Comparative Study on the Inhibition of Iron Corrosion in Aerated

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A comparative study on the inhibition of iron corrosion in aerated stagnant 3.5 wt.% sodium chloride solutions by 5-phenyl-1H-tetrazole and 3-amino-1,2,4-triazole El-Sayed M Sherif Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie400725z • Publication Date (Web): 20 Sep 2013 Downloaded from http://pubs.acs.org on September 26, 2013

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Industrial & Engineering Chemistry Research

A comparative study on the inhibition of iron corrosion in aerated stagnant 3.5 wt.% sodium chloride solutions by 5-phenyl-1H-tetrazole and 3-amino1,2,4-triazole

El-Sayed M. Sherif*,†,‡ †

‡

College of Engineering, King Saud University, P. O. Box 800, Al-Riyadh 11421, Saudi Arabia

Electrochemistry and Corrosion Laboratory, Department of Physical Chemistry, National

Research Centre (NRC), Dokki, 12622 Cairo, Egypt

*E-mail: [email protected]; [email protected], Tel.: 00966533203238, Fax: 0096614670199

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ABSTRACT: A comparative study on the inhibition of iron corrosion in 3.5 wt.% NaCl solutions by 5-phenyl-1H-tetrazole (PHTA) and 3-amino-1,2,4-triazole (ATA) was investigated using variety of electrochemical measurements. The potential-time curves revealed that PHTA and ATA shift the potential of iron towards the positive values. Electrochemical impedance spectroscopy measurements indicated that the presence of PHTA and ATA and the increase of their concentrations decrease the iron corrosion by increasing the solution and polarization resistances. This effect also decreases the corrosion current and corrosion rate for iron as confirmed by potentiodynamic polarization data. Potentiostatic current-time curves indicated that the presence of PHTA and ATA molecules decreases the absolute current and severity of pitting corrosion of iron in the test solutions. In-situ Raman spectra for iron in chloride solution containing PHTA and ATA confirmed that the inhibition of iron corrosion is achieved by the adsorption of PHTA and ATA molecules onto its surface.


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INTRODUCTION Iron and steel alloys have been widely used in huge applications due to their properties. Corrosion of iron due to the contact with harsh environments presents a serious economic problem. It has been reported1-3 that the corrosion of iron in corrosive solutions occurs through the dissolution of iron initially from Fe(0) into Fe(II) and further to Fe(III), Fe = Fe2+ + 2e‒

(1)

Fe2+ = Fe3+ + e‒

(2)

In aerated solutions, the presence of oxygen accelerates the consumption of the produced electrons and helps in the formation of iron oxides according to the following reactions,4-6 2H2O + O2 + 4e− = 4OH−

(3)

Fe + ½ O2 + H2O = Fe(OH)2

(4)

3Fe(OH)2 +½ O2 = Fe3O4 +3H2O

(5)

If the solutions contain high concentration of chloride ions, the dissolution of iron into ferrous cations occurs on multi-steps as follows,7 Fe + H2O = Fe(OH)ads + H+

(6)

Fe + Cl─ = Fe(Cl─)ads

(7)

Fe(OH)ads + Fe(Cl─)ads = Fe + FeOH+ + Cl─ + 2e─

(8)

FeOH+ + H+ = Fe2+aq + H2O

(9)

The corrosion and corrosion inhibition of iron in different environments have been reported in many research studies.7-11 One of the most important methods to protect metals and alloys including iron against corrosion in a corrosive medium is the use of corrosion inhibitors.12,13 Azole derivatives have been reported to be effective inhibitors against corrosion of metals in corrosive media.12-14 The effectiveness of these compounds is generally believed to depending on its functional groups, steric effects, electronic density of donor atoms, and porbital character of donating electrons.12-18 The inhibition mechanism usually invokes their interactions with the metallic surfaces via their adsorption sites where polar functional groups 3 ACS Paragon Plus Environment


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are usually regarded as the reaction centers.19 Where, the inhibitor molecules get bonded to the metal surface by chemisorption, physisorption, or complexation with the polar groups acting as the reactive centers in the molecules.20 This work reports the inhibition of the electrochemical corrosion of iron in aerated stagnant 3.5 wt.% NaCl solutions by 5-phenyl-1H-tetrazole (PHTA) and 3-amino-1,2,4-triazole (ATA) using different electrochemical measurements. The chemical structure of these two compounds is depicted in Figure 1. Figure 1 shows that these compounds contain many donor nitrogen groups and amino groups in their heterocyclic structures. The presence of such a combination in the molecule of these compounds has been reported to increase their inhibition effectiveness against corrosion in the corrosive media.

