Study on the inhibition of Mild Steel Corrosion by Cationic Surfactant in HCl Medium

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1 IOSR Journl of Applied Chemistry (IOSRJAC) ISSN : Volume 2, Issue 1 (Sep-Oct. 212), PP Study on the inhibition of Mild Steel Corrosion by Ctionic Surfctnt in HCl Medium Prthibh B.S 1 P.Kotteeswrn 2, V. Bheem Rju 3, 1 Deprtment of chemistry, BNM Institute of Technology, Bengluru-7, Indi 2 Deprtment of chemistry, Klslingm University, Tmil Ndu, Indi 3 Deprtment of chemistry, Dr. Ambedkr Institute of Technology, Bengluru, Indi Abstrct: The inhibition effect of N,N,N-trimethyldodecylmmonium bromide(tdab) s ctionic surfctnt on the corrosion of mild steel in 1M HCl hs been studied t different tempertures by weight loss, Tfel polriztion nd Electrochemicl impednce spectroscopy. Morphology of the mild steel specimens were exmined using scnning electron microscopy nd AFM in presence nd bsence of inhibitor. The results show tht TDAB is good inhibitor, nd the inhibition efficiency (IE) increses with the inhibitor concentrtion s well s incresing the temperture. The dsorption of inhibitor on the mild steel surfce obeys the Lngmuir dsorption isotherm eqution. Polriztion curves show tht TDAB is mixed-type inhibitor in hydrochloric cid. Activtion prmeters nd thermodynmic prmeters were lso discussed. The results obtined from weight loss, polriztions nd EIS re in good greement. Keywords: AFM, Ctionic surfctnt,, Corrosion inhibition, mild steel, Polriztion I. Introduction Acids re widely used in vrious technologicl processes in industry, e.g., in pickling bths, in the extrction nd processing oil nd gs nd in other chemicl nd petrochemicl industries. Also, in the technicl crcking of petroleum, cids pper s result of hydrolysis of slts nd my destructive effect on the equipment. Corrosion due to cids re importnt nd expensive problem in the petroleum refining units nd it represents significnt portion of loss s result of lost production, inefficient opertion, high mintennce nd the cost of corrosion control chemicls. Inhibitors should be effective in low concentrtions for economy. The use of inhibitors is the most prcticl methods for protection ginst corrosion, especilly in cid medi[1]. Most of the well known cid inhibitors re orgnic compounds contining nitrogen, sulphur nd oxygen toms. The influence of orgnic compounds contining nitrogen, such s mines nd heterocyclic compounds, on the corrosion of steel in cidic solutions hs been investigted by severl workers [2-5]. In previous studies, SDBS [6], Dithizone nd thiosemicrbzide [7], Benzyl triethnol mmonium chloride [8], Cetyl trimethyl mmonium bromide, etc hve been studied s corrosion inhibitors for steel in cidic medium.the existing dt shows tht the most orgnic inhibitors cts by dsorption on the metl surfce. Surfctnt inhibitors hve mny dvntges, for exmple, high inhibition efficiency, low price, low toxicity, nd esy production [9,1,]. Moreover, the investigtion of surfctnts dsorbed on metl surfce is extremely importnt in electrochemicl studies such s corrosion inhibition, dhesion, lubriction nd detergency [1]. Nowdys, surfctnts re widely used nd find very lrge number of pplictions in the petroleum industry. This is ttributed to their significnt cpbility to influence the properties of surfces nd interfces. An importnt corrosion inhibition tool is the use of surfctnt inhibitors, becuse of very little considertion towrds this study. The most importnt ction of inhibition is the dsorption of the surfctnt functionl group on to the metl surfce, dsorption is criticl to corrosion inhibition. The