Effect of Cefazolin on the corrosion of mild steel in HCl solution

Corrosion Science 52 (2010) 152–160

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Effect of Cefazolin on the corrosion of mild steel in HCl solution Ashish Kumar Singh, M.A. Quraishi * Department of Applied Chemistry, Institute of Technology, Banaras Hindu University, Varanasi, Uttar Pradesh 221 005, India

a r t i c l e

i n f o

Article history: Received 22 May 2009 Accepted 26 August 2009 Available online 31 August 2009 Keywords: A. Mild steel B. AFM B. Weight loss C. Acid inhibition C. Kinetic parameters

a b s t r a c t The adsorption and inhibition effect of Cefazolin on mild steel in 1.0 M HCl at 308–338 K was studied by weight loss, EIS, potentiodynamic polarization and atomic force microscopy techniques. The results showed that inhibition efficiency increased with inhibitor concentration. The adsorption of Cefazolin on mild steel surface obeys the Langmuir adsorption isotherm equation. Both thermodynamic (enthalpy of adsorption DHads , entropy of adsorption DSads and free energy of adsorption DGads ) and kinetic parameters (activation energy DEa and pre-exponential factor A) were calculated and discussed. Polarization curves showed that Cefazolin acted as mixed-type inhibitor controls predominantly cathodic reaction. Ó 2009 Elsevier Ltd. All rights reserved.

1. Introduction The damage by corrosion generates not only high cost for inspection, repairing and replacement, but in addition these constitute a public risk, thus the necessity of developing novel substances that behave like corrosion inhibitors especially in acid media [1]. There always exists a need for developing new corrosion inhibitors. Acid solutions are widely used in industry such as acid pickling of iron and steel, chemical cleaning and processing, ore production and oil well acidification. The use of hydrochloric acid in pickling of metals, acidization of oil wells and in cleaning of scales is more economical, efficient and trouble-free, compared to other mineral acids [2]. The corrosion inhibition efficiency of organic compounds is related to their adsorption properties. Studies reported that the adsorption of organic inhibitors mainly depends on some physiochemical properties of the molecule, related to its functional groups, to the possible steric effects and electronic density of donor atoms. Adsorption also depends on the possible interaction of porbital of the inhibitor with d-orbital of the surface atoms, which induces greater adsorption of the inhibitor molecules on the surface of mild steel [3–6]. A large number of organic compounds including heterocyclic compounds [7–12] were studied as corrosion inhibitors for mild steel [13–15]. Most of them are toxic in nature. This has led to the development of non-toxic corrosion inhibitors such as Tryptamine [16], L-ascorbic acid [17], Sulfamethoxazole [18], and Cefa-

* Corresponding author. Tel.: +91 9307025126; fax: +91 542 2368428. E-mail addresses: [email protected], [email protected] (M.A. Quraishi). 0010-938X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2009.08.050

trexyl [19], Ceftriaxone [20], Cefotaxime [21], sulfa drugs [22], antibacterial drugs [23], antifungal drugs [24], rhodanine azosulpha drugs [25]. Prabhu et al. [26] reported the inhibitor activity of tramadol on mild steel in HCl and H2SO4. Cefazolin is a first generation cephalosporin antibiotic [27]. It is mainly used to treat bacterial infections of the skin. It can also be used to treat moderately sever bacterial infections involving the lung, bone, stomach, blood, heart valve [28]. It is clinically effective against infections caused by Staphylococci and Streptococci of Gram positive bacteria [29]. Cefazolin is the commercial name of (6R,7R)-3-{[(5-methyl-1,3,4-thiadiazol-2-yl)thio]methyl}-8-oxo-7[(1H-tetrazol-1-ylacetyl)amino]-5-thia-1-azabicyclo[4.2.0]oct-2ene-2-carboxylic acid. It is a first generation cephalosporin antibiotic. In the present work, we have investigated the inhibitive action of Cefazolin on corrosion of mild steel in 1 M HCl solution at 308 K using weight loss, polarization resistance, Tafel polarization and electrochemical impedance techniques. The effects of temperature, acid concentration, immersion time were also studied. Several isotherms were tested for their relevance to describe the adsorption behaviour of the compound studied.

