Anodic Polarization Behavior of Copper in Concentrated Aqueous Lithium Bromide Solutions and Comparison with Pourbaix Diagrams

• Published in: Corrosion (Houston, Tex.) Tex.), 2005-05, Vol.61 (5), p.464-472
• Main Authors: Muñoz-Portero, M.J., García-Antón, J., Guiñón, J.L., Pérez-Herranz, V.
• Format: Article
• Language: English
• Subjects: Anodic dissolution; Anodic polarization; Applied sciences; Chemical evolution; Copper; Copper bromide; Copper compounds; Corrosion; Corrosion environments; Corrosion mechanisms; Current density; Diffusion layers; Dissolution; Dissolving; Electrode polarization; Electrodissolution; Exact sciences and technology; Heavy metals; Hydroxides; Lithium; Metals. Metallurgy; Oxidation; Oxygen; pH effects; Polarization; Pourbaix diagrams; Thin films
• ISSN: 0010-9312; 1938-159X
• DOI: 10.5006/1.3280646

ABSTRACTThe anodic polarization behavior of copper was studied in 400-g/L and 700 g/L (4.61 M and 8.06 M) lithium bromide (LiBr) solutions between 25°C and 40°C. In all cases, an initial active region of copper dissolution was followed by a decrease in current density. In the 400-g/L LiBr solutions, four anodic current peaks were observed, whereas in the 700-g/L LiBr solutions, only two well-defined peaks were observed. The low-activation energy values obtained for the copper dissolution process in the 400-g/L and 700-g/L LiBr solutions were consistent with the formation of poorly structured thin passive layers via a diffusion-controlled metal electrodissolution process. The anodic polarization behavior of copper in the 400-g/L and 700-g/L LiBr solutions at 25°C was compared with the respective Pourbaix diagrams (potential-pH diagrams). In the 400-g/L LiBr solution (pH = 6.80), the initial anodic dissolution region exhibited Tafel behavior attributed to the formation of CuBr2­ complexes. At higher potentials, passivation was observed, associated with the formation of copper(I) bromide (CuBr) and copper(II) oxide-copper(II) hydroxide (CuO-Cu[OH]2) films. Lastly, a new active region appeared, initially associated with the oxidation of CuBr2­ to Cu2+, and then with the oxidation of water to oxygen. In the 700-g/L LiBr solution (pH = 5.65), the initial active region of formation of CuBr2­ was followed by the formation of CuBr and copper trioxybromide (CuBr2·3Cu[OH]2) passive films. Finally, the increase in anodic current density was attributed to oxygen evolution.Lithium bromide (LiBr) is one of the most widely used absorbents in refrigeration technology because of its favorable thermophysical properties.1 In these systems, copper is used for heat exchangers because of its high thermal conductivity. However, the operating conditions (i.e., high concentrations of LiBr and high temperatures) can generate serious corrosion problems for the structural materials.2-7 The anodic polarization behavior of copper has been the topic of numerous electrochemical studies ­ in solutions containing bicarbonate (HCO3),8-12 car2­ 8,12 2­ 8-9,11,13-14 sulfate (SO4 ), et al. Most of bonate (CO3 ), the available information about the anodic polarization of copper in halide solutions refers to chlorides (Cl­).8,10-11,13-17 A few references have been found for bromide (Br­)2-7,18-21 and iodide (I­)22 solutions. In all these studies, the halide concentrations were significantly lower