Sers and impedance study of the equilibrium between complex formation and adsorption of benzotriazole and 4-hydroxybenzotriazole on a copper electrode in sulphate solutions

0

00134%6/90 s3oo+oal 1990 Perpmon Pm9 plc

SERS AND IMPEDANCE STUDY OF THE EQUILIBRIUM BETWEEN COMPLEX FORMATION AND ADSORPTION OF BENZOTRIAZOLE AND 4-HYDROXYBENZOTRIAZOLE ON A COPPER ELECTRODE IN SULPHATE SOLUTIONS RINJU YOUDA, HIROSHINISHIHARA and KUNITSUGU ARAMAKI Department of Chemistry, Faculty of Science and Technology, Keio Umverslty, Yokohama 223, Japan (Recewed 28 June 1989, tn reutsedform 29 August 1989)

Abstract-The corros.lonmlubltron mechamsm of benzotnazole and 4-hydroxybenzotnazole for copper m sulphate solutlons was mvestlgated by SERS spectroscopy and impedance measurements These mlubltors form complex polymers on the copper surface at high pH of the solution, positive potential of the electrode, and high concentration of the mhibitors At low solution pH, negative electrode potential and low mhlbltor concentration, single molecules of the mlubltors are adsorbed chemically on copper Fqmhbrmm between the complex formation and the adsorption relates strongly with the corrosion mlnbltlon effect 4Hydroxybenzotrlazole shows a lngher mlubitlon efficiency at the high solution pH than benzotnazole, at low pH values this order IS reversed

and then the equlhbrmm constant K IS given by

INTRODUCTION

Roughly two types of mechamsms have been reported for the mhlbltlon of copper corrosion by benzotrmzole (BTAH,” la). One 1s formation of polymeric complexes with cuprous ion, [Cu(I)(BTA)], (2)[ l-S] and the other 1s adsorption of benzotrlazole on the copper surface[b8] It has been reported that the complex polymer is underlaid with a cuprous oxide layer to form a bdayer structure[9,10], and that the formation of the benzotrlazole complex depends on pH of the solution and potential of the copper electrode[l1,12] However, a study dealing with the relation between the complex formation and the adsorption has not been published We have previously reported a study on the mhlbltlon mechanism of benzotrlazole and its hydroxy denvatlves for copper corrosion m sulphate solutions using surface enhanced Raman scattering (SERS) spectroscopy[ 131 The 4-hydroxy denvatlve (4-OHBTAH, lb)[14] showed a higher inhibition efficiency m the neutral solution than BTAH In this solution, SERS spectra of their polymenc complexes were observed, and we concluded that the higher mhlbltlon effect of 4-OH-BTAH than BTAH was attnbuted to the formation of its complex m a two- or threedlmenslonal structure by hydrogen bonding with hydroxyl groups In an acidic solution, SERS spectra of the complexes were observed at positive potentials and those of adsorbed molecules were seen at less positive potentials The change of these spectra occurred reversibly with potential The results described above suggested the idea that the adsorption and the complex formation are m eqmhbnum as IS wntten m equatlon (1) n(BTAH),,, +nCu$[Cu(BTA)],

+nH+ +ne-

K = [[Cu(BTA)],][H’]“[e-j”[(BTAH),,,I-”[Cu]-” (2) Provided that the pH value is lowered or the potential changes to more negative values, the eqmhbnum 1s shifted to the left-hand side, that is, the adsorption becomes more favourable compared wrth the complex formation This can explain the previous results, although available data are limited It 1s also deduced from equation (2) that the complex formation IS unfavourable at the low BTAH concentration because of a decrease m [(BTAH),,,] This study alms at the confirmation of this equthbnum and its relation to corrosion mhlbltlon Therefore, dependencies of the complex formation and the adsorption of BTAH and 4-OH-BTAH on solution pH, Cu electrode potential, and their concentration were investigated m sulphate solutions In addition to SERS spectroscopy, impedance measurements which can detect changes m the X

a

N+ N:;

a, X: H b, X: OH

I Structure 1

‘cu\

(1)

