Dissertations / Theses on the topic 'Pure mg'

L'objectif de cette thèse est d’analyser l'électrochimie des phases pures, composants des alliages de revêtement Zn-Al-Mg. Les données électrochimiques ont été utilisées pour prédire du comportement à la corrosion des revêtements d’alliage multiphasé. A cette fin, une base de données de courbes de polarisation élémentaire a été établie en fonction du pH en utilisant la spectroélectrochimie d'émission atomique (AESEC). Le désalliage de la phase intermétallique MgZn2 et de la phase α de Zn-Al (Zn-68Al) ont été étudiés à pH=10,1 représentent les extrêmes contiennent Mg et en Al dans le revêtement d'alliage Zn-Al-Mg, respectivement. Dans la polarisation cathodique, la couche enrichie en Zn (0) a été formée dans les deux cas par dissolution sélective de Mg et Al, respectivement. Cependant, l’influence de cette couche sur le désalliage cathodique différait : pour MgZn2, la dissolution sélective de Mg était restreinte par la couche désalliée, alors que pour Zn-68Al, la dissolution sélective de l'Al n'était pas affectée par cette couche. Il a été observé que le début de la dissolution active de Zn coïncidait avec une réduction de la vitesse de dissolution de l’Al, suggérant un effet inhibitif de la dissolution de Zn sur la dissolution de l’Al. Il a aussi été observé que la dissolution de l’Al dans des milieux alcalins était limitée par la vitesse de dissolution du film de Al(OH)3, mise en évidence par une dissolution de l’Al indépendante de potentiel. Les produits de corrosion les plus stables formés pendant des mesures électrochimiques, les solides précipités dans la solution pendant la titration et la simulation thermodynamique étaient raisonnablement cohérents entre eux. La plupart des espèces précipitées formées dans la solution correspondaient bien à celles prédites par la base de données thermodynamique. Il était en bon accord avec les produits de corrosion de l'alliage, caractérisés après les mesures électrochimiques. Par conséquent, on peut conclure que la base de données thermodynamique peut être utilisée pour prédire et éventuellement modéliser la situation de corrosion réelle
The objective of this Ph.D. project is to investigate the electrochemistry of the pure phases, components of the Zn-Al-Mg coating alloys. The electrochemical data was used as an input for the prediction of corrosion behavior of the multi-phase alloy coatings. To this end, a database of elemental polarization curves was established as a function of pH by using atomic emission spectroelectrochemistry (AESEC). Dealloying of the MgZn2 intermetallic and α-phase of Al-Zn (Zn-68Al) were investigated at pH=10.1 represent the extremes of Mg and Al content in the Zn-Al-Mg alloy coating, respectively. In the cathodic polarization, the Zn(0) enriched layer was formed in both cases by selective dissolution of Mg and Al, respectively. However, the influence of this layer on cathodic dealloying differed: for MgZn2, Mg selective dissolution was restrained by the dealloyed layer, whereas for Zn-68Al, Al selective dissolution was not affected by this layer. It was observed that the onset of active Zn dissolution coincided with a reduction in the Al dissolution rate, suggesting an inhibitive effect of Zn dissolution on Al dissolution. It was observed that Al dissolution in alkaline media was limited by the dissolution rate of the Al(OH)3 film, evidenced by potential independent Al dissolution. The most stable corrosion products formed by electrochemical measurements, precipitated species in the solution during titration experiment and the thermodynamic simulation were reasonably coherent with each other. Most of the precipitated species formed in the solution corresponded reasonably well to those predicted by thermodynamic database. It was in a good agreement with the corrosion products of the alloy, characterized after the electrochemical measurements. Therefore, it can be concluded that the thermodynamic database can be used to predict and eventually model the real corrosion situation

