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De nos jours, la galvanisation continue par immersion à chaud est largement utilisée dans les structures métalliques pour protéger les aciers contre la corrosion. Le zinc offre une barrière protectrice grâce à la formation d'un oxyde de surface et d'un effet de protection sacrificielle. Cependant, les procédés de fabrication de la structure ou les assemblages mécaniques par déformation plastique peuvent créer des dommages affectant les performances de corrosion du revêtement.L’objectif de ce travail était d’étudier la durabilité, en environnement agressif, par des essais d’immersion et en enceinte climatique, de revêtements galvanisés déformés à la suite d’une mise en forme. Trois revêtements différents ont été choisis. Un revêtement de zinc utilisé comme référence, un revêtement Zn-Al-Mg dans lequel l’ajout de magnésium et d’aluminium permet une meilleure tenue à la corrosion et enfin un revêtement Zn-55Al choisi pour sa très bonne durabilité en environnement agressif en raison de la quantité importante d’aluminium présente dans sa composition. / Nowadays continuous hot-dip galvanizing is widely used in metallic structures to protect steels against corrosion. Zinc provides a protective barrier thanks to the for-mation of a surface oxide and a sacrificial protection effect. However, structure manufacturing processes or mechanical assemblies by plastic deformation can create damage affecting the corrosion performance of the coating.The objective of the present work is to study changes of corrosion resistance induced by plastic deformation using immersion and climatic chamber tests. Three different coatings were chosen. A zinc coating used as a reference, a Zn-Al-Mg coating in which the addition of magnesium and aluminum allows a better resistance to corrosion and finally a Zn-55Al coating chosen for its very good durability in aggressive environment in Because of the large amount of aluminum present in its composition.

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Made available in DSpace on 2015-03-26T13:53:16Z (GMT). No. of bitstreams: 1 texto completo.pdf: 2894312 bytes, checksum: 8e4e6d33bfbb1f07f987dfb380479055 (MD5) Previous issue date: 2010-07-23 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The coffee tree is a demanding plant in micronutrients, especially Zn, and the P x Zn interaction is an important issue for the management of tropical soils, due to the use of high doses of P in soils with low availability of this nutrient. In this work was studied the seedlings response of Coffea arabica L. cv. Catuaí to doses of Zn and P, including the supply of P corresponding to a high availability of P, therefore, a high antagonism potential to the availability of Zn. The experiment was carried out in a greenhouse in the period between the October/2009 and January/2010 (122 days of conducting the experiment), using 4 × 4 factorial design, distributed in randomized blocks, with three replications, being four doses of Zn (0, 5, 15, and 45 mg / dm 3 of soil) and P (0, 200, 600 and 1,800 mg / dm 3 of soil). On the soil, having as a source ZnSO 4 .7 H 2O, the doses of Zn were applied trough a soil solution and P levels were incorporated, being the source the triple superphosphate. It was used samples of a Red Yellow sandy-loam originating from Três Marias - MG and coffee seedlings with four pairs of leaves, which were transplanted to pots (2 dm 3 of soil), maintaining soil moisture near to field capacity. It was evaluated the total content of Zn in plant parts (leaf, stem and root), the soluble fraction of Zn (leaf), the levels of total P (leaf, stem and root), the enzyme superoxide dismutase (SOD) , plant height, number of nodes per plant, average length of internodes and dry matter production (leaf, stem and root). There were no significant changes in levels of total Zn in leaves with increasing doses of P added to soil, although the levels of soluble Zn (active) have fallen, indicating, in this case, antagonistic interaction between the variables. The SOD activity was reduced with increasing doses of Zn added to soil. The growth of coffee seedlings was influenced by the interaction between P and Zn. / O cafeeiro é uma planta exigente em micronutrientes, especialmente, em Zn, e a interação P x Zn é uma questão importante para o manejo de solos tropicais, haja vista a utilização de altas doses de P em solos com baixa disponibilidade deste nutriente. Neste trabalho foi estudada a resposta de mudas de Coffea arabica L. cv. Catuaí às doses de Zn e P, incluindo-se o suprimento de P que correspondeu a uma alta disponibilidade de P, portanto, a um alto potencial de antagonismo em relação à disponibilidade de Zn. O experimento foi conduzido em casa-de-vegetação entre o período de outubro/2009 a janeiro/2010 (122 dias de condução do experimento), utilizando