1. INTRODUCTION
The corrosion of iron and mild steel is a fundamental academic and industrial concern that has received a considerable amount of attention [1]. The use of inhibitors is one of them most practical methods for protection against corrosion, especially in acidic media [2]. The progress in this field has been phenomenal in recent years and is borne out by the output of literature [3]. Acid solutions are widely used in industry, the most important field of application being acid pickling, industrial acid cleaning, acid descaling and oil well acidizing. Because of the general aggressively of acid solutions, inhibitors are commonly used to reduce the corrosive attack on metallic materials. Most of the well known acid inhibitors are organic compounds containing nitrogen, sulphur and oxygen atoms. The influence of organic compounds containing nitrogen, such as amines and heterocyclic compounds, on the corrosion of steel in acidic solutions has been investigated by several works [4-7]. The existing data show that most organic inhibitors act by adsorption on the metal surface.
The most important prerequisites for compounds to be ancient inhibitors are: substances should form a compact barrier ®lm, they should chemosorb on the metal surface, have high adsorption energy on the metal surface, and the barrier layer thus formed should increase the inner layer thickness [8]. In this paper, we have studied the effect of addition of Vitamin -B2 on the corrosion inhibition of mild steel in acidic media using gravimetric measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization.
2. MATERIALS AND METHODS:
2.1 Preparation of Stock solution:
Vitamin B-2 was purchased from NICE chemicals.0.1g of sample was dissolved in ethanol, and made up to 100 ml. The solution was used as corrosion inhibitor in the present study
2.2 Preparation of specimens:
Carbon steel specimens (0.022% S, 0.038% Mn, 0.027% P, 0.086 C) of dimension 1.0 cm x4.0cmx 0.2cm were polished to a mirror finished with the emery sheets of various grades and degreased with trichloroethylene.
2.3 Weight loss method.
Carbon steel specimens in triplicate were immersed in 100 mL of the inhibited and uninhibited 0.5 M H2SO4 solutions in the presence and absence of KI for two hours. The weight of each specimen before and after immersion was determined using Shimadzu balance, model Ay 62.The inhibition efficiency (IE) was then calculated using the expression.
 |
 |
W1 – W2
IE%= W1 x
100
Where, W1and W2 are the corrosion rates in the absence and presence of the inhibitor, respectively.
2.4 Electrochemical impedance measurements
The impedance measurements were performed using a computer–controlled potentiostat (Model Solartron SI-1260) and the data were analysed using gain phase analyser electrochemical interface (Solartron SI-1287). A three electrode set up was employed with Pt foil as the auxiliary electrode and a saturated calomel electrode as the reference electrode. The Teflon coated mild steel rod, with the surface prepared as described in the weight loss experimental method, served as the working electrode. The measurements were carried out in the frequency range 106–10−2 Hz at the open circuit potential by superimposing sinusoidal AC signal of small amplitude, 10 mV, after an immersion period of 30 min in the corrosive media. The double layer capacitance (Cdl) and charge transfer resistance (Rct) were obtained from the impedance plots as described elsewhere 25. Because Rct is inversely proportional to corrosion current density, it was used to determine the inhibition efficiency (IE%) using the relationship;
Rct – Roct
IE%= x 100
Rct
Where, Rct and R0ct are the charge transfer resistance values in the inhibited and uninhibited solutions respectively.
2.5. Polarization measurements
The potentiodynamic polarization curves were recorded using the same cell setup employed for the impedance measurements. The potentials were swept at the rate of 1.66mV/s, primarily from a more negative potential than Eocp to a more positive potential than Eocp through Ecorr. The inhibition efficiencies were calculated using the relationship 26;
Iocorr – Icorr
IE%= x 100
Iocorr
Where, I0corr and Icorr are the corrosion current densities in the absence and in the presence of inhibitor, respectively
3. RESULTS AND DISCUSSION:
3.1 Analysis of results of mass loss method:
The corrosion rates and inhibition efficiency values, calculated using weight loss data, for various concentrations of Vitamin B-2 in the presence and absence of TBAB the corrosion of carbon steel in 0.5M H2SO4 solution are presented in Table.1. It is apparent that the inhibition efficiency increased with the increase in inhibitor concentration in the presence and absence of TBAB. This behavior can be explained based on the strong interaction of the inhibitor molecule with the metal surface resulting in adsorption. The extent of adsorption increases with the increase in concentration of the inhibitor leading to increased inhibition efficiency. The maximum inhibition efficiency was observed at an inhibitor concentration of 100 ppm. Generally, inhibitor molecules suppress the metal dissolution by forming a protective film adsorbed to the metal surface and separating it from the corrosion medium. The corrosion suppressing ability of the inhibitor molecule originates from the tendency to form either strong or weak chemical bonds with Fe atoms using the lone pair of electrons present on the O and p electrons in benzene ring. It is also seen from table.1 that the leaf extract of Vitamin B-2 at 10 ppm and 50 ppm concentrations shows 59.38 % and 76.04 % inhibition efficiencies respectively, Then the values increased to 91.66 % after adding 25 ppm of TBAB solution in 0.5M H2SO4 solutions containing 50 ppm of Vitamin B-2 respectively. This showed a good synergistic effect between Vitamin B-2 and TBAB.
