Corrosion Inhibition Properties of Triazine Derivatives Containing

Subscriber access provided by University of Pennsylvania Libraries

Article

Corrosion inhibition properties of triazine derivatives containing carboxylic acid and amine groups in 1.0 M HCl solution Seung-Hyun Yoo, Young-Wun Kim, Keunwoo Chung, Nam-Kyun Kim, and JOON-SEOP KIM Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie303092j • Publication Date (Web): 26 Jun 2013 Downloaded from http://pubs.acs.org on July 23, 2013

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 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

Industrial & Engineering Chemistry Research

Corrosion inhibition properties of triazine derivatives carboxylic acid and amine groups in 1.0 M HCl solution

containing

Seung-Hyun Yoo1, Young-Wun Kim1,*, Keunwoo Chung1, Nam-Kyun Kim1, and Joon-Seop Kim2,* 1

Green Chemistry Research Division, Surfactant & Lubricant Research Team, KRICT,

Daejeon 305-600, South Korea 2

Department of Polymer Science & Engineering, Chosun University, Gwangju 501-759,

South Korea __________________________________________________________________ *Corresponding authors Phone: +82-42-860-7605, +82-62-230-7211 FAX: +82-42-860-7669, +82-62-232-2474 e-mail: [email protected], [email protected]

1

ACS Paragon Plus Environment


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 2 of 28

Abstract In the present work, the corrosion inhibition properties of three amino acid compounds, i.e. glycine (Gly), 2,2'-azanediyldiacetic acid (IDA), 5-aminopentanoic acid (5-APA), and two triazine (Tris) derivatives containing Gly or IDA units were investigated. It was found that the amino acids and their triazine derivatives behaved like mixed type corrosion inhibitors that reduced oxidative dissolution and retarded a hydrogen emission reaction. In the case of the three amino acids, it was found that the increase in the length and the number carboxylic acid groups of the molecules enhanced the corrosion inhibition properties. It was also observed that the presence of triazine ring enhanced the corrosion inhibition properties significantly. It was suggested that the adsorption of triazine derivatives on a metal surface was the Langmuir isotherm adsorption and mainly physisorption. In the case of Tris-IDA, the six acetic acid moieties emanating from the triazine ring led to partial negative charges on the outer layer and disrupted the physisorption and chemisorption of Tris-IDA on the metal surface. In addition, two acetic acid moieties per IDA caused steric hindrance when Tris-IDA adsorbed onto the metal surface. These results made the corrosion inhibition properties of Tris-IDA lower than those of Tris-Gly.

1. Introduction Mild steel has been used widely as the constituent materials in various industry fields because of its excellent mechanical properties and relatively low cost. For example, the applications of the mild steel used in related industry fields include reactors, petrochemical process devices, boilers, drums, and heat exchangers. In oil industries, however, aqueous acidic solution is used for de-scaling, acid pickling, and acid treatment. In this case, the exposal of metal to aqueous acidic solution causes corrosion, which puts safety and economic parts at high risk. Thus, corrosion inhibitors are used to decrease the corrosion rate and prevent the metal from corrosion. This naturally implies that it is very important for the workers in the oil and related industries to find effective corrosion inhibitors.

As known, corrosion inhibitors usually have electron-rich elements such as N, O, S, P and/or multiple bonds and/or aromatic rings, which provide a physical or chemical adsorption zone for the metal surface.1-4 In addition, from an environmental acceptability aspect, it would be 2


Page 3 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


better for the corrosion inhibitors to have non-toxicity and biodegradability.5-8 Recently, the corrosion-inhibition properties of glycine9,10 and 12-aminododecanoic acid11 were reported. These compounds contained functional groups such as amine and carboxylic acid groups that show anti-corrosion effects. The research group of Amin observed that at room temperature the presence of glycine in 1.0 M HCl solutions increased the corrosion inhibition efficiency of the system up to ca. 75 % when the mild steel was immersed in the solutions containing 50 mM (equivalent to ca. 3800 ppm) of glycine.9 In addition, they also found that the modification of glycine enhanced rust preventing properties. Those results suggest that glycine could be used as eco-friendly alternative mixed-type inhibitors, and the inhibitors containing glycine moiety would increase corrosion inhibition efficiency. Thus, in the present work, for the enhancement of the anti-corrosion properties, we attempted to study the corrosion inhibition behavior of materials containing the glycine moiety.

Cyanuric chloride derivatives are essential organic compounds and one of commercial chemicals used as herbicides or light stabilizers for polymers.12,13 The three chlorine atoms of the cyanuric chloride can be substituted with −NH2, −OH, −SH or −NHR.14,15 Thus, in this work, to prepare the materials containing the glycine moiety, we chose cyanuric chloride to introduce more amine groups and/or carboxyl groups into it. First of all, we investigated the corrosion inhibition properties of two amino acids, i.e. 2-aminoacetic acid (glycine, Gly) and 5-aminopentanoic acid (5-APA). The former has two carbon atoms, but the latter has five carbon atoms; thus, the latter is around twice as long as the former. Then, we also employed iminodiacetic acid (IDA), having one amino and two carboxylic acid groups; its length is similar to that of 5-aminopentanoic acid, but the amine group is placed in the middle of the molecule. Lastly, two 1,3,5-triazine derivatives containing Gly and IDA moieties were synthesized and their corrosion inhibition properties were studied.

2. Experimental 2.1. Materials and characterization In this study, glycine (Sigma, ≥99%), iminodiacetic acid (Aldrich, 98%) and 5aminopentanoic acid (Aldrich, 97%) were used to investigate the corrosion inhibition behavior of some of amino acids. For the synthesis of 2,4,6-tris(carboxyalkylamino)-1,3,53



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 4 of 28

triazine, cyanuric chloride (Aldrich, 99%) and the chemicals mentioned above were used. The chemical structures of 2,4,6-tris(carboxyalkylamino)-1,3,5-triazine derivatives were characterized by using 300 MHz 1H-NMR and 13C-NMR (BRUKER), FTS165 FT-IR (BIORAD), 1112 Series Flash Elemental Analyzer (EA) (Thermo Finnigan), and JMS-700 and JMS-DX303 Mass Spectrometer (MS) (JEOL) instruments. To prepare aqueous 1.0 M HCl solution used for the electrochemical impedance experiments, concentrated hydrochloric acid (Sigma-Aldrich, 37%) was diluted with double-distilled water. The notations used for glycine, iminodiacetic acid, and 5- aminopentanoic acid were Gly, IDA, 5-APA, and those for 2,4,6tris(n-carboxyalkylamino)-1,3,5-triazine derivatives containing glycine and iminodiacetic acid moieties were Tris-Gly and Tris-IDA, respectively. The notations, names, and molecular weights of the compounds are listed in Table S1 (Supporting Information).

