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Les phonons mous et le couplage électron-phonon sont considérés comme responsables d’un grand nombre de transition de phase. Pour en comprendre complétement les mécanismes, il est nécessaire d’étudier à la fois les modifications structurales, les changements de configuration électronique et les dynamiques de réseau cristallin. De toute évidence, cela représente une charge de travail expérimental et théorique considérable, voire même hors d’atteinte.Néanmoins, il est parfois possible d’introduire certaines simplifications et d’ainsi rendre une telle étude réalisable. C’est le cas pour les deux systèmes au cœur de ce travail de thèse, pour lesquels la transition de phase peut être diviser en deux instabilités : l’une est structurale, intrinsèque aux éléments constitutifs du système et l’autre, superposée, provient de la configuration électronique. L’interaction entre ces instabilités est illustrée à travers l’exemple de deux systèmes à priori hétérogènes, la famille des bronzes monophosphate de tungstène d’une part et l’antimoine d’autre part, qui révèleront finalement posséder des similarités inattendues. La combinaison des techniques de diffusion diffuse et de diffusion inélastique de rayons X permet des observations qualitatives et une meilleure compréhension de la situation pour les deux systèmes.Les bronzes monophosphate de tungstène font partie de la famille des oxydes quasi-2D, (PO2)4(WO3)2m, qui ont la particularité d’être sujet à des instabilités de type onde de densité de charges (ODC). Ces bronzes sont constitués d’une structure de perovskite vide composée par des couches octaédriques (WO3)2m. L’épaisseur de chacune de ces couches est définie par la valeur de m, qui mène ainsi à différents types de phase d’ODC. Le cas du terme m=2 a aussi été étudié car le fait que les chaînes zig-zag y soient isolées conduit à une instabilité quasi-1D. La présence d’une phase d’ODC a été découverte à TC=270K avec q=0.25b*. Cette phase est engendrée par le mouvement à corps rigide, plus exactement, par les basculements corrélés des octaèdres. Pour les autres termes (m=6,7 et 8), l’instabilité structurale a une origine différente et est liée à l’agencement en couches de WO3, plus particulièrement aux déplacements corrélés des chaînes W-O-W-O. Ces derniers sont la cause d’une forte diffusion diffuse sur des plans spécifiques, résultant de la présence de phonons ’relativement’ mous localisés dans la même région. Ensuite, l’emboitement de la surface de Fermi quasi-2D est à l’origine de l’ancrage du vecteur de modulation sur une valeur spécifique de transfert de moment, définit par l’interaction de deux instabilités, structurale et électronique. De façon remarquable, l’amplitude des déplacements des atomes de tungstène dans le terme m=8 est beaucoup plus élevée que dans le m=6.L’antimoine à température ambiante possède une structure rhomboédrique, dérivant d’une légère distorsion de la structure cubique primitive (CP) par transition de Peierls. Sous pression, la distorsion se réduit sans toutefois disparaître complétement, puisque l’antimoine se transforme dans un premier temps en une série de structures complexes, pour finalement adopter celle possédant la plus grande symétrie, la structure cubique centrée (CC). De la même façon que pour les bronzes, les caractéristiques de la diffusion diffuse ainsi que, dans une certaine mesure, les particularités de la dynamique du réseau rhomboédrique, s’expliquent à travers de l’instabilité du réseau cubique primitif. Cette dernière est liée aux déplacements corrélés dans les chaînes avec direction pseudo-cubique <100>. En outre, les détails de la transition de phase peuvent être explicités par l’association de l’analyse des vecteurs critiques de la transformation CC-CP avec les résultats expérimentaux obtenus sur la dépendance en pression de l’énergie des phonons. / A large number of phase transitions can be interpreted as being driven by phonon softening and/or electron-phonon coupling. Thus, a full mechanistic description requires the understanding of structural transformation, changes in electronic structure and lattice dynamics. All together this represents an enormous, for many cases unrealisable, experimental and theoretical effort.However, with the introduction of appropriate assumptions the problem may be simplified. Here we concentrate on two systems, where the interpretation of the phase transition may be split into an intrinsic instability of the building blocks combined with a superimposed electronic instability. We illustrate the interplay between the framework and electron-phonon-related instabilities using the seemingly heterogeneous examples of phosphate tungsten bronzes and elementary antimony. Based on the combined results from diffuse and inelastic X-ray scattering, we propose for the two systems a picture that explains the experimental observations. The similarities found between these two systems are deemed to be rather surprising.Monophosphate tungsten bronzes are a family of quasi-2D-oxides, (PO2)4(WO3)2m, that exhibits charge density wave (CDW) instability. They contain empty perovskite WO3 slabs with varying thickness