Made available in DSpace on 2014-06-11T19:35:45Z (GMT). No. of bitstreams: 0 Previous issue date: 2012-04-27Bitstream added on 2014-06-13T19:25:22Z : No. of bitstreams: 1 scachetti_tp_dr_bauru.pdf: 2317656 bytes, checksum: f3ccf09db890d68a4ff230b606ab2176 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / No presente trabalho foram estudadas as reações de oxidação de etileno glicol e glicerol sobre a superfície dos intermetálicos PtSb/C e PdSb/C, em meio alcalino (NaOH) e ácido (HCIO4). As nanopartículas intermetálicas de PtSb/C e PdSb/C foram preparadas pelo método de redução de poliol e caracterizadas por DRX, MEV-EDX e MET, cujos resultados indicaram que a metodologia utilizada foi eficaz para a obtenção dos materiais na estequiometria desejada. A análise morfológica da superfície dos intermetálicos mostrou a formação de aglomerados e tamanho médio de partículas entre 1nm e 2nm, para o material PdSb/C e PtSb/C, respectivamente. A eletrocatálise das reações de oxidação dos alcóois foi avaliada por voltametria cíclica e cronoamperometria, em temperatura ambiente. Os resultados revelaram que o material PtSb/C apresenta maior desempenho eletroquímico que a Pt/C E-TEK na oxidação do glicerol em meio alcalino. O intermetálico PdSb/C não apresenta atividade eletroquímica em meio ácido. Contudo, em meio alcalino, o PdSB/C exibe maior tolerância ao bloqueio de intermediários adsorvidos do que a superfície da Pt/C E-TEK, e desloca o potencial de início de oxidação do glicerol para valores mais negativos, em relação ao Pd/C. Por meio de experimentos de espectroscopia de infravermelho in situ foram propostas rotas reacionais para as oxidações investigativas. A formação de CO2 em ácido, e carbonato em meio alcalino, foi observada para a superfície do PtSb/C na oxidação de ambos os alcóois, indicando que a clivagem da ligação C-C é efetiva sobre a superfície deste material. Contudo, o ácido glicólico é o principal produto formado durante a oxidação do etileno glicol, em meio ácido e alcalino, sobre a superfície do PtSb/C; e também na oxidação de ambos os alcoóis, sobre o eletrodo intermetálico... / In this work, the oxidation reaction of ethylene glycol and glycerol on the surface of the intermetallics PtSb/C and PdSb/C electrodes were investigated in both alkaline (NaOH) and acid (HCIO4) media. The intermetallics PdSb/C and PtSb/C nanoparticles were prepared via the polyol reduction method, and the resulting nanoparticles were characterized by XRD, SEM-EDS, and TEM techniques. The characterization data have indicated that the employed methodology indeed furnished materials with the desidered chemical identity stoichiometry. Surface morphology analysis revealed the presence of particles with mean sizes of 1 nm and 2 nm for PdSb/C and PtSb/C, respectively, as well as the formation of agglomerates. Oxidation reactions of the investigated alcohols were studied by cyclic voltammetry and chronoamperometry at room temperature. The obtained results have demonstrated that the PtSb/C electrode performed better than Pt/C E-TEK for glycerol oxidation in alkaline medium. The intermetallic PdSb/C electrode did not display any electrochemical activity in acidic medium. However, in alkaline medium, the PdSb/C electrode exhibited higher tolerance to active site blockage as compared to the Pt/C R-TEK electrode surface. Moreover, the PdSb/C electrode shifted the onset of glycerol oxidation to less positive potential values as compared to Pd/C. In situ infrared spectroscopy experiments aided the proposal of reaction pathways for the studied oxidation reactions. The formation of Co2, in acidic medium, and carbonate, in alkaline medium, were detected for the reaction taking place on the surface of the PtSb/C electrode for the oxidation of both alcohols, showing that the C-C bond cleavage effectivelly took place on the surface of this material. Nevertheless, glycolic acid was the main product from ethylene glycol... (Complete abstract click electronic access below)

Magister Scientiae - MSc (Physics) / Rare-earth intermetallic compounds continue to draw considerable attention, due to their fundamental importance in understanding physical properties and potential applications based on a variety of phenomena. The focus of this project is to employ two family of rare-earth intermetallic compounds: RE2Pt2In (RE = Pr, Nd) and RE8Pd24Ga (RE = Gd, Tb, Dy) ternary intermetallic systems as a model candidate to uncover the underlying ground state properties that result in a strong coupling between the conduction electron and the 4f-electron of the rare-earth ions.