EXPERIMENTAL SECTION 3-Amino-1,2,4-triazole-5 (ATA, Sigma-Aldrich, 95%), 5-phenyl-1H-tetrazole (PHTA, Sigma-Aldrich, 95%), sodium chloride (NaCl, Merck, 99%), and absolute ethanol (C2H5OH, Merck, 99.9%) were used as received. A three-electrode configuration electrochemical cell was used for electrochemical measurements; an iron rod (Fe, Goodfellow, 99.98%, 9.5 mm in diameter), a platinum foil, and a Metrohm Ag/AgCl electrode (in 3 M KCl) were used as a working, counter, and reference electrodes, respectively. A stock solution of 7.0 wt.% NaCl was prepared by dissolving 70 g of NaCl in 1 L glass flask. The test solution (3.5 wt.% NaCl) was prepared from the stock by dilution. The iron rods for electrochemical analysis were prepared by attaching an insulated copper wire to one face of the sample using an aluminum conducting tape, and cold mounted in resin. The samples were then left to dry in air for 24 h at room temperature. To prevent the possibility of crevice corrosion during measurement, the interface between sample and resin was coated with Bostik Quickset, a polyacrylate resin. Before measurements, the iron electrode was first polished successively with metallographic emery paper of increasing fineness of up to 800 grits, and then


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further with 5, 1, 0.5 and 0.3 µm alumina slurries (Buehler). The electrode was then washed with doubly distilled water, degreased with acetone, washed using doubly distilled water again and finally dried with tissue paper. Electrochemical experiments were performed by using a PARC Parstat-2273 Advanced Electrochemical System after immersing the iron electrode for 1 h in freely aerated stagnant 3.5 wt.% NaCl solution without and with 5x10-4, and 1x10-3 M of PHTA and ATA present. The frequency in the electrochemical impedance spectroscopy (EIS) experiments was scanned at the open-circuit potential from 100 kHz to 0.1 Hz with an ac wave of ±5 mV peak-to-peak overlaid on a dc bias potential, and the Nyquist plots were acquired using Powersine software at a rate of 10 points per decade change in frequency. For the potentiodynamic polarization measurements, the potential of the iron electrode was swept from -1200 mV in the positive direction up to -300 mV vs. Ag/AgCl at a scan rate of 1 mV/s. Potentiostatic current-time measurements were carried out by applying a constant potential value of -500 mV vs. Ag/AgCl for 3600 seconds. The curves of the open-circuit potential vs. time were recorded from the first moment of iron immersion in all test solutions for 12000 seconds. The in-situ Raman spectroscopy investigations for iron in NaCl solutions alone and containing either 1x10-3 M PHTA or 1x10-3 M ATA were collected using JY T64000 Raman spectrometer in single spectrograph mode with a holographic dispersive grating of 600 g/mm, giving a resolution of 2 cm−1. All solutions were prepared using 99.0% doubly distilled water and only 1.0% ethanol (Vol. / Vol.) and all measurements were carried out at room temperature.

RESULTS AND DISSCUSION Open-Circuit Potential Measurements. Figure 2 shows the open-circuit potential (OCP) curves of the iron electrode in aerated stagnant 3.5 wt.% NaCl solutions in the absence (1) and presence (2) 5 x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA, respectively. It is seen from Figure 2 (curve 1) that the potential of iron in chloride solution without inhibitor increased



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towards the more negative values from the first moment of electrode immersion as a result of the dissolution of an air oxide film formed on iron before its immersion in the solution. The potential then slightly shifted in the more negative direction with increasing time till the end of the run due to the chloride ions attack on the iron surface. The addition of PHTA and ATA molecules shifted the initial potential of iron to less negative values. This is due to the decreased effect of chloride ions attack by the presence of the organic compounds. It is clearly seen from Figure 2 (curves 2 and curves 3) that the increase of the immersion time shifts the iron potential towards the less negative values and this effect increases with increasing the concentration of PHTA and ATA from 5x10-4 M to 1x10-3 M. This is probably due to the adsorption of PHTA and ATA molecules onto the iron surface, which decreases the aggressive action of chloride ions and thus decreases its dissolution.

