Self-assembled monolayer of carbazoles derivates for corrosion protection of copper in NaCl solution by IJournals

iJournals: International Journal of Software & Hardware Research in Engineering ISSN-2347-9698 Volume 6 Issue11 November 2018

Self-assembled monolayer of carbazoles derivates for corrosion protection of copper in NaCl solution Mounim Lebrini and Christophe Roos Laboratoire Matériaux et Molécules en Milieux Agressif ; EA 7526, Département Scientifique Interfacultaire, Campus Universitaire de Schoelcher B.P. 7209 F - 97275 Schoelcher, Martinique E-mail: mounim.lebrini@univ-antilles.fr and christophe.roos@martinique.univ-ag.fr <DOI: 10.26821/IJSHRE.6.11.2018.61006>

Keywords: Carbazoles derivates; Self-assembled films; Copper; NaCl solution

compounds. There have been some reports on the application of carbazole and its derivatives as a selfassembled films to the protection of metal corrosion [9,10]. These films offered significant protection against copper corrosion in neutral aqueous NaCl solution. Others authors have been reported the copolymerization of carbazole derivatives with methylpyrrole by chemical and electrochemical methods [11]. The purpose of the present work was to study the protection offered by 9-Ethylcarbazole (EtCZ) and 9Ethanolcarbazole (EnCZ) self-assembled monolayers on copper surface in NaCl solution at room temperature. We used electrochemical impedance spectroscopy (EIS), polarization and cyclic voltammograms to measure the protection ability. The interaction among the adsorbed molecules was discused using the Frumkin adsorption isotherm.

1. INTRODUCTION

2. EXPERIMENTAL

Copper is the preferred metal for creating multilevel interconnects structures in ultra-large scale integrated circuits due to its high electrical conductivity and resistance to electromigration [1]. However, it is an active metal which does not resist well to corrosion [2]. One effective approach which can be taken to solve the problem is surface medication using selfassembled monolayers (SAMs) that have the potential to inhibit the corrosion. Self-assembled monolayers are are molecular assemblies formed spontaneously on surfaces by adsorption and are organized into more or less large ordered domains [3]. The use of SAMs as corrosion inhibitors have been reported in the literature on copper [4–8]. Carbazole and its derivatives molecules are nitrogen-containing heterocyclic

2.1 Electrode and solution

ABSTRACT Self-assembled films of 9-Ethylcarbazole (EtCZ) and 9-Ethanolcarbazole (EnCZ) were prepared on copper surfaces. The corrosion protection abilities of the films were evaluated in NaCl solution at room temperature solution using electrochemical impedance spectroscopy (EIS), polarization and cyclic voltammetry. The adsorption of the EtCZ and EnCZ molecules was in accordance with the Frumkin isotherm. The value of free energy of adsorption (ΔG°ads) were calculated and discussed.The results obtained show that these SAM formed by EtCZ and EnCZ could serve as an effective inhibitor for the corrosion protection of copper in NaCl solution.

Chemicals - 9-Ethylcarbazole (EtCZ) and 9Ethanolcarbazole (EnCZ) were obtained as high-grade commercial reagents, purity >95%, from SigmaAldrich Inc. The chemical structures of the inhibitors are shown in Figure 1. They were dissolved in absolute ethanol to obtain a concentration of 1 mmol/L. Testing electrolyte of 0.5 mol/L NaCl aqueous solution was prepared by dissolving NaCl in distilled water. Pretreatment of copper - The working electrodes were fabricated from a sheet of Copper (≥ 99.9%). The specimens were embedded in epoxy resin leaving a working area of 0.78 cm2. Successive grades of SiCtype emery papers down to 180 and up to 1200 are

Mounim Lebrini and Christophe Roos , Vol 6 Issue 11, pp 1-7, November 2018

iJournals: International Journal of Software & Hardware Research in Engineering ISSN-2347-9698 Volume 6 Issue11 November 2018 employed. The working electrodes are etched in 6 mol/L HNO3 solution for 30 s to provide a fresh and oxide-free surface; after rinsing with distilled water, the electrodes are rinsed with absolute ethanol.

