Structural and electrochemical characteristics of Mg((55-x))Ti(x)Ni((45-y))Pt(y) metal hydride electrodes

In recent years, Mg-Ni-based metastable alloys have been attracting attention due to their large hydrogen sorption capacities, low weight, low cost, and high availability. Despite the large discharge capacity and high activity of these alloys, the accelerated degradation of the discharge capacity after only few cycles of charge and discharge is the main shortcoming against their commercial use in batteries. The addition of alloying elements showed to be an effective way of improving the electrode performance of Mg-Ni-based alloys. In the present work, the effect of Ti and Pt alloying elements on the structure and electrode performance of a binary Mg-Ni alloy was investigated. The XRD and HRTEM revealed that all the investigated alloy compositions had multi-phase nanostructures, with crystallite size in the range of 6 nm. Moreover, the investigated alloying elements demonstrated remarkable improvements of both maximum discharge capacity and cycling life. Simultaneous addition of Ti and Pd demonstrated a synergetic effect on the electrochemical properties of the alloy electrodes. Among the investigated alloys, the best electrochemical performance was obtained for the Mg(51)Ti(4)Ni(43)Pt(2) composition (in at.%), which achieved 448 mAh g(-1) of maximum discharge capacity and retained almost 66% of this capacity after 10 cycles. In contrast, the binary Mg(55)Ni(45) alloy achieved only 248 mAh g(-1) and retained 11% of this capacity after 10 cycles. (C) 2010 Elsevier By. All rights reserved.

Study of ethanol electro-oxidation in acid environment on Pt(3)Sn/C anode catalysts prepared by a modified polymeric precursor method under controlled synthesis conditions

A carbon-supported binary Pt(3)Sn catalyst has been prepared using a modified polymeric precursor method under controlled synthesis conditions This material was characterized using X-ray diffraction (XRD). and the results indicate that 23% (of a possible 25%) of Sn is alloyed with Pt, forming a dominant Pt(3)Sn phase. Transmission election microscopy (TEM) shows good dispersion of the electrocatalyst and small particle sizes (3 6 nm +/- 1 nm) The polarization curves for a direct ethanol fuel cell using Pt(3)Sn/C as the anode demonstrated Improved performance compared to that of a PtSn/C E-TEK. especially in the intrinsic resistance-controlled and mass transfer regions. This behavior is probably associated with the Pt(3)Sn phase. The maximum power density for the Pt(3)Sn/C electrocatalyst (58 mW cm(-2)) is nearly twice that of a PtSn/C E-TEK electrocatalyst (33 mW cm(-2)) This behavior is attributed to the presence of a mixed Pt(9)Sn and Pt(3)Sn alloy phase in the commercial catalysts (C) 2009 Elsevier B V All rights reserved

Activation Energies of the Electrooxidation of Formic Acid on Pt(100)

The electrooxidation of small organic molecules on platinum surfaces usually involves different structure-dependent steps that include adsorption and desorption of various species and multiple reaction pathways. Because temperature plays a decisive role on each individual step, understanding its global influence on the reaction mechanism is often a difficult task, especially when the system is studied under far from equilibrium conditions in the presence of kinetic instabilities. Aiming at contributing to unravel this problem, herein, we report an experimental study of the role played by temperature on the electrooxidation of formic acid on a Pt(100) electrode. The system was investigated under both close and far from equilibrium conditions, and apparent activation energies were estimated using different strategies. Overall, comparable activation energies were estimated under oscillatory and quasi-stationary conditions, at high potentials. At low potentials, the poisoning process associated with the formic acid dehydration step presented a negligible dependence with temperature and, therefore, zero activation energy. On the basis of our experimental findings, we suggest that formic acid dehydration is the main, but maybe not the unique, step that differentiates the temperature dependence of the oscillatory electrooxidation of formic acid on Pt(100) with that on polycrystalline platinum.

