Corrosion of Hydrides of Nickel and Cu30Ni Alloy in Oxygen Containing Solutions

Abstract

yan, Sirota, Pchel'nikov. As was shown earlier [1], nickel hydride quickly decomposes at its open-circuit potential E c in an oxygen-saturated sulfuric-acid solution (1 N H 2 SO 4 ), which is accompanied by hydrogen evolution. As a result, attempts to determine the corrosion rate of nickel hydride by using the oxygen compensation (OC) method has failed.In this work, we study the corrosion behavior of the nickel and Cu30Ni alloy hydrides in oxygen-saturated alkaline, neutral, and weakly acidic solutions.Corrosion tests were carried out in oxygen atmosphere by the OC method [2, 3] in a modernized cell with thermal control [4] and additionally by spectrophotometry (SF) [5].We used samples of 1-3 cm 2 surface areas and the following solutions: 1 N NaOH; 0.01 N NaOH + 0.16 N Na 2 SO 4 ; 0.16 N Na 2 SO 4 (pH 7); 10 -3 N H 2 SO 4 + 0.16 N Na 2 SO 4 at 20 ° C.The essence of OC method lies in compensation of oxygen consumed in corrosion by oxygen obtained in electrolyzer. The corrosion rate is estimated from the charge ∆ Q consumed in the electrolyzer for a time ∆ twhere S is the surface area of the sample, m 2 .Hydrides of nickel and alloy were synthesized by hydrogenation (HG) of samples during cathodic polarization in 1 N H 2 SO 4 solution containing 0.2 g/l thiourea ( i HG = 170 A/m 2 , t HG = 0.5-2 h) in a separate cell, i.e., under the conditions of hydride formation, according to [6]. Then, the samples were quickly (10-30 s) washed in twice distilled water, transferred to the working chamber of the OC cell, in which time variations of i c ∆Q/∆tS Ä/m 2 ( ), = E c and the charge Q consumed in the corrosion process were measured.Being placed in the OC cell, nickel hydride immediately begins to uptake oxygen (Fig. 1). Therewith, upon longer nickel hydrogenation, and, correspondingly, for thicker hydride layers, one needs greater charges in order to replenish oxygen consumed in hydride corrosion (curves 1 and 2 ). The corrosion rate i c calculated from the slope of Q vs. t curves (Fig. 2a, curves 1 and 2 ) decreases in time and reaches the value observed for corrosion of original nickel ( i c < 0.1 A/m 2 ). In the process, at first, E c decreases insignificantly, passes a flat Abstract -Corrosion behavior of nickel hydride is studied in alkaline, neutral, and weakly acidic oxygen-containing solutions by compensating oxygen consumed in corrosion and spectrophotometric analysis of solution for nickel. It is shown that in the course of nickel hydride corrosion in alkaline solutions, oxygen is consumed solely in its interaction with hydrogen formed at hydride decomposition, while nickel remains at the surface. It is concluded that, in a pH range from 7 to 14, hydrogen oxidation is limited by its solid-phase diffusion, whereas the rate of nickel hydride decomposition is pH-independent. The difference in the corrosion behavior of the original alloy and its hydride is attributed to the fact that the original alloy evolves copper ions, whereas the hydride evolves hydrogen. 9 8 7 6 5 4 3 2 1 0 50 100 150 200 t , min Q , C 1 2...