Triazolyl blue tetrazolium bromide as a novel corrosion inhibitor for steel in HCl and H2SO4 solutions

Corrosion Science 53 (2011) 302–309

Contents lists available at ScienceDirect

Corrosion Science journal homepage: www.elsevier.com/locate/corsci

Triazolyl blue tetrazolium bromide as a novel corrosion inhibitor for steel in HCl and H2SO4 solutions Xianghong Li a,⇑, Shuduan Deng b, Hui Fu a a b

Department of Fundamental Courses, Southwest Forestry University, Kunming 650224, PR China Faculty of Wood Science and Decoration Technology, Southwest Forestry University, Kunming 650224, PR China

a r t i c l e

i n f o

Article history: Received 18 July 2010 Accepted 9 September 2010 Available online 17 September 2010 Keywords: A. Steel B. EIS B. Polarization B. Weight loss C. Acid inhibition

a b s t r a c t The inhibition effect of triazolyl blue tetrazolium bromide (TBTB) on the corrosion of cold rolled steel (CRS) in 1.0 M HCl and 0.5 M H2SO4 solution was investigated for the first time by weight loss, potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS) methods. The results show that TBTB is a very good inhibitor, and is more efficiency in 1.0 M HCl than 0.5 M H2SO4. The adsorption of TBTB on CRS surface obeys Langmuir adsorption isotherm. Polarization curves reveal that TBTB acts as a mixed-type inhibitor in both acids. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction The use of inhibitors is one of the most practical methods for protection metal against corrosion, especially in acidic media [1]. As acidic media, hydrochloric acid (HCl) and sulfuric acid (H2SO4) are often used as industrial acid cleaners and pickling acids. Among various acid organic inhibitors, N-heterocyclic compounds are considered to be the most effective corrosion inhibitors [2]. Up to now, many N-heterocyclic compounds with one or several N heteroatoms are reported as good corrosion inhibitors for iron or steel in acidic media, such as imidazoline derivatives [3–5], 1,2,3-triazole derivatives [6], 1,2,4-triazole derivatives [2,7–19], pyrrole [20], pyridine derivatives [21–23], pyrazole derivatives [24–27], bipyrazole derivatives [28–30], pyrimidine derivatives [31], pyridazine derivatives [32], indole derivatives [33–35], benzimidazole derivatives [36–40], quinoline derivatives [41], purine derivatives [42–44]. It is generally accepted that N-heterocyclic compounds exert their inhibition by adsorption on the metal surface through N heteroatom, as well as those with triple or conjugated double bonds or aromatic rings in their molecular structures. Furthermore, inhibition efficiency of N-heterocyclic organic inhibitor always increases with the number of aromatic systems and the availability of electronegative atoms in the molecule [7]. Besides containing N heteroatom, some N-heterocyclic compounds possessing N and O heteroatoms simultaneously such as

⇑ Corresponding author. Tel.: +86 871 3863377; fax: +86 871 3863150. E-mail address: [email protected] (X. Li). 0010-938X/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2010.09.036

isoxazolidines [45,46], isoxazole derivatives [47], benzoxazole derivatives [48], oxadiazole derivatives [14,49–51], have shown high efficiency for steel in acidic media. Other N-heterocyclic compounds containing N and S herteroatoms at the same time, like thiadiazole derivatives [52–56], thiazole derivatives [57,58] and benzothiazole [59] were also widely used in protection steel corrosion in acid solutions. It has been assumed that the main adsorption of these N-heterocyclic compound inhibitors takes place through N heteroatom, as well as O and S herteroatoms in their molecular structures, and inhibition efficiency usually increase in the order: O < N < S. As another typical kind of N-heterocyclic compound, tetrazole derivatives whose molecules possess the tetrazole ring with 4-N heteroatoms have also been received some attention. In 1996, Kertit and Hammouti [60] studied the inhibition of 1-phenyl-5mercapto-1,2,3,4-tetrazole (PMT) on the corrosion of iron in 1.0 M HCl, and its maximum inhibition efficiency (E) was 98% at 2  103 M. Bensajjay et al. [61] extended their work to study the inhibition effect of PMT on steel in 0.5 M H2SO4 and 1/3 M H3PO4. Results obtained showed that E also reached an optimum value of 98% at 103 M PMT. Afterwards, Morales-Gil et al. [62] reported the inhibition effect of 5-mercapto-1-tetrazoleacetic sodium salt (MTAc) on steel in 1.0 M H2SO4. Their results showed that E was about 69% at 200 mg l1, while then decreased with the MTAc concentration. In our recent works [63–65], the inhibition effect of red tetrazolium (RT) on the corrosion of cold rolled steel (CRS) in HCl, H2SO4 and H3PO4 solutions. The results show that maximum E value of 500 mg l1 RT at 20 °C is 94% in 1.0 M HCl [63]; 79%, 1.0 M H2SO4 [64]; and 63%, 3.0 M H3PO4 [65].

X. Li et al. / Corrosion Science 53 (2011) 302–309

Noticeably, these tetrazole compounds studied contain only one tetrazole ring, the literature available to date about the corrosion inhibition of the tetrazole compound which simultaneously possesses one tetrazole ring and another N-heterocyclic ring is very scarce. Triazolyl blue tetrazolium bromide (TBTB) is the tetrazole compound containing one tetrazole ring and one thiazole ring at the same time, which could be seemed as a good potential inhibitor. However, to the best of our knowledge, TBTB has not been treated as a corrosion inhibitor. In the present work, the inhibition effect of TBTB on cold rolled steel (CRS) in 1.0 M HCl and 0.5 M H2SO4 solutions is studied for the first time by weight loss, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) methods. Meanwhile, the adsorption mode of TBTB on steel surface was obtained, and the adsorption free energyDG0 were calculated and discussed. A probable inhibitive mechanism is proposed from the viewpoint of adsorption theory. 2. Experimental

303

of TBTB using glass hooks and rods. The temperature was controlled at 30 ± 0.1 °C by a water thermostat. All the aggressive acid solutions were open to air. After immersion for 6 h, the specimens were taken out, washed with bristle brush under running water in order to remove the corrosion product, dried with a hot air stream, and reweighed accurately. In order to get good reproducibility, experiments were carried out in triplicate. The average weight loss of three parallel CRS sheets was obtained. The corrosion rate (v) is calculated by the following equation [64]:

v¼

W St

ð1Þ

where W is the average weight loss of three parallel CRS sheets, S the total area of one CRS specimen, and t is immersion time (6 h). With the calculated corrosion rate, the inhibition efficiency (Ew) is calculated as follows [64]:

Ew % ¼

v0  v  100 v0

ð2Þ

where v0 and v are the values of corrosion rate without and with inhibitor, respectively.