2. Experimental 2.1. Materials Tests were performed on mild steel having composition (wt.%) C = 0.17, Mn = 0.46, Si = 0.26, S = 0.017, P = 0.019 and balance Fe were used for weight loss as well as electrochemical studies. The aggressive solution of hydrochloric acid (AR grade) of 1 M

A.K. Singh, M.A. Quraishi / Corrosion Science 52 (2010) 152–160

concentration was used for all studies (except in the study of effect of acid concentration). 2.2. Inhibitor Cefazolin was purchased from medicine shop as a trade name Cefacidal powder injection (m.p.  463 K) and used without further purification. Fig. 1 shows the molecular structure of Cefazolin. Cefazolin is a N–S heterocyclic compound containing eight nitrogen atoms which could be easily protonated in acid solution, and a great deal of p-electrons exists in this molecule. 2.3. Solutions The aggressive solutions, 1.0 M HCl, were prepared by dilution of AR grade 37% HCl in distilled water. The stock solution of Cefazolin was diluted to a certain conc. of Cefazolin. The inhibitor concentration in the weight loss and electrochemical study was in the range of 2.19  104 M to 10.95  104 M and 4.76  104 M to 8.76  104 M, respectively. 2.4. Weight loss measurements The mild steel strips of 2.5 cm  2.0 cm  0.025 cm sizes were abraded with a series of emery paper (grade 600–800–1000– 1200) and then washed with distilled water and acetone. After weighing accurately, the specimens were immersed in 100 ml of 1.0 M HCl with and without addition of different concentrations of Cefazolin. After 3 h, the strips were taken out washed, dried and weighed accurately. Duplicate experiments were performed in each and the mean value of the weight loss was reported. The inhibition efficiency ðgW% Þ and surface coverage (h) was determined by using following equation:

gW% ¼ h¼

Wo  Wi  100 Wo

Wo  Wi Wo

ð1Þ

ð2Þ

where Wi and Wo are the weight loss values in the presence and in the absence of inhibitor, respectively.

Potentiostat/Galvanostat (Model G-300) with EIS software Gamry Instruments Inc., USA. Prior to the electrochemical measurement, a stabilization period of 30 min was allowed, which was proved sufficient to attain a stable value of Ecorr. For linear polarization resistance measurements, the potential of the electrode was scanned from 0.02 to +0.02 V vs. corrosion potential at scan rate of 0.5 mV/s. From the measured polarization resistance value, the inhibition efficiency was calculated using the relationship;

gRp % ¼

R0p  Rop R0p

 100

ð3Þ

where Rop and R0p are the polarization resistance in the absence and in the presence of inhibitor, respectively. The Tafel polarization curves were obtained by changing the electrode potential automatically from (+250 mV to 250 mV) at open circuit potential with a scan rate 0.5 mV s1 to study the effect of inhibitor on mild steel corrosion. The linear Tafel segment of cathodic and anodic curves were extrapolated to corrosion potential to obtain the corrosion current densities (Icorr). The inhibition efficiency was evaluated from the calculated Icorr values using the relationship;

gP% ¼

Iocorr  I0corr  100 Iocorr

ð4Þ

where Iocorr and I0corr are the corrosion current in the absence and in the presence of inhibitor, respectively. The impedance studies were carried out using ac signals of 10 mV amplitude for the frequency spectrum from 100 kHz to 0.01 Hz. The charge transfer resistance values were obtained from the diameter of the semi circles of the Nyquist plots. The inhibition efficiency of the inhibitor was obtained from the charge transfer resistance values using the following equation:

gRct % ¼

R0ct  Roct  100 R0ct

ð5Þ

where Roct and R0ct are the charge transfer resistance in the absence and in the presence of inhibitor, respectively. The values of interfacial double layer capacitance (Cdl), were estimated from the impedance value using bode plot by the formula;

2.5. Electrochemical measurements

jZj ¼ The electrochemical studies were carried out using a three-electrode cell assembly at room temperature. Mild steel coupons of 1 cm  1 cm (exposed area) with a 7.5 cm long stem (isolated with commercially available lacquer) were used for electrochemical measurements. A platinum foil of 1 cm2 was used as counter electrode and saturated calomel electrode as reference electrode. The working electrode was polished with different grades of emery papers, washed with water and degreased with acetone. All electrochemical measurements were carried out using a Gamry

153

1 2pfC dl

ð6Þ

2.6. Atomic force microscope The mild steel strips of 1.0 cm  1.0 cm  0.025 cm sizes were prepared as described in section 2.4. After immersion in 1.0 M HCl with and without addition of 8.76  104 M of Cefazolin at 308 K for 3 h, the specimen was cleaned with distilled water, dried and then used for AFM.

Fig. 1. Molecular structure of Cefazolin.

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inhibitor in acid solution at the studied concentration of the acid solution.

