Electrocrystallization - theory and applications

Winand, René

doi:10.1016/0304-386x(92)90033-v

Cited by 145 publications

(85 citation statements)

References 27 publications

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“…Because of the high values of the exchange current density, noncoherent deposits (dendritic or powdery) are expected if organic additives and/or close hydrodynamic control are not in use [47][48][49][50]. In fact, this type of electrolyte was used to study the growth of zinc dendrites [51].…”

Section: Acid Chloride Zinc Bathsmentioning

confidence: 99%

“…Current densities ranging from 90 to 150 A dm À2 are currently used, and values up to 300 A dm À2 were successfully used at large pilot scale for 5-15 mm thick deposits [47-49, 107, 108], while 450 A dm À2 was reported for lower thicknesses, around 1 mm [47]. These processes, used now at large industrial scale, are mainly for protecting car bodies against corrosion, and they require close control of current density and hydrodynamic conditions at the surface of the continuous plate.…”

Section: Continuous Platingmentioning

confidence: 99%

“…. Those where the steel sheet moves horizontally between the anodes, the current feeder rolls being outside the electrolytic cell (Nippon steel jet cell [112], Nippon steel liquid cushion cell [112,122,123], Sumitomo horizontal cell and its modified version [124], Cockerill-Sambre flash cell [47]: Figs. 10.12-10.16).…”

Section: Continuous Platingmentioning

confidence: 99%

“…. Those where the steel sheet moves horizontally, pressed against a cathode feeder facing the anode directly in the electrolytic cell (Cockerill-Sambre belt cell [47]: Fig. 10.17)…”

Section: Continuous Platingmentioning

confidence: 99%

“…At the same time, due to the high hydrogen overpotential on pure zinc, cathodic current efficiencies higher than 95% are obtained, as shown in Figure 10.18 [107,110], despite rather high temperatures (50 C). Figure 10.19 [47,108] shows very dearly how a surface structure of 10-mm-thick zinc deposits is improved at high current density compared with low-current-density plating in the same electrolyte without the organic additive. It should be emphasized that bright deposits are not required.…”

Section: Continuous Platingmentioning

confidence: 99%

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Electrodeposition of Zinc and Zinc Alloys

Winand¹

2010

Modern Electroplating

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Zinc has a standard reversible potential [À0.76 V/standard hydrogen electrode (SHE)] that is more negative than that of iron (Fe/Fe 2 þ -0.44V/SHE). For this reason zinc is used for sacrificial cathodic protection of steel against corrosion.According to Fischer [1], in metal electrodeposition, zinc can be considered as an intermediate metal, giving rise to medium values of overpotentials due to secondary inhibition resulting from adsorbed hydrolized species.In acid sulfate solutions without an organic additive, BR metallographic cross-sectional structures are obtained (BR: basis reproduction; coherent deposits with coarse crystals whose diameter increases with the deposit thickness; see Fig. 10.1). In chloride electrolytes, even coarser grains are observed, because of the more activating character of chloride ions against sulfate ions [2] and despite the complex formation in solution [3, p. 464]. In cyanide baths, on the other hand, much finer grains are obtained, and the deposits pertain to the FT (field-oriented texture: coherent deposits, with elongated crystals perpendicular to the substrate, with almost constant diameter throughout the deposit thickness) or UD types (UD: unoriented dispersion type; coherent deposit, with small crystals showing three-dimensional nucleation to occur all the time during electrodeposition). Figure 10.2 shows a deposit obtained in a cyanide solution without an organic additive: the structure is initially FT, but it becomes progressively bad. Going from a cyanide bath to a noncyanide alkaline bath should result in still worse deposits because electrolyte complexation decreases [3] and exchange current density increases [4, pp. 528-543].Accordingly, when rather thick deposits are needed and/or if a bright surface is required, organic additives are always present at high concentration (1 g L À1 or more). This always occurs in barrel-and-rack plating of small pieces of equipment, because the local current densities will vary over a wide range. For continuous plating on steel sheets or wires, constant current density and rather good hydrodynamic control may be achieved over the whole cathodic surface, and organic additives are not so much in use.Whatever the pH, zinc is always more negative than hydrogen [5]. In electrolytes where zinc is complexed, its standard reversible potential is still more negative; for instance, for cyanide baths, the reversible potential for reactionin alkaline solution is À1.26 V/SHE [6]. Consequently hydrogen evolution occurs at the cathode as a competitor to zinc deposition, resulting in a decrease of current efficiency and eventually in some atomic hydrogen diffusion into the substrate.Finally, in industrial processes electrolytic plating is an alternative to hot-dip galvanizing. Both processes have advantages and disadvantages. Continual technological improvements make it difficult to conclude in favor of one process over the other. However, hot dip always includes some surface alloying by diffusion, and the deposit thickness is less easily controlled th...

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Section: Acid Chloride Zinc Bathsmentioning

confidence: 99%

Section: Continuous Platingmentioning

confidence: 99%

Section: Continuous Platingmentioning

confidence: 99%

“…. Those where the steel sheet moves horizontally, pressed against a cathode feeder facing the anode directly in the electrolytic cell (Cockerill-Sambre belt cell [47]: Fig. 10.17)…”

Section: Continuous Platingmentioning

confidence: 99%

Section: Continuous Platingmentioning

confidence: 99%

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