Structure 2

‘BTAH dissociates into BTA- and H’ 1011

1012

R

structure of the metal-solutron used

mterface[15,16]

YOUDA

eta1

were

RESULTS AND DISCUSSION Polarlzatron measurement

Copper electrode

Figures 1 and 2 show polarmatron curves of the copper electrode m 0 5 M H,SO, and 0 5 M Na,SO, wtth and without the inhrbttor Both BTAH and 4-OH-BTAH inhibited the anodrc copper Qssolutron and the cathodic hydrogen evolution reaction They did not suppress the cathodrc process m the potentral regton between - 0 1 and - 0 6 V(sce) The polarrzatron curves m this potential regron were not reproducrble since tt was ddhcult to control the effects of reductron of a trace amount of dissolved oxygen or copper ton In the prevrous paper[13], corroston mhrhtron effictency was esttmated from the anodrc and cathodic Tafel hnes, however, the lack of reproductbrhty m the cathodic polartzatton curve may cause some errors m the deduced efficrency Thus, this time we estrmated the mhrbrtron efficrency, I,, from a current density of the extrapolated anodtc Tafel hne at the open-crrcmt potential E,,, tp, by equatron (3),

A copper rod (Johnson Matthey Chemrcals, purrty 99 999%,5 mm dra) was embedded m a Teflon holder, a cross section of the rod was pohshed with emery papers and with 10 and 0 3 pm alumina abrastve and somcated m acetone and m redistilled water The electrode was pre-electrolyzed at - 10 V&e) m H,SO, for 5 mm before the measurements

z, = lOO(1- r&,0), (3) where r, and 1; refer to the current densities for the mhrbrted and unmhrbtted electrodes, respectively The values of I, were plotted agamst pH of the solutron m Ftg 3 The efficrency of BTAH was htgher at low pH but lower at htgh pH than 4-OH-BTAH

EXPERIMENTAL Materrals BTAH was obtamed as a high-grade reagent and 4-OH-BTAH was prepared by the pubhshed method[ 141 They were purified by recrystalhzatton before use The solutrons used for SERS and electrochemrcal measurements were 0 5 M H,SO, and 0 5 M Na,SO, prepared by drlutmg high-grade H,SO, and Na,SO, with redtstrlled water The pH of the latter solutron was adlusted to 10, 2 0, 3 0, 5 0 and 7 0 with H,SO, or NaOH The concentratton of the mhrbrtors was 2 x 10m3 M, unless otherwtse noted

-2

Electrochemxal measurements

For the electrochemtcal measurements, the copper electrode was put m a glass cell eqmpped with a platmum counter electrode and a saturated calomel electrode (see) Srmultaneous potentrostatrc polarmatron and impedance measurements of the copper electrode m the deaerated solutton were carried out at 30°C using a potentiostat, a frequency response analyser, and a personal computer After the determmatron of steady-state currents at a grven potentral, sme wave voltages (10 mV rms) at frequencres between 100 kHz and 100 mHz were superimposed on the potential The measurements were automatically controlled with the aid of programs[17] Several runs were made for each of the solutrons with and wtthout the mhrbttors All electrode potentrals are quoted us see SERS spectroscopy

The apparatus for measuring the SERS spectra has been described prevrously[ 131 Throughout the measurements, the copper electrode surface was tllummated wrth the 640 0 nm radiation of a dye laser at a power of 40-60 mW Three oxrdatron-reductron cycles between - 0 4 V (see) and a potentral at which 40 mA cm-* of anodrc current density for roughemng and acttvatmg the surface were camed out m the solutron without addttron of the mhtbrtors m order to avoid suppression of the cathodic and anodtc currents by the mhrbrtors Potential sweep rates were 0 05 V s- ’ m the posrtrve drrectron and 0 2 V s- ’ m the negative one The measurement of SERS spectra was carried out under a mtrogen atmosphere after addttron of the mhrbrtors to the solution

-3

Gi 'E 4"-4 . Z $ -5

4

50

-I

0

-0 5 E / V (SCE)

0

D

Frg 1 Polanzatron curves (current densrty I vs potentral E) and mterfacral capacitance C of copper in 0 5 M H,SO, wnhout (- --) and with BTAH (---) and COH-BTAH (---1

Corrosion mhlbltlon of Chydroxybenzo-

and benzotrmzole

1013

-3

-6

00

-7 I

\ \ \

\

\

r

0 .