concern of these mterils rises from their significnce in recent civiliztion. In the present investigtion the corrosion inhibition of mild steel in 1M HCl solution in the bsence nd presence of surfctnt, N,N,N-trimethyldodecylmmonium bromide(tdab) hs been studied using weight loss, potentiodynmic polriztion nd Electrochemicl impednce spectroscopy techniques. The effects of temperture nd concentrtion hve been studied. The surfce morphology of the mild steel surfce fter exposing to optimum concentrtion is lso exmined using AFM nd SEM. II. Experimentl 2.1 Preprtion of specimen Mild steel specimen with composition (Fe, 98.7; C,.223; Mn,.55; Si,.164; S,.5) ws used. For the weight loss mesurement mild steel specimen (2cm x 1cm) ws used nd for electrochemicl polriztion investigtion, The cylindricl rod specimen ws welded with copper wire for electricl connection nd embedded in Teflon holder using epoxy resin with n exposed re 1cm 2. Before ech experiment, the electrode 45 Pge

2 Study On The Inhibition Of Mild Steel Corrosion By Ctionic Surfctnt In Hcl Medium ws first mechniclly polished with vrious grdes of emery pper (/, 2/, 3/, & 4/) nd then clened with methnol nd cetone followed by clening with double distilled wter. 2.2 Inhibitor nd electrolyte TDAB is dissolved in 1M HCl solution t vrious concentrtions (1-2, 6X1-3, 4X1-3, 2x1-3 nd 1-3 M) nd the solution in the bsence of TDAB ws tken s blnk for comprison. Aggressive solution (1MHCl), ws prepred by dilution of regent grde 34% HCl with double distilled wter. 2.3 weight loss studies MS smples (2cm x 1cm) were used for weight loss mesurement studies t vrious tempertures (298K-328K) for 3h exposure time. The % IE ws clculted by using n eqution 1: %IE = W W W X1 (1) Where W = weight loss without inhibitor, W= weight loss with inhibitor 2.4 Electrochemicl experiment Electrochemicl experiments were performed in conventionl three electrode cell, mild steel welded with copper wire nd embedded in Teflon holder using epoxy resin with n exposed re 1cm 2 s Working electrode, pltinum foil of 1cm 2 ws used s counter electrode & the reference electrode ws sturted clomel electrode (SCE) with Luggin cpillry. All potentils re mesured with respect to the SCE. Mesurements were performed using CHI 66C model Electrochemicl worksttion. Potentiodynmic polriztion curves were obtined by scnning the potentil rnge from -2mv + E corr to +2 mv + E corr t scn rte of 1mv/s fter 1h immersion time in 1M HCl nd 1M HCl + inhibitor solutions. Potentiodynmic polriztion curves were lso obtined t different tempertures to clculte the ctivtion energy of the inhibitor dsorption to mild steel surfce. The %IE ws clculted from the mesured I corr vlues using the eqution 2: %IE = I corr I x1 (2) I corr Where, I corr & I re the corrosion current densities in bsence nd presence of inhibitor respectively Electrochemicl impednce mesurements were crried out t open circuit potentil over frequency rnge of.1hz 1 KHz. The sinusoidl potentil perturbtion ws 1mv in mplitude. Electrochemicl dt were obtined fter 1h of immersion with the working electrode t the rest potentil & ll tests hve been performed in non-deerted solutions under stirred conditions. The %IE ws clculted from the Chrge trnsfer resistnce (R ct ) vlues using the following eqution 3: %IE = R ct R ct x 1 (3) R ct Where R ct & R ct re the chrge trnsfer resistnce in presence nd bsence of inhibitor respectively 2.5 Surfce nlysis by SEM nd AFM The morphology of the smple surfce before nd fter being treted with optiml concentrtion of inhibitor ws exmined by SEM nd AFM. III. Results nd discussion 