2.1. Materials Tests were performed on a cold rolled steel (CRS) of the following composition (wt.%): 0.05% C, 0.28% Mn, 0.023% P, 0.019% S, 0.02% Si, and the remainder Fe. 2.2. Inhibitor Triazolyl blue tetrazolium bromide (TBTB, C18H16BrN5S) was obtained from Shanghai Chemical Reagent Company of China. Fig. 1 shows the molecular structure of TBTB. Clearly, it contains both tetrazole ring and thiazole ring (5-N heteroatoms and 1-S heteroatom). Thus, a great deal of lone electrons and p-electrons exists in this molecule. 2.3. Solutions The aggressive solutions of 1.0 M HCl and 0.5 M H2SO4 was prepared by dilution of AR grade 37% HCl and 98% H2SO4 with distilled water, respectively. The concentration range of TBTB employed was 0.02–0.50 mM (2.0  105 to 5.0  104 M). 2.4. Weight loss measurements The CRS sheets of 2.5  2.0  0.04 cm were abraded by a series of emery paper (grade 320–500–800) and then washed with distilled water, degreased with acetone, and finally dried with a cold air stream. After weighing accurately by digital balance with sensitivity of ±0.1 mg, the specimens were immersed in beaker containing 250 ml acid solution without and with different concentrations

CH3 N

N

_ Br + N

S

CH3

2.5. Electrochemical measurements Electrochemical experiments were carried out in the conventional three-electrode cell with a platinum counter electrode (CE) and a saturated calomel electrode (SCE) coupled to a fine Luggin capillary as the reference electrode. In order to minimize ohmic contribution, the Luggin capillary was kept close to working electrode (WE) which was in the form of a square CRS embedded in PVC holder using epoxy resin so that the flat surface was only surface in the electrode. The WE surface area was 1.0  1.0 cm, abraded with emery paper (grade 320–500–800) on test face, rinsed with distilled water, degreased with acetone, and dried with a cold air stream. Before measurement the electrode was immersed in test solution at open circuit potential (OCP) for 2 h at 30 °C to be sufficient to attain a stable state. All electrochemical measurements were carried out using PARSTAT 2273 advanced electrochemical system (Princeton Applied Research). Each experiment was repeated at least three times to check the reproducibility. The potential of potentiodynamic polarization curves was started from a potential of 250 to +250 mV versus OCP at a sweep rate of 0.5 mV s1. Inhibition efficiency (Ep%) is defined as:

Ep % ¼

Icorr  IcorrðinhÞ  100 Icorr

ð3Þ

where Icorr and Icorr(inh) represent corrosion current density values without and with inhibitor, respectively. Electrochemical impedance spectroscopy (EIS) was carried out at OCP in the frequency range of 10 mHz–100 kHz using a 10 mV peak-to-peak voltage excitation. Inhibition efficiency (ER%) is calculated on the basis of the equation:

ER % ¼

RtðinhÞ  Rtð0Þ  100 RtðinhÞ

ð4Þ

where Rt(0) and Rt(inh) are charge transfer resistance values in the absence and presence of inhibitor, respectively. 3. Results and discussion

N N

Fig. 1. Chemical molecular structure of triazolyl blue tetrazolium bromide (TBTB).

3.1. Weight loss measurements 3.1.1. Effect of TBTB concentration on corrosion rate The weight loss method of monitoring corrosion rate and inhibition efficiency is useful because of its simple application

X. Li et al. / Corrosion Science 53 (2011) 302–309

and reliability [66]. For the present study, the reproducibility of results obtained for both corrosion rate and percentage inhibition efficiency values for triplicate determination was very precise (within range of ±5%). Fig. 2 shows the corrosion rate (v) values of CRS with different concentrations of TBTB in both 1.0 M HCl and 0.5 M H2SO4 solutions at 30 °C. In both acidic media, v decreases noticeably with an increase in TBTB concentration, i.e. the corrosion inhibition enhances with the inhibitor concentration. In the presence of 0.5 mM TBTB, the corrosion rate values are decreased to 0.53 and 2.00 g m2 h1 in 1.0 M HCl and 0.5 M H2SO4 solutions, respectively. This behavior is due to the fact that the adsorption amount and coverage of inhibitor on CRS surface increase with the inhibitor concentration [67]. It should be noted that when the inhibitor concentration reaches about 0.20 mM, the corrosion rate value reaches certain data and does not change markedly. At any given inhibitor concentration, the corrosion rate in 0.5 M H2SO4 is comparatively higher than that in 1.0 M HCl solution. 3.1.2. Effect of TBTB concentration on inhibition efficiency The values of inhibition efficiency obtained from the weight loss (Ew) for different inhibitor concentrations in 1.0 M HCl and 0.5 M H2SO4 solutions at 30 °C are shown in Fig. 3. When the concentration of TBTB is less than 0.20 mM, Ew increases sharply with an increase in concentration, while a further increase causes no appreciable change in performance. The maximum Ew values are 95.1% (1.0 M HCl) and 88.2% (0.5 M H2SO4) at 0.50 mM (5.0  104 M), and at 0.25 mM (2.5  103 M) concentration Ew values are higher than 90% in HCl, and 80% in H2SO4, respectively, which indicates that TBTB is a very good inhibitor for steel in both acids. At the same inhibitor concentration, Ew values follow the order: Ew (1.0 M HCl) > Ew (0.5 M H2SO4). Under similar conditions, the inhibition efficiency obtained by weight loss measurements for 1-phenyl-5-mercapto-1,2,3,4-tetrazole (PMT) is 34.8% at 5.0  104 M in 1.0 M HCl [60]; for 5-mercapto-1-tetrazoleacetic sodium salt (MTAc), 69% at 200 mg l1 (about 1.1  103 M) in 1.0 M H2SO4 [62]; and for red tetrazolium (RT), 93.0% in 1.0 M HCl [63] and 52.5% in 1.0 M H2SO4 [64] at 200 mg l1 (about 6.0  104 M). Therefore, comparing with PMT, MTAc and RT studied, TBTB shows better inhibition performance. This result could be explained as follows: the main adsorption centre of tetrazole derivative is tetrazole ring [60–65]. PMT, MTAc or RT has only one tetrazole ring, while TBTB contains not only one tetrazole ring but also one thiazole ring, which favors more adsorption of TBTB and improves the inhibitive ability. Furthermore, the

100 90 80 70 60 Ew (%)

304

40

20 10 0 0.0

0.1

0.2 0.3 0.4 concentration of TBTB c (mM)

0.5

0.6

Fig. 3. Relationship between inhibition efficiency (Ew) obtained from weight loss method and concentration of TBTB (c) in 1.0 M HCl and 0.5 M H2SO4 at 30 °C (immersion time is 6 h).

molecular weight of TBTB is 414.32 g mol1, which is higher than that of PMT (178.21 g mol1), MTAc (182.14 g mol1) or RT (334.81 g mol1), and likely to efficiently cover more surface area (due to adsorption) of metal. 3.1.3. Adsorption isotherm and standard adsorption free energy Basic information on the interaction between the inhibitor and CRS surface can be provided by the adsorption isotherm. Attempts were made to fit experimental data to various isotherms including Frumkin, Langmuir, Temkin, Freundlich, Bockris-Swinkels, and Flory–Huggins isotherms. By far the results were best fitted by Langmuir adsorption isotherm equation [64]:

c 1 ¼ þc h K

ð5Þ

where c is the concentration of inhibitor, K the adsorptive equilibrium constant, and h is the surface coverage calculated as follows [64]:

h¼

v0  v v0

ð6Þ

Plots of c/h against c yield straight lines as shown in Fig. 4, and the linear regression parameters are listed in Table 1. Both linear 0.6

16

1.0 M HCl 0.5 M H2SO4

14

0.5

0.4

12

c/θ (mM)

-2

-1

1.0 M HCl 0.5 M H2SO4

30

18

corrosion rate v (g m h )

50

10 8 6

0.3 1.0 M HCl 0.5 M H2 SO4

0.2

4

0.1 2 0 0.0

0.1

0.2 0.3 0.4 concentration of TBTB c (mM)

0.5

0.6

Fig. 2. Relationship between corrosion rate (v) and concentration of TBTB (c) in 1.0 M HCl and 0.5 M H2SO4 at 30 °C (weight loss method, immersion time is 6 h).