Electrochemical

Impedance

Spectroscopy

Measurements.

Electrochemical

impedance spectroscopy (EIS) is an excellent technique that has been used in understanding the mechanism of corrosion and passivation phenomena of metals and alloys in their surrounding environments.21-24 Our EIS experiments were performed to report the effect of PHTA and ATA on the inhibition of iron and to determine the kinetic parameters for electron transfer reactions at the iron/electrolyte interface. Figure 3 shows the typical Nyquist plots obtained for iron rod after its immersion for 1 h in 3.5 wt.% NaCl solutions in the absence (1) and the presence of (2) 5x104

M, and (3) 1x10-3 M of (a) PHTA and (b) ATA, respectively. The same plots were recorded for

iron in the same solutions after 12 hours immersion and the curves are shown in Figure 4. The spectra represented in Figure 3 and Figure 4 were analyzed by best fitting to the equivalent circuit model shown in Figure 5. The EIS parameters obtained by fitting the equivalent circuit shown in Figure 5, as well as the values of the percentage of the inhibition efficiency (IE%), which were calculated using Eq. (10) and listed in Table 1.


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IE % =

RP − RP

Ο

(10)

RP

Where R P and R P Ο are polarization resistances with and without inhibitors, respectively. The parameters of the circuit shown in Figure 5 can be defined according to usual convention, as follows; RS represents the solution resistance, Rp the polarization resistance, and Q the constant phase elements (CPEs). For all the spectra shown in Figure 3 and Figure 4, only one semicircle is depicted for iron after 1 h and 12 h immersion either in chloride solution alone or in the presence of inhibitors. It is also shown that the diameter of the semicircle increases in the presence of the organic molecules and upon the increase of its concentrations. Also, this effect increases with increasing time from 1 h (Figure 3) to 12 h (Figure 4). It is clearly seen from Table 1 that the values of solution and polarization resistances are low in chloride solution alone and increase by increasing the immersion time as well as the presence of organic molecules and the increase of their concentrations. The constant phase elements (CPEs, Q) with their n values around 0.8 represent double layer capacitors with some pores; the CPEs decrease with increasing the immersion time and upon addition and the increase of inhibitors’ concentrations. This indicates that the formed film on the iron surface is non homogenous and having little porosities, which allows it to get thicker and becomes more compact with time and with the presence of PHTA and ATA molecules and the increase of their concentrations. This was also confirmed by the increase of IE% values listed in Table 1. The increase of Rs, Rp and IE% as well as the decrease of the CPE (Y0) values in the solutions containing increased concentrations of PHTA and ATA indicate that these compounds are good corrosion inhibitors for iron in the 3.5 wt.% NaCl medium.

Potentiodynamic Polarization Measurements. Figure 6 shows the potentiodynamic polarization (PDP) curves obtained for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M of (a) PHTA and (b) ATA 7 ACS Paragon Plus Environment


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present, respectively. These curves were obtained to study the effect of PHTA and ATA on the inhibition of iron corrosion in the chloride test solution. The values of cathodic (βc) and anodic (βa) Tafel slope, corrosion potential (ECorr), corrosion current density (jCorr), polarization resistance (Rp), corrosion rate (KCorr) and percentage of the inhibition efficiency (IE%) obtained for iron electrode from Figure 6 is listed in Table 2. The values of ECorr and jCorr parameters were obtained from the extrapolation of anodic and cathodic Tafel lines located next to the linearized current regions. Stern–Geary equation was used to calculate the values of Rp and KCorr for iron corrosion as follows:

RP =

K Corr =

 1  βc .βa   jCorr  2.3 ( β c + β a ) 

(11)

j Corr k E W dA

(12)

