Surfactants as Corrosion Inhibitors for Carbon Steel in Hydrochloric acid Solution
Diwan Singh Rajan1* and Dr. Shiv Darshan Malik2
1Research Scholar, Department of Chemistry, JJT University, Jhunjhunu (Rajasthan) India
2Research Guide, Department of Chemistry, JJT University, Jhunjhunu (Rajasthan) India
*Corresponding Author E-mail: rdsingh0220@gmail.com
ABSTRACT:
The role of some surfactants in the corrosion of carbon steel in 1.0 M HCl has been studied using weight loss and galvanostatic polarization techniques. Results showed that the inhibition occurs through adsorption of the inhibitor molecules on the metal surface. The inhibition efficiency was found to increase with increasing inhibitor concentration and decreased with increasing temperature which is due to the fact, that the rate of corrosion of carbon steel is higher than the rate of adsorption The inhibiting action of these compounds are considerably enhanced by the addition of KI, due to the increase of the surface coverage and therefore indicate the joint adsorption of these compounds and iodide ions. Thermodynamic parameters for adsorption and activation processes were determined. Galvanostatic polarization data indicated that these compounds act as mixed-type inhibitors. Results obtained from the two techniques are in good agreement.
KEYWORDS: Corrosion inhibitors, surfactant, Carbon Steel, adsorption, electrochemical polarization, activation energy
Carbon steel has remarkable economic and attractive materials for engineering applications owing to its low cost, easy availability and high mechanical strength. The interest of the materials arises from their importance in recent civilization. Inhibition of metal corrosion by organic compounds is a result of adsorption of organic molecules or ions at the metal surface forming a protective layer. This layer reduces or prevents corrosion of the metal. The extent of adsorption depends on the nature of the metal, the metal surface condition, the mode of adsorption, the chemical structure of the inhibitor, and the type of corrosion media [1]. To prevent the attack of acid, it is very important to add a corrosion inhibitor to decrease the rate of metal dissolution in such solutions. Thus, many studies concerning the inhibition of carbon steel corrosion using organic substances are conducted in acidic and basic solutions [2-6].
The present study aimed to investigate the efficiency of some surfactants as corrosion inhibitors for carbon steel in acidic media. An attempt was also made to clarify the effects of concentration and temperature on the inhibition efficiency of the studied surfactant as corrosion inhibitors for carbon steel.
The measurements of corrosion rate and percentage inhibition efficiency of different anionic surfactant towards corrosion of carbon steel by weight loss and electrochemical polarization technique were performed in 1.0 M HCl without and with the presence of the investigated surfactants in the concentration range (10 to 100 ppm). The name and molecular structures of the anionic surfactants as corrosion inhibitor for carbon steel in acidic medium are:
(a) Decyl sulphate sodium salt (SSDS).
(b) - Dodecyl sulphate sodium salt (SSDDS).
(c) - Hexadecyl sulphate sodium salt (SSHDS).
(d) - Dodecyl benzene sulfonate sodium salt (SSDDBS).
EXPERIMENTAL:
Carbon steel used for the investigations was in the form of sheet (0.25 mm thick) and had the following composition.
|
Element |
C |
Si |
Mn |
S |
P |
Ni |
Cu |
Cr |
Fe |
|
Weight percentage (w/w) |
0.14 |
0.03 |
0.32 |
0.05 |
0.20 |
0.01 |
0.01 |
0.01 |
Balance |
All the chemicals used were of AR grade and the solutions were prepared using triple distilled water. Duplicate or in some cases triplicate experiments have been performed to verify the reproducibility and consistency of the experimental data.
For weight loss measurements, carbon steel specimens of 3 × 1.5 cm2 size were cut from the carbon steel sheet whereas for electrochemical polarization investigations, specimens of size 5 × 1.0 cm2 were used. All the specimens were mechanically polished successively with the help of emery papers of grades 100, 200, 300, 400 and 600µ and then thoroughly cleaned with plenty of triple distilled water and then with acetone. The specimens were dried with hot air blower and stored in desiccators over silica gel.
After recording the initial weights of carbon steel specimens on a Mettler Toledo, Japan AB 135-S/FACT, single pan analytical balance, (with a precision of 0.01mg), they were immersed in tilted position in 250 ml beakers each having 200 ml of acidic solution as corroding medium with or without the inhibitor. Experiments were carried out in an electronically controlled air thermostat at 30, 40 and 500C with in an accuracy of ±0.10C. After exposing the specimens for 24 hours, the specimens were taken out from the beaker and washed initially under the running tap water. Loosely adhering corrosion products were removed with the help of rubber cork and the specimen was again washed thoroughly with triple distilled water and dried with hot air blower and then weighed again. Corrosion rate in mils per year (mpy) and percentage inhibition efficiency were calculated using the following equations.
