Sample records for electrochemistry
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1

Eletroquímica de flotação de minerais de sulfetos de chumbo e zinco/ Electrochemistry of lead and zinc sulfide mineral flotation

Alexandrino, Júnia Soares; Rocha, Geriane Macedo; Russo, Mário Cabello; Peres, Antônio Eduardo Clark; Pereira, Carlos Alberto
2009-12-01

Resumo em português Esse trabalho foi realizado com amostras provenientes da mina de Morro Agudo, visando a verificar a influência do potencial Eh na flotação de chumbo e zinco. As amostras foram provenientes da britagem primária. Durante o processo de flotação, o potencial redox foi monitorado, continuamente, usando um eletrodo de platina. Nesse estudo, foram avaliados os efeitos da adição de sulfeto de sódio e sulfito de sódio na recuperação de galena e esfalerita na presença (mais) e na ausência de nitrogênio, como gás de flotação. Uma análise estatística dos resultados de recuperação foi feita através do software MINITAB. A interação do sulfeto de sódio com o gás nitrogênio diminui a recuperação de chumbo no concentrado e o gás nitrogênio, isoladamente, aumentou a recuperação de zinco no concentrado, para uma flotação composta por dois circuitos em série, recuperação da galena, seguida da esfalerita. Resumo em inglês The work was done with samples from the "Morro Agudo" mine and aimed to verify the influence of the pulp Eh potential on lead and zinc flotation. The samples were from the primary crushing. During the flotation process, the potential was continuously monitored by a platinum electrode. The effects of sodium sulfite and sodium sulfide on galena and sphalerite recovery in the presence and absence of nitrogen, as gas flotation, were evaluated. The software MINITAB was used fo (mais) r the statistical analysis of the recovery results. The interaction between sodium sulfide and nitrogen decreased the lead recovery and the nitrogen by itself increased the zinc recovery.

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2

Eletroquímica de latossolos brasileiros após a remoção da matéria orgânica humificada solúvel/ Eletrochemistry of Brazilian oxisols after removal of soluble organic matter

Dobbss, Leonardo Barros; Canellas, Luciano Pasqualoto; Alleoni, Luis Reynaldo Ferracciú; Rezende, Carlos Eduardo de; Fontes, Maurício Paulo Ferreira; Velloso, Ary Carlos Xavier
2008-06-01

Resumo em português A eletroquímica e a concentração de matéria orgânica nos horizontes superficiais de Latossolos correlacionam-se estreitamente. No presente trabalho, avaliaram-se as propriedades eletroquímicas do horizonte superficial de sete Latossolos brasileiros após a remoção das substâncias húmicas em meio alcalino. Os solos foram separados em dois grupos, segundo sua mineralogia, caulinítica e oxídica. O extrator NaOH 0,1 mol L-1 solubilizou substâncias húmicas corres (mais) pondentes a menos de 3 % da MO total, indicando forte adsorção específica do material orgânico à fração mineral. A extração de ácidos húmicos e fúlvicos foi capaz de inverter o sinal de carga da superfície; no entanto, o efeito mais acentuado da retirada das substâncias húmicas solúveis foi a perda da capacidade-tampão das cargas do solo. A capacidade da dupla camada elétrica, uma medida indireta desse poder-tampão, aumentou de 3 a 15 vezes depois da extração das substâncias húmicas alcalino-solúveis. Solos com mineralogia predominantemente oxídica apresentaram maiores valores do ponto de efeito salino nulo, da capacidade da dupla camada elétrica, além da diminuição na capacidade de troca de cátions do que aqueles de natureza caulinítica. Resumo em inglês Electrochemistry and organic matter concentrations in the surface horizons of Oxisols are closely related. This study evaluated the electrochemical properties in the surface horizon of seven Brazilian Oxisols after the removal of humic substances by alkaline extraction. Based on their mineralogy the soils were grouped as kaolinitic or oxidic. Less than 3 % of the total organic matter were soluble humic substances extractable by NaOH 0.1 mol L-1, indicating their strong sp (mais) ecific adsorption to the inorganic mineral sites. The removal of the humic and fulvic acids reversed the soil surface charge and also led to a marked loss in the buffering capacity of the soil charge. The electric double layer capacity, an indirect measure of this buffer capacity, increased 3 to 15 times after extracting humic substances. The point of zero salt effect and the electric double layer capacity values were higher and the cation exchange capacity was lower in the oxidic than in the kaolinitic soils.

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3

Eletroquímica das partículas coloidais e sua relação com a mineralogia de solos altamente intemperizados/ Electrochemistry of colloidal particles and its relationship with the mineralogy of highly weathered soils

Fontes, Maurício Paulo F.; Camargo, Otávio Antônio de; Sposito, Garrison
2001-09-01

Resumo em português O conhecimento das propriedades eletroquímicas das partículas minerais dos solos altamente intemperizados é imprescindível para o avanço dos estudos em diferente áreas da Ciência do Solo, como, Física, Manejo e Conservação, Fertilidade e Poluição do Solo. Nesse contexto, o comportamento das cargas superficiais e seu relacionamento com a mineralogia dos solos de carga variável é de importância fundamental para o entendimento e a melhoria da capacidade predit (mais) iva de diversos fenômenos, tais como dispersão e floculação de colóides, troca catiônica, adsorção de ânions, especialmente os fosfatos, adsorção de metais pesados, etc. Assim, essa revisão de literatura faz uma abordagem científica do tema "Eletroquímica das partículas coloidais e sua relação com a mineralogia de solos altamente intemperizados", na qual é contemplado o histórico da evolução do conhecimento nesse campo e os desafios para o aprofundamento das pesquisas futuras na área. As diferentes tendências e posicionamentos existentes na literatura sobre Pontos de Carga Zero (PCZs), Caracterização e Medição de Cargas, Nomenclatura e Simbologia de PCZs e Relacionamento entre Cargas e Minerais de solos altamente intemperizados são também apresentados. Conceituações básicas são revisitadas e conceitos novos ou pouco utilizados na Ciência do Solo são apresentados e discutidos, com o intuito de se melhorar o entendimento e aprimorar a interpretação de tão importante ramo da Química, Mineralogia e Poluição de Solos. Resumo em inglês The knowledge of the electrochemical properties of the mineral particles of highly weathered soils is indispensable for the advance of the studies in different Soil Science areas, like as, Soils Physics, Conservation and Management, Fertility and Pollution. In this context, the surface charge behavior and its relationship with the mineralogy of variable charge soils is of fundamental importance to the understanding and the improvement of the predictive capability of sever (mais) al phenomena, such as, floculation and dispersion of colloids, cations exchange, anion adsorption, specially phosphates, heavy metals adsorption, etc. Therefore, this literature review aims at to make a scientific approach of the topic "Electrochemistry of colloidal particles and its relationship with the mineralogy of highly weathered soils", in which, the historical evolution of the knowledge in this field is covered and the challenges to the development of the research in this area are raised. Different tendencies and views existing in the literature about Zero Points of Charge (ZPC), Charge Characterization and Measurement, ZPCs Terminology and Simbology and Relationship between Charge and Minerals of the highly weathered soils are also presented. Basic concepts are revisited and new or seldom used concepts in Soil Science are presented and discussed with the objective of improving the understanding and refining the interpretation of such important branch of the Soil Chemistry and Mineralogy field.