between different members, characterised by the $m$ value. This thickness defines the sequence of charge density wave phases that appear on cooling. The degenerate case of $m$=2, presenting a quasi-1D instability, was explored since the WO3-octahedra zig-zag chain is isolated. A CDW phase (TC=270K and q=0.25b*) is found to be linked to a rigid-body motion, precisely, to a correlation in the tilting of the octahedra. For the others studied members, as m=6,7 and 8, we found another kind of structural instability. In this case the origin comes from the WO$_3$ slabs framework, realised as correlated displacements of tungsten atoms along the octahedral 4-fold axis direction (W-O-W-O direction). This leads to a strong x-ray diffuse scattering localised in specific planes, linked to relatively soft phonons modes. Specific Fermi surface nesting, close to the 2D case, gives rise to a freezing of the modulations at the specific momentum transfer, defined by the interplay of two instabilities, the structural and electronic one. Remarkably, the displacements of W for m=8 are much superior than in m=6.Elemental antimony at ambient condition has an A7 rhombohedral structure, obtained by small distortion from primitive cubic (PC) lattice through a Peierls transition. Under pressure, the distortion is reduced, but remains finite, as antimony transforms through a series of highly complex structures, before adopting as last the highest-symmetry body-centred cubic (BCC) phase. The main diffuse scattering features and to some extent the peculiarities in the lattice dynamics of the A7 phase – as above - can be explained by the instability of the primitive cubic network with respect to correlated displacements along the chains with <100> pseudo-cubic directions. Analysis of critical vectors for the BCC-PC transformation together with experimentally obtained phonon-energies pressure dependence provides further insights into the details of the phase transformation.

Antimoine et tungstène, deux "petits métaux" qui, à différentes périodes, eurent une importance stratégique liée à l'industrialisation et l'armement. L'antimoine, connu depuis l'Antiquité, fut exploité en France à partir du XVIe siècle mais c'est aux XIXe et XXe siècles qu'il fit l'objet d'une exploitation significative. Les applications industrielles du tungstène, plus récentes, datent de la fin du XIXe siècle. Aux XIXe et XXe siècles, plusieurs périodes présentent une convergence entre la taille des gisements, les méthodes d'exploitation et de traitement employées, la structure des entreprises et la consommation de ces métaux. Cette conjonction s'avère favorable à la prospérité, dans la période préindustrielle puis au XXe siècle, au développement des mines métropolitaines. La dispersion des compagnies et la multitude de petits gisements fut, au contraire, préjudiciable à la prospérité de cette activité. Dans les années 1960, l'implication de l'Etat dans la recherche minière, à travers le BRGM, puis les mesures de soutien à la prospection privée, aboutirent à la découverte de nouveaux gisements de métaux non-ferreux. En revanche, l'implication de l'Etat dans l'exploitation minière, à travers COFRAMINES, fut moins favorable. La gestion administrative et peu réactive s'avéra inadaptée à la versatilité du marché de ces métaux. Aujourd'hui, en France, la mine se heurte à de telles contraintes, sociales, administratives et environnementales, que la relance d'une exploitation de l'antimoine et du tungstène parait peu probable, dans les conditions économiques actuelles. / Antimony and tungsten, two "small alloy metals" that both, at different periods of time, had a strategic importance, linked to industrialisation and armament. Antimony which was known in Antiquity, has been mined in France since the 16th century, but it was truly during the 19th and 20th centuries. Industrial applications of tungsten are recent, dating back to the last decade of the 19th century. During the 19th and 20th centuries, several periods present a convergence between the size of deposits, the methods used to exploit and process, the companies' structure, and the consumption of these two metals. This conjunction was favourable to the antimony mines' prosperity during the pre-industrial period then, in the 20th century, to the development of several mines. The dispersion of companies, on a multitude of small deposits, is prejudicial to the development of antimony and wolfram-rich districts like those of the Massif Central. The French State's implication, through the BRGM's actions starting in the 1960s, then by the establishment of aids towards private prospecting, was beneficial for the discovery of non-ferrous metals deposits. However, the State's decision to change from exploration to mining, through COFRAMINES, was less favourable. The administration management, sometimes burdened and slow to react, showed itself to be inadequate in a context as versatile as the antimony and tungsten market. Today the mining industry, in its whole, faces such social, administrative and environmental constraints, that the antimony and tungsten mining industry's revival, in today's economic and political situation, remains improbable.

