Pulse plating of Zn-Ni alloy coatings

Alfantazi, Akram; Page, John A.; Erb, U.

doi:10.1007/bf00249924

Cited by 64 publications

(59 citation statements)

References 7 publications

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“…Recent investigations on the mechanism of the reaction [149,165,167,[194][195][196][197][198][199][200][201][202][203][204][205][206][207][208] show that this phenomenon is linked to a local rise in pH at the surface of the cathode, due to hydrogen evolution, resulting in some zinc hydroxide adsorbed species through which the discharge of the iron metal is slowed down. Moreover, these alloys show large discrepancies of crystal structure with thermal equilibrium ones, as shown in Figure 10.28 [196] and Figure 10.29 [110].…”

Section: Continuous Platingmentioning

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: Continuous Platingmentioning

confidence: 99%

Electrodeposition of Zinc and Zinc Alloys

Winand¹

2010

Modern Electroplating

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“…Alfantazi and Erb et al 12) prepared nanocrystalline Zn-Ni coatings in the same electrolyte by pulse plating. However, we have been successful in obtaining nanocrystalline alloys with a grain size as low as 20 nm, with simple DC plating at 700 Am À2 .…”

Section: Nanocrystallinity Of the Depositmentioning

confidence: 99%

“…Other additives are also added for improving the leveling. On the other hand, Erb et al 12,13) has employed boric acid without addition of ammonia or acetate. They were able to prepare good deposits by pulse plating.…”

Section: Introductionmentioning

confidence: 99%

Deposition of Nanocrystalline Zinc-Nickel Alloys by D.C. Plating in Additive Free Chloride Bath

et al. 2007

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Nanocrystalline zinc-nickel alloy coatings were electro-deposited in chloride bath containing ZnCl 2 (50-200 gL À1 ), NiCl 2 .6H 2 O (50-200 gL À1 ) and H 3 BO 3 (40 gL À1 ) at 45 C. The initial alloy composition, as investigated by voltammetry, chronopotentiometry or EDX analysis, exhibited a pronounced dependence on the composition of plating bath. However, the alloy composition tended to approach an upper limit of 18 atomic percent when deposits grew thicker, for most of the plating bath compositions. The process was clearly the anomalous codeposition, which was considered to be due to the formation of an adsorbed layer of Zn(OH) 2 containing nickel cations, as an intermediate product, whose composition determines the composition of the electro-deposited alloy. The electro-deposited coatings comprised of single-phase structure of -phase (Ni 5 Zn 21 ) for about 12-18 atomic percent nickel and a mixture of -and -phases (hcp) for nickel atom percent below 8. The grain size decreased from about 50 nm to 20 nm with decrease in nickel content away from the stoichiometric composition of Ni 5 Zn 21 along with a decrease in hardness from about 450KHN to 150KHN. The decrease in hardness with a decrease in grain size seems attributable to the grain boundary sliding as predominant deformation mechanism. Anodic dissolution of the alloys involved pronounced dezincification, forming -phase (fcc) that dissolved at the end.

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“…Normal and anomalous Zn-Ni codeposition is determined by numerous factors, such as cathodic current density i c [1], the electrodeposition potential (E c ) [2,3], the ratio of Zn ?2 and Ni ?2 ions in the electrolyte, as well as pH and temperature of the solution [4][5][6][7]. Literature reports mostly deal with conditions for normal and anomalous codeposition and do not investigate the codeposition mechanism.…”

Section: Introductionmentioning

confidence: 98%

Influence of voltammetric parameters on Zn–Ni alloy deposition under potentiodynamic conditions

Petrauskas¹,

Grincevičienė²,

Češūnienė³

2009

J Appl Electrochem

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The phase composition of Zn-Ni alloys electrodeposited from acetate-chloride plating solutions containing Zn ?2 and Ni ?2 ions at ratio of 1-12.8 at 50°C was investigated by the potentiodynamic stripping method. Two anodic current density (i a ) peaks emerged in potentiodynamic stripping curves (PDC) at E \ 0.0 V and E [ 0.0 V (vs. Ag/AgCl/KCl sat ), that were attributed to oxidation of certain phases of the Zn-Ni alloy. The ratio of these phases in deposited Zn-Ni alloys under potentiodynamic conditions was affected by the potential sweep rate (m) and maximum cathodic current density (i c ) The ratio of Zn and Ni in certain phases of Zn-Ni alloy was determined by the partial potentiodynamic stripping technique. Experimental data show that Zn-Ni alloy, containing 6.5 at.% Zn and 93.5 at.% Ni and dissolved in i a peak H (E [ 0.0 V), provides the black coloration of the Zn-Ni alloy.

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Pulse plating of Zn-Ni alloy coatings

Cited by 64 publications

References 7 publications

Electrodeposition of Zinc and Zinc Alloys

Electrodeposition of Zinc and Zinc Alloys

Deposition of Nanocrystalline Zinc-Nickel Alloys by D.C. Plating in Additive Free Chloride Bath

Influence of voltammetric parameters on Zn–Ni alloy deposition under potentiodynamic conditions

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