Electrodeposition electrolysis

The anionic composition of the cathodic product is not the only parameter that can be controlled through electrolysis conditions. Grinevitch et al. [559] reported on the investigation of the co-deposition of tantalum and niobium during the electrolysis of fluoride - chloride melts. Appropriate electrodeposition conditions were found that enable to obtain either pure niobium or alloys. 

If the electrolysis parameters (precursor concentrations, pH, temperature, cur-rent/potential, substrate) be defined in a precise manner, a self-regulated growth of the compound can be established, and highly (111 )-oriented zinc blende (ZB) deposits up to several p,m thickness are obtained at potentials lying at the anodic limit of the diffusion range (Fig. 3.3) [60]. Currently, the typical method of cathodic electrodeposition has been developed to yield quite compact and coherent, polycrystalline, ZB n-CdSe films of well-defined stoichiometry. The intensity of the preferred ZB(f 11) orientation obtained with as-deposited CdSe/Ni samples has been quite high [61]. 

It has been shown that the electrodeposition of molybdenum chalcogenides from high-temperature molten salts can give large, well-defined crystals of these compounds. The preparation of M0S2 as well as WS2 by electrolytic reduction of fused salts was first reported by Weiss [145], who produced small hexagonal blue-gray platelets under drastic conditions of electrolysis. Schneemeyer and Cohen... 

Eatas E, Herrasti P, Aijona F, Garcia Camarero E (1987) Characterization of CdS thin films electrodeposited by an alternating current electrolysis method. J Electrochem Soc 134 2799-2801... 

Chromatography including extraction, ion exchange, adsorption Distillation, volatilization Electrolysis, electrodeposition... 

It has been pointed out that metals residing below the position held by manganese (and, therefore, much below hydrogen) in the electrochemical series (Table 6.11) cannot be electrodeposited from aqueous solutions of their salts. These metals are called base metals or reactive metals and can be electrodeposited only from nonaqueous electrolytes such as solutions in organic solvents and molten salts. As with an aqueous electrolyte, there is a minimum voltage which is required to bring about the electrolysis of a molten salt. 

In the case of molten salts, the functional electrolytes are generally oxides or halides. As examples of the use of oxides, mention may be made of the electrowinning processes for aluminum, tantalum, molybdenum, tungsten, and some of the rare earth metals. The appropriate oxides, dissolved in halide melts, act as the sources of the respective metals intended to be deposited cathodically. Halides are used as functional electrolytes for almost all other metals. In principle, all halides can be used, but in practice only fluorides and chlorides are used. Bromides and iodides are thermally unstable and are relatively expensive. Fluorides are ideally suited because of their stability and low volatility, their drawbacks pertain to the difficulty in obtaining them in forms free from oxygenated ions, and to their poor solubility in water. It is a truism that aqueous solubility makes the post-electrolysis separation of the electrodeposit from the electrolyte easy because the electrolyte can be leached away. The drawback associated with fluorides due to their poor solubility can, to a large extent, be overcome by using double fluorides instead of simple fluorides. Chlorides are widely used in electrodeposition because they are readily available in a pure form and... 

The electrolysis temperature affects the electrolyte conductivity, the overpotential, and the solubility of the electrodeposit in aqueous as well as in molten salt systems. The effect of temperature is particularly important in the latter case. The lower limit of the temperature of operation is set by the liquidus temperature of the bath and the solubility of the solute. Generally, the temperature chosen is at least 50 °C above the melting temperature of... 

In electrogravimetry, also called electrodeposition, an element, e.g., a metal such as copper, is completely precipitated from its ionic solution on an inert cathode, e.g., platinum gauze, via electrolysis and the amount of precipitate is established gravimetrically in the newer and more selective methods one applies slow electrolysis (without stirring) or rapid electrolysis (with stirring), both procedures either with a controlled potential or with a constant current. Often such a method is preceded by an electrolytic separation using a stirred cathodic mercury pool, by means of which elements such as Fe, Ni, Co, Cu, Zn and Cd are quantitatively taken up from an acidic solution whilst other elements remain in solution. 

Electrogravimetry is one of the oldest electroanalytical methods and generally consists in the selective cathodic deposition of the analyte metal on an electrode (usually platinum), followed by weighing. Although preferably high, the current efficiency does not need to be 100%, provided that the electrodeposition is complete, i.e., exhaustive electrolysis of the metal of interest this contrasts with coulometry, which in addition to exhaustive electrolysis requires 100% current efficiency. 

Chonglun F., Piron D.L., Paradis R, Hydrogen evolution on electrodeposited nickel-cobalt-molybdenum in alkaline water electrolysis, Electrochim. Acta, 39(18), 2715-2722,1994. 

Singh R.N., Pandey J.P., Anitha K.L., Preparation of electrodeposited thin films of nickel-iron alloys on mild steel for alkaline water electrolysis. Part I Studies on oxygen evolution, Int. J. Hydrogen Energ., 18(6), 467-473,1993. 

A hanging mercury drop electrodeposition technique has been used [297] for a carbon filament flameless atomic absorption spectrometric method for the determination of copper in seawater. In this method, copper is transferred to the mercury drop in a simple three-electrode cell (including a counterelectrode) by electrolysis for 30 min at -0.35 V versus the SCE. After electrolysis, the drop is rinsed and transferred directly to a prepositioned water-cooled carbon-filament atomiser, and the mercury is volatilised by heating the filament to 425 °C. Copper is then atomised and determined by atomic absorption. The detection limit is 0.2 pg copper per litre simulated seawater. 

Bruhn D, Dietz W, Muller K-J and Reynvaan C, EPA 86109265.8(1986) through ref (247) 248a. Dietz W (1986) Electrodeposition of metals from an electrolysis bath, Eur Pat Appl EP... 

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