N C2H5

N CH2CH2OH

Fig 1: Chemical formulas of the inhibitors (b) 9Ethylcarbazole (EtCZ) and (c) 9-Ethanolcarbazole (EnCZ).

was calculated from the charge transfert resistance using the Equation 1. The results showed in the first time that the surface coverge increases with immersion time from 0.5 to 14 h, while remains almost constant for 14-72 h. This result shows also that the formation process of the self-assembled can be categorized by two phases, a fast adsorption followed by rearrangement at a relatively slow rate. We consider that the saturated adsorption time is about 14 h, which is used for all the next experimental tests. We note that the formation process of the self-assembled in the case of EnCZ is slightly importante than EtCZ

(1-θ) = Rt0/ Rtinh

(1)

2.2 Electrochemical measurements Electrochemical measurements, including polarization curves, electrochemical impedance spectroscopy and cyclic voltammograms, were performed in a threeelectrode cell. Pure copper specimen was used as the working electrode, a platinum wire as the counter electrode and a saturated calomel electrode (SCE) as the reference electrode. The anodic and cathodic polarisation curves were recorded by a constant sweep rate of 10 mV/min. Electrochemical impedance spectroscopy (EIS) measurements were carried out, using ac signals of amplitude 5mV peak to peak at different conditions in the frequency range of 100 kHz to 10 mHz. Cyclic voltammograms were recorded from -0.4 to 0.6 V at a scan rate of 10 mV/s. Electrochemical measurements were performed through a VSP electrochemical measurement system (Bio-Logic). The above procedures were repeated for each concentration of the two tested inhibitors. The Tafel and EIS data were analysed and fitted using graphing and analyzing impedance software, version EC-Lab V9.97.

3. RESULTS AND DISCUSSION 3.1 Effect of immersion time on film formation The immersion time is important parameter in assessing the film formation, so it is necessary to evaluate the inhibition efficiency for a long immersion time. In the present study, effect of immersion time (30 min to 72h) on corrosion inhibition was investigated using EIS measurements. The self-assembled films formed in solution of ethanol with 10 -3 mol/L of EnCZ and EtCZ. Figure 2 shows the surface coverge values plotted in function of time. The the surface coverge (θ) © 2018, iJournals All Rights Reserved

Where Rt0 and Rtinh are the charge transfert resistance of the bare copper electrode and film covered electrode.

3.2 Electrochemical impedance spectroscopy The electrochemical impedance spectroscopy was used in order to give evidence of the inhibitive activity of the EtCZ and EnCZ against copper corrosion in NaCl solution. All the impedance spectra were measured at the corresponding open-circuit potentials. The Nyquist plots obtained in NaCl solution for 10-3 mol/L EtCZcovered copper; 10-3 mol/L EnCZ-covered copper and bare copper are shown in Figure3. Inspections of the data reveal that each impedance diagram consists of a large capacitive loop. However, for EtCZ-covered copper and EnCZ-covered copper, at lower frequencies, the Nyquist diagram shows one depressed capacitive semicircle. The appearance of this depressed capacitive loop can be attributed to the dispersion of the points during the recording of the spectrum due to a sharp change in potential and are therefore not significant. Indeed, at low frequencies, the acquisition points last several minutes. The low frequency portion for the bare copper represents the solid-state Warburg diffusion of copper ions into the porous electrode. The Nyquist impedance plots were analysed by fitting the experimental data to a simple equivalent circuit model, Figure 4a, that include the solution resistance Rs and the constant phase element (CPE) which is placed in parallel to charge transfer resistance element, Rct. Often a CPE is used in a model in place of a capacitor to compensate for non-homogeneity in the system [12-14]. In the circuits (Figure 4b), W stands www.ijournals.in

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iJournals: International Journal of Software & Hardware Research in Engineering ISSN-2347-9698 Volume 6 Issue11 November 2018 for the Warburg impedance.The CPE is described by two parameters, the capacitance Q and an exponent n, according to the Equation 2. ZCPE = Q-1 (iw)-n

(2)

Where Q is the CPE constant, ω is the angular frequency in rad. S-1, ω = 2πf, and f is the frequency in Hz. According to the fit, the bare copper electrode had the parameters of Rt = 0.602 k cm2, Q = 19.04 μS sα/cm2 and n = 0.702. When covered with EtCZ and EnCZ film, the Rt increased to 10.91 and 12.63 k cm2, Q decreased to 9.45 and 4.56 μS sα/cm2 and n increased to 0.801 and 0.853, respectively. The coverage of EtCZ and EnCZ are 94.48% and 95.23%, respectively. The EnCZ film has higher Rt, lower Q, higher n and higher coverage than EtCZ, indicating the EnCZ film had higher quality than the EtCZ film. This is due to the presence of the hydroxyl substituent group in EnCZ, which increases the delocalization effect of the aromatic ring by mesomerism in conjugated systems. In addition the same group having inductive effect (+I), would assist increasing electron density.

