Monatshefte fiir Chemie 126:1087-1095 (1995) Monatshefte///r Chem/e Chemical Monthig © Springer-Yerlag 1995 Printed in Austria

Inhibition of Copper Corrosion by Arylazotriazoles in Nitric Acid Solution

L. H. Madkour, M. A. Elmorsi, and M. M. Ghoneim

Chemistry Department, Faculty of Science, Tanta University, Tanta, Egypt

Summary. A study has been made to investigate the effect of some azoheterocyclic dyes of the type 3-arylazo 1,2,4-triazole (AT) on the corrosion of copper exposed to 0.5M nitric acid solution at different temperatures and at different AT concentrations. Using potentiodynamic polarization and Tafel electrochemical methods, it can be shown that AT compounds are good inhibitors of copper corrosion in HNO 3 solution. The kinetic and thermodynamic parameters of the inhibited system were determined. The high inhibition efficiency of these compounds may be due to the adsorption of the additive itself and/or the adsorption of the formed Cu(II)-AT complexes at the polarized electrode interface. Cathodic polarization measurements showed that AT dyes are predominantly cationic inhibitors.

Keywords. Acid medium; Arylazotriazoles; Inhibition; Copper.

Hemmung der Korrosion yon Kupfer in salpetersaurer Liisung durch Arylazotriazole

Zusammenfassung. Der Effekt einiger azoheterocyclischer Farbstoffe des Typs 3-Arylazo-1,2,4-triazol (AT) auf die Korrosion yon Kupfer in 0.5M Salpeters/iure bei verschiedenen Temperaturen und unterschiedlichen AT-Konzentrationen wurde untersucht. Potentiodynamische Polarisation und elektrochemische Methoden nach Tafel zeigen, dab Verbindungen vom Typ AT gute Korrosions- inhibitoren fiir Kupfer gegeniiber HNO 3 sind. Die kinetischen und thermodynamischen Parameter des inhibierten Systems wurden bestimmt. Die hohe inhibitorische Wirksamkeit der untersuchten Verbindungen kann auf die Adsorption des Additivs selbst oder auf jene des Cu(II)-A T-Komplexes an der polarisierten Elektrodenoberfl/iche zuriickzufiihren sein. Kathodenpolarisationsmessungen zeigen, dab A T-Farbstoffe vorwiegend kationische Inhibitoren sind.

Introduction

C o p p e r is widely used in var ious industr ia l and cons t ruc t iona l opera t ions . Consequen t ly , the s tudy of its co r ros ion inhib i t ion is of great im p o r t an ce today. M a n y studies have been devo ted to the inhib i t ion of coppe r co r ros ion in neut ra l and acidic med ia by benzot r iazo le or to ly t r iazole c o m p o u n d s [1 -5 ] , but there are relat ively few invest igat ions on arylazotr iazoles . It has been suggested that the benzo t r i azo le c o m p o u n d s act by forming an o rganometa l l i c complex molecu la r layer at the e lec t rode surface. In this work, the au thor s present a s tudy of the inhibi t ing effect of some 3-arylazo 1,2,4-triazoles on the co r ros ion of co p p e r in ae ra ted 0.5 M H N O 3 solut ion.

1088 L.H. Madkour et al.

Results and Discussion

Inhibitor's effect on corrosion

Potentiodynamic measurements were performed in the presence of different concentrations of arylazotriazole dyes added to 0.5 M HNO 3 solutions at 295 K. The results are shown in Table 1 and Fig. 1. The three arylazotriazole dyes D 1, D 2, and D 3 attain an optimum inhibition of > 95% at a concentration of 10 .4 M. The high inhibition efficiency of the applied dyes towards copper can be explained as follows. As the dye molecule approaches the electrode surface, the electric field of the double layer increases the polarization of the molecule and induces additional charges on both the N and O atoms, thus enhancing the adsorption of the dye molecule. In the case of D 1 and D 2, the formation of Cu(II)-dye complexes in solution can be assumed which consequently are adsorbed at the electrode surface. The formation of these complexes between Cu 2÷ and D1 or D2 and the mechanism of their chelation was explained by a proton displacement from the phenolic OH group by the Cu 2 + ion [6]. Thus, the bonding of the Cu 2 ÷ ion to the dye molecule takes place through a covalent linkage with the oxygen of the phenolic group, whereas the N=N group contributes to a coordination bond as follows:

N - - T N : N ~ O \ /OH2 L _N ~ Cu--H20 -Y" 1".o

H H20 Cu(ll)-D1 complex H I

f N\N Me N- ~1 N%

H20 N~,~ ))

o_ o _o t \OH2

~ / %N--~-- N Me I~.