3. Results and discussion 3.1. Weight loss measurements 3.1.1. Effect of inhibitor concentration The corrosion rate values of mild steel with the addition of Cefazolin in 1.0 M HCl at various temperatures are presented in Table 1. From Table 1, it can be seen that corrosion rate values in 1.0 M HCl solution containing Cefazolin, decreased as the conc. of inhibitor increased. This result is due to fact that the adsorption amount and coverage of inhibitor on mild steel surface increases with inhibitor concentration. 3.1.2. Effect of temperature The values of inhibition efficiencies obtained from weight loss measurement for the different inhibitor concentrations in 1.0 M HCl are shown in Fig. 2a. From Fig. 2a, it can be seen that inhibition efficiency decreased with increasing temperature, which indicates desorption of inhibitor molecule [30]. However, this decrease in gW% is small at higher inhibitor concentration. 3.1.3. Effect of immersion time Fig. 2b shows the effect of immersion time (3–12 h) at 308 K on the inhibition efficiency of Cefazolin at different concentrations. Fig. 2b shows that Cefazolin inhibits the corrosion of mild steel for all immersion times. At lower concentration (2.19– 6.57  104 M), gW% decreased continuously with immersion time but at higher concentration, gW% was almost constant for different immersion times. 3.1.4. Effect of acid concentration The effect of acid concentration on corrosion behaviour of mild steel in the presence of 8.76  104 M inhibitor concentration was studied and the results are shown in Fig. 2c. It is clear that change in acid concentration from 0.5 to 2.5 M results in the inhibition efficiency varying from 93.76% to 88.9%. This change in the inhibition suggests that the compound is an effective corrosion Table 1 Corrosion rate and Inhibition efficiency (%IE) values for the corrosion of mild steel in aqueous solution of 1 M HCl in the absence and in the presence of different concentrations of Cefazolin from weight loss measurements at different temperatures. Inhibitor concentration (M  104)

Temperature (K)

Corrosion rate (mm/y)

gW%

Blank

308 318 328 338

40.4 58.2 100.9 174.5

– – – –

2.19

308 318 328 338

12.6 22.7 49.1 114.3

68.8 60.9 51.2 34.4

4.38

308 318 328 338

8.5 17.5 39.4 91.1

78.9 69.8 60.8 47.8

6.57

308 318 328 338

5.5 12.3 30.9 72.6

86.3 78.8 69.3 58.4

8.76

308 318 328 338

2.5 9.5 25.9 58.1

93.7 83.7 74.3 66.7

10.95

308 318 328 338

2.4 9.3 24.9 56.5

93.9 82.8 75.2 67.5

3.1.5. Adsorption isotherm Basic information on the interaction between the inhibitor and the mild steel surface can be provided using the adsorption isotherm. For this purpose, the values of surface coverage (h) at different concentrations of Cefazolin in 1 M HCl acid in the temperature range (308–338 K) were calculated to explain the best isotherm to determine the adsorption process from the experimental data obtained. Attempts were made to fit these h values to various isotherm including Frumkin, Langmuir, Temkin, Freundlich isotherms. By far, the experimental data the results were best fitted by Langmuir adsorption isotherm equation [31]:

C 1 ¼ þC h K

ð7Þ

Fig. 3 shows the relationship between C/h and C at temperature ranges studied. These results show that all the linear correlation coefficients (R2) are almost equal to unity and all the slopes are very close to unity, which indicates that the adsorption of Cefazolin follows Langmuir adsorption isotherm. 3.1.6. Thermodynamic parameters of Cefazolin on mild steel surface Thermodynamic parameters are important to study the inhibitive mechanism. The thermodynamic functions for dissolution of mild steel in the absence and in the presence of various concentrations of Cefazolin were obtained by applying the Arrhenius equation and the transition state equation [32–35]:

logðrÞ ¼

r¼

Ea þ log A 2:303RT

    RT DSa DHa exp exp  Nh R RT

ð8Þ

ð9Þ

where Ea apparent activation energy, A the pre-exponential factor, DHa the apparent enthalpy of activation, DSa the apparent entropy of activation, h the Planck’s constant and N the Avogadro number, respectively. The regression between log(r) and 1/T was calculated and the parameters were calculated and presented Table 2. Arrhenius plots of log(r) vs. 1/T for the blank and different concentrations of Cefazolin are shown in Fig. 4a, and from the Table 2, it can be seen that apparent activation energy increased with increasing concentration of Cefazolin. The increase in apparent activation energy Ea may be interpreted as physical adsorption [36]. Szauer and Brand [37] explained that the increase in activation energy can be attributed to an appreciable decrease in the adsorption of the inhibitor on the mild steel surface with increase in temperature and a corresponding increase in corrosion rates occurs due to the fact that greater area of metal is exposed to the acid environment. According to Eq. (8), corrosion rate (r) is being effected by both Ea and A. In general, the influence of Ea on the mild steel corrosion was higher than that of A on the mild steel corrosion. However, if the variation in A was drastically higher than that of Ea , the value of A might be the dominant factor to determine the mild steel corrosion. In the present case, Ea and A increased with concentration (the higher Ea and lower A led to lower corrosion rate). As it can be seen from Table 1, the corrosion rate of steel decreased with increasing concentration; hence, it was clear that increment of Ea was the decisive factor affecting the corrosion rate of mild steel in 1.0 M HCl. Fig. 4b shows a plot of log(r/T) vs. 1/T. A straight lines were obtained with a slope equal to ðDH =2:303RÞ and intercept equal to ½logðR=NhÞ þ ðDS =2:303RÞ, from which the values of DHa and DSa

