G. Trejo

Influence of polyethoxylated additives on zinc electrodeposition from acidic solutions

The influence of several ethoxylated additives (ethyleneglycol and polyethyleneglycol polymers of different molecular weights) on the nucleation, growth mechanism and morphology of zinc electrodeposited from an acidic chloride bath is reported. The electrochemical study was carried out using cyclic voltammetry, inversion potential and chronoamperometric techniques. The dimensionless graphs model was applied to analyse the nucleation process and the results showed that the studied additives have a blocking effect on the electrodeposition of zinc. This effect occurs in the first stages of the nucleation process and is dependent on the molecular weight of the additive. Changes induced by the presence of additives in the morphology and grain size of the deposits were observed using SEM analysis. Results show that the presence of additives modifies the nucleation process and determines the final properties of the deposits.

Nucleation and Growth of Zinc from Chloride Concentrated Solutions

The electrodeposition of metals is a complex phenomenon influenced by a number of factors that modify the rates of nucleation and growth and determine the properties of the deposits. In this work the authors study the influence of the zinc chloride (ZnCl{sub 2}) concentration on the zinc nucleation process on glassy carbon, in a KCl electrolyte under conditions close to those employed in commercial acid deposition baths for zinc. The electrochemical study was performed using cyclic voltammetry and potentiostatic current-time transients. The charge-transfer coefficient and the formal potential for ZnCl{sub 2} reduction were evaluated from cyclic voltammetry experiments. The nucleation process was analyzed by comparing the transients obtained with the known dimensionless (i/i{sub m}){sup 2} vs. t/t{sub m} response for instantaneous or progressive nucleation. The results show that the nucleation process and the number density of sites are dependent on ZnCl{sub 2} concentration. Scanning electron microscopy analysis of the deposits shows that the deposits are homogeneous and compact although a change in the morphology is observed as a function of ZnCl{sub 2} concentration. Evaluation of the corrosion resistance reveals the influence of the nucleation process on the subsequent corrosion resistance of the zinc deposits.

Effect of benzylideneacetone on the electrodeposition mechanism of Zn–Co alloy

The influence of benzylideneacetone (BA) on the mechanism of Zn–Co alloy electrodeposition onto AISI 1018 steel was studied in chloride acidic solutions. Results indicate that BA modifies the exchange current densities of zinc and cobalt such that the alloy is electrodeposited via a normal codeposition mechanism. Analysis of the deposits by Auger spectroscopy and X-ray diffraction shows that BA increases the cobalt concentration in the electrodeposited alloys and gives deposits with a constant concentration profile of both Zn and Co. BA also inhibits the formation of zinc hydroxide in the initial deposition stages, which supports the proposed mechanism of normal codeposition. Finally, it is shown that BA modifies the morphology of the deposits by inducing a reduction in the cluster size, leading to compact, smooth and shiny coatings.

Effects of organic additives on zinc electrodeposition from alkaline electrolytes

This work reports the effects of four organic compounds (referred to as levelers) on the electrodeposition of Zn on steel from alkaline free-cyanide electrolytes. The additives tested included polyvinylalcohol (PVA) and the condensation products of epichlorhydrin with amines, called polyamines (PAs), that were synthesized using an aliphatic amine (PA-I, from diethylamine and PA-II from diethylamine-triethylamine), and a heterocyclic quaternary imidazolium molecule (PA-Imid, from imidazole). These compounds were evaluated in the absence and in addition to a quaternary ammonium brightener, N-benzyl-3-carboxylpyridinium chloride (3NCP). The imidazole derivative-based polyamine (PA-Imid) causes greater inhibition of the zinc reduction process than the aliphatic polyamine, and more cathodic overpotential is necessary to promote massive metal deposition. The morphology of the deposits is modified when polyamines are added to the bath; more compact and smaller crystals are obtained with PVA as well as with polyamine PA-I. The addition of PA-II as well as PA-Imid yields crystals growing perpendicular to the substrate. The addition of 3NCP with PVA, PA, or PA-Imid increased the deposition overpotential and modified the morphology by diminishing the grain size. In the absence of additives, crystallographic orientation favored the basal Zn(002) with high atomic packing. The addition of the levelers favored the high-angle pyramidal Zn(101) with low atomic packing. The combination of the levelers with (3NCP) favored the prismatic Zn(100) crystallographic orientation. Additives decrease the size of zinc crystals and tend to increase the energy of lattice favoring the growth of pyramidal and prismatic planes.

Temperature Effect on the Electrocrystallization Processes of Gold in Ammoniacal Medium

Gold electrodeposition has been studied on glassy carbon from Au(I) ammoniacal solution. The current transients obtained from potential step perturbations show a typical metallic nucleation growth controlled by diffusion ; this process is influenced by adsorption of the different chemical species on the surface. Diffusion coefficients were calculated for Au(I) at different temperatures. It was also found that the increase in the temperature provokes the modification of the nucleation mechanism.