Scientific Electronic Library Online (Portuguese)

4

Determinação eletroquímica da capacidade antioxidante de sucos de frutas industrializados usando o CRAC assay/ Electrochemical determination of the antioxidant capacity of industrialized fruits juices using the CRAC assay

Ferreira, Rafael de Queiroz; Avaca, Luis Alberto
2008-01-01

Resumo em inglês Fruits juices are natural sources of several compounds that present antioxidant action. Together with the fruits, they contribute with almost 40% of the antioxidant capacity in a healthy diet avoiding and preventing diseases deriving from oxidative stress. The present study determined the antioxidant capacity of seven samples of industrialized fruits juices applying CRAC (Ceric Reducing/Antioxidant Capacity) assay, a new electrochemistry assay that evaluates, by means of (mais) chronoamperometric measurements, the ability of a sample in reducing species Ce4+ in acid media. At the end of the assay was obtained the following classification: cashew > guava > grape > mango > apple > orange > passion fruit.

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5

Investigação eletroquímica de alguns compostos organopaládio (ll): Determinação dos processos de redução do centro metálico em ciclopaladados/ Electrochemical investigation of some organopalladium(II) compounds. Determination of the metallic center reduction process in cyclopalladated complexes

ANANIAS, Sandra Regina; MAURO, Antonio Eduardo; NOGUEIRA, Vânia Martins; HADDAD, Paula Silvia; ALMEIDA, Eduardo Tonon de
2001-01-01

Resumo em português Investigou-se o comportamento eletroquímico dos dímeros ciclopaladados [Pd(dmba)(mi-X)]2 [X = Cl (1), NCO (2), NCS (3), CN (4)] (dmba = N,N-dimetilbenzilamina) e do monômero [Pd(dmba)(MeCN)2][NO3] (MeCN = acetonitrila). Os resultados experimentais mostraram redução de Pd(II) para Pd(I) para os compostos 1-3, enquanto que somente para 1 observou-se a redução de Pd(I) para Pd(0) em uma única etapa. O complexo 5 mostrou redução de Pd(II) para Pd(0). Observou-se que (mais) a estabilidade eletroquímica destes compostos diminuem na seguinte ordem: [Pd(dmba)(mi-CN)]2 (4) > [Pd(dmba)(mi-NCO)]2 (2) > [Pd(dmba)(mi-SCN)]2 (3) > [Pd(dmba)(MeCN)2][NO3] (5) > [Pd(dmba)(mi-Cl)]2 (1). Resumo em inglês The electrochemistry behaviour of compounds [Pd(dmba)(mu-X)]2 [X = Cl (1), NCO (2), NCS (3), CN (4)] and [Pd(dmba)(MeCN)2][NO3] (5) (dmba = N,N-dimethylbenzylamine, MeCN = acetonitrile) are reported. The experimental results showed the reduction of Pd (II) to Pd (I) for complexes 1- 3 while 1 was the only one to show the reduction of Pd (I) to Pd (0). It was observed that the electrochemical stability of these compounds decreased in the order: [Pd(dmba)(mu-CN)]2 (4) > [Pd(dmba)(mu-NCO)]2 (2) > [Pd(dmba)(mu-SCN)]2 (3) > [Pd(dmba)(MeCN)2][NO3] (5) > [Pd(dmba)(mu-Cl)]2 (1).

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6

A história, evolução e crescimento da Eletroquímica: Eletroanalítica nestes últimos 25 anos/ The history, evolution and growth of Electrochemistry: Electroanalytical chemistry in the past 25 years

Avaca, Luis Alberto; Tokoro, Roberto
2002-05-01

Resumo em inglês This text describes the development of Electrochemistry and Electroanalytical Chemistry in Brazil from the pioneers at the IQ/USP in the 70's to the present day status. It explains how the members of the scientific community organized themselves before the establishment in 1993 of a specific division within the Brazilian Chemical Society (SBQ) through bi-ennial meetings (Brazilian Symposium of Electrochemistry and Electroanalytical Chemistry - SIBEE). Those SIBEE meetings (mais) , in a present number of 12, are described individually giving some emphasis on their organizers, the invited speakers and the statistics and overall structure of the event. The activities of the Electrochemistry and Electroanalytical Chemistry Division of the SBQ from 1993 are also briefly discussed as well as some considerations are made on the present and future of these fields.