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(a) 100

(b)

90

70

η W%

η W%

80

60 50 40 30

95 90 85 80 75 70 65 60 55 50 45

2 4 6 8 10 12 -4 Inhibitor concentration (M x 10 )

(c)

5 4

3

2

1

2

4

6

8

10

12

Immersion time (h)

97.5

ηW%

95.0

92.5

90.0

0.5

1.0

1.5

2.0

2.5

Acid concentration (M) Fig. 2. Variation of inhibition efficiency in 1 M HCl on mild steel of surface area 10 cm2 with (a) different conc. of Cefazolin inhibitor at different temperatures, (b) immersion time at different conc. and (c) different acid conc. at optimum inhibitor conc. (8.76  104 M).

are higher than in the absence of inhibitor. The positive sign of enthalpies reflect the endothermic nature of steel dissolution process meaning that dissolution of steel is difficult [38]. On comparing the values of the entropy of activation ðDSa Þ given in Table 2, it is clear that entropy of activation increased positively in the presence of Cefazolin than in the absence of inhibitor. The increase of DSa reveals that an increase in disordering takes place on going from reactant to the activated complex [39]. The constant of adsorption, Kads, is related to the standard free energy of adsorption, DGads from the following equation:

18 308 K 318 K 328 K 338 K

16

-4

Cinh/ θ (10 M)

14

2

(R = 0.9966) 2 ( R = 0.9990 ) 2 (R = 0.9988) 2 (R = 0.9987)

12 10 8 6 4

K ads ¼ 2 2

4

6

C inh (10

8 -4

10

12

M)

Fig. 3. Langmuir’s adsorption isotherm plots for the adsorption of Cefazolin at different conc. in 1 M HCl on the surface of mild steel.

were calculated and listed in Table 2. Inspection of these data reveals that the thermodynamic parameters ðDHa and DSa Þ of dissolution reaction of mild steel in 1 M HCl in the presence of Cefazolin

  1 DGads exp 55:5 RT

ð10Þ

The value 55.5 in the above equation is the concentration of water in solution in mol l1 [40]. The standard free energy of adsorption ðDGads Þ were calculated and the negative values of DGads obtained indicates the spontaneity of the adsorption process and stability of the adsorbed layer on the mild steel surface. Generally values of ðDGads Þ up to 20 kJ mol1 are consistent with the electrostatic interactions between the charged metal (physisorption) while those around 40 kJ mol1 or higher are associated with chemisorption as a result of sharing or transfer of unshared electron pair or

Table 2 The values of activation parameters Ea , DHa and DSa for mild steel in 1 M HCl in the absence and in the presence of different concentrations of Cefazolin. Inhibitor conc. (M  104) 1 M HCl 2.19 4.38 6.57 8.76 10.95

Ea (kJ mol1) 42.72 63.13 67.71 74.02 89.41 89.24

DHa (kJ mol1) 39.55 60.47 65.06 71.37 86.76 86.59

DSa (J mol1 K1) 86.75 28.82 16.90 0.0103 44.60 43.83

A (mg cm2) 8

5.31  10 5.66  1011 2.37  1012 1.81  1013 3.87  1015 3.53  1015

Linear regression coefficient (R2) 0.9881 0.9900 0.9970 0.9985 0.9918 0.9911

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(a)

-0.2

(b)

-0.4

-1

1.5

-0.8

-1

log r/T(mmy K )

-0.6

-1

log r (mmy )

2.0

-1.0

Blank -4

1.0

2.19 x 10 M -4

4.76 x 10 M -4

6.57 x 10 M -4

8.76 x 10 M -4

0.5

10.95 x 10 M

-1.2 -1.4

Blank

-1.6

4.76 x 10 M

-1.8

6.57 x 10 M

-2.0

10.95 x 10 M

-4

2.19 x 10 M -4 -4 -4

8.76 x 10 M -4

-2.2 2.95 3.00 3.05 3.10 3.15 3.20 3.25

2.95 3.00 3.05 3.10 3.15 3.20 3.25 3 0

[(1/T).10 ] K

(c)

3 0

-1

[(1/T).10 ] K

-1

-93

-1

-1

Δ Gads /T(JK mol )

-96 -99 -102 -105 -108 -111 -114 -117 2.95 3.00 3.05 3.10 3.15 3.20 3.25 3 0

[(1/T).10 ] K

-1

Fig. 4. (a) Adsorption isotherm plot for log (CR) vs. 1/T; (b) adsorption isotherm plot for log (CR/T) vs. 1/T; (c) adsorption isotherm plot for DG/T vs. 1/T.

p-electrons of organic molecules to the metal surface to form a co-

This equation can be rearranged to give the following equation.

ordinate type of bond (chemisorption) [41,42]. Free energy of adsorption ðDGads Þ was calculated using the following equations and listed in Table 3.

