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International Journal of ChemTech Research CODEN (USA): IJCRGG, ISSN: 0974-4290, ISSN(Online):2455-9555 Vol.10 No.4, pp 143-150, 2017
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V.Prathipa1*, A.Sahaya Raja2
1Department of chemistry, PSNA College Engineering and Technology, Dindigul, Tamilnadu, India
2PG& Research Department of Chemistry, G.T.N. Arts College, Dindigul,
Tamilnadu, India
Abstract : The corrosion and inhibition behaviors of carbon steel in the presence of L-Methionine and ZnSO4 have been studied using gravimetric method and electrochemical techniques. Results obtained by various techniques are close to each other and maximum Inhibition efficiency is 93%. Synergistic parameters and Statistical study of “F” test suggest that a synergistic effect exists between L-Methionine and Zn2+. The protective film on the metal surface has been analyzed by FT – IR spectra. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from weight loss study, electrochemical study and surface analysis technique. The inhibitor L-Methionine – Zn2+ system may find application in cooling water system.
Keywords : Carbon steel, L-Methionine, ZnSO4, synergistic effect, F-Test, FT-IR spectra.
Introduction:
Carbon steel finds a lot of application in industries like metal finishing, boiler scale removal, pickling baths etc. It gets rusted when it comes in contact with any aqueous medium. The use of inhibitors is one of the best methods for protecting metals against corrosion. Corrosion is a chemical or electrochemical process in nature with four components are: an anode, a cathode, an electrolyte and some direct electrical connection between the anode and cathode, the adsorbed inhibitor then acts to slow corrosion process by either:1.Increasing the anodic or cathodic polarization behaviour; 2.Reducing the movement or diffusion of ions to the metallic surface. Corrosion inhibitors are used to prevent the effect of corrosion in such cases. The majority of well –known inhibitors are organic compounds containing heteroatom, such as O, N, S and multiple bonds1. Most of the organic compounds are not only expensive but also toxic to both human beings and environments2 and therefore the use of hazardous chemical inhibitors is totally reduced because of environmental regulations. It is better to look for environmentally safe inhibitors. Many researchers investigated the inhibition effect of environment friendly inhibitors like amino acids on metal corrosion3-13. This is due to the fact that amino acids are non-toxic, biodegradable, relatively cheap, and completely soluble in aqueous media and produced with high purity at low cost. Various amino acids have been used to inhibit the corrosion of metals and alloys14-17. Eco–Friendly Inhibitor L–Cysteine–Zn2+ System to control corrosion of carbon steel in Aqueous Medium6. The corrosion of SS 316L has been inhibited by glycine, leucine, valine, and arginine7. Sivakumar et al have used L-Histidine to prevent corrosion on carbon steel 8. Cystein, glycine, glutamic acid, and glutathione have been used as corrosion inhibitor to prevent the corrosion of copper in HCl9. Amino acid such as DL-Phenylalanine has been used to prevent corrosion of carbon steel10 .The corrosion of brass in O2-free NaOH has been prevented by methionine11. Sahaya Raja et al have used Glycine along with Zn2+ to prevent
corrosion of carbon steel in well water12. Synergistic and Antagonistic Effect of L – Alanine for carbon steel in aqueous medium has been investigated18. Prathipa et al was studied corrosion inhibition of carbon steel using green inhibitor (L-Alanine)19. Arginine - Zn2+ system has been used to inhibit corrosion of carbon steel13, 20. L – Alanine as inhibitor for carbon steel in well water was studied21.