0.0 0.0

0.1

0.2 0.3 0.4 concentration of TBTB c (mM)

0.5

0.6

Fig. 4. Langmuir isotherm adsorption mode of TBTB on the CRS surface in 1.0 M HCl and 0.5 M H2SO4 at 30 °C from weight loss measurement.

305

X. Li et al. / Corrosion Science 53 (2011) 302–309 Table 1 Parameters of the straight line of c/h-c and adsorption free energy (DG0).

1.0 M HCl 0.5 M H2SO4

Linear correlation coefficient (r) 0.9984 0.9964

Slope 0.99 0.94

DG0(kJ mol1)

K(M1) 4

3.51  10 1.15  104

36.5 33.7

-0.4

correlation coefficient (r) and slope are very close to 1, indicating the adsorption of TBTB on steel surface obeys the Langmuir adsorption isotherm in 1.0 M HCl or 0.5 M H2SO4 solution. Table 1 also shows that K of 1.0 M HCl is higher than that of 0.5 M H2SO4, which indicates that TBTB exhibits a stronger tendency to adsorb on steel surface in 1.0 M HCl solution. The adsorptive equilibrium constant (K) is related to the standard free energy of adsorption (DG0) as shown the following equation [68]:

K¼

-0.3

1 DG0 expð Þ 55:5 RT

ð7Þ

where R is the gas constant (8.314 J K1 mol1), T the absolute temperature (K), and the value 55.5 is the concentration of water in solution expressed in M [68]. The DG0 values are also listed in Table 1. The negative values of DG0 indicate that the adsorption of inhibitor molecule on steel surface is a spontaneous process. Generally, values of DG0 up to 20 kJ mol1 are consistent with the electrostatic interaction between the charged molecules and the charged metal (physical adsorption) while those more negative than 40 kJ mol1 involve sharing or transfer of electrons from the inhibitor molecules to the metal surface to form a co-ordinate type of bond (chemisorption) [12,61,69]. In the present study, the value of DG0 is found to be within the range 40 to 20 kJ mol1; probably means that the adsorption of TBTB on CRS surface involves both physical adsorption and chemical adsorption. 3.2. Potentiodynamic polarization curves Potentiodynamic polarization curves for CRS in 1.0 M HCl and 0.5 M H2SO4 solutions containing various concentrations of TBTB at 30 °C are shown in Figs. 5 and 6 (immersion time is 2 h), respectively. In both acid solutions, addition of TBTB causes a remarkable decrease in the corrosion rate i.e., shifts the both anodic and cathodic curves to lower current densities. In other words, both cathodic

-0.2

E (V vs. SCE)

Acid solution

-0.2

-0.5 blank 0.05 mM 0.10 mM 0.20 mM 0.30 mM 0.50 mM

-0.6

-0.7

-0.8

-6

-5

-4

-3 -2 log I (A cm )

-2

-1

Fig. 6. Potentiodynamic polarization curves for CRS in 0.5 M H2SO4 without and with different concentrations of TBTB at 30 °C (immersion time is 2 h).

and anodic reactions of CRS electrode are drastically inhibited by TBTB. This may be ascribed to adsorption of inhibitor over the corroded surface [70]. The electrochemical corrosion parameters including corrosion current densities (Icorr), corrosion potential (Ecorr), cathodic Tafel slope (bc), anodic Tafel slope (ba), and inhibition efficiency (EP) are presented in Table 2. It is apparent that Icorr decreases considerably in the presence of TBTB inhibitor, and decreases with increasing the inhibitor concentration. Correspondingly, Ep increases with the inhibitor concentration, due to the increase in the blocked fraction of the electrode surface by adsorption. Ep of 0.50 mM TBTB reaches up to a maximum of 93.8% in 1.0 M HCl; and 90.7% in 0.5 M H2SO4. In 1.0 M HCl solution, the presence of TBTB does not change the Ecorr, which indicates TBTB acts as a mixed-type inhibitor, and the inhibition of TBTB on CRS is caused by geometric blocking effect [71]. In other words, the inhibition effect comes from the reduction of the reaction area on the surface of the corroding metal [71]. On the other hand, in 0.5 M H2SO4 solution, Ecorr shifts to positive, which indicates that inhibitor molecules are more adsorbed on the anodic sites resulting in an inhibition of the anodic reactions. Generally, if the displacement in Ecorr is >85 mV with respect to Ecorr in uninhibited solution, the inhibitor can be seen as a cathodic or anodic type [12,64]. In our study the maximum displacement is 46.6 mV, which indicates that TBTB can be arranged as a mixedtype inhibitor. The similar results were also reported with red tetrazolium (RT) for steel in H2SO4 media [64]. In the presence of TBTB

-0.3 Table 2 Potentiodynamic polarization parameters for the corrosion of CRS in 1.0 M HCl and 0.5 M H2SO4 solutions containing different concentrations of TBTB at 30 °C.

E (V vs. SCE)

-0.4

-0.5 blank 0.05 mM 0.10 mM 0.20 mM 0.30 mM 0.50 mM

-0.6

-0.7

-0.8

Acid solution

c Ecorr Icorr -bc ba Ep (mM) (mV vs. SCE) (lA cm2) (mV dec–1) (mV dec–1) (%)

1.0 M HCl

0 0.05 0.10 0.20 0.30 0.50 0 0.05 0.10 0.20 0.30 0.50

0.5 M H2SO4

-6

-5

-4 -3 -2 log I (A cm )

-2

-1

Fig. 5. Potentiodynamic polarization curves for CRS in 1.0 M HCl without and with different concentrations of TBTB at 30 °C (immersion time is 2 h).