DGads DHads ¼ þk T T

DGads ¼ RT lnð55:5 KÞ K¼

ð11Þ

h Cð1  hÞ

ð12Þ

where h is degree of coverage on the metal surface, C is concentration of inhibitor in mol l1, R is the molar gas constant and T is temperature. The DGads value of the inhibitor was found 35.54 kJ mol1 indicated that it is adsorbed on the metal surface by both physical and chemical process [43–45]. The negative values of DGads indicated the spontaneous adsorption of inhibitor on surface of mild steel. The enthalpy of adsorption was calculated from the Gibbs– Helmholtz equation:

  @ðDGads =TÞ DHads ¼ @T T2 P

The variation of DGads =T with 1/T gives a straight line with a slope that equals DHads (Fig. 4c). It can be seen from the figure that DGads =T decreases with 1/T in a linear fashion. The calculated values are depicted in Table 3. The adsorption heat could be approximately regarded as the standard adsorption heat ðDHads Þ under experimental conditions [33,46]. The negative sign of DHads in HCl solution indicates that the adsorption of inhibitor molecule is an exothermic process. Generally, an exothermic adsorption process signifies either physisorption or chemisorption while endothermic process is attributable unequivocally to chemisorption [47]. Typically, the enthalpy of physisorption process is lower than that 41.86 kJ mol1 while the enthalpy of chemisorption process approaches 100 kJ mol1 [48]. In the present study, the absolute value of enthalpy is 57.04 kJ mol1, which is an intermediate case. Then the standard adsorption entropy ðDSads Þ was obtained using the thermodynamic basic equation:

ð13Þ

DSads ¼

Table 3 Thermodynamic parameters for the adsorption of Cefazolin in 1 M HCl on the mild steel at different temperatures. Temperature (K)

K (mol1)

DGads (kJ mol1)

DHads (kJ mol1)

DSads (J mol1 K1)

308 318 328 338

19,379 6594 3719 2576

35.54 33.85 33.35 33.34

57.04 57.04 57.04 57.04

69.80 72.90 72.20 70.11

ð14Þ

DHads  DGads T

ð15Þ

The DSads values in the presence of inhibitor are large and negative, meaning a decrease in disordering on going from reactants to the metal adsorbed species. 3.2. EIS measurements Electrochemical impedance measurements were performed over the frequency range from 100 kHz to 0.01 Hz at open circuit potential. The simple equivalent randle circuit for studies is shown in Fig. 5, where RX represents the solution resistance, Rct the charge transfer resistance and double layer capacitance (Cdl). Nyquist plots

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Fig. 5. Electrical equivalent circuit (RX, uncompensated solution resistance; Rct, polarization resistance; Cdl, double layer capacitance).

frequencies. The fact that this semicircle can not be observed after the addition of higher concentration of Cefazolin supports our view. Inhibition efficiencies and other calculated impedance parameters are given in Table 4. As it can be seen from Table 4, the Rct values increased with increasing the concentration of the inhibitor and the values of Cdl decreased with an increase in the inhibitor concentration. This situation was the result of an increase in the surface coverage by this inhibitor, which led to an increase in the inhibition efficiency. The thickness of the protective layer, dorg, is related to Cdl by the following equation [53]:

dorg ¼

-Z im ag ( Ω cm 2 )

250

10

-4

2 = 6.57x10 M -4

3 = 8.76x10 M

5 0

200

5 10 15 2 Zreal(Ω cm )

2

150

3.3. Tafel polarization 100

50

0

1

0

50

2

100

3

150

200

250

300

2

Zreal (Ω cm ) Fig. 6. Nyquist plots of mild steel in 1 M HCl with different concentration range of Cefazolin.

of mild steel at various concentrations of Cefazolin in 1 M HCl solution are presented in Fig. 6. The impedance spectra for mild steel in 1 M HCl are similar in shape with a high frequency (HF) capacitive loop and low frequency (LF) inductive loop (except at 8.76  104 M). The HF capacitive loop can be attributed to the charge transfer reaction and time constant of the electric double layer. The time constant at high frequencies may be attributed to formation of surface film [49,50]. On the other hand, the inductive loop has been attributed to a surface or bulk relaxation process or to a dissolution process [51,52]. We have correlated the low frequency inductive loop seen in the free acid solution with a surface dissolution process. The low frequency inductive loop in inhibited acid solution containing lower concentration of Cefazolin might be attributed to the relaxation process obtained by adsorption of species as Hads þ and Cl on the electrode surface. It might be also attributed to the re-dissolution of the passivated surface at low

