Nickel electrolytic deposition

So-called ultrafine metal powders below 1 i in diameter can be made by pyrogenic dissociation of the vapors of the carbonyls of iron, nickel, and cobalt. Aluminum of a particle size below the resolving power of the electron microscope has been formed by evaporation and condensation under vacuum in an inert atmosph e. Similarly, evaporated magnesium has been quenched by JP-4 fuel for directly making a slurry fuel. Also, long ball-milling fine magnesium powder in the presence of a surfactant can lead to particles below I n. Iron or nickel electrolytically deposited on a mercury cathode form very active, often pyrophoric, fine powdm that, however, can be stabilized in order to be handled in air. 

In atomization, a stream of molten metal is stmck with air or water jets. The particles formed are collected, sieved, and aimealed. This is the most common commercial method in use for all powders. Reduction of iron oxides or other compounds in soHd or gaseous media gives sponge iron or hydrogen-reduced mill scale. Decomposition of Hquid or gaseous metal carbonyls (qv) (iron or nickel) yields a fine powder (see Nickel and nickel alloys). Electrolytic deposition from molten salts or solutions either gives powder direcdy, or an adherent mass that has to be mechanically comminuted. 

Electroless nickel engineering deposits Electroless nickel is not usually deposited to thicknesses greater than about 125/xm. Where a greater total thickness is required, an electrolytic nickel undercoat should be used. 

Noble metal coatings (e.g., nickel) can be effective, but only if they remain unbroken and are of sufficient density and thickness. Electrolytic deposits of tin, lead, copper or silver on steel are also considered as protectors and probably do not modify the normal features of fatigue because they suppress contact with the surrounding environment. Observations made on the use of deposits of nickel or chromium are contradictory.7... 

Nickel plating is also extensively used for decorative and corrosion resistance applications. In most cases, it is electrolytically deposited. However, some applications can require high purity films or good conformal coverage that can be better performed by the CVD process. 

Caron (C9) developed an electrolytic method for separating cobalt and nickel from alloys of the two metals. The ammoniacal electrolyte composition is chosen to favor the plating of cobalt from nickel. The electrolyte is passed through a number of cells in series, with continuous deposition of cobalt at the cathode and the discharge of a cobalt-free high-nickel electrolyte. Distillation of this solution after the addition of Ca(OH)2 or NaOH converts the nickel to the hydroxide and the regenerated ammonia is returned to the process. 

Under standard conditions and in the absence of kinetic hindrance, the electrode potential (versus a hydrogen electrode) determines the potential at which the corresponding metal will be deposited out of an aqueous solution. Therefore, metals that have a more negative electrode potential than the hydrogen electrode cannot be deposited from aqueous electrolytes. Kinetic barriers often disfavor the production of hydrogen over metal deposition. Thus, technically important metals, such as tin, nickel, and zinc can be electrolytically deposited out of aqueous solutions without any problems, even though their electrode potentials are lower than that of the hydrogen electrode. 

Up until now, there has been little interest in electrolytic deposition of iron metals and chromium from nonaqueous solutions, because such deposits are easily obtained from aqueous electrolytes. On the other hand, adhesive layers can be applied to reactive metals like titanium, beryllium, and magnesium, for example through nickel deposition from nonaqueous solutions. By depositing such metals out of nonaqueous solutions, hydrogen sensitive materials, such as low-alloy high-strength steel, can be coated without danger of embrittlement. Materials coated in this way with a compact poreless metal layer can be further coated in an aqueous electrolyte. 

The INCO, Thompson plant in Manitoba, Canada, electrolyzes 240 kg sulfide anodes in a sulfate-chloride electrolyte. The approximate composition of the electrolyte is 60 g L x Ni2+, 95 g L 1 SC>42, 35 g L 1 Na+, 60 g L 1 Cl-, and 16 g L 1 H3BO4, and the temperature is 60 °C. Nickel, cobalt, and copper dissolve from the anode, while sulfur, selenium, and the noble metals form an insoluble sludge or slime, from which they can be recovered. The anode sludge contains 95% elemental sulfur, sulfide sulfur, nickel, copper, iron, selenium, and precious metals. Nickel is deposited on to pure nickel starting sheets. The anode cycle is 15 days and the cathode cycle is 5 to 10 days. Electrolysis is carried out at a current density of 240 A m-2 giving a cell voltage of 3 to 6 V [44, 46]. 

Colombier measured the potential of NiSO4(0.5 M) Ni against a calomel reference electrode at 20°C. When the electrolyte was appropriately degassed and kept air-free the same equilibrium potentials were found for massive or powdered nickel, the latter having been electrolytically deposited or prepared by hydrogen reduction of NiO. As the author presented no details about the experimental data, the reference potential selected, how the liquid junction potential and the activity coefficients were accounted for, the final result, °(Ni Ni, 293.15 K) = (0.227 + 0.002) V, cannot be recalculated and was not being considered any further. 

Carbyl sulfate 68 is a useful reagent in various patented industrial processes, including the production of nitroethio-nate <2001W00160787>, an intermediate in the production of dyes and a synthesis of l-(2-sulfoethyl)pyridinium betaine <1999W09941236>, important as a secondary brightener in the electrolytic deposition of nickel. 

Most modern nickel electrolytes are based on the composition proposed by Watts [26], which contains boric acid besides nickel chloride and sulfate. The chloride facilitates the dissolution of the anodes, but also increases the internal tensile stresses of the deposit. Boric acid serves as a buffering agent. The throwing power can be improved by adding inorganic salts. Recently, it... 

As with all high-performance electrolytes, continuous monitoring of the composition is necessary, which can be performed by spectroscopic or chromatographic methods. In addition, cyclic voltammetry [33] and electrochemical impedance spectroscopy [34] have been proposed for the screening of nickel electrolytes and the deposits obtained from them. 

When nickel is deposited electrolytically on a mercury cathode, it appears to form an intermetallic compound containing about 24% nickel, but when the mercury is distilled off, finely divided, strongly pyrophoric nickel is formed. Iron and cobalt are deposited by electro-... 

Figure 12.18 Rinsing procedure applied in a dual bath plating of copper-nickel. After deposition the samples are rinsed twice in water and in the electrolyte before the next layer is deposited.

Data have also been obtained ((>4) for composite membranes in which copper or nickel were deposited electrolytically upon palladium. The deposited films were very thin, about 10 cm. 

Pure nickel (99.9%) can be produced by electrolytic refining. Generally, an impure metal anode (produced by reducing nickel oxide) and a cathode starting sheet are placed in an acidic electrolytic solution. When a current flows, nickel and other metals are dissolved from the anode. The electrolyte is then removed, purified, and returned to the cathode compartment, where nickel is deposited on the cathode. 

Electrolytic nickel/electrolytic gold Electroless gold Direct immersion gold Solid solder deposit... 

Other surface finishes include reflowed tin-lead, electrolytic nickel/electrolytic gold, antitarnish and reflux, electroless palladium, electroless gold, direct immersion gold, and solid solder deposit. 

---