3.3 Linear Polarization Figure 5 shows the polarization curves for copper with and without self-assembled films of EnCZ and EtCZ. The experimental conditions were identical with the EIS measurements. For the bare copper electrode (Figure 5a), a linear relation is observed in the active dissolution region and the existence of apparent Tafel slope was also observed. The presence of a Tafel slope is revealing of an electrode reaction controlled by charge transfer. The anodic current peak centers is observed at -13 mV and current minimum seems at 7 mV which is affected by CuCl precipitation species [15]. The lower anodic and cathodic current seen in Figure 5, indicates that the SAMs films inhibit both anodic and cathodic electrochemical processes. That is, mutually films increase the charge transfer resistance of anodic dissolution of copper, slowing down the corrosion rate of copper in solution. Both anodic and cathodic current were more reduced for EnCZ-covered copper than EtCZ-covered copper. Similar results were found for Schiff base, carbazole and N-vinylcarbazole adsorptions on copper [16,9].

3.4 Cyclic voltammograms Figure 6 shows cyclic voltammograms of EtCZ and EnCZ film covered and a bare copper electrode in NaCl solution. For the bare copper electrode, three anodic peaks and one cathodic peak are observed. The peak (a) represents the anodic reaction from Cu to CuCl, peak (b) refers to the formation of CuCl -2, peak (c) corresponds to the reaction of CuCl-2 to CuCl and peak (d) represents the process of reduction from CuCl to Cu. For the electrode covered with the EtCZ and EnCZ self-assembled film, the oxidation peaks (a), (b), (c) and the reduction peak (d), are smaller than those of the bare electrode. The potential values of the oxidation peaks were shifted to the negative values and the potential values of the reduction peak were shifted to the positive values for the EtCZ and EnCZ selfassembled film. These results show that the SAMs film inhibits the oxidation of the copper substrate and limits the following reduction reaction.

3.5 Adsorption behavior The degree of surface coverage (θ) for the inhibitor obtained from Equation 1 was used to find the isotherm adsorption behavior. EIS of EtCZ-covered copper and EnCZ-covered copper in concentration from 10-3 to 10-7 mol/L were measured. The experimental data were fitted to the Langmuir adsorption isotherm equation first, but 1/(1- θ) against concentration was not linear. The adsorption EtCZcovered copper and EnCZ-covered copper were then modelled using Frumkin adsorption isotherm via Equation 3 Figure 7. The linear regression coefficient (R2) is equal to 0.99. Similar adsorption isotherms were found for Schiff base, carbazole and N-vinylcarbazole adsorptions on copper [16,9]. Ln[θ/c(1-θ)] = lnK+2aθ

(3)

Where K is the constant of the adsorption equilibrium including the adsorption free energy and a is the attraction constant characterizing the lateral interaction among the molecules. The constant of adsorption, K, is related to the standard free energy of adsorption (∆Gads) with the following Equation:

K = 1/55.5 exp(-ΔGads/RT)

(4)

The value 55.5 in the above Equation is the concentration of water in solution in mol/L [17]. The ∆Gads values at studied temperature are -23.41 kj/mol and -22.79 kJ/mol for EtCZ-covered copper and EnCZwww.ijournals.in

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iJournals: International Journal of Software & Hardware Research in Engineering ISSN-2347-9698 Volume 6 Issue11 November 2018 covered copper, respectively. Then, the adsorption processes can be considered as chemisorption. The higher value â&#x2C6;&#x2020;Gads for EnCZ-covered copper confirms

the higher inhibition witch due to the presence of the hydroxyl substituent group.

Fig 2: Dependence of the film coverge of EtCZ and EnCZ on the immersion time.

Fig 3: Nyquist plots in NaCl solution for EtCZ-covered copper; EnCZ-covered copper and bare copper.

Fig 4: Equivalent circuit used to fit impedance data.

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iJournals: International Journal of Software & Hardware Research in Engineering ISSN-2347-9698 Volume 6 Issue11 November 2018

Fig 5: Polarization curves for EtCZ-covered copper; EnCZ-covered copper and bare copper in NaCl solution.

Fig 6: Cyclic voltammograms in NaCl solution for EtCZ-covered copper; EnCZ-covered copper and bare copper.

Fig 7: Frumkin isotherm of EtCZ-covered copper and EnCZ-covered copper.

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iJournals: International Journal of Software & Hardware Research in Engineering ISSN-2347-9698 Volume 6 Issue11 November 2018

4. CONCLUSIONS The SAMs formed by EtCZ and EnCZ on copper surface offers excellent corrosion protection of copper in NaCl solution. The inhibition efficiencies obtained from electrochemical impedance studies and polarization studies are in good agreement. The adsorption of EtCZ and EnCZ molecules on copper surface typically processes with a two-step adsorption consisting of a fast initial adsorption and a slowly following reorganization in NaCl solution. Adsorption models Langmuir, Temkin and Frunkin isotherms were tested graphically for the data and the best fit was obtained with the Frunkin isotherm.

5. ACKNOWLEDGMENTS The authors are pleased to acknowledge MOM (Ministère des Outre-Mer) for providing the financing of their research.

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