2.2. Synthesis of 2,4,6-tris(carboxyalkylamino)-1,3,5-triazine The 2,4,6-tris(carboxyalkylamino)-1,3,5-triazine derivatives were prepared by nucleophilic aromatic substitution reaction (SNAr) of primary and secondary amines with cyanuric chloride. For the convenience of readers, here we give a procedure of a synthesis of 2,2’,2”((1,3,5-triazine-2,4,6-triyl)tris(azanediyl))triacetic acid (Tris-Gly). Cyanuric chloride (10 g, 54.2 mmol) was placed in a 1000 mL one-neck round-bottom flask containing doubledistilled water (100 mL), and the solution was stirred at 0 °C using an ice bath. Then, glycine (4.27 g, 56.9 mmol) was added to the solution, and the solution was stirred for10 min. To this solution, aqueous NaOH (25 wt%) was slowly added to keep the pH of the solution at 10–11. After 1.5 hr stirring of the solution at 0–5 °C, glycine (8.33 g, 111 mmol) and double-distilled water (200 mL) were added to the solution, and the temperature of the solution increased to room temperature by removing the ice bath. While keeping the solution pH at 10–11, the reaction was continued for 5 hr. Then, the solution temperature increased to 110 °C, and the reaction was continued for 3–6 hr. When the reaction was complete, the solution temperature was decreased to room temperature, and double-distilled water (300 mL) was added to the solution. The solution was stirred for 30 min, and concentrated HCl was added to the solution to make the solution pH 3–4, and the solution was stirred for another 30 min.16,17 The solid product was filtered, washed with a mixture of water/acetic acid (30/1 v/v) (100 mL) and double-distilled water (500 mL), and dried in a vacuum oven at 60 °C. The yield percentage was 86.2 %. Tris-IDA was obtained in a similar way, with 76.1 % yield percentage. 4


Page 5 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


2.3. Corrosion inhibition property measurements The corrosion inhibition properties of Gly, IDA, 5-APA and 1,3,5-triazine derivatives were investigated using potentiodynamic polarization and AC electrochemical impedance spectroscopy (EIS) methods. The mild steel used in the present work (composition (wt%) = C: 3.56, O: 1.14, Mn: 0.62, S: < 0.01, P: 0.02, Fe: balance) was in a type of disc (plate dimension = 1 cm × 1 cm). The surface of the steel specimens was smoothed with 320-, 600-, 800-, 1500-grit sandpapers to make the surface smooth. Then, the surface was washed with ethanol and distilled water using a sonicator for 5 min each. The steel specimens were dried in an oven at 70 °C for over 1 hr, and kept in a desiccator for over 12 hr before using them as working electrodes.

A WEIS510 Multichannel EIS System (WonATech Co., Ltd) was used to measure the rust preventing properties of the amino acids and triazine derivatives. The electrochemical cells consisted of a saturated Ag/AgCI reference electrode (3 M), a mesh type platinum counter electrode (plate dimension = 2.5 cm × 2.5 cm), and a working electrode. The exposed area of the working electrode in the solution was 1 cm2. The potentiodynamic polarization and the EIS measurements were conducted at 21 ± 1 °C in 1.0 M HCl solution. The concentration of corrosion inhibitors in the solution was in the range of 500−5000 ppm.

For the Potentiodynamic Polarization, the voltage was scanned from +300 mV of open circuit potential (OCP) to -300 mV with the scanning rate of 1 mV/s; the voltage was determined when the fluctuation of voltage was less than 10-5 V/s. The corrosion potential, corrosion current density, cathodic and anodic Tafel slopes, and corrosion rate were obtained using the WonATech’s IVMAN software. The percentage inhibition efficiency (η(%)) was calculated as follows: η(%) = (Iblank – Icorr)/ Iblank × 100

(1)

Here, Iblank is the corrosion current density of 1.0 M HCl solution without inhibitor, and Icorr is that of the HCl solution containing varying amounts of inhibitors.

In the case of AC EIS experiments conducted under potentiostatic conditions, the sine wave of AC voltage was maintained at 10 mV; the frequency was changed from 100 kHz to 10 5



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 6 of 28

mHz. The constant phase element constant, constant phase exponent, charge transfer resistance, and solution resistance were obtained using the WonATech’s ZMAN software. The η(%) value was calculated as follows: η(%) = (R’ct – Rct)/ R’ct × 100

(2)

Here, R’ct is the resistance of 1.0 M HCl solution containing varying amounts of inhibitors, and Rct is that of the HCl solution without inhibitor. For the electrochemical measurements, the working electrode was immersed in the 300 mL solution containing varying amounts of inhibitors for 3 hr. Before electrochemical measurements, the system was purged with nitrogen at least 40 min to remove dissolved oxygen in the solution. Then, the electrochemical measurements were carried out in the unstirred electrochemical cell under an aeration condition.

3. Results and discussion 3.1. Characterization of 2,4,6-tris(carboxyalkylamino)-1,3,5-triazine The 1H- and 13C-NMR, and FT-IR data of Tris-Gly and Tris-IDA and the data of elementary analysis (EA) and mass spectra (MS) using 3-nitrobenzyl alcohol as a matrix are listed in Table S1 (Supporting Information). In the Supporting Information section, for the convenience of readers, we discuss the data but only those for Tris-Gly. The spectroscopic data and the EA and MS data of Tris-IDA indicate the reaction completed successfully.

