Nickel in acids

In many aqueous solutions nickel has the ability to become passive over a wide range of pH values. The mechanism of passivation of nickel and the properties of passive nickel have been studied extensively—perhaps more widely than for any other element, except possibly iron. In recent years the use of optical and surface analytical techniques has done much to clarify the situation . Early studies on the passivation of nickel were stimulated by the use of nickel anodes in alkaline batteries and in consequence were conducted in the main in alkaline media. More recently, however, attention has been directed to the passivation of nickel in acidic and neutral as well as alkaline solutions. 

The alloying elements molybdenum and copper do not, by themselves, enhance passivity of nickel in acid solutions, but instead ennoble the metal. This means that, in practice, these alloying elements confer benefit in precisely those circumstances where chromium does not, viz. hydrogen-evolving acidic solutions, by reducing the rate of anodic dissolution. In more oxidising media the anodic activity increases, and, since binary Ni-Mo and Ni-Cu alloys do not passivate in acidic solutions, they are generally unsuitable in such media. 

Standard solutions, a solution of nickel in acid with a quoted mass/volume concentration, a solution of sodium hydroxide with a quoted concentration as a molarity and a solution of pesticides with quoted mass/volume concentrations. Matrix RMs - natural materials, river sediment with quoted concentrations of metals, milk powder with a quoted fat content and crab paste with quoted concentrations of trace elements. 

The same two-step mechanism of metal dissolution has also been delivered for the anodic dissolution of nickel in acid solutions [Sato-Okamoto, 1964]. The mechanistic concepts for iron dissolution other than the two-step mechanism have also been presented in the literature [Heusler, 1958], 6ind the mechanism of metal dissolution is still a subject of research [Plonski, 1996]. 

The corrosion behavior and dissolution mechanism of nickel in acid solutions with hydrogen sulfide (H2S) was studied. It was found that the dissolution of nickel is influenced by both the nickel sulfide layer formed on the electrode surface and the acceleration effect of H2S [56]. 

Burke and Yoe (8) described the simultaneous spectrophotometric determination of cobalt and nickel in acidic ethanol. An analogous procedure in acidic dimethylformamide (DMF) was described by Ayers and Annand (3). By simultaneously solving Beer s law equations, the concentration of each metal can be determined (Eqs. 1 and 2). In general, the results of these two methods were similar. However, Burke and Yoe (8) found that iron and copper interfered with the measurement while Ayers and Annand (3) found interference from manganese. 

Frumkin and Kolotyrkin (25) have applied the concept and techniques successfully to the dissolution of lead and nickel in acids and iron in alkalies. The author (18, 26) has shown that the dissolution of aluminum in acid and alkaline solutions containing various oxidation-reduction systems behaves according to this principle. He also showed that the rate of dissolution of aluminum, zinc and their alloys in various acid, neutral, and alkaline solutions may be obtained from polarization data (27). 

It is suggested that the anodic dissolution will be inhibited if the adsorbed anion and the reaction intermediate are stable and hardly dissolve in aqueous solution. On the contrary, if the reaction intermediate is relatively unstable and readily dissolves into aqueous solution, the anion will function as an electrocatalyst accelerating the metal dissolution rate. It is now common knowledge that hydroxide ions, OH, catalyze the anodic dissolution of metallic iron and nickel in acid solution [81,82]. It is also known that chloride ions inhibit the anodic dissolution of iron in acidic solution [83]. No clear-cut understanding is however seen in literature on why hydroxide ions catalyze but chloride ions inhibit the anodic dissolution of iron, even though the two kinds of anions are in the same group of hard base. We assume that the hardness level in the Lewis base of adsorbed anions will be one of the most effective factors that determine the catalytic activity of the adsorbates. Further clarification on the catalytic characteristics will require a quantum chemical approach to the adsorption of these anions on the metal surface. 

Figure 9.7 Corrosion of nickel in acid solution. Concentration of chloride ion ...

Cowan, R. L. and Staehle, R. W., The Thermodynamics and Electrode Kinetic Behaviour of Nickel in Acid Solution in the Temperature Range 25-300°C , J. Eiectrochem. Soc., 118,557... 

The method of attacking a scratch by bromine (see page 537) can also be used this permits the detection of nickel in acid-resistant steel. ... 

Cowan RL, Staehle RW. The thermodynamics and electrode kinetic behavior of nickel in acid solution in the temperature range 25° to 300°C. Journal of the Electrochemical Society, 1971 118 557-68. 

Passive and Transpassive Dissolution of Nickel in Acidic Solutions The kinetics of nickel dissolution in the passive and transpassive ranges M remained totally unclear until the application of a very low frequency impedance technique. A general model was proposed on the basis of an extensive study of anion effects [143]. In the passive state, the fiequency domain had to be extended far below ImHz and long-term stability was obtained only by using single-crystal electrodes [144]. 

A. Jouarmeau, M. Keddam, and M. C. Petit, A general model of the anodic behaviour of nickel in acidic media, Electrochim. Acta 27 287 (1976). 

The overall problem of the nonsteady-state passive iron has been reexamined with the purpose of reaching a consistent interpretation of the empirical equation firmly esfablished in acidic [135] and neutral [133,134] media and also for nickel in acidic solutions [135] in classical papers. As stated earlier [141], this equation contradicts the high-field mechanism because it predicts a direct logarithmic Q t) relationship consistent with a place exchange mechanism, whereas the high field should generate an inverse logarithmic dependence [4]. 

Passive and Transpassive Dissolution of Nickel in Acidic Solutions... 

Nickel sulfuric acid Reductions with Raney nickel in acidic medium Aldehydes from nitriles... 

A selective hydrogenation of optically active cyanohydrins directly yielding 2-hydroxy-aldehydes under complete retention of configuration is possible with Raney nickel in acidic medium but only with moderate yields [37]. O-Protected hydroxy aldehydes (R)-12 are... 

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