Electrodeposition of gold in ammoniacal medium: influence of substrate and temperature

Gold electrodeposition was studied on glassy carbon and platinum electrodes from Au(1) ammoniacal solution. The current transients obtained from potential step perturbations, show a typical metallic nucleation growth controlled by diffusion. This process is influenced by adsorption of the different chemical species on the surface. Change in the type of nucleation and morphology of the deposit was observed when the nature of the substrate was changed. It was also found that increase in temperature produces modification of the nucleation mechanism.

Electrochemical growth of Au architectures on glassy carbon and their evaluation toward glucose oxidation reaction

Arrow-like, flower, splintery flower-like and pin wheel Au architectures were obtained using cyclic voltammetry (I), differential pulse amperometry (II), square wave voltammetry (III) and second harmonic AC voltammetry (IV) as electrochemical methods of synthesis, named systems I, II, III and IV respectively. Architecture sizes were 610, 380, 590 and 480 nm, meanwhile crystal sizes were 48, 76, 120 and 210 nm, respectively. XRD patterns showed that systems I, III and IV preferentially exhibited the (111) plane and system II preferentially exhibited the (200) plane. The catalytic properties of the architectures were tested employing D-(+)-glucose at 10, 50 and 100 mM, where the results showed that two processes occur in the glucose electrooxidation: at ∼−0.2 V vs. NHE, glucose is oxidized to gluconolactone, and after at ∼0.3 V vs. NHE the successive oxidation of the gluconolactone by-product were carried out. Systems with the (111) preferential plane favor gluconolactone oxidation; while system II with the (200) plane enhanced glucose oxidation toward the gluconolactone by-product. Also, system II showed a higher current density with 26.4 mA cm−2 at 100 mM glucose.

Effect of Quaternary Ammonium Compounds on the Electrodeposition of ZnCo Alloys from Alkaline Gluconate Baths

The effect of quaternary ammonium compounds on the electrodeposition of ZnCo alloys from an alkaline chloride-gluconate electrolyte was studied. A thermodynamic analysis was performed which indicated that Zn(OH) 2- 4 should be the predominant zinc species, whereas for cobalt the mixed hydroxy-gluconate complexes CoL 3 (OH) 2 and CoL(OH) 2 are expected to be prevalent. The electrodeposition of the alloy from this alkaline medium was found to be anomalous, but increasing the cobalt content in the bath caused the cobalt content in the deposit to increase. The effects of three quaternary ammonium compounds, N-benzyl-3-carboxylpyridinium chloride (3NCP), N-benzyl-triethylammonium chloride, and tetraethylammonium hydroxide, on the electrochemical behavior of ZnCo deposition were studied. The incorporation of these additives in the electrolytes modified the composition, morphology, and crystallographic structure of the ZnCo-alloy deposits. Cyclic voltammetry indicated the formation of several alloy phases as cobalt was added to these zinc baths. 3NCP had the greatest impact on the process, limiting the Co content and changing the structure of the deposit.

Micromorphological characterization of zinc/silver particle composite coatings

The aim of this study was to evaluate the three‐dimensional (3D) surface micromorphology of zinc/silver particles (Zn/AgPs) composite coatings with antibacterial activity prepared using an electrodeposition technique. These 3D nanostructures were investigated over square areas of 5 μm × 5 μm by atomic force microscopy (AFM), fractal, and wavelet analysis. The fractal analysis of 3D surface roughness revealed that (Zn/AgPs) composite coatings have fractal geometry. Triangulation method, based on the linear interpolation type, applied for AFM data was employed in order to characterise the surfaces topographically (in amplitude, spatial distribution and pattern of surface characteristics). The surface fractal dimension Df, as well as height values distribution have been determined for the 3D nanostructure surfaces. Microsc. Res. Tech. 78:1082–1089, 2015.

ZnCo-Electrodeposition Baths Based on Alkaline Chloride-Gluconate Electrolytes Containing Quaternary Ammonium Compounds

This paper reports a study of the electrodeposition of Zn–Co alloys from alkaline chloride-gluconate electrolytes containing quaternary amines as additives. The effects on the electrochemical behavior of ZnCo deposition of two quaternary ammonium compounds, N -benzyl-3-carboxylpyridinium chloride (3NCP) and a polyamine (PA) were investigated, and the influence of the cobalt content in the plating bath was studied. The mechanism of electrodeposition of the ZnCo alloys in these alkaline media was anomalous. The two additives caused different inhibition degrees of the cathodic process, the effect of PA being stronger. Also, the results first showed that the cobalt complexes shift the cathodic peak of ZnCo electrodeposition due to de-adsorption of cobalt-gluconate complexes. According to the results, the adsorption of PA partially inhibited the zinc–alloy deposition, and the deposition of ZnCo occurred in two voltammetric steps. The incorporation of the organic additives in the bath modified the composition, morphology, and crystallographic structure of the ZnCo deposits, with PA forming compact grains oriented preferentially to high index pyramidal and prismatic textures and 3NCP producing more highly oriented, compact, and fine-grained deposits. The combination of the two additives induced a synergistic effect, producing deposits whose morphology was refined, with crystals formed on the nanometric scale with a prismatic orientation.