Elsevier

Corrosion Science

Volume 48, Issue 12, December 2006, Pages 4065-4079
Corrosion Science

2-Amino-5-ethyl-1,3,4-thiadiazole as a corrosion inhibitor for copper in 3.0% NaCl solutions

https://doi.org/10.1016/j.corsci.2006.03.011Get rights and content

Abstract

2-Amino-5-ethyl-1,3,4-thiadiazole (AETDA) has been evaluated as a corrosion inhibitor for copper in 3.0% NaCl solutions using weight loss, pH, potentiodynamic polarization, potentiostatic current–time, and electrochemical impedance spectroscopic (EIS) measurements. The study was also complemented by scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) investigations. Weight loss measurements gave an inhibition efficiency of about 60% with 1.0 × 10−3 M AETDA present, increasing to about 97% at the AETDA concentration of 5.0 × 10−3 M. Potentiodynamic polarization measurements showed that the presence of AETDA in de-aerated, aerated and oxygenated 3.0% NaCl solutions decreases cathodic, anodic, and corrosion currents to a great extent and shifts the corrosion potential slightly towards more negative values. Potentiostatic current–time measurements, SEM and EDX investigations also confirmed that the protection of the copper surface is achieved by strong adsorption of AETDA molecules. EIS measurements revealed that the surface and the charge transfer resistances increase upon increasing the AETDA concentration. Results together showed clearly that AETDA is a good mixed-type inhibitor for copper corrosion and its inhibition efficiency increases in the order of oxygenated > aerated > de-aerated 3.0% NaCl solutions.

Introduction

Copper has been one of more important materials in industry owing to its high electrical and thermal conductivities, mechanical workability, and its relatively noble properties. It is widely used in many applications in electronic industries and communications as a conductor in electrical power lines, pipelines for domestic and industrial water utilities including sea water, heat conductors, and heat exchangers [1]. Thus, corrosion of copper and its inhibition in a wide variety of media, particularly when they contain chloride ions, have attracted attention of a number of investigators [1], [2], [3], [4], [5], [6], [7], [8]. It is generally accepted that anodic dissolution of copper in chloride environments is influenced by the chloride concentration. At chloride concentrations lower than 1 M, the copper dissolution occurs through the formation of CuCl, which is not protective enough and is converted to soluble CuCl2- by reacting with excess chloride [8]. According to Bacarella and Griess [3], the anodic dissolution of copper is under mixed control by the electrodissolution of copper and the diffusion of soluble CuCl2- from the Helmholtz plane into the bulk solution. On the other hand, at concentrations higher than 1 M, higher cuprous complexes such as CuCl32- and CuCl43- are formed in addition to the ones with fewer chlorides such as CuCl and CuCl2- [4].

Azole derivatives like benzotriazole, mercaptobenzothiazole, benzimidazole, and imidazole are well-known corrosion inhibitors for copper. Azole compounds contain nitrogen atoms, which coordinate with Cu(0), Cu(I) or Cu(II) through lone pair electrons to form complexes [9]. These complexes are generally believed to be polymeric in nature and form an adherent protective film on the copper surface, which acts as a barrier to aggressive ions such as chloride [9]. According to Ammeloot et al. [10], the efficiency of an azole inhibitor towards copper corrosion correlates with the semiconducting properties of the underlying copper(I) oxide. They found also that a well-protective film shows simultaneously p- and n-type properties: p-type at the film/electrolyte interface and n-type during the formation of a heterogeneous oxide layer with excess Cu(I) in the inner layer and Cu(I) vacancies in the outer layer. Sutter et al. [11] claimed that the nature of the binding between Cu(I) and the organic molecules is not the only parameter to be taken into account for understanding the mechanism of corrosion inhibition and the properties of the copper oxide need to be considered. In general, organic compounds containing polar groups including nitrogen, sulfur, and oxygen [12], [13], [14], [15], [16], [17], [18], [19], [20], and heterocyclic compounds with polar functional groups and conjugated double bonds [21], [22], [23], [24] have been reported to inhibit copper corrosion. The inhibiting action of these organic compounds is usually attributed to their interactions with the copper surface via their adsorption. Polar functional groups are regarded as the reaction center that stabilize the adsorption process [25]. In general, the adsorption of an inhibitor on a metal surface depends on the nature and the surface charge of the metal, the adsorption mode, its chemical structure, and the type of the electrolyte solution [26].