3.2. Potentiodynamic polarization Figure 1 shows the polarization curves of the mild steel in 1.0 M HCl with or without varying amounts of Gly, IDA, 5-APA, Tris-Gly and Tris-IDA. Except for the 5000 ppm Gly system, the inhibitor concentration does not change the shapes of the anodic and cathodic Tafel plots significantly. This indicates that the inhibitors act as adsorptive rust preventing materials, without metal dissolution or proton reduction at the interface. That is, the inhibitors cover the active sites on the metal surface, which leads to the protection of metal surface against corrosive attacks and reduces oxidative dissolution and retards a hydrogen emission reaction.18-20 Corrosion potentials (Ecorr), cathodic and anodic Tafel slopes (bc and ba) (obtained by the extrapolation of the straight line portions of the anode and the cathode current-potential curves), and corrosion rates (CR) are listed in Table 1. It is seen that the Ecorr 6


Page 7 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


values do not change much in the inhibitor concentration range of 0−5000 ppm; the average value is -399 ± 1.6 mV. In addition, it is also observed that with increasing amount of inhibitors the anodic and cathodic curves shift to lower corrosion current density (Icorr). In the cases of the bc and ba values, they are similar to each other; bc = -150 ± 11.8 and ba = 112 ± 9.6. This implies that the mechanisms of the cathodic and anodic reactions are not changed by the addition of the inhibitors. However, the larger absolute value of bc, compared to ba, suggests that the cathode is more polarized when the external current is applied; this can be understood because amine groups are known to act as bases in the strong acid medium.21 As expected, the corrosion rate decreases with increasing inhibitor concentration.

Figure 2 shows the Icorr values as a function of inhibitor concentration. It is clear that Icorr values decrease strongly and then slowly with increasing concentration of inhibitors, indicating the strong and subsequently weak retardation of corrosion, respectively. Since this type of results is seen for the mixed type inhibitors,22 it can be suggested that the inhibitors in the present work are also the mixed type inhibitors. As proposed elsewhere, this kind of corrosion inhibition is due to the simple adsorption of the corrosion inhibitors on the steel surface to form a protective layer, which leads to the slow corrosion reaction.23 In Figure 2(a), it is seen that the Icorr values of Tris-Gly and Tris-IDA are lower than those of Gly and IDA, respectively, at comparable concentrations, the Icorr of Tris-Gly is the lowest. This indicates that the triazine ring having three nitrogen atoms affects the Icorr strongly. In addition, the difference of Icorr values of Gly and Tris-Gly is larger than that of IDA and TrisIDA, at comparable concentrations. This means that the presence of Gly on the triazine ring affects the corrosion inhibition more significantly, compared to IDA on the triazine ring. In addition, it is seen that at low concentrations, the Icorr values of Gly are larger than those of IDA, but at high concentrations, the results are opposite. This will be discussed later in the section dealing with corrosion inhibition efficiency. At this point, it should be noted that the concentration of the inhibitors is based on the weight of the inhibitor in the solution. Therefore, it would be useful to examine the Icorr values on the basis of mole concept. Figure 2-(b) shows the Icorr values as a function of concentration of inhibitor divided by molecular weight of the inhibitor. It is clear that when one adds the same amount of inhibitors in moles to the solution, the Icorr value decreases drastically for the two triazine derivatives. The decreasing rate of Icorr values is in the following order: Tris-Gly > Tris-IDA > 5-APA > IDA > 7



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 8 of 28

Gly.

At this point, it would be useful to discuss the adsorption mechanism of inhibitors onto the metal surface in HCl solution. Firstly, the adsorption of inhibitors involves the adsorption of Cl- anions onto the positively charged metal surface via electrostatic interactions at the metal/electrolyte interface at a given Ecorr,24,25 which makes the metal surface negatively charged. Secondly, the protons of HCl molecules transfer to inhibitors to make a protonadded form, i.e. inhibitor-H+. Thirdly, these two species, i.e. inhibitor-H+ and Cl- anion on the metal surface, make the physisorption of inhibitor-H+ onto the metal surface via electrostatic interactions possible. Lastly, uncharged inhibitors can also adsorb directly onto the metal surface via chemisorption: the chemisorption occurs when the unshared electron pairs of the inhibitors in a high energy level transfer to the unoccupied electron orbital of metal in a low energy level to form coordinate bonds.

Figure 3-(a) shows the percentage inhibition efficiency (η(%)) values as a function of concentration of inhibitors. It is seen that with increasing concentration of inhibitors, the η(%) values increase strongly and then weakly. It is also observed that at low concentrations the η(%) of IDA is larger than that of Gly, but at high concentrations the former becomes smaller than the latter. This might be due to the fact that IDA has two electron-rich functional groups, i.e. carboxylic acid groups, instead of one for Gly. Thus, at low concentrations, the metal surface area covered by two acetic acid units of IDA is larger than that by one acetic acid unit of Gly. This might lead to higher η(%) for IDA. However, at this point, it should also be considered that the carboxylic acid groups form hydrogen bonding with water molecules. Thus, above a certain concentration of IDA or Gly, the amount of water molecules bound to the acid groups of the inhibitors in the vicinity of metal surface becomes so sufficient that the corrosion inhibition effect by the presence of acetic acid units on the metal surface becomes weaker. Furthermore, the steric hindrance and electron richness of carboxylic acid groups should also be taken into account. Since the amine of IDA is a secondary amine, it might experience severe steric hindrance when the sufficient amount of IDA molecules is bound to the metal surface via electrostatic interactions, compared to that of Gly. Thus, IDAs are bound to the metal surface relatively weakly and/or less densely. As a result, at high concentrations, IDA molecules are not effectively adsorbed onto the metal surface, compared 8


Page 9 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


to Gly. Thus, the η(%) value of IDA becomes smaller than that of Gly. In the case of the η(%) value of 5-APA, it is larger than that of Gly at comparable concentrations. It can be understood; the protonated amine group of the inhibitors absorbs onto the metal surface, and the rest part of molecule, i.e. alkyl carboxylate, stretches outward. It is natural that with increasing chain length the hydrophobicity increases. Thus, the rust preventing property improves with increasing chain length of alkyl amine.26 It should also be noted that since the molecular weight of Gly is smaller than that of 5-APA, i.e. 75.07 g/mol vs. 117.15 g/mol, at the same concentration, the mole of Gly is ca. 1.5 times larger than that of 5-APA. Thus, the higher η(%) of 5-APA, compared to that of Gly, indicates that when the moles of 5-APA and Gly in the systems are the same, 5-APA with a long alkyl group (i.e. more hydrophobic) shows better corrosion inhibition than Gly with a short alkyl group (i.e. less hydrophobic). In the case of the triazine derivatives, when one compares the η(%) values of Gly and IDA to those of Tris-Gly and Tris-IDA, one finds that the η(%) values of the latter two systems are larger than those of the former two systems at comparable concentrations. Certainly, this is due to the presence of 1,3,5-triazine ring in the center of the molecule, which has π-electrons of aromatic ring and unshared electron pairs of nitrogen atoms. This type of synergistic factors enhances the adsorption of inhibitors onto the metal surface.27 Lastly, the η(%) of Tris-Gly is larger than that of Tris-IDA. This can be understood because the η(%) of Gly is larger than that of IDA. At this point, it should be noted that the η(%) of Gly obtained by Amin et al. was ca. 75%, but that of the present work was only ca. 30%; this difference is due to the different experiment conditions. From this difference in the η(%) values, it can be expected that if one conduct potentiodynamic polarization or AC electrochemical impedance spectroscopy experiments under the Amin et al.’s experiment condition, one will obtain much higher the η(%) values than those of the present work. This indicates that IDA and 5-APA can be suitable for corrosion inhibitors, and Tris-Gly and Tris-IDA can be very effective inhibitors.