Orientador: Antonio Carlos Dias Ângelo / Banca: Aroldo Geraldo Magdalena / Banca: Adalgisa Rodrigues de Andrade / O Programa de Pós Graduação em Ciência e Tecnologia de Materiais, PosMat, tem carácter institucional e integra as atividades de pesquisa em materiais de diversos campi / Resumo: Atualmente uma quantidade demasiadamente grande de glicerol tem sido produzida. O desenvolvimento de materiais que consigam eletro-oxidar essa molécula é de extrema importância, para que assim, este composto possa ter ter aplicações na geração de energia ou mesmo produzir produtos de interesse industrial. No presente trabalho foram estudadas as reações de oxidação do glicerol sobre as nanopartículas intermetálicas ordenadas PtSn/C, PdSn/C e as ligas PtSn/C, PdSn/C em meio alcalino. A caracterização físico-química dos materiais foi realizada por Difração de Raios-X, Espectroscopia de Energia Dispersiva por Raios-X, Microscopia Eletrônica de Transmissão de Alta Resolução e Espectroscopia de Absorção de Raios-X. Estas análises indicaram a formação de fases intermetálicas quando utilizado o método de redução por poliol, e a formação de ligas metálicas quando empregado o método da microemulsão. O desempenho eletroquímico foi avaliado pelas técnicas de voltametria cíclica e cronoamperometria. Todas as nanopartículas apresentaram atividade frente à reação de oxidação do glicerol, sendo que os materiais à base de Pt se destacaram em relação aos de Pd. Além disso, foi o intermetálico ordenado PtSn/C que demonstrou melhor desempenho eletroquímico, o que pode ser substituído ao efeito eletrônico provocado pela adição do segundo metal (Sn). Através das análises dos espectros de massas foi identificado que para os materiais PtSn/C os produtos formados durante eletrólise foram gliceraldeído, ácido glicólico e ácido fórmico, evidenciando a clivagem entre as ligações C-C. Em relação a PdSn/C, a quebra entre as ligações C-C não ocorreu, e os produtos formados foram gliceraldeído ou dihidroxiacetona para o intermetálico ordenado PdSn/C, e ácido tartrônico para a liga PdSn/C. Foi sugerido o mecanismo da reação de oxidação do glicerol nos materiais estudados / Abstract: Nowadays, the huge amount of glycerol produced from biodiesel obtaining process becomes an important environmental concern in our country. So, development of new and improvement of ancient methods of using glycerol urges to avoid the unappropriated discard of this compound and the consequent environmental pollution. Among the several methods early proposed, the enhancement of electrode materials able to electrooxidize glycerol appears as viable alternative to produce energy and/or high aggregated value chemicals. In the present work, it was investigated the performance of ordered intermetallic nanoparticles PtSn/C and PdSn/C and the alloys PtSn/C and Pd/Sn/C as anode materials to electrooxidize glycerol molecule in alkaline medium. The physical-chemical characterization of the synthesized nanoparticles was performed by using X-Ray Diffraction, Energy-Dispersive Spectrometry, High Resolution Transmission Electronic Microscopy and X-ray Absorption Spectroscopy techniques. The physical-chemical characterization confirmed the prevalence of ordered intermetallic structure from the synthetic route via polyol-modified protocol as well as the alloy structure prevalence as the materials were synthesized via micro-emulsion protocol. The electrochemical performance of the materials was investigated by using cyclic voltammetry and chronoamperometry techniques. All materials proved to be active for the glycerol electrooxidation reaction and it was observed the superior performance of the materials based on Pt as compared to the similar ones based on Pd. Moreover, ordered intermetallic PtSn/C presented the best performance among all the studied materials, which was proposed to be a consequence of the electronic effect of the neighbor Sn atom towards the Pt adsorption site. From mass spectra analysis, glyceraldehyde, glycolic acid and formic acid were detected as main products as the electrooxidation took place... / Mestre

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Made available in DSpace on 2014-10-09T12:29:34Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:00:27Z (GMT). No. of bitstreams: 1 01338.pdf: 15640302 bytes, checksum: 4fae24b5feb8211558ce2044fac55ec5 (MD5) / Tese (Doutoramento) / IEA/T / Escola Politecnica, Universidade de Sao Paulo - POLI/USP

M.Sc. / Please refer to full text to view abstract

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published_or_final_version / abstract / Mechanical Engineering / Master / Master of Philosophy

