The corrosion inhibition of mild steel in acidic media by a new triazole derivative

\ PERGAMON

Corrosion Science 30 "0888# 678Ð792

The corrosion inhibition of mild steel in acidic media by a new triazole derivative F[ Bentissa\ M[ Lagreneea\\ M[ Traisnelb\ J[C[ Hornezb\c a

Laboratoire de Cristallochimie et Physicochimie du Solide\ URA CNRS 341 ENSCL\ BP[097\ 48541 Villeneuve d|Ascq Cedex\ France b Laboratoire de Ge nie des Proce de s d|Interactions Fluides Re actifsÐMate riaux\ ENSCL\ BP[097\ 48541 Villeneuve d|Ascq Cedex\ France c Groupe de Recherche sur les Biomate riaux\ Laboratoire de Biophysique\ Faculte de Me decine\ Lille\ France Received 03 November 0886^ accepted 01 October 0887

Abstract A new corrosion inhibitor\ namely\ 2\4!bis"1!thienyl#!3!amino!0\1\3!triazoles "1!TAT# has been synthesised and its inhibiting action on the corrosion of mild steel in acid baths "0 M HCl and 9[4 M H1SO3# has been investigated by various corrosion monitoring techniques\ such as corrosion weight loss tests and electrochemical impedance spectroscopy[ The electrochemical study reveals that this compound is an anodic inhibitor[ Changes in impedance parameters "Rt and Cdl# are indicative of the adsorption of 1!TAT on the metal surface\ leading to the formation of a protective _lm which grows with increasing exposure time[ 1!TAT is able to reduce the steel corrosion more e}ectively in 0 M HCl than in 9[4 M H1SO3[ The adsorption of this inhibitor is also found to obey the Langmuir adsorption isotherm in both acids[ 1!TAT is considered as a non!cytotoxic substance[ Þ 0888 Elsevier Science Ltd[ All rights reserved[ Keywords] triazole^ corrosion inhibitors^ mild steel^ electrochemical impedance spectroscopy^ adsorption

0[ Introduction The use of inhibitors is one of the most practical methods for protection against corrosion\ especially in acidic media ð0Ł[ The progress in this _eld has been phenomenal in recent years and is borne out by the output of literature ð1Ł[ Acid solutions are generally used for the removal of rust and scale in several industrial processes[ Inhibitors are generally used in these processes to control the metal dissolution[ HCl

 Corresponding author[ 9909!827X:88:, ! see front matter Þ 0888 Elsevier Science Ltd[ All rights reserved[ PII] S 9 9 0 9 ! 8 2 7 X " 8 7 # 9 9 0 4 2 ! X

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and H1SO3 are widely used in the pickling of steel and ferrous alloys[ Most of the well known acid inhibitors are organic compounds containing nitrogen\ sulphur and oxygen atoms[ The in~uence of organic compounds containing nitrogen\ such as amines and heterocyclic compounds\ on the corrosion of steel in acidic solutions has been investigated by several workers ð2\ 3Ł[ The existing data show that most organic inhibitors act by adsorption on the metal surface[ This phenomenon is in~uenced by the nature and surface charge of metal\ by the type of aggressive electrolyte and by the chemical structure of inhibitors ð4Ł[ The aim of this paper is to study the inhibiting action of a new organic compound containing nitrogen\ sulfur and aromatic rings[ The electrochemical behaviour of steel in acidic media in the absence and presence of inhibitor has been studied by electrochemical impedance spectroscopy and gravimetric methods[ The toxicity of their inhibitors has been determined using the cell culture system[

1[ Experimental details 1[0[ Inhibitor Figure 0 shows the molecular structure of the investigated compound\ which has been labelled 1!TAT[ 1[0[0[ Synthesis of 1!TAT A mixture of 1!thiophenecarbonitrile "38[5 g\ 9[1 mole# and excess of hydrazine hydrate "19 ml# was warmed on a oil bath for 2 hr[ Aqueous hydrochloric acid "009 ml\ 1 N# was slowly added to the reaction mixture and was then boiled for 04 minutes ð5Ł[ The solution was cooled to 9>C and made alkaline with ammonia solution "d9[77#[ The white precipitate was collected and crystallised from ethanol\ mp 179>C[ The reaction yields is about 45)[ The compound structure was con_rmed by nuclear magnetic resonance spectroscopy "NMR#[ 0