In Figure 3-(a), it is also observed that the difference in the η(%) values of Gly and Tris-Gly is larger than that of IDA and Tris-IDA . This might be due to the fact that nitrogen atoms of 2,4,6-positions of triazine ring of Tris-IDA have two acetic acid units, instead of one of TrisGly. Thus, the nitrogen atoms with two acetic acid units of Tris-IDA experience more steric hindrance when they adsorb onto the metal surface via electrostatic interactions. This leads to 9



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 10 of 28

the less and weak adsorption and, thus, smaller η(%) value of Tris-IDA, compared to that of Tris-Gly. According to the 3-dimentional structure of Tris-IDA (Figure 4), the electron-rich 1,3,5-triazine ring, the nitrogen of which can be protonated in an acid medium, is covered by the six acetic acid units of three IDAs, and, thus, the partial positive charge effect of the triazine ring is reduced significantly. In addition, the negative charge on the outer layer prevents Tris-IDA from approaching to the negatively charged metal surface, which is unfavorable to Tris-IDA for densely packing. Furthermore, the hydrogen bonding between the carboxylic acid groups of IDA and water molecules decreases the η(%) of Tris-IDA. Figure 3-(b) shows the percentage inhibition efficiency values as a function of inhibitor concentration divided by the MW of inhibitors, as done in Figure 2. It is seen that the increasing rate of η(%) is in the following order: Tris-Gly > Tris-IDA > 5-APA > IDA > Gly. If all of Gly and 5-APA absorbed onto the metal surface, the alkyl chain length, in other word, hydrophobicity, would a determining factor for the corrosion inhibition because the corrosion inhibition of 5-APA is better than that of Gly. Conclusively, the above findings clearly indicate four aspects. Firstly, the η(%) value increases drastically for triazine derivatives because of the presence of three nitrogen atoms of triazine ring. Secondly, however, the steric hindrance of acetic acid units also influences the η(%); i.e. a higher η(%) of Tris-Gly, compared to that of Tris-IDA. Thirdly, a hydrophobicity effect leads to a higher η(%) for 5APA, compared to those of IDA and Gly. Lastly, the number of carboxylate groups per molecule affects weakly the η(%) values, but the alkyl chain length (i.e. hydrophobicity) does strongly. 3.3. AC electrochemical impedance spectroscopy Shown in Figure 5 are Nyquist plots and phase Bode plots. Except for the 500 ppm Gly system, in all the Nyquist plots it is seen that with increasing concentration of inhibitors the diameter of capacitive loop in the form of depressed semi-circle increases. This indicates that with increasing amount of inhibitor, the inhibitors are more densely packed on the metal surface and form a monolayer. According to the principles of EIS, the ideal Nyquist plot should consist of perfect semi-circles; however, the semicircles in Figure 5 are depressed. This is the characteristic of solid electrodes and attributed to frequency dispersion due to the roughness of electrode surface and interfacial heterogeneity.28,29 The impedance and phase angle in a high frequency range represent a non-uniform surface layer related with adsorption 10


Page 11 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


phenomena, porous membrane formation and non-porous layer, and those in a low frequency range express a kinetic response to a charge transfer reaction.30 The phase Bode plots (i.e. the phase angle vs. log f plots) consist of depressed capacitive loops, which coincident with one time constant and show largest phase angles corresponding to each condition; the log Z vs. log f plots show the impedance of double layer. At this point, it should be mentioned that the equivalent circuit consists of the series connection of a solution resistance (Rs) with a parallel connection of a double layer capacitance (Cdl) and a charge transfer resistance (Rct) for impedance analysis. However, this type of equivalent circuit is not appropriate to be applied to the present system for the modeling of metal-acid solution interface in the presence of inhibitor in the solution because the Nyquist plots are not in the shape of ideal semi-circles. Thus, as suggested elsewhere as one of proper models, we applied an equivalent circuit using Constant Phase Element (CPE) instead of Cdl to the ideal semi-circles in the Nyquist plots.31,32 In the present work, the equivalent circuit is a parallel connection between the Rct and CPE (i.e. frequency dispersion element at the metal-solution interface), which is now connected with the Rs in series (not shown here). The impedance of CPE (ZCPE), described as a frequency independent phase shift at a given AC potential and its responding current, is defined as follows:33 ZCPE = Yo-1 (iω)-n

(3)

Here Yo is the CPE constant, ω is the angular frequency (in rad/s), i (= √1) is the imaginary number, and n is the CPE exponent and a criteria for the judgment of the roughness of metal surface or interfacial heterogeneity. Depending on the exponent, the characteristics of ZCPE can be expressed as follows: resistance for n = 0, capacitance for n = 1, inductance for n = -1, and Warburg impedance for n = 0.5.34 In the present work, we can obtain Yo and n values, and convert Yo into Cdl using the following equation: Cdl = Yo × (ω˝m) n-1

(4)

Here ω˝m = 2πfmax (angular frequency), fmax is the frequency at a maximum point of imaginary part impedance. The EIS data are also listed in Table 1. It is seen that, as expected, the Rs values are similar to each other, and the average value is 3.45 ± 0.27 Ω cm2. In the case of Yo value, it decreases with increasing inhibitor concentration. The CPE exponents are found to be constant at 0.88 ± 0.01, suggesting that the ZCPE is related with the capacitance (i.e. n = 1). At this point, it should be mentioned that the CPE exponents 11