Table1.Corrosion rate (CR) of mild steel in 0.5M H2SO4 solutions the absence and presence of inhibitor and the inhibition efficiency (IE) obtained by mass loss method.
|
Inhibitor concentration (ppm) |
TBAB (0) ppm |
|
|
CR (mg cm-2 h-1) |
IE % |
|
|
0 |
192.00 |
- |
|
10 |
78.00 |
59.38 |
|
20 |
66.04 |
65.60 |
|
30 |
59.50 |
69.01 |
|
40 |
54.46 |
71.63 |
|
50 |
46.00 |
76.04 |
3.2 Influence of TBAB on the inhibition efficiency of Vitamin b-2:
Table 2.Corrosion rate (CR) of mild steel in 0.5M H2SO4 solutions the presence of inhibitor with TBAB and the inhibition efficiency (IE) obtained by mass loss method
|
Inhibitor concentration (ppm) |
TBAB (5) ppm |
|
|
CR (mg cm-2 h-1) |
IE % |
|
|
50 |
16.00 |
91.66 |
3.3 Electrochemical impedance spectroscopic measurements (EIS):
Impedance spectra obtained for corrosion of mild steel in 0.5 M H2SO4 contains a semicircle, representing the interaction of metal surface with the corrosive environment. The -R(CR) model best describes this situation. The semicircle in the impedance plots contain depressed semicircles with the centre below the real axis. The size of the semicircle increases with the inhibitor concentration, indicating the charge transfer process as the main controlling factor of the corrosion of mild steel. It is apparent from the plots that the impedance of the inhibited solution has increased with the increase in the concentration of the inhibitor. The experimental results of EIS measurements for the corrosion of mild steel in 0.5 M H2SO4 in the absence and presence of inhibitor are given in Table 3. Said that sum of charge transfer resistance (Rct) and adsorption resistance (Rad) is equivalent to polarization resistance (Rp).
Table 3. Impedance parameters obtained from electrochemical impedance studies.
|
Inhibitor concentration (ppm) |
Rct Ohm cm2 |
Cdl µF |
IE% |
|
0 |
17.2 |
9.2578×10-3 |
- |
|
50 |
76.7 |
4.149×10-6 |
77.6 |
|
50+ 25ppm(TBAB) |
260.6 |
1.309×10-6 |
93.4 |
Fig.1 Impedance spectra obtained from electrochemical impedance studies
3.3 Polarization measurements:
Fig 2. Potentiodynamic polarization curves of mild steel immersed in 0.5M H2SO4 solution in the absence and presence of inhibitors
Table 4.Corrosion parameters in the presence and absence of inhibitor obtained from polarization measurements.
|
Inhibitor concentration mL |
Ecorr (mV) |
βc (mV/) |
βa (mV) |
Icorr×10x6 µA |
IE% |
|
0 |
447 |
181 |
85 |
1.35 |
|
|
10 |
439 |
204 |
106 |
0.207 |
84.7 |
|
10+25ppmTBAB |
435 |
207 |
109 |
0.081 |
94.0 |
The polarization curves obtained for the corrosion of mild steel in the inhibited (100 ppm) and uninhibited 0.5 M H2SO4 solutions in Fig.2. Electrochemical parameters such as corrosion potential (Ecorr), corrosion current density (Icorr), cathodic and anodic tafel slopes (βc and βa ) and percentage inhibition efficiency according to polarization studies are listed in table 3. Here Icorr decreased with increasing inhibitor concentration. From the figures, it can be interpreted that the addition of this inhibitor to corrosive media changes the anodic and cathodic tafel slopes. The changes in slopes showed the influence of the inhibitor both in the cathodic and anodic reactions. However, the influence is more pronounced in the cathodic polarization plots compared to that in the anodic polarization plots. Even though βc and βa values (table.3) change with an increase in inhibitor concentrations, a high βc value indicates that the cathodic reaction is retarded to a higher extent than the anodic reaction11.
