Effect of Brij35 on mild steel corrosion in acidic medium

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1 Indian Journal of Chemical Technology Vol. 18, September 2011, pp Effect of Brij35 on mild steel corrosion in acidic medium Mukta Sharma 1 & Gurmeet Singh 2 1 Department of Chemistry, Faculty of Engineering & Technology, Manav Rachana International University, Faridabad , India 2 Department of Chemistry, University of Delhi, Delhi , India Received 20 September 2010; accepted 8 July 2011 The effect of polyoxyethylene glycol dodecyl ether (Brij35), a surfactant, on corrosion of mild steel in 1N sulphuric acid has been studied using three techniques, namely galvanostatic, potentiostatic and scanning electron microscopic (SEM) studies. The galvanostatic and potentiostatic studies are performed to determine the corrosion current, inhibition efficiency, passivation current and passivation potential range. The parameters so obtained have been used to explain the effectiveness of inhibitor when present in different concentrations. SEM studies also help to understand the changes that take place on the surface layer with respect to change in Brij35 concentration. The extent of corrosion inhibition has also been evaluated by comparing the micrographs obtained from SEM. The results obtained are in direct agreement with the electrochemical studies. It is also revealed that Brij35 acts as an efficient inhibitor and shows very good inhibition efficiency. Keywords: Adsorption, Brij35, Corrosion inhibitor, Mild steel, Surfactants The corrosion involves the interaction between a metal or alloy and its environment. It is affected by the properties of both the metal or alloy and the environment. Although corrosion is only nature s method of recycling or of returning a metal to its lowest energy form, it is an insidious enemy that destroys cars, building, engines, factories, etc. The consequences of corrosion are many and its effects on the safe, reliable and efficient operation of equipment or structure are often more serious than the simple loss of a mass of metal. The failures of various kinds and the need for expensive replacements may occur even though the amount of metal destroyed is quite small. Mild steel is widely used in variety of industries especially for structural applications. It may come in contact with various acid solutions and corrodes heavily during chemical processes like acid cleaning, transportation of acids, storage of acids, etc. The use of corrosion inhibitors is one of the most practical methods for the protection against corrosion, especially in acidic media 1. Uhlig 2 quoted list of 112 compounds that are most effective inhibitors for sulphuric acid. Singh and Addyyemi 3 studied the effect of some hetrocyclic compounds like pyridine, pyrrole and thiophene on the corrosion of coppert in perchloric acid. The mild steel corrosion in acid Corresponding author. muktapragya@gmail.com solution has been effectively controlled by the use of organic substances containing N, O or S in the conjugated system as inhibitors 4,5 through which they get adsorbed on metal surface. The excellent protection of metals surface depends on nature of chemical bond of inhibitor on metal surface 6,7. Every and Riggs 8 listed many individual compounds that were subjected to laboratory tests for their inhibiting action in acids. Quarishi et al. 9 reported the use of four triazoles as inhibitors for the corrosion of mild steel in acid solution. Chick et al. 10 studied the effect of 1,12-bis(1,2,4-triazole) dodecane on carbon steel in hydrochloric solution by using electro-chemical and analytical techniques. The corrosion inhibition by surfactant molecules is related to the surfactant's ability to aggregate at interfaces and in solution. Surfactants adsorb on surfaces due to their amphiphilic nature and form aggregates with different morphologies, which potentially provide different extent of corrosion inhibition. The effectiveness of surfactant inhibitor can be studied on the basis of their micellar properties in a particular medium. The most well-known inhibitors are surfactants containing long chain of carbon atoms and heteroatoms like nitrogen, sulphur and oxygen atoms. Corrosion inhibition of carbon steel by nonionic polyoxy ethylene (80) monopalmitate, cationic hexadecyltrimethylammonium bromide (HTABr) and anionic sodium

