Emilse Maria Agostini Martini

Corrosion behaviour of iron and AISI 304 stainless steel in tungstate aqueous solutions containing chloride

O comportamento do ferro e do aco inoxidavel AISI 304 frente a corrosao em solucao aquosa de tungstato de sodio em presenca de cloreto foi investigado usando as tecnicas de voltametria ciclica, medidas de potencial de circuito aberto e impedância eletroquimica. Os resultados mostraram que a acao inibidora do ânion tungstato esta relacionada com sua adsorcao sobre a superficie eletrododica e depende marcadamente da presenca de oxigenio dissolvido no meio. Filmes formados por polarizacao anodica a baixas velocidades de varredura de potencial e rotacao do eletrodo sao mais estaveis permitindo um decrescimo na taxa de corrosao. Medidas de impedância eletroquimica em potencial de circuito aberto mostraram que a acao inibidora do tungstato e consideravelmente favorecida em tempos de imersao prolongados.

Transport Properties of Binary Solutions Containing the Ionic Liquid BMI.BF4 and Ethylene Glycol

The ionic conductivity values of the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate (BMI.BF4) and ethylene glycol (EG) electrolytes in different concentrations and over a wide temperature range were determined. The results are discussed in terms of the interactions between the cations and anions of the ionic liquid and the organic solvent. The temperaturedependence of the ionic conductivity for BMI.BF4, as well as solutions containing BMI.BF4 and EG as electrolytes, in the temperature range of 248-358 K, obeys the Vogel-Tammann-Fulcher equation. The highest ionic conductivity was 42 mS cm-1 obtained with a solution of BMI.BF4 in EG at a molar fraction of 0.50 (358 K) due to the high ionic mobility. The critical micellar concentration (cmc) of 0.1 mol L-1 determined through the ionic conductivity indicates that BMI.BF4 behaves as a weak electrolyte above this value. The results obtained indicate that binary solutions based on BMI.BF4 and EG are appropriate for use in technological applications, such as capacitors.

Passivation of iron in solutions containing borate using rotating ring-disc measurements

Investigou-se o comportamento eletroquimico do ferro em solucoes neutras de perclorato de sodio contendo pequenas concentracoes de borato de sodio, atraves da tecnica de voltametria ciclica e empregando-se eletrodo rotatorio de disco e anel. Nas solucoes de perclorato, a passivacao do ferro ocorreu apos o pico anodico correspondente a zona ativa, no qual foi observada a dissolucao de especies Fe 2+ e Fe 3+ . Quando e adicionado borato a solucao, tanto a densidade de corrente do pico anodico quanto a quantidade de especies ativas de ferro soluveis diminuem. Para uma concentracao constante de perclorato e borato, o aumento do pH do meio mostrou ser menos efetivo na promocao da passivacao do ferro do que a presenca de borato. Os resultados demonstraram que a interacao entre o ion borato e a superficie eletrodica ocorre por adsorcao quimica, de acordo com a isoterma de Langmuir. The electrochemical behavior of iron in neutral solutions of perchlorate and low borate concentrations was investigated using cyclic voltammetry and the rotating ring-disc electrode techniques. In solutions containing just perchlorate, iron passivation was observed at potentials higher than the potential of an anodic peak corresponding to the active range at which the dissolution of Fe 2+ and Fe 3+ species was detected. When borate is added to the solution, this anodic peak decreased as well as the amount of the active soluble species. The increase of pH, keeping the borate and perchlorate concentrations constant, was found to be less effective at promoting iron passivation than the increase of borate concentration. The results demonstrated that the interaction between borate ion and the electrode surface occurs by chemical adsorption according to the Langmuir isotherm.

Electrochemical behavior of nickel in electrolytes based on 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid for capacitor applications

Electrochemical studies were performed using Ni electrodes in solutions of a mixture of ethylene glycol or of γ-butyrolactone with 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid. The aim of the study was to evaluate the use of these systems in electrochemical double-layer capacitor. Cyclic voltammetry experiments showed a potential range at which the Ni electrode behaved as a polarizable electrode. Ni oxidizes at high anodic potentials. Inside the potential range without electrochemical activity, the capacitance and the solution resistance, which were evaluated by impedance electrochemical spectroscopy, were compared for the two solutions tested. Conductivity measurements of the electrolytes with different compositions were also acquired. The results of cyclic voltammetry indicated that the Ni has a wide electrochemical window and low current peak densities of oxidation in the γ-butyrolactone medium than in ethylene glycol medium. The γ-butyrolactone and 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid solutions had the highest conductivity values. Decreased 1-n-butyl-3-methylimidazolium tetrafluoroborate ionic liquid content in different solvent mixtures resulted in an increase in the capacitance value at the Ni/electrolyte interface. The highest capacitance values were obtained for Ni in ethylene glycol and 1-n-butyl-3-methylimidazolium tetrafluoroborate medium.

Um equipamento de eletroforese capilar com detecção condutométrica construído em laboratório

A new construction of a capillary electrophoresis instrument with a universal conductivity detector (oscillometric detector) is described. The performance of the electrophoresis equipment was evaluated through the separation and detection of inorganic anions and cations in aqueous solutions. The results reproduced those found in the literature for the investigated probe ions, showing an efficient separation and good repeatability.