Electrochemical Cementation of Copper onto Zinc

International audienceActual interpretation of the enhancement of Cu/Zn cementation kinetics by a “cement critical specific mass” is reconsidered. Working with a rotating disk electrode and varying the initial concentration of copper and zinc ions over a large range, we show that copper deposit is not responsible for the kinetic transition. First, cement peeling off does not change the delay for the appearance of the second stage and the amplitude of the kinetic transition is a function of the initial concentration of zinc ions. Furthermore, the first stage duration decreases, and even this stage may disappear, on a substrate precorroded in the same solution replacing copper ions by Ce(IV) ions. On the other hand, the stage duration increases if a constant polarization is imposed to the substrate. Operating conditions at the Zn2+/Zn interface appear to be the essential parameter. Discussion includes morphological examinations

Validity of the (Z+1) ion-core approximation for deep and shallow levels as studied by the extended energy-loss fine-structure technique

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Precipitation variance analysis of the Taboão river watershed (RS)

O objetivo deste trabalho foi determinar a distribuição de probabilidade que melhor se ajuste à variância da série histórica de precipitações diárias em seis estações na bacia hidrográfica do rio Taboão, região noroeste do Estado do Rio Grande do Sul, durante um período de sete anos, distribuídos nos intervalos de 05/05/03 a 09/05/06 e 01/07/07 a 04/06/11. Para isso, foram determinados os padrões de agrupamento, em relação à variância. Na comparação do ajustamento das distribuições observadas da variável variância com as distribuições teóricas, foi utilizado o teste de ajustamento de Shapiro-Wilk. Determinadas as distribuições Log Pearson e Gama, realizou-se o agrupamento das estações de acordo com sua variância pela distância Euclidiana através do método de Ward. Os agrupamentos propostos foram verificados através da ANOVA e teste de Tukey, resultando que os agrupamentos propostos não se sustentavam, demonstrando a homogeneidade entre a média das variâncias das séries históricas das estações analisadas. Os resultados obtidos permitem concluir que a precipitação na bacia do rio Taboão é homogênea.The objective of this paper was to determine the probabilistic distribution that fits the variance of the precipitation data obtained in six stations located at Taboão river watershed, northwestern region of Rio Grande do Sul State, during a seven years period from 5/May/2003 to 9/May/2006 and from 1/July/2007 to 4/June/2011. Group patterns were determined in relation to the variance. The Shapiro-Wilk test was used for a comparison between the observed and theoretical distributions of the variance. After determining the Log Pearson and Gama distribution, the grouping of stations was performed based on theirs variances by the Euclidean distance using the Ward’s method. The evaluation with the ANOVA and Tukey’s test showed that the proposed groupings were not sustainable, which implies the homogeneity among the mean values of the historical series variances from the six analyzed precipitation stations. The obtained results permit to conclude that the precipitation is homogeneous in the Taboão river watershed

Electrocristallization of copper from non-cyanide alkaline solution containing glycine

International audienceA thermodynamic study by means of potential-pH (Pourbaix type) and species repartition diagrams is presented in this work with the view to better understand the electrodeposition of copper from noncyanide alkaline solution containing glycine. The parameters studied were glycine concentration,temperature and scanning rate. The voltametric studies also indicate control by diffusion for the copper electrodeposition. In order to compare the effect of the temperature, we measured the kinetic parameters: charge transfer coefficient (αc) and rate constant ( ). The morphological study indicatedthat the temperature plays a role on grain size of the copper coating obtained. X-ray diffraction studies showed that the deposit obtained at 40°C has a crystallite structure, which differs from that found at 25°

Electrodeposition of copper from non-cyanide alkaline solution containing tartrate

International audienceA thermodynamic study of the aqueous copper(II)-tartrate-chloride system is presented in this work with the view to better understand the electrodeposition of copper from a non-cyanide alkaline solution. Additionally, an electrochemical study onto the initial stages of copper electrodeposition on glassy carbon electrode (GCE) is presented in this work. Upon scanning in the negative direction, two cathodic peaks were observed, which are associated with two reduction processes with different energies that involve the same species of copper (II). Analysis of chronoamperograms obtained indicates that the nucleation mechanism involved during the initial stages of Cu deposition is consistent with the model of 3D diffusion-controlled nucleation. The morphological study indicated that the potential plays a role on grain size and shape of the copper coating obtained. Non-linear fitting methods were applied to obtain the growth and nucleation kinetic parameters from theoretical equations proposed to describe this system

Nucleation and Growth of Zinc from Chloride Concentrated Solutions

International audienceThe 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 we study the influence of the zinc chloride ZnCl2 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 ZnCl2 reduction were evaluated from cyclic voltammetry experiments. The nucleation process was analyzed by comparing the transients obtained with the known dimensionless (i/i m)2 vs. t/t m reponse for instantaneous or progressive nucleation. The results show that the nucleation process and the number density of sites are dependent on ZnCl2 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 ZnCl2 concentration. Evaluation of the corrosion resistance reveals the influence of the nucleation process on the subsequent corrosion resistance of the zinc deposits

EXTENDED FINE STRUCTURES IN THE AUGER SPECTRA

Les structures fines observées dans le spectre Auger de divers matériaux (Fe, Co, Ni, Cu) ont été exploitées avec le formalisme d'EXAFS. Leurs transformées de Fourier permettent de déduire la distance interatomique des premiers voisins qui est en bon accord avec les résultats obtenus par la technique EXAFS effectuée à l'aide du rayonnement synchrotron.We have observed extended fine structures above core-valence-valence Auger transitions on several materials (Fe, Co, Ni, Cu). We analyse these oscillating structures following the same formalism used in EXAFS. The lattice parameters obtained by Fourier transform are in good agreement with those deduced from synchrotron radiation EXAFS data