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7

Técnicas in situ de baixo custo em eletroquímica: a microbalança a cristal de quartzo/ Low cost in situ techniques in electrochemistry: the quartz crystal microbalance

Varela, Hamilton; Malta, Marcos; Torresi, Roberto M.
2000-10-01

Resumo em inglês Among in situ techniques, the electrochemical quartz crystal microbalance (EQCM) is a powerful tool for the study of electrochemical reactions that produce mass changes in the electrode/solution interface. This review present some systems in which the EQCM combined with classical electrochemical techniques, gives relevant information for understanding the charge transport process at a molecular level. The aim of this review is to do a brief description of experimental arr (mais) angements, with emphasis on some special cares that must be considered by the users. Secondly, some chosen electrochemical systems where the technique was successfully applied are discussed. Finally, a brief analysis of electroacoustic impedance experiments was done in order to show when the Sauerbrey equation can be used.

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9

Estudo da adsorção de hidrogênio e sulfeto na superfície de paládio: aspectos experimentais (eletroquímica) e teóricos (ab initio e Teoria do Funcional da Densidade)/ Experimental (electrochemistry) and theoretical (ab initio and Density Functional Theory) studies of hydrogen and sulfide adsorption on palladium (100) surface

Ângelo, Antônio Carlos D.; Souza, Aguinaldo R. de; Morgon, Nelson H.; Sambrano, Júlio R.
2001-08-01

Resumo em inglês The adsorption of H and S2- species on Pd (100) has been studied with ab initio, density-functional calculations and electrochemical methods. A cluster of five Pd atoms with a frozen geometry described the surface. The computational calculations were performed through the GAUSSIAN94 program, and the basis functions adapted to a pseudo-potential obtained by using the Generator Coordinate Method adapted to the this program. Using the cyclic voltammetry technique through a M (mais) odel 283 Potentiostat/Galvanostat E.G.&G-PAR obtained the electrochemical results. The calculated chemisorption geometry has a Pd-H distance of 1.55Å, and the potential energy surface was calculated using the Becke3P86//(GCM/DFT/SBK) methodology. The adsorption of S2- ions on Pd surface obtained both through comparison between the experimental and theoretical results, at MP2 level, suggest a S2- absorption into the metallic cluster. The produced Pd-(S2-) system was show to be very stable under the employed experimental conditions. The paper has shows the powerful aid of computational methods to interpret adsorption experimental data.

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10

O coulômetro de sódio: um experimento interessante de eletroquímica/ The sodium coulometer: an interesting electrochemistry experiment

Bonapace, José Alberto P.
2004-08-01

Resumo em inglês The diffusion of sodium through glass, the basis of a sodium coulometer, was revised and modified for the application to present-day light bulbs. Low pressure inert gas-filled incandescent lamps are useless to attain satisfactory results. The inclusion of a 450 V power supply in series with the electrolysis cell provided sufficient potential to overcome the effect of the inert gas molecules inside the bulb.

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11

Alterações eletroquímicas em solos inundados/ Electrochemical changes in wetland soils

Camargo, Flávio Anastácio de Oliveira; Santos, Gabriel de Araújo; Zonta, Everaldo
1999-03-01

Resumo em português O presente trabalho tem o objetivo de revisar alguns conceitos da eletroquímica (descritos pela físico-química) dos solos inundados. As principais alterações eletroquímicas que ocorrem após a inundação são a diminuição do potencial redox, aumento do pH em solos ácidos e decréscimo em solos alcalinos, aumento da condutividade elétrica e de reações de troca iônica. Essas modificações produzidas no sistema influenciam diretamente o desenvolvimento de plan (mais) tas através do controle da disponibilidade e toxidez de nutrientes, regulando a absorção na rizosfera. Resumo em inglês This paper aims to review some concepts on electrochemistry of wetland soils. The main electrochemical changes after inundation are a decrease in redox potential, an increase in pH in acid and a decrease in alkaline soils and increases in conductivity and ion exchange reactions. These modifications in the system might influence plant growth, by affecting the availability on toxicity of nutrients, regulating uptake in the rhizosfere.

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12

Utilização de técnicas eletroquímicas na avaliação da porosidade de camadas fosfatizadas/ Use of electrochemical techniques in porosity phosphate coatings evaluation

Santos, Célia A. Lino dos; Leite, Edwilson; Filho, Antenor Ferreira; Panossian, Zehbour
2006-10-01

Resumo em português A porosidade de camadas de fosfato de zinco sobre aço baixo carbono, processadas em diferentes tempos de imersão (30 s, 45 s e 85 s), foi avaliada por meio das seguintes técnicas eletroquímicas: polarização anódica (P A), polarização linear catódica (P LC), cronoamperometria (C A), voltametria cíclica (VC), espectroscopia de impedância eletroquímica (EIE); e também por microscopia eletrônica de varredura (MEV). As técnicas de P A, VC e EIE foram exploradas (mais) qualitativamente, enquanto que as de P LC e C A quantitativamente. As análises qualitativas (P A, VC, EIE) indicaram que a porosidade das camadas fosfatizadas aumentou com a diminuição do tempo de imersão. Os valores porcentuais de porosidade (P LC, C A) e as imagens de MEV confirmaram estes resultados. Resumo em inglês The porosity of zinc phosphate layers on low carbon steel processed in different immersion times (30 s, 45 s and 85 s) was evaluated through the following electrochemistry techniques: anodic polarization (P A), cathodic linear polarization (P CL/P LC), cronoamperometry (C A), cyclic voltammetric (CV/VC), spectroscopy impedance electrochemistry (EIS/EIE); and also scanning electron microscopy (SEM/MEV). The techniques P A, CV and EIS were qualitatively explored, while the (mais) P CL and C A quantitatively. The qualitative analyses (P A, CV, EIS) indicated that the phosphated layers porosity increased with the decrease of the immersion time. The porosity percents values (P CL, C A) and MEV images confirmed these results.

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13

Estudo do biomaterial Ti-6Al-4V empregando-se técnicas eletroquímicas e XPS/ Study of Ti-6Al-4V biomaterial using electrochemistry and XPS techniques

Ramires, Ivan; Guastaldi, Antonio Carlos
2002-02-01

Resumo em inglês The Ti-6Al-4V alloy used as biomaterial has been used over the last years. The literature shows controversies concerning the kind and the chemical composition of the film naturally and elctrochemically formed on the surface of the titanium alloy. The presente work studies the film composition before and after the electrochemical polarization tests using the x Ray photoelectron spectroscopy (XPS) technique. The results showed that the film naturally formed on the metallic (mais) surface is constituted of a variety of oxides which do not cover the whole surface of the metallic alloy and therefore, metallic Ti, Al and V can be found on the uncovered areas. The tests of XPS made after the polarization up to 4V (SCE) showed that the electrochemically formed film is constituted only of TiO2 and that the peak current observed around 1,5 V (SCE) is due to the oxidation of any kind of titanium oxide or the growth of the film.