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 12 of 28

of a rough or porous surface of a double-layer capacitance are in the range of 0.9−1.35 This implies that the metal surface in the present work is also rough. With increasing concentration of inhibitors, the Rct is seen to increase, except for the 500 ppm Gly sample that shows a smaller Rct value than that of a system without inhibitor. The increasing Rct is possibly due to the formation of a protective layer on the metal surface.20 On the other hand, with increasing concentration of inhibitors, the Cdl value decreases. Again, the formation of the inhibitor layer on the metal surface, which retards the metal dissolution and the charge transfer significantly, causes this result.36 Since the inhibitor molecules of low dielectric constant replace water molecules of high dielectric constant in the vicinity of metal surface, the local dielectric constant of the protective layer decreases; the increase in the amount of inhibitors absorbed on the metal surface leads to a thicker barrier layer.37 The double layer of charged metal surface and solution can be considered as electric capacitance. Then, the capacitance of this double layer is decreased by the replacement of corrosion inhibitors with water molecules or/and ions that are stuck to the metal surface. According to the Helmholtz model, the capacitance of a double layer is inversely proportional to the thickness of a protective layer,35 and, thus the decrease in the Cdl value indicates that the protective layer becomes thicker with increasing inhibitor concentration; this makes the corrosion inhibition more effective. In Table 1, it is seen that the η(%) values are also in the following order: Tris-Gly > 5-APA > Tris-IDA > Gly > IDA; this is the same trend found in potentiodynamic polarization study. The above results imply that, as mentioned before, the number of acetic acid units per molecules also affects the corrosion inhibition, and, furthermore, the alkyl chain length is more important than the number of carboxyl groups of the molecule, and the presence of triazine ring also improves the corrosion inhibition significantly.

3.4. Adsorption isotherm The adsorption isotherm provides information on the behavior of corrosion inhibitors and the interactions between the inhibitors and electrode surface.35,38.39 Thus, it is useful to discuss the adsorption phenomena here. To interpret adsorption phenomena of the inhibitors on the steel electrode surface, there are some models that include Tempkin, Langmuir, Freundlich, Frumkin isotherm adsorption models.39 Among the four models, we attempted to find the suitable model to fit the experimental data (i.e. the fractional surface coverage (θ) (= η(%)/100) data obtained from potentiodynamic polarization and EIS methods). Judging from 12


Page 13 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


the highest correlation coefficient, R2, we concluded that the Langmuir isotherm adsorption model was suitable to explain the adsorption behavior of the inhibitors onto the metal surface: The equation associated with the Langmuir model is as follows: Cinh/θ = 1/ Kads + Cinh

(5)

Here, Kads is the adsorption equilibrium constant of adsorption-desorption process, and Cinh is the concentration of the inhibitor. Figure 6 shows Cinh/θ values as a function of Cinh, including straight lines calculated from the Langmuir model. As mentioned, the straight lines fit the experimental data well with high R2 values. The slopes and R2 values are listed in Table 2. It is seen that the R2 values, very close to one, indicate that the triazine derivatives indeed act as corrosion inhibitors.40 It is also observed that the slopes are deviated from an ideal value, i.e. one, which is due to the interactions between the inhibitors adsorbed onto the metal surface.41 With Kads value, one can evaluate Gibbs free energy of adsorption (△Goads) as follows:42 △Goads = – RTln(Csol Kads)

(6)

Here, R is the gas constant, T is the absolute temperature, and Csol is the mole concentration of solvent (in the present work, the Csol of water is 55.5 mol/L). The △Goads values are also listed in Table 2. Thermodynamically, the negative △Goads value indicates the adsorption process is a spontaneous process, and the inhibitors form a stable adsorbed layer on the metal surface.43-45 In general, it is known that the electrostatic interactions between anionic metal surface and cationic adsorbed molecules, i.e. physical adsorption, lead to less negative △Goads value than -20 kJ/mol.41 On the other hand, the formation of coordinate bonds via the transfer of electrons from the inhibitor molecules to the metal surface or the sharing of the electrons of the inhibitors with metal surface, i.e. chemical adsorption, leads to more negative △Goads value than -40 kJ/mol.46,47 Thus, the △Goads values obtained in the present work suggest that the adsorption of the triazine derivatives is close to the physical adsorption, as expected. In addition, slightly more negative △Goads values and slightly larger Kad values of Tris-Gly, compared to those of Tris-IDA, indicate that the interactions between Tris-Gly and metal surface is slightly stronger than those between Tris-IDA and metal surface.

It has been known that the carboxylic acid groups of the inhibitors enhance corrosion inhibition properties;9-11 this implies that the η(%) of Tris-IDA would be higher than that of Tris-Gly, but we obtained the opposite results. This can be understood; when one considers the chemical structure of Tris-IDA, one finds that Tris-IDA compound does not have a planar 13



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 14 of 28

structure, as seen in Figure 4. In addition, the 1,3,5,-triazine ring of Tris-IDA is surrounded with the six side groups, compared to only three side groups for Tris-Gly; this leads to the less chemical adsorption of Tris-IDA on the steel surface. Furthermore, the presence of six electron withdrawing carboxylic acid groups on the triazine ring makes the outer layer of Tris-IDA partially charged, which reduces the physical adsorption of Tris-IDA on the negatively charged metal surface, at least to some extent. The slightly larger Kad values of Tris-Gly than that of Tris-IDA supports these aspects, which is in good accordance with the larger η(%) values of Tris-Gly, compared to that of Tris-IDA 3.5. Schematic illustration of the adsorption of triazine inhibitors In HCl solution, triazine derivatives exist as neutral and/or protonated molecules. The adsorption of the protonated triazine derivatives onto the negatively charged metal surface is schematically shown in Figure 7. It is seen that the triazine derivatives can be adsorbed onto the metal surface via one or more methods mentioned bellow: (1) Electrostatic interactions between the protonated inhibitors and the negatively charged metal surface made by the adsorption of Cl- anions, i.e. physical adsorption (Figure 7-a), (2) electron donor-acceptor interactions between the π−electrons of imine (C=N) groups of 1,3,5-triazine ring and the empty d-orbital of iron atoms (Figure 7-b), and (3) the interactions between the unshared electron pairs of nitrogen atoms of triazine ring and alkyl chains, and the empty d-orbital of iron atoms on the metal surface, i.e. chemical adsorption (Figure 7-c). Again, one or more types of interactions are involved in the adsorption behavior of triazine derivatives on the metal surface in HCl solution.