La qualité de l’air extérieur (QAE) a fait l’objet d’une législation dès 1996 avec la loi LAURE. Depuis 2008, la directive européenne 2008/50/CE a instauré des obligations de mesure et de seuils à ne pas dépasser pour certains polluants à l’échelle européenne. Selon de nombreuses données toxicologiques et épidémiologiques, la pollution de l’air est à l’origine d’insuffisances respiratoires, d’asthme, de maladies cardiovasculaires et de cancers.Les composés organiques volatils (COV) et notamment le benzène, le toluène, l’ethylbenzène et les xylènes (les composés BTEX) sont des polluants avérés et participent grandement à la dégradation de la qualité de l’air intérieur et extérieur. Ce travail de thèse a concerné la réalisation d’un multicapteur de gaz à base d’oxyde métallique pour la détection de traces de BTEX dans le cadre du projet SMARTY (SMart AiR qualiTY). Un système de caractérisation électrique complet a été conçu et mise au point pour la détection de très faibles concentrations de BTEX (le ppb). Après une étude bibliographique, plusieurs matériaux ont été sélectionnés (WO3, ZnO, SnO2). Les caractérisations électriques des couches sensibles sélectionnées ont été effectuées sous air sec et sous différents taux d’humidité en présence de BTEX et de gaz interférents (NO2, CO2). Le WO3 a montré les meilleures performances en présence d’humidité et a été choisi pour le transfert de technologie qui accompagne les nouveaux transducteurs brevetés AMU. Le multicapteur à base de WO3 a montré une détection limite de 1 ppb sous 50% d’humidité relative et a permis de détecter et de quantifier de manière efficace les BTEX. / Outdoor air quality is subjected to the law LAURE since 1996. In 2008, the european directive 2008/50/EC introduced measurement requirements and thresholds that should not be exceeded for certain pollutants on a european scale. According to several toxicological and epidemiological studies, air pollution causes respiratory failure, asthma, cardiovascular diseases and cancers. In Europe, air pollution is responsible for more than 300 000 early deaths a year.Volatile organic compounds (VOCs), particularly benzene, toluene, ethylbenzene and xylenes (BTEX compounds) are proven pollutants and play a major role in the degradation of indoor and outdoor air quality. This thesis is dedicated to the development of a metal oxide based multi-gas sensor for the detection of traces of BTEX within the framework of the SMARTY project (SMart AiR qualiTY). A complete electrical characterization system was designed and implemented for the detection of sub-ppm concentrations of BTEX.Based on the state-of-art, several materials were selected (WO3, ZnO, SnO2). The electrical characterizations of the selected sensitive layers were carried out under dry air and under different humidity levels in the presence of BTEX and interfering gases (NO2, CO2). Tungsten oxide (WO3) exhibits the best performance in the presence of moisture and is chosen for the technology transfer that accompanies the new patented AMU transducers. The WO3-based multi-sensor has a lower limit of detection (LOD) of 1 ppb at 50% relative humidity and effectively detects and quantifies BTEX.