Corrosion rate (mpy) = ….(1)
The working electrode was carbon steel under study, platinum electrode was used as counter electrode or an auxiliary electrode. All the potentials were measured against a pencil type luggin capillary saturated calomel electrode as reference electrode. A Luggin capillary filled with the test solution was used to connect the reference electrode with the cell. The tip of the Luggin capillary was kept very close to the working area of the electrode but without touching it in order to minimize the IR drop and this distance was kept constant during the whole study. Only 1 cm2 area of specimen was used as working area and the rest of the area of the specimen was covered with a lacquer except the other tip of specimen which was used for making electrical connection. The specimen was left in the test solution until a constant open circuit potential (OCP) was attained.
Linear polarization resistance measurements were carried out potentiostatically by scanning through a potential range of 14 mV above and below the OCP value in steps of 2 mV. Experiments were carried out in absence and presence of inhibitors at their different concentrations at 30, 40 and 500C. The resulting current is plotted against the potential and slope of the line is measured.
RESULTS AND DISCUSSION:
Table 1 gives the values of percentage corrosion inhibition efficiency for different concentrations of investigated surfactant compounds at 30 0C. Figure 1 shows percentage corrosion inhibition efficiency of all the four organic surfactants for carbon steel at 300C in presence of 1.0 M hydrochloric acid solution. It is observed from the Table 1and Figure 1 Table 1 gives the values of percentage corrosion inhibition efficiency for different concentrations of investigated surfactant compounds at 30 0C. Figure 1 shows percentage corrosion inhibition efficiency of all the four organic surfactants for carbon steel at 300C in presence of 1.0 M hydrochloric acid solution. It is observed from the Table 1and Figure 1 that the weight loss decreased, percentage inhibition efficiency increased and therefore the corrosion inhibition strengthened with increase in inhibitor concentration from 10 to 100 ppm. This trend may result from the fact that adsorption and surface coverage increases with the increase in concentration. Thus, the surface is efficiently separated from the medium [7-8]. The linear variation of weight loss with time in uninhibited and inhibited 1.0 M HCl indicates the absence of insoluble surface films during corrosion. It is clear from Tables 1 that percentage corrosion inhibition efficiency increases with increase in inhibitor concentration. The percentage corrosion inhibition efficiency for different investigated anionic surfactants as corrosion inhibitor increases in the following order a > b > c > d.
Table 2 gives the values of percentage corrosion inhibition efficiency for different concentrations of investigated surfactant compounds and 10-2 M KI. Figure 2 shows synergistic effect of KI on the percentage corroison inhibition efficiency of all the four organic surfactants for carbon steel at 300C in 1.0 M hydrochloric acid solution. It is observed from tha Table 2 and Figure 2 that the addition of KI improves the percentage corrosion inhibition efficiency of the investigated compounds significantly. The synergistic effect between Investigated compounds and KI is due to interactions between chemisorbed I- and organic compounds. The stabilization of adsorbed organic cations on the surface, which may be exhibited by electrostatic interactions with I- ions, leads to higher surface coverage and greater corrosion inhibition.
Table 1 Percentage corrosion inhibition efficiency at different concentrations of anionic surfactant for the corrosion of carbon steel after immersion in 1.0 M HCl at 30 0C.
|
Conc. of Surfactant (ppm) |
Percentage Corrosion Inhibition Efficiency of Surfactants |
|||
|
( a ) |
( b ) |
( c ) |
( d ) |
|
|
10 |
65.6 |
70.5 |
73.2 |
77.0 |
|
30 |
67.2 |
72.6 |
75.1 |
79.5 |
|
50 |
68.9 |
75.0 |
77.9 |
80.3 |
|
70 |
69.7 |
77.2 |
78.6 |
82.8 |
|
90 |
71.2 |
79.5 |
81.7 |
83.6 |
|
100 |
71.8 |
80.5 |
82.1 |
84.9 |
Table 2 Percentage corrosion inhibition efficiency at different concentrations of the four investigated surfactants (a to d) with addition of 1.0 ×10-2 M KI for the corrosion of carbon steel after 24 hours of immersion in 1.0 M HCl at 30 0C.
|
Conc. of Surfactant (ppm) |
Percentage Corrosion Inhibition Efficiency of Surfactants |
|||
|
( a ) |
( b ) |
( c ) |
( d ) |
|
|
10 |
79.5 |
80.3 |
83.6 |
85.2 |
|
30 |
82.0 |
83.5 |
84.4 |
85.3 |
|
50 |
82.8 |
83.6 |
84.4 |
85.4 |
|
70 |
83.1 |
84.3 |
85.7 |
87.7 |
|
90 |
83.6 |
86.1 |
86.1 |
87.8 |
|
100 |
85.2 |
86.9 |
87.7 |
90.9 |
CONCLUSIONS:
· The investigated surfactant compounds act as corrosion inhibitors for the carbon steel in hydrochloric acid solution.