2 352 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2011 dodecyl sulfate (SDS) in sea water has been evaluated by weight loss method, correlated with adsorption measurements and X-ray analysis. The inhibition efficiency of these compounds increases with their concentration and reaches a maximum value around their critical micelle concentration (CMC). Sodium oleic sulfonate (SOS), polyoxyethylene (20) sorbitan monooleate and their mixtures have been studied as acid corrosion inhibitors for mild steel in 1M HCl using adsorption and gravimetric techniques 11. Shalaby and Osman 12 discussed the application of some commercial nonionic surfactants in the field of corrosion inhibition. The inhibition efficiency increases with increasing the concentration as well as the hydrophilic chain length of these compounds. This paper reports the study on the inhibition of corrosion of mild steel in acidic medium using Polyoxyethylene glycol dodecyl ether (Brij35) by using different techniques. The effectiveness of the inhibitor is explained on the basis of electrochemical parameters obtained from galvanostatic and potentiostatic studies. The use of scanning electron microscopy (SEM) has been made to obtain a clear understanding of the nature of adsorption on mild steel specimen exposed to the inhibited and uninhibited solutions of different concentrations. Experimental Procedure Materials Flat mild steel of size 1cm 1cm (with data C= 0.15%, Si = 0.8%, S = 0.025%, P = 0.025% and Mn = 0.02%) was used. The solutions used for the corrosion studies were prepared in conductivity water. Sulphuric acid (E Merck, India) was used for the preparation of solutions. Polyoxyethylene glycol dodecyl ether (Brij35) was obtained from Fluka. All reagents were used as received and were of analytical grade. Preparation of working electrode A square mild steel rod was soldered on one end with an insulated copper wire and carefully coated with an epoxy resin (araldite) leaving the circular flat surface exposed uncoated for the corrosion studies. The exposed metal surface was then abraded with different grades of emery papers of variety 150, 320, 400, 600 and 1200 respectively. This was finally polished by 4/0 polishing paper to mirror like surface followed by washing and dried for 24 h. These mild steel coupons were used as working electrodes for the corrosion studies immediately. Galvanostatic polarization studies The potential of the metal electrode vs. reference electrode was measured by using galvanostat assembled indigenously having the range of mA. A constant distance of ~1-2 mm between the tip of Luggin capillary and the working electrode surface was maintained for all the experiments. Platinum electrode was used as a counter electrode. The potential of working electrode was measured against saturated calomel electrode (SCE). Steady state potentials were achieved in 3 h. Potentiostatic polarization studies A saturated calomel electrode (SCE) was used as a reference electrode. The steady state potentiostatic polarization was done through the potentiostat by applying potentials of 20 mv increments after every one minute and the corresponding current values were recorded one minute after the potential was applied. The anodic polarization experiments were repeated for a number of times for each set and the reproducible data have been recorded. Scanning electron microscopy (SEM) An scanning electron microscope (JEOL 840) has been used for the study of surface morphology. Polished specimen having a smooth pit free surface was subjected to corrosion exposure. Then these specimens were thoroughly washed in distilled water and dried in a desiccator. Thereafter, mild steel coupons were dipped into solutions of 10-3 M and 10-7 M concentration of inhibitors in one normal sulphuric acid for 24 h at room temperature. Then, they were thoroughly washed with distilled water, dried in a desiccator and thereafter subjected to SEM examination. Results and Discussion Galvanostatic polarization studies Galvanostatic cathodic and anodic polarization studies on mild steel in 1N H 2 SO 4 in the presence and absence of Brij35 at different temperatures, viz. 308, 318, 328 and 338 K, have been studied. The effect of change in concentrations of Brij35 on tafel polarization curves for mild steel has also been studied. Figures 1 and 2 show the plots of Logarithms of true current density against the corresponding electrode potential for mild steel in H 2 SO 4 in the presence and absence of Brij35 at different temperatures, which are measured against SCE. The electrochemical parameters so obtained are listed in Table 1. It is clear from the table that Brij35 inhibits