Where, k is a constant that defines the units for the corrosion rate (= 3272 mm/ (amp.cm.year)), EW the equivalent weight in grams/equivalent of iron alloy (EW = 27.93 grams/equivalent), d the density in gcm−3 (= 7.86), and A the area of the exposed surface of the electrode in cm2. In addition, the IE% values were calculated from the polarization data according to the equation,25,26

PE % =

1 2 − jCorr jCorr x 100 1 jCorr

(13)

Here j1Corr and j2Corr are the corrosion current densities in the absence and presence of the inhibitors’ molecules, respectively. Figure 6 (curve 1) shows that the current of iron increases in the anodic branch with increasing the applied potential and its value is the highest in the chloride free inhibitor solution. The anodic reaction for iron at this condition has been reported2 to be the dissolution of iron initially from Fe(0) into Fe(II), Eq. (1), then the oxidation of Fe(II) with the increase of applied potential in the less negative values to Fe(III) as shown by Eq. (2). The dissolution of iron gets


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accelerated when the released electrons by Eq. 1 and Eq. 2 are consumed at the cathodic areas of the iron surface due to the oxygen reduction reaction represented by Eq. 3. The passive region shown on the anodic side of the PDP curves is formed due to the formation of iron hydroxides (Eq. 4) then its transfer to form magnetite on the iron surface, Eq. 5. This leads to decreasing the dissolution of iron as well as the formation of the long passive region shown on the PDP curves. Further increasing the anodic potential leads to a rapid increase in the current of iron due to the breakdown of the formed oxide (magnetite) film and the occurrence of pitting corrosion. It is clearly seen from Figure 6 a (curve 2) and Table 2 that the addition of 0.5 mM PHTA shifted the values of ECorr to the less negative direction and decreased the values of jCorr, KCorr, while increased the values of Rp for iron. Increasing the concentration of PHTA to 1x10-3 M further decreased the corrosion parameters with more shift of the corrosion potential towards the positive direction. A higher effect was also observed in the presence of ATA molecules (Figure 6b), where jCorr and KCorr, recorded much smaller values and the obtained Rp values were higher, which means ATA shows better performance as a corrosion inhibitor compared to PHTA at the same concentration. It is also seen from the polarization curves of Figure 6 that the presence of the inhibitors, PHTA and ATA, decreases the formed passive region on the iron surface in the chloride solutions in the absence of inhibitors, Figure 6 (curve 1). This is because the presence of the inhibitor decreases the dissolution of iron and thus decreases the formation of corrosion products and iron oxides and that effect increases with the increase of the concentration of the inhibitor. The decrease of jCorr and KCorr and the increase of Rp values with the presence and the increase of the concentration of the organic compounds resulted due to the decrease of chloride ions attack on the iron surface. This was also confirmed by the increased values of IE% obtained on the iron surface for PHTA and ATA with the increase of their concentrations.



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Potentiostatic Current-Time Measurements. Our potentiostatic current-time (PCT) experiments were performed for iron after 1 h of its immersion in 3.5 wt.% NaCl solution without and with PHTA and ATA present before applying a constant potential value of -0.5 V vs. Ag/AgCl for 120 min. This was to confirm the data obtained from impedance and polarization measurements and to study the effect of PHTA and ATA on the inhibition of pitting and uniform corrosion of iron in the chloride test solution. The PCT curves obtained at -0.50 V vs. Ag/AgCl for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M of (a) PHTA and (b) ATA present, respectively are shown in Figure 7. It is clearly seen from Figure 7, that the initial current values for iron in chloride solution that contains no inhibitors, curves 1, started from lower values and rapidly increased with increasing the time of the experiment. It is also noted that these current values were the highest due to the aggressive attack of the chloride ions for the iron surface at this active potential, -0.5 mV, which leads to a continuous dissolution of iron and thus severe pitting and uniform corrosion. Where, the chloride ions target iron and form ferrous and ferric chloride on its surface and in the solution as well;27,28 Fe (s) + 2Cl− (aq) = FeCl2 (s) + 2e−

(14)

FeCl2 (s) + Cl− (aq) = FeCl3 (s) + e−

(15)

According to Eq. 14 and Eq. 15, the film formed on the iron surface is a mixed porous film of a precipitated ferrous chloride, FeCl2 and ferric chloride, FeC13. These species at the interface diffuse through the porous film and the diffusion boundary layer because of the active applied potential and the concentration gradients. These compounds will be carried away to the bulk solution by convection and will lead to the continuous uniform and pitting corrosion of iron with increasing the time of the applied potential on its surface.


