Yunny Meas

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.

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.

Electrochemical Deposition of Silver from a Low Cyanide Concentration Bath

The silver reduction process was studied in a new, low cyanide concentration solution in which the predominant species is the ion Ag(CN) 2 - and the pH is fixed by the presence of potassium pyrophosphate. The electrochemical reduction of silver occurs via an adsorbed electroactive species assumed to be Ag(CN) 2 - . The silver reduction appears to be a quasi-reversible process at 20°C, and its kinetic parameters are presented as well as the effect of temperature in a 10 to 60°C range ; silver reduction is fast when the temperature is high, and the activation energy was evaluated. Linear sweep voltammetry and the use of an electrochemical quartz crystal microbalance prove the existence of the adsorbed electroactive species and additional evidence was found by chronopotentiometry.

Electrochemical Incineration of Phenolic Compounds from the Hydrocarbon Industry Using Boron-Doped Diamond Electrodes

Electrochemical incineration using boron-doped diamond electrodes was applied to samples obtained from a refinery and compared to the photo-electro-Fenton process in order to selectively eliminate the phenol and phenolic compounds from a complex matrix. Due to the complex chemical composition of the sample, a pretreatment to the sample in order to isolate the phenolic compounds was applied. The effects of the pretreatment and of pH on the degradation of the phenolic compounds were evaluated. The results indicate that the use of a boron-doped diamond electrode in an electrochemical incineration process mineralizes 99.5% of the phenolic sample content. Working in acidic medium (pH = 1), and applying 2 A at 298 K under constant stirring for 2 hours, also results in the incineration of the reaction intermediates reflected by 97% removal of TOC. In contrast, the photo-electro-Fenton process results in 99.9% oxidation of phenolic compounds with only a 25.69% removal of TOC.

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.

Surface Activation of C-sp3 in Boron-Doped Diamond Electrode

C-sp2 (graphite) impurities are undesirable in synthetic diamond electrodes (C-sp3), because they can affect the electrochemical response. In this work, we demonstrate that C-sp3 surfaces can be activated successfully by applying an anodic current density corresponding to sufficiently high potential where the hydroxyl radicals (●OH) are generated. The effectiveness of this activation process was verified by Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and cyclic voltammetry.

Electrodeposition of zinc in the presence of quaternary ammonium compounds from alkaline chloride bath

Abstract The effects of several quaternary ammonium compounds on electrodeposition of zinc onto AISI 1018 carbon steel were studied in an alkaline zincate electrolyte. Tetraethylammonium, tetrabutylammonium, N-benzyltriethylammonium and N-benzyl-3-carboxyl pyridinium cations were examined. The electrochemical behavior and the inhibition of dendrite formation are related to the structure of the ammonium compounds. The presence of either long-chain aliphatic groups or aromatic groups, i.e., with tetrabutylammonium hydroxide (TBAOH) or N-benzyltriethylammonium chloride (NBT) exerts a more effective inhibition of dendrite formation. N-benzyl-3-carboxylpyridinium (3NCP) and tetraethylammonium hydroxide (TEAOH) additives lead to slightly deformed deposit morphology. Crystallographic measurements of the zinc deposits revealed a highly oriented deposit formed in the presence of 3NCP, which favors the dense atomic packing basal plane (002). The presence of TEAOH diminishes slightly the peak of plane (002) and introduces some pyramidal (101) orientation. Addition of NBT or TBAOH favors the formation of low-atomic packing prismatic planes. Additives that increase the overpotential for Zn(II) reduction tend to promote the formation of high-energy low-atomic packing crystallographic planes. Comparison of the effects of these ammonium compounds indicates that the observed effects are related to the hydrophobic and steric interactions introduced to the interface by the size and structure of the ammonium compounds.