Leakage current, ferroelectric and structural properties in Pb(1-x)Ba(x)TiO(3) thin films prepared by chemical route

Single-phase perovskite structure Pb(1-x)Ba(x)TiO(3) thin films (x = 0.30, 0.50 and 0.70) were deposited on Pt/Ti/SiO(2)/Si substrates by the spin-coating technique. The dielectric study reveals that the thin films undergo a diffuse type ferroelectric phase transition, which shows a broad peak. An increase of the diffusivity degree with the increasing Barium contents was observed, and it was associated to a grain decrease in the studied composition range. The temperature dependence of the phonon frequencies was used to characterize the phase transition temperatures. Raman modes persist above tetragonal to cubic phase transition temperature, although all optical modes should be Raman inactive. The origin of these modes was interpreted in terms of breakdown of the local cubic symmetry by chemical disorder. The absence of a well-defined transition temperature and the presence of broad bands in some interval temperature above FE-PE phase transition temperature Suggested a diffuse type phase transition. This result corroborates the dielectric constant versus temperature data, which showed a broad ferroelectric phase transition in these thin films. The leakage Current density of the PBT thin films was studied at different temperatures and the data follow the Schottky emission model. Through this analysis the Schottky barrier height values 0.75, 0.53 and 0.34 eV were obtained to the PBT70, PBT50 and PBT30 thin films, respectively. (C) 2008 Elsevier Ltd. All rights reserved.

Effect of the catalyst composition in the Pt-x(Ru-Ir)(1-x)/C system on the electro-oxidation of methanol in acid media

The effect of variations in the composition for ternary catalysts of the type Pt-x(Ru-Ir)(1-x)/C on the methanol oxidation reaction in acid media for x values of 0.25, 0.50 and 0.75 is reported. The catalysts were prepared by the sol-gel method and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic absorption spectroscopy (AAS) and energy dispersive X-ray (EDX) analyses. The nanometric character (2.8-3.2 nm) of the sol-gel deposits was demonstrated by XRD and TEM while EDX and AAS analyses showed that the metallic ratio in the compounds was very near to the expected one. Cyclic voltammograms for methanol oxidation revealed that the reaction onset occur at less positive potentials in all the ternary catalysts tested here when compared to a Pt-0.75-Ru-0.25/C (E-Tek) commercial composite. Steady-state polarization experiments (Tafel plots) showed that the Pt-0.25(Ru-Ir)(0.75)/C catalyst is the more active one for methanol oxidation as revealed by the shift of the reaction onset towards lower potentials. In addition, constant potential electrolyses suggest that the addition of Ru and Ir to Pt decreases the poisoning effect of the strongly adsorbed species generated during methanol oxidation. Consequently, the Pt-0.25 (Ru-Ir)(0.75)/C Composite catalyst is a very promising one for practical applications. (c) 2007 Elsevier B.V. All rights reserved.

Synthesis, Characterization, and Electrocatalytic Activity toward Methanol Oxidation of Carbon-Supported Pt(x)-(RuO(2)-M)(1-x) Composite Ternary Catalysts (M = CeO(2), MoO(3), or PbO(x))

Carbon-supported platinum is commonly used as an anode electrocatalyst in low-temperature fuel cells fueled with methanol. The cost of Pt and the limited world supply are significant barriers for the widespread use of this type of fuel cell. Moreover, Pt used as anode material is readily poisoned by carbon monoxide produced as a byproduct of the alcohol oxidation. Although improvements in the catalytic performance for methanol oxidation were attained using Pt-Ru alloys, the state-of-the-art Pt-Ru catalyst needs further improvement because of relatively low catalytic activity and the high cost of noble Pt and Ru. For these reasons, the development of highly efficient ternary platinum-based catalysts is an important challenge. Thus, various compositions of ternary Pt(x)-(RuO(2)-M)(1-x)/C composites (M = CeO(2), MoO(3), or PbO(x)) were developed and further investigated as catalysts for the methanol electro-oxidation reaction. The characterization carried out by X-ray diffraction, energy-dispersive X-ray analysis, transmission electron microscopy, X-ray photoelectron spectroscopy, and cyclic voltammetry point out that the different metallic oxides were successfully deposited on the Pt/C, producing small and well-controlled nanoparticles in the range of 2.8-4.2 nm. Electrochemical experiments demonstrated that the Pt(0.50)(RuO(2)-CeO(2))(0.50)/C composite displays the higher catalytic activity toward the methanol oxidation reaction (lowest onset potential of 207 mV and current densities taken at 450 mV, which are 140 times higher than those at commercial Pt/C), followed by the Pt(0.75)(RuO(2)-MoO(3))(0.25)/C composite. In addition, both of these composites produced low quantities of formic acid and formaldehyde when compared to a commercially available Pt(0.75)-Ru(0.25)/C composite (from E-Tek, Inc.), suggesting that the oxidation of methanol occurs mainly by a pathway that produces CO(2) forming the intermediary CO(ads).

