Electrodeposition, zinc

In electroplating industrial iron metals, zinc metal electrodeposition is accompanied by the formation of Zn-Ni, Zn-Co, and Zn-Fe alloys, where zinc electrodeposition is known to be anomalous in some cases. The ratio of zinc metal to iron metal in those alloys is sometimes higher than that of the electroplating bath solution, and zinc ions occasionally deposit at potentials positive to the equilibrium potential of zinc ions on zinc metal although is very negative to the equilibrium potentials of iron metals. It can be seen from the study of underpotential deposition of zinc ions " that this is not anomalous, but could be explained as an underpotential deposition phenomenon, to be clarified in further work. 

The influence of ethylene glycol and water content on the zinc electrodeposition from ZnBr2-Tethyl-3-methylimidazolium bromide (EMIB) was investigated [178]. The structure of the deposits was dependent on the mole ratio of ZnBr2 to EMIB, water concentration, and presence of ethylene glycol. 

Wang etal. [213] investigated the effect of bismuth ion and tetrabutylammonium bromide (TBAB) on the dendritic growth of zinc in alkaline zincate solution on Zn electrode. It was found that this growth is inhibited by the synergistic effect of Bi(III) and TBAB at higher overpotentials. The zinc electrodeposits... 

Fig. 6 Zinc electrodeposits at = —0.200 V (a) from the alkaline solutions, (b) from the alkaline solutions containing 0.1 g Bi(lll) [213], (c) as in b but with addition of 0.02 g TBAB.

Using the rotating disk electrode, Seliv-anov et al. [214] have investigated the zinc electrodeposition from zincate electrolyte containing polyethylene polyamine. The limiting current density of [Zn(OH)4] ion diffusion through a film of zinc oxides and hydroxides is shown to be responsible for the formation of dark zinc deposits in the potential range from —1.33 to —1.47 V. 

Zinc electrodeposition on zinc electrode with rough surface exhibited potential oscillations accompanied by fern-leafshaped deposits, contrary to the case... 

The influence of Pb + ions on the kinetics of zinc electrodeposition on Zn electrode in acidic sulfate electrolyte was discussed [217] in terms of a reaction model involving hydrogen adsorption and evolution, a multistep mechanism for zinc deposition and the overall reaction for zinc dissolution. The strongly adsorbed Pbads inhibited all the reactions taking place on the zinc electrode. 

Trejo etal. [225, 226] have also investigated the influence of several ethoxylated additives (ethyleneglycol and PEG polymers of different molecular weights) on the nucleation, growth mechanism, and morphology of zinc electrodeposited on GG from an acidic chloride bath. Results have shown that the presence of additives modifies the nucleation process and determines the properties of the deposits. 

Chronoamperometric experiments on zinc electroreduction on GC from acetate solutions showed that the nucleation density increases with increase of temperature [44]. M oreover, the nucleation rate constant is always very large, equal to 1.41 x 10 s . This indicates that the mechanism of zinc electrodeposition on the GC electrode follows a three-dimensional instantaneous nucleation and growth model within the controlled temperature range. 

The same mechanism of zinc electrodeposition on the GC electrode was observed in sulfate, chloride, and acetate ion solutions [227]. The anions mainly affected the nucleation densities during zinc deposition, which resulted in a different surface morphology. The nucleation rate constant was the same in the chloride and sulfate solutions and was equal to 1.22 x 10 s h In the presence of acetate and chloride ions, the deposited zinc film tends to grow in a multilayered pattern, while in sulfate solution, the zinc deposition forms irregular grains. A new approach to the estimation of zinc electrocrystallization parameters on the GC electrode from acetate solutions was described by Yu et al. [228]. 

The influence of quaternary aliphatic polyamine (QAA) on zinc electrodeposition from an alkaline non-cyanide bath was investigated [230]. In the presence of QAA, the exchange current density decreased and zinc deposit had a smaller grain size. 

An experimental study of zinc electrodeposition on copper wire from 0.1 M zincate solution in 1.0 M KOH was presented by Simicic et al. [232]. A possible mechanism of the formation of spongy zinc deposits was considered. Also, it was shown that in the case of a square-wave pulsating overpotential regime, the deposit was less... 

Also, the influence of benzylideneace-tone on the mechanism of zinc electrodeposition on Pt electrode in a chloride acidic bath was studied [234]. 

Mechanism of zinc electrodeposition on steel in acidic solution of zinc chloride was investigated [408] as a function of pH, grain-refining additives, and current density. 

Zinc electrodeposition was studied using three-dimensional electrodes [413,... 

The effect of potential on the cathodic efficiency of a zinc electrodeposition in a cyanide-free alkaline bath was also investigated [416]. 

O. Devos, O. Aaboubi, J. P. Chopart, E. Merienne, A. Olivier, C. Gabrielli, and B. Tribollet, "EIS Investigation of Zinc Electrodeposition in Basic Media at Low Mass Transfer Rates Induced by a Magnetic Eield," Journal of Physical Chemistry B, 103 (1999) 496-501. 

The same authors also investigated zinc electrodeposition from acidic and alkaline electrolytes without and with inhibitors [6.82-6.86]. It was suggested that the deposition mechanism involves an autocatalytic step... 

Trejo, G., Ruiz, H., Borges, R.O., and Meas, Y. 2001. Influence of polyethoxylated additives on zinc electrodeposition from acidic solutions. Journal of Applied Electrochemistry 31, 685-692. 

FIGURE 20.5 A typical cathodic polarization curve of zinc electrodeposition in the solution used for this study. 

B.K. Thomas and D.J. Fray, The Effect of Additiyes on the Morphology of Zinc Electrodeposited from a Zinc Chloride Electrolyte at High Current Densities , Journal of Applied Electrochemistry. Vol. 11, 1981,677-683. 

---