Cathode deposition, alloys

Matsuda and co-workers [39-41] proposed the addition of some inorganic ions, such as Mg2+, Zn2+, In3+, Ga3+, Al3+,and Sn2+, to PC-based electrolytes in order to improve cycle life. They observed the formation of thin layers of Li/M alloys on the electrode surface during the cathodic deposition of lithium on charge-discharge cycling. The resulting films suppress the dendritic deposition of lithium [40, 41]. The Li/Al layer exhibited low and stable resistance in the electrolyte, but the... 

Kroger FA (1978) Cathodic deposition and characterization of metallic or semiconducting binary alloys or compounds. J Electrochem Soc 125 2028-2034... 

One recognizes three main steps in the cathodic deposition of alloys or single metals ... 

Although at least four different technologies [cold rolling, flame spraying, Zn and A1 melt dipping, cathodic deposition of Ni/Zn precursor alloys (76)] have been described, only cold rolling and cathodic deposition of precursor alloys are used for commercial production of Raney-nickel-coated cathodes. 

Cathodic deposition of magnesium from various chloride melts on different substrates has been studied by several authors [288-290], In dilute solutions of Mg(II) species the cathode process has been found to be controlled by diffusion of the reactant. Alloy formation has been observed on platinum, as reported by Tunold [288] and Duan et al. [290], The rate constant of the charge transfer process on a Mg/Ni electrode in molten NaCl-CaCl2-MgCl2 was reported by Tunold to have a value of about 0.01 cm s 1. This author also reported underpotential deposition of a monolayer on iron electrodes, at potentials approximately 100 mV positive to the Mg deposition potential. 

Sacrificial anode — is a piece of metal used as an anode in electrochemical processes where it is intended to be dissolved during the process. In -+ corrosion protection it is a piece of a non-noble metal or metal alloy (e.g., magnesium, aluminum, zinc) attached to the metal to be protected. Because of their relative -+ electrode potentials the latter is established as the -+ cathode und thus immune to corrosion. In -+ electroplating the metal used as anode may serve as a source for replenishing the electrolyte which is consumed by cathodic deposition. The sodium-lead alloy anode used in the electrochemical production of tetraethyl lead may also be considered as a sacrificial anode. 

Depolarization of metal deposition sometimes occurs when two metals which separate simultaneously form compounds or solid solutions. The reversible potential of a solid solution generally lies in between those of the pure constituents hence an alloy containing both metals may be deposited at a potential that is less cathodic than that necessary for the less noble constituent in the pure state. This probably accounts for the fact that zinc and nickel are deposited simultaneously at a potential of about — 0.6 volt, whereas that required for pure zinc is nearly 0.2 volt more cathodic. The simultaneous deposition of the iron-group metals is partly due to the similarity of the discharge potentials, but the formation of solid solutions also plays an important part. Although the deposition potentials of cobalt and nickel are lower than that of iron, the cathodic deposit almost invariably contains relatively more of the latter metal. ... 

Postdeposition plasma modifications to the plasma polymer of TMS have been seen to greatly improve bonding to various primers and paints [18-20]. One particular system has been observed to have tremendous adhesion between plasma-coated A1 alloy panels and paint applied to them. This system involves cathodic DC plasma deposition of a roughly 50-nm primary plasma polymer film from TMS onto a properly pretreated alloy substrate, followed by the deposition of an extremely thin fluorocarbon film by DC cathodic deposition of hexafluoroethane (HFE). It was the superadhesion aspect of this particular system that triggered the series of ESR studies [3,21]. 

C. H. Lee and F. A. Kroger, Cathodic deposition of amorphous alloys of silicon, carbon and fluorine,... 

Meyer claimed that both Ni and Co seem to stabilize the presence of ReO4 anions near the cathode. He proposed that there was a catalytic effect of Ni on the decomposition of ReOT. Sadana and Wang studied the effects of bath composition, pH, temperature, stirring, current density and pulsed current on the characteristics of Au-Re deposits, which contained 0.25-63.4 wt.% Re. The solution consisted of citric acid and potassium perrhenate. The Re-content of the deposit was found to increase markedly as a result of stirring, increase in current density, decrease in bath pH and temperature, and the use of pulsed current. In addition, the as-deposited alloys exhibited XRD patterns of supersaturated solid... 

Typical applications comprise the cathodic deposition of metal and alloy layers for surface finishing applications. Many recipes can be found in Schlesinger and Paunovic (2010). 

Analysis of these data gives the impression of chaos and disorder. The results and conclusions of different authors are often controversial, and the data do not fit any logical pattern (possibly, that is the reason why no comprehensive reviews or monographs are available in this field). Some experimental phenomena did not receive satisfactory theoretical explanations, such as, for example the formation of metal-salt cathode deposits, the breakdown of the industrial electrowinning of Al-Si alloys and the anode effect. 

The classification of electrode film systems is proposed based on the above ideas, and main qualitative regularities of the electrolytic processes in the film systems of different kind are envisaged in Chap. 4. In particular, the mechanism of formation of cathode deposits is considered. It is shown that the deposition of metal-salt carrots or compact metal layers depends on the properties of the cathode film system (prevailing type and ratio of the electronic and ionic conductivity of the film). The nature of crisis phenomena at the electrodes is also analysed (anode effect in fluoride melts, complications at the electrolytic production of Al-Si alloys in industrial-scale electrolytic cells), the mechanisms are elaborated and the means to escape the crises situations are developed. 

The electrochemical and electroflotation methods are widely used to prepare of chemisorbed macromolecules bound to colloidal metal particles generated in situ. Electrochemical polymerization reactions are heterogeneous They are initiated on the electrode surface, while other stages (chain growth or termination) occm, as a rule, in the liquid phase. The yield of a polymer depends on the chemical and physical nature of the electrodes and their surface, electrode overvoltage, potential rmder which the reaction occurs, and electrical current density. The nature of the electrode material (metals or alloys, thin metallic coats, etc.) determines the characteristics of electron-transfer initiation and polymerization. Direct electron transfer between the electrode and monomer, cathodic deposition, and anodic solubilization of metals are optimum for electrochemical polymerization. Metal salts are the precursors of nanoparticles, which may act as specific electrochemical activators. Nanoparticles can influence activations through direct chemical binding to the monomer and by virtue of transfer, decomposition, or catalytic effects. Nonetheless, electrochemical polymerization has found only limited use in the preparation of polymer-immobilized nanoparticles. 

Also highly catalytically active Raney nickel electrodes have been developed. Their production is possible at remarkably low cost by cathodic deposition of a Ni/Zn alloy and subsequent activation by a treatment with hot K0H[6]. These electrodes are used as cathode and anode. Their oxygen overvoltage is below 200 mV and their hydrogen overvoltage less than 100 mV at current densities of 4000-6000 A m and 100°-120 C[7]. 

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