As células a combustível são dispositivos eletroquímicos que produzem energia elétrica limpa. Entretanto, o seu uso em larga escala ainda é limitado devido às enormes perdas de potencial que ocorrem no cátodo em função da lenta cinética da reação de redução de oxigênio (RRO). Portanto, é necessário o desenvolvimento de novos catalisadores que sejam viáveis comercialmente, apresentem alta atividade eletrocatalítica e grande estabilidade para esta reação. Neste trabalho, a RRO foi estuda em meio ácido em eletrocatalisadores à base de platina suportadas em carbetos de tungstênio (WC) e molibdênio (MoC) com diferentes estruturas cristalinas. Os carbetos foram preparados pelos métodos de decomposição térmica (MDT) e carburação (MC) e, subsequentemente, utilizados para a preparação dos catalisadores do tipo Pt-carbeto pelo método do ácido fórmico ou borohidreto de sódio. Estes materiais foram caracterizados por difração de raios-X (XRD), espectroscopia de energia dispersiva de raios-X (EDX), microscopia eletrônica de transmissão (TEM), espectroscopia de absorção de raios-X (XAS) in situ e espectroscopia de fotoelétrons excitados por raios-X (XPS). As medidas eletroquímicas foram realizadas em meio ácido usando a técnica de eletrodo disco-anel rotativo de camada fina. Os resultados de XRD, em conjunto com as medidas de TEM, indicaram que o MDT e MC fornecem carbetos com estruturas cúbicas (&beta;-WC1-x e &delta;-MoC) e hexagonais (&alpha;-WC e &alpha;-Mo2C) com tamanho de partícula < 2 nm e entre 10 e 40 nm, respectivamente. Os estudos eletroquímicos evidenciaram que os catalisadores Pt-carbeto/C apresentam diferenças de atividade específica (SA) e mássica (MA) para a RRO em função da estrutura e composição e que todos os catalisadores do tipo Pt-&beta;-WC1-x/C, Pt- &alpha;-Mo2C/C e Pt-&delta;-MoC/C e Pt2Ni- &alpha;-WC/C apresentam maior SA em comparação à Pt/C. A concentração de carbeto na matriz de carbono também influenciou significativamente os valores de SA, porém não há uma tendência clara que permita unificar um efeito comum para todos os catalisadores. Dentre todos estes catalisadores, o Pt-&beta;-WC1-x40/C e o Pt-&delta;-MoC40/C são 3,6 e 2,5 vezes mais ativos (SA) em comparação ao catalisador Pt/C. Também foi observado que a via predominante da RRO envolve cerca de 4 elétrons por molécula de oxigênio, com baixa produção de H2O2 em todos os casos. No caso dos materiais baseados em Pt-&beta;-WC1-x/C, análises de XANES in situ mostraram um pequeno aumento na ocupação da banda 5d da Pt, o que deve levar a uma interação Pt-OHx mais fraca, aumentando a cinética da RRO como observado. Além disso, os resultados de XPS evidenciam que a melhora na atividade específica está relacionada a um efeito sinérgico entre Pt ou Pt2Ni com as espécies do tipo WOx ou MoOx; exceto para os catalisadores de ligas Pt2Ni, para o qual os resultados de XPS indicaram a presença de WC na superfície do catalisador. Os testes de estabilidade mostraram que apesar do Pt/C ser mais ativo após 12.000 ciclos, o catalisador Pt-&alpha;-WC20/C é o mais estável em relação a sua AS, indicando que as interações benéficas das fases remanescente de Pt e WC/WOx são mantidas após o teste de durabilidade. / Fuel cells are electrochemical devices that produce clean electrical energy. However, their use on large scale is still limited due to the enormous potential losses that occur at the cathode due the slow kinetics of the oxygen reduction reaction (ORR). Therefore, the development of new catalysts that are commercially viable, present high electrocatalytic activity and great stability for this reaction is still necessary. In this work, the ORR was studied in acid medium on platinum-based electrocatalysts supported on tungsten (WC) and molybdenum (MoC) carbides with different crystalline structures. Carbides were prepared by the thermal decomposition (TDM) and a carburizing (CM) methodes and, subsequently used for the preparation of the Pt-carbide type catalysts by the formic acid or sodium borohydride method. These materials were characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The electrochemical measurements were performed in acid medium using the thin-layer rotating disk-ring electrode technique. The results of XRD, together with those of TEM, indicate that the MDT and MC provide carbides with cubic (&beta;-WC1-x and &delta;-MoC) and hexagonal ( &alpha;-WC and &alpha;-Mo2C) structures with particle size < 2 nm and between 10 and 40 nm, respectively. The Pt-carbide/C catalysts exhibit differences in the specific activity (SA) and mass (MA) for the ORR as a function of structure and composition. All catalysts of the types Pt-&beta;-WC1-x/C, Pt- &alpha;-Mo2C/C, Pt-&delta;-MoC/C and Pt2Ni- &alpha;-WC/C presented higher SA as compared to Pt/C. The concentration of carbide in the carbon matrix significantly influence the SA, but no tendency was clearly found so to identify a common effect catalysts overall. Among all catalysts, Pt-&beta;-WC1-x40/C and Pt-&delta;-MoC40/C are 3.6 and 2.5 times more active (SA) compared to the Pt/C catalyst. It was also observed that the predominant ORR mechanism involve &cong; 4 electrons per oxygen molecule, and so with negligible production of H2O2. In the case of the materials based on Pt-&beta;-WC1-x/C, in situ XANES analyzes evidenced a small increase in the Pt 5d-band, occupancy leading to a weaker Pt-OHx interaction, increasing ORR kinetics as observed. In addition, XPS results show that the improvement in SA is related to a synergistic effect between Pt or Pt2Ni with WOx or MoOx species, except for the Pt2Ni alloy catalysts, for which the XPS results indicated the presence of some WC on the catalyst surface. Stability tests show that although Pt/C is more active after 12,000 cycles, the Pt-&alpha;-WC20/C catalyst is the most stable relative to its SA, indicating that the beneficial interactions of the remaining phases of Pt and WC/WOx are maintained after the durability test.

Na indústria hidrometalúrgica, diversos materiais são utilizados para a construção dos equipamentos, a fim de satisfazer as necessidades dos processos que estão sujeitos, tendo em conta a importância deles em condições complexas, tais como erosão e a corrosão. Neste trabalho é avaliado o comportamento de um aço inoxidável martensítico AISI 410 tratado termicamente com têmpera e revenimento, frente aos revestimentos Carbeto de Tungstênio (86WC-10Co4Cr) obtido por aspersão térmica (High Velocity Oxygen Fuel-HVOF), e um elastômero PUR comercial MetaLine 785 em condições de desgaste do tipo lama, analisando a perda de volume, a determinação da área e profundidade erodida das amostras, para os ângulos de incidência de 30∘ e 90∘ entre o eixo de simetria do fluxo do fluido e a superfície das amostras. Os ensaios foram realizados para os diferentes tipos de materiais em um equipamento para ensaios simulados de lama, desenvolvido como parte da pesquisa no LACER (Laboratório de Materiais Cerâmicos) da Universidade Federal do Rio Grande do Sul (UFRGS), sob controle de parâmetros como ângulo de impacto e sua velocidade, temperatura de ensaio e concentração de partículas erosivas na suspensão, neste caso foi usada alumina eletrofundida ALO marrom da companhia Treibacher. Realizou-se a caracterização dos materiais, na sua microestrutura Microscopia Eletrônica de Varredura (MEV), Microscopia Óptica (M.O), espessura, rugosidade, porosidade, microdureza e estruturalmente na identificação de fases Difração de Raios X (DRX), Espectroscopia por Energia Dispersiva (EDS), o analise térmico Perda ao Fogo (LOI) para o caso do elastômero PUR, e a distribuição de tamanho de partícula (LG) e morfologia para o erodente. Com a pesquisa conseguiu-se estabelecer as relações entre o desgaste erosivo por lama e as propriedades físicas relacionadas aos materiais avaliados, nas condições estabelecidas no ensaio de erosão do equipamento, e concluiu-se que o revestimento de 86WC-10Co4Cr carbeto de Tungstênio apresentou uma melhor resistência ao desgaste erosivo tipo lama, em comparação com o aço inoxidável martensítico AISI 410 e o elastômero PUR comercial MetaLine 785. / In the hydrometallurgical industry, many materials are used in the construction of the equipment in order to satisfy the needs of the processes to which they are subjected, taking into account their importance in complex conditions such as erosion and corrosion. In this work, the behavior of a quenched and tempered AISI 410 martensitic stainless steel is compared to tungsten carbide (86WC-10Co4Cr) obtained by thermal spray (High Velocity Oxygen Fuel - HVOF) and to a commercial elastomer PUR MetaLine 785 under slurry erosion conditions. Volume loss, area determination and eroded depth of the samples were