Progress in Organic Coatings 63 (2008) 424–433

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Progress in Organic Coatings

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Electrochemical synthesis and characterization of poly(pyrrole-co-o-toluidine)

Süleyman Yalcinkaya ∗, Tunc Tüken, Birgül Yazici, Mehmet ErbilCukurova University, Science and Letters Faculty, Chemistry Department, 01330 Adana, Turkey

a r t i c l e i n f o

Article history:Received 8 October 2007Received in revised form 19 June 2008Accepted 7 July 2008

Keywords:o-ToluidinePyrroleCopolymerCorrosion

a b s t r a c t

The electrochemical polymerization of o-toluidine has been investigated in oxalic acid solution. It wasshown that the oxidation of monomer could be achieved but this process does not yield a stable, homoge-nous polymer film on either platinum or mild steel electrodes. Therefore the copolymerization betweenpyrrole and o-toluidine has been studied as an alternative method for obtaining good quality coating (lowpermeability and water mobility, high stability), which could also be easily synthesized on steel. For thisaim, various monomer feed ratio solutions of pyrrole:o-toluidine 9:1, 8:2 and 7:3 have been examined,in aqueous oxalic acid solution. By using cyclic voltammetry technique, copolymer films were realizedon platinum and steel, successfully. The temperature of synthesis solution was found to have a vital roleon polymerization and film growth, as much as the monomer feed ratio. The synthesis of homogenouscopolymer film could only be achieved under ≤25 ◦C conditions with using the 9:1 ratio, while the 8:2ratios could only produce stable films below 5 ◦C. As the amount of o-toludine increased the requiredtemperature value decreased further, 7:3 ratio could only give a stable copolymer film below 2 ◦C. Thecharacterization of deposited copolymer coating has been realized by using SEM micrographs, UV–vis

and FT-IR spectroscopy techniques and cyclic voltammetry. The protective behaviour of these coatingswas also investigated against mild steel corrosion in 3.5% NaCl solution, by means of electrochemicalimpedance spectroscopy (EIS) and anodic polarization curves. It was found that the monomer feed 8:2

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. Introduction

The studies aiming to develop conducting polymer films for vari-us applications (electrochromic devices [1], photoelectrochemicalevices [2], rechargeable batteries [3], sensors [4,5] and corrosionrotection [6–9]) frequently involve structural modification of theolymer backbone to enhance the properties, e.g. incorporationf various functional groups changes conductivity and porosity.olyaniline, polypyrrole and their derivatives have been regardeds the most important conducting polymers, owing to their stabil-ty and synthesis advantages [10,11]. The electropolymerization ofniline (and its derivatives) brings about some difficulties like slowucleation and film growth, but its high stability and interestinglectrochemical properties have attracted much attention [10]. Onhe other hand, polypyrrole films generally exhibit better conduc-ivity and are more easily synthesized by electropolymerization,

hen compared to polyaniline [12,13].

The role of anticorrosive polymer coatings on oxidizable met-ls is to hinder the attack of corrosive environment and reducehe corrosion rate [14,15]. The conducting polymer films gener-

∗ Corresponding author. Tel.: +90 322 338 60 81; fax: +90 322 338 60 70.E-mail address: syalcinkaya@cu.edu.tr (S. Yalcinkaya).

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300-9440/$ – see front matter © 2008 Elsevier B.V. All rights reserved.oi:10.1016/j.porgcoat.2008.07.002

ating against the corrosion of mild steel.© 2008 Elsevier B.V. All rights reserved.

lly have nobler reduction potentials with respect to mild steelnd this give rise to an interesting phenomena; the anodic protec-ive effect of conducting polymer films. The protection comes fromormation of more stable ferric compounds under oxidizing andtabilizing effect of polymer film [16–18]. On the other hand, theydrophilic and porous nature of conducting polymer films lead toerious drawbacks for anticorrosive applications under severe con-itions. The copolymerization has long been utilized to improvearious properties (conductivity, stability, porosity, etc.) of polymerlms [19]. The similar structural properties of pyrrole and anilinellow the copolymerization between these species. It was reportedhat this process undergoes exothermically. Li et al. have reportedhat copolymer film of pyrrole–toluidine (feed ratio of 3:7) coulde realized at 2 ◦C temperature, with chemical synthesis technique20].

