Hydroxide nickel particles

Ni/SiOj-SO m /g ). This is probably due to the fact that 1 1 nickel phyllosilicate is reducible at higher temperature than nickel hydroxide, which induces less sintering. When silica is nonporous, the nickel particles are even smaller because of the better surface of contact between the support and the Ni(II) phase. 

Two types of electrolytes for Ni powder electrodeposition were investigated acid electrolytes [74—82] and ammoniacal electrolytes [74, 77, 83]. For acid electrolytes it is characteristic that the increase of current density and decrease of nickel ion concentration in solution cause a lowering of powder fragility. The powder is free from oxides and basic salts and dry powder could be stored in a dry place indefinitely without oxidation or structure change [74—82]. Characteristic of ammoniacal electrolytes is that the increase of ammonia concentration cause disperse and pure (without hydroxide impurities) deposit formation consisting of dark nickel particles of 4—10 pm and of larger particles of about 400 pm [74, 77, 83]. 

Capacitor device consisting of electrodes of mesoporous particles (nickel hydroxide nickel oxide nickel oxy-hydroxide manganese dioxide nickel-manganese oxides and Hthiated forms titanium dioxide and hthiated forms tin, tin alloys and Hthiated forms) with at least 75 wt% of the particles larger than 15pm is used. To increase structural strength, particles may be deposited on a substrate. Binders and other inactive materials that improve electrical conductivity may be added. 

Reduction of expensive inactive cell components is focused on the positive electrode, including the nickel foam substrate and cobalt metal and cobalt monoxide used to form the conductive network. Several approaches are being studied replacement of the cobalt compounds by metallic nickel fibers use of reduced quantity and less expensive cobalt compounds. An innovative approach being studied is the use of inherently more conductive nickel hydroxide accomplished by multielement modification, and by heterogeneous nickel hydroxide powder particles where filamentary metallic fibers have been embedded into the base nickel hydroxide to make contact with the overall conductive network. To reduce the cost of the foam substrate, development activities include less expensive nickel coating processes and elimination of the foam entirely by enhancing the conductivity of the nickel hydroxide and the conductive network. 

Figure 12. Nickel hydroxide particles for active materials.

From the above, it could be observed that ultrasound broke down the agglomerated precipitate of Ni-DMG complex to very fine particles, resulting in the formation of colloidal solution of Ni-DMG complex in the presence of an ultrasonic held. The settlement of particles was slow in the sonicated sample than in control sample. However, in the normal reaction, green precipitate of nickel (II) hydroxide dissolved in the excess NH3 solution and formed deep blue solution of hexammi-nenickel(II) ions, as under ... 

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). 

A Raney nickel surface is also suitable for electrocatalytic hydrogenation [205]. This surface is prepared by electrodepositing nickel from a solution containing suspended Raney nickel alloy (Ni 50% A1 50%). Some alloy particles stick to the surface, which is then activated by leaching the aluminium using hot aqueous sodium hydroxide. Cyclohexanone, acetophenone and benzil have been converted to the corresponding alcohol and there is no stereoselectivity for the formation of hydrobenzoin from benzil. 

Whatever the precursor, the formation of an intermediate solid phase was always observed. It can be inferred from X-ray diffraction (Fig. 9.2.7) and infrared spectroscopy that this intermediate phase shows a lamellar, incompletely ordered structure (turbostratic structure) built up with parallel and equidistant sheets like those involved in the lamellar structure of the well-crystallized hydroxides Ni(OH)2 or Co(OH)2, these sheets are disoriented with intercalation of polyol molecules and partial substitution of hydroxide ions by alkoxy ions (29). The dissolution of this solid phase, which acts as a reservoir for the M(I1) solvated species, controls the concentration of these species and then plays a significant role in the control of the nucleation of the metal particles and therefore of their final morphological characteristics. For instance, starting from cobalt or nickel hydroxide as precursor in ethylene glycol, the reaction proceeds according to the following scheme (8) ... 

In these experimental conditions the precipitation of cj>, and the reduction of Co(II) and Ni(II) species occur simultaneously, and then < >, is not able to act as a reservoir for these species. Thus, sodium hydroxide was added in a large excess to the reaction medium in the synthesis of CoNi monodisperse particles in order to provide an excess of hydroxide ions (8,30). This method can be extended to obtain nickel-noble metal alloys. Thus PVP-protected Ni-Pd colloids were obtained by Toshima et al. (31) for different Ni/Pd ratios. 

Spontaneous nucleation. Monodisperse micrometer-size Co or Ni particles have been obtained as follows (16,18) cobalt or nickel hydroxide was suspended in EG (250 mL) the molar ratio hydroxide/polyol was varied from 0.01 to 0.15. The suspension was stirred and brought to boil (195°C). The metal precipitation does not occur immediately when the boiling point is reached but only after an induction time. The water and the volatile products resulting from the oxidation of ethylene glycol were distilled off, while the main part of the polyol was refluxed. For Co the reduction was completed in a few hours. For nickel hydroxide it was difficult to achieve a complete reaction due to an incomplete dissolution of this hydroxide. This could be overcome by adding a small amount (a few milliliters) of... 

The active material used in pocket plate cells consists of Ni(OH)2 together with up to 5% of Co(OH)2, Ba(OH)2, etc. to improve cell capacity and cycle life, and 20% of graphite in various forms to increase the electronic conductivity. The nickel hydroxide is precipitated from nickel sulphate in a controlled manner to produce fine particles of large surface area. As in the case of the cadmium electrode, the nickel hydroxide powder may be formed into pellets before insertion into the pockets. 

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