I-

io

It

F

:

k

,\\

---0 5

-1.0

E/

V (SCE)

capacttance on the potenttal obtained by ac Impedance measurements are described m a later section SERS spectra of BTAH and 4OH-BTAH copper electrode

100

= . -0 50

1

12

I

5(

1000

Fig 4 SERS spectra for BTAH m 0 5 M H,SO, at various potentials Asterisk refers to a signal of SOi-

1

0

Fig 2 Polanzatlon and C-E curves of copper in 0 5 M Na,SO, at pH 7 0 without (- - -) and with BTAH (-) and 4-OH- BTAH (- -)

I

1500

Ramn shift / cm-'

,____:

I

I

I

I

3

4

5

6

L

7

PH Fig 3 Anodlc mhlbltlon efficiency I, of BTAH (0) and 4-OH-BTAH (A)

The figure shows high mhlbltron efficiencies of the benzotnazoles for the copper dlssolutlon m the acid solutions The efficlenctes of the mhlbltors m the neutral solutions were not high, as compared with those shown m the previous paper This IS because the difference m the esttmatton method of corroston current density as described above causes different corroston current densities Corrosion mhlbltton efficiency esttmated from faradalc conductance and dependency of mterfactal

on a

In the previous report, we showed the SERS spectra of BTAH and 4-OH-BTAH molecules chemlsorbed on the copper surface and those of the complex polymers [Cu (BTA)], and [Cu(4-OH-BTA)], formed at the mterface[13] The prevtous results are summartsed as follows The adsorptton of the molecules took place m 0 5 M H,SO,, complex formatlon occurred m the neutral solution or at electrode potentials more postttve than - 300 mV (see) m the acid solution The band assigned to the m-plane NH bending mode at 1140 cm-’ for BTAH and 4-OHBTAH characterized the molecules adsorbed on the surface, and the spectrum m which thts band appeared was called “adsorption spectrum” The “complex spectrum” was characterized by the appearance of a peak assigned to a stretching mode of the trlazole rmg at ca 1200 cm- ’ for both the mhtbttors and by disappearance of the 6, band These charactenzatton methods were apphed m this study The bdayer structure of cuprous oxide/complex polymer was not discussed here since no signal due to vtbratlonal modes of cuprous oxide was observed m the SERS spectra reported subsequently Figures 4 and 5 show the spectra for BTAH and 4-OH-BTAH adsorbed on a copper electrode m 0 5 M H,SO, at vanous electrode potentials, respectively The typical adsorption spectrum of BTAH was observed at - 0 5 V and the complex spectrum at - 0 2 V The peak at 1140 cn- ’ m the former spectrum disappeared at electrode potenttals more positive than -0 3 V, and the peak at 1190 cm-l

R YOUDAet al I

0V

I

(SCE)

1500

1

I1

1

1500

I1

I1

11

I

1003 Roman shift / cm-l

I

500

5 SERS spectra for COH-BTAH m 0 5 M H,SO, at vanous potent& Astensk refers to a signal of SOi-

Rg

0

%F //A

-L

--

A

l Complex formatlon

Li

1000 Roman shift / cm-'

500

Rg 7 SERS spectra of BTAH at 2 x 10m3 M (a), 2 x 10e4 M (b), and 2 x lo-’ ystj)m 0 5 M H,SO, at - 0 3 V

spectra of BTAH and 4-OH-BTAH m the sulphate solution at each pH Because of hydrogen gas evolution from the electrode surface, no SERS spectrum could be obtained at the potential more negative than - 0 8 V even m a neutral solution The potential limits of the complex formation and molecular adsorption for BTAH and 4-OH-BTAH are plotted agamst the pH of the solution m Fig 6 The potential repon for the transltlon between the complex formation and the molecular adsorption shifted m the negative direction with increase of pH for both inhibitors Dependence of the SERS spectra on concentration of BTAH and 4-OH-BTAH