HÐNMR data "in DMSO#] 5[4 "s\ 1H#\ 6[2 "m\ 1H#\ 6[7 "m\ 1H#\ 7[1 "m\ 1H#[ CÐNMR data in "DMSO#] "C3\ 010[0#\ "C2\ 018[7#\ "C4\ 020#\ "C1\ 026#\ "C0\ 037[2#[

02

1[1[ Specimens Mild steel strips containing 9[98) P\ 9[27) Si\ 9[90) Al\ 9[94) Mn\ 9[10) C\ 9[94) S and the remainder iron were used for the gravimetric and electrochemical

Fig[ 0[ Chemical formula of 2\4!Bis"1!thienyl#!3!amino!0\1\3!triazole[

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measurements[ Strips were mechanically polished on wet SiC paper "grades 019Ð599Ð 0199#\ rinsed with bidistilled water\ degreased ultrasonically in ethanol before use and dried at room temperature[

1[2[ Solutions The aggressive solutions used were made of AR grade HCl and H1SO3[ Appropriate concentrations of acids were prepared using bidistilled water[ The concentration range of the inhibitor employed was 19 to 099 mg:l in both acids[

1[3[ Gravimetric measurements The weight loss of the rectangular steel specimens of size 4×1×9[914 cm in 0 M HCl and 9[4 M H1SO3\ with and without the addition of di}erent concentrations of 1!TAT\ was determined after a 13 hr period of immersion\ at a temperature of 29>C\ in air atmosphere without bubbling[

1[4[ Electrochemical measurements Electrochemical experiments were performed in a conventional three!electrode glass cell assembly with a mild steel rod as the working electrode "we# and a platinum foil of 2×2 cm as the auxiliary electrode "ce#^ Hg:Hg1Cl1:KCl satured "sce# for the 0 M HCl medium\ or Hg:Hg1SO3:K1SO3 satured "sse# for the 9[4 M H1SO3 medium were used as the reference electrodes[ The electrolytic solution was an acidic solution maintained at 29>C in air atmosphere without bubbling[

1[4[0[ The electrochemical impedance spectroscopy "EIS# The EIS measurements were carried out at Ecorr after immersion on standing in air atmosphere with the electrochemical system "TACUSSEL#\ which included a digital potentiostat model Z COMPUTER[ Squared sheets of mild steel of size 4×4×9[914 cm\ exposing a circular surface of 6[44 cm1 to the solution\ were used as the working electrode[ After the determination of steady!state current at a given potential\ sine wave voltages "09 mV# peak to peak\ at the frequencies between 099 kHz and 09−1 Hz\ were superimposed on the rest potential[ The measurements\ performed at rest potentials after 19 hr of immersion\ were automatically controlled with the aid of computer programs[ 1[5[ Viability test 1[5[0[ Cell culture system L021 cells derived from normal human embryonic lung epithelium "cell!line] ATCC

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CCL4# were cultured in plastic bottles in MEM 9900 medium "Eurobio# supplemented with 09) fetal calf serum[ 1[5[1[ Survival rate Survival curves were determined by using the colony!forming method ð6\ 7Ł[ Depending upon the number of surviving colony!forming units expected after a given treatment\ known but di}erent numbers of cells are plated in Petri!dishes[ The number of cells seeded was such that an average of 099 colonies per Petri!dish was obtained[ Cells were incubated for 01 days in a 09) CO1 atmosphere[ These cells were con! tinuously exposed to variable concentrations] 14 to 399 mg:ml for the powder of the tested compound and 4 to 79 mg:ml for pure Nickel!powder "Goodfellow# with a particle size ³4 mm\ as positive control ð8Ł[ The growth medium was not renewed during the experiments[ At the end of the experiments\ clones were stained with Crystal Violet[ At least 5 repeated experiments were performed in triplicate for each concentration[ The survival rate of the exposed cells was calculated with respect to control cultures "099)#[