4. Conclusions (1) According to the potentiodynamic polarization, three amino acids and their 1,3,5-triazine derivatives acted as mixed type corrosion inhibitors that reduce oxidative dissolution and retard a hydrogen emission reaction. (2) The EIS results indicated that the corrosion inhibition occurred when the inhibitors were adsorbed onto the steel surface; with increasing inhibitor concentration, the Cdl value decreased because the local dielectric constant decreased and the thickness of double layer increased, which led to increasing η(%). (3) In the case of the three amino acids, it was observed that the amino acid with a longer 14


Page 15 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


chain was more effective for the corrosion inhibition. In addition, the increase in the number of acetic acid units per molecule decreased the η(%) value. (4) It was found that the adsorption of triazine ring improved the rust-preventing properties noticeably and was the Langmuir isotherm adsorption; the thermodynamic parameters of the adsorption of the triazine derivatives indicated that the adsorption was spontaneous and mainly physisorption. (5) In the case of Tris-IDA, the presence of six acetic acid units on the triazine ring made the outer layer of the molecule partially negatively charged and caused the steric hindrance (i.e. the crowding effect of six acetic acid units) when Tris-IDA adsorbed on the metal surface. These reduced physisorption and chemisorption of Tris-IDA on the steel surface, which caused the lower η(%) value, compared to that of Tris-Gly. ASSCOIATED CONTENT ⓢ Supporting Information An additional table. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected],

[email protected]

Notes The authors declare no competing financial interest. ACKNOWLEDGMENTS This study was supported by the R&D Center for Valuable Recycling (Global-Top Environmental Technology Development Program) funded by the Ministry of Environment (Project No.:GT-11-C-01-270-0).

REFERENCES (1) (2) (3)

Quraishi, M. A.; Jamal, D. Inhibition of mild steel corrosion in the presence of fatty acid triazoles. J. Appl. Electrochem. 2002, 32, 425. Khaled, F.; Babić-Samardžija, K.; Hackerman, N. Piperidines as corrosion inhibitors for iron in hydrochloric acid, J. Appl. Electrochem. 2004, 34, 697. Wang, H.-L.; Liu, R.-B.; Xin, J. Inhibiting effects of some mercapto-triazole derivatives 15



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

(4)

(5) (6)

(7)

(8) (9)

(10)

(11) (12)

(13) (14) (15) (16) (17)

(18) (19) (20)

(21)

(22)

Page 16 of 28

on the corrosion of mild steel in 1.0 M HCl medium. Corros. Sci. 2004, 46, 2455. Bentiss, F.; Lebrini, M.; Lagrenée, M. Thermodynamic characterization of metal dissolution and inhibitor adsorption processes in mild steel/2,5-bis(n-thienyl)-1,3,4thiadiazoles/hydrochloric acid system. Corros. Sci. 2005, 47, 2915. Quraishi, M. A.; Jamal, D. CAHMT—A new and eco-friendly acidizing corrosion inhibitor. Corrosion 2000, 56, 983. Salasi, M.; Shahrabi, T.; Roayaei, E.; Aliofkhazraei, M. The electrochemical behaviour of environment-friendly inhibitors of silicate and phosphonate in corrosion control of carbon steel in soft water media. Mater. Chem. Phys. 2007, 104, 183. Blustein, G.; Di Sarli, A. R.; Jaén, J. A.; Romagnoli, R.; Del Amo, B. Study of iron benzoate as a novel steel corrosion inhibitor pigment for protective paint films. Corros. Sci. 2007, 49, 4202. Morad, M. S. Inhibition of iron corrosion in acid solutions by Cefatrexyl: Behaviour near and at the corrosion potential. Corros. Sci. 2008, 50, 436. Amin, M. A.; Khaled, K. F.; Fadl-Allah, S. A. Testing validity of the Tafel extrapolation method for monitoring corrosion of cold rolled steel in HCl solutions– Experimental and theoretical studies. Corros. Sci. 2010, 52, 140. Amin, M. A.; Ibrahim, M. M. Corrosion and corrosion control of mild steel in concentrated H2SO4 solutions by a newly synthesized glycine derivative. Corros. Sci. 2011, 53, 873. Ghareba, S.; Omanovic, S. 12-Aminododecanoic acid as a corrosion inhibitor for carbon steel. Electrochim. Acta 2011, 56, 3890. Azenha, M. E. D. G.; Burrows, H. D.; Canle L., M.; Coimbra, R.; Fernández, M. I.; Garcia, M. V.; Rodrigues, A. E.; Santaballa, J. A.; Steenken, S. On the kinetics and energetics of one-electron oxidation of 1,3,5-triazines. Chem. Commun. 2003, 1, 112. Hollink, E.; Simanek, E. E.; Bergbreiter, D. E. Strategies for protecting and manipulating triazine derivatives. Tetrahedron Lett. 2005, 46, 2005. Konstatinova, T.; Petrova, P. On the synthesis of some bifunctional reactive triazine dyes. Dyes Pigments 2002, 52, 115. Petrova-Miladinova, P.; Konstatinova, T. N. On the synthesis of some reactive triazine azodyes containing tetramethylpiperidine fragment. Dyes Pigments 2005, 67, 63. Clark, D. R. Triazine carboxylic acids as corrosion inhibitors for aqueous systems. US Patent 4,402,907 (1983). Zhu, Q.; Sheng, T.; Fu, R.; Hu, S.; Chen, J.; Xiang, S.; Shen, C.; Wu, X. Novel structures and luminescence properties of lanthanide coordination polymers with a novel flexible polycarboxylate ligand. Cryst. Growth Des. 2009, 9, 5128. Aal, M. S. Abdel; Radwan, S.; El Saied, A. Phenothiazines as corrosion inhibitors for zinc in NH4Cl solution. Br. Corros. J. 1983, 18, 102. Abd El-Maksoud, S. A.; Fonda, A. S. Some pyridine derivatives as corrosion inhibitors for carbon steel in acidic medium. Mater. Chem. Phys. 2005, 93, 84. Khaled, K. F.; Al-Qahtani, M. M. The inhibitive effect of some tetrazole derivatives towards Al corrosion in acid solution: Chemical, electrochemical and theoretical studies. Mater. Chem. Phys. 2009, 113, 150. Abd El Rehim, S. S.; Ibrahim, M. A. M.; Khaled, K. F. The inhibition of 4-(2′-amino5′-methylphenylazo) antipyrine on corrosion of mild steel in HCl solution. Mater. Chem. Phys. 2001, 70, 268. Abdallah, M.; Helal, E. A.; Fouda, A. S. Aminopyrimidine derivatives as inhibitors for corrosion of 1018 carbon steel in nitric acid solution. Corr. Sci. 2006, 48, 1639. 16