3.1 weight loss Fig. 1 shows the plot of %IE versus inhibitor concentrtion, it is evident tht the %IE nd corrosion rte re concentrtion dependent. Tble 1 shows the vrition of inhibition efficiency obtined from weight loss mesurements t different concentrtion of TDAB. The inhibition efficiency increses with increse in inhibitor concentrtion; the mximum inhibition efficiency ws obtined t 1-2 M. The influence of temperture on inhibition efficiency is shown in Fig. 2. The inhibition efficiency increses by incresing the temperture from 298K-328K.The increse in efficiency with temperture s shown in Tble 1 my be ttributed to the stbility of dsorbed film of inhibitor molecules on the metl surfce, which re dsorbed strongly even t higher temperture. 3.2 Potentiodynmic polriztion The Tfel polriztion behviors of mild steel in 1M HCl with the ddition of vrious concentrtions of TDAB t different tempertures re shown in Fig. 3. The Corrosion kinetic prmeters derived from these curves re presented in Tble 2. From the Tble 2 it is cler tht the corrosion current (I corr ), vlues of mild steel decreses with the ddition of TDAB in 1M HCl. Further the E corr vlue shifts to positive direction but no significnt chnge is observed, which suggests mixed type of inhibition effect of TDAB. 46 Pge

3 Study On The Inhibition Of Mild Steel Corrosion By Ctionic Surfctnt In Hcl Medium 3.3 Electrochemicl impednce spectroscopy The experimentl results obtined from EIS mesurements for the corrosion of mild steel in the presence nd bsence of inhibitor t 25 o C re summrized in Tble 3. The impednce spectr for mild steel in 1M HCl with nd without the vrious concentrtions of TDAB t 25 o C re presented s Nyquist plot shown in Fig. 4. It cn be concluded from the Fig. 4 the impednce response of mild steel significntly chnged fter the ddition of TDAB in the corrosive solution. Fig. 5 nd b represents the equivlent circuit design used to fit the experimentl dt of EIS for hydrochloric cid in the bsence nd presence of inhibitor. The circuit elements for the obtined dt include solution resistnce (R s ), constnt phse element (CPE) d corresponds to dsorption resistnce(r ), chrge trnsfer resistnce (R ct ), dsorption resistnce (R ). The proposed models successfully described the phenomenon occurring in the studied system. Tble 3 indictes tht the chrge trnsfer resistnce (Rct), incresed with incresing TDAB concentrtion. The decrese in C dl, which resulted from decrese in locl dielectric constnt nd or n increse in the thickness of the electricl double lyer, suggests tht TDAB cted vi dsorption t the metl/ solution interfce [11]. The vlues of Y nd Y dl (Y & Y dl cn be regrded to be pproximtion to the vlues of the dsorption cpcitnce nd double lyer cpcitnce respectively) hs decresed trend for the dsorption of the inhibitor on the metl surfce, suggesting the inhibitor molecules displce the wter molecules nd other ions originlly dsorbed on the metl surfce. The vlues of n ssocited with (CPE) re found to be in the.96-1 intervl reveling tht dsorbed film re reltively homogeneous. On the other hnd, the different vlues of n is due to modifiction of the chemicl composition of the dsorbed film in combintion with their thickness s suggested by the R vlues. The vlues of n dl relted to (CPE) dl re found in the intervl indicting the electrode surfce re prtilly heterogeneous. 