ARAÚJO, Márcia de Mesquita. Henriqueta Lisboa: teoria e prática de poesia pura. 2013. 107f. – Dissertação (Mestrado) – Universidade Federal do Ceará, Programa de Pós-graduação em Letras, Fortaleza (CE), 2013.
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Esta pesquisa consiste fundamentalmente no estudo crítico de uma seleção de poemas de Henriqueta Lisboa, em especial da obra Flor da morte (1949), naquilo que ela tem de “poesia pura”, segundo concepções estabelecidas a partir das pesquisas de autores que se pronunciam sobre o tema, como Henri Brémond, Henry Decker, Paul Valéry e Robert Penn Warren, e considerando as concepções de poesia expressas pela própria poeta em seus textos ensaísticos. Consideramos, também, textos de estudiosos da obra de Henriqueta Lisboa e da “poesia pura”, como forma de enriquecer nosso estudo, buscando refletir e tentar responder a alguns questionamentos: como a “poesia pura” comparece na obra de Henriqueta Lisboa? A partir dessa inquisição surgem, por conseguinte, outras indagações: em que quantidade, em quais poemas da obra Flor da Morte, segundo qual conceito de poesia pura, em que possível diversidade de manifestações? O fundamento teórico da pesquisa provém de teóricos como de Giorgio Agamben, Jacques Derrida, Emanuel Levinas, Maurice Blanchot, principalmente, Martin Heidegger, entre outros. Por fim, relacionamos os textos estudados para o estabelecimento das conclusões, acrescidas das possibilidades de descobertas geradas por essas leituras, além de levantarmos questões relativas à arte, à literatura brasileira, à escritura, especialmente, e a crítica literária contemporânea, de forma enriquecida e sistematizada, tudo sob o viés da literatura contemporânea.

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências da Educação. Programa de Pós-Graduação em Educação.
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Análise do processo variável da emergência étnica no entorno do Parque Estadual da Serra do Brigadeiro na Zona da Mata de Minas Gerais. A Cultura Puri foi silenciada durante os últimos duzentos anos, a partir da Educação Popular, seu processo intercultural possibilitou a recriação de identidades. Através de entrevistas, de rodas de narração de histórias e das notas de campo em comunidades rurais recupera fontes orais. Capta um encadeamento discursivo recorrente entre violência, fabulações naturalísticas e vontade de liberdade. Se inscreve na tradição da crítica cultural como motor da transformação social. Associa-se à saga colonial migratória, e recoloca a temática dos movimentos sociais. Critica o monoculturalismo do saber através da inteligibilidade dos movimentos sociais e da ecologia de saberes. Enfatiza a constituição de uma outra temporalidade e da dilatação do tempo presente, o que aprofunda as análises de longa duração. Aborda conceitos que se interrelacionam complexamente, tais como: estrutura de sentimentos, hegemonia, residual e emergencial. Toma como referências os estudos de Raymond Williams e de Boaventura de Sousa Santos.