esquema fatorial 4 × 4, distribuído em blocos casualizados, com três repetições, sendo quatro doses de Zn (0, 5, 15, e 45 mg/dm3 de solo) e quatro doses de P (0, 200, 600 e 1.800 mg/dm3 de solo). No solo, tendo como fonte ZnSO4.7H2O, as doses de Zn foram aplicadas em solução via solo, e as doses de P foram incorporadas, sendo a fonte o superfosfato triplo. Utilizaram-se amostras de um Latossolo Vermelho Amarelo textura franco-arenosa originário de Três Marias – MG e mudas de café com quatro pares de folhas, que foram transplantadas para vasos (2 dm3 de solo), mantendo-se a umidade do solo próxima à capacidade de campo. Avaliaram-se o teor total de Zn nos órgãos das plantas (folha, caule e raiz) e a fração solúvel de Zn (folha), os teores totais de P (folha, caule e raiz), atividade da enzima superóxido dismutase (SOD), altura de plantas, número de nós por planta, comprimento médio dos entrenós e produção de matéria seca (folha, caule e raiz). Não houve alterações significativas nos teores de Zn total nas folhas com o aumento das doses de P adicionadas ao solo, embora os teores de Zn solúvel (ativo) tenham diminuído, indicando, neste caso, interação antagônica entre as variáveis. A atividade da SOD foi reduzida com o aumento nas doses de Zn adicionadas ao solo. O crescimento das mudas de café foi influenciado pela interação P e Zn.

Made available in DSpace on 2014-06-12T23:03:11Z (GMT). No. of bitstreams: 2 arquivo9292_1.pdf: 822972 bytes, checksum: 213d0dd310c54a76a28e18307e5da832 (MD5) license.txt: 1748 bytes, checksum: 8a4605be74aa9ea9d79846c1fba20a33 (MD5) Previous issue date: 2002 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Alquilfenilselenetos são intermediários sintéticos versáteis especialmente para a formação de duplas ligações carbono-carbono em condições suaves. Um método alternativo aos métodos tradicionais foi desenvolvido por Lothar Bieber e colaboradores, a partir da reação do PhSeSePh com haletos orgânicos na presença de zinco em pó em meio aquoso, abrangendo uma ampla classe de substratos. A falta de precedentes em termos do entendimento desta nova reação algumas vezes acarreta na escolha de condições desfavoráveis à obtenção dos melhores resultados. Isso impulsionou a realização de uma investigação que possibilite um entendimento mais detalhado da reação, culminando com a formulação de um mecanismo para a mesma. O estudo consiste na utilização do relógio radicalar ciclopropilcarbinil, muito difundido em investigações mecanísticas que objetivam a determinação do envolvimento de intermediários radicalares. Para isso utiliza-se halometilciclopropanos (precursor deste relógio radicalar) na reação tipo Barbier com o disseleneto de difenila (PhSeSePh) na presença de zinco em meio aquoso. Na reação realizada com iodometilciclopropano verificou-se a formação do produto de substituição sem rearranjo, o (metilciclopropil)-fenilseleneto (produto 1) e do produto de substituição após rearranjo o (3-butenil)-fenilseleneto (produto 2), sempre em menor proporção que o produto (1). As proporções entre os produtos mostraram-se dependentes do pH do meio, da concentração de PhSeSePh e da granulação do zinco e por outro lado pouco sensível ao uso de promotores radicalares; já nas reações em que se utilizou o cloro- ou o bromometilciclopropano observou-se a formação quase exclusiva do produto (1), com a proporção entre os produtos permanecendo praticamente inalterada com variação do pH ou da concentração do PhSeSePh. Mecanismos clássicos, tais como substituição nucleofílica e substituição homolítica, foram descartados devido à incapacidade destes mecanismos de esclarecer completamente todos os efeitos observados na reação, embora a presença de alguns aspectos característicos a ambos os mecanismos seja inegável

Aqueous zinc ion storage system has been deemed as one of the most promising alternatives due to its high capacity of zinc metal anode, low cost, and high safety characteristics. Recently, significant attempts have been made to produce highperformance aqueous Zn batteries. (AZBs) and great progress has been achieved. Yet there are a lot of issues still exist and need to be further optimized. In this thesis, we proposed several strategies to tackle these challenges and finally optimize the overall battery performance, including metal anode protection, cathode structural engineering, and rational electrolyte design. In the present thesis, we first developed the ZnF2 layer coated Zn metal anode via a simple plasma treatment method. The plasma treated Zn anode leads to dendrite-free Zn electrodeposition with lower overpotential. Density function theory calculation results demonstrate that the Zn diffusion energy barrier can be greatly reduced on the ZnF2 surface. Benefiting from these merits, the symmetric cell and full cell exhibited much improved electrolchemical performance and