Poly(o-toluidine) homopolymer film exhibit good stability.andana et al. have reported that electrochemically synthesizedoly(o-toluidine) could protect copper against corrosion in chlo-ide media, successfully [21]. However, the attempts aiming the

lectrosynthesis of poly(o-toluidine) film on mild steel surface haveailed. This was attributed to slow nucleation and low surface cover-ge. Therefore the anodic oxidation of steel continues at monomerxidation region and inhibits the formation of stable-adherentlm on the surface. In order to obtain a film which combines the

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dvantages of pyrrole (ease of synthesis and conductivity) and-toluidine (low permeability and high stability), poly(pyrrole-o-o-toluidine) coating have been electrosynthesized on mildteel. The copolymer films were characterized by FT-IR, UV–vispectroscopy, cyclic voltammetry measurement and SEM micro-raphs. The corrosion behaviour of poly(pyrrole-co-o-toluidine)opolymer was investigated in 3.5% NaCl solution.

. Experimental

All the electrochemical studies were carried out in a conven-ional three-electrode set up, open to the atmosphere, by usingHI604 model electrochemical analyzer. The counter electrode wasplatinum foil with 2 cm2 surface area and Ag/AgCl electrode wassed as the reference, all the potential values were referred tohis electrode. Mild steel samples were cylindrical rods measur-ng 0.40 cm in the radius and with the following composition (W%).082, C; 0.621, Mn; 0.181, Si; 0.0129, P; 0.0162, S; 99.0866, Fe, theorking are 0.5024 cm2 while rest of electrode was isolated with

hick polyester block.The copolymer films were electrochemically synthesized by

sing cyclic voltammetry technique. The synthesis solution (all

hemicals were purchased from Merck) composition was 0.1 Mxalic acid +0.1 M monomer, varying the ratio pyrrole:o-toluidine9:1, 8:2, 7:3) but keeping constant the total concentration of

onomers. Each monomer feed ratio was studied for a set of tem-eratures, then the most appropriate values were determined and

3

(

Fig. 1. The voltammograms recorded for Pt electrode in 0.3 M oxalic acid +

ic Coatings 63 (2008) 424–433 425

pplied, these temperatures were 25, 5 and 2 ◦C for 9:1, 8:2 and 7:3onomer feed ratios, sequentially. These temperatures were yield-

ng stable copolymer films on mild steel surface. The solution of 8:2onomer feed ratio did not give a stable polymer film above 5 ◦C,hile the ratio of 7:3 involved lower temperature like 2 ◦C. Thereas a monomer oxidation which was observed as current increase,ut this process could not lead to a sufficiently thick and homoge-ous film. The thickness of coatings was approximately the same,y balancing the CV numbers and passing charges within monomerxidation potential regions. The applied charge density value was.17 C/cm2 for each sample.

UV–vis spectra of the copolymer solution in dimethyl sulfoxideDMSO) were recorded on a PerkinElmer Lambda 25 UV–Vis spec-rophotometer. FT-IR spectra measurements were conducted usingPerkinElmer spectrum RX1 FT-IR system instrument. For this aim,

he polymer coatings electrosynthesized on mild steel were peeledff the surface and their pellets were prepared with bulk KBr. Elec-rochemical impedance spectroscopy (EIS) and anodic polarizationurves were used to investigate the corrosion performance of theseoatings.