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The presence of PHTA and the increase of its concentration from 5x10-4 M to 1x10-3 M, Figure 7a, curve 2 and curve 3, significantly reduced the chloride ions attack as indicated by the recorded low absolute current values of iron. This behavior also indicates that PHTA at these concentrations not only decreased the uniform corrosion but also prevented the pitting corrosion of iron to occur and this effect increases with increasing PHTA content. Similar PCT behavior was obtained for iron in the chloride solutions containing ATA molecules, which indicates that ATA highly decreases the dissolution of iron. The PCT curves confirm the data obtained by impedance spectroscopy and polarization ones and that both PHTA and ATA are good corrosion inhibitors for iron in 3.5 wt.% NaCl solution and their effect increases with the increase of their concentration.

Raman Spectroscopy Investigations. In order to investigate the film and/or the corrosion products formed on the iron surface after its immersion for 1h in the chloride solution with and without PHTA and M ATA, in situ Raman spectroscopy measurements were carried out. The in situ Raman spectra obtained on the iron surface after its immersion for 1 hour in (a) 3.5 wt.% NaCl solution alone and in the presence of (b) 1x10-3 M PHTA and (c) 1x10-3 M ATA, respectively are shown in Figure 8. It is seen that only few weak bands at 610, 859, 1168, and 1305 cm-1 were recorded for the surface of iron in chloride solution alone (curve a). The appearance of these weak bands particularly the band at 680 cm-1 is related to a very thin iron oxide film, most probably magnetite (Fe3O4).29-32 On the other hand, the iron surface in chloride solution containing PHTA, curve b of Figure 8, shows several bands were appeared at 880, 1038, 1079, 1232, 1316, and 1350 cm-1. Similar bands were also obtained for iron surface in the presence of ATA, curve c; these are 880, 1047, 1087, 1283 and 1452 cm-1. The strong band at 880 cm-1 is due to ring breathing of both PHTA and ATA molecules. Moreover, the bands 1038 and 1047 cm−1 are inplane ring-stretching vibrations of PHTA− and ATA− anions interacting with Fe(II),



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respectively.33 The two bands at1079 and 1087 cm-1 are due to the –N=N– stretches for PHTA and ATA, respectively. The presence of PHTA and ATA thus decreases the corrosion of iron in the chloride solution through the adsorption of these organic molecules or their complexes onto the surface.

CONCLUSION The inhibition of the electrochemical corrosion of iron in aerated stagnant 3.5 wt.% NaCl solutions by PHTA and ATA using variety of electrochemical and spectroscopic measurements has been reported and the obtained results can be summarized as follows: 1. The test chloride, 3.5 wt.% NaCl, solution has the ability to attack iron causing its uniform and pitting corrosion, where a top layer of Fe(OH)2 is first formed and rapidly transferred to Fe3O4 on the surface. The chloride ions present in the solution attack the layer of Fe3O4 and convert it to ferric chloride, FeCl3, which leaves the surface and goes to the solution causing the dissolution of iron. This effect decreases with increasing the immersion time of iron from 1h to 12 h. 2. Adding low concentrations namely 5x10-4 M and 1x10-3 M of PHTA and ATA reduces the aggressiveness action of the chloride ions and thus decreases the corrosion of iron. The effect of PHTA and ATA as corrosion inhibitors for iron was found to increase with the increase of their concentrations. This is because the presence of PHTA and ATA molecules prevents the formation of Fe(OH)2 and thus prevents the formation of Fe3O4. 3. The effectiveness of PHTA and ATA as corrosion inhibitors is due to their ability in decreasing the cathodic and anodic reaction rates for iron in the chloride solution. This was proven by the increase of solution and polarization resistances and the degree of inhibition efficiency as well as, the decrease of the corrosion current and corrosion rate for iron in the presence and the increase of PHTA and ATA molecules’ concentration.