L’hydrolyse des déchets d’alliages de magnésium dans l’eau de mer (i.e. solution aqueuse à 3,5% en masse de NaCl) est une nouvelle approche qui permet à la fois la production de l’hydrogène in-situ et la valorisation de déchets a priori non recyclables. L’objectif de ce travail de thèse est d’optimiser la réactivité de ces déchets par broyage mécanique en présence d’additif(s). Nous avons donc investigué les principaux paramètres de broyage (e.g. atmosphère de broyage, vitesse de broyage, ordre d’ajout des additifs) sur la réactivité d’un alliage WE43 et des déchets d’alliages Mg–Al. Un « scale-up » du procédé de traitement des matériaux a été mené pour explorer la possibilité d’industrialisation du procédé. En outre, nous avons montré que le broyage sous argon est plus avantageux que celui sous hydrogène.Les alliages Mg–Al (plus précisément AZ91) sont les plus utilisés. Dans ces alliages, l’aluminium forme avec le magnésium l’intermétallique Mg17Al12. Pour comprendre le mécanisme de production d’hydrogène à partir d’alliages Mg–Al biphasés (i.e. Mg + Mg17Al12), l’évaluation du comportement de chacun de leurs constituants et de leurs interactions est primordiale. A cet égard, les aspects chimique (i.e. hydrolyse) et électrochimique (i.e. corrosion) de la réaction de Mg17Al12 avec une solution similaire à l’eau de mer et l’effet du broyage en présence d’additifs (e.g. graphite, NaCl, MgCl2 et AlCl3) ont été étudiés. L’évolution de la chimie de surface lors des tests de polarisation a prouvé expérimentalement (par spectroscopie Raman), pour la première fois, la formation d’intermédiaires réactionnels et nous a permis de proposer un mécanisme de formation de H2.L’interaction entre Mg et Mg17Al12 a été explorée en comparant les propriétés de matériaux modèles « AZ91 » (Mg + Mg17Al12). Grâce à la microscopie électrochimique à balayage, l’effet du couplage galvanique est étudié à l’interface des deux composants du matériau. La contribution de Mg17Al12 dans la corrosion des alliages AZ91 a ainsi été clarifiée. L’intermétallique est résistant à la corrosion et accélère la corrosion de Mg en raison du couplage galvanique. Les diverses stratégies de broyage adoptées dans ce travail ont été comparées en les appliquant sur un alliage commercial AZ91. Le matériau traité mécaniquement en présence de graphite et d’AlCl3 présente les meilleures performances en hydrolyse.Finalement, nous avons évalué semi-quantitativement la pureté de H2 (la composition du mélange gazeux et son humidité) produit. L’incidence de certaines conditions expérimentales (e.g. composition de la solution, température, rapport de la masse de poudre au volume de la solution) est reportée. Il a ainsi été montré qu’un réacteur d’hydrolyse de Mg opérant à température ambiante avec l’eau de mer produit de l’hydrogène « propre » in-situ et peut être considéré comme un générateur d’hydrogène « vert » à la demande
The hydrolysis of magnesium alloys wastes in seawater (i.e. 3.5 wt.% of NaCl aqueous solution) is a new approach which allows both in-situ hydrogen production and the valorization of a priori non-recyclable wastes. The objective of this research work is to optimize the reactivity of magnesium-based wastes by ball milling with additives. Therefore, we investigated the effects of the main milling parameters (e.g. milling atmosphere, milling rotation speed, order of the addition of additives) on the reactivity of WE43 alloys and Mg – Al alloys wastes. A « scale-up » of the materials treatment process was conducted to explore the possibility of industrializing the process. In addition, we have shown that milling under argon is more advantageous than under hydrogen.Mg – Al alloys (more precisely AZ91) are the most widely used. In these alloys, Al forms with Mg the intermetallic Mg17Al12. To better understand the mechanism of hydrogen production from these binary Mg – Al alloys (Mg + Mg17Al12), evaluating the behavior of each of their constituents and their interactions is essential. In this regard, the chemical (i.e. hydrolysis) and electrochemical (i.e. corrosion) aspects of the reaction of Mg17Al12 with the model seawater solution and the effect of milling in the presence of additives (e.g. graphite, NaCl, MgCl2 and AlCl3) were studied. The evolution of the surface chemistry during polarization tests has proven experimentally (by Raman spectroscopy), for the first time, the formation of reaction intermediate and has allowed us to propose a mechanism of H2 formation.The interaction between Mg and Mg17Al12 was explored by comparing the properties of model materials of « AZ91 » (Mg + Mg17Al12). Using scanning electrochemical microscopy, the effect of galvanic coupling was studied at the interface of the two components of the material. In view of these studies, the contribution of Mg17Al12 in the corrosion of AZ91 alloys was clarified. The intermetallic is corrosion resistant and accelerates the corrosion of Mg due to galvanic coupling. The various milling strategies adopted in this work were compared by applying them to a commercial AZ91 alloy. Mechanical treated materials with graphite and AlCl3 showed the highest hydrolysis performances.Finally, we semi-quantitatively evaluated the purity of H2 (the composition of the gas mixture and its humidity) produced. The impact of few experimental conditions (e.g. composition of the solution, temperature, ratio of the mass of powder to the volume of solution) is reported. Thus, it has been shown that an Mg hydrolysis reactor operating at room temperature with seawater produces « clean » hydrogen in-situ and can be considered as a « green » hydrogen on demand generator