3.4 Adsoprtion isotherms nd thermodynmic prmeters Adsorption of the inhibitor molecule depends minly on the chrge nd the nture of metl surfce, electronic chrcteristics of metl surfce, dsorption of solvent nd other ionic species, on the electrochemicl potentil t solution interfce. The dsorption of isotherm study describes the dsorptive behvior of inhibitor in order to know the dsorption mechnism of inhibitor to the metl surfce. The most frequently used dsorption isotherms re Lngmuir, Temkin, Frumkin nd Freundlich isotherms. The Lngmuir dsorption isotherm ws found to provide the best description of the dsorption behvior (Fig.6). This suggest tht the Lngmuir dsorption isotherm provides the best description for the dsorption of TDAB on mild steel surfce. The Lngmuir dsorption isotherm is given by the following eqution C + C (4) Ѳ = 1 K Where C is the inhibitor concentrtion nd K is equilibrium constnt of dsorption, which is relted to stndrd free energy of dsorption ΔG ds by: K = exp( ΔG ds ) (5) RT ΔG ds is obtined t given temperture. K is obtined from the intercept of plot of C/Ѳ s function of C. As seen from the Fig. 6, plot of C/Ѳ s function of C yields stright line with regression co-efficient higher thn.99, showing tht the dsorption of the inhibitor is fitted to Lngmuir dsorption isotherm. The dt reported in the Tble 4 revels tht, the dsorptive equilibrium constnt (K) increses with incresing the temperture indicting tht it is strongly dsorbed even t high temperture. These results suggest tht, the inhibition of mild steel is dsorptive process. Thermodynmic prmeters ply n importnt role in understnding the inhibition mechnism. The enthlpy of dsorption nd entropy of dsorption re clculted from the following equtions log θ 1 θ = loga + logc inh Q ds 2.33RT Where A is constnt, nd Q ds is the het of dsorption equl to enthlpy of dsorption Enthlpy of dsorption (ΔH ds ) is obtined from the slope of plot of log θ vs 1/T t vrious 1 θ concentrtions. The entropy of ctivtion (ΔS ds ) is obtined from the eqution : ΔG ds = ΔH ds - T ΔS ds (7) Fig. 7 indictes tht there is good liner reltionship between log Ѳ 1 Ѳ (6) nd 1/T. The negtive sign of ΔG ds Indictes tht the inhibitor is spontneously dsorbed on the metl surfce [12]. In the present study, the ΔG ds vlues obtined rnges from -28. to kj/mol, which re lower thn -4 kj/mol but higher thn -2 kj/mol. This indictes tht the dsorption is neither typicl physisorption nor typicl chemisorptions but it is 47 Pge

4 Study On The Inhibition Of Mild Steel Corrosion By Ctionic Surfctnt In Hcl Medium complex mixed type. Tht is the dsorption inhibitor molecules on the mild steel surfce in the present study involves both physisorption nd chemisorptions (Comprehensive dsorption). As for the vlue of ΔH ds in Tble 4, the sign of ΔH ds is positive indictes the endothermic nture of steel dissolution process. The positive sign of ΔS ds which indictes tht n increse in disordering tkes plce in going from rectnts to metldsorbed species rection complex. 3.5 Kinetic prmeters The kinetic prmeters for the corrosion process were clculted from Arrhenius eqution nd the trnsition stte eqution: i corr = Aexp E RT Where i corr is the corrosion current density, A is the Arrhenius constnt, E is the ctivtion energy nd R is the universl gs constnt. i corr = RT ΔS# exp Nh R (8) exp ( ΔH # RT ) (9) Where N is Avogdro s constnt, h is plnck s constnt, ΔS is the chnge in entropy of ctivtion nd ΔH is the chnge in enthlpy of ctivtion. E is obtined from the slope of plot of ln (i corr ) vs 1/T (Fig.8), ΔS is obtined from the intercept of plot of log ( i corr ) vs 1/T nd T ΔH is obtined from the slope of plot of log ( i corr ) vs 1/T (Fig. 9). T The kinetic prmeters clculted re given in Tble 5. It is cler from tht Tble 5 tht the E decresed with incresing concentrtion of studied inhibitor. Also it is