. Results and discussion

.1. Synthesis

Fig. 1 shows the cyclic voltammograms recorded for platinumPt) electrode in 0.3 M oxalic acid +0.1 M o-toluidine (at 25 ◦C) by

0.1 M o-toluidine scan rate, 10 mV/s (a), 20 mV/s (b) and 50 mV/s (c).

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26 S. Yalcinkaya et al. / Progress in

pplying various scan rates 10 mV/s (a), 20 mV/s (b) and 50 mV/sc). The monomer oxidation process was observed as currentncrease at ∼+0.70 V, in the first forward scan for all scan rates.ven though the oxidation current value increased with increas-ng scan rate (from 10 to 50 mV/s), it decreased at the second andollowing cycles. This oxidation process led to formation of poly(o-oluidine), but a stable homogenous film could not be obtained onhe surface. During the successive CVs applied for film growth (forncreasing the thickness), the oxidation–reduction process of pro-uced poly(o-toluidine) was observed as anodic and cathodic wavesetween approximately +0.2 and +0.4 V, in the forward and reversecans. However, none of the scan rates gave sufficiently thick anddherent polymer film which could cover the surface successfully.lso, it should be noted that the hydrogen reduction process wasbserved beyond −0.3 V (toward negative direction) for all scanates.

Fig. 2 shows the voltammograms of MS electrode obtained in.3 M oxalic acid +0.1 M o-toluidine solution by applying variouscan rates, at 25 ◦C. The typical oxidation–passivation behaviourf MS appeared as broadened anodic peak starting at −0.6 V, dur-ng the first forward scan. This process occurs via oxidation of MSo give Fe(II) ions which give rise to Fe(II) oxalate complex for-

ation and passivation of the surface. The increasing scan rateaused greater oxidation–passivation peak due to higher dissolu-ion rate. The monomer oxidation process was also observed atround +0.70 V, during the first forward scan. In the case of MS sub-trate the amount of adhered polymer product was observed to be

tacms

Fig. 2. The voltammograms recorded for MS electrode in 0.3 M oxalic acid +

ic Coatings 63 (2008) 424–433

igher than the platinum. This was also observed by naked eye withhe presence of a polymeric film on the surface after a few cycles.owever the surface coverage of this film was not sufficient so that

he re-passivation peak was observed for each reverse scan. Duringhis re-passivation process the passivity is broken due to reductionf Fe(III) compounds to yield Fe(II). Then the formation of Fe(II)xalate provides the passivity, once again [14]. The appearance ofhis peak was indicating of an interaction between the solution andhe substrate thus that the film was not homogenously covering theurface.

Since it was not possible to obtain a stable and adherentoly(o-toluidine) film on metal surface (neither platinum norteel) via electropolymerization, the copolymer of pyrrole and-toluidine was studied. It was believed that this copolymer woulde electrosynthesized easily and has the advantages of pyrrole and-toluidine. Figs. 3 and 4 shows the CVs obtained on Pt electrode inarious monomers feed ratio of pyrrole and o-toluidine. In Fig. 3,uccessive three cycles were given for a potential range of −0.6 and.2 V. During these measurements, a scan of 50 mV/s was applied.he CVs exhibited remarkably different pattern when comparedo single o-toluidine solutions. The monomer oxidation potentialalue of pyrrole was also reported to be around +0.70 V, in litera-

ure [8]. Therefore, the oxidation of these two monomers could bechieved simultaneously. Then the formed radical cations couldombine to yield a copolymer structure. However, the studiedonomer feed ratios could only yield stable polymer film under

pecific temperature conditions. These temperature values were

0.1 M o-toluidine scan rate, 10 mV/s (a), 20 mV/s and (b) 50 mV/s (c).

S. Yalcinkaya et al. / Progress in Organic Coatings 63 (2008) 424–433 427

F .01 M5 V/s.

defioifbtf

oofmnatodthrTwocet

vfi

iotefmcr9wsweaafic

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ig. 3. The voltammograms recorded for Pt in (0.3 M oxalic acid +0.09 M pyrrole +0◦C) (b) and (0.3 M oxalic acid +0.07 M pyrrole +0.03 M o-toluidine, at 2 ◦C) (c), 50 m

etermined after many attempts with various temperatures forach monomer feed ratio. The ratio of 9:1 did not give a polymerlm above the 25 ◦C temperature, while the 8:2 ratios couldnly produce stable films below 5 ◦C. As the ratio of o-toluidinencreased the required temperature value was found to decreaseurther, therefore a stable copolymer film could only be realizedelow 2 ◦C, with the ratio of 7:3. This case could be explained byhe exothermic nature of polymerization mechanism suggestedor aniline derivatives in literature [20].