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14

Propriedades redox de ácidos húmicos isolados de um solo cultivado com cana-de-açúcar por longo tempo/ Redox properties of humic acids isolated from a soil Under long-term sugarcane cultivation

Baldotto, Marihus Altoé; Canellas, Luciano Pasqualoto; Canela, Maria Cristina; Rezende, Carlos Eduardo; Velloso, Ary Carlos Xavier
2008-06-01

Resumo em português A matéria orgânica do solo é o maior reservatório de C nos sistemas naturais. Em tais sistemas a qualidade e a estabilidade do C podem ser estimadas pelo aumento da concentração das frações humificadas que, dentre outros fatores, está condicionada ao balanço entre as perdas e os ganhos que envolvem as reações de oxidação e de redução da matéria orgânica do solo. O objetivo deste estudo foi avaliar a eletroquímica, usando titulações redox iodimétricas (mais) , de ácidos húmicos isolados de solos cultivados continuamente com cana-de-açúcar submetida ou não à queima da palha para a colheita ou à adição anual de vinhaça. Os ácidos húmicos apresentaram valores do potencial formal padrão do eletrodo entre 0,760 e 0,779 V a 25 ºC. A capacidade de oxidação dos ácidos húmicos variou de 1,01 a 3,44 mol c kg-1 a pH 5,0 e de 1,64 a 6,44 molc kg-1 a pH 7,0. Observou-se correlação positiva e significativa entre a capacidade de oxidação dos ácidos húmicos e suas concentrações de grupos funcionais fenólicos, quinonas e semiquinonas. Resumo em inglês Soil organic matter is the largest carbon reservoir in natural systems. In such systems the carbon quality and stability can be estimated based on the increase of humified fractions which, among other factors, is related to the balance between losses and accumulations involving oxidation and reduction reactions of the soil organic matter. The objective of this study was to evaluate the electrochemistry of humic acids isolated from soils cultivated continually with sugar-c (mais) ane, with or without pre-harvest burning and annual vinasse application using iodimetric redox titrations. The formal electrode potentials of the humic acids had a similar pattern, with values between 0.760 and 0.779 V, at 25 ºC. The oxidation capacity of humic acids varied from 1.01 to 3.44 mol c kg-1 at pH 5.0 and from 1.64 to 6.44 mol c kg-1 at pH 7.0. Positive and significant correlations were observed between the oxidation capacity and the humic acid contents of phenolic, quinone and semiquinone functional groups.

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15

Estudo espectro eletroquímico de sistemas estruturados argila-corante/ Espectroelectrochemical behavior of clay-dye structured systems

Souza, G. R. de; Fertonani, F. L.; Pastre, I. A.
2003-01-01

Resumo em português O comportamento eletroquímico e espectroeletroquímico do sistema montmorilonita-azul de metileno (MM-AM)/AMsolução foi investigado empregando-se a técnica de voltametria cíclica e de transiente, I x t (corrente versus tempo) sobre eletrodo de vidro ITO modificado pela deposição mecânica de filmes do compósito MM-AM. Os filmes foram preparados empregando três procedimentos: 1- na ausência de CTACl (surfactante, cloreto de cetiltrimetilamônio); 2- com incorpora (mais) ção do CTACl à região interlamelar; e 3- na presença do CTACl, porém, não incorporado à região interlamelar. A técnica espectrofotométrica foi empregada para a caracterização e para o estudo eletrocrômico dos filmes formados. Os resultados experimentais permitiram observar que: i- os filmes preparados com a incorporação prévia do AM a região interlamelar fornecem uma resposta eletroquímica mais eficiente com o aparecimento de um par de picos bem definido; ii- a adição do CTACl, de forma geral permite a obtenção de filmes mecanicamente mais estáveis; iii- com a inclusão prévia do CTACl na região interlamelar não ocorre o aparecimento da forma protonada do AM (AMH+); iv- na ausência da forma protonada o compósito não apresenta comportamento eletrocrômico. Resumo em inglês The eletrochemical and espectroelectrochemical behavior of the montmorilonita methylene-blue system (MM-AM)/AMsolution have been investigated using cyclic volta mmetry and transient (I x t) techniques on modified ITO glass electrodes by film of composite (MM-AM) mechanically deposited. These films were prepared by three way: 1- in the absence of surfactant CTACl (cetyltrimethyl-ammonuim chloride); 2- with incorporation of CTACl into the interlayer region; and 3- in the pr (mais) esence of CTACl, however, not incorporated into the interlayer region. The spectroelectrochemistry technique was used for characterization and study of the formed films. The experimental results allowed assumptions as follows: 1- films prepared with AM previous incorporated into interlayer region supply a more efficient electrochemistry answer with the appearance of a couple of well defined peaks; 2- CTACl, in general, allows to obtain mechanically stable films; 3- when CTACl is previously included into interlayer region it doesn't exist intercalated protonated specie, AMH+; 4- when protonated specie is absent the composite doesn't shows electrochromic behavior.