cler tht E vlues in the presence of inhibitor re lower thn tht in the bsence of inhibitor indicting tht the inhibition efficiency increses with increses with temperture. The positive sign of enthlpy of ctivtion reflect the endothermic nture of steel dissolution process mening tht dissolution of steel is difficult. It is cler from the Tble 5 tht the entropy of ctivtion is lrge nd negtive imply tht the ctivted complex in the rte determining step represents n ssocition rther thn dissocition step, mening tht decrese in disordering tke plce on going from rectnt to the ctivted complex [13, 14]. 3.6 SCANNING ELECTRON MICROSCOPY (SEM) nd AFM The SEM microgrphs of the corroded mild steel in 1M HCl in the bsence nd presence of inhibitor re shown in Fig.1 ( - b). In Figure 1 of bre mild steel electrode surfce, defects nd notches were observed, while lyer of closely pcked film ws obtined in Figure 1b, nd the surfce ws free from pits nd it ws smooth. It cn be concluded from Figure 1-b tht corrosion does not occur in presence of inhibitor nd hence corrosion ws inhibited strongly when the inhibitor ws present in the solution, then scnning electron microscopy (SEM) observtion, confirmed the existence of n bsorbed protective film on the mild steel surfce. AFM is powerful technique to investigte the surfce morphology t nno to micro-scle nd hs become new choice to study the influence of inhibitor on the genertion nd the progress of the corrosion t the metl/solution interfce. The three dimentionl AFM imges of the MS surfce exposed to 1M HCl with nd without 1-2 M TDAB for 3h re shown in the Fig. 11 (,b nd c). it is clerly evident tht, the surfce is more uniform(fig.11c) thn the surfce (Fig.b)in the bsence of inhibitor. 3.7 Conclusion The inhibition efficiency obtined by the TDAB is very good t ll tempertures. This cts s surfctnt which is widely used s surfce cting gents, ntimicrobils, in detergents, etc. Moreover surfctnts re less toxic, esily vilble, less cost etc. The future work is to investigte the synergetic effect of Surfctnts nd plnt extrcts. Surfctnt cts hs good biocide ctivity. Acknowledgement: I thnk Roop Singh, generl mnger, SINSIL Interntionl, Bnglore for extending the electrochemicl chrcteriztion fcility. References [1]. Tdros A.B., Abd-el-Nbey B.A, Inhibition of the cid corrosion of steel 4-mino-3-hydrzino-5-thio-1,2,4-trizoles, J. Electronl. Chem. 246, 1988, 433. [2]. Stoynov A.E., E.I. Sokolov E.I.. Richev S.N., The inhibition of mild steel corrosion in 1M HCl in the presence of liner nd cyclic thiocrbmides- Effect of concentrtion nd temperture of the corrosion medium on their protective ction, Corros. Sci. 39, 1997, [3]. Alshkel A.G., Hefny M.M., Ismil A.R., Corrosion prevention control, 155, [4]. Omr A.M.A., Abdel-Khlek N.A., J. Chem. Engg. 43, 1998, 117 [5]. El-Etre A.Y., Abdllh M., Bull. Of Electrochem. 1, 1994, Pge

5 Study On The Inhibition Of Mild Steel Corrosion By Ctionic Surfctnt In Hcl Medium [6]. H. Luo, Y.C. Gun, K.N. Hn, Inhibition of mild steel corrosion by sodium dodecy benzene sulphonte nd sodium olete in cidic solutions, Corrosion 54 (8), 1998, 619. [7]. A. Singh, R.S. Chudhry, Dithizone nd thiosemicrbzide s inhibitors of corrosion of type 34 stinless steel in 1 M sulphuric cid solution, Br. Corros. J. 31 (4), 1996, 3. [8]. M.M. Osmn, A.M. Omr, A.M. Al-Sbgh,Corrosion inhibition of benzyl triethnol mmonium chloride nd its ethoxylte on steel sulphuric cid solution, Mt. Chem. Phys. 5, 1997, 271. [9]. A. Kumr, E-Journl of chemistry, 5, 28, 275. [1]. M. El-Azhr, B. Mernri, M. Trisnel, F. Bentiss, M. Lgrenee, Corrosion inhibition of