It must be noted that the observed current values for monomerxidation and polymerization increased with respect to single-toluidine. This could simply be explained with significantly dif-erent mechanism of polymerization, in presence of pyrrole. As a

atter of fact, the current decrease observed in this region couldot be observed for single pyrrole polymerization [10]. This waslso related to a decreasing conductivity with incorporation of o-oluidine into the structure. The produced copolymer film was inxidized state and its reduction was observed as cathodic waveuring the reverse scan, also re-oxidation process was observed athe following forward scan. The surface coverage of the producedomogenous film could be considered as well, since the hydrogeneduction process could not be observed at the first reverse scan.he copolymer film inhibited the hydrogen gas evolution which

as observed beyond −0.3 V (towards negative direction) previ-usly for single o-toluidine conditions. The CVs recorded for theopolymer film growth on platinum electrode are given in Fig. 4, forach monomer feed ratio. It was apparent that the copolymer filmhickness could be increased with successive cycles. The current

irts

o-toluidine, at 25 ◦C) (a), (0.3 M oxalic acid +0.08 M pyrrole +0.02 M o-toluidine, at

alues corresponding to oxidation–reduction behaviour of polymerlm increased gradually with the cycle numbers.

The convenient temperature values determined for copolymer-zation of pyrrole and o-toluidine were also applied for film growthn mild steel substrate and Figs. 5 and 6 shows the CVs obtained. Theypical oxidation–passivation behaviour of MS appeared as broad-ned anodic peak starting at −0.6 V, during the first forward scanor the all monomer feed ratios. However, it was clear that the

onomer feed ratio altered the rate of film growth and the resultingopolymer in aspect of conductivity and surface coverage. Thus, thee-passivation peak could be observed as a little wave for the ratio:1 while this event was observed for the other ratios; however itas apparent that the increasing o-toluidine ratio decreased the

urface coverage and polymerization rate. The re-passivation peakas observed even after third cycle, but it became smaller after

ach cycle due to film growth. The monomer oxidation process waslso observed at around +0.7 V, during the first forward scan. It ispparent from Fig. 6 that adherent and homogeneous copolymerlms could be realized on MS surface, at convenient temperatureonditions.

.2. Spectroscopic characterization of copolymer films

FT-IR spectra of polypyrrole and copolymer samples are shownn Fig. 7. It was reported that the band centered at 3250 cm−1 waselated to characteristic –NH– stretching vibration. This indicatedhe presence of –NH– groups in o-toluidine and pyrrole units thathowed in all spectra [12,22]. Both polypyrrole and copolymer spec-

428 S. Yalcinkaya et al. / Progress in Organic Coatings 63 (2008) 424–433

F rowth

t–zpmoii[oo

srttpmi[tcF

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tt9tTsrit[drteesRwcTia

ig. 4. The voltammograms recorded during the poly(pyrrole-co-o-toluidine) film g

ra showed the peaks at 1500–1600 cm−1 which was attributed toC C– stretching of reduced and oxidized quinoid form of ben-ene and pyrrole ring, respectively [23]. In the FT-IR spectrum ofolypyrrole, the peak at 1033 cm−1 is due to –C–H in-plane defor-ation of the pyrrole unit [12]. It was reported that in the spectrum

f the copolymer sample the peak at 3040 cm−1 is due to character-stic aromatic –C–H– stretching [24]. Also, the peak at 1380 cm−1

s attributed to methyl group in the structure of o-toluidine unit25]. The peaks observed in the FT-IR spectrum of poly(pyrrole-co--toluidine) were indicating to presence of o-toluidine unit in thebtained copolymer structure.