analyzed at angles of incidence of 30∘ and 90∘ between the axis of symmetry of the fluid flow and the surface of the samples. The tests were carried out for the different types of materials in a slurry erosion simulation device, developed as part of the research in LACER (Laboratory of Ceramic Materials) of the Federal University of Rio Grande do Sul (UFRGS), via the control of parameters such as angle and speed of impact, test temperature and concentration of erosive particles in the suspension. In this case, electrofused brown ALO alumina (Treibacher) was used. The materials were characterized with regard to their microstructure (SEM), thickness, roughness, porosity, microhardness, structure in the phase identification (DRX) (EDS), thermal analysis (LOI) in the case of the PUR elastomer and the particle size distribution (LG) and morphology for the erodent. The research was able to establish the relationships between the slurry erosive wear and the physical properties related to the evaluated materials, under the conditions established in the erosion test of the equipment. It was concluded that the coating 86WC-10Co4Cr tungsten carbide presented better resistance to the slurry erosion wear when compared to AISI 410 martensitic stainless steel and the PUR commercial elastomer MetaLine 785.

Este trabalho apresenta os resultados da síntese e caracterização de nanoestruturas de óxido de tungstênio (WO3) obtidos por via ultrassônica em meio não aquoso. Esta técnica tem como vantagens o uso de pouco material e o tempo empregado. A caracterização das nanoestruturas foi realizada por Microscopia Eletrônica de Transmissão (TEM), Microscopia Eletrônica de varredura (MEV), espectroscopia Raman e no infravermelho, termogravimetria e difração de raios-X. A imobilização das nanoestruturas foi realizada em substratos condutores transparentes (ITO) por automontagem camadas por camadas (LbL) e deposição eletroforética (EPD). Foram efetuadas caracterizações eletroquímicas e espectroeletroquímicas com medidas in situ usando UV-Vis. Os resultados eletrocrômicos demostraram a estrutura nanométrica dos filmes obtidos, com parâmetros eletrocrômicos como contraste óptico, tempo de resposta e eficiência eletrocrômica típicos de sistemas nanoestruturados. Alguns aspectos relacionados com o uso de um líquido iônico prótico (PIL) foram mostrados, conferindo melhora na durabilidade dos filmes em relação ao eletrólito H2SO4 1,0 mol L-1. Com o objetivo de modular e incrementar a coloração dos filmes de WO3, foi preparado um viológeno para imobilização superficial através de um grupo ancorador. Os filmes modificados foram investigados por espectroeletroquímica e coordenadas de cor. As coordenadas de cromaticidade foram obtidas por um colorímetro virtual baseado na convenção CIE 1931, dados de cromaticidade para as reações eletrocrômicas dos filmes de WO3 modificado são mostrados em espaços de cor. / The present work describes the synthesis and characterization of WO3 nanoplates in a non-aqueous solvent using ultrasonic irradiation process. This method presents some advantages such as the small amount of reactants and time consumed. WO3 nanoplates have been characterized by TEM and SEM microscopies, Raman and Infrared spectroscopies, thermogravimetric analysis and X-ray diffraction. The nanostructured nanoplates were immobilized by electrostatic layer by layer and Electrophoretic Deposition (EPD) processes onto ITO substrates. Spectroelectrochemical experiments were carried out showing electrochromic performance of the WO3 films such as optical density, response time and chromatic efficiency in a typical way for nanostructured films of WO3. The results using a protic ionic liquid (PIL) as electrolyte, instead of H2SO4, showed improvement in cyclic durability. Cyclic voltammograms were combined with transmittance measurements for all films that undergo typical reversible electrochromic reaction. In order to modulate and improve the colorimetric changes, viologen molecules were prepared with an anchoring group for modifying the surface by the chemisorption of a monolayer. WO3 films with viologen monolayer were investigated using Spectroelectrochemical and color coordinates analysis. A virtual colorimeter was applied for the accurate calculation of CIE 1931 xy color coordinates investigation during the electrochromic reaction of modified films.