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16

Espectroscopia de impedância para avaliar o efeito do molibdato de sódio incorporado no concreto/ Impedance spectroscopy to evaluate the effect of sodium molybdate in concrete

Tommaselli, Maria Aparecida Garcia; Kuri, Sebastião Elias; Mariano, Neide Aparecida
2008-09-01

Resumo em português O concreto armado tem cada vez mais despertado interesse científico e tecnológico, principalmente no que se refere a sua melhoria e inovação, seja pela utilização de novos materiais ou pelo estudo da corrosão para evitar a deterioração das estruturas. Dessa forma, têm-se intensificado os estudos da corrosão em concreto armado, sendo que a maior dificuldade está em detectar o início da corrosão na armadura. Uma das causas de degradação do concreto armado e (mais) sua posterior corrosão da sua armadura é a sua exposição a ambientes industriais. Assim, é necessário melhorar o desempenho das estruturas, prevendo a vida útil e conhecendo as formas de prevenção para minimizar o processo corrosivo. Há métodos de controle da corrosão do aço, como a incorporação de inibidores no concreto, como o molibdato de sódio, que é um inibidor anódico e não poluente tóxico. Nesse trabalho, foi avaliada a eficiência do molibdato de sódio, nas concentrações de 0, 1, 2 e 4% em relação à massa de cimento, empregando espectroscopia de impedância eletroquímica, simulando uma atmosfera ácida como agente agressor. A concentração de 4% do inibidor foi a mais eficiente. Resumo em inglês The reinforced concrete has more and more arisen scientific and technological interest concerned mainly to its innovation and improvement either by the utilization of new materials or by the study of corrosion to avoid structure deterioration. In that way, the study of corrosion in reinforced concrete has been intensified but the biggest difficult is to detect the beginning of the corrosion in the steel. One of the reasons of the reinforced concrete degradation and afterw (mais) ards the corrosion in the steel is its exposition to industrial environments. Thus, it is necessary to improve the performance of the structures, foreseeing its useful life and knowing the manners of prevention to minimize the corrosive process. There are methods to control the corrosion of the steel as the annexation of concrete inhibitors such as the sodium molybdate, an anodic inhibitor and not a toxic pollutant. In this work the efficacy of the sodium molybdate was evaluated with concentrations of 0, 1, 2 and 4% related to the cement mass, employing the electrochemistry impedance spectroscopy, simulating an acid atmosphere as an aggressive agent. The concentration of 4% in the inhibitor was the most efficient.

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17

Ultramicroeletrodos. Parte II: construção e aplicações/ Ultramicroelectrodes. Part II: construction and applications

Silva, S. M.; Alves, C. R.; Correia, A. N.; Martins, R. M.; Nobre, A. L. R.; Machado, S. A. S.; Mazo, L. H.; Avaca, L. A.
1998-02-01

Resumo em inglês This work describes the techniques of construction and several applications of ultramicroelectrodes in electrochemistry and electroanalytical chemistry. Disc shaped UME are produced by embedding metal wires on insulating materials such as glass or epoxy resin. In the field of electrochemistry, UME have been applied in studies of the hydrogen evolution reaction and the electrocrystallization of metals. The negligible values of sensibility for ohmic drop and the enhanced ma (mais) ss transport rate by spherical diffusion are the main advantages of UME in these applications. New important conclusions regarding the phenomena under study were drawn from the experimental results. The applications in electroanalytical chemistry involved the determination of contaminants such as heavy metals and nitrites in natural waters and food products. The use of UME requires little sample manipulation and, in general, no need for oxygen removal or the addition of supporting electrolytes.

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18

Síntese e caracterização de novos compostos de coordenação de cobre (II) com ligantes não-simétricos N,O-doadores: contribuições para o sítio ativo da galactose oxidase/ Synthesis and characterization of new copper (II) coordination compounds with unsymmetrical N,O-donor ligands: contributions for the galactose oxidase active site

Romanowski, Stela Maris de Moraes; Mangrich, Antonio Sálvio; Neves, Ademir
2001-10-01

Resumo em inglês The reactions of four new unsymmetrical N,O-donor ligands, {H2BBPETEN= [N-(2-hydroxybenzyl) - N,N' - bis(2 methylpyridyl) -N'-(hydroxyethyl) ethylenodiamine], H3BPETEN=[N,N'- bis(2-hydroxybenzyl) -N- (2-methylpyridyl) -N'- (hydroxyethyl) ethylenodiamine], HTPETEN=[N,N,N'- tris(2-methylpyridyl) -N'- (hydroxyethyl) ethylenodiamine] and H3BIMETEN=[N,N'-(2-hydroxybenzyl)-N-(1-methylimidazol-2-il-methyl)-N'- (hydroxyethyl)ethylenodiamine]}, with Cu(II) salts afforded the follo (mais) wing mononuclear compounds: [CuII(HBBPETEN)]ClO4, [CuII(H2BPETEN)]ClO4 , [CuII(HTPETEN)](PF6)2 and [CuII(H2BIMETEN)]ClO4 . All were characterized by EPR, electronic spectroscopy and electrochemistry. The four copper (II) compounds showed interesting electrochemistry properties. All presented an anodic wave that can be attributed to the Cu (I) oxide formation at the electrode surface, or to a Cu0 sediment at the same surface or yet, to Cu(I) -> Cu(II) oxidation process with coupled chemistry reaction, due to their irreversibility. Two of the complexes are described as interesting synthetic models for the active site of the metalloenzyme galactose oxidase.

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Study of the Electrochemical Behaviour of Tolitriazole in Phosphating Bathings of Carbon Steel 1008

Banczek, Everson P.; Oliveira, Marilei F.; Cunha, Maico T.; Rodrigues, Paulo R.P.
2005-01-01