We have been studying corrosion and corrosion inhibition of copper [8], [27] and aluminum [28], [29] as well as other metals [30] and alloys [31] in a variety of media. In the previous work [8], pitting corrosion of copper at different concentrations of sodium chloride has been studied. The XPS study of the copper surface showed that the predominant species in the surface film at lower chloride concentrations (⩽1.0 × 10−3 M) is Cu2O, while it is CuCl at higher concentrations (⩾0.1 M), and the copper dissolution occurs via the formation of the soluble complex, CuCl2-. Furthermore, the pitting corrosion of copper was found to occur in a chloride solution when a Cu2O film was on its surface in contact with an aerated or oxygenated NaCl solution (⩾0.1 M). More recently [27b], the inhibition of copper corrosion in 3.0% NaCl by N-phenyl-1,4-phenylenediamine (NPPD) was carried out. We found that NPPD is a good mixed-type inhibitor for copper corrosion by strongly adsorbing on the copper surface, decreasing the cathodic, anodic, and corrosion currents, as well as shifting the potential slightly to the more negative values, and the inhibition efficiencies increase in the order of oxygenated > aerated > de-aerated solutions. Moreover, various experiments revealed that NPPD molecules adsorb on the copper surface and form a complex with CuCl2- on the copper surface.

The present paper reports on the behavior of 2-amino-5-ethyl-1,3,4-thiadiazole (AETDA, Scheme 1) as an inhibitor for copper corrosion in de-aerated, aerated, and oxygenated 3.0% NaCl solutions. This compound is expected to show a high inhibition efficiency for copper corrosion because it is a heterocyclic compound containing a variety of donor atoms; in addition, it is nontoxic and inexpensive. It has been reported that [32], [16], [33] compounds having such a structure are capable of inhibiting copper corrosion with a high efficiency.

Section snippets

Experimental

AETDA (Sigma–Aldrich, 97%), sodium chloride (NaCl, Shinyo Pure Chemicals, 99.99%), and absolute ethanol (C2H5OH, Fisher, 99.9%) were used as received. An electrochemical cell with a three-electrode configuration was used; a copper rod (Cu, Goodfellow, 99.999%, 5.0 mm in diameter), a platinum foil, and an Ag/AgCl electrode (in saturated KCl) were used as working, counter, and reference electrodes, respectively. The copper electrode was first polished successively with metallographic emery paper

Weight loss and pH measurements

Fig. 1 shows: (a) the weight losses vs. time for the copper coupons in 200 cm3 of aerated 3.0% NaCl solutions without (1) and with 1.0 × 10−3 (2) and 5.0 × 10−3 M AETDA (3) present and (b) the accompanying change in pH. One can see easily that the weight loss and the accompanying increase in pH decrease significantly when 1.0 × 10−3 or 5.0 × 10−3 M AETDA is added (lines 2 and 3 in Fig. 1a and b). It has been reported [8], [27](b), [34] that the dissolution of copper occurs through oxidation of Cu(0) to Cu+

Conclusion and summary

2-Amino-5-ethyl-1,3,4-thiadiazole (AETDA) has been evaluated as a corrosion inhibitor for copper in de-aerated, aerated, and oxygenated 3.0% NaCl solutions, and the results are summarized as follows:

  • 1.

    Weight loss–time measurements for copper in aerated chloride solutions indicate that the dissolution rate decrease to a minimum even after 10 days of immersion due to the presence of AETDA, especially at 5.0 × 10−3 M; at the same time, the accompanying change in pH values decrease noticeably also. The

Acknowledgement

This work was supported by the grant from the Korea Science and Engineering Foundation (KOSEF Grant R11-2000-070-06001-0) through the Center for Integrated Molecular Systems at POSTECH. The stipends for EMS were provided by the KOSEF postdoctoral fellowship program.

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    Permanent address: Electrochemistry and Corrosion Laboratory, Department of Physical Chemistry, National Research Centre, Dokki, 12622 Cairo, Egypt.

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