Page 17 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


(23) Ashassi-Sorkhabi, H.; Majidi, M. R.; Seyyedi, K. Investigation of inhibition effect of some amino acids against steel corrosion in HCl solution. Appl. Surf. Sci. 2004, 225, 176. (24) Amin, M. A.; Abd El Rehim, S. S.; El-Sherbini, E. E. F.; Bayoumi, R. S. The inhibition of low carbon steel corrosion in hydrochloric acid solutions by succinic acid: Part I. Weight loss, polarization, EIS, PZC, EDX and SEM studies. Electrochim. Acta 2007, 52, 3588. (25) Hassan, H. H.; Abdelghani, E.; Amin, M. A. Inhibition of mild steel corrosion in hydrochloric acid solution by triazole derivatives: Part I. Polarization and EIS studies. Electrochim. Acta 2007, 52, 6359. (26) Braun, R. D.; Lopez, E. E.; Vollmer, D. P. Low molecular weight straight-chain amines as corrosion inhibitors. Corros. Sci. 1993, 34, 1251. (27) Yoo, S.-H.; Kim, Y.-W.; Chung, K.; Baik, S.-Y.; Kim, J.-S. Synthesis and corrosion inhibition behavior of imidazoline derivatives based on vegetable oil. Corros. Sci. 2012, 58, 42. (28) Morad, M. S. An electrochemical study on the inhibiting action of some organic phosphonium compounds on the corrosion of mild steel in aerated acid solutions. Corros. Sci. 2000, 42, 1307. (29) Gonçalves, R. S.; Azambuja, D. D.; Serpa Lucho, A. M. Electrochemical studies of propargyl alcohol as corrosion inhibitor for nickel, copper, and copper/nickel (55/45) alloy. Corros. Sci. 2002, 44, 467. (30) Benedetti, A. V.; Sumodjo, P. T. A.; Nobe, K.; Cabot, P. L.; Proud, W. G. Electrochemical studies of copper, copper-aluminium and copper-aluminium-silver alloys: Impedance results in 0.5M NaCl. Electrochim. Acta 1995, 40, 2657. (31) Popova, A.; Raicheva, S.; Sokolova, E.; Christov, M. Frequency dispersion of the interfacial impedance at mild steel corrosion in acid media in the presence of benzimidazole derivatives. Langmuir 1996, 12, 2083. (32) Ahamad, I.; Quraishi, M. A. Mebendazole: New and efficient corrosion inhibitor for mild steel in acid medium. Corros. Sci. 2010, 52, 651. (33) Stoynov, Z. Impedance modelling and data processing: structural and parametrical estimation. Electrochim. Acta 1990, 35, 1493. (34) Jeyaprabha, C.; Sathiyanarayanan, S.; Venkatachari, G. Effect of cerium ions on corrosion inhibition of PANI for iron in 0.5 M H2SO4. Appl. Surf. Sci. 2006, 53, 432. (35) Bentiss, F.; Jama, C.; Mernari, B.; El Attari, H.; El Kadi, L.; Lebrini, M.; Traisnel, M.; Lagrenée, M. Corrosion control of mild steel using 3,5-bis(4-methoxyphenyl)-4-amino1,2,4-triazole in normal hydrochloric acid medium. Corros. Sci. 2009, 51, 1628. (36) Keddam, M.; Mattos, O. R.; Takenouti, H. Reaction model for iron dissolution studied by electrode impedance II . Determination of the reaction model. J. Electrochem. Soc. 1981, 128, 257. (37) Babić-Samardžija, K.; Lupu, C.; Hackerman, N.; Barron, A. R.; Luttge, A. Inhibitive properties and surface morphology of a group of heterocyclic diazoles as inhibitors for acidic iron corrosion. Langmuir 2005, 21, 12187. (38) Noor, E. A.; Al-Moubaraki, A. H. Thermodynamic study of metal corrosion and inhibitor adsorption processes in mild steel/1-methyl-4[4′(-X)-styryl pyridinium iodides/hydrochloric acid systems. Mater. Chem. Phys. 2008, 110, 145. (39) Morales-Gil, P.; Negrón-Silva, G.; Romero-Romo, M.; Ángeles-Chávez, C.; PalomarPardavé, M. Corrosion inhibition of pipeline steel grade API 5L X52 immersed in a 1 M H2SO4 aqueous solution using heterocyclic organic molecules. Electrochim. Acta 17



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 18 of 28

2004, 49, 4733. (40) Badawy, W. A.; Ismail, K. M.; Fathi, A. M. Corrosion control of Cu–Ni alloys in neutral chloride solutions by amino acids. Electrochim. Acta 2006, 51, 4182. (41) Negm, N. A.; Elkholy. Y. M.; Zahran, M. K.; Tawfik, S. M. Corrosion inhibition efficiency and surface activity of benzothiazol-3-ium cationic Schiff base derivatives in hydrochloric acid. Corros. Sci. 2010, 52, 3523. (42) Flis, J.; Zakroczymski, T. Impedance study of reinforcing steel in simulated pore solution with tannin. J. Electrochem. Soc. 1996, 143, 2458. (43) Scendo, M. The effect of purine on the corrosion of copper in chloride solutions. Corros. Sci. 2007, 49, 373. (44) Amar, H.; Tounsi, A.; Makayssi, A.; Derja, A.; Benzakour, J.; Outzourhit, A. Corrosion inhibition of Armco iron by 2-mercaptobenzimidazole in sodium chloride 3% media. Corros. Sci. 2007, 49, 2936. (45) Avci, G. Corrosion inhibition of indole-3-acetic acid on mild steel in 0.5 M HCl. Colloids Surf. A: Physicochem. Eng. Aspec. 2008, 317, 730. (46) Umoren, S. A.; Ebenso, E. E. The synergistic effect of polyacrylamide and iodide ions on the corrosion inhibition of mild steel in H2SO4. Mater. Chem. Phy. 2007, 106, 387. (47) Özcan, M.; Solmaz, R.; Kardaş, G.; Dehri, I. Adsorption properties of barbiturates as green corrosion inhibitors on mild steel in phosphoric acid. Colloids Surf. A 2008, 325, 57.