stability. Afterthen, We synthesised a layered Mg2+-intercalated V2O5 as the cathode material for AZBs. The large interlayer spacing reachs up to 13.4 A, allowing for efficient Zn2+ (de)insertion. As a result, the porous Mg0.34V2O5・nH2O cathodes can provide high capacities as well as long-term durability. We then recongnized that most of the parasitic side reactions are related to the aqueous electrolyte. We therefore further designed a hybrid electrolyte to realize the anode-free Zn metal batteries. It is demonstrated that in the presence of propylene carbonate, triflate anions are involved in the Zn2+ solvation sheath structure. The unique solvation structure results in the reduction of anions, thus forming a hydrophobic solid electrolyte interphase. Consequently, in the hybrid electrolyte, both Zn anodes and cathodes show excellent stability and reversibility. More importantly, we design an anode-free Zn metal battery, which exhibits good cycling stability (80% capacity retention after 275 cycles at 0.5 mA cm–2).

Protein folding and stability are essential for protein function. Changes in these characteristics can lead to altered physiological states and to the development of certain pathologies. While extensive research has focused on the stability of soluble proteins, membrane protein stability has received much less attention. Understanding the stability of membrane proteins can provide insight into folding mechanisms and the etiology of various pathologies. The purpose of this project is to prepare molecular tools to perform comparative studies of homologous membrane proteins that are found in various environments. To this end, thermophilic (Pyrococcus abyssi), mesophilic (Escherichia coli), and psychrophilic (Exiguobacterium 255-15) transmembrane Zn2+ transporting ATPases were cloned, expressed, and functionally characterized to correlate thermostability with optimal functional temperatures. In addition, the lipid environments and composition (rigid or fluid lipids) may also be involved in determining the stability of membrane proteins. Toward exploring the role of extremophilic lipids, Archaeoglobus fulgidus and Thermotoga maritima were grown and lipids were extracted. Availability of these molecular tools will enable physical-chemical studies toward understanding the structural factors that determine functional stability.

Mg-Zn-Zr (ZK) alloys are widely employed in weight critical applications due to their high specific strength properties. Zinc and zirconium are added into the alloy for the purpose of forming precipitation hardening and grain refinement, respectively. However, both elements are likely to form some intermetallic compounds and may have effect on strengthening of the alloys. The purpose of this work was to explore this interaction to understand how to optimise the composition and processing of ZK alloys. In the present study, ZK60 with composition of 6 wt.%Zn and 0.6 wt.%Zr was heat treated by solutionizing and aging at various temperatures and times. The resultant microstructure was characterised by using optical microscope, X-ray Diffractometer (XRD), Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and the age hardening response determined by using Vicker's microhardeness testing. The results show that the interaction between zinc and zirconium causes stable compound formation, including hcp (Zn_2Zr) Laves phase and cubic Zn_2Zr phase. These compounds are distributed unevenly, causing beta'_1 strengthening precipitate to form inhomogeneously during aging. This reduces the strengthening effect of aging, e.g. low age hardening response. It has been shown that the areas containing Zn_2Zr particles are essentially free of strengthening beta'_1 precipitates, an undesirable microstructure. The aged hardening and strengthening of ZK60 alloys accounting for the interaction between Zn and Zr has been explored through a new model for ZK alloys. The simulated age hardening strengthening in ZK60 is similar to the combination of the grain size strengthening and solution strengthening. The prediction has shown that the benefit of adding zirconium, which is grain boundary strengthening improvement by refining grain size, is balanced by a depletion in age hardening response. The total strength is estimated to increase by 15% if the grain size, that is normally obtained by zirconium alloying, could be achieved by another grain refinement method without the loss of zinc solute. The experiments and the models have identified the importance of considering the interaction between Zn and Zr when optimising the processing and composition of ZK magnesium alloys. That had never been emphasised and very well presented. In particular, when ZK alloys are used in wrought applications, control of grain size by recrystallisation rather than Zr may be beneficial in enabling a greater age hardening response.