Resumo em português As características inibidoras de corrosão do tolitriazol (TTA) para o aço de carbono 1008, revestidos por fosfato de zinco ou tricatiônico (Mn, Zn, Ni) nos meios de H2SO4 0.1 mol.L -1 e NaCl 0.5 mol L-1, foram investigadas por métodos físicos e electroquímicos. Os resultados obtidos na ausência do inibidor TTA mostraram que as propriedades de protecção à corrosão do fosfato tricatiônico (Ptri) são melhores do que as observadas para o fosfato de zinco (PZn), (mais) provavelmente devido a porosidade existente na camada do PZn. As curvas de polarização anódicas apresentaram densidades de corrente (j) menores para as peças de aço fosfatizadas com Ptri quando comparadas aos dos substratos sem fosfato e com PZn. Os resultados de impedância electroquímica (IE) mostraram uma resistência de polarização (Rp) maior para os electrodos fosfatizados com Ptri. As medidas electroquímicas das amostras de aço fosfatizadas, com PZn e/ou Ptri, na presença de [TTA] = 1.10 -3 mol L-1, apresentaram j menor que Rp maior do que as observadas para as amostras de aço fosfatizadas na ausência do TTA. No processo de fosfatização do açocarbono com PZn + TTA, observou-se j e Rp semelhantes as observadas nas amostras de aço fosfatizadas com Ptri sem TTA. Estes resultados sugerem que o banho de fosfato de zinco contendo [TTA] = 1.10 -3 mol L-1 pode substituir o mundialmente consagrado banho industrial de fosfato tricatiônico. Os ensaios em câmara de Salt Spray de amostras de aço fosfatizadas com PZn e PZn + TTA, pintadas com tinta pó poliéster branca, confirmaram os resultados electroquímicos obtidos. Resumo em inglês The characteristics of corrosion inhibitors of the tolitriazole (TTA) for the carbon steel 1008, covered by zinc or tricationic phosphate (Mn, Zn, Ni), in the means of H2SO4 0.1 mol L-1 and NaCl 0.5 mol L-1, were investigated by physical and electrochemical methods. The results obtained in the absence of the inibidor TTA showed that the corrosion protection properties of the tricationic phosphate (Ptri) are better than those observed for the zinc phosphate (PZn), probably (mais) due to the presence of vacancies in the layer of PZn. The curves of anodic polarization presented current densities (j) smaller for the steel phosphatized with Ptri, when compared with the metal substrate without phosphate and with PZn. The results of impedance electrochemistry (IE) showed a polarization resistance (Rp) larger for the electrodes phosphatized with Ptri. The electrochemistry measurements of the samples of steel phosphatized, with PZn and/or Ptri, in the presence of [TTA] = 1x10-3 mol L-1, present smaller j and larger Rp when compared with the absence of TTA. In the process of phosphatization of the carbon steel with PZn + TTA, it was observed similar j and Rp in the samples of steel phosphatized with Ptri without TTA. These results suggest that the bathing of zinc phosphate with [TTA] = 1x10-3 mol L-1 can substitute the well known industrial bathing of tricationic phosphate. Corrosion testing by Salt Spray of steel phosphatized with PZn and PZn + TTA, painted with white polyester ink, confirmed the eletrochemical results.

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Química de complexos de (etilenodiaminatetraacetato)rutenato(III/II)/ Ruthenium complexes containing ethylenediaminetetraacetate

Rein, Francisca N.; Rocha, Reginaldo C.; Toma, Henrique E.
2004-02-01

Resumo em inglês This paper provides a survey of general aspects involved in the coordination chemistry of low-valent (mainly +III,+II), low-spin (d p5,d p6) ruthenium ions with ethylenediamine-N,N,N',N'-tetraacetate (edta) and their substituted derivatives. The topics covered herein include structure, reactivity, kinetics, thermodynamics, electrochemistry and spectroscopy. The contributions from either our research group or the literature over the last three decades are focused in this review.

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21

Potencialidades da utilização de compostos de ródio na confecção de sensores eletroquímicos: uma breve revisão/ Potentiality of the rhodium compounds utilization in electrochemical sensors development: a brief review

Gil, Eric de Souza; Kubota, Lauro Tatsuo; Najjar, Renato
1998-11-01

Resumo em inglês The electrochemistry field has increased in recent years, specially in the search for new sensors to monitor specific analyte in complex samples. In order to improve electrodes, many rhodium compounds have been used as electron mediators for novel sensors development. The most used compounds for this purpose are metal, metal complexes and some organic dyes. Rhodium complexes are known by their good catalytic properties and it could be useful in the sensor field. However, (mais) there are only a few reports, on the use of rhodium complexes in sensors and biosensors. A brief review of the electrochemistry of rhodium complexes and some discription of their properties which make those compounds suitable for development of sensor and biosensor.

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22

Métodos sintéticos para preparação de 2,2'-bipiridinas substituídas/ Synthetic methods for preparation of substituted 2,2'-bipyridines

Donnici, Claudio Luis; Oliveira, Ione Maria Ferreira de; Temba, Eliane Sílvia Codo; Castro, Maurício Costa Rogério de
2002-07-01

Resumo em inglês The 2,2'-bipyridine has been entitled as the most widely used ligand. Nowadays there is a large variety of known molecules comprising at least two 2,2'-bipyridine units and the number of applications in many areas such as catalysis, new materials, optoeletronics and electrochemistry have increased very much in the past decades. Nevertheless, there is no article that gives an overview of the main synthetic methods for obtaining the substituted 2,2'-bipyridines, generally n (mais) on available. This article presents a synthetic discussion about the three different methods (coupling reaction, ciclo-functionalization and functionalization of the heteroaromatic rings of 2,2'-bipyridine) for preparing these heterocyclic compounds and also provides a practical and fundamental guide, for obtaining more than eighty different symmetric and unsymmetrical substituted 2,2'-bipyridines, shown in a table with the corresponding references.

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23

Montagem e caracterização elétrica de pilhas a combustível de óxido sólido (PaCOS)/ Assembly and electrical characterization of solid oxide fuel cell stacks

Tarôco, Hosane Aparecida; Andrade, Samuel Tadeu de Paula; Brant, Márcia Caldeira; Domingues, Rosana Zacarias; Matencio, Tulio
2009-01-01

Resumo em inglês This paper is focused on a review of the design features and the electrochemistry characterization of anode-supported planar SOFC. Studies and results of metallic alloy interconnectors and recovery for protection against corrosion and for contact layer are showed. Moreover a discussion of examples of measurements of impedance spectrometry, according to the literature and our experimental results are made. For the anode supported fuel cells the power density varies from 0. (mais) 1 to 0.5 Wcm², according to results in the literature (showed in this paper). For electrolyte supported fuel cell the power density can be 10 Wcm-2 for high temperatures. An English-Portuguese glossary of most used terms in SOFC stack is given for greater clarity and to introduce new terms to the reader.

