Electrochemical Behavior of Nickel Hydride in Sodium Hydroxide Solutions

Sirota, D. S.; Pchel'nikov, A. P.

doi:10.1023/b:prom.0000043061.81634.d0

Protection of Metals

2004

DOI: 10.1023/b:prom.0000043061.81634.d0

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Electrochemical Behavior of Nickel Hydride in Sodium Hydroxide Solutions

D. S. Sirota

A. P. Pchel'nikov

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Cited by 5 publications

(28 citation statements)

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“…The cathodic curve of the hydrogen discharge in itself does not change, either. Even one-hour hydrogenation by a current of 5 A/dm 2 in 1 N H 2 SO 4 solution doped with 0.2 g/l of thiourea results in the appearance of neither cathodic nor anodic limiting currents observed on nickel hydride [3,4]. This agrees with conclusions that copper during its cathodic polarization either forms no hydride [8,9] or the latter is very unstable [10].…”

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confidence: 79%

“…With an increase in v , the peaks grow, while anodic peaks, shift in the positive, and cathodic ones, , in the negative direction. Such potential changes agree with the theory of irreversible processes [11], which is also indicated by the fact that the difference -, at a preassigned v , exceeds 0.058 V. Hence, the voltammograms prove that the electrochemical processes on hydrogenated copper and nickel are similarly irreversible [1]. Moreover, the anodic current peak in CVA itself, as well as its linear dependence on the square root of v , proves that the anodic process rate is determined by the diffusion of reacting particles in solid phase.…”

supporting

confidence: 75%

“…Reactions (1) and (2) correspond to these current peaks, as in the case of nickel [1,3], respectively:…”

mentioning

confidence: 98%

“…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].…”

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confidence: 99%

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confidence: 99%

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The anodic behavior of hydrogenated copper in sodium hydroxide solutions

Sirota

Pchel'nikov

2005

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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 ...

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supporting

confidence: 79%

supporting

confidence: 75%

“…Reactions (1) and (2) correspond to these current peaks, as in the case of nickel [1,3], respectively:…”

mentioning

confidence: 98%

mentioning

confidence: 99%

mentioning

confidence: 99%

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The anodic behavior of hydrogenated copper in sodium hydroxide solutions

Sirota

Pchel'nikov

2005

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

2005

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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...

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The Electrochemical Behavior of β-Phase in the Cu30Ni-H System in Sodium Hydroxide Solutions

Sirota

Pchel'nikov

2005

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During cathodically hydrogenizing a copper-nickel alloy, hydrogen is incorporated into the solid. It was long ago shown by X-ray diffraction analysis [1] that such alloys containing more than 60% copper and hydrogenized in a 0.2 N H 2 SO 4 + 5 × 10 -3 g/l As 2 O 5 solution ( i h = 30 mA/cm 2 , t h = 30 min) form with hydrogen only α -phase, that is, an interstitial solid solution. In alloys not so rich in copper, two phases, that is, α -and β -(a hydride one), are formed. It was also shown that it is the copresence of the α -and β -phases, rather than the total hydrogen content that makes the alloy embrittle and destruct under mechanical load [1].It is known that intermetallic compounds of LaNi 5 type form hydrides under cathodic polarization [2,3]. Partial substitution of copper for nickel makes the hydride phase more stable and significantly enhances the hydrogen absorption by the alloy. Therefore, we aimed at studying the electrochemical behavior of Cu30Ni alloy hydride in alkaline solutions and interpreting it taking into account our former data on the electrochemical behavior of hydrogenated copper [4] and nickel [5,6] and nickel hydride as well [7,8].The experiments were carried out in 1 N NaOH solution in N 2 (of PNG grade) atmosphere at 20 ° C. Prior to the experiments, the alloy was cleaned with emery paper, degreased, and rinsed with twice-distilled water. The hydride ( β -phase) was synthesized in 1 N H 2 SO 4 + 0.2 g/l thiourea solution under cathodic polarization ( i h = 500 A/m 2 , t h = 1 h) [9]. On the completion of the synthesis, samples were rinsed with twice-distilled water and placed into working cell filled with a 1 N NaOH degassed solution. Potentials were measured against silver-silver chloride reference electrode and converted to the SHE scale. The electrochemical measurements were performed by transient electrochemical methods and potentiostatic voltammetric curves (VACs).In Fig. 1 we show cathodic and anodic VACs of the hydrogenated alloy ( α -phase) (curve 1 ) [10] and of the alloy hydride ( β -phase) (curve 2 ) recorded by shifting the potential in the positive direction by steps of 0.01 V. The onset of hydrogen evolution at the hydride is observed at a potential by 0.2 V more negative than at the α -phase; oxygen evolution does not depend on the hydrogen content in the alloy. Cathodic voltammetric curves of the alloy hydride contain a cathodic limiting current plateau at -0.9 to -0.35 V like that for nickel hydride [7,8]. The initial segment slope of the anodic curve equals 0.06 V/dec. At a potential of -0.2 V, anodic current peak is observed, whereas from 0 to 0.7 V, we see a limiting anodic current, like at a hydrogenated alloy (curve 1 ).The cathodic limiting current in the hydride curve (curve 2 ) can be associated, like in the case of nickel hydride [7,8], with preceding chemical reaction of the hydride phase decomposition in the alloy. From the shape of the curve 2 it follows that the alloy hydride decomposition kinetics can be studied only in a potential range more negative tha...

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Electrochemical Behavior of Nickel Hydride in Sodium Hydroxide Solutions

Cited by 5 publications

References 4 publications

The anodic behavior of hydrogenated copper in sodium hydroxide solutions

The anodic behavior of hydrogenated copper in sodium hydroxide solutions

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

The Electrochemical Behavior of β-Phase in the Cu30Ni-H System in Sodium Hydroxide Solutions

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