Ce travail porte sur la préparation et la caractérisation de catalyseurs bimétalliques Cu-Zn, Ni-Zn et Fe-Zn supportés sur TiO2 avec des rapports atomiques variables et sur l'étude de leurs propriétés catalytiques pour l'hydrogénation sélective d'hydrocarbures polyinsaturés. Les méthodes de co-dépôt-précipitation à l'urée (DPu) et co-dépôt-précipitation à pH fixe (DP8) ont été utilisées pour la préparation des matériaux. Les ions métalliques se déposent séquentiellement sur la surface de TiO2 (selon la séquence CuII < ZnII ?FeII <NiII) durant la méthode DPu, alors qu'ils se déposent simultanément en utilisant la méthode DP8. Après réduction de l'échantillon à une température appropriée (350°C pour Cu-Zn, 450°C pour Ni-Zn et 500°C pour Fe-Zn), les analyses par DRX et STEM-HAADF couplé à EDS ont montré que des nanoparticules bimétalliques étaient formées pour les systèmes Cu-Zn/TiO2 (alliage Cu3Zn1 ou Cu0.9Zn0.1) et Ni-Zn/TiO2 (alliage Ni1Zn1 ou Ni4Zn1) avec une taille moyenne de particule inférieure à 5 nm. Seul du fer métallique a été détecté par DRX dans le cas de Fe-Zn/TiO2. Zn est inactif pour l'hydrogénation sélective du butadiène et agit comme un modificateur des catalyseurs monométalliques dont l'activité suit la séquence: Cu < Fe < Ni. L'ajout de Zn diminue légèrement l'activité, influence la sélectivité en butènes, mais augmente fortement la stabilité des catalyseurs. Cette plus grande stabilité des catalyseurs bimétalliques a été attribuée à la formation d'une quantité inférieure de dépôt carboné pendant la réaction, ceci résultant de la modification de la taille des ensembles de surface du métal actif par alliage avec Zn. / This work investigates the preparation and characterization of titania-supported non-noble bimetallic Cu-Zn, Ni-Zn and Fe-Zn catalysts with various atomic ratios and their catalytic properties for the selective hydrogenation of polyunsaturated hydrocarbons. Co-deposition-precipitation with urea (DPu) and co-deposition-precipitation at fixed pH (DP8) methods were employed for the samples preparation. The metal ions were sequentially deposited onto the TiO2 surface (the sequence of pH for ions deposition being CuII < ZnII ≈FeII < NiII) during the DPu, while they were simultaneously deposited using DP8 method. After sample reduction at proper temperature (350 °C for Cu-Zn, 450 °C for Ni-Zn and 500 °C for Fe-Zn), XRD and STEM-HAADF coupled with EDS showed that bimetallic nanoparticles were formed in Cu-Zn/TiO2 (Cu3Zn1 or Cu0.9Zn0.1 alloy) and Ni-Zn systems (Ni1Zn1 or Ni4Zn1 alloy) with average particle size smaller than 5 nm. Only metallic Fe was detected by XRD in Fe-Zn/TiO2. Zn is inactive for butadiene selective hydrogenation, and acts as a modifier of the monometallic catalysts whose activity follows the sequence: Cu < Fe < Ni. The addition of Zn slightly decreases the activity and influences the selectivity to butenes, but provides much more stable catalysts. The higher stability of the bimetallic catalysts was ascribed to the formation of lower amount of carbonaceous species during the reaction, resulting from the change in the size of the active metal surface ensembles by alloying with Zn.