L'objectif de cette these a ete d'etudier le compose cugeo3, pour determiner le regime des fluctuations structurales pretransitionnelles, ainsi que l'effet du dopage dans un compose de type spin-peierls. Ceci afin de comprendre le mecanisme de cette transition dans un compose inorganique. Nous avons ainsi realise des experiences de diffraction de rayons x par deux methodes (diffractometrie, et laue monochromatique) sur le compose cugeo3 pur, ainsi que sur les alliages obtenues en substituant le cuivre par du zinc, du magnesium, du nickel, et du titane, et le germanium par du silicium, et de l'aluminium. Dans chaque compose nous avons analyse les correlations des fluctuations structurales pretransitionnelles. De plus, afin de comparer les composes entre eux, et d'etudier les effets dynamiques, nous avons etudie, avec la collaboration de m. Poirier, pierre fertey, et de m. Castonguay du laboratoire de matiere condensee de sherbrooke (quebec, canada), la constante elastique c33 dans les composes dopes presentes precedemment. Ceci nous a permis d'avoir un ensemble de donnees permettant de comparer les echantillons entre eux, et d'essayer d'apprehender l'effet du dopage sur la transition de spin-peierls.

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Após séculos de opressão e de lutas, muitos dos grupos indígenas brasileiros sobreviveram apenas nas narrativas da história. Contudo, em alguns casos, eles deixaram fragmentos de cultura entrelaçados aos modo de vida urbana na atualidade. Na Zona da Mata mineira, região das últimas fronteiras liberadas para ocupação territorial a partir do último quarto do século XVIII e início do século XIX, encontrou-se registros paroquiais de batismos com evidências de resistência de um desses povos de floresta, o povo indígena Puri. Estes índios habitaram também no território da atual cidade de Miraí, antiga Freguesia de Santo Antônio do Muriahé, e parte de suas tradições estão mantidas, ainda que de forma esmaecida, como fragmentos de cultura ancestral presentes nas famílias que se auto-declaram como descendentes deste povo de floresta. Investigá-las no entanto, é um exercício da memória.
After centuries of oppression and fights, many aborigine Brazilians groups survived just in the narratives of history. However, in some cases, they culture. They left fragments of the culture interlaced the urban way of life in the present. The Forest Zone of Minas Gerais, of the last frontiers released for territorial occupation form the last quarter of the eighteenth century and early nineteenth century. We found registration of documents of Parish church of baptism with evidence of resistance to one of these people of the forest, the Puri aborigine. These aborigines also lived in the territory at the present Miraí, older Parish of Santo Antonio do Muriahé, and part of their traditions are maintained. Still dimmed form, an ancestral culture fragments investigate them. However, it is an exercise of memory.

Etude experimentale de l'influence de la nature de la cible sur la pression induite par le laser d'une part et par l'utilisation du processus de desadaptation pour amplifier la pression de l'onde de choc dans des cibles multimateriaux d'autre part. Developpement d'analyses numeriques conduisant a la mise en place d'un code monodimensionnel multimateriaux et d'un code bidimensionnel. Ces codes ont permis de preciser les mecanismes de compression du milieu. Application a l'analyse des resultats experimentaux obtenus sur des materiaux de numero atomique tres different (al, au, cu, mo, mg, ta)

Les joints de grains peuvent etre decrits comme des joints en relation d'orientations de coincidence. Cette description necessite l'introduction d'une serie de parametres necessaires et suffisants pour caracteriser completement la relation d'orientation. Le rapport c/a de la symetrie hexagonale introduit une difficulte supplementaire qui conduit a discuter de la dimension de la coincidence et a envisager la notion de coincidence approchee. Applications aux macles de deformation des metaux hexagonaux compacts que l'on peut decrire comme des joints de coincidence. La notion de symetrie permet de choisir entre les differentes configurations atomiques possibles d'une relation d'orientation donnee. Pour le macle (1012), une configuration de symetrie maximale permet de proposer une description simple du processus de maclage. On confirme par microscopie electronique le role des dislocations dans la structrure des macles de deformation

Etude par mesure de conductivite electrique, par retrodiffusion rutherford et par microscopie ionique en transmission des differents aspects du melange ionique dans le systeme mt/al (mt=fe, co, ni) et fe-mg. Analyse des differents facteurs controlant la formation d'une phase et celle d'une phase amorphe. Analyse des mecanismes de transformation cristal-amorphe de l'alliage ni::(50)al::(50) en couche mince. Influence des parametres d'irradation sur cette transformation

