Effect of sulfide pollution on the stability of the protective film of benzotriazole on copper
Introduction
Benzotriazole (C6H5N3 BTAH) is widely used as a corrosion inhibitor for copper and its alloys in many industries, for example, chemical mechanical polishing [1], [2], [3], [4], [5], desalination [6], petrochemical industries [7], refrigeration [6], [8], and in gliding arc plasma in humid air [9]. Many aspects of the process have been studied in efforts to reveal the mechanisms involved and the nature of the interaction between the metal, the inhibitor and/or the environment [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26]. Two mechanisms have been proposed to explain the high inhibiting efficiency of BTAH. One mechanism attributes it to the formation of a protective film of Cu(I)BTA on the surface, which inhibits the anodic dissolution reaction, that is,Cu(aq)+ + BTAH(aq) = Cu(I)BTA(s) + H(aq)+The other mechanism postulates an adsorbed layer of BTAH, that is,Cu(s) + BTAH = Cu:BTAH(ads)where Cu:BTAH(ads) refers to BTAH adsorbed on the copper surface. Under oxidizing conditions, this adsorbed species can be oxidized to give the complex Cu(I)BTA [16], that is,Cu:BTAH = Cu(I)BTA + H+ + e−Eq. (3) indicates that the complex Cu(I)BTA is favored at more anodic potentials in less acidic media, while the adsorbed species is formed in more acidic media under cathodic potentials. It has also been well substantiated that the inhibiting efficiency increases with the concentration of BTAH and time of immersion of the metal in the inhibited medium.
The above mechanisms are well accepted in clean (unpolluted) media. It is now widely recognized that many of the service environments of copper and its alloys are polluted. For example, formation waters in sour oil and gas wells are heavily contaminated with dissolved sulfides, which are mostly in the form of HS− ions in nearly neutral media. In such environments, these metallic components serve in media that are inhibited by BTAH and polluted with sulfide ions. Sulfide ions are known to promote the corrosion of copper [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37]. The process involves an adsorption step, that is,HS− + Cu = Cu:HS−where Cu:HS− refers to an adsorbed HS− ion on the copper surface. This adsorbed species is oxidized to give CuS, that is,Cu:HS− = CuS + H+ + 2e−
Hence, copper and its alloys face service environments containing corrosion promoting sulfide ions and corrosion protecting benzotriazole. This raises questions regarding the potential interaction of HS− and BTAH on the copper surface and the ensuing effects on the protection efficiency of BTAH against the corrosion of copper.
The objective of this paper is to study the interaction of benzotriazole and sulfide ions on the surface of copper.
Section snippets
Experimental
Electrodes were prepared from Cu (99.9%) obtained from Goodfellow. The electrodes were in the form of rods having 0.96 cm diameter. The working electrode was the cross sectional area of the rod while the immersed length of the rod was coated with a protective adhesive, so that only the cross sectional area is exposed to the solution. Electrical contact to the external circuit was made through the rod. The working electrodes were polished using SiC papers successively down to 2400 grits, followed
Polarization curves
Fig. 1 shows the effect of the concentration of BTAH on the polarization behavior of copper. The presence of BTAH decreases the rate of anodic dissolution by 3–4 orders of magnitudes, depending on its concentration. A passive region appears in the anodic branch which is attributed to the formation of a protective film of the Cu(I)BTA complex (Eqs. (1), (2), (3)). This passive region ends at the break down potential, Eb, beyond which the current increases rapidly as the potential becomes more
Conclusions
Sulfide ions decrease the inhibiting efficiency of benzotriazole against the corrosion of copper in chloride media. The extent of this effect depends on the relative concentrations of both species (Fig. 5, Fig. 6). The current transients reveal interesting interactions between the injected sulfide ions and the BTAH on copper surface. An order of magnitude increase in the concentration of sulfide ions (at a certain concentration of BTAH) increases the intensity of sulfide attack by more than one
Acknowledgement
The authors gratefully acknowledge the support of this work by the Research Administration of Kuwait University, under Grant Number SC03/02 and the use of the X-ray photoelectron spectrometer under General Facility Project GS01/01.
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2016, Journal of Molecular LiquidsCitation Excerpt :Similar results were achieved by Avramovic and Antonijević (2004) [56]. According to the literature data [57], the introduction of a proper substituent in the molecule of 1H-benzotriazole might increase its anti-corrosive properties. The obtained results refer that the higher protection degree of copper in aggressive medium is achieved in the presence of MBTAH and potassium sorbate in comparison with BTAH and potassium sorbate.
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