The UV–vis spectra of the polypyrrole and copolymer samplesolution in DMSO recorded at 25 ◦C are shown in Fig. 8. The spectraepresenting homopolymer of polypyrrole exhibites the charac-eristic peak located at the 260 nm, which is attributed to �–�*ransition (K band) of the pyrrole ring [26]. It was found that thiseak shifted to 245 nm (K band) in the spectrum of the copoly-er. The second band in the spectrum of copolymer at 279 nm

s assigned to the �–�* transition (B band) of the benzene ring26]. This band appearing in the spectrum of poly(pyrrole-co-o-oluidine) indicates that the o-toluidine unit is in the copolymerhain. The structure of synthesized copolymer films were given inig. 9.

The SEM micrographs of polypyrrole film and the copolymerlms deposited on mild steel from 9:1 and 8:2 monomer feed ratio

olutions are given in Fig. 10. It was apparent that the synthe-ized copolymer films had a structure significantly different fromauliflower like structure of polypyrrole. The particle size decreasedith increasing o-toludine ratio and the appearance became more

ikely a globular structure of aniline derivatives.

fir

(i

on Pt electrode 9:1 at 25 ◦C (a), 8:2 at 5 ◦C (b) and 7:3 at 2 ◦C (c); scan rate, 50 mV/s.

.3. Corrosion tests

The EIS measurement results are given in Figs. 11–13 as a func-ion of immersion time in corrosive solution. After 4 h of exposureime, the obtained Nyquist plot for the coating deposited from:1 monomer feed ratio solution was made up of two distinc-ive regions which were in appearance of semi-ellipses or arcs.he uncompensated ohmic resistance (Ru) is always a small con-tant for given electrolyte solution and appeared as a shift on theeal axis. The first region (from 100 kHz down to 10 Hz) includednformation about the electrochemical process occurring withinhe active pores of polymer film reaching the substrate surface27–30]. Therefore the resistance depicted by this region was han-led as pore resistance (Rpo), which included the charge transferesistance (Rct) arising from kinetically controlled metal dissolu-ion at the bottom of the pores, any species giving rise to resistiveffect and diffuse layer resistance (Rd) along the pore. In the case ofxtremely thin and porous conducting polymer coating, the corro-ion process could only occur within the pores. Moreover, the saidpo values were observed to decrease with time due to increase ofater held by coating. This phenomenon increases the mobility of

orrosive species towards the metal and increasing corrosion rate.he second region at lower frequency was related to polymer coat-ng resistance; this Rf value includes both the corrosion productsccumulating within the pores of polymer coating and the intact

lm itself. The sum of Rpo and Rf values were equal to polarizationesistance Rp [31–33].

It must be noticed that the measured open circuit potential valueEcorr) of sample was −0.54 V, which indicated a metal/solutionnterface at the bottom of the pores. Once the solution reached

S. Yalcinkaya et al. / Progress in Organic Coatings 63 (2008) 424–433 429

Fig. 5. The voltammograms recorded for MS in (0.3 M oxalic acid +0.09 M pyrrole +0.01 M o-toluidine, at 25 ◦C) (a), (0.3 M oxalic acid +0.08 M pyrrole +0.02 M o-toluidine, at5 ◦C) (b) and (0.3 M oxalic acid +0.07 M pyrrole +0.03 M o-toluidine, at 2 ◦C) (c), 50 mV/s.

Fig. 6. The voltammograms recorded during the poly(pyrrole-co-o-toluidine) 9:1 at 25 ◦C (a), 8:2 at 5 ◦C (b) and 7:3 at 2 ◦C (c) film growth on MS electrode; scan rate, 50 mV/s.

430 S. Yalcinkaya et al. / Progress in Organic Coatings 63 (2008) 424–433

Fig. 7. FT-IR spectra of the polypyrrole (a) and poly(pyrrole-co-o-toluidine) (9:1) (b).

tppr

Fig. 9. The structural representation of polypyrrole (a) and the copolymer (b).