447 442 446 442 449 448 507 491 484 480 476 460

354 145 89 49 32 26 1502 975 712 352 264 146

132 105 106 112 115 105 135 138 130 114 134 118

72 50 48 39 46 52 77 52 52 40 74 39

– 59.0 74.9 86.2 91.0 92.7 – 35.1 52.6 76.6 82.4 90.3

306

X. Li et al. / Corrosion Science 53 (2011) 302–309

inhibitor, the slight change of both bc and ba in both acid solutions indicates that the corrosion mechanism of steel does not change. Furthermore, the inhibition efficiencies obtained from weight loss, electrochemical polarization curves are in reasonable good agreement. Namely, TBTB is a good inhibitor in both acid solutions, and inhibition efficiency in 1.0 M HCl is higher than that in 0.5 M H2SO4 solution. 3.3. Electrochemical impedance spectroscopy (EIS) Figs. 7 and 8 show the Nyquist diagrams for CRS in 1.0 M HCl and 0.5 M H2SO4 at 30 °C, respectively. In 1.0 M HCl solution, the impedance spectra exhibit one single depressed semicircle, which indicates that the corrosion of steel is mainly controlled by a charge transfer process. In contrast, in 0.5 M H2SO4 solution, the impedance spectra consist of large capacitive loop at high frequencies followed by a small inductive loop at low frequency values. The high frequency capacitive loop is usually related to the charge transfer of the corrosion process and double layer behavior. On the other hand, the low frequency inductive loop may be attributed to the relaxation process obtained by adsorption species like FeSO4 [72] or inhibitor species [73] on the electrode surface. It might be

450

25

0.05 mM 0.10 mM 0.20 mM 0.30 mM 0.50 mM

350 300

blank

20 -Z r (Ω cm 2)

400

15 10

C dl ¼ Q dl  ð2pfmax Þa1

2

-Zr (Ω cm )

5

250 0

200

0

5

10

15

20

25

2

Zr (Ω cm )

150 100 50 0 0

50

100

150

200 250 2 Zr (Ω cm )

300

350

400

450

Fig. 7. Nyquist plots of the corrosion of CRS in 1.0 M HCl without and with different concentrations of TBTB at 30 °C (immersion time is 2 h).

0.05 mM 0.10 mM 0.20 mM 0.30 mM 0.50 mM

70

2

80

8 -Zr (Ω cm )

90

60

6 4 2 0

2

-Zr (Ω cm )

blank

0

50

2

40

4 6 2 Z r ( Ω cm )

8

10

30

ð8Þ

where fmax represents the frequency at which imaginary value reaches a maximum on the Nyquist plot. The electrochemical parameters of Rt, Cdl and ER are calculated by ZSimpWin software and presented in Table 3. Inspection of Table 3 reveals that Rt value increases prominently while Cdl reduces with the concentration of TBTB in both acid media. The greatest effect was observed at 0.50 mM of TBTB which gives Rt value of 418.6 Xcm2 in 1.0 M HCl, and 96.9 Xcm2 in 0.5 M H2SO4; Cdl value of 84.1 lF cm2 in 1.0 M HCl, and 169.2 lF cm2 in 0.5 M H2SO4. A large charge transfer resistance is associated with a slower corroding system. In contrast, better protection provided by an inhibitor can be associated with a decrease in capacitance of the metal. According to Helmholtz model [78]:

C dl ¼

10

100

also attributed to the re-dissolution of the passivated surface at low frequencies [73]. In both acid solutions, comparing with blank solution, the shape is maintained throughout all tested concentrations, indicating that almost no change in the corrosion mechanism occurs due to the inhibitor addition [74]. These capacitive loops in both acid solutions are not perfect semicircles which can be attributed to the frequency dispersion effect as a result of the roughness and inhomogeneous of electrode surface [75]. Furthermore, the diameter of the capacitive loop in the presence of inhibitor is bigger than that in the absence of inhibitor (blank solution) and increases with the inhibitor concentration. This indicates that the impedance of inhibited substrate increases with the TBTB concentration. The EIS results of these capacitive loops are simulated by the equivalent circuit shown in Fig. 9 to pure electric models that could verify or rule out mechanistic models and enable the calculation of numerical values corresponding to the physical and/or chemical properties of the electrochemical system under investigation [76]. The circuit employed allows the identification of both solution resistance (Rs) and charge transfer resistance (Rt). It is worth mentioning that the double layer capacitance (Cdl) value is affected by imperfections of the surface, and that this effect is simulated via a constant phase element (CPE) [77]. The CPE is composed of a component Qdl and a coefficient a. The parameter a quantifies different physical phenomena like surface inhomogeneousness resulting from surface roughness, inhibitor adsorption, porous layer formation, etc. Therefore, the capacitance is deduced from the following relation [72]:

e0 e d

A

ð9Þ

where e0 is the permittivity of air, e the local dielectric constant, d the thickness of the film and A is the surface area of the electrode. Therefore, the decrease in Cdl in comparing with that in blank solution (without inhibitor), which can result from a decrease in local dielectric constant and/or an increase in the thickness of the electrical double layer, suggests that the inhibitor molecules function by adsorption at the metal/solution interface [72]. ER increases with the concentration of TBTB, and follows the order: ER (HCl) > ER (H2SO4). The maximum ER values are 94.9% and 91.3% in 1.0 M

20 10

CPE

0 -10

Rs 0

10

20

30

40

50 60 2 Zr (Ω cm )

70

80

90

100

Fig. 8. Nyquist plots of the corrosion of CRS in 0.5 M H2SO4 without and with different concentrations of TBTB at 30 °C (immersion time is 2 h).

Rt Fig. 9. Equivalent circuit used to fit the capacitive loop.

X. Li et al. / Corrosion Science 53 (2011) 302–309 Table 3 EIS parameters for the corrosion of CRS in 1.0 M HCl and 0.5 M H2SO4 solutions containing TBTB at 30 °C. Acid solution

c (mM)

Rt (Xcm2)

Cdl (lF cm2)

ER (%)

1.0 M HCl

0 0.05 0.10 0.20 0.30 0.50 0 0.05 0.10 0.20 0.30 0.50

21.4 60.0 90.3 193.3 286.6 418.6 8.3 13.6 18.4 40.1 59.5 96.9

309.9 269.4 223.8 204.5 122.8 84.1 551.7 487.5 306.8 295.2 264.0 169.2

– 64.3 76.3 88.9 92.5 94.9 – 38.9 54.9 79.3 86.1 91.4

0.50 M H2SO4

HCl and 0.5 M H2SO4, respectively. These results again confirm that TBTB exhibits good inhibitive performance for CRS in both acid solutions, and it is more efficient to inhibit the corrosion of steel in 1.0 M HCl than 0.5 M H2SO4. Inhibition efficiencies obtained from weight loss (Ew), potentiodynamic polarization curves (Ep) and EIS (ER) are in good reasonably agreement. 3.4. Explanation for inhibition The inhibition mechanism can be proposed from the adsorption of inhibitor on steel surface. It is well known that the adsorption of inhibitor on steel/solution interface is affected by the chemical structures of the inhibitors, the nature and charged surface of the metal and the distribution of charge over the whole inhibitor molecule. In general, owing to the complex nature of adsorption and inhibition of a given inhibitor, it is impossible for single adsorption mode between inhibitor and metal surface. In the present system, based on the chemical structure of TBTB, TBTB has many active sites for the adsorption process. Thus, five types of adsorption may take place in the inhibiting phenomena involving TBTB molecules on steel surface as follows: (i) TBTB can be classified as an electrolyte, namely, the organic part (TBTB+) is the cation and the inorganic part (Br) is the anion:

TBTB ! TBTþ þ Br

ð10Þ

Owing to neutral N and S atoms in TBT+, TBT+ could further be protonated in the acid solution as following:

TBTþ þ xHþ $ ½TBTHx ðxþ1Þþ

ð11Þ

Thus, in aqueous acidic solutions, the TBTB exists as protonated cations of TBT+ and [TBTHx](x+1)+. The charge of the metal surface can be determined from the value of Ecorr–Eq=0 (zero charge potential) [78]. The Eq=0 of iron is 530 mV vs. SCE in HCl [79], and 550 mV vs. SCE in H2SO4 [80]. In the present system, the values of Ecorr obtained in 1.0 M HCl and 0.5 M H2SO4 are 447 mV vs. SCE and 507 mV vs. SCE, respectively. So the steel surface charges positive charge in both HCl and H2SO4 solutions because of Ecorr– Eq=0 (zero charge potential) > 0. Since the anions of Cl, SO2 4 and Br (produced as a result of the reaction (10)) could be specifically adsorbed, they create an excess negative charge towards the solution and favor more adsorption of the cations [49], TBT+ and [TBTHx](x+1)+ may adsorb on the negatively charged metal surface. In other words, there may be a synergism between anions (Cl, SO2 and Br) and protonated inhibitor. It is generally accepted 4 that Cl ions have stronger tendency to adsorb do SO2 4 ions [81], and the electrostatic influence on the inhibitor adsorption may

307

be the reason for an increased protective effect in halide-containing solution [82]. Moreover, the lesser interference by SO2 ions 4 with the adsorbed protonated cations may lead to lower adsorption and inhibition of acid corrosion [83]. So, the adsorption of TBTB on the steel surface is greater from 1.0 M HCl solution, which leads to better inhibition performance than that in 0.5 M H2SO4. (ii) Besides to the physical adsorption, TBT+ and [TBTHx](x+1)+ may be adsorbed on the metal surface via the chemisorption mechanism, involving to the coordinate bonds that may be formed between the lone electrons pairs of the unprotonated N and S atoms and the empty orbitals of Fe atoms which enhanced the combination intension between the inhibitor molecule and electrode surface. (iii) It should be noted that the molecular structure of TBT+ and [TBTHx](x+1)+ remains unchanged with respect to TBTB, that is, both N and S atoms on the ring remaining strongly blocked. TBT+ and [TBTHx](x+1)+ have plentiful p-electrons owing to aromatic rings, they can be also adsorbed on the metal surface on the basis of donor–acceptor interactions between p-electrons of the heterocycles (tetrazole and thiazole ring) and vacant d-orbitals of Fe. The simultaneous adsorption of the tetrazole and thiazole rings induces greater adsorption greater adsorption of the inhibitor molecules onto the surface of cold rolled steel. The larger molecule area plays an important role in retarding the corrosion [84]. (iv) Due to the chelating action of tetrazole ring or thiazole ring, some metal complexes of Fe2+—tetrazole compounds [85,86] or Fe2+—thiazole compounds [87,88] have been widely prepared. Thus, TBT+ and [TBTHx](x+1)+ may combine with freshly generated Fe2+ ions on steel surface forming metal inhibitor complexes:

Fe ! Fe2þ þ 2e

ð12Þ

TBTþ þ Fe2þ $ ½TBTAFe3þ

ð13Þ

½TBTHx ðxþ1Þþ þ Fe2þ $ ½TBTHx AFeðxþ3Þþ

ð14Þ

These complexes might get adsorbed onto steel surface by the van der Waals force to form a blocking barrier to keep CRS from corrosion. (v) A combination of the above. 4. Conclusions (1) TBTB acts as a good inhibitor for the corrosion of CRS in 1.0 M HCl and 0.5 M H2SO4 solutions. Inhibition efficiency (Ew) increases with the inhibitor concentration, and the maximum Ew values are 95.1% (1.0 M HCl) and 88.2% (0.5 M H2SO4) at 0.50 mM (5.0  104 M). Inhibition performance in 1.0 M HCl is higher than that in 0.5 M H2SO4. (2) In both acid media, the adsorption of TBTB is a spontaneous process and obeys Langmuir adsorption isotherm. The parameter of adsorption free energy (DG0) indicates that the adsorption of TBTB involves both physical adsorption and chemical adsorption. (3) TBTB acts as a mixed-type inhibitor in 1.0 M HCl and 0.5 M H2SO4, while prominently retards anodic reaction in 0.5 M H2SO4. (4) EIS spectra exhibit one capacitive loop in 1.0 M HCl, while one large capacitive loop at high frequencies followed by a small inductive loop at low frequency values in 0.5 M H2SO4. The presence of TBTB in both acid solutions enhances Rt values while reduces Cdl values. (5) The adsorption of TBTB involves electrostatic attraction between anions (Cl, SO2 4 ) and protonated inhibitor molecules, sharing electrons between the N, S atoms and Fe,