"~N / I H

Cu(II)-D2 complex (1:2; at high concentration of D2)

H2Ox." ?H2

/______~O -- (iu \ NO2

~( ))-~ N. OH2 ~ " / ~ N ~ N

Me 1~. --.N j

I H

Cu(II)-D 2 complex (1:1; at low concentration of £)2)

Inhibition of Copper Corrosion 1089

• I.gO~ . Free acid / tg xxxxx 1x l t~ 'M O 1 / / ; J /

. . . . . . 1,1o4M o2 I , ' : /

. . . . . ,,,o,Mo3 / # / +20C / ' g

j +I00 ~ ~ , ~ " '~

-10C -.... "-....... , % ,,

-20C ""-... ""-% %.,.

I ] I i , I

103 10 z 105 106 10 7 108 109

i, n ,4 cm -2

Fig. 1. Potentiodynamic polarization curves of Cu in 0.5 M HNO 3 alone and containing 10-4M arylazotriazoles (Dx, D 2, and D3) at 295 K

LU

t~

(b

25

1.5

0 . 5 -

2OO

f~

400 600 wove lengfh ~rim

Fig. 2. Absorption spectra of Cu in 0.5 M HNO 3 con- taining l0 -4 M D2; : no corrosion; .: corrosion at 313 K; xxxx: corrosion at 333 K

+0.35

+0.15

z,, -O.O5

- 0..25

-0.~5 ÷0.25

,-, / /

",, . , "> . i ' " ",~,i"

, _t , I , 1

*0.05 -0.15 -q35

E(v vs. ,4g*)

Fig. 3. Cyclic voltammograms of Cu in 0.5 M , H N O 3 containing I 0 - 4 M D 3 ; - - : no

-0 .50 corrosion; ; corrosion at 295K; ..... : corrosion at 333 K

1090 L .H. Madkour et al.

¢,q

N

i

rN

© N

b

._=

..=

0 C)

0 "m

8 Z

q3

..=

O

9

I

I

i

O

I

O

i¢)

I

4 ~

~ g

>,

?

x

¢N

c5 + +

% ¢d

i

~d

I

P- p..

~ ~ l l ~ ~

X X X X X X X X X X X

8 ~ 8 8 Z Z Z Z

~ + ~ + +

d ¢ 5 x c5 x ¢5 x

v~

8

b, ca

o

b~

ca

o

G)

Inhibition of Copper Corrosion 1091

C u 2 + complexes readily forms with the title dyes D1 and D2; it has been proved that the ratio of the metal ion to the ligand either is 1:1 or 1:2. The structure of the resulted complexes was substantiated by their analytical data, by cyclic voltammetry, and by spectral analysis (mainly ultraviolet spectra) as shown in Figs. 2 and 3.

The inhibition effect of the three studied arylazotriazole compounds D 1, D2, and D 3 are likely due to the interaction of the adsorbed dye molecules with the Cu 2 + ions at the electrode surface formed during the polarization at the interface via the triazole ring forming a chemisorbed complex [7]. From Table 1, Ecorr becomes more negative at the addition of the inhibitors which indicates that these tested dyes are predominantly effective in the cathodic region.

Tqfel constants for Cu corrosion

The cathodic Tafel constant (CTC) in the free nitric acid solution corresponds to oxygen reduction, whereas the higher anodic Tafel constant (ATC) values (Table 1) mainly correspond to the dissolution reactions [8] as fellows:

C u ~ C u + + e - and C u ~ C u 2 + + 2 e -

At different concentrations of the tested 3-arylazo 1,2,4-triazoles, it was found that CTC varied from 66-170 inV. dec-l , whereas ATC changed from 73-141 mV-dec-1. These higher Tafel constant values support the probability of the presence of a complicated surface processes involving Cu ions and A T molecules. Moreover, Tafel slopes of about 90 mV.dec-1 can be attributed to a surface kinetic process rather than a diffusion controlled process [91.

Temperature effect on corrosion

Ioorr and Rcorr increase with increasing temperature as shown in Table 2. This is due to the thermal activation of the surface polarization of the following reactions:

C u ~ C u + + e - and C u ~ C u 2 + + 2 e -

The increase of Rco~r is due to the absence of protective oxide layers at the Cu surface in nitrate medium. Thus, the increase of temperature enhances both the copper corrosion and the additive desorption processes without leading to Cu(II)-AT complex formation. For O2, the inhibiting efficiency value decreased to 56~o at 313 K, then increased again to 83~ at 343 K. It was also found that the colour of the electrolyte solution containing D 2 changed from yellow to reddish at 313 K and became violet at higher temperatures. The phenomenon of the colour changes for the inhibitor D 2 can be explained as follows:

(1) The transformation of the tetrahedral Cu(II)-D2 complex into the octahedral form by coordination of two solvent molecules leads to the six coordinate complex.