2

z-o.5 Y

Adsorption

-I 0

'0

l?g 6 E-pH diagram obtamed from SERS spectra for BTAH (0) and 4-OH-BTAH (A) Hatched zones show coexistence of complex and adsorbed molecule Sohd marks m&ate open-arcmt potentials of the electrode mhlblted with BTAH (0) and COH-BTAH (A)

emerged at potentials positive to - 042 V Both peaks coexisted between E = - 0 42 and - 0 3 V, as shown m Fig 4 Slmllar spectral changes occurred m the solution of 4-OH-BTAH as displayed m Fig 5 The adsorption spectrum appeared at the potential more negative than - 0 04 V and the complex spectrum at potentials positive to - 0 34 V, respectively Potential limits of the complex formation and the molecular adsorption were determined m the SER.9

The SERS spectra of BTAH and 4-OH-BTAH on copper m 0 5 M H,SO, and 0 5 M Na,SO, (pH 7 0) were measured at concentration of 2 x lo-‘, 2 x 10e4, and 2 x lo-‘M of the mhlbltor Examples of SERS spectra are shown m Fig 7, for BTAH in 0 5 M H,SO, at - 0 3 V The spectra of the benzotnazoles could be detected even at 2 x 10mSM m the acid solution While the complex spectrum of BTAH was observed at 2 x 10e3M m this figure, the adsorptlon was determined at 2 x 10e4, and spectrum 2 x lo-‘M In 0 5 M Na,SO, at pH 7 0, the adsorption spectrum of BTAH was predommant over the complex spectrum at 2 x lo-‘M and more negative than - 0 6 V These tendencies were analogous to those m the SERS spectra for 4-OH-BTAH It IS thus concluded that the adsorption of BTAH and 4-OH-BTAH occurs more readdy than the complex formation at their low concentration Impedance measurements

Examples of the Nyqmst diagram for copper in 0 5 M Na,SO, at pH 2 0 with COH-BTAH at 0 00, - 082 V are shown m Fig 8 -020 and

Corrosion mhlbltlon of Chydroxybenzo- and benzotnazole

0

16

Zrml

36

54

1015

72

I kQcm2

‘0

I

2I

1

3I

41

51

6I

L 7

PH

Fig 9 Inhlbmon

0

3.0

Zreal

60

90

120

I lORcm2

Fig 8 Nyqulst diagrams for copper m 0 5 M Na,SO, at pH 2 0 with 4-OH-BTAH at E = 0 00, - 0 20 and - 0 82 V

A semlclrcle 1s observed m the high frequency regon at all three potentials The plots at low frequencies are dlsperslve at 0 00 and - 0 20 V but gve a second semlclrcle at - 0 82 V These low-freq&cy plots should involve effects of drffuslon, partial charge transfer, and/or adsorption of reactants[15,16] Smce the data obtained m this study were not enough for the discussion of such effects, we estimated charge transfer resistance R, and mterfacral capacitance C from a semlclrcle fitted to the plots at high frequencles m the Nyqmst diagram, assuming a simple eqmvalent circuit, a parallel capaator-resistor combmatlon at the electrode mterface[l& 161 The mhlbltlon efficiency I, was determined from faradalc conductance K,, a reciprocal of R,, at E,,, as I, = lOO(1 - K,/K;)

efficiency I, of BTAH (0) and 4-OHBTAH (A)