308

X. Li et al. / Corrosion Science 53 (2011) 302–309

donor–acceptor interactions between p-electrons of aromatic rings and vacant d-orbitals of Fe ,adsorption of the complexes of [TBT-Fe]3+ and [TBTHx-Fe](x+3)+. Acknowledgements This study was carried out in the scope of research project funded by Key Laboratory for Forest Resources Conservation and Use in the Southwest Mountains of China (Southwest Forestry University) Ministry of Education, Key Construction Course of Chemical Engineering for Forest Products of Southwest Forestry University (XKX200907), Natural Science Foundations of Southwest Forestry University (200715M) and Educational Department of Yunnan Province (09C0181). The electrochemical measurements were carried out using PARSTAT 2273 advanced electrochemical system (Princeton Applied Research) provided by Advanced Science Instrument Sharing Center of Southwest Forestry University. References [1] G. Trabanelli, Inhibitors an old remedy for a new challenge, Corrosion 47 (1991) 410–419. [2] F. Bentiss, M. Traisnel, L. Gengembre, M. Lagrenée, Inhibition of acidic corrosion of mild steel by 3, 5-diphenyl-4H–1, 2, 4-triazole, Appl. Surf. Sci. 161 (2000) 194–202. [3] J. Cruz, R. Martínez, J. Genesca, E. García-Ochoa, Experimental and theoretical study of 1-(2-ethylamino)-2-methylimidazoline as an inhibitor of carbon steel corrosion in acid media, J. Electroanal. Chem. 566 (2004) 111–121. [4] M.H. Wahdan, G.K. Gomma, Effect of copper cation on electrochemical behaviour of steel in presence of imidazole in acid medium, Mater. Chem. Phys. 47 (1997) 176–183. [5] G. Bereket, E. Hür, C. Ög˘retir, Quantum chemical studies on some imidazole derivatives as corrosion inhibitors for iron in acidic medium, J. Mol. Struct. (Theochem) 578 (2002) 79–88. [6] A.M.S. Abdennaby, A.I. Abdulhady, S.T. Abu-Oribi, H. Saricimen, The inhibition action of 1 (benzyl)1-H-4,5-dibenzoyl-1,2,3-triazole on mild steel in hydrochloric acid media, Corros. Sci. 38 (1996) 1791–1800. [7] S.L. Granese, B.M. Rosales, C. Oviedo, J.O. Zerbino, The inhibition action of heterocyclic nitrogen organic compounds on Fe and steel in HCl media, Corros. Sci. 33 (1992) 1439–1453. [8] F. Bentiss, M. Traisnel, L. Gengembre, M. Lagrenée, A new triazole derivative as inhibitor of the acid corrosion of mild steel: electrochemical studies, weight loss determination, SEM and XPS, Appl. Surf. Sci. 152 (1999) 237–249. [9] L. Wang, Inhibition of mild steel corrosion in phosphoric acid solution by triazole derivatives, Corros. Sci. 48 (2006) 608–616. [10] M.A. Quraishi, H.K. Sharma, 4-Amino-3-butyl-5-mercapto-1,2,4-triazole: a new corrosion inhibitor for mild steel in sulphuric acid, Mater. Chem. Phys. 78 (2002) 18–21. [11] E. García-Ochoa, J. Genesca, Understanding the inhibiting properties of 3-amino-1,2,4-triazole from fractal analysis, Surf. Coat. Tech. 184 (2004) 322–330. [12] W.H. Li, Q. He, S.T. Zhang, C.L. Pei, B.R. Hou, Some new triazole derivatives as inhibitors for mild steel corrosion in acidic medium, J. Appl. Electrochem. 38 (2008) 289–295. [13] H.L. Wang, R.B. Liu, J. Xin, Inhibiting effects of some mercapto-triazole derivatives on the corrosion of mild steel in 1.0 M HCl medium, Corros. Sci. 46 (2004) 2455–2466. [14] F. Bentiss, M. Traisnel, H. Vezin, M. Lagrenée, Linear resistance model of the inhibition mechanism of steel in HCl by triazole and oxadiazole derivatives: structure–activity correlations, Corros. Sci. 45 (2003) 371–380. [15] M. Lebrini, M. Traisnel, M. Lagrenée, B. Mernari, F. Bentiss, Inhibitive properties, adsorption and a theoretical study of 3, 5-bis(n-pyridyl)-4amino-1, 2, 4-triazoles as corrosion inhibitors for mild steel in perchloric acid, Corros. Sci. 50 (2008) 473–479. [16] F. Bentiss, M. Lagrenee, M. Traisnel, J.C. Hornez, The corrosion inhibition of mild steel in acidic media by a new triazole derivative, Corros. Sci. 41 (1999) 789–803. [17] W.H. Li, X. Zhao, F.Q. Liu, B.R. Hou, Investigation on inhibition behavior of S-triazole–triazole derivatives in acidic solution, Corros. Sci. 50 (2008) 3261–3266. [18] F. Bentiss, C. Jama, B. Mernari, H. El Attari, L. El Kadi, M. Lebrini, M. Traisnel, M. Lagrenée, Corrosion control of mild steel using 3,5-bis(4-methoxyphenyl)-4amino-1,2,4-triazole in normal hydrochloric acid medium, Corros. Sci. 51 (2009) 1628–1635. [19] Z.H. Tao, S.T. Zhang, W.H. Li, B.R. Hou, Corrosion inhibition of mild steel in acidic solution by some oxo-triazole derivatives, Corros. Sci. 51 (2009) 2588– 2595. [20] R.M. Hudson, T.J. Bulter, C.J. Warning, The effect of pyrrole-halide mixtures in inhibiting the dissolution of low-carbon steel in sulphuric acid, Corros. Sci. 17 (1977) 571–581.