I microrganismi selezionati sono impiegati non solo per il processo di trasformazione della materia grezza in prodotto fermentato, ma anche per migliorare la shelf-life, il gusto, l’aroma, la sicurezza e il valore nutrizionale dei prodotti. La globalizzazione del mercato ha portato a considerare non solo i prodotti tipici popolari europei, come per esempio il vino, ma anche i prodotti tipici dei paesi non europei come la cassava. Per quanto riguarda il settore enologico lo scopo della ricerca è quello di migliorare un tipico vino: l'Ortrugo dei Colli Piacentini con ceppi autoctoni di Saccaromyces cerevisiae. Nelle fermentazioni spontanee i lieviti sono associati all'area geografica, alle condizioni climatiche e alla varietà di vitigno. Alcuni ricercatori sostengono che il micro-ambiente è caratterizzato da specifi Saccaromyces cerevisiae che possono influenzare gli aromi dell'uva. Sfortunatamente le fermentazioni spontanee possono causare aromi indesiderati e arresti fermentativi. L'inoculo del mosto con lieviti selezionati è ormai una pratica consolidata per eliminare i rischi delle fermentazioni spontanee, ma questi lieviti non riescono a enfatizzare le caratteristiche della varietà di uva in quanto derivano da ecosistemi differenti. Nasce quindi l'esigenza di utilizzare ceppi starter autoctoni selezionati, isolati dalle microaree dove i vini sono prodotti in quanto tali ceppi sono potenzialmente meglio adattati a svilupparsi in uno specifico microambiente e meglio esaltano la tipologia di un particolare prodotto. Per quanto riguarda la cassava (Manihot esculenta Crantz) microrganismi selezionati possono essere utilizzati per ridurre la concentrazione di glucoside cianogenetico (linamarina e lotaustralina), molecole tossiche. il consumo di cassava e dei suoi prodotti può causare avvelenamento da cianide con sintomi di vomito, nausea, debolezza e occasionalmente la morte. L'introduzione di cianide tramite il consumo di cassava è quasi certamente la causa dell'insorgenza di neuropatie come per esempio il Konzo (irreversibile paralisi alle gambe) che colpisce particolari zone dell'Africa. La World Health Organisation (WHO)ha stabilito il livello di sicurezza di cianide nella farina di cassava a 10 ppm (FAO/WHO, 1991).
Selected microrganisms are important as agents of the main processes of transformation of the raw materials in fermented product but also as responsible of the improvement in the shelf-life, texture, taste, aroma, as well as safety and nutritional value. The market globalization made us to consider not only popular food and/or beverage in Europe but also in non European countries. In this research I consider wine and cassava products. As regards wine the aim is to improve the Ortrugo wine typicalness by Saccaromyces cerevisiae autochtonous strains. In spontaneous fermentations the yeasts vary according to geography location, climatic conditions and/or grape variety. Some researchers believe that each micro-environment is characterised by specific Saccaromyces cerevisiae that may enhance the grape flavours. Unfortunately spontaneous fermentations may cause off-flavours and fermentation stuck. The selected yeast inoculum in must is one of the consolidated practices to eliminate the risks of spontaneous fermentation, but these yeast are not able to emphasise the characters of grape variety because they are from different ecosystems. Autochthonous yeasts e.g. yeasts isolated from a definite micro-environment are adapted to operate in a must whose characteristics are determined by the variety of the grapes and the “terroir” and, therefore, they able to enhance the peculiarities of a wine. As regards the cassava (Manihot esculenta Crantz) selected microorganisms will be used to reduce the cyanogenic glucosides (mainly linamarin and lotaustralin) toxic molecules. Consumption of cassava and its products may cause cyanide poisoning with symptoms of vomiting, nausea, dizziness, stomach pains, weakness, headache and diarrhoea and occasionally death. Cyanide intake from cassava is almost certainly the cause of Konzo (irreversible paralysis of the legs) in eastern, central and southern Africa. The World Health Organisation (WHO) has set the safe level of cyanogens in cassava flour at 10 ppm (FAO/WHO, 1991).