(4)

where K, and KF denote the faradalc conductances for the inhibited and umnhlblted electrodes respectively The values of I, for the benzotnazoles decreased m the low pH region and Increased m the high pH with an increase of pH, as shown m Fig 9 The efficiency of BTAH was higher m the acid solution but lower m the neutral one than 4-OH-BTAH Interfacial capacitance expressed by C = ll(%l.P*) (5) where w_ls the angular frequency at the maximum of the semlarcle, are also shown as a function of electrode potential m Figs 1 and 2, respectively The values of C at the open-circuit potential E,,, were plotted agamst pH of the sulphate solutions without and with the mhlbltors m Fig 10 The capacitances for the umnhlblted electrode decrease with mcreasmg the pH The values of C for the inhibited electrode are low, a few IF cm-’ over the whole pH range except for the electrode with 4-OH-BTAH m the low pH

loo1

0

1

2

3

4

5

6

7

DH

Fig 10 Interfaclal capacitance C at open-arctut potential for copper electrode unmhlblted (Cl) and mhlblted with BTAH (0) and COH-BTAH (A)

repon This low capacitance 1s attributed to the formation of complex polymer on the electrode because low capacitances have been reported to be due to the formation of benzotnazole complex film[18,19] As shown m Ftg 1, the C values for BTAH and 4-OH-BTAH m 0 5 M H,SO, were low at the potential more positive than 0 V and - 0 1 V, respectively, and increased up to 20 or 30 pF cm-’ at potentials negative to those potentials The potentials of these changes correspond to those at which the copper complexes [Cu(BTA)], and [Cu(4-OH-BTA)], begm to change to the molecules BTAH and 4-OH-BTAH adsorbed on the copper surface, respectively The capacitance values, a few and 20-30 FF cm- 2 are reasonable for the complex polymer formatlon[ 18,193 and adsorption, respectively In the C-E curves m Fig 1, peaks are observed at - 0 37 and -062 V for BTAH and -037 and -058V for 4-OH-BTAH These peaks should relate to changes m the structure of the metal-solution Interface such as

R

1016

YOUDA

the complex polymer m the neutral solution more easdy than BTAH but less easily m the acid solution as shown m the diagrams This result agreed with the relatlonshlp between the inhibition efficiency I, or I, and the pH of solution The open circuit potential 1s also plotted in Figs 6 and 11 Most of the potentials for the benzotriazoles m the solutions at the various pH are located m the region of complex formation whereas E,,, for 4-OHBTAH are m the region of adsorption This means that not only the complex polymer but also adsorbed molecule of 4-OH-BTAH contribute to the mhlbltlon of copper corrosion m the acid solution The lower efficiency of 4-OH-BTAH than BTAH for the acid corrosion 1s caused by a structural change from [Cu(COH-BTA)], to 4-OH-BTAH adsorbed on the copper surface

C

Gj =: >-0

5

\ w

AdsorptIon

-I

c

et al

1

I

I

1

2

3

1

1

I

I

0

5

6

7

DH

Fig 11 Potential E-pH diagram obtained from mterfaclal capacitance of copper electrode mhlhted with BTAH (0) and COH-BTAH (A) Sohd marks mdlcate open-arcult potentials of the electrode mhlblted with BTAH (0) and COH-BTAH (A)

