Benzotriazole as a volatile corrosion inhibitor during the early stage of copper corrosion under adsorbed thin electrolyte layers
Graphical abstract
Highlights
► Inhibition effect under adsorbed thin electrolyte layer is investigated. ► Copper corrosion process is found under the control of CuCl2− mass-transport. ► An adsorption model of benzotriazole on copper surface is proposed.
Introduction
Copper is susceptible to atmospheric corrosion caused by O2 and trace amounts of atmospheric pollutants such as Cl− and CO2. Atmospheric corrosion generally occurs under thin electrolyte layers (TEL) or adsorbed thin electrolyte layers (ATEL). The thickness of ATEL is usually less than 10 μm, when relative humidity (RH) is between 65% and 100% [1], [2], [3]. Several investigations on metal or alloy corrosion under TEL (thickness >10 μm) have been reported in the past decades [4], [5], [6], [7], [8]. However, experimental studies on metal or alloy corrosions under ATEL using conventional electrochemistry methods are very limited [1], [9].
Several methods exist for preventing the atmospheric corrosion of copper. Among them, volatile corrosion inhibitor (VCI) is the most effective and affordable for industrial use. In recent years, VCI rapidly developed, and was extensively applied as an advanced corrosion-resistant material [10], [11], [12], [13]. The main advantage of VCI compared with conventional corrosion control methods is its gas-phase transport that enables metallic surfaces to be reached. The VCI film is very thin and does not interfere with subsequent use or treatment of the protected surface [14]. The VCI film that adsorbs on the metal surface by means of physisorption or chemisorption may change the rate of electrochemical reactions such as the dissolution of metal and the reduction of oxygen [15]. However, no report has been made about the effect of corrosion inhibition of the inhibitor on metal under ATEL using conventional electrochemistry methods and in situ surface analysis techniques. Therefore, the study of inhibition effect on copper corrosion under ATEL is significant.
Benzotriazole (BTAH) and its derivatives are widely used to protect copper and its alloys from corrosion, which are, specifically, atmospheric copper corrosion protection and aqueous phase protection [16], [17], [18], [19], [20], [21], [22], [23], [24]. Although BTAH has been in use for a long time and numerous investigations have focused on the mechanism of BTAH interacting with copper in the aqueous phase, the mechanism of this compound as a copper inhibitor under ATEL is not completely clear, especially during the early stage.
Using electrochemical measurement, this paper studies the inhibition of copper corrosion by BTAH as VCI during the early stages of corrosion under ATEL. The adsorption of BTAH on the copper surface was measured by in situ atomic force microscopy (AFM) and by scanning electron microscopy (SEM). Interactions of BTAH with copper were examined by X-ray photoelectron spectroscopy (XPS) and by attenuated total reflectance Fourier-transform infrared (ATR-FTIR) measurements. The purpose of this study is to verify the film formation process and its inhibition mechanism under ATEL. To demonstrate the practical significance of the experiment, the addition of BTAH was carried out when copper was undergoing corrosion rather than before the film formation process.
Section snippets
Materials and solutions
Commercially pure copper (99.99 wt.%, Aladdin Chemical Plant, China) was used in this study. The specimens (3.0 mm × 5.0 mm × 7.0 mm) were sealed using epoxy resin with 0.15 cm2 exposed areas, and were employed in electrochemical tests as the working electrode (WE) and the counter electrode (CE). The specimens with 5 mm × 5 mm × 1 mm dimensions were used for AFM, XPS, ATR-FTIR, and SEM analysis. All test surfaces were ground with 1200 grit silicon carbide paper, and polished with 1.5 μm diamond pastes and 0.3 μm
Polarization curve measurements
Fig. 3 presents the polarization curves for copper under ATEL in the absence and in the presence of BTAH at 90% RH and 50 °C. Fig. 3 indicates that BTAH has a strong inhibition effect on the rate of anodic dissolution of copper by decreasing it at 2–3 orders of magnitudes. This inhibition effect prevails throughout a passive region that extends from the corrosion potential (−220 mV vs. SCE) to the breakdown potential (+430 mV vs. SCE).
The corresponding corrosion potential (Ecorr), corrosion
Absence of BTAH
The EDX results reveal that the corrosion products of copper under ATEL in the absence of BTAH mainly consist of Cu, O, and small amounts of Cl. The XPS results indicate that no Cu(II) is present in the corrosion products. Therefore, the corrosion products are primarily Cu2O and CuCl. Due to the activation effect of chloride ions, the anodic dissolution for the blank specimen under ATEL proceeded according to the following equations [6], [37], [47].
Conclusions
The corrosion process of copper under ATEL in the absence of BTAH is mainly controlled by CuCl2− diffusion. The corrosion products are CuCl2− and Cu2O. BTAH acts as a mixed corrosion inhibitor of copper under ATEL and mainly inhibits anodic reaction. BTAH quickly interacts with Cu(0) via the N atom to form a thin protective film in non-corroded areas and with Cu(I) via the N atom to form a thick polymeric [Cu+BTA−]n complex on the Cu2O substrate in defect sites.
Acknowledgements
The authors acknowledge the support of the National Natural Science Foundation of China (Grant No. 51101066) and the Analytical and Testing Centre of the Huazhong University of Science and Technology.
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