Uma célula eletroqu��mica de fluxo para modifica����o permanente de tubo de grafite empregado em absor����o at��mica

A flow cell assembled on the original geometry of a graphite tube to achieve permanent chemical modifier is proposed. The graphite tube operates as the working electrode. A stainless steel tube, positioned downstream from the working electrode, was used as the auxiliary electrode. The potential value applied on the graphite electrode was measured against a micro reference electrode (Ag/AgCl) inserted into the auxiliary electrode. Palladium solutions in acetate buffer (100 mmol L-1, pH = 4.8), flowing at 0.5 mL min-1 for 60 min was used to perform the electrochemical modification. A mercury solution (1 ng) was used to evaluate the performance of the permanent palladium modifier.

Estudos de prote����o da célula de saccharomyces cerevisiae para utiliza����o em rea����es de redu����o em meio org��nico

New methodologies for protection of Saccharomyces cerevisiae (FP) cells when supported in montmorillonite K10 (K10), recovered or not with gelatin (G) and in the presence or absence of sucrose (S) are presented. These systems were used for the enantioselective reduction of ethyl acetoacetate and a-chloroacetophenone in hexane, under FP/K10/G/S and FP/S at 20��C during 24 hours, affording S-(+)-ethyl-3-hydroxybutanoate in 100% conversion and 99% ee, and R-(-)-2-chloro-1-phenylethanol 79% and 78% ee at 20 and 30 ��C, respectivelly.

Constru����o e avalia����o de célula de fluxo para estudo da tens��o interfacial din��mica da interface fluxo l��quido - s��lido por despolariza����o da fluoresc��ncia

A simple low-cost flow cell was developed, built and optimized in order to observe dynamic interfacial tension of continuous flow systems. Distinct materials can be used in one of the cell walls in order to observe the intermolecular forces between the flowing liquid and the chemical constitution of the walls. The fluorescence depolarization was evaluated using Rhodamine B as fluorescent probe seeded in ethylene glycol. The effects of the positioning angles on the data acquired across the cell are reported. The reproducibility of the data was evaluated with a spectrometer assembled in-house and the relative standard deviation was below 3%.

Montagem de um sistema para medidas galvanost��ticas simult��neas em mais de uma célula

The present work deals with the design and construction of an equipment for muti-cell accelerated stability test measurements (AST) of dimensionally stable anodes (DSA). The equipment was built using only components that were available in the laboratory. Measurements of three electrochemical cells can be performed using the developed software. The acquisition time interval and the cut-off potencial can be set by the user. Experimental data for RuO2 electrodes obtained with the built equipment are in agreement with the literature.

Avalia����o da efici��ncia de uma célula a combust��vel estacion��ria de ��cido fosf��rico

Operation and performance of a commercial PAFC power plant were analyzed. Processes influencing energy conversion efficiency were studied in each module of the fuel cell power plant. The main processes were simulated using mass and energy balance equations, and the results were validated by means of experimental data. It was concluded that the electrical efficiency is higher in comparison with microturbines. The main result achieved is a better understanding of balance of plant processes, knowledge necessary for fuel cell power plant development.

Efeito dos di��xidos de enxofre e de nitrog��nio no desempenho de uma célula a combust��vel de membrana de interc��mbio de pr��tons

There is presently much interest in the clean and efficient generation of energy by proton exchange membrane fuel cells (PEMFC), using hydrogen as fuel. The generation of hydrogen by the reforming of other fuels, anaerobic fermentation of residual waters and other methods, often produce contaminants that affect the performance of the cell. In this work, the effect of gaseous SO2 and NO2 on the performance of a H2/O2 single PEMFC is studied. The results show that SO2 decreases irreversibly the performance of the cell under operating conditions, while NO2 has a milder effect that allows the recovery of the system.

Determina����o espectrofotom��trica em fluxo de cloro em ��gua usando célula de longo caminho ��ptico e multicomuta����o

A multicommuted method for determination of chlorine in water samples using a 100-cm cell was developed. In this method, orto-Tolidine reacts with chlorine and the product was monitored at 438 nm. The analytical curve for chlorine was linear in concentration range from 1.34x10-6 to 2.01x10-5 mol L-1 with a detection limit of 9.40x10-8 mol L-1. A sampling rate of 45 h-1and a RSD of 1.0 % (n = 15) were obtained. The method was applied with success for chlorine determination in six water samples.

Desenvolvimento de conjunto membrana-eletrodos para célula a combust��vel de metanol direto passiva

Direct methanol fuel cells (DMFCs) without external pumps or other ancillary devices for fuel and oxidant supply are known as passive DMFCs and are potential candidates to replace lithium-ion batteries in powering portable electronic devices. This paper presents the results obtained from a membrane electrode assembly (MEA) specifically designed for passive DMFCs. Appropriated electrocatalysts were prepared and the effect of their loadings was investigated. Two types of gas diffusion layers (GDL) were also tested. The influence of the methanol concentration was analyzed in each case. The best MEA performance presented a maximum power density of 11.94 mW cm-2.