Table 1The Rp (ohm), Ecor (V), E% and P values after various exposure time (t) in 3.5% NaClsolution

Electrode t (h) Rp (ohm) Ecor (V) E% P

Uncoated MS 24 58 −0.661 – –MS/9:1 4 2511 −0.540 98 0.23

24 1585 −0.598 96 0.1248 1259 −0.603 95 0.14

MS/8:2 4 2487 −0.568 98 0.1424 1995 −0.585 97 0.1248 1585 −0.593 96 0.13

M

catssmitct(

Fig. 8. UV–vis absorption spectra of polypyrrole (- -) and 9:1 copolymer (—).

he metal surface, the corrosion process starts at the bottom of theores and the measured potential of the electrode becomes a mixedotential value. Then this region should be considered as the poreesistance, since it is related to charge transfer and diffusion pro-

slfio

Fig. 10. The SEM micrographs of polypyrrole (A),

S/7:3 4 708 −0.569 92 0.4824 708 −0.602 92 0.2448 1122 −0.587 95 0.21

ess taking place within the pores. Considering the polymer filmnd the substrate as two separated metals connected in an elec-rolyte, the mixed potential reached by the couple depends on theurface ratio of noble and less noble metals in contact with theolution. Here, the polymer film behaves like the nobler syntheticetal, since it has the ability to oxidize the metal when it is found in

ts oxidized state. Then, electron transfer could take place betweenhe metal and coating, at metal/coating interface. As the amount oforrosive solution interacting with the substrate metal increased,he Emix value approached the Ecorr value of the base metalTable 1).

The second region of Nyquist plot was related to the coating

ystem which consisted of polymer film and the passive oxideayer formed at metal/polymer interface. The reduction of polymerlm and the accumulation of corrosion products (within the poresf coating) would increase the film resistance with time; it was

and copolymer coatings 9:1 (B) and 8:2 (C).

S. Yalcinkaya et al. / Progress in Organic Coatings 63 (2008) 424–433 431

Fig. 11. EIS results of 9:1 copolymer for 4 h (�); 24 h (�); 48 h (©) exposure times in % 3.5 NaCl.

); 24

orrnTwdww

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Fig. 12. EIS results of 8:2 copolymer for 4 h (�

bserved that the total resistance decreased with time. This waselated to water up taking process, during immersion period in cor-osive solution. Also the pore and coating resistance regions couldot be identified neither in Nyquist plot nor log f–log Z diagram.his could be explained with the ratio of these resistance values,

ith respect to each other. Therefore, the total resistance was han-led as the polarization resistance value (Rp) and given in Table 1,ith respect to exposure time. These EIS results could be handledith an equivalent circuit including the resistive elements for the

ts8v

Fig. 13. EIS results of 7:3 copolymer for 4 h (�); 24

h (�); 48 h (©) exposure times in % 3.5 NaCl.

oating (Rf), the resistance against corrosion (Rpo) and the uncom-ensated ohmic resistance (Ru); the capacitive elements of intactoating Cf and the double layer capacitance (Cdl), as it frequentlyppeared in the literature [27].

It was clearly seen that the other coating systems also exhibited

he same feature with that deposited from 9:1 monomer feed ratioolution. However the highest resistance values were obtained with:2 ratio. Also this coating gave slightly nobler corrosion potentialalues with respect to others.

h (�); 48 h (©) exposure times in % 3.5 NaCl.

432 S. Yalcinkaya et al. / Progress in Organ

F(

(igtdnam

litpat

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HiascuccswpoeaTanticorrosive behaviour of coatings and showed that the polymer

ig. 14. Anodic polarization curves for coated and uncoated samples, MS (�), 9:1); 8:2 (�); 7:3 (�) copolymer coated samples in % 3.5 NaCl.