adsorptlon+iesorptlon phenomena[20,21] Completion of the transition between adsorption and complex formation of the mhlbltors, deprotonation of adsorbed BTAH and 4-OH-BTAH, and adsorption of atomic hydrogen formed by proton reduction can be supposed as such phenomena A peak 1s observed at - 0 5 V m the C-E curve m the solution wlthout the mhlbltors (see Fig 1) This peak can be attributed to adsorptlon+iesorptlon of atomic hydrogen since the potential 0 5 V 1s near the potential where current due to proton reduction begins to increase as 1sseen m the t-E curve m Fig 1 Thus, the peaks at - 0 62 V for BTAH and at - 0 58 V for 4-OH-BTAH m the C-E curves may relate to the hydrogen adsorptlon Low peak heights m solutions with the mhlbltors can be explained because the adsorption of hydrogen should be suppressed by adsorption of the mhlbltors However, it was lmposslble to obtain a support of this speculation by SERS spectra because hydrogen evolution from the electrode surface prevented an observation of SERS spectra at potentials negative to - 0 5 V m 0 5 M H,SO, A detail study on the peaks m the C-E curves 1s now under way Figure 11 shows the pH-potential diagrams obtamed from the impedance measurements The potential where capacitance increases from a few FF cm-* (ex 0 and 0 1 V for BTAH and 4-OH- BTAH respectively, m Fig 1) 1s plotted us pH of the solution A part of the curves of this diagram corresponds to the limits of adsorptlon shown with solid curves m the E-pH diagram obtained from SERS spectroscopy m Fig 6 This result confirms that the capacitance change 1s due to the adsorption-complex formatlon transition The potential limits in Fig 6 shifts to some extents toward more negative potential than those m Fig 11 This 1s because the SERS spectra provide information from only a few monolayers of species on the surface whereas the impedance data are derived from the complete electrode interphase 4-OH-BTAH formed

Corrosaon mhlbztron mechamsms of BTAH and 4-OH-BTAH

Effects of the pH of solutions, the potential of the copper electrode and the concentration of mhlbltors on the SERS spectra and the mterfaclal capacitances for BTAH and 4-OH-BTAH are summarized as follows (1) The complex polymers [Cu(BTA)], [Cu(4-OH-BTA)], are readdy formed at more posltrve potential, the higher pH, and higher concentration, otherwise the BTAH 4-OI$BTAH molecules are adsorbed

and the the and

(u) The complex [Cu(4-OH-BTA)], is more easily dlssoclated m the acid solution than [Cu(BTA)],, but more hardly m the neutral solution As ISwritten m the introduction, the result (1)can be explained quahtatlvely by the concept of adsorption-complex formation eqmhbrmm as gven m equation (1) It should be noted that the equation represents a phenomenon only for the surface monolayer In the real system, there 1s a process of polymer growth (accumulation of the layers), and the film thickness and porosity should be significant factors of the corrosion mhlbltlon Thus, neglecting this process may yield mlsleadmg conclusions on the overall corrosion mhlbrtlon mechanism In order to Judge this point, we used m this study two different techniques One 1s SERS spectroscopy which gives mformatlon on a few monolayers on the surface and the other 1s the impedance method from which capacitance values of the interface can be obtained The capacitance includes mformatlon on the whole surface film Simtlarlty of the results obtained from both techniques as shown m Figs 6 and 11 indicates the validity of the concept expressed m equation (1) for the conslderatlon of the corrosion mhlbltlon mechanism The presence of complete complex layer on the surface at E,, IS shown in the pH-E diagrams obtamed from the SERS spectra of the benzotnazoles m the acid and neutral solutions The diagrams estimated from the impedance data for 4-OH-BTAH indicate the presence. of the adsorbed molecules on copper m the acid solution at E,, suggesting the formation of a less protective film with a low degree of

Corrosion mhlbltlon of Chydroxybenzo- and benzotnazole polymerlzatlon on the surface as compared with the complete layer This should be the reason of the lower mhlbltlon efficiency of 4-OH-BTAH than BTAH m the acid solution On the other hand, the protective layer of [Cu(4-OH-BTA)], forms on the surface m the neutral solution because of a two- or three-dlmenslonal structure of the film by brldgmg between the hnear polymers with hydrogen bonding of hydroxyl groups, as has been dlscussed m the previous paper [ 133 This results m the higher mhlbttlon efficiency of 4-OH-BTAH than BTAH m the neutral solution The mhlbltlon efficiency of BTAH and 4-OHBTAH decreased with pH greater than 3 0, as shown m Fig 9 The decreasing efficiency can be ascribed to the formation of a low molecular waght polymer complex caused by the mcrease of [H’] m equation (2) On the contrary, the increase of the efficiency with decreasing pH m the acid solution may arlse from the marked mhlbltlon of anodlc reaction m the acid solution, as shown m Fig 3 Cuprous ion formed in the anodlc reaction can favour the formatlon of the complex polymer