(2) The thermochromic property of Cu-D2 chelates results from a changed resonance by chelate ring formation; this is due to the intramolecular H-bond and/or metal chelation.

The effect of temperature on the potentiodynamic polarization plot of Cu exposed to 0.5M HNO3 acid and in the presence of inhibitor D z is plotted in Fig. 4.

1092 L .H . M a d k o u r et al.

Table 2. Effect of t empera tu re on the corrosion parameters of Cu in 0.5 M H N O 3 in absence and in

presence of 1 x 1 0 - 4 M A T , 295 ~< T~< 3 4 3 K

System Temp. Rp x 10 -2 I . . . . R .... E ....

(K) (f~) (#A 'cm -2) (MPY) (mV vs. SCE)

0.5 M H N O 3 295 0.1870 1609.00 1483.00 + 54

333 0.1470 2839.00 2617.00 + 22

343 0.1159 3862.00 3561.00 + 27

0.5 M H N O 3 295 4.9810 47.86 44.13 - 1 1

+ D1 303 3.0830 99.85 92.06 + 8

313 2.7870 111.10 102.40 + 3

323 0.8687 308.10 284.00 + 11

333 0.3867 1009.00 930.70 + 17

343 0.2690 1508.00 1390.00 + 19

0.5 M H N O 3 295 3.2910 67.32 62.07 - 34

+ D 2 303 1.3200 261.20 240.80 - 341

313 0.2771 2357.00 2173.00 - 2 1 3

323 0.3188 1177.00 1085.00 - 149

333 0.2778 1249.00 1151.00 - 121

343 0.6696 631.70 582.40 + 2

0.5 M H N O 3 295 3.8400 43.57 40.17 - 12

+ D 3 303 2.7560 62.54 57.66 - 81

313 2.8230 93.29 86.01 - 34

323 1.4700 189.30 174.50 - 2 1

333 0.3965 874.60 806.30 + 1

+ 800

+ 600

.4- 400

+200

u2 o.o

-200

-400

g g

2 2

• i /@.,. :

44- +

. . . . . . . . . . . _ . - - ' - . . . . . .

[ i ~ I I

103 10 g 10 5 106 107 108 109

i, n A c m -2

Fig. 4. Po ten t iodynamic polar iza t ion curves of Cu in 0.5 M H N O 3 conta in ing 10 . 4 M D 2 at different

temperatures; : 303 K; .: 313 K; . . . . . . ". 333 K; xxxxx: 343 K

Inhibition of Copper Corrosion 1093

8

6

2 2

"*, \ .... D1 '~ - - D2 \ ,k. I . . . . . D3

~__L (K ) '~ I"

Fig. 5. logk vs. 1/T plot of Cu in 0.5M HNO3 x I0" containing 10 4M arytazotriazole dyes; xxxxx:

D1; : D2; . . . . . : D3

It is clear that the passive layer region decreases as the temperature increases. Thus, D 2 may act as an anodic inhibitor rather than a cathodic one, whereas Ecorr becomes more positive as the temperature increases (Table 2 and Fig. 4).

The UV spectroscopic investigations and cyclic voltammetric analyses of the electrolyte solutions containing D 2 and/or D 3 at different temperatures are plotted in Figs. 2 and 3, respectively. Before the corrosion process, a strong absorption peak at 303 nm was observed, corresponding to the azo group. During the corrosion processes, another additional broad absorption band was recorded at 542nm, corresponding to the formation of the Cu(II)-D2 complex in solution (Fig. 2).

Cyclic voltammetric analysis of the electrolyte solution containing 10 -4 M D 3 (Fig. 3) revealed one redox peak before the corrosion process. During corrosion at different temperatures, another additional redox shoulder and redox peak were observed corresponding to the stepwise reduction of the free Cu 2 + ions present in solution.

Both UV spectral and cyclic voltammetric analyses indicate that the increase of temperature enhances both the Cu corrosion and the dye desorption processes.

Kinetic and thermodynamic parameters

The activation energy (AE #) for the copper corrosion in 0.5 M HNO 3 containing 10--4M of different inhibitors (D1, D2, and D3) was calculated from Eyring's

equation k = K T e x p [10]. It was found that AE # increases in the order

D 2 > D 3 > D 1. An Arrhenius plot indicating the variation of log k or logRcorr with the temperature is shown in Fig. 5. The higher entropy value (AS #) in the case of D 2 compared to the values ofD 1 and D 3 as shown in Table i indicates a slower reaction [11].

Conclusion

The general corrosion of Cu exposed to 0.5 M HNO 3 solution containing arylazo 1,2,4-triazole (A T) dyes can be summarized as follows:

(1) A higher corrosion inhibition efficiency was observed for Cu exposed to 0.5 M HNO 3 solution containing A T compounds due to the formation of Cu(II)-A T complexes at the polarized electrode surface. The adsorption process is endothermic in nature and causes a reasonable of corrosion inhibition at high temperatures.

