Electrochemical corrosion mitigation of copper in 3.5 wt.% NaCl solution using cerium (III) chloride salt

Abstract

Background

Rare earth salts have been known as a promising environmentally friendly inhibitor for various metals and their alloy due to their ability to prevent electrochemical corrosion reactions by forming a rare earth oxide/hydroxide film. This film may result from the hydrolysis of rare earth trivalent ions which are strongly promoted via electrochemical corrosion reactions. However, a rare earth salt, particularly cerium (III) chloride (CeCl₃), has not been demonstrated its inhibitory efficiency for copper and its alloy in chloride environment. Indeed, it motivates this study to understand behaviors of CeCl₃ in improving the corrosion resistance of copper. The work comprehensively investigates electrochemical properties of copper in the 3.5 wt.% NaCl solution without and with varying concentrations of CeCl₃.

Methods

Electrochemical properties of the copper as immersed in the 3.5 wt.% NaCl solution are characterized by both non-destructive (open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS)) and destructive techniques (potentiodynamic polarization (PD), cathodic polarization (CP), dynamic electrochemical impedance spectroscopy (DEIS), and wire beam electrode (WBE)) for 24 hours. In addition, post-corrosion surfaces of the target electrodes after 24-hour immersion in the testing solution without and with the addition of CeCl₃ are characterized using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS mapping), and X-ray photoelectron spectroscopy (XPS).

Significant Findings

CeCl₃ demonstrates its effectiveness as a potential inhibitor, with the highest inhibition efficiency of 76.16 ± 0.49% at 1.22 mM. Based on analyzing electrochemical results and elemental analysis, this work clarifies that copper-based products form on the copper surface along with CeCuO_x to develop a composite multilayer, where cerium-based compounds can effectively enhance the stability of the protective film by restricting diffusion occurring at the interface between the electrode and electrolyte. In addition, localized corrosion inhibition of CeCl₃ is obviously observed via random distribution of minor anodes and major cathodes on the copper surface. Therefore, the finding highlights the novelty of the work and contributes to understanding inhibition mechanism of CeCl₃ for protecting copper in the 3.5 wt.% NaCl environment.