By the help of Rp values the percent protection efficiency valuesE%) were calculated for coated electrodes according to follow-ng E% = ((R−1

p (uncoated) − R−1p (coated))/R−1

p (uncoated)) × 100 equation andiven in Table 1. Even though, the amount of electrolyte solu-ion increased at the metal/polymer interface and the Ecorr value

ecreased with increasing exposure time. The %E values were foundot to decrease with increasing exposure time; this case provideddditional evidence for the anodic protective behaviour of the poly-er film.

cmmo

Fig. 15. Successive CVs recorded for 9:1 (a), 8:2 (b) and 7:3 (c) co

ic Coatings 63 (2008) 424–433

The approximate values for porosity of coatings were also calcu-ated for the aim of comparison, by using the EIS results and givenn Table 1 [34]. The relevant equation is derived from Tafel equa-ions written for coated and uncoated samples under the same overotential value, by doing so it is assumed that the coating blocks thenodic surface and decreases the metal dissolution. Thus the pro-ective efficiency of coating is strictly related to surface coverage, �.

= 1 − � = Rp (uncoated)

Rp (coated)× 10−(�E/ˇA)

owever, the anodic protective effect of conducting polymer films known to lead a passive layer (ferric compounds) on corrodedrea, therefore the corrosion process at the bottom of the poreshould be better considered to take place under oxygen diffusionontrol. Under these circumstances, the value of ˇA should besed as 0.120 V/dec which could be derived from B value. Then thealculated porosity (P) values became more reliable in aspect ofomparison. However, it was seen that he calculated P values werelightly high, considering the E% values. This case is explainedith the charge transfer process occurring between metal andolymer film, which increased the total current value measured allver the surface. It was seen from Table 1 that the porosity valuesxhibited a tendency to decrease with immersion time. This waslso indicative for anodic protective behaviour of coating systems.he porosity is one of the important parameters in aspect of

oatings were able to hinder the access of corrosive solution toetal substrate. However it must be noted that the results sum-arized in Table 1 were indicating to better protective behaviour

f the coating obtained in 8:2 monomers feed ratio solution.

polymer coated samples on the Pt electrode in 3.5% NaCl.

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S. Yalcinkaya et al. / Progress in

The anodic polarization curves recorded for coated samples andare sample are given in Fig. 14. It was apparent that the coatingsould effectively lower the anodic dissolution rate of substrate thathe current values decreased remarkably. Also, the over oxidation ofolymer coating becomes an important phenomena at high anod-

cally polarized conditions, but the current values still remainedower than bare sample. The corrosion process could only take placehrough the pores of coating and once the coating prevented the

ass transfer between the corrosive environment and substrate,he corrosion rate will decrease. The lowest dissolution rate wasbserved for the coating obtained from 8:2 monomer feed ratio.his also showed that this coating exhibited lower permeabilitynd higher stability than the other coatings.

In order to examine the stability of copolymer films obtainedrom different monomer feed ratio solutions, they have been syn-hesized on Pt electrode (applying the same conditions as before)nd the successive cycles were recorded in 3.5% solution (Fig. 15).he oxidation of polymer film was observed in the forward scan andhe reduction was realized at the reverse scan. The current densityalues involved during these successive cycles were informative inspect of polymer film’s electroactivity and degradability. It waslearly seen that the current values increased with increasing cycleumbers for the coating deposited from 9:1 ratio. Also the highestnd most stable current values were observed for the coating of 8:2atio.

. Conclusions

The synthesis of o-toluidine could not be achieved on mild steel,y direct oxidation of monomer from the solution. However, theynthesis of copolymer between pyrrole and o-toluidine could beealized electrochemically on mild steel. The increasing ratio of-toluidine requires lower synthesis temperature; this could bexplained with exothermic nature of polymerization. The depositedoatings were compact and adherent on the surface that very thinlms could provide significant protection behaviour against theorrosion of steel. The ratio of 8:2 gave the coating with highest

fficiency when compared to other coatings examined. Also thisoating was shown to have high stability and low permeability inggressive solution. The porosity value of this film was 0.13 and itsrotection efficiency was 96%, after 48 h immersion period in 3.5%aCl solution.

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ic Coatings 63 (2008) 424–433 433

cknowledgment

This study has been financially supported by Cukurova Uni-ersity research fund. The authors are grateful to the Cukurovaniversity research fund (Project No: FEF2006D21).

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