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4. In situ Raman spectra confirmed the existence of PHTA and ATA molecules in the formed layer film on the iron surface after its exposure in chloride solutions containing inhibitors. The adsorption of PHTA and ATA molecules is thus the main reason for inhibiting the iron surface against corrosion in the chloride test solution.

ACKNOWLEDGEMENTS The authors extend their appreciation to the Deanship of Scientific Research at KSU for funding the work through the research group project No. RGP-VPP-160.



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List of Figures

Figure 1. Chemical structure of (a) 5-phenyl-1H-tetrazole and (b) 3-amino-1,2,4-triazole. Figure 2. The variation of open-circuit potential with time for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA present, respectively. Figure 3. Typical Nyquist plots obtained for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA present, respectively. Figure 4. Typical Nyquist plots obtained for iron electrode after its immersion for 12 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA present, respectively. Figure 5. The equivalent circuit model used to fit the EIS experimental data. Figure 6. Potentiodynamic polarization curves for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA present, respectively. Figure 7. Potentiostatic current-time curves obtained at -0.50 V vs. Ag/AgCl for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M of (a) PHTA and (b) ATA present, respectively. Figure 8. In-situ Raman spectra obtained on the iron surface after its immersion in 3.5 wt.% NaCl solutions without (a) and with (b) 1x10-3 M PHTA and (c) 1x10-3 M ATA present, respectively.


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(9) Veawab, A.; Tontiwachwuthikul, P.; Bhole, S. D. Studies of Corrosion and Corrosion Control in a CO2−2-Amino-2-methyl-1-propanol (AMP) Environment. Ind. Eng. Chem. Res. 1997, 36, 264. (10) Lai, B.; Zhou, Y.; Yang, P. Passivation of Sponge Iron and GAC in Fe0/GAC MixedPotential Corrosion Reactor. Ind. Eng. Chem. Res. 2012, 51, 7777. (11) Veawab, A. Tontiwachwuthikul, P.; Chakma, A. Investigation of Low-Toxic Organic Corrosion Inhibitors for CO2 Separation Process Using Aqueous MEA Solvent. Ind. Eng. Chem. Res. 2001, 40, 4771. (12) Zerfaoui, M.; Oudda, H.; Hammouti, B.; Kertit, S.; Benkaddour, M. Inhibition of corrosion of iron in citric acid media by aminoacids. Prog. Org. Coat. 2004, 51, 134. (13) Abdel-Rehim, S. S.; Khaled, K. F.; Al-Mobarak, N. A. Corrosion inhibition of iron in hydrochloric acid using pyrazole Arab. J. Chem. 2011, 4, 333. (14) Feng, Y.; Chen, S.; Guo, W.; Zhang, Y.; Liu, G. Inhibition of iron corrosion by 5,10,15,20-tetraphenylporphyrin and 5,10,15,20-tetra-(4-chlorophenyl)porphyrin adlayers in 0.5 M H2SO4 solutions. J. Electroanal. Chem. 2007, 602, 115. (15) Zhang, Z.; Chen, S.; Li, Y.; Li, S.; Wang, L. A study of the inhibition of iron corrosion by imidazole and its derivatives self-assembled films. Corros. Sci. 2009, 51, 291. (16) Sagues, A. A.; Davis, B. H.; Johnson, T. Coal liquids distillation tower corrosion. Synergistic effects of chlorides, phenols, and basic nitrogen compounds. Ind. Eng. Chem. Proc. Des. Dev., 1983, 22, 15. (17) Wahbi, Z.; Guenbour, A.; Abou El Makarim, H.; Ben Bachir, A.; El Hajjaji, S. Study of the inhibition of the corrosion of iron steel in neutral solution by electrochemical techniques and theoritical calculations. Prog. Org. Coat. 2007, 60,224. (18) Colorado-Garrido, D.; Ortega-Toledo, D. M.; Hernández, J. A.; González-Rodríguez, J. G.; Uruchurtu, J. Neural networks for Nyquist plots prediction during corrosion inhibition of a pipeline steel. J. Solid. State Electrochem. 2009, 13, 1715. 16 ACS Paragon Plus Environment