碩士
國立中興大學
奈米科學研究所
105
Zinc oxide (ZnO) is a wide band gap (~3.37 eV) and higher excitation energy (~60 meV) at room temperature (RT) semiconductor. These characteristics allow ZnO been widely used in photo-electric devices. In this study, we use spin-coating to make ZnO seed layer, then fabricate massive single crystalline ZnO nanowires(NWs) by using aqueous solution method at 90 ˚C for 3 hours. We also use some other elements (eg. Mn, Mg …etc) to make dopant at ZnO NWs. The morphology of ZnO NWs has been examined by SEM. The XRD diffraction spectrum demonstrates that the ZNO NWs growing by aqueous solution method are single crystalline along the (002) direction. The TEM also shows the same result. We used Raman spectrum, XPS spectrum …etc instrument to study the material characteristics. We can checked that the ZnO nanowires were mainly wurtzite structure by using Raman spectrum, and the XPS spectrum showed that the orbital of ZnO is mainy 2p3/2 and sp1/2. We can fabricated single ZnO nanowires devices by using FIB, and measuring the IV curve of each devices and measure the CO sensing at room temperature. The sensing results showed that the pure ZnO nanowires on sapphire can clearly measure the current variation when the CO gas was added into the chamber.

碩士
國立中興大學
材料科學與工程學系所
100
Mg-Fe-CO3 layer double hydroxide (Mg-Fe-CO3 LDH) has been investigated that is highly biocompatible and is low cytotoxicity. LDH usually be synthesized into powder, and is utilized to be a drug delivery. This work presents a method for directly forming Mg-Fe-CO3 LDH on the pure Mg substrate and the coating of the Mg-Fe-CO3 LDH could increase the ability of corrosion-resistant in C-SBF at 37.5 。C. Moreover, the size of the platelet-like structure of Mg-Fe-CO3 LDH is affected by the pH value of the Fe3+/HCO3-/CO32- at 70 。C. the size of the platelet-like structure of Mg-Fe-CO3 LDH the CO2pH6.0/20h sample is bigger than the CO2pH4.6/20h sample. Repeatedly sliding on the CO2pH4.6/20h sample could be an effective way to change the morphology of the CO2pH4.6/20h sample. From the cross-sectional observation of the CO2pH4.6/20h sample by TEM, Mg-Fe-CO3 LDH (the top layer), the middle layer and inner layer were observed. The thickness of Mg-Fe-CO3 LDH is around 1um, the middle layer is around 2~2.5um and the inner layer is 1~2um. The Mg-Fe-CO3 LDH is composed of Mg, Fe, C and O. Moreover, the middle layer and the inner layer are composed of Mg, C and O.

碩士
國立中興大學
材料科學與工程學系所
99
In this study, an environmental friendly treatment of CO2 recycling was used to form a composite soft-magnetic layer on magnesium sample’s surface by chemical reaction in Fe3+/HCO3-/CO32- and pH 9.5 HCO3-/CO32- solutions. The layer was composed of soft magnetic iron particles and Mg-Fe-CO3 layered double hydroxides (Mg-Fe-CO3 LDH). The size and quantity of crystalline Fe can be raised by increasing immersing time of samples in the Fe3+/HCO3-/CO32- solution. And the soft magnetic property of the layer on Mg sample can also be enhanced. The Mg-Fe-CO3 LDH LDH layer played an important part in covering the Fe particles and enhancing the adhesion of the Fe particles on the sample surface. The thickness of the Mg-Fe-CO3 LDH layer is concerned with reaction time of sample in the pH 9.5 HCO3-/CO32- solutions. The quantity of the Mg-Fe-CO3 LDH on the sample surface would increase with prolonging treatment time in the pH 9.5 HCO3-/CO32- solution. The rolled magnesium samples present better soft magnetic property than the magnesium sample from as-cast ingot after these samples conducted by the same treatment. Based on the same treatment process, a rolled Mg sample could have better soft magnetic property that a casted Mg sample did.

碩士
國立中央大學
機械工