The anodic behavior of hydrogenated copper in sodium hydroxide solutions

Abstract

Alloys of the copper-nickel system are widely used in various industry branches, in particular in marine shipbuilding including desalting plants with their corrosive sea-water steam, not so rarely containing hydrogen sulfide. Under some operation conditions hydrogen can evolve at the alloy surface. Penetrating into the alloy, it may affect its corrosion-electrochemical and mechanical properties. In NaOH solutions, we have already investigated the anodic behavior of two characteristic objects of the Ni-H system, namely, α -phase (Ni-0.03 at. % H) [1, 2] and β -phase (hydride N 2 H) [3,4].In the present work, we use the same solution (1 N NaOH) to investigate the electrochemical behavior of cathodically hydrogenated copper.Similarly to the previous works, the potential range chosen should make the absorbed hydrogen selectively dissolve anodically, leaving copper immune. According to literature data, copper begins to dissolve at a potential of -0.2 V (SHE) [5,6]. Hence, one may suppose that in a still lower potential range, only the electrochemical dehydrogenation of copper can be observed.The experiments were carried out in 1 N NaOH (Sodu Wodorotlenek cz grade (Poland)) solution in bidistilled water in an atmosphere of high-purity N 2 at a temperature of 20 ° C. Prior to starting the experiment, a copper sample was ground by abrasive paper, finishing with the paper No. 0. The sample was then washed with bidistilled water, dried with filtering paper, and placed into a cell with a preliminarily deaerated electrolyte. The potential was measured relative to a reference silver-chloride electrode and recalculated to the standard hydrogen electrode. The electrochemical measurements were carried out with the use of a PI-50-1 potentiostat, a PR-8 programmer, a PDA-1 recorder, and a IPT 1 coulometer.The hydrogenation was carried out galvanostatically ( i c = 5 × 10 2 A/m 2 , t c = 1 h). On stopping it, without changing the solution, the sample underwent voltammetry, deenergized chronopotentiometry, and some special transient electrochemical measurements. Figure 1 shows cathodic (1) and anodic (2) voltammetric curves of copper consecutively plotted by stepwise (0.02 V on each step) changing the polarization. The discharge of water hydrogen occurs at a noticeable rate, starting from -0.8 V with a Tafel's slope of 0.15 to 0.17 V. Copper starts to ionize at E = -0.3 V. The anodic curve exhibits two distinctly pronounced current peaks.Abstract -The anodic behavior of cathodically hydrogenated copper in 1 N NaOH solution is investigated with the use of its free-corrosion chronopotentiometry ( E cor ) and cyclic voltammetry (CVA). The former proves that while being cathodically hydrogenated, copper, unlike nickel, does not form hydride. An analysis of the CVAs shows that during anodic dissolution of hydrogenated copper, two forms of adsorbed hydrogen are ionized, while the ionization is limited by the diffusion in solid phase. Under the same hydrogenation conditions, copper sorbs ten times less hydrogen than nickel does. -1.0 -0.5 ...