Polarization curves for mild steel in 1.0 M HCl at various concentration of Cefazolin are presented in Fig. 7. The values of corrosion current densities (Icorr), corrosion potential (Ecorr), the anodic Tafel slopes (ba), cathodic Tafel slopes (bc) and inhibition efficiency ðgP% Þ as function of Cefazolin concentration were calculated from the curves of Fig. 7 and presented in Table 4. It reveals that the corrosion current (Icorr) decreased prominently and inhibition efficiency increased with inhibitor concentration. The presence of Cefazolin does not remarkably shift the corrosion potential (Ecorr) and hence, can be said to be a mixed-type inhibitor in 1.0 M HCl. The anodic Tafel slopes changes slightly whereas the change in cathodic Tafel slopes are larger which means that Cefazolin

-200

Potential (mV vs SCE)

-Z imag ( Ω cm )

0

ð16Þ

C dl

where eo is the dielectric constant and er is the relative dielectric constant. This decrease in the Cdl, which can result from a decrease in local dielectric constant and/or an increase in the thickness of the electrical double layer, suggested that Cefazolin molecules function by adsorption at the metal/solution interface. Thus, the change in Cdl values was due to the gradual replacement of water molecules by the adsorption of the organic molecules on the metal surface, decreasing the extent of metal dissolution [54].

Blank

15

-4

1 = 4.38x10 M

eo er

1 2 3 4

-300

= = = =

Free Acid Solution -4 4.38x10 M -4 6.57x10 M -4 8.76x10 M

-400 -500 -600 -700 4

-800 0.000

0.001

0.010

0.100

1.000

3 2

10.000

1

100.000

-2

Current density (mA cm ) Fig. 7. Tafel Polarization behaviour of mild steel in 1 M hydrochloric acid with different concentration range of Cefazolin.

Table 4 Electrochemical parameters for corrosion of mild steel in 1 M HCl in the presence of different concentrations of Cefazolin. Conc. of inhibitor (M  104)

Blank HCl Inh 4.38 6.57 8.76

Tafel data

Impedance data

Ecorr (mV vs. SCE)

Icorr (lA cm

469 487 480 481

730 124 85 39

2

)

2

Linear polarization 2

ba (mV/dec)

bc (mV/dec)

gP%

Rct (X cm )

Cdl (lF cm

73 54 62 67

127 152 152 186

– 83.0 88.3 94.7

17.3 87.3 126.5 262.6

1006 118 109 81

)

gRct %

Rp (X cm2)

gRp %

– 80.1 86.3 93.4

18.7 101.8 128.9 256.6

– 81.6 85.5 92.7

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A.K. Singh, M.A. Quraishi / Corrosion Science 52 (2010) 152–160

Fig. 8. Atomic force micrographs of mild steel surface (a) polished mild steel, (b) mild steel in 1 M HCl and (c) inhibited mild steel (1 M HCl + 8.76  104 inhibitor).

molecules are adsorbed on both sites but under prominent cathodic control resulting in inhibition of anodic dissolution and cathodic reduction reaction. 3.4. Linear polarization resistance The polarization resistance (Rp) values of mild steel in 1 M HCl increases from 18.7 X for the blank to 256.6 X for 8.76  104 M concentration of Cefazolin (Table 4). The increase in the Rp value suggests that the inhibition efficiency increases with the increase in the inhibitor concentration. 3.5. Surface characterization: AFM study The atomic force microscope provides a powerful means of characterizing the microstructure. The three-dimensional AFM images are shown in Fig. 8a–c. As it can be seen from Fig. 8a the mild steel surface before immersion seems smooth compared to the mild steel surface after immersion in uninhibited 1.0 M HCl for 3 h. The average roughness of polished mild steel (Fig. 8a) and mild steel in 1.0 M HCl without inhibitor (Fig. 8b) was calculated to be 66 and 395 nm, respectively. It is clearly shown in Fig. 8b that mild steel sample is getting cracked due to the acid attack on mild steel surface. However in the presence of optimum concentration of inhibitor, the average roughness was reduced to 167 nm (Fig. 8c).

cess. Furthermore, the size, orientation, shape and electric charge on the molecule determine the degree of adsorption and hence the effectiveness of inhibitor. On the other hand, iron is well known for its co-ordination affinity to heteroatom bearing ligands. Increase in inhibition efficiencies with the increase of concentration of Cefazolin shows that the inhibition action is due to adsorption on the steel surface. Four types of adsorption may take place by organic molecules at metal/solution interface namely. (1) Electrostatic attraction between the charged molecules and charged metal. (2) Interaction of unshared electron pairs in the molecule with the metal. (3) Interaction of p-electrons with the metal. (4) Combination of (1) and (3) [55]. In HCl solution the following mechanism is proposed for the corrosion of iron and steel [56]. According to this mechanism anodic dissolution of iron follows: 



Fe þ Cl ðFeCl Þads 

ðFeCl Þads ðFeClÞads þ e þ

ðFeClÞads ! ðFeCl Þ þ e þ



ðFeCl Þ Fe2þ þ Cl

The cathodic hydrogen evolution follows:

Fe þ Hþ ðFeHþ Þads 4. Mechanism of inhibition A clarification of mechanism of inhibition requires full knowledge of the interaction between the protective compound and the metal surface. Many of the organic corrosion inhibitors have at least one polar unit with atoms of nitrogen, sulphur, oxygen and in some cases phosphorous. It has been reported that the inhibition efficiency decreases in the order to O < N < S < P. The polar unit is regarded as the reaction centre for the chemisorption pro-

ðFeHþ Þads þ e ðFeHÞads ðFeHÞads þ Hþ þ e ! Fe þ H2 In acidic solution, carbonyl group, secondary amine group as well as nitrogen atoms in tetrazole ring (Fig. 9) and adjacent carbonyl group (O23) can be protonated easily because they all are planar and having greater electron density (N20, N25, N27, N28 and N29). Physical adsorption may take place due to electrostatic interaction between protonated molecule and (FeCl)ads species. Co-ordinate

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159

Fig. 9. Three-dimensional representation of Cefazolin molecule.

covalent bond formation between electron pairs of unprotonated S atom and two N-atoms in thiadiazole ring (S4, N1 and N2) and metal surface can take place. Further, Cefazolin molecules are chemically adsorbed due to interaction of p-orbitals with metal surface following deprotonisation step of the physically adsorbed protonated molecules. In the presented case, the value of DGads is 35.54 kJ mol1, hence, indicated that adsorption of Cefazolin on the surface of mild steel involves both physical and chemical process. But, as it can be seen from Table 3, the values of DGads decreased with increasing temperature hence, indicated that adsorption of Cefazolin does not favour at higher temperature, indicating that Cefazolin adsorbed predominantly physically on the surface of mild steel. 5. Conclusion

(1) Cefazolin acts as a good inhibitor for the corrosion of mild steel in 1.0 M HCl. (2) The inhibition efficiency of Cefazolin decreased with temperature, which leads to an increase activation energy of corrosion process. (3) The adsorption of Cefazolin obeys Langmuir adsorption isotherm. The adsorption process is a spontaneous and exothermic process accompanied by an increase of entropy. (4) Potentiodynamic polarization curves reveals that Cefazolin is a mixed-type but predominantly cathodic inhibitor. (5) The results obtained from weight loss, impedance and polarization studies are in a good agreement.

Acknowledgement One of the author A.K.S. is thankful to University Grant Commission (UGC), New Delhi, for Senior Research Fellowship. References [1] [2] [3] [4] [5] [6] [7]

G. Trabanelli, Corrosion 47 (1991) 410. D.D.N. Singh, T.B. Singh, B. Gaur, Corros. Sci. 37 (1995) 1005. F. Bentiss, M. Lagrenee, M. Traisnel, J.C. Hornez, Corros. Sci. 41 (1999) 789. F.B. Growcock, W.W. Frenier, P.A. Andreozzi, Corrosion 45 (1989) 1007. I. Lukovits, E. Kalman, G. Palinkas, Corrosion 51 (1995) 201. M.A. Quraishi, H.K. Sharma, Mater. Chem. Phys. 78 (2002) 18. M.A. Quraishi, R. Sardar, Corrosion 58 (2002) 103.

