Nickel oxides and hydroxides

Nickel oxides and hydroxides play an important role in the passivity of nickel in aqueous solutions, in oxidizing ionic... 

Tewari, P.H. and Campbell, A.B., Temperature dependence of point of zero charge of cobalt and nickel oxides and hydroxides, J. Colloid Interf. Sci., 55, 531, 1976. 

In nickel battery systems, y-NiOOH(s) is in equilibrium with a-Ni(OH)2(s) but there is a lack of thermochemical data on the latter solid (Gamsjager et al., 2005). More importantly, the couple between these two solids is actually a solid solution between nickel oxide and hydroxide solids in the divalent, trivalent andtetravalent states. Thermochemical data have been derived for the following reaction (Gamsjager et al., 2005) ... 

With nickel/alumina catalysts (cf. 4 ) preparation by coprecipitation or by the decomposition of a high dispersion of nickel hydroxide on fresh alumina hydrogel, yields nickel aluminate exclusively. On the other hand, when, as in impregnation, larger particles of nickel compound are deposited, the calcination product is a mixture of nickel oxide and nickel aluminate. The proportion of nickel oxide increases when occlusion of the impregnation solution leads to a very nonuniform distribution (49). 

Similar mechanisms may be proposed for the hydrolysis of amino acid esters and amides co-ordinated to labile metal centres such as copper(n) or nickel(n), although mechanistic studies at these centres are much more difficult to perform in view of the rapidity of ligand exchange processes. Further complications arise from the formation of insoluble or colloidal suspensions of metal oxides and hydroxides at higher pH values. In general,... 

Among the commonly observed spectral overlap problems due to molecular oxide and molecular hydroxide ions are those due to TiO+ (with 5 isotopes of Ti from mass 46 to 50) that result in overlaps with a minor isotope of nickel, 62Ni+ both isotopes of copper, 63Cu+ and 65Cu + and the two major isotopes of zinc, MZn+ and 66Zn+. Calcium oxide and hydroxide ions overlap with all five isotopes of nickel, both isotopes of zinc, and three of the four isotopes of iron. The analysis of rare earth elements is particularly complicated by molecular oxide and hydroxide ion spectral overlaps [141,142]. 

A metal hydride battery similar to the nickel-cadmium battery has been developed by Sharp corporation. The battery is shaped in the form of a button of 20 mm diameter and can give 1.2 V. The anode in the battery is made of La-Ni-Sn alloy hydride, and the cathode is nickel oxide. Potassium hydroxide solution in polyamide-resin is the electrolyte. The battery exhibits high energy density (i.e.) 1.5 to 2.0 times that of the Ni-Cd battery, good cycling life and superior low temperature behaviours. 

The potential-pH diagram of nickel is shown in Fig. 20. In acidic solutions, dissolution to Ni " " can appear at potentials above the equilibrium potential. In alkaline solutions, HNi02 ions can be formed. Various oxides and hydroxides can be formed on nickel, for example, Ni(OH)2, Ni304, Ni203, and Ni02. In contradiction to the thermodynamic expectations, nickel... 

The most traditional approach for the electrodeposition of metal oxides and hydroxides is based on the cathodic electrogeneration of base [6]. Depending upon the deposition potential, choice of the anion and the pH of the solution, various reactions take place at the cathode, such as the reduction of nitrate ions in aqueous solutions. These reduction reactions cause a local pH increase in vicinity of the cathode either by the consumption of protons or by the generation of hydroxide ions as in the case of nitrate reduction, which subsequently leads to the precipitation of metal hydroxides. The best known application of this technique is the synthesis of nickel hydroxide by the electroreduction of aqueous nickel nitrate solutions. Depending on the metal and deposition conditions, this cathodic technique often yields hydroxides rather than oxides, making a post-deposition calcination for the transformation of the hydroxide to the oxide necessary. Unfortunately, the deposited amorphous hydroxides are often metastable. Other cathodic electrodeposition methods involve the direct reduction of the oxidation state of the metal cation and deposition of the oxide onto the electrode [9]. 

Ellipsometry was used hy Giannoulis et al. [9] to study fihn thicknesses of therapeutic sOicon-based microdevices under development. In situ characterization of the growth of electroactive films of oxides and hydroxides of transition metals has been done with scanning tunneling microscopy (STM), atomic force microscopy (AFM), and intermittent contact atomic force microscopy (ICAFM). Shrinkage and enhanced thicknesses of films can be measured with these methods. Films of iridium oxide, nickel oxides, and polyaniline were studied here. 

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