1094 L.H. Madkour et al.

(2)

(3)

T h e Cu c o r r o s i o n inh ib i t ion process due to the f o r m a t i o n of C u ( I I ) - A T

complexes is e n t r o p y con t ro l l ed r a the r t h a n ac t iva t ion energy cont ro l led , since

the ac t iva t ion ene rgy values are re la t ively high (Table 1).

The h igher ca thod ic Tafe l c o n s t a n t value in free acid (0.5 M H N O 3 ) is a t t r i bu ted to the oxygen reduc t ion , whereas the anod i c Tafe l c o n s t a n t value represen ts the

Cu dissolut ion. After add i t ion of the A T c o m p o u n d s , the ca thod ic and anod ic reac t ions m a i n l y involve A T molecules , i.e. a surface kinet ic con t ro l l ed process

takes place.

E x p e r i m e n t a l

The copper metal (99.99~ Copper Egyptian Company) was used as foils with a surface area of 1-1.3 c m 2, containing 0.001~o Pb as impurity. These foils were sealed in glass tubes using epoxy resin. The copper electrodes were mechanically polished and rinsed in an ultrasonic bath containing distilled water before each experiment.

A stock solution of HNO3 (0.5 M) was prepared. Potentiodynamic measurements were maintained using a computerized corrosion measurement console 350 A-PARC (from EG & G) connected to a K-47 corrosion cell containing twin high density, non-permeable graphite counter electrodes and a saturated calomel electrode (SCE) fitted in a bridge tube incorporating an ultra-low leakage Vycor frit. The cell was immersed in a thermostatted water bath. In the Tafel condition, a controlled potential scan was applied to the copper electrode starting at E .... and extending in either the anodic or the cathodic direction for a few hundred millivolts. An extension of the linear region defines i .... at the intersection with Eoor,. The corrosion rate R .... in milli-inches per year (MPY) can be obtained from the following equation:

R .... =0.13i .... EW/d

Here, i .... is the corrosion current density (#A-cm-2), EW is the equivalent weight of copper, and d is its density. Further corrosion measurement details have been given elsewhere [12-14].

The UV/Vis spectra were recorded with a UV-160 A Shimadzu spectrophotometer. The cyclic voltammograms were recorded using the polarographic analyzer Model 264A and the electrode assembly (303A) of 2.6 x 10-2 cm 2 area with a sweep rate of 20 mV" sec-1.

The synthesis of the investigated azo-heterocyclic dyes of the type 3-arylazo 1,2,4 triazole compounds was accomplished directly via the coupling reaction of the diazonim salt of 3-amino 1,2,4-triazole with different types of phenolic compounds.

The investigated arylazatriazole dyes were:

GHO

N--~1~N:N~~ OH ~.N/N

I H

3-( 3-formyl-4-hydroxg- l-phenylazo)- l ,2,4-triazole ( D1)

HO

N 7-N=N- LN N

I H

3-( 2-hydroxy-5-methyl- l -phenylazo )- l ,2, 4-triazole (D2)

Inhibition of Copper Corrosion 1095

N , [ - - N : N - ~ O H II i~ L..N/N

I H

3-(4-hydroxy-l-phenylazo)-l,2,4-triazole (/:)3)

References

[1] Mansfeld F, Smith T, Parry EP (1971) corrosion 27:289 [2] Poling GW (1970) Corros Sci 10:359 [3] Fox PG, Lewis G, Bonden PJ (1979) Corros Sci 19:457 [4] Hollander O, May PC (1985) Corros Nace 41:39 [5] Zichuman G, Tong R, Notoya T (1991) B Electrochem 7:60 [6] Gaber M, Hassanein M, Ahmed HA (1986) Indian J Textile Res ll: 48 [7] Chadwick D, Hashemi T (1978) Corros Sci 18:39 [8] Faita G, Fiori G, Salvadore D (1975) Corros Sci 15:383 [9] Dahar HP, White RE, Burnell G, Cornwell LR, Griffin RB, Darby R (1985) Corros Nace 41:317

[10] Parhetier; Souchay "Chemical Kinetics". Elsevier, New York (1967): 155 [11] Taqui Khan MM, Shukla RS (1991) Polyhedron 10:2711 [123 Elmorsi MA, Mabrouk EM, Issa RM, Ghoneim MM (1987) Surface Coatings Technol 30:277 [13] Elmorsi MA, Ghoneim MM, Issa FM, Mabrouk EM (1987) Surface Coatings Technol 31:389 [14] Elmorsi MA, El-Sheikh MY, Bastawessy AM, Ghoneim MM (1991) B Electrochem 7:158

Received January 10, I995. Accepted (revised) April 24, 1995