[8] M.A. Quraishi, R. Sardar, Corrosion 58 (2002) 748. [9] E. Norr, Corros. Sci. 47 (2005) 33. [10] M. Lebrini, M. Lagrenee, H. Vezin, L. Gengembre, F. Bentiss, Corros. Sci. 47 (2005) 485. [11] F. Bentiss, M. Bovanis, B. Mernari, M. Traisnel, H. Vezin, M. Lagrenee, Appl. Surf. Sci. 253 (2007) 3696. [12] Z. Ait Chikh, D. Chebabe, A. Dharmraj, N. Hajjaji, A. Srhirri, M.F. Montemor, M.G.S. Ferreira, A.C. Bastos, Corros. Sci. 47 (2005) 447. [13] M. Lagrenee, B. Mernari, M. Bouanis, M. Traisnel, F. Bentiss, Corros. Sci. 44 (2002) 573. [14] M.A. Quraishi, I. Ahamad, A.K. Singh, S.K. Shukla, B. Lal, V. Singh, Mater. Chem. Phys. 112 (2008) 1035. [15] S.K. Shukla, A.K. Singh, I. Ahamad, M.A. Quraishi, Mater. Lett. 63 (2009) 819. [16] G. Moretti, F. Guidi, G. Grion, Corros. Sci. 46 (2004) 387. [17] E.S. Ferreira, C. Giacomelli, F.C. Giacomelli, A. Spinelli, Mater. Chem. Phys. 83 (2004) 129. [18] E.E.F. ElSherbini, Mater. Chem. Phys. 60 (1999) 286. [19] M.S. Morad, Corros. Sci. 50 (2008) 436. [20] S.K. Shukla, M.A. Quraishi, J. Appl. Electrochem. doi:10.1007/s10800-0099834-1. [21] S.K. Shukla, M.A. Quraishi, Corros. Sci. 51 (2009) 1007. [22] M.M. El-Naggar, Corros. Sci. 49 (2007) 2226. [23] M. Abdallah, Corros. Sci. 46 (2004) 1981. [24] I.B. Obot, N.O. Obi-Egbedi, S.A. Umoren, Corros. Sci. 51 (2009) 1868. [25] M. Abdallah, Corros. Sci. 44 (2002) 717. [26] R.A. Prabhu, A.V. Shanbhag, T.V. Venkatesha, J. Appl. Electrochem. 37 (2007) 491. [27] A.S. Dajani, K.A. Taubert, W.W. Wilson, et al., JAMA 277 (1997) 1794. [28] L.O. Gentry, B.J. Zeluff, D.A. Cooley, Ann. Thorac. Surg. 46 (1988) 167. [29] C.A. Gustaferro, J.M. Steckelberg, Mayo Clin. Proc. 66 (1991) 1064. [30] M. Schorr, J. Yahalom, Corros. Sci. 12 (1972) 867. [31] X.H. Li, S.D. Deng, G.N. Mu, H. Fu, F.Z. Yang, Corros. Sci. 50 (2008) 420. [32] J.O’M. Bockris, A.K.N. Reddy, Modern Electrochemistry, vol. 2, Plenum Press, New York, 1977. [33] X.H. Li, S.D. Deng, H. Fu, G.N. Mu, Corros. Sci. 50 (2008) 2635. [34] Z. Wei, P. Duby, P. Somasundaran, J. Colloid Interface Sci. 259 (2003) 97. [35] A. Ostovari, S.M. Hoseinieh, M. Peikari, S.R. Shadizadeh, S.J. Hashemi, Corros. Sci. (2009), doi:10.1016/j.corsci.2009.05.024. [36] E.F. El Sherbini, Mater. Chem. Phys. 60 (1999) 286. [37] T. Szauer, A. Brand, Electrochim. Acta 26 (1981) 1219. [38] N.M. Guan, L. Xueming, L. Fei, Mater. Chem. Phys. 86 (2004) 59. [39] E. Khamis, A. Hosney, S. El-Khodary, Afinidad 52 (1995) 95. [40] J. Flis, T. Zakroczymski, J. Electrochem. Soc. 143 (1996) 2458. [41] E. Khamis, F. Bellucci, R.M. Latanision, E.S.H. El-Ashry, Corrosion 47 (1991) 677. [42] F.M. Donahue, K. Nobe, J. Electrochem. Soc. 112 (1965) 886. [43] S. Brinic, Z. Grubac, R. Babic, M. Metikos-Hukovic, in: 8th Eur. Symp. Corros. Inhib., vol. 1, Ferrara, Italy, 1995, p. 197.. [44] E. Geler, D.S. Azambuja, Corros. Sci. 42 (2000) 631. [45] M. Bouklah, N. Benchat, B. Hammouti, A. Aouniti, S. Kertit, Mater. Lett. 60 (2006) 1901. [46] T.P. Zhao, G.N. Mu, Corros. Sci. 41 (1999) 1937. [47] W. Durnie, R. De Marco, B. Kinsella, A. Jefferson, J. Electrochem. Soc. 146 (5) (1999) 1751. [48] S. Martinez, I. Stern, Appl. Surf. Sci. 199 (2002) 83. [49] C.M.A. Brett, Corros. Sci. 33 (1992) 203. [50] E.M. Sherif, S.M. Park, Electrochim. Acta 51 (2006) 1313.

160

A.K. Singh, M.A. Quraishi / Corrosion Science 52 (2010) 152–160

[51] Z. Tao, S. Zhang, W. Li, B. Hou, Corros. Sci. (2009), doi:10.1016/ j.corsci.2009.06.042. [52] J.W. Lenderink, M. Linden, J.H. Wit, Electrochim. Acta 39 (1993) 1989. [53] F. Bentiss, B. Mehdi, B. Mernari, M. Traisnel, H. Vezin, Corrosion 58 (2002) 399. [54] E. McCafferty, N. Hackerman, J. Electrochem. Soc. 119 (1972) 146.

[55] H. Shorky, M. Yuasa, I. Sekine, R.M. Issa, H.Y. El-Baradie, G.K. Gomma, Corros. Sci. 40 (1998) 2173. [56] M. Morad, J. Morvan, J. Pagetti, in: Proceedings of the Eighth European Symposium on Corrosion Inhibitors (8SEIC), Sez V, Suppl. N. 10, Ann. Univ. Ferrara, NS, 1995, p. 159.