R. Ortega

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.

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.

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.

Electrochemical Syntheses of Sodium Percarbonate in Aqueous Solution

The present research is focused on electrochemical production of sodium percarbonate as both the 2Na2CO3.3H2O2 form and the Na2C2O6 formulation. The routes to these two electrochemical syntheses from carbonate solution proceed through oxygen reduction at the cathode and electrochemical oxidation of water at the anode, respectively. We have studied each of these reactions separately, potentiostatically for the cathodic reaction and galvanostatically for the anodic side. In both cases, the effects of experimental conditions, such the addition of a stabilizer or the use of a cation-permeable membrane, have been investigated; products were analyzed for % active oxygen content in dry samples according standard methods.