Electrocrystallization of metal

Cathodic deposition (electrocrystallization) of metals is the basic process in electrometallurgy and electroplating. 

Until the advent of modem physical methods for surface studies and computer control of experiments, our knowledge of electrode processes was derived mostly from electrochemical measurements (Chapter 12). By clever use of these measurements, together with electrocapillary studies, it was possible to derive considerable information on processes in the inner Helmholtz plane. Other important tools were the use of radioactive isotopes to study adsorption processes and the derivation of mechanisms for hydrogen evolution from isotope separation factors. Early on, extensive use was made of optical microscopy and X-ray diffraction (XRD) in the study of electrocrystallization of metals. In the past 30 years enormous progress has been made in the development and application of new physical methods for study of electrode processes at the molecular and atomic level. 

Electrociystallization denotes nucleation and crystal growth in electrochemical sterns under the influence of an electric field [1.1-1.21]. Electrocrystallization of metals takes place at an electronic conducting substrate / ionic conducting electrolyte interface including, in general, three stages ... 

A N. Baraboshkin, Electrocrystallization of Metals from Molten Salts (in Russian), Nauka, Moscow, 1976. 

Chemical and physical control of electrocrystallization of metals and their solid discharge products... 

Wranglen G (1960) Dendrites and growth layers in the electrocrystallization of metals. Electrochim Acta 2 130-146... 

Klapka V (1970) To the problem of crystallization overvoltage during electrocrystallization of metals. Coll Czechoslov Chem Comun 35 899-906... 

Baraboshkin A.N. 1916) Electrocrystallization of metals from molten salt, Nauka Publishers, Moscow 2. Esina N.O., Valeev Z.I., Pankratov A. A. (1996) Structure of molybdenum electrodeposited from chloride melt with various contents of oxygen impurity in the melt. Extend Abstracts, Baltic Conference of Interface... 

Baraboshkin, A.N., (1976) Electrocrystallization of Metals from Molten Salts, Nauka, Moscow. Kuznetsova, S.V., Glagolevskaya A.L., and Kuznetsov, S.A. (1989). Effect of electrolysis parameters and the anionic composition of the electrolyte on the roughness of the hafiiium coatings, Zh.Prikl.Khim. 63, 536-539. 

Budevski E, Staikov G, Lorenz WJ. Fundamentals of electrocrystallization of metals. In Electrochemical phase formation and growth. An introduction to the initial stages of metal deposition. New York Wiley-VCH, 1996. 

Baraboshkin, A.N. (1976) Elektrokristallizotsiya metallov rasplavlennykh solei Electrocrystallization of Metals from Fused Salts, Nauka, Moscow. 

The structure of metallic deposits is determined primarily by the size, shape (faceting), type of arrangement, and mutual orientation of the crystallites. Two factors may influence the orientation and spatial alignment of the microcrystals in electrocrystallization the field direction (or direction of the electric current) and the nature of the substrate. The deposits are said to have texture when the crystallites are highly oriented in certain directions. Epitaxy implies that the lattice is altered under the influence of the substrate. 

Sections 5.6.2 and 5.6.3 dealt with the deposition of metals from complexes these processes follow the simple laws dealt with in Sections 5.2 and 5.3, particularly if they take place at mercury electrodes. The deposition of metals at solid electrodes (electrocrystallization) and their oxidation is connected with the kinetics of transformation of the solid phase, which has a specific character. A total of five different cases can be distinguished in these processes ... 

The kinetics of electrocrystallization conforms to the above description only under precisely defined conditions. The deposition of metals on polycrystalline materials again yields products with polycrystalline structure, consisting of crystallites. These are microscopic formations with the structure of a single crystal. 

Walsh, F.C. and M.E. Herron, Electrocrystallization and electrochemical control of crystal growth fundamental considerations and electrodeposition of metals. Journal of Physics D Applied Physics, 1991. 24(2) p. 217. 

Despite the vast quantity of data on electropolymerization, relatively little is known about the processes involved in the deposition of oligomers (polymers) on the electrode, that is, the heterogeneous phase transition. Research - voltammetric, potential, and current step experiments - has concentrated largely on the induction stage of film formation of PPy [6, 51], PTh [21, 52], and PANI [53]. In all these studies, it has been overlooked that electropolymerization is not comparable with the electrocrystallization of inorganic metallic phases and oxide films [54]. Thus, two-or three-dimensional growth mechanisms have been postulated on the basis that the initial deposition steps involve one- or two-electron transfers of a soluted species and the subsequent formation of ad-molecules at the electrode surface, which may form clusters and nuclei through surface diffusion. These phenomena are still unresolved. 

Refs. [i] Staikov G, MilchevA (2007) The impact of electrocrystallization on nanotechnology. In Staikov G (ed) Electrocrystallization in nanotechnology. Wiley-VCH, Weinheim [ii] Budevski E, Staikov G, Lorenz WJ (1996) Electrochemical phase formation an introduction to the initial stages of metal deposition. VCH, Weinheim [Hi] Milchev A (2002) Electrocrystallization fundamentals ofnucleation and growth. Kluwer, Boston... 

For other oxide systems, the processes in electrolyte solutions have been studiei in less detail. In salt melts at not too high an acidity, interesting results have beei obtained by electrocrystallization of various transition-metal compounds [20-25 which, however, cannot be directly used in HTSC electrosynthesis. 

Unfortunately, the electrodeposition of metals summarized in Table 4 is accompanied by increased HTSC degradation under cathodic polarization [53, 55]. In nonaqueous media, electrocrystallization processes can be inhibited due to the peculiarities of the intermediate Cu+ species solvation [286]. Moreover, the surface morphology of deposits can be adversely affected by the formation of dendrites this can be overcome by the addition of a brightening agent [497]. 

Me UPD processes involving formation of 2D Meads phases, 2D Me-S surface alloy phases and 3D Me-S bulk alloy phases in the underpotential range (cf. eq. (1.7)) are due to a strong Me-S interaction and represent the initial step of metal electrocrystallization. 

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