18


Page 19 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


Table 1. Concentration (Conc.), Ecorr, bc, ba,CR, Rs, Yo, n, Rct, Cdl and η(%) of Gly, IDA, 5-APA, Tris-Gly and Tris-IDA potentiodynamic polarization notation

chemical structure

conc. (ppm)

-Ecorr -bc (mV vs. Sat. (mV/dec) Ag/AgCl) 400 156

Blank

0

Gly

500 1000 2000 5000

401 400 401 397

IDA

500 1000 2000 5000

AC electrochemical impedance spectroscopy

ba CR (mV/dec) (mm/year)

Yo (µF/cm2)

n

Rct (Ω cm2)

115

15.7

273.37

0.89

28.1

158 165 159 144

116 121 114 93

15.9 14.9 12.8 11.2

353.7 217.2 197.0 190.1

0.89 0.89 0.87 0.87

398 400 400 399

156 137 144 169

118 99 112 129

15.0 13.6 13.1 12.6

216.0 216.2 221.1 205.7

5-APA

500 1000 2000 5000

401 400 399 400

152 158 148 146

119 112 114 113

13.0 11.8 10.1 7.13

TrisGly

500 1000 2000 5000

399 397 400 398

169 143 132 127

124 101 104 91

TrisIDA

500 1000 2000 5000

398 400 400 398

131 148 153 151

118 115 117 112

Cdl Rs (Ω cm2) (µF/cm2)

η(%)

145.2

--

21.4 28.7 35.9 39.1

3.72 2.81 3.00 3.94 3.46

187.8 115.4 93.3 92.7

-2.1 21.9 28.1

0.90 0.89 0.87 0.87

30.6 31.5 32.4 35.2

3.36 3.59 3.31 3.79

121.5 114.9 111.2 100.3

8.2 10.8 13.3 20.3

205.1 191.3 185.1 151.9

0.89 0.88 0.88 0.87

33.7 37.4 44.1 60.4

3.27 3.25 3.20 3.40

111.7 98.6 95.4 76.4

16.7 25.0 36.4 53.5

11.7 7.75 7.18 4.57

213.6 163.6 142.2 134.4

0.89 0.87 0.86 0.85

37.8 56.9 69.1 97.4

3.13 3.24 3.61 3.15

116.3 82.2 67.8 60.7

25.8 50.6 59.4 71.2

13.5 12.9 11.5 10.0

201.7 197.9 179.2 171.8

0.89 0.88 0.88 0.87

32.8 34.2 39.1 43.5

3.75 3.98 3.49 3.56

107.1 99.2 89.9 83.8

14.4 17.9 28.1 35.4

19



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 20 of 28

Table 2. Fitting parameter of the adsorption isotherms of inhibitors at 21°C R2

Slope

Kads (M-1)

△Goads (kJ/mol)

inhibitors Tafela

EISb

Tafela

EISb

Tafela

EISb

Tafela

EISb

Tris-IDA

2.16

2.31

0.99

0.99

1.62 × 102

1.71 × 102

-22.3

-22.4

Tris-Gly

1.16

1.19

0.99

0.99

2.54 × 102

2.81 × 102

-23.4

-23.6

a

Data were calculated using surface coverage (θ) given in Figure 3.

b

Data were calculated using surface coverage (θ) given in Table 1.

20


Page 21 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


Figure captions Figure 1. Polarization curves for mild steel in 1.0 M HCl in absence and presence of various concentrations of (A) Gly, (B) IDA, (C) 5-APA, (D) Tris-Gly, and (E) Tris-IDA. Figure 2. Corrosion current densities obtained from Figure 1 and as a function of (a) concentration of inhibitors and (b) concentration of inhibitors/molecular weight (MW) of inhibitor. Figure 3. Percentage inhibition efficiency obtained from Figure 1 as a function of (a) concentration of inhibitors and (b) concentration of inhibitors/molecular weight (MW) of inhibitor. Figure 4. The expected three-dimensional structure of Tris-IDA.

Figure 5. Nyquist (left) and phase Bode plots (right) of mild steel in 1.0 M HCl containing various concentrations of (A) Gly, (B) IDA, (C) 5-APA (D) Tris-Gly and (E) Tris-IDA. Figure 6. Langmuir adsorption isotherm of Tris-IDA and Tris-Gly on the mild steel in 1.0 M HCl, obtained from EIS (filled symbols) and potentiodynamic measurements (open symbols).

Figure 7. Schematic representation of the adsorption of the 2,4,6-tris(carboxyalkylamino)1,3,5-triazines on mild steel in 1.0 M HCl solution. (a) Physical adsorption, (b) feedback bond and (c) chemical adsorption.

21



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

Figure 1. Polarization curves for mild steel in 1.0 M HCl in absence and presence of various concentrations of (A) Gly, (B) IDA, (C) 5-APA, (D) Tris-Gly, and (E) Tris-IDA.

22


Page 23 of 28

1200 (a)

(b)

900

Icorr (µA/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


600

Gly IDA 5-APA Tris-Gly Tris-IDA

300

0 0

1500

3000

4500

Concentration (ppm)

0

20

40

60

80

Concentration (ppm)/MW

Figure 2. Corrosion current densities obtained from Figure 1 and as a function of (a) concentration of inhibitors and (b) concentration of inhibitors/molecular weight (MW) of inhibitor.

23



100 Gly IDA 5-APA Tris-Gly Tris-IDA

80

(a)

(b)

60

η (%)

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

40

20

0 0

1500

3000

4500 0

Concentration (ppm)

20

40

60

80

Concentration (ppm)/MW

Figure 3. Percentage inhibition efficiency obtained from Figure 1 as a function of (a) concentration of inhibitors and (b) concentration of inhibitors/molecular weight (MW) of inhibitor.

24


Page 25 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


Figure 4. The expected three-dimensional structure of Tris-IDA.

25



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

Figure 5. Nyquist (left) and phase Bode plots (right) of mild steel in 1.0 M HCl containing various concentrations of (A) Gly, (B) IDA, (C) 5-APA (D) Tris-Gly and (E) Tris-IDA. 26


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


30

Tris-IDA Cinh/θ (mM)

Page 27 of 28

20

Tris-Gly 10

0 0

5

10

15

Cinh (mM)

Figure 6. Langmuir adsorption isotherm of Tris-IDA and Tris-Gly on the mild steel in 1.0 M HCl, obtained from EIS (filled symbols) and potentiodynamic measurements (open symbols).

27



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

Figure 7. Schematic representation of the adsorption of the 2,4,6-tris(carboxyalkylamino)1,3,5-triazines on mild steel in 1.0 M HCl solution. (a) Physical adsorption, (b) feedback bond and (c) chemical adsorption.

28


Corrosion Inhibition Properties of Triazine Derivatives Containing

Recommend Documents