Ph.D. (Physics) / Please refer to full text to view abstract

by Kwong Wai Kuen = 鋁銘金屬間化合物的製造和性能測試 / 鄺偉權. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2003. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Kwong Wai Kuen = Lü ming jin shu jian hua he wu de zhi zao he xing neng ce shi / Kuang Weiquan. / Acknowledgement --- p.i / Abstract --- p.ii / 摘要 --- p.iii / List of tables --- p.iv / List of figures --- p.v / Table of contents --- p.xi / Chapter Chapter 1 --- Background / Chapter 1.1 --- Introduction --- p.1-1 / Chapter 1.2 --- Aluminum --- p.1-1 / Chapter 1.3 --- Chromium --- p.1-3 / Chapter 1.4 --- Intermetallics --- p.1-4 / Chapter 1.4.1 --- Alloys and intermetallics --- p.1-4 / Chapter 1.4.2 --- Properties of intermetallics --- p.1-5 / Chapter 1.4.3 --- Intermetallics 一 past to present --- p.1-6 / Chapter 1.4.4 --- Commonly used intermetallics --- p.1-7 / Chapter 1.4.5 --- Prospects of intermetallic compounds --- p.1-9 / Chapter 1.5 --- Previous works --- p.1-11 / Chapter 1.6 --- Current work --- p.1-12 / Chapter 1.7 --- Outline of thesis --- p.1-12 / References --- p.1-14 / Tables and figures --- p.1-17 / Chapter Chapter 2 --- Methodology and Instrumentation / Chapter 2.1 --- Experimental approaches --- p.2-1 / Chapter 2.2 --- Sample preparation --- p.2-2 / Chapter 2.2.1 --- Powder mixture --- p.2-2 / Chapter 2.2.2 --- Cold-pressing --- p.2-2 / Chapter 2.2.3 --- Pressureless sintering --- p.2-2 / Chapter 2.2.4 --- Hot-pressing --- p.2-3 / Chapter 2.2.5 --- Arc-melting --- p.2-4 / Chapter 2.3 --- Sample characterization --- p.2-5 / Chapter 2.3.1 --- DTA --- p.2-5 / Chapter 2.3.2 --- TMA --- p.2-5 / Chapter 2.3.3 --- Density measurement --- p.2-6 / Chapter 2.3.4 --- Microhardness measurement --- p.2-7 / Chapter 2.3.5 --- Scanning electron microscopy --- p.2-8 / Chapter 2.3.6 --- X-ray powder diffractometry --- p.2-9 / References --- p.2-10 / Figures --- p.2-11 / Chapter Chapter 3 --- Thermal analysis of Al-Cr powder mixtures / Chapter 3.1 --- Introduction --- p.3-1 / Chapter 3.2 --- Experiments --- p.3-1 / Chapter 3.3 --- Results and discussions --- p.3-2 / Chapter 3.3.1 --- DTA results --- p.3-2 / Chapter 3.3.2 --- Al-23wt%Cr --- p.3-2 / Chapter 3.3.3 --- Al-28wt%Cr and Al-33wt%Cr --- p.3-5 / Chapter 3.3.4 --- Al-46wt%Cr --- p.3-8 / Chapter 3.3.5 --- Al-55wt%Cr --- p.3-9 / Chapter 3.3.6 --- Al-79wt%Cr --- p.3-10 / Chapter 3.4 --- Reaction mechanisms in the formation of Al-Cr intermetallic compounds --- p.3-12 / Chapter 3.5 --- Summary --- p.3-12 / References --- p.3-14 / Tables and figures --- p.3-15 / Chapter Chapter 4 --- Fabrication of Al-Cr samples by hot-pressing and by arc-melting / Chapter 4.1 --- Introduction --- p.4-1 / Chapter 4.1.1 --- Hot-pressing method --- p.4-1 / Chapter 4.1.2 --- Arc-melting method --- p.4-2 / Chapter 4.2 --- Experiments --- p.4-2 / Chapter 4.3 --- Results and discussions --- p.4-3 / Chapter 4.3.1 --- Hot-pressing method for some specific compositions --- p.4-3 / Chapter 4.3.2 --- Hot-pressing method to produce low Cr content (LC) samples --- p.4-5 / Chapter 4.3.3 --- Effects of hot-pressed time and temperature --- p.4-6 / Chapter 4.3.4 --- Arc-melting method for some specific compositions --- p.4-8 / Chapter 4.3.5 --- Arc-melting method to produce LC samples --- p.4-10 / Chapter 4.4 --- Summary --- p.4-11 / Reference --- p.4-12 / Tables and figures --- p.4-13 / Chapter Chapter 5 --- Thermal expansion coefficients of arc-melted Al-Cr samples / Chapter 5.1 --- Introduction --- p.5-1 / Chapter 5.1.1 --- Thermal expansion --- p.5-1 / Chapter 5.1.2 --- Relations between thermal expansion and structural material --- p.5-1 / Chapter 5.2 --- Experiments --- p.5-2 / Chapter 5.3 --- Results and discussions --- p.5-3 / Chapter 5.3.1 --- TMA results of A1 and Cr --- p.5-3 / Chapter 5.3.2 --- TMA for Al-Cr IMCs --- p.5-3 / Chapter 5.4 --- Summary --- p.5-4 / References --- p.5-6 / Figures --- p.5-7 / Chapter Chapter 6 --- Physical properties of Al-Cr intermetallic compounds / Chapter 6.1 --- Introduction --- p.6-1 / Chapter 6.2 --- Results and discussion --- p.6-1 / Chapter 6.2.1 --- Hot-pressed samples --- p.6-1 / Chapter 6.2.1.1 --- Hot-pressed LC samples --- p.6-2 / Chapter 6.2.1.2 --- Effects of hot-pressing temperature and time --- p.6-3 / Chapter 6.2.2 --- Arc-melted samples --- p.6-4 / Chapter 6.2.3 --- Comparison between the hot-pressed sample and the arc-melted sample --- p.6-6 / Chapter 6.3 --- Summary --- p.6-7 / Tables and figures --- p.6-9 / Chapter Chapter 7 --- Conclusions / Chapter 7.1 --- Summary --- p.7-1 / Chapter 7.2 --- Future works --- p.7-2