1017

Acknowledgements-The authors wish to acknowledge Drs M Ito and M Takahashl for useful advlce on the SERS measurements REFERENCES 1 G W Polmg, Corros Scl 10, 359 (1970) 2 N Monto and W Suetaka, J Jpn Inst Metals 35,1165 (1971) 3 J J Kester, T E Furtak and A J Bevolo, J electrochem Sot 129, 1716 (1982)

4 M Flelschmann, I R Hdl, G Mongoh and M M Muslam, Electrochtm Acta 28, 1325 (1983)

5 C Tornkvlst, D Thierry, J Bergman, B Lledberg and C Leygraf J Electrochem Sot 136, 58 (1989)

6 F Mansfeld, T Smith and E P Parry, Corrosion 27,289 (1971)

7 G Lewis, Br Corros J 16, 169 (1981) 8 D Thlerry and C Leygraf, J electrochem Sot 132, 1009 (1985)

9 T Notoya and G W Pohng, Corrosion 32, 216 (1976) 10 R Alkxe and A Cangellan, J electrochem Sot 136,913 (1989)

11 I C G Ogle and G W Poling, Can Metals Q 14, 37 (1975)

12 M M Muslam, G Mengoh, M Flelschmann and R B Lowry, J electroanal Chem 217, 187 (1987)

CONCLUSIONS Inhlbltlon behavlours of BTAH and 4-OH-BTAH for copper corrosion m sulphate solutions at various pH were mvestlgated by the SERS spectroscopy and the impedance techmque The mhrbltors react more readily with cuprous Ion to form protective films of the polymenc complexes, [Cu(BTA)], and [Cu(4OH-BTA)], at high pH of the solution, posltlve potential of the electrode, and high concentration of the mhlbltor than they are absorbed on the copper surface These facts indicate an equdlbrmm between the complex formation and adsorption The protective films of the complex polymers play an Important role m the mhlbltlon of copper corrosion The mhlbltlon efficiency of 4-OH-BTAH 1s higher m the neutral solution than BTAH because of the formation of the complex layer m the two- and threedlmenslonal structure In the acid solution, BTAH 1s more effective than 4-OH- BTAH smce the complex of 4-OH-BTAH 1s m part dlssoclated at the open clrcult potential of the electrode

13 R Youda. H Nlshlhara and K Aramakl. Corros Scl 28. 87 (1988)

14 D R Randell and E A Cox, US Pat 3720616 (1967) 15 M Sluyters-Rehbach and J H Sluyters, Comprehensne Treatise of Electrochernutry, J O’M Bockns, B E Conway 9. D 177. Plenum Press. New 16 A j Barh and L R Failkner,

(Edlted by E Yeager, and S Sarangapam), Vol York (1984)

Elec&he&al Methods, Fundamentals and Appkcatlons, p 316, Wdey, New York

(1984)

17 K Slnmura, H Nisluhara and K Aramakl, Boshoku G~utsu 35, 289 (1986)

18 F E Heakal and S Haruyama, Corros Scl 20, 887 (1980)

19 M Fkxschmann, G Mengoh, M M Muslam and C Paeura. Electrochlm Acta 30. 1591 (1985) 0 A Petru’ and q V’ Batrakov, Adsorption of Orgamc Compounds on Electrodes, p 35, Plenum, New York (1971) 21 E Grleadi, E Kxowa-Elsner and J Pencmer, Interfacral Electrochemutry, An ExperImental Approach, p 36, Ad&son-Wesley, London (1975) 22 J O’M Bockns and A K N Reddy, Modern Electrochemutry, VoI 2, p 633, Plenum Press, New York (1970)

20 B B -Da&askm,