Methanol and ethanol electro-oxidation on Pt-SnO(2) and Pt-Ta(2)O(5) sol-gel-modified boron-doped diamond surfaces

The search for more efficient anode catalyst than platinum to be used in direct alcohol fuel cell systems is an important challenge. In this study, boron-doped diamond film surfaces were modified with Pt, Pt-SnO(2) and Pt-Ta(2)O(5) nano-crystalline deposits by the sol-gel method to study the methanol and ethanol electro-oxidation reactions in acidic medium. Electrochemical experiments carried out in steady-state conditions demonstrate that the addition of SnO(2) to Pt produces a very reactive electrocatalyst that possibly adsorbs and/or dissociate ethanol more efficiently than pure Pt changing the onset potential of the reaction by 190 mV toward less positive potentials. Furthermore, the addition of Ta(2)O(5) to Pt enhances the catalytic activity toward the methanol oxidation resulting in a negative shift of the onset potential of 170 mV. These synergic effects indicate that the addition of these co-catalysts inhibits the poisoning effect caused by strongly adsorbed intermediary species. Since the SnO(2) catalyst was more efficient for ethanol oxidation, it could probably facilitate the cleavage of the C-C bond of the adsorbed intermediate fragments of the reaction. (C) 2009 Elsevier B.V. All rights reserved.

Hamiltonian constraint analysis of vector field theories with spontaneous Lorentz symmetry breaking

Recent investigations of various quantum-gravity theories have revealed a variety of possible mechanisms that lead to Lorentz violation. One of the more elegant of these mechanisms is known as Spontaneous Lorentz Symmetry Breaking (SLSB), where a vector or tensor field acquires a nonzero vacuum expectation value. As a consequence of this symmetry breaking, massless Nambu-Goldstone modes appear with properties similar to the photon in Electromagnetism. This thesis considers the most general class of vector field theories that exhibit spontaneous Lorentz violation-known as bumblebee models-and examines their candidacy as potential alternative explanations of E&M, offering the possibility that Einstein-Maxwell theory could emerge as a result of SLSB rather than of local U(1) gauge invariance. With this aim we employ Dirac's Hamiltonian Constraint Analysis procedure to examine the constraint structures and degrees of freedom inherent in three candidate bumblebee models, each with a different potential function, and compare these results to those of Electromagnetism. We find that none of these models share similar constraint structures to that of E&M, and that the number of degrees of freedom for each model exceeds that of Electromagnetism by at least two, pointing to the potential existence of massive modes or propagating ghost modes in the bumblebee theories.

Página 10 e PT : jornalismo e política na sociedade de comunicação

Esta dissertação observa como se dá a relação entre a coluna política PÁGINA 10, do jornal Zero Hora, e o Partido dos Trabalhadores do Rio Grande do Sul, num período de três anos e meio até as eleições de 1998, quando o PT conquistou o governo do Estado. Neste período, em diferentes oportunidades, muitos textos da coluna motivaram manifestações de integrantes do PT, contestando a informação do colunista ou aproveitando-a para fazer críticas a adversários. A análise considera que a política e a comunicação – e dentro desta o jornalismo - são dois campos representados por PT e PÁGINA 10, respectivamente. Por isso, relata-se a formação da sociedade de comunicação, detalhando a formação do colunismo político no Rio Grande do Sul e seu posicionamento político e a formação do Partido dos Trabalhadores. Toma-se a hipótese de agenda-setting, que diz que os meios de comunicação têm capacidade de agendar a pauta da sociedade. Para ilustrar a tese, são reproduzidos tópicos da coluna que originaram manifestações de integrantes ou da direção do PT e suas respostas, como demonstração da importância dos meios de comunicação na política. Conclui-se que o PT movimenta-se para contestar muitas das manifestações do colunista – ou apenas corrigi-las, utiliza o espaço de imprensa para realizar seus embates internos ou comunicar-se com filiados e simpatizantes, que o colunismo político gaúcho tem características específicas diferentes do praticado no resto do País e que tem um perfil ideológico conservador.