mild steel by the new clss of inhibitors [2,5-bis(n-pyridyl)-1,3,4- thidizoles] in cidic medi, Corros. Sci. 43 (12), 21, [11]. K. Bbic-Smrdzij, K.F. Khled, N. Hckermn, Heterocyclic mines nd derivtives s corrosion inhibitors for iron in perchloric cid, Anti Corros. Method nd Mter. 52, 25, [12]. Avci G Corrosion inhibition of indole-3-cetic cid on mild steel in.5m HCl, Colloids Surf., 317, 28, [13]. Mrsh J. Advnced orgnic chemistry, Wiley Estern 3 rd edition, [14]. Bentiss F. Lebrini M. nd Lgrenee M., Thermodynmic chrcteriztion of metl dissolution nd inhibitor dsorption process in mild steel/2,5-bis(n-thienyl)1,3,4-thidizoles/hydrochloric cid system, Corros. Sci. 47, 25, Tble 1. Inhibition efficiency of vrious concentrtions of TBAB for the corrosion of mild steel in.5mh 2 SO 4 by weight loss method t different tempertures (298K-328K). Temperture Inhibitor concentrtion (M) %IE Corrosion rte(mm/y) %IE Corrosion rte(mm/y) %IE Corrosion rte(mm/y) %IE Corrosion rte(mm/y) Blnk Χ Χ Χ Χ Χ Tble 2. Electrochemicl polriztion prmeters for MS in 1MHCl contining different concentrtion of TDAB t different tempertures. Concentrtion(M) 298K E corr (mv) i corr (μa/cm 2 ) b (mv/decde) b c (mv/decde) HCl IE 1 (%) x x x K HCl x x x K HCl x x x Pge

6 %IE Study On The Inhibition Of Mild Steel Corrosion By Ctionic Surfctnt In Hcl Medium K HCl x x x Tble 3 Impednce prmeters of mild steel in 1M HCl bsence nd presence of different concentrtion of TDAB t 25 C. Concentr Y n R C (μf/cm 2 ) Y n R C dl dl ct dl tion(m) (μ -1 cm -2 (μ) (μ -1 cm -2 (μ) (μf/cm 2 S ndl 1-4 ) S ndl 1-4 ) ) Blnk x x x Tble 4 Dt obtined from the Lngmuir dsorption isotherm for mild steel in 1M HCl t the temperture rnge of 298K -328K. Temperture(K) R Slope K ds G o ds(kjmol -1 ) H o ds(kjmol -1 ) S o ds(jmol -1 K -1 ) Tble 5 Corrosion kinetic prmeters for mild steel in 1M HCl in the bsence nd presence of different concentrtions of TDAB. Concentrtion(M) E (kj/mol) ΔH (kj/mol) ΔS (J/mol/K -1 ) Blnk x x x IE (%) o C 35 o C 45 o C 55 o C CONCENATRTION (M) Fig. 1 Vrition of %IE with concentrtion obtined from weight loss method. 5 Pge

7 %IE Study On The Inhibition Of Mild Steel Corrosion By Ctionic Surfctnt In Hcl Medium M 2x1-3 M 3 4x1-3 M 2 6x1-3 M M T(K) Fig. 2 Vrition of %IE with temperture for different concentrtion of TBAB Fig. 3Typicl Tfel plots of MS in.5mh 2 SO 4 in presence nd bsence of different concentrtion of TDAB t ) 25 o C b) 35 o C c) 45 o C & d) 55 o C Fig. 4 Nyquist Plots of mild steel in 1M HCl bsence nd presence of TDAB 51 Pge

8 log( C/ Study On The Inhibition Of Mild Steel Corrosion By Ctionic Surfctnt In Hcl Medium Fig. 5 The equivlent circuit model used to fit the impednce dt for mild steel in the bsence () nd in the presence (b) of TDAB C 35 C.2 45 C 55 C C(M) Fig. 6 Lngmuir dsorption isotherms of TDAB t different tempertures M 2X1-3 M 4X1-3 M 6X1-3 M 1-2 M 1/T(K -1 ) Fig. 7 Vrition of log Ѳ 1 Ѳ vs 1/T lni corr M HCl 1-3 M 2X1-3 M 4X1-3 M 6X1-3 M 1-2 M /T(K -1 ) Fig. 8 Arrhenius plots for mild steel in 1M HCl without nd with vrious concentrtion of TDAB 52 Pge

9 logi corr /T Study On The Inhibition Of Mild Steel Corrosion By Ctionic Surfctnt In Hcl Medium M HCl 1-3 M 2X1-3 M 4X1-3 M 6X1-3 M 1-2 M 1/T(K -1 ) Fig. 9 Trnsition stte plots for mild steel in 1M HCl without nd with vrious concentrtion of TDAB b c Fig. 1 Surfce Chrcteriztion by SEM for mild steel in 1M HCl ) Polished surfce b) in the bsence of inhibitor c) in the presence of TDAB b C Fig. 11 Surfce Chrcteriztion by AFM for mild steel in 1M HCl ) Polished surfce b) in the bsence of inhibitor c) in the presence of TDAB 53 Pge