Evaluation of organic additives as levelling agents for zinc electrowinning from chloride electrolytes

Mackinnon, D. J.; Brannen, J. M.

doi:10.1007/bf01112061

Cited by 64 publications

(30 citation statements)

References 8 publications

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“…In fact, this type of electrolyte was used to study the growth of zinc dendrites [51]. Even for electrowinning, the need of organic additives was recognized [52][53][54][55], also at high current density (up to 31 A dm À2 ; see [56]). However, while for electrowinning rather low concentrations of organics are enough (less than 0.1 g L À1 ), such is not the case in plating if bright deposits are required.…”

Section: Acid Chloride Zinc Bathsmentioning

confidence: 99%

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%

Electrodeposition of Zinc and Zinc Alloys

Winand¹

2010

Modern Electroplating

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“…However, PEG molecules raise the overpotentials for reduction of both zinc ions and protons by effectively blocking the electrode surface. Mackinnon and Brannen [4] studied the effects of adding various organic compounds to a ZnCl 2 electrolyte on zinc deposit morphology and crystallite orientation. Tetrabutylammonium chloride (TBACl) was the most effective of several tetraalkylammonium chlorides in smoothing and refining the grain and eliminating dendritic growth.…”

Section: Introductionmentioning

confidence: 99%

Voltammetric and morphological characterization of zinc electrodeposition from acid electrolytes containing boric–polyalcohol complexes

Oliveira

Carlos

2008

J Appl Electrochem

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The influence of sorbitol or glycerol polyalcohols on the electrodeposition of zinc and on morphology of the zinc film is discussed. The deposition current efficiency, in the potential range -1.30 V to -2.50 V, was *90% in all baths. Increasing the sorbitol concentration in the bath shifted the deposition to more negative potentials, *50 mV, and decreased the current density (j p ) of the zinc deposition significantly. On the other hand, adding glycerol did not significantly affect either j or the deposition potential of zinc. Scanning electron microscopy (SEM) showed that either sorbitol or glycerol lead to the formation of granular deposits. The best zinc morphology was obtained with 0.52 M sorbitol or glycerol in the plating bath. The presence of sorbitol or glycerol in the plating bath was beneficial, since the resulting zinc deposits were compact and without holes.

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“…The addition of organic compounds to the electrolytic baths can modify deposit characteristics such as structure, morphology, porosity and grain size [12][13][14]. In fact, a reduction in the grain size implies an increase in the hardness of the deposit [6], and thus an improvement in its mechanical properties.…”

Section: Introductionmentioning

confidence: 99%

Formation of nanocrystalline Zinc on ITO and Silicon substrates by electrochemical deposition

Juárez

Alonso

2006

J Appl Electrochem

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Zn was deposited by means of cyclic voltammetry (CV) and square wave pulsating overpotential (OP) methods on ITO (indium tin oxide) and n-doped silicon (n-Si) substrates from an acetate-based electrolyte at two different temperatures in the absence of additives. The surface morphology of the Zn deposits was studied by scanning electron microscopy (SEM). The preferred orientation and the average size of the Zn electrodeposited particles on n-Si substrates were obtained by X-ray diffraction and the microhardness of the deposits was measured by standard means. The results show that the grain size of the electrodeposits increases as the temperature rises, and on the other hand that the PO method yields smaller grains and higher hardness values compared with those obtained by CV, irrespective of the temperature. Furthermore, in PO conditions a preferential (101) orientation is obtained for the growth of the Zn electrodeposits, but for long deposition times the growth direction is that [100] corresponding to the basal plane (002).

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Evaluation of organic additives as levelling agents for zinc electrowinning from chloride electrolytes

Cited by 64 publications

References 8 publications

Electrodeposition of Zinc and Zinc Alloys

Electrodeposition of Zinc and Zinc Alloys

Voltammetric and morphological characterization of zinc electrodeposition from acid electrolytes containing boric–polyalcohol complexes

Formation of nanocrystalline Zinc on ITO and Silicon substrates by electrochemical deposition

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