum of the film formed on the surface of the metal after immersion in the solution containing seawater and 4 ml of Cuminum cyminum extract is shown in Figure 6(b). The peaks appeared at 252 nm confirming the presence of Fe2+-Cuminum cyminum extract complex formed on the metal surface.
The corrosion inhibition by aqueous solution of Jeera extract in the presence and absence of inhibitor was studied by weight-loss study and electrochemical measurements. The results show that inhibitor has the ability of reducing the corrosion rate of carbon steel in aqueous solution containing Jeera extract, and it acts as an anodic inhibitor. This effectiveness is confirmed by electrochemical impedance spectra and potential polarization analysis.
The authors are thankful to DRDO, India, for help and encouragement and to Mrs R. Nagalakshmi for useful suggestions.
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