2[ Results 2[0[ Gravimetric measurements The inhibition e.ciency of the inhibitor for the corrosion of mild steel is calculated as follows h")#

$

%

W−Winh ×099\ W

"0#

where W and Winh are the values of the corrosion weight loss of steel after immersion in solutions without and with inhibitor\ respectively[ Table 0 gives values for the inhibition e.ciency obtained from the weight loss

Table 0 Inhibition e.ciencies for various concentrations of 1!TAT for the corrosion of mild steel in 0 M HCl and 9[4 M H1SO3 obtained from weight loss measurements Inhibition e.ciency h ")# Inhibitor concentration "mg:l#

0 M HCl

9[4 M H1SO3

19 39 59 79 099

80[2 81[2 85[2 87[1 87[2

56[6 73[0 78[4 81[8 83[0

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measurements for di}erent concentrations of 1!TAT in 0 M HCl and 9[4 M H1SO3[ An identical trend is observed in both media as inhibition e.ciency increases with increasing inhibitor concentration in the test solution[ The inhibition is estimated to be superior at 89) in HCl even at very low concentration "19 mg:l# and the optimum concentration required to achieve this e.ciency is found to be 099 mg:l of 1!TAT in the test solutions "Table 0#[ The e.ciency in 9[4 M H1SO3 is comparatively lower than that in 0 M HCl solutions[ 2[1[ Electrochemical impedance spectroscopy "EIS# The corrosion behaviour of mild steel\ in acidic solutions in the presence of 1!TAT\ was investigated by the EIS method at room temperature after immersion for 19 hr[ The locus of the Nyquist plots was regarded as one part of a semicircle[ The equivalent circuit models employed for this system are as previously reported ð09Ł[ Nyquist plots of mild steel in inhibited and uninhibited acidic solutions containing various concentrations of 1!TAT are shown in Figs[ 1 and 2[ The impedance diagrams obtained are not perfect semicircles and this di}erence has been attributed to fre! quency dispersion ð00\ 01Ł[ The charge transfer resistance "Rt# values are calculated from the di}erence in impedance at lower and higher frequencies\ as suggested by Haruyama and Tsuru ð02Ł[ To obtain the double layer capacitance "Cdl#\ the frequency

Fig[ 1[ Nyquist diagrams for mild steel in 0 M HCl containing 1!TAT] "a# 19 mg:l\ "b# 39 mg:l\ "c# 59 mg:l\ "d# 79 mg:l and "e# 099 mg:l[

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Fig[ 2[ Nyquist diagrams for mild steel in 9[4 M H1SO3 containing 1!TAT] "a# 19 mg:l\ "b# 39 mg:l\ "c# 59 mg:l\ "d# 79 mg:l and "e# 099 mg:l[

at which the imaginary component of the impedance is maximum\ "−Zmax ý#\ is found and Cdl values are obtained from the equation[ f "−Zmax ý# 

0 [ 1pCdl Rt

"1#

The inhibition e.ciency of the corrosion of steel is calculated by charge transfer resistance\ as follows h")# 

−0 Rt−0 corr −R t corr"inh#

R t−0 corr

×099\

"2#

where Rt corr and Rt corr"inh# are the charge transfer resistance values without and with inhibitor\ respectively[ The impedance parameters derived from these investigation are given in Table 1[ It is found "Table 1# that as the 1!TAT concentration increases\ the Rt values increase\ but the Cdl values tend to decrease[ The decrease in the Cdl values is due to the adsorption of 1!TAT on the metal surface[ The values of the corrosion potential shift towards the positive direction when the concentration of the inhibitors increases[ Similar behaviour is observed in both media[ This observation is indicative of the anodic!type control and an inhibition of this type in both media acts mainly as an anodic!type inhibitor[ According to the study undertaken by EIS\ we can establish the curves of R t−0 and Ct versus the inhibitor concentration of 1!TAT[ We can notice that the shape of these two curves "Figs[ 3 and 4# is the same\ so we can conclude that more the concentration of inhibitor increases\ the more the charge transfer resistance increases and the more