Este trabalho apresenta os resultados da síntese e caracterização de nanoestruturas de óxido de tungstênio (WO3) obtidos por via ultrassônica em meio não aquoso. Esta técnica tem como vantagens o uso de pouco material e o tempo empregado. A caracterização das nanoestruturas foi realizada por Microscopia Eletrônica de Transmissão (TEM), Microscopia Eletrônica de varredura (MEV), espectroscopia Raman e no infravermelho, termogravimetria e difração de raios-X. A imobilização das nanoestruturas foi realizada em substratos condutores transparentes (ITO) por automontagem camadas por camadas (LbL) e deposição eletroforética (EPD). Foram efetuadas caracterizações eletroquímicas e espectroeletroquímicas com medidas in situ usando UV-Vis. Os resultados eletrocrômicos demostraram a estrutura nanométrica dos filmes obtidos, com parâmetros eletrocrômicos como contraste óptico, tempo de resposta e eficiência eletrocrômica típicos de sistemas nanoestruturados. Alguns aspectos relacionados com o uso de um líquido iônico prótico (PIL) foram mostrados, conferindo melhora na durabilidade dos filmes em relação ao eletrólito H2SO4 1,0 mol L-1. Com o objetivo de modular e incrementar a coloração dos filmes de WO3, foi preparado um viológeno para imobilização superficial através de um grupo ancorador. Os filmes modificados foram investigados por espectroeletroquímica e coordenadas de cor. As coordenadas de cromaticidade foram obtidas por um colorímetro virtual baseado na convenção CIE 1931, dados de cromaticidade para as reações eletrocrômicas dos filmes de WO3 modificado são mostrados em espaços de cor. / The present work describes the synthesis and characterization of WO3 nanoplates in a non-aqueous solvent using ultrasonic irradiation process. This method presents some advantages such as the small amount of reactants and time consumed. WO3 nanoplates have been characterized by TEM and SEM microscopies, Raman and Infrared spectroscopies, thermogravimetric analysis and X-ray diffraction. The nanostructured nanoplates were immobilized by electrostatic layer by layer and Electrophoretic Deposition (EPD) processes onto ITO substrates. Spectroelectrochemical experiments were carried out showing electrochromic performance of the WO3 films such as optical density, response time and chromatic efficiency in a typical way for nanostructured films of WO3. The results using a protic ionic liquid (PIL) as electrolyte, instead of H2SO4, showed improvement in cyclic durability. Cyclic voltammograms were combined with transmittance measurements for all films that undergo typical reversible electrochromic reaction. In order to modulate and improve the colorimetric changes, viologen molecules were prepared with an anchoring group for modifying the surface by the chemisorption of a monolayer. WO3 films with viologen monolayer were investigated using Spectroelectrochemical and color coordinates analysis. A virtual colorimeter was applied for the accurate calculation of CIE 1931 xy color coordinates investigation during the electrochromic reaction of modified films.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering; and, (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 70-73. / by William Vincent Moody. / M.S.