2. Material and Methods:
Determination of corrosion rate - All the weight of the carbon steel specimens before and after corrosion was carried out using Shimadzu Balance-AY62.Corrosion rates were calculated using the following relationship. Corrosion Rate (mm/y) = [loss in weight (mg) X 1000 / surface area of the specimen (dm2) X period of the immersion (days)] X (0.0365/ ρ).Electrochemical and Impedance measurements - Potentiodynamic polarization studies and AC Impedance measurements are carried out using CHI electrochemical impedance analyzer (model 660A Surface characterization studies- FTIR Spectra were recorded in a Perkin – Elmer 1600 spectrophotometer. All solutions were prepared using well water collected from N.S.Nagar, Dindigul, Tamil Nadu, India. The study was carried out at room temperature (303K). The chosen environmental well water and its physicochemical parameters are pH – 8.0, Conductivity 1770 µmhos/cm, TDS – 1219ppm, TH - 424ppm, Chloride – 669ppm
3. Result and discussion
3.1. Analysis of the weight loss method and Influence of Zn2+ on the inhibition efficiencies of L-Methionine
L-Methionine shows some inhibition efficiencies. 50 ppm of L-Methionine has 24 percent IE, as the concentration of L-Methionine increases, IE increases some extent but the influence of Zn2+ on the inhibition efficiencies of L-Methionine is shown in Fig - 1. It is observed that as the concentration of L-Methionine increases the IE increases. Similarly, for a given concentration of L-Methionine the IE increases as the concentration of Zn2+ increases. It is also observed that a synergistic effect exists between L-Methionine and Zn2+. For example, 5 ppm of Zn2+ has 10 percent IE; 250 ppm of L-Methionine has 59 percent IE. Interestingly their combination has a high IE, namely, 93 percent. In presence of Zn2+ more amount of L-Methionine is transported towards the metal surface. Thus the anodic reaction and cathodic reaction are controlled effectively. This accounts for the synergistic effect existing between Zn2+ and L-Methionine.
Fe-----Fe2+ + 2e- (Anodic reaction)
Fe2+ + Zn2+ - L-Methionine complex ------------ Fe2+- L-Methionine complex + Zn2+
O2 + 2H2O + 4e- ---------- 4OH- (Cathodic reaction)
Zn2+ +2OH- -----------Zn(OH)2 ↓
3.2 Synergism parameters (SI)
Synergism parameter (SI) have been used to know the synergistic effect existing between two inhibitors22-24. Synergism parameter (SI) can be calculated using the following relationship.Synergism parameters (SI) = 1-θ1+2/1-θ,1+2
Where θ1+2 = (θ1+θ2)–(θ1θ2), θ1 = Surface coverage by L-Methionine,
θ2 = Surface coverage by Zn2+ ,
θ,1+2 = Surface coverage by both L-Methionine and Zn2+,
θ = surface coverage = IE%/100
The synergism parameters of L-Methionine -Zn2+ system is shown in Fig - 1. For different concentrations of inhibitors, SI approaches 1 when no interaction between the inhibitor compounds exists. When SI > 1, it points to synergistic effects. In the case of SI < 1, it is an indication that the synergistic effect is not significant23.From Fig - 1, it is observed that value of synergism parameters (SI) calculated from surface coverage were found to be one and above. This indicates that the synergistic effect exists between L-Methionine and Zn2+ 24.Thus, the enhancement of the inhibition efficiency caused by the addition of Zn2+ ions to L-Methionine is due to the synergistic effect.
Figure – 1: Inhibition efficiencies of L-Methionine and Synergism parameters
3.3 'F'-test
To know whether the synergistic effect existing between L-Methionine and Zn2+ is statistically significant or not, F-test was used19,22-24. The results are given in Table 1. It is observed that the calculated F-value 25.04 is greater than the table value 5.32 for 8 degrees of freedom at 0.05 level of significance. Hence it is concluded that the synergistic effect existing between L-Methionine and Zn2+ (5 ppm) is statistically significant. Therefore, it is concluded that the synergistic effect existing between L-Methionine and Zn2+ (5 ppm) is statistically significant.
Table 1: Distribution of F-Value between the inhibition efficiency of various concentration of L-Methionine (0ppm of Zn2+) and the inhibition efficiencies of L-Methionine in the presence of 5 ppm of Zn2+.