Scientific Electronic Library Online (Portuguese)

24

Microeletrodos: III. arranjos de microeletrodos, construção e caracterização/ Microelectrodes: III. Arrays of microelectrodes, construction and characterization

FABER, Marcelo; FERTONANI, Fernando Luis; YAMANAKA, Hideko; BENEDETTI, Assis Vicente
2000-01-01

Resumo em português Neste trabalho procurou-se descrever detalhadamente o procedimento de preparo de um arranjo de eletrodos com geometria em forma de microdiscos (20,2 (mais) mV s-1, observou-se uma excelente sobreposição dos voltamogramas cíclicos experimental e simulado, entretanto, velocidades desta ordem de grandeza são pouco práticas do ponto de vista experimental. Observou-se, também para todos os microeletrodos estudados, uma transição da condição de corrente estacionária para quase-estacionária, com o aumento dos valores de v. Equações que permitem avaliar a contribuição das correntes radial e difusional, para a corrente total, ajustam-se perfeitamente as curvas I/E em todo o intervalo de raios dos eletrodos e valores de v empregados. Os voltamogramas obtidos para o arranjo de eletrodos operando na condição de curto circuito apresentou um fator de amplificação de 19 vezes, referente ao sinal obtido a partir de um único microeletrodo. Tal fator confirma a condição de ausência de sobreposição das camadas de difusão dos eletrodos e, portanto, reflete a contribuição individual de cada eletrodo para a corrente total. Resumo em inglês In this work we are able to describe in detail the procedure to prepare an array of microelectrodes with flat disc geometry (20,2 (mais) l and simulated I / E profiles, however, v of this magnitude are no practice from na experimental point of view. For all of microelectrodes studied, it was observed a transition from the steady state to a near-steady state condition, when the scan rate was increased. The mathematical equations used to evaluate the ciclic voltammograms considering the contribution of the linear and radial diffusion to the total current fitted very well the I / E profiles. These equations also allowed a simultaneous evaluation of all electrodes of the array regarding microelectrodes individual behaviour. These results agree with voltammograms obtained for the array operating in externally short circuited condition.

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25

Improving electrocatalityc activity of LaNiO3 coatings by deposition on foam nickel substrates

Soares, C. O.; Carvalho, M. D.; Jorge, M. E Melo.; Gomes, A.; Silva, R. A.; Rangel, C. M.; Pereira, M. I.da Silva

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Híbridos inorgânico-orgânicos derivados da reação de filossicatos com organossilanos/ Inorganic-organic hybrids derived from the reaction of phyllosilicates with organosilanes

Fonseca, Maria Gardênnia da; Airoldi, Claudio
2003-10-01

Resumo em inglês Silylation reactions involving hydroxylated surfaces are an important route for synthesis of new materials that could present selected properties, for application in different areas such as catalysis, chromatography, adsorption and electrochemistry. An overview of many synthetic routes, comprising organosilanes to yield phyllosilicates is now presented.

Scientific Electronic Library Online (Portuguese)

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Gold electrodeposition from ionic liquids: an alternative to conventional aqueous baths

Sá, A. I. Correia de; Rangel, C. M.; Quaresma, S.; Eugénio, S.; Vilar, R.

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Filmes de diamante CVD dopado com boro. Parte I . Histórico, produção e caracterização/ Boron-doped CVD diamond films. Part I. History, production and characterization

Barros, Rita de Cássia Mendes de; Ribeiro, Mauro Celso; An-Sumodjo, Paulo Teng; Julião, Murilo Sérgio da Silva; Serrano, Sílvia Helena Pires; Ferreira, Neidenêi Gomes
2005-03-01

Resumo em inglês This review presents a brief account concerning the production, characterization and evolution of the knowledge in the area of diamond and boron-doped diamond films. The most important methods used for the growth of these films, such as chemical vapor deposition and high pressure/high temperature systems, as well as the several kinds of reactors which can be employed are reviewed. However, larger emphasis is given to the CVD method. Morphological, structural and electric (mais) properties of these films, as well as their role in the performance of voltammetric electrodes for electrochemistry and electroanalytical chemistry are also discussed.

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Eletrodos modificados com polímeros perfluorados e sulfonados: aplicações em análises ambientais/ Perfluorinated and sulfonated polymers modified electrodes: applications to environmental analysis

Fungaro, Denise Alves; Brett, Christopher M. A.
2000-12-01

Resumo em inglês Perfluoro and sulfonated ion-exchange polymers are recognized as a very useful material for various mechanistic studies and applications in electrochemistry. These polymers are characterized by high equivalent weights and by a low number of ion-exchange sites interposed between long organic chains. The solubility enables a preparation of stable polyelectrolyte films on the electrode surface. Examples of the determination of trace metals and organic componds in real environmental samples are presented.

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30

Eletrodos modificados com DNA: uma nova alternativa em eletroanálise/ DNA-modified electrodes: a new alternative for electroanalysis

La-Scalea, Mauro A.; Serrano, Silvia H. P.; Gutz, Ivano G. R.
1999-06-01

Resumo em inglês The first studies about DNA electrochemistry appeared at the end of the fifties. The voltammetric techniques became important tool for the DNA conformational analysis, producing evidences about DNA double helix polimorphism. The new techniques based on electrodes modification with nucleic acid enlarged the use of the electrochemical methods on the DNA research. DNA electrochemical biosensors are able to detect specific sequences of DNA bases, becoming important alternativ (mais) e for the diagnosis of disease, as well as in the carcinogenic species determination. Besides, the use of DNA biosensors in the mechanism study of biological drug actions can be useful for drug design.

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31

Eletrodo de hidrogênio: o que há nos livros didáticos além de E¸ = 0?/ The hydrogen electrode: what is there in the textbooks beyond E¸ = 0?