Jornalismo e interesses econômico-políticos : o caso das montadoras e o governo do PT em Zero Hora : 1999, o ano em que o jornal abandona o neoliberalismo e se torna "Keynesiano"

Este trabalho analisa a cobertura do jornal Zero Hora sobre o impasse entre o governo do Rio Grande do Sul e as montadoras de automóveis Ford e General Motors, no período de 16/03/1999 a 03/05/1999. É um estudo que procura, através do referencial da hermenêutica de profundidade, demonstrar como é construída a ideologia no jornalismo do grupo RBS – maior conglomerado de mídia da região Sul do Brasil –, com base no conceito proposto por Thompson de “sentido a serviço do poder”. A minuciosa pesquisa possibilitou perceber não só o agendamento de Zero Hora no caso envolvendo o governo do Partido dos Trabalhadores (PT) e as montadoras, mas a construção ideológica empreendida pelo jornal, legitimando o discurso das montadoras e da oposição, e desqualificando os argumentos do governo. O discurso neoliberal de redução das atribuições do Estado, hegemônico nas páginas de Zero Hora durante a década de 90, é trocado – nos primeiros meses do governo petista – por um discurso fragmentado, oportunista e descontextualizado do pensamento keynesiano, defendendo o papel importante do Estado na geração de emprego e renda, como propulsor do desenvolvimento através de investimentos e outras políticas de incentivos capazes de gerar um círculo virtuoso na economia. A cobertura tendenciosa de Zero Hora se tornaria um dos elementos constitutivos de um Cenário de Representação da Política (CR-P) desfavorável à candidatura petista na eleição para o governo do Rio Grande do Sul em 2002.

Impasses decisórios na relação executivo-legislativo: o plano diretor da cidade de São Paulo no governo do PT (1989-1992)

Este trabalho tem por objeto a análise da relação entre os Poderes Executivo e Legislativo Municipal, tal como se constituiu nas negociações do Plano Diretor na Câmara Municipal de São Paulo, durante a administração da prefeita Luíza Erundina de Souza, no período de 1989 a 1992.

Partidos políticos e educação: os projetos neoliberal e socialista: PFL, PRN, PDT e PT

O objeto de estudo desse trabalho é a análise da concepção de política educacional de partidos políticos atuantes no cenário político brasileiro: PFL, PRN, PDT e PT. O trabalho foi subdividido em quatro partes. Na parte inicial é detalhado o quadro teórico que permeará a análise dos referidos partidos a partir de dois enfoques. O primeiro trata dos referenciais teóricos utilizados nos estudos acerca das políticas sociais e especificamente das educacionais. O segundo aborda a relação entre educação e trabalho no modo de produção capitalista. A segunda parte do trabalho é relativa aos pressupostos teóricos que embassam os partidos políticos: Neoliberalismo e Socialismo. Nela são delineados os pontos principais do conceito de educação de cada vertente. Na terceira parte são efetuadas considerações sobre os partidos adeptos do neoliberalismo (PFL e PRN) e do Socialismo (PT e PDT). São sintetizados os pontos principais dos programas desses partidos. Na última parte é procedida a análise da concretização de duas políticas educacionais: a do Governo Collor e a do Partido dos Trabalhadores nos municípios sob sua administração.

Líquidos iônicos aplicados na síntese e estabilização de nanopartículas de Pt(0) e Pd/Pt(0), caracterização e estudos em reações de hidrogenação catalítica

A presente tese descreve a síntese e estabilização de nanopartículas de Pt (0) nos líquidos iônicos BMI.PF6, BMI.BF4 e BMI.CF3SO3, a síntese de nanopartículas bimetálicas de Pd/Pt (0) em líquido iônico BMI.PF6, a caracterização destes materiais por TEM, HRTEM, XRD, SAXS e XPS, e principalmente o estudo da aplicação destes materiais como catalisadores em reações de hidrogenação. A decomposição do precursor catalítico Pt2(dba)3 e redução do precursor PtO2 dissolvidos nos líquidos iônicos BMI.PF6, BMI.BF4 e BMI.CF3SO3 utilizando hidrogênio molecular como agente redutor resultou em nanopartículas de Pt (0) com um diâmetro médio entre 2-3 nm. Essas partículas, devidamente caracterizadas, foram utilizadas como catalisadores na hidrogenação de compostos olefínicos e aromáticos. Estudos cinéticos e mecanísticos de formação das nanopartículas metálicas, utilizando a hidrogenação de cicloexeno como sonda química, foram aplicados para avaliar e confirmar que as espécies ativas presentes nas reações de hidrogenação eram compostas de Pt (0). Os resultados obtidos foram complementados por TEM. As caracterizações das nanopartículas de Pt (0) (TEM, SAXS e XPS), os estudos cinéticos de formação destas, assim como, os dados de hidrogenação catalítica; evidenciaram que os líquidos iônicos utilizados são um excelente agente estabilizante para a síntese de nanopartículas de Pt (0) e Pd/Pt (0), bem como um meio ideal para reações de hidrogenação catalítica.