Source of variance |
Sum of squares |
Degrees of freedom |
Mean square |
F-value |
Level of significance |
Between the sample |
760.5 |
1 |
760.5 |
< 0.05 |
25.04 |
Within the sample |
243 |
8 |
30.3745 |
3.4 Analysis of potentiodynamic polarization study
Polarization study has been used to confirm the formation of protective film formed on the metal surface during corrosion inhibition process6,8,10. If a protective film is formed on the metal surface, the corrosion current value (Icorr) decreases. The potentiodynamic polarization curves of carbon steel immersed in well water in the absence and presence of inhibitors are shown in Fig-2. The corrosion parameters are given in Table 2. When carbon steel was immersed in well water the corrosion potential was -680 mV vs SCE. When L-Methionine (250 ppm ) and Zn2+ (5 ppm) were added to the above system the corrosion potential shifted to -699 mV vs SCE. This suggests that a protective film is formed on the metal surface. Further the corrosion current decreases from 8.476 x10-6 A/cm2 to 5.956 X10-6. Thus polarization study confirms the formation of a protective film on the metal surface.
Table 2: Corrosion parameters of carbon steel immersed in well water in the absence and presence of inhibitor system obtained from potentiodynamic polarization study
System |
Tafel Results |
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Ecorr mV vs SCE |
Icorr A/cm2 |
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Well water |
-680 |
8.476 x10-6 |
Well water+ L-Methionine (250ppm)+ Zn2+ (5ppm) |
-699 |
5.956 X10-6 |
a) Well water (Blank) b) Well water + L- Methionine (250 ppm) + Zn2+ (5 ppm)
Fig 2: Polarization curves of carbon steel immersed in various test solutions
3.5 Analysis of AC Impedance spectra
AC impedance spectra (electro chemical impedance spectra) have been used to confirm the formation of protective film on the metal surface11,13. If a protective film is formed on the metal surface, charge transfer resistance (Rt) increases; double layer capacitance value (Cdl) decreases. The AC impedance spectra of carbon steel immersed in well water in the absence and presence of inhibitors (L-Methionine -Zn2+) are shown in Fig-3 (Nyquist plot). The AC impedance parameters namely charge transfer resistance (Rt) and double layer capacitance (Cdl) derived from Nyquist plot are given in Table 3. It is observed that when the inhibitors (L-Methionine (250 ppm) +Zn2+ (5 ppm)) are added the charge transfer resistance (Rt) increases from 1184 Ω cm2 to 1830 Ω cm2. The Cdl value decreases from 1.6297x10-9 F/cm2 to 1.0544x10-9 F/cm2. These results lead to the conclusion that a protective film is formed on the metal surface.
Table 3: Corrosion parameters of carbon steel immersed in well water in the absence and presence of inhibitor system obtained from AC impedance spectra.
System |
Nyquist plot |
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Rt Ω cm2 |
Cdl F/cm2 |
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Well water |
1184 |
1.6297x10-9 |
Well water+ L-Methionine (250ppm)+Zn2+ (5ppm) |
1830 |
1.0544x10-9 |
a) Well water (Blank) b)Well water + L- Methionine (250 ppm) + Zn2+ (5 ppm)
Fig 3: AC impedance spectra of carbon steel immersed in various test solutions (Nyquist plots)
3.6 Analysis of FTIR spectra
Analysis of FTIR spectra are given the Table 4. FTIR spectra have been used to analyze the protective film formed on the metal surface 19-25. The FTIR spectrum (KBr) of pure L-Methionine is shown in Fig.4 (a). The C=O stretching frequency of carboxyl group appears at 1598 cm-1. The CN stretching frequency appears at 1049 cm-1. The SH stretching frequency appears at 2365 cm-1. The NH stretching frequency of the amine group appears at 2926 cm-1 26-28. The FTIR spectrum of the film formed on the metal surface after immersion in the solution containing well water, 250 ppm of L-Methionine and 5 ppm Zn2+ is shown in Fig.4 (b). The C=O stretching frequency has shifted from 1598 to 1591 cm-1. The CN stretching frequency has shifted from 1049 to 1020 cm-1. The NH stretching frequency has shifted from 2926 to 2923 cm-1. The SH stretching frequency has shifted from 2365 to 2177 cm-1.This observation suggests that L-Methionine has coordinated with Fe2+ through the oxygen atom of the carboxyl group, nitrogen atom of the amine group and the sulphur atom of the thiol group resulting in the formation of Fe2+ - L-Methionine complex on the metal surface. The peak at 706cm-1 corresponds to Zn-O stretching. The peak at 3427 cm-1 is due to OH- stretching. This confirms that Zn(OH)2 is formed on the metal surface19. Thus the FTIR spectral study leads to the conclusion that the protective film consist of Fe2+- L-Methionine complex and Zn(OH)2.