3 SHARMA & SINGH: EFFECT OF Brij35 ON MILD STEEL CORROSION 353 corrosion of mild steel to different extent when present in different concentrations. The variation in the inhibitor concentration is found to cause considerable change in the corrosion current. The increase in concentration of Brij35 leads to low value of corrosion current (i corr ). The percentage decrease in corrosion current is found to increase with respect to increase in concentration of surfactant. The effect is most pronounced at 10-3 M concentration. It is further seen that at a given inhibitor concentration, the corrosion current is higher at higher temperatures and this trend is observed at all concentrations of the inhibitor. At lower temperature, the decrease in corrosion current with an increase in concentration of Brij35 is more pronounced than at higher temperature. For example, at 308 K, the Fig. 1 Cathodic and anodic polarization curves for H 2 SO 4 at different temperatures corrosion current decreases from ma/cm 2 for the uninhibited solution to ma/cm 2 for the solution containing the inhibitor (10-3 M), while this change is from ma/cm 2 to ma/cm 2 for the above inhibitor concentration at 338 K. At the highest temperature, i.e. at 338 K, the inhibition efficiency is reduced to 51.47% as compared to that of 84.15% at 308 K for 10-3 M. Brij35 has produced no appreciable shift in open circuit potential towards Table 1 Corrosion parameters of mild steel in 1 N H 2 SO 4 in presence of Brij 35 Temp. K Conc. mol L -1 -E corr mv I corr ma/cm 2 I % Fig. 2 Tafel polarization curves for mild steel in 1 N H 2 SO 4 solution containing various concentrations of Brij-35 at (a) 308 K, (b) 318 K, (c) 328 K and (d) 338 K

4 354 INDIAN J. CHEM. TECHNOL., SEPTEMBER 2011 any direction. This indicates that this additive acts as the mixed type inhibitor and influences both the cathodic and anodic partial processes to an equal extent. Potentiostatic polarization studies A detailed sudy of potentiostatic behaviour of anodic dissolution of mild steel in sulphuric acid in the presence and absence of various concentrations of Brij 35 has been carried out in the present work. The current density and potential values were obtained and plotted with the help of a potentiostat (Fig. 3). The corresponding electrochemical parameters are given in Table 2. The passivation behaviour of mild steel in Brij35 can be seen in Fig. 4. Fig.3 Potentiostatic polarization curve for mild steel dissolution in 1N H 2 SO 4 at 298 K Fig. 4 Potentiostatic polarization curves for mild steel in 1N H 2 SO 4 containing various concentrations of Brij 35 at 298 K Table 2 Electrochemical parameters for anodic dissolution of mild steel in 1 N H 2 SO 4 in the presence of Brij 35 Additive Concentration mol L -1 Critical current (i c ) 10-2 ma cm -2 Passivation current (i p ) ma cm -2 Passivation potential (E p), mv (Range) Nil Brij The effect of Brij35 has been studied in terms of the electrochemical parameters, e.g. current maximum or critical current density (i c ), flade potential (E pp ) and passivation current (i p ). The anodic dissolution parameters (i c, E pp and i p) of mild steel in 1N H 2 SO 4 solution at various concentrations of this inhibitor are shown in Table 2. The passivation current (i p ) is found to be lower at higher concentration as compared to that at lower concentration of Brij35. The value of i p decreases from 0.32 macm -2 to 0.15 macm -2 as the concentration of Brij35 is increased from 10-7 M to 10-3 M. The pasivation range is more in the presence of additive than that of pure acid and increases with the increase in the concentration of Brij35. These values show that Brij35 acts as a good passivator of mild steel in 1N H 2 SO 4 solution Brij35 decreases the passivation current to a considerable extent. This shows that protonated inhibitor which is ineffective towards metal dissolution in the active potential range become effective in the passivation potential. The satisfactory explanation to this effect is that the adsorbed [Fe(OH)] ads interacts with the protonated inhibitor molecules forming neutral organic compounds which forms insoluble polymeric films on the surfaces and possible insoluble complexes are shown below: Fe s [Fe(OH) 3 ]-oxide phase + In H + [Fe s In (OH) 3 ]-oxide phase where In stands for inhibitor. The additional inclusion of inhibitor molecules along with the passive Fe 2 O 3 reinforces the protective activity and decreases the passivation current. The appearance of dark covering on the surface and a slight change in colour of the solution is indicative of the resistive layer formation along with oxide layers on the metal surface. This passive current starts increasing and transforms into transpassive region where once again evolution of oxygen starts violently and passivity is destroyed. The breakdown of passivity (the breaking of the protective film/barrier provided by the passive film) initiates the most damaging kinds of corrosion like pitting corrosion, crevice corrosion, stress corrosion, etc. This, therefore, gives a clear potential range in which these additives are effective and at higher potential regions the passive layer is broken and oxygen evolution starts.