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(19) Tao, Z.; Zhang, S.; Li, W.; Hou, B. Adsorption and Corrosion Inhibition Behavior of Mild Steel by One Derivative of Benzoic−Triazole in Acidic Solution. Ind. Eng. Chem. Res. 2010, 49, 2593. (20) Lukovits, I.; Kalman, E.; Zucchi, F. Corrosion Inhibitors-Correlation Between Electronic Structure and Efficiency. Corrosion 2001, 57, 3. (21) Alam, M. A.; Sherif, E.-S. M.; Al-Zahrani, S. M. Fabrication of Various Epoxy Coatings for offshore applications and evaluating their mechanical properties and corrosion behavior. Inter. J. Electrochem. Sci. 2013, 8, 3121. (22) Gopiraman, M.; Selvakumaran, N.; Kesavan, D.; Kim, I. S.; Karvembu, R. Chemical and Physical Interactions of 1-Benzoyl-3,3-Disubstituted Thiourea Derivatives on Mild Steel Surface: Corrosion Inhibition in Acidic Media. Ind. Eng. Chem. Res. 2012, 51, 7910. (23) Khalil, A. K.; Sherif, E.-S. M.; Almajid, A. A. Corrosion Passivation in Simulated Body Fluid of Magnesium/Hydroxyapatite Nanocomposites Sintered by High Frequency Induction Heating. Inter. J. Electrochem. Sci. 2011, 6, 6184. (24) Macdonald, J. R. Impedance Spectroscopy; Wiley: New York, 1987. (25) Rajeswari, V.; Kesavan, D.; Gopiraman, M.; Viswanathamurthi, P. Physicochemical studies of glucose, gellan gum, and hydroxypropyl cellulose—Inhibition of cast iron corrosion. Carb. Poly. 2013, 95, 288. (26) Roomi, Y. A.; Hussein, K. F.; Riazi, M. R. Inhibition efficiencies of synthesized anhydride based polymers as scale control additives in petroleum production. J. Petrol. Sci. Eng. 2012, 81, 151. (27) Li, W.; Nobe, K.; Pearlstein, A. J. Potential/current oscillations and anodic film characteristics of iron in concentrated chloride solutions. Corros. Sci. 2009, 31, 615. (28) Williams, G.; McMurray, H. N. The mechanism of group (I) chloride initiated filiform corrosion on iron. Electrochem. Commun. 2003, 5, 871.



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(29) Melendres, C. A.; O'Leary, T. J.; Solis, J. Effect of thiocyanate on the corrosion and passivation behaviour of copper and iron: laser Raman spectroscopy and photoelectrochemical studies. Electrochim. Acta 1991, 36, 505. (30) Nguyen, H.; Le, T.; Bernard, M. C.; Garcia-Renaud, B.; Deslouis, C. Raman spectroscopy analysis of polypyrrole films as protective coatings on iron. Synthetic Metals 2004, 140, 287. (31) Dubois, F.; Mendibide, C.; Pagnier, T.; Perrard, F.; Duret, C. Raman mapping of corrosion products formed onto spring steels during salt spray experiments. A correlation between the scale composition and the corrosion resistance. Corros. Sci. 2008, 50, 3401. (32) Johnston, C. In situ laser Raman microprobe spectroscopy of corroding iron electrode surfaces. Vibrational Spectroscopy 1990, 1, 87. (33) Mennucci, M. M.; Banczek, E. P.; Rodrigues, P. R. P.; Costa, I. Evaluation of benzotriazole as corrosion inhibitor for carbon steel in simulated pore solution Cement Concrete Composites 2009, 31, 418.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 1. Chemical structure of (a) 5-phenyl-1H-tetrazole and (b) 3-amino-1,2,4-triazole.



0.48

(a) 0.54

-EOCP / V (Ag/AgCl)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.60

3 2

0.66 0.72

1 0

3000

6000

9000

12000

0.48

(b) 0.54 0.60

3 2

0.66 0.72

1

0

3000

6000

9000

12000

time / s Figure 2. The variation of open-circuit potential with time for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA present, respectively.


Page 21 of 28

-Z" / kΩ.cm2

750

3

(a)

600 450

2 1

300 150 0

-Z" / kΩ.cm2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


750

0

300

600

900

1200

1500

(b)

600 450

2

1

300

3

150 0

0

300

600

900

1200

1500

2

Z' / kΩ.cm

Figure 3. Typical Nyquist plots obtained for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA present, respectively.