Table 4: Analysis of FTIR spectra
Fourier transform infrared spectroscopy |
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Functional group |
Frequency (cm-1) |
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FTIR spectrum of pure L – Methionine |
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C=O stretching |
1598 cm-1. |
|
CN stretching |
1049 cm-1. |
|
NH stretching |
2926 cm-1 |
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SH stretching |
2365 cm-1. |
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FTIR spectrum of the film formed on the metal surface after immersion in the solution containing well water, 250 ppm of L-Methionine and 5 ppm Zn2+ |
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Functional group |
Frequency (cm-1) shifted from |
Frequency (cm-1) shifted to |
C=O stretching |
1598 cm-1. |
1591 cm-1 |
CN stretching |
1049 cm-1 |
1020 cm-1 |
NH stretching |
2926 cm-1 |
2923 cm-1. |
SH stretching |
2365 cm-1 |
2177 cm-1 |
Zn – O stretching |
706 cm-1 |
|
OH- stretching |
3427 cm-1 |
4(a) FTIR Spectra for Pure L- Methionine
4 (b) FTIR Spectra for Film formed on Metal Surface immersion in test solution containing 250ppm L Methionine + 5ppm Zn2+
4. Mechanism of Corrosion inhibition
The results of the weight-loss study show that the formulation consisting of 250 ppm L-Methionine and 5 ppm of Zn2+ has 93% IE in controlling corrosion of carbon steel in well water. A synergistic effect exists between Zn2+ and L-Methionine. Polarization study reveals that this formulation functions as cathodic inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra reveal that the protective film consists of Fe2+– L-Methionine complex and Zn(OH)2. In order to explain these facts the following mechanism of corrosion inhibition is proposed.
Zn2+ - L-Methionine + Fe2+ ----------> Fe2+ - L-Methionine + Zn2+
Zn2+ + 2OH- -------------> Zn(OH)2
5. Conclusion
Weight loss study reveals that the formation consisting of 250ppm of L-Methionine and 5ppm of Zn2+ has 93% inhibition efficiency, in controlling corrosion of carbon steel in well water. A Synergistic effect exists between Zn2+and L-Methionine system. Statistical study of F-test revealed that the synergistic effect existing between L-Methionine and Zn2+ is statistically significant. Polarization study reveals that L-Methionine system function as cathodic inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectral study suggests that L-Methionine has coordinated with Fe2+ through the oxygen atom of the carboxyl group, nitrogen atom of the amine group and sulphur atom of the thiol group resulting in the formation of Fe2+- L-Methionine complex and Zn(OH)2 is formed. Thus the FTIR spectral study leads to the conclusion that the protective film consist of Fe2+- L-Methionine complex and Zn(OH)2 on the metal surface thereby inhibiting the corrosion of carbon steel, which is protective in nature.
Acknowledgement
The authors are thankful to their respective management, Principal, G.T.N.Arts College, Dindigul, Tamil Nadu, India for providing the required facilities for completion of the work.
References
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