From Fig.2 it is also clear that the addition of the inhibitor shifts the cathodic curves to a greater extent toward the lower current density when compared to the anodic curves. The Ecorr value is also shifted to the more negative side with an increase in the inhibitor concentration. These shifts can be attributed to the decrease in the rate of the hydrogen evolution reaction on the mild steel surface caused by the adsorption of the inhibitor molecule to the metal surface12. It has been reported that a compound can be classified as an anodic and cathodic type inhibitor on the basis of shift of Ecorr value. If displacement of Ecorr value is greater than 85 mv, towards anode or cathode with reference to the blank, then an inhibitor is categorized as either anodic or cathodic type inhibitor otherwise inhibitor is treated as mixed type13,14. In our study, maximum displacement in Ecorr value was around 6 mV, indicating the inhibitor is a mixed type and more anodic nature and does not alter the reaction mechanism. The inhibition effect has occurred due to simple blocking of the active sites, thereby reducing available surface area of the corroding metal15-18.
4. CONCLUSION:
1. Vitamin B-2 inhibited mild steel corrosion in Acid solutions.
2. Corrosion inhibition of mild steel in acid solution is under mixed control.
3. Inhibition efficiency of plant extracts increases with increase in concentration.
4. The mass loss measurements are in good agreement with electrochemical method.
5. ACKNOWLEDGEMENTS:
The authors generously acknowledge the support by Dr. R. Somasundaram M.D., Dr. R. Arul M.Sc., Ph.D., Dr. S. Vedanayaki M.Sc., Ph.D., President, Principal and Head of the Department Chemistry, respectively of Kandaswami Kandar’s College, P. Velur for providing necessary chemical and lab facilities to carry out chemical studies.
6. REFERENCES:
1 Uhlig. H.H., Revie. R.W., Corrosion and Corrosion Control, Wiley, New York, 1985.
2 Trabanelli. G., Corrosion 47 ;1991; 410.
3 Schmitt. G., Br Corrs. J 19 ;1984;165.
4 Sykes. J.M., ibid 25 ;1990; 175.
5 Elachouri. M., Hajji. M.S., Kertit. S, Essassi. E.M, Salem. M, Coudert. R, Corros. Sci 37 ;1995;381.
6 Chatterjee. P., Benerjee. M.K, Mukherjee. K.P., Indian J. Technol 29 ;1991; 191.
7 Mernari. B., Elattari. H., Traisnel. M., Bentiss. F., Lagrene. M. Â e, Corros. Sci 40 ;1998; 391.
8 Muralidharan. S., Phani. K.L.N., Pitchumani. S., Ravichandran. S., Iyer. S.V.K., J. Electrochem. Soc 142 (1995) 1478.
9 Ashassi-Sorkhabi. H,. Shaabani. B, Seifzadeh. D, Electrochim. Acta, 2005 ,50 ,3446.
10 Shahin.M, Bilgie.S, Yilmaz.H, Appl. Surf. Sci.2003,195, 1.
11 Silverman D. C., "Practical Corrosion Prediction Using Electrochemical Techniques", ch. 68 in Uhlig's Corrosion Handbook, 2nd edition (Revie,. R.W, ed.), The Electrochemical Society, 2000.
12 Prabhu., T.V. Venkatesha, A.V. Shanbhag. Praveen. B.M, Kulkarni. G.M,.Kalkhambkar R.G, Mater. Chem. Phys. 2008,108 , 283
13 Sanghvi. R.A, M.J., et al., Bull. Electrochem.1999, 13, 358.
14 Felicia Rajammal Selvarani, S. Santhanalakshmi, J. Wilson sahayaraja, A. John Amalraj and Susai Rajendran, Bull. Electrochemistry. 2004, 20 , 561-565.
15 Susai Rajendran S. Mary Reenkala, Noreen Anthony and Ramaraj, R. Corros Sci, 2002, 44, 2243-2252.
16 Scully. J. R., Polarization Resistance Method for Determination of Instantaneous Corrosion Rates", Corrosion, Vol. 2000,56, p. 199.
17 Kumaravel Mallaiyaa, Ramesh Kumar Subramaniama, Subramanian Sathyamangalam Srikandana, S. Gowria, N. Rajasekaranb, A. Selvaraj. Electrochemical characterization of the protective film formed by the unsymmetrical Schiff’s base on the mild steel surface in acid media, Electrochimica Acta 56; 2011; 3857–3863
18 Ananth Kumar S, Sankar. A, and Ramesh Kumar S. The Electrochemical Synthesis and Corrosion Inhibitive Nature of DI N-propyl Malonic Acid Doped Poly Aniline Coating on Stainless Steel. International Journal of Chemistry and Chemical Engineering. Volume 3, Number 1; 2013; pp. 7-14
Received on 13.08.2013 Modified on 12.09.2013
Accepted on 22.09.2013 © AJRC All right reserved
Asian J. Research Chem. 6(11): November 2013; Page 992-995