-Z" / kΩ.cm2

900

(a)

3

750 600

2

450

1

300 150 0

-Z" / kΩ.cm2

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 28

900

0

300

600

900

1200

1500

1800

(b)

750 600

3

450

1

300

2

150 0

0

300

600

900

1200

1500

1800

Z' / kΩ.cm2 Figure 4. Typical Nyquist plots obtained for iron electrode after its immersion for 12 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA present, respectively.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. The equivalent circuit model used to fit the EIS experimental data.



4

10

(a)

3

10

2

-2

10

Current Density / µA cm

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 28

3 2

1

1

10

0

10

-1

10 1250 4 10

1000

750

2

250

500

250

(b)

3

10 10

500

1 2

1

10

3

0

10

-1

10 1250

1000

750

-E / mV (Ag/AgCl) Figure 6. Potentiodynamic polarization curves for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M (a) PHTA and (b) ATA present, respectively.


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Current Density / mAcm-2

Page 25 of 28

3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0

(a)

1

2 3 0

600

1200

1800

2400

3000

3600

1

(b)

2 3 0

600

1200

1800

2400

3000

3600

time / s Figure 7. Potentiostatic current-time curves obtained at -0.50 V vs. Ag/AgCl for iron electrode after its immersion for 1 h in 3.5 wt.% NaCl solutions without (1) and with (2) 5x10-4 M, and (3) 1x10-3 M of (a) PHTA and (b) ATA present, respectively.



(c) Intensity / Counts

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 26 of 28

(b)

(a) 1400

1200

1000

Raman Shift / cm

800

600

-1

Figure 8. In-situ Raman spectra obtained on the iron surface after its immersion in 3.5 wt.% NaCl solutions without (a) and with (b) 1x10-3 M PHTA and (c) 1x10-3 M ATA present, respectively.


Page 27 of 28

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Table 1. Parameters obtained from EIS spectra for iron electrode after 1 hour and 12 hours of its immersion in 3.5 wt.% NaCl solutions without and with the presence of PHTA and ATA, respectively. Parameter Solution 3.5 wt.% NaCl alone (1 h)

6.23

Q YQ / F cm-2 0.844

+ 5x10-4 M PHTA (1 h)

8.21

0.491

0.82

1541

57.14

+ 1x10-3 M PHTA (1 h)

10.99

0.326

0.79

1923

65.62

+ 5x10-4 M ATA (1 h)

8.45

0.388

0.83

2134

69.01

+ 1x10-3 M ATA (1 h)

11.12

0.193

0.83

2673

75.28

3.5 wt.% NaCl alone (12 h)

Rs / Ω cm2

n 0.83

Rp / Ω cm2

IE / %

662

−

7.08

0.652

0.78

719

−

-4

8.67

0.473

0.81

1995

63.82

-3

10.16

0.312

0.82

2744

73.72

-4

9.01

0.279

0.82

2732

73.63

-3

11.54

0.165

0.84

3445

79.07

+ 5x10 M PHTA (12 h) + 1x10 M PHTA (12 h) + 5x10 M ATA (12 h) + 1x10 M ATA (12 h)



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 28 of 28

Table 2. Parameters obtained from polarization curves shown in Fig. 6 for iron in aerated stagnant 3.5 wt.% NaCl solutions in absence and presence of PHTA and ATA molecules. Parameter βc / mVdec-1

ECorr / mV

jCorr / µAcm-2

βa / mVdec-1

Rp / Ω cm2

RCorr / mmy-1

IE / %

3.5 wt.% NaCl alone

117

-989

22

90

1013

0.256

−

+ 0.5 mM PHTA

122

- 975

7.8

105

3139

0.091

64.54

+ 1x10-3 M PHTA

128

- 948

5.6

115

4698

0.071

74.55

+ 0.5 mM ATA

126

-890

6.1

107

4122

0.071

72.27

+ 1x10-3 M ATA

134

-810

5.3

118

5154

0.062

75.91

Solution


Comparative Study on the Inhibition of Iron Corrosion in Aerated

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