[21] M. Bouklah, A. Ouassini, B. Hammouti, A. El Idrissi, The effect of pyrrole-halide mixtures in inhibiting the dissolution of low-carbon steel in sulphuric acid, Appl. Surf. Sci. 250 (2005) 50–56. [22] M. Lashkari, M.R. Arshadi, DFT studies of pyridine corrosion inhibitors in electrical double layer: solvent, substrate, and electric field effects, Chem. Phys. 299 (2004) 131–137. [23] M.A. Veloz, I.G. Martinz, Effect of some pyridine derivatives on the corrosion behavior of carbon steel in an environmental like NACE TM0177, Corrosion 62 (2006) 283–292. [24] A. Ouchrif, M. Zegmout, B. Hammouti, S. El-Kadiri, A. Ramdani, 1,3-Bis(3hyroxymethyl-5-methyl-1-pyrazole) propane as corrosion inhibitor for steel in 0.5 M H2SO4 solution, Appl. Surf. Sci. 252 (2005) 339–344. [25] G.K. Gomma, Corrosion of low-carbon steel in sulphuric acid solution in the presence of pyrazole-halides mixture, Mater. Chem. Phys. 55 (1998) 241–246. [26] M. Abdallah, M.M. El-Naggar, Cu+2 cation+ 3,5-dimethyl pyrazole mixture as a corrosion inhibitor for carbon steel in sulfuric acid solution, Mater. Chem. Phys. 71 (2001) 291–298. [27] M. Abdallah, Corrosion behaviour of 304 stainless steel in sulphuric acid solutions and its inhibition by some substituted pyrazolones, Mater. Chem. Phys. 82 (2003) 786–792. [28] A. Chetouani, B. Hammouti, T. Benhadda, M. Daoudi, Inhibitive action of bipyrazolic type organic compounds towards corrosion of pure iron in acidic media, Appl. Surf. Sci. 249 (2005) 375–385. [29] M. Elayyachy, M. Elkodadi, A. Aouniti, A. Ramdani, B. Hammouti, F. Malek, A. Elidrissi, New bipyrazole derivatives as corrosion inhibitors for steel in hydrochloric acid solutions, Mater. Chem. Phys. 93 (2005) 281–285. [30] K. Tebbji, A. Aouniti, M. Benkaddour, H. Oudda, I. Bouabdallah, B. Hammouti, A. Ramdani, New bipyrazolic derivatives as corrosion inhibitors of steel in 1 M HCl, Prog. Org. Coat. 54 (2005) 170–174. [31] S.A. Abd El-Maksoud, The influence of some arylazobenzoyl acetonitrile derivatives on the behaviour of carbon steel in acidic media, Appl. Surf. Sci. 206 (2003) 129–136. [32] A. Chetouani, A. Aouniti, B. Hammouti, N. Benchat, T. Benhadda, S. Kertit, Corrosion inhibitors for iron in hydrochloride acid solution by newly synthesised pyridazine derivatives, Corros. Sci. 45 (2003) 1675–1684. [33] G. Moretti, G. Quartarone, A. Tassan, A. Zingales, 5-amino and 5-chloro-indole as mild steel corrosion inhibitors in 1N sulphuric acid, Electrochim. Acta 41 (1996) 1971–1980. [34] M. Düdükcü, B. Yazici, M. Erbil, The effect of indole on the corrosion behaviour of stainless steel, Mater. Chem. Phys. 87 (2004) 138–141. [35] A.A. Ismail, S.H. Sanad, A.A. El-Meligi, Inhibiting effect of indole and some of its derivatives on corrosion of C-steel in HCl, J. Mater. Sci. Technol. 16 (2000) 397–400. [36] L. Wang, Evaluation of 2-mercaptobenzimidazole as corrosion inhibitor for mild steel in phosphoric acid, Corros. Sci. 43 (2001) 2281–2289. [37] A. Popova, M. Christov, T. Deligeorigiev, Influence of the Molecular Structure on the inhibitor properties of benzimidazole derivatives on mild steel corrosion in 1 M hydrochloric acid, Corrosion 59 (2003) 756–764. [38] A. Popova, M. Christov, S. Raicheva, E. Sokolova, Adsorption and inhibitive properties of benzimidazole derivatives in acid mild steel corrosion, Corros. Sci. 46 (2004) 1333–1350. [39] K.F. Khaled, The inhibition of benzimidazole derivatives on corrosion of iron in 1 M HCl solutions, Electrochim. Acta 48 (2003) 2493–2503. [40] M.H. Wahdan, The synergistic inhibition effect and thermodynamic properties of 2-mercaptobenzimidazol and some selected cations as a mixed inhibitor for pickling of mild steel in acid solution, Mater. Chem. Phys. 49 (1997) 135–140. [41] L.B. Tang, X.M. Li, Y.S. Si, G.N. Mu, G.H. Liu, The synergistic inhibition between 8-hydroxyquinoline and chloride ion for the corrosion of cold rolled steel in 0.5 M sulfuric acid, Mater. Chem. Phys. 95 (2006) 29–38. [42] Y. Yan, W.H. Li, L.K. Cai, B.R. Hou, Electrochemical and quantum chemical study of purines as corrosion inhibitors for mild steel in 1 M HCl solution, Electrochim. Acta 53 (2008) 5953–5960. [43] X.H. Li, S.D. Deng, H. Fu, Adsorption and inhibition of 6-benzylaminopurine on cold rolled steel in 1.0 M HCl, Electrochim. Acta 54 (2009) 4089–4098. [44] X.H. Li, S.D. Deng, H. Fu, G.N. Mu, Inhibition effect of 6-benzylaminopurine on the corrosion of cold rolled steel in H2SO4 solution, Corros. Sci. 51 (2009) 620– 634. [45] S.A. Ali, M.T. Saeed, S.U. Rahman, The isoxazolidines: a new class of corrosion inhibitors of mild steel in acidic medium, Corros. Sci. 45 (2003) 253–266. [46] S.A. Ali, H.A. Al-Muallem, M.T. Saeed, S.U. Rahman, Hydrophobic-tailed bicycloisoxazodidines: A comparative study of the newly synthesized compounds on the inhibition of mild steel corrosion in hydrochloric and sulfuric acid media, Corros. Sci. 50 (2008) 664–675. [47] E.E. Foad El Sherbini, Sulphamethoxazole as an effective inhibitor for the corrosion of mild steel in 1.0 M HCl solution, Mater. Chem. Phys. 61 (1999) 223–228. [48] S.A.M. Refaey, F. Taha, A.M. Abd El-Malak, Inhibition of stainless steel pitting corrosion in acidic medium by 2-mercaptobenzoxazole, Appl. Surf. Sci. 236 (2004) 175–185. [49] F. Bentiss, M. Traisnel, M. Lagrenée, The substituted 1,3,4-oxadiazoles: a new class of corrosion inhibitors of mild steel in acidic media, Corros. Sci. 42 (2000) 127–146. [50] F. Bentiss, M. Traisnel, N. Chaibi, B. Mernari, H. Vezin, M. Lagrenée, 2,5-Bis(nmethoxyphenyl)-1,3,4-oxadiazoles used as corrosion inhibitors in acidic media: correlation between inhibition efficiency and chemical structure, Corros. Sci. 44 (2002) 2271–2289.

X. Li et al. / Corrosion Science 53 (2011) 302–309 [51] M. Bouklah, B. Hammouti, M. Lagrenée, F. Bentiss, Thermodynamic properties of 2,5-bis(4-methoxyphenyl)-1,3,4-oxadiazole as a corrosion inhibitor for mild steel in normal sulfuric acid medium, Corros. Sci. 48 (2006) 2831–2842. [52] F. Bentiss, M. Traisnel, H. Vezin, H.F. Hildebrand, M. Lagrenée, 2,5-Bis(4dimethylaminophenyl)-1,3,4-oxadiazole and 2,5-bis(4-dimethylaminophenyl)1,3,4-thiadiazole as corrosion inhibitors for mild steel in acidic media, Corros. Sci. 46 (2004) 2781–2792. [53] M. El Azhar, B. Mernari, M. Traisnel, F. Bentiss, M. Lagrenée, Corrosion inhibition of mild steel by the new class of inhibitors [2,5-bis(n-pyvidyl)-1,3,4thiadiazoles] in acid, Corros. Sci. 43 (2001) 2229–2238. [54] F. Bentiss, M. Lebrini, H. Vezin, M. Lagrenée, Experimental and theoretical study of 3-pyridyl-substituted 1,2,4-thiadiazole and 1,3,4-thiadiazole as corrosion inhibitors of mild steel in acidic media, Mater. Chem. Phys. 87 (2004) 18–23. [55] F. Bentiss, M. Lebrini, H. Vezin, F. Chai, M. Traisnel, M. Lagrenée, Enhanced corrosion resistance of carbon steel in normal sulfuric acid medium by some macrocyclic polyether compounds containing a 1,3,4thiadiazole moiety: AC impedance and computational studies, Corros. Sci. 51 (2009) 2165–2173. [56] A.K. Singh, M.A. Quraishi, The effect of some bis-thiadiazole derivatives on the corrosion of mild steel in hydrochloric acid, Corros. Sci. 52 (2010) 1373–1385. [57] M.A. Quraishi, H.K. Sharma, Thiazoles as corrosion inhibitors for mild steel in formic and acetic acid solutions, J. Appl. Electrochem. 35 (2005) 33–39. [58] H.Q. Lian, R.Q. Liu, L.Q. Zhu, J.D. Wang, Inhibition corrosion of thiazole derivatives on A3 steel in 1 mol/L HCl solution, Chin. J. Appl. Chem. 23 (2006) 676–681 (in Chinese). [59] M.A. Quraishi, M.A.W. Khan, M. Ajmal, S. Muralidharan, S.V. Iyer, Influence of heterocyclic anils on corrosion inhibition and hydrogen permeation through mild steel in acid chloride environments, Corrosion 53 (1997) 475–480. [60] S. Kertit, B. Hammouti, Corrosion inhibition of iron 1 M HCl by 1-phenyl-5mercapto-1,2,3,4-tetrazole, Appl. Surf. Sci. 93 (1996) 59–66. [61] E. Bensajjay, S. Alehyen, M. El Achouri, S. Kertit, Corrosion inhibition of steel by 1-phenyl-5-mercapto 1, 2, 3, 4-tetrazole in acidic environments (0.5 M H2SO4 and 1/3 M H3PO4), Anti-Corros. Meth. Mater. 50 (2003) 402–409. [62] P. Morales-Gil, G. Negrón-Silva, M. Romero-Romoa, C. Ángeles-Chávez, M. Palomar-Pardavé, Corrosion inhibition of pipeline steel grade API 5L X52 immersed in 1 M H2SO4 aqueous solution using heterocyclic organic molecules, Electrochim. Acta 49 (2004) 4733–4741. [63] X.H. Li, S.D. Deng, H. Fu, Corrosion inhibition of red tetrazolium for cold rolled steel in hydrochloric acid media, Chin. J. Appl. Chem. 26 (2009) 1075–1079 (in Chinese). [64] X.H. Li, S.D. Deng, H. Fu, Synergism between red tetrazolium and uracil on the corrosion of cold rolled steel in H2SO4 solution, Corros. Sci. 51 (2009) 1344–1355. [65] X.H. Li, S.D. Deng, H. Fu, Synergistic inhibition effect of red tetrazolium and uracil on the corrosion of cold rolled steel in H3PO4 solution: weight loss, electrochemical, and AFM approaches, Mater. Chem. Phys. 115 (2009) 815–824. [66] I.B. Obot, N.O. Obi-Egbedi, Adsorption properties and inhibition of mild steel corrosion in sulphuric acid solution by ketoconazole: experimental and theoretical investigation, Corros. Sci. 52 (2010) 198–204. [67] X.H. Li, G.N. Mu, Tween-40 as corrosion inhibitor for cold rolled steel in sulphuric acid: weight loss study, electrochemical characterization, and AFM, Appl. Surf. Sci. 252 (2005) 1254–1265. [68] E. Cano, J.L. Polo, A. La Iglesia, J.M. Bastidas, A study on the adsorption of benzotriazole on copper in hydrochloric acid using the inflection point of the isotherm, Adsorption 10 (2004) 219–225.