5 SHARMA & SINGH: EFFECT OF Brij35 ON MILD STEEL CORROSION 355 Surface characterization by SEM In the present investigation, surface chemistry of mild steel specimen exposed to the uninhibited and inhibited solutions has been undertaken to supplement the studies. It is quite apparent from the micrographs that the surfaces treated with the inhibitor show lesser corrosion as compared to those of the metal immersed in the acid alone. Figure 5(a) shows the scanning electron micrographs of unexposed specimen, i.e. plain mild steel surface without dipping in any solution. As it is seen, the uncorroded surface is found to be absolutely free from any noticeable defects such as cracks and pits. The streak marks on the surface are made during polishing with emery papers. Figure 5(b) shows the scanning electron micrographs of corroded surface of mild steel after immersion in 1N sulphuric acid solution. The surface of mild steel coupon becomes badly corroded as a large number of pits and cracks are observed on the steel surface. In Fig. 5(c) it is quite apparent from the micrographs that when the specimen is treated with Brij35 (10-3 M), the surface of mild steel appears less corroded as compared to 1N sulphuric acid. No pits are identifiable on the surface so it can be seen that the metal surface is fully covered with the inhibitor molecules giving it a high degree of protection against corrosion. The extent of corrosion, as visible from micrographs, is much less as compared to specimen exposed to 1N sulphuric acid giving it quite a good protection. Figure 5(d) shows the micrograph of mild steel when treated with 10-7 M concentration of Brij35. The metal surface is not completely covered with inhibitor molecules so more corrosion can be seen, thereby giving less protection to the surface as compared to 10-3 M concentration of Brij35. It is also observed that the inhibition action of this additive reduces with the reduction of the concentration of the additive. Conclusion The extent of corrosion of mild steel in 1N H 2 SO 4 in presence of Brij35 has been studied by using different techniques. Brij35 has produced no appreciable shift in open circuit potential towards any direction. This indicates that this additive acts as the mixed type inhibitor and influences both the cathodic and anodic partial processes to an equal extent. It can also be concluded that inhibition efficiency of Brij35 increases with the decrease in temperature and increase in concentration. Fig.5 Scanning electron micrographs of (a) polished mild steel, (b) corroded specimen in acid solution, (c) specimen treated with 10-3 M Brij35 and (d) specimen treated with 10-7 M Brij 35 References 1 Kaesche H, Corrosion of Metal: Physiochemical Principles and Current Problems (Springer), Uhlig H H, The Corrosion Handbook, 2 nd edn (John Wiley and Sons) 2000, Gurmeet Singh & Olufemi O Adeyyemi, Trans Saest, 24(1) (1989) Bereket G & Pinarbasi A, Corr Engg Sci Technol, 38 (2004) Bansiwal A, Anthony P & Mathu S P, Bri Corros J, 35(2000) 301.

6 356 INDIAN J. CHEM. TECHNOL., SEPTEMBER Keera S T, Br Corros J, 36 (2001) Al-Mayout A M, et al., Corros Sci, 57 (2001) Every R L & Riggs O L, Mater Prot, 46 (3) (1964)9. 9 Quarishi M A & Sharma N K, Indian J Chem Technol, 12 (2005) Chick Z Ait, et al., Corros Sci, 47 (2005) Hong Y, et al., Electrochem Solid-state Lett, 8 (11) (2005) Shalaby M N & Osman M M, Anti corrosion Methods Mater, 48 (2001) 5.