Constru����o de célula eletroqu��mica para observa����o de amostras in situ em estereomicrosc��pio

The electrochemical study of glass like tungsten oxide derivatives requires the construction of special electrodes due to the fact that these glasses are not conductive. Electrodes modified with WO3 change their color when submitted to some potential perturbation. The color change of the electrochromic materials was observed in situ by coupling an electrochemical cell to a stereomicroscope. The constructed cell is versatile and may represent a great contribution to the electrochemical studies of materials, especially in the systems where it is interest to observe the working electrode surface during the electrochemical experiment.

Constru����o de uma célula de g��s de baixo custo para an��lise no infravermelho

Infrared spectroscopy is a versatile technique used for qualitative and quantitative determination of all types of molecular species. As far as analysis of confined or flowing gases is concerned, different types of cell can be found in the market, but they are often very expensive. This study describes the construction of a very efficient gas cell with good reproducibility for qualitative infrared analysis of confined or flowing gases, using easily available and low-cost materials.

Constru����o de uma célula-autoclave para medidas eletroqu��micas a altas temperaturas

Measurements at high temperature using liquid solutions require special cells and materials which are able to support the temperature and pressure developed inside. The constructed cell was designed to support pressures up to 20 bar, temperatures relatively high up to around 200 ��C, depending on the pressure developed inside the system. It also supports aggressive solutions since its inner wall is made of Teflon. The electrolyte has no contact with the metallic body of the cell. Then, it is supposed that this work represents a great contribution to the electrochemical studies of materials in solutions at high pressure and temperature

A utiliza����o de etanol em célula a combust��vel de ��xido s��lido

This work reports a review on the status and technical feasibility of the application of ethanol as fuel for Solid Oxide Fuel Cells (SOFC), presenting both external reform and cell with direct utilization of ethanol. Based on this survey, both experimental results and mathematical modeling indicated the technical feasibility of power generation by ethanol SOFC, with cell units producing 450 mW/cm��, sufficient for scale up to large stationary plants. The quantitative assessments in the literature show this field to be promising for researchers and private sector investment as well being a strategic technology for government policy in the short and long term.

AVALIA����O DE PROPRIEDADES F��SICAS E QU��MICAS DE ELETRODEP��SITOS DE Ni-W-P OBTIDOS EM C��LULA DE HULL

Ni–W–P electrodeposits were synthesized in a Hull cell in order to simulate the obtainment under industrial conditions. Complete coverage of panels was accomplished by applying total currents of 1.0 and 2.0 A. Panels obtained with a current of 1.0 A appeared brighter. The best compositional uniformities, as determined by Energy Dispersive Spectrometer (EDS) occurred in the current density ranges of 0.6 to 3.0 A dm−2 and 1.6 to 6.0 A dm−2 obtained with 1.0 and 2.0 A, respectively. However, the best morphological characteristics, as determined by Scanning Electro Microscope (SEM), were observed in those obtained with a total current of 1.0 A. Analysis of corrosion resistance by Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Linear Polarization (PLP) in NaCl have shown significant variations in the amount of corrosion potential, polarization resistance, and even total impedance. The alloys exhibited amorphous character (XRD) and crystallized above 400 ��C to Ni and Ni3P phases, and possibly Ni–W, with a subsequent increase in hardness. The results suggest that under industrial conditions, current density variations due to the large and complex geometric shapes of substrates lead to formation of distinct alloys. Furthermore, these materials are potential substitutes for chromium deposits in many applications.

Estabilidade do ant��geno de célula total de Brucella abortus para uso no diagn��stico sorol��gico da brucelose bovina pela rea����o de fixa����o de complemento

A rea����o de fixa����o de complemento �� um dos testes usados no diagn��stico confirmat��rio da brucelose bovina, e para sua realiza����o emprega-se o mesmo ant��geno usado na prova de soroaglutina����o lenta, por��m n��o foi poss��vel encontrar na literatura estudos sobre a estabilidade desse ant��geno para uso na prova de fixa����o de complemento, de modo a estabelecer um prazo de validade para o mesmo. Por isso, esta investiga����o teve por objetivo avaliar a estabilidade do ant��geno de célula total de Brucella conservado sob refrigera����o, para uso na rea����o de fixa����o de complemento. Analisaram-se 14 partidas de ant��geno, preparado com Brucella abortus amostra 1119/3 e padronizado para uso na prova de soroaglutina����o lenta, com tempo de fabrica����o variando de 9 meses a 23 anos e 11 meses. Testaram-se 167 soros bovinos com t��tulos vari��veis de anticorpos contra Brucella, adotando-se a t��cnica com incuba����o a 37��C nas duas fases da rea����o e 5 unidades hemol��ticas 50% de complemento. Considerou-se como positivo o soro com pelo menos 25% de fixa����o de complemento na dilui����o 1:4. Compararam-se os resultados obtidos com as 13 partidas de ant��geno com aqueles obtidos com a partida com 9 meses de fabrica����o, usando o teste de chi2 de McNemar e o coeficiente kappa. A grande maioria dos soros apresentou resultados muito pr��ximos quando testados com as diversas partidas de ant��geno, e n��o se observou rela����o entre tempo de fabrica����o do ant��geno e diferen��as nos resultados obtidos.