309

[69] F. Bentiss, M. Lebrini, M. Lagrenée, Thermodynamic characterization of metal dissolution and inhibitor adsorption processes in mild steel/2,5-bis(n-thienyl)1,3,4-thiadiazoles/hydrochloric acid system, Corros. Sci. 47 (2005) 2915–2931. [70] G.N. Mu, X.H. Li, Q. Qu, J. Zhou, Molybdate and tungstate as corrosion inhibitors for cold rolling steel in hydrochloric acid solution, Corros. Sci. 48 (2006) 445–459. [71] C. Cao, On electrochemical techniques for interface inhibitor research, Corros. Sci. 38 (1996) 2073–2082. [72] M. Lagrenée, B. Mernari, M. Bouanis, M. Traisnel, F. Bentiss, Study of the mechanism and inhibiting efficiency of 3,5-bis(4-metylthiophenyl)-4H-1,2,4triazole on mild steel corrosion in acidic media, Corros. Sci. 44 (2002) 573–588. [73] A.K. Singh, M.A. Quraishi, Effect of cafazolin on the corrosion of mild steel in HCl solution, Corros. Sci. 52 (2010) 152–160. [74] N. Labjar, M. Lebrini, F. Bentiss, N.E. Chihib, S. El Hajjaji, C. Jama, Corrosion inhibition of carbon steel and antibacterial properties of aminotris(methylnephosnic) acid, Mater. Chem. Phys. 119 (2010) 330–336. [75] M. Lebrini, M. Lagrenée, H. Vezin, M. Traisnel, F. Bentiss, Experimental and theoretical study for corrosion inhibition of mild steel in normal hydrochloric acid solution by some new macrocyclic polyether compounds, Corros. Sci. 49 (2007) 2254–2269. [76] A.R.S. Priya, V.S. Muralidharam, A. Subramania, Development of novel acidizing inhibitors for carbon steel corrosion in 15% boiling hydrochloric acid, Corrosion 64 (2008) 541–552. [77] P. Bommersbach, C. Alemany-Dumont, J.P. Millet, B. Normand, Hydrodynamic effect on the behaviour of a corrosion inhibitor film: characterization by electrochemical impedance spectroscopy, Electrochim. Acta 51 (2006) 4011–4018. [78] D.P. Schweinsberg, V. Ashworth, The inhibition of the corrosion of pure iron in 0.5 M sulphuric acid by n-alkyl quaternary ammonium iodides, Corros. Sci. 28 (1988) 539–545. [79] G. Banerjee, S.N. Malhotra, Contribution to adsorption of aromatic amines on mild steel surface from HCl solutions by impedance, UV, and Raman spectroscopy, Corrosion 48 (1992) 10–15. [80] S.C. Roy, S.K. Roy, S.C. Sircar, Critique of inhibitor evaluation by polarization measurement, Br. Corro. J. 32 (1988) 102–104. [81] J.O.M. Bockris, B. Yang, Mechanism of corrosion inhibition of iron in acid solution by acetylenic alcohols, J. Elecrochem. Soc. 135 (1991) 2237–2252. [82] M. Lebrini, M. Lagrenée, M. Traisnel, L. Gengembre, H. Vezin, F. Bentiss, Enhanced corrosion resistance of mild steel in normal sulfuric acid medium by 2, 5-bis(n-thienyl-1, 3, 4-thiadiazoles: electrochemical, X-ray photoelectron spectroscopy and theoretical studies, Appl. Surf. Sci. 253 (2007) 9267–9276. [83] S. Rengamati, S. Muralidharan, M. Anbu Kulandainathan, S. Venkatakrishna Iyer, J. Appl. Electrochem. 24 (1994) 355. [84] A.K. Singh, M.A. Quraishi, Effect of 2,20 benzothiazolyl disulfide on the corrosion of mild steel in acid media, Corros. Sci. 51 (2009) 2752–2760. [85] A.F. Stassen, E. Dova, J. Ensling, H. Schenk, P. Gütlich, J.G. Haasnoot, J. Reedijk, Spin crossover in hexakis(1-(2-chloroethyl)-tetrazole)iron(II) complexes; synthesis and magnetic properties, Inorg. Chim. Acta 335 (2002) 61–68. [86] N. Hassan, P. Weinberger, F. Kubel, G. Molnar, A. Bousseksou, L. Dlhan, R. Bocˇa, W. Linert, Two new Fe(II) spin crossover complexes with tetrazol-1-ylcycloalkane ligands, Inorg. Chim. Acta 362 (2009) 3629–3636. [87] M. James, H. Kawaguchi, K. Tatsumi, Synthesis and crystal structure of a novel mixed valence tri-iron complex salt: [hexakis(thiazole)iron(II)][l-oxobis(trichloroiron(III))], Polyhedron 16 (1997) 4279–4282. [88] L. Zhu, K.L. Yao, Z.L. Liu, Theoretical studies on the spin distribution on the dihalide-bridged polymer metallic antiferromagnet Fe(thiazole)2 Cl2, Phys. Lett. A 353 (2006) 245–249.