· Surfactant compounds adsorb on carbon steel surface according to the Freundlich adsorption isotherm.
· The inhibitors increase the value of activation energy of corrosion and consequently, decrease the rate of dissolution of Carbon steel in HCl solution.
· Polarization data showed that these investigated surfactant compounds acted as mixed-type inhibitors.
· The inhibition efficiencies obtained from polarization and weight loss measurements are in good agreement with each other.
· Increase of temperature leads to the decrease in corrosion rate of carbon steel in HCl solution.
· Addition of KI to inhibitor formulation shows synergistic effect on corrosion inhibition efficiency of organic surfactant towards carbon steel.
Figure 1 Percentage corroison inhibition efficiency of all the four organic surfactants for Carbon steel at 300C in presence of 1.0 M hydrochloric acid solution.
Figure 2 Synergistic effect of KI on the percentage corroison inhibition efficiency of all the four organic surfactants for carbon steel at 300C in 1.0 M hydrochloric acid solution.
Figure 3 Effect of increasing temperature i.e. 30 to 50 0C on percentage corrosion inhibition efficiency of surfactant D in case of carbon steel.
Figure 4 Activation parameters i.e. activation energy, change in enthalpy and change in entropy for carbon steel in case of surfactant D at different concentrations.
REFERENCES:
1. A. A. Mazhar, W.A. Badaway and M.M. Abou-Romia, Surf. Coat. Techol., 29 (1986) 335
2. M. Stern and A.I.J. Geary, J. Electrochem. Soc., 104 (1957) 56
3. A. K. Maayta and N.A.F. Al-Rawashdeh , Corros Sci., 46 (2004) 1129
4. E. E. Ebenso ,P.C.Okafor and U. J. Ekpe, Anti-Corrosion Methods and Materials, 37 (2003)381
5. G. Bereket, A.Pinarbasi and C. Ogretir, Anti-Corrosion Methods and Materials, 51 (2004) 282
6. A. S. Fouda, M. N. Moussa, F. I. Taha and A. I. Elneanaa, Corros. Sci., 26 (1986) 719
7. T. Zhao and G. Mu. Corros. Sci. 41 (1999)1937
8. N. Al-Andis, E. Khamis, A.Al-Mayouf and H. Aboul-Enein, Corros. Prev. Cont., 42 (1995) 13
9. A. Kazaraji, S. Keertit, J.Aride, K.Bougrin and M.Soufiaoui, Bull. Electrochem., 16 (3) (2000) 97
10. E. E. Oguzie, Corros. Sci., 49 (2007) 1527
11. M. Kliskic, J.Radosevic, S.Gudic and V. Katalinik, J. Appl. Electrochem., 30 (2000) 823.
12. A.Yurt, S.Ulutas and H. Dal, Appl.Surf.Sci., 253 (2006) 919.
13. S. A. Abd E L-Maksoud and A. S. Fouda, Mater. Chem. Phys., 93 (2005)84.
14. O. K. Abiiola,and N.C.Oforka, Corros. Sci. & Eng., 3 (2002) 21
15. E. E. Ebenso, Nig. Corros. J., 1 (1) (1998) 29
16. B. B. Damaskin, Adsorption of organic Compounds on electrodes (Plenum press) N.Y., p. 221 (1971)
17. E. E. Ebenso, Mater.Chem.Phys., 79 (2003) 58
18. G. K. Gomma and M.H.Wahdan, Mater. Chem. Phys., 30 (1995) 209
19. J. Marsh, Advanced Organic Chemistry 3rd ed., Wiley Eastern New Delhi, (1988).
20. M. S. Soliman, The use of rotating cylinder electrode to study the effect of 1,3-dihydroxypropane on copper electrorefining , Ph. D. Thesis, Alex. Univ., Egypt (1995)
Received on 10.03.2012 Modified on 19.03.2012
Accepted on 25.03.2012 © AJRC All right reserved
Asian J. Research Chem. 5(4): April 2012; Page 520-525