Oliveira, Wanda de; Tiedemann, Peter Wilhelm; Cecchini, Renato Giovanni; Osorio, Viktoria Klara Lakatos
2009-01-01

Resumo em inglês The results of an exercise on electrochemistry for General Chemistry students are presented. The difficulty encountered by students in predicting the shift in the potential of the hydrogen electrode under non-standard conditions prompted a search in textbooks on how the subject is developed. Besides several instances of inconsistencies in defining the standard state, such as including the temperature in the definition, a number of incorrect depictions of the hydrogen elec (mais) trode were discovered. Of the 28 General Chemistry books, 16 Physical Chemistry books and 24 Internet pages, 30, 20 and 46%, respectively, showed devices that would not work in practice.

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Cyclic Voltammetry of Ruthenium Complexes for Nonlinear Optics

Mendes, Paulo J. G.

We report herein the cyclic voltammetry studies of the compounds [RuCp(P_P)(NC{SC4H2}nNO2)][PF6] (P_P=DPPE, (+)-DIOP; n=1-3) in dichloromethane and acetonitrile. The electronic richness of the organometallic moiety together with the evaluation of the corresponding HOMO-LUMO gaps and correlation with...

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Cyclic Voltammetry of Organometallic Acetylide Complexes

Mendes, Paulo J. G.; Silva, Tiago J. L.

We report herein the cyclic voltammetry behavior of the compounds [RuCp(L2)(CC{SC4H2}nA)] (L2=DPPE, 2 PPh3; A= NO2, CHO; n=1,2). The effect of the phosphines, length of the conjugated thiophene chain and acceptor (A) group will be addressed. Both the electrochemical and spectroscopic data will be co...

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34

Cathodic Behaviour of Pyrite With Molten Salts Electrolyte

Vieira, M.J.P.; Rupp, M.T.C.; Kohler, H.M.
2003-01-01

Resumo em inglês Iron disulphide molten salt electrochemical cells are among the most promising technological options for batteries. The electrochemical behaviour of pyrite allies excellent cathodic characteristics to optimal performance and low operational costs. The cathodic iron disulphide mechanism involves many processes, encompassing from polysulphides formation to the reduction of iron to the metallic state. The use of X-ray diffraction together with scanning electronic microscopy (mais) analysis on cells of the Li/KCl-LiCl/FeS2 system made possible to identify intrinsic and extrinsic parameters to the electrochemical process involved in the establishment of the polysulphides stoichiometry. It is necessary to note that the augmentation of the cell's internal resistance and loss of electrical capacity are directly related with the formation of these same substances. Researches in the electrochemistry of these phenomena aim to elucidate the cathodic interphase processes and the effect of every reaction in the global mechanism.

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Avaliação da limpeza de CDtrodo construídos a partir de CD de ouro gravável/fita adesiva de galvanoplastia/ Evaluation of the CDtrode cleaning constructed from gold recordable CD/galvanoplasty tape

Foguel, M. V.; Uliana, C. V.; Tomaz, P. R. U.; Marques, P. R. B. Oliveira; Yamanaka, H.; Ferreira, A. A. Pupim
2009-01-01

Resumo em português Os eletrodos de ouro são largamente utilizados em estudos eletroquímicos e eletroanalíticos, devido à sua elevada pureza, ampla faixa de potencial de trabalho, bem como a possibilidade de controle e modificação da superfície eletródica. Neste trabalho são descritos procedimentos para construção e limpeza de eletrodos a partir de CDs de ouro graváveis, denominados CDtrodos. Inicialmente, os CDs foram submetidos à ação de HNO3 concentrado para retirada da cam (mais) ada polimérica protetora e exposição da camada metálica, posteriormente, para a construção dos CDtrodos, delimitou-se a área eletródica com fita de galvanoplastia. Diversos métodos para a limpeza da superfície do ouro foram empregados, após ataque do HNO3, tais como, aplicação de potencial fixo em solução de NaCl, ciclagens sucessivas em H2SO4 e aplicação de ultra-som, sendo que os melhores resultados foram obtidos por tratamento com H2SO4. A literatura tem registrado vários trabalhos empregando CDtrodo no entanto são focados na aplicação e pouco se descreve sobre a limpeza do eletrodo; nenhum trabalho foi registrado empregando a fita de galvanoplastia para delimitar a área do eletrodo. A utilização desse tipo alternativo de eletrodo é de suma importância, uma vez que o mesmo apresenta desempenho eletroquímico comparável aos eletrodos comerciais, além de grande versatilidade e baixo custo. Resumo em inglês Gold electrodes are widely used in electrochemistry and electroanalytical chemistry, due to the high purity, broad range of work potential as well as the possibility to control and modify the surface. On this work construction and cleaning of electrodes from gold recordables compact discs (CD-Rs), namely CDtrodes, are described. The CDs was submitted to the action of concentrated HNO3 in order to remove the protection layer and to expose the metallic layer; the electrode (mais) area was delimited by using galvanoplasty tape. The literature has been published many articles on CDtrode focused on the application but not on the cleaning; there is no register on galvanoplasty tape to define electrode area. Several methods for gold surface cleaning after attack of HNO3 were investigated, such as application of fixed potential in NaCl solution, successive scans in H2SO4 and ultrasound application, and best results were obtained in H2SO4 solution. This electrode material is interesting due to the performance comparable to the commercial electrodes, besides great versatility and low cost.

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Aspectos mecanísticos da bioatividade e toxicidade de nitrocompostos/ Aspects of bioactivity and toxicity of nitrocompounds

Paulai, Fávero Reisdorfer; Serrano, Silvia Helena Pires; Tavares, Leoberto Costa
2009-01-01

Resumo em inglês Nitrocompounds are bioactive molecules used as antibacterial, antiparasitic and antitumoral agents. In the past of years, these molecules have been broadly studied in several fields, such as medicinal chemistry, organic chemistry, biochemical, toxicology and electrochemistry. The nitrocompounds mode of action involves the biotransformation of the nitro group, releasing intermediates in the redox process. Some of those intermediates attack enzymes, membranes and DNA, provi (mais) ding the basis for their biological activity and adverse effects. In this report, some aspects regarding the biological activity, mechanism of action and toxicity of nitrocompounds are explored, purposing the research of new bioactive derivatives having low toxicity.

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