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Table 1 Impedance measurements for mild steel in 0 M HCl and 9[4 M H1SO3 containing di}erent concentrations of 1!TAT 0 M HCl Inhibitor concentration "mg:l#

Rt "V[cm1#

Ecorr:sce "mV#

Blank 19 39 59 79 099

05[3 569 834[5 0166[6 0283[8 1559

−419 −497 −358 −352 −337 −318

Cdl "mF[cm−1# 406[1 64[3 31[0 17[3 16[8 10[6

h ")#

86[4 87[1 87[6 87[7 88[2

9[4 M H1SO3 Inhibitor concentration "mg:l# Blank 19 39 59 79 099

Rt "V[cm1# 07[1 004[8 175[8 276 289 490[4

Ecorr:sse "mV#

Cdl "mF[cm−1#

h ")#

−819[3 −896 −780 −775[5 −765[6 −763[0

0493 045[8 008[5 84[8 76[8 68[7

73[2 82[5 84[2 84[3 85[3

Fig[ 3[ The inverse charge transfer resistance for mild steel in 0 M HCl containing di}erent concentrations of 1!TAT[

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Fig[ 4[ The double layer capacitance for mild steel in 0 M HCl containing di}erent concentrations of 1!TAT[

the double layer capacitance decreases up to a concentration of 39 mg:l\ where it remains almost constant[ Similar behaviour is observed in both media[ The relationship between Rt and Cdl values with the immersion time are shown in Figs[ 5Ð8[ It can be found that the Rt values for mild steel in 0 M HCl and 9[4 M H1SO3 without 1!TAT "blank# decrease with immersion time\ but the Rt values for steel in 0 M HCl and 9[4 M H1SO3 "Figs[ 5 and 7# with the inhibitor\ increase with immersion time[ At the same time\ the Cdl values in the blank solution "Figs[ 6 and 8# increase with immersion time[ The change in the Rt and Cdl values is due to the gradual replacement of water molecules by the anions of the acid and by the adsorption of the organic molecules on the metal surface\ decreasing the extent of the dissolution reaction[ From Figs[ 09 and 00\ it can be seen that inhibition e.ciencies obtained from weight loss and electrochemical impedance spectroscopy measurements are in good agreement[ 2[2[ Viability test The cells were exposed up to very high concentrations of this organic compound simulating a worst case experiment[ The survival rate at the highest concentration "399 mg:ml# was 7424)^ thus\ 1!TAT is considered as non!cytotoxic substance with respect to Ni!powder\ the 49) lethal concentration of which was established to be 14 mg:ml "Table 2 and Fig[ 01#[

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Fig[ 5[ Relation between Rt and immersion time for mild steel in 0 M HCl containing 099 mg:l of 1!TAT] "a# 0 M HCl and "b# 0 M HCl ¦099 mg:l 1!TAT[

Fig[ 6[ Relation between Cdl and immersion time for mild steel in 0 M HCl containing 099 mg:l of 1!TAT] "a# 0 M HCl and "b# 0 M HCl ¦099 mg:l 1!TAT[

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Fig[ 7[ Relation between Rt and immersion time for mild steel in 9[4 M H1SO3 containing 099 mg:l of 1! TAT] "a# 9[4 M H1SO3 and "b# 9[4 M H1SO3 ¦099 mg:l 1!TAT[

Fig[ 8[ Relation between Cdl and immersion time for mild steel in 9[4 M H1SO3 containing 099 mg:l of 1!TAT] "a# 9[4 M H1SO3 and "b# 9[4 M H1SO3 ¦099 mg:l 1!TAT[

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Fig[ 09[ Inhibition e.ciency for mild steel in 0 M HCl containing di}erent concentrations of 1!TAT "n# weight loss measurement and "u# the charge transfer resistance[

Fig[ 00[ Inhibition e.ciency for mild steel in 9[4 M H1SO3 containing di}erent concentrations of 1!TAT "n# weight loss measurement and "u# the charge transfer resistance[

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F[ Bentiss et al[ : Corrosion Science 30 "0888# 678Ð792 Table 2 Survival rates of L021!cells cloned in the continuous presence of pure nickel and powder 1!TAT mg:ml

Nickel

SD

mg:ml

1!TAT

SD

9 4 09 19 39 79

099) 88) 73) 50) 23) 01)

) 0) 8) 7) 3) 2)

9 14 49 099 199 399

099) 84) 88) 86) 81) 74)

) 3) 0) 3) ) 4)

Fig[ 01[ Survival rates of L021!cells cloned in the continuous presence of pure Nickel and powder 1!TAT[

3[ Discussion The adsorption of 1!TAT on the metal surface can occur either directly on the basis of donorÐacceptor interactions between the p!electrons of the heterocycle compound and the vacant d!orbitals of iron surface atoms\ or the interaction of 1!TAT with already adsorbed chloride or sulfate ions ð03Ł[ The better performance of amino! triazoles in 0 M HCl can be explained in the following way[ In aqueous acidic solutions\ the aminotriazole exist either as neutral molecules or in the form of cations[ Amines may be adsorbed on the metal surface in the form of neutral molecules\ involving the deplacement of water molecules from the metal surface and sharing of

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electrons between the nitrogen atoms and the metal surface ð04Ł[ Amines and hetero! cyclic nitrogen compounds may also adsorb trough electrostatic interactions between the positively charged nitrogen atom and the negatively charged metal surface ð05Ł[ It has been observed that the adsorption of the amine can be in~uenced by the nature of anions in acidic solution ð06\ 07Ł[ The speci_c adsorption of anions having a smaller degree of hydration\ such as chloride ions\ is expected to be more pronounced[ Being speci_cally adsorbed\ they create an excess negative charge towards the solution and favour more adsorption of the cations ð08Ł[ Strong adsorption of organic molecules is not always a direct combination of the molecule with the metal surface[ In some cases\ the adsorption can occur through the already adsorbed chloride or sulfate ions\ which interfere with the adsorbed organic molecules[ The molecular structure of the organic compound is important in synergistic inhibition ð02Ł[ The greatest synergistic inhibition is to be expected for an anionÐcation pair in which both ions have appreci! able tendencies toward covalent binding[ The lesser interference by sulfate ions may lead to lower adsorption and inhibition of corrosion ð19Ł[

3[0[ Adsorption isotherm The degree of surface coverage "u# for di}erent concentrations of the inhibition in acidic media have been evaluated from weight loss and electrochemical measurements\ using the equations ð10Ł] W"u9# −Wu u W"u9# −W"u0# and Cdl"u9# −Cdlu u [ Cdl"u9# −Cdl"u0#

"3#

The surface coverage values "u# were tested graphically for _tting a suitable adsorption isotherm[ The plots of Cinh:u versus Cinh yields a straight line\ proving that the adsorption of the 1!TAT from HCl and H1SO3 solutions on the mild steel surface obeys the Langmuir adsorption isotherm "Figs[ 02 and 03#[

4[ Conclusion It can be concluded that] 0[ 1!TAT inhibits the corrosion of mild steel in both acids\ but better performance\ are seen in the case of HCl[ 1[ 1!TAT behaves as an anodic inhibitor[ 2[ Strong adsorption of 1!TAT molecules on the actives of a metal surface suppress

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Fig[ 02[ Langmuir adsorption plots for mild steel in 0 M HCl containing di}erent concentrations of 1!TAT] "a# weight loss measurements and "b# the double layer capacitance[

Fig[ 03[ Langmuir adsorption plots for mild steel in 9[4 M H1S93 containing di}erent concentrations of 1!TAT] "a# weight loss measurements and "b# the double layer capacitance[

the dissolution reaction and adsorption leads to the formation of a protective _lm which grows with increasing exposure time[ 3[ The adsorption of 1!TAT on the mild steel surface from 0 M HCl and 9[4 M H1SO3 follows a Langmuir adsorption isotherm[ 4[ 1!TAT is considered as non!cytotoxic substance[

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References ð0Ł ð1Ł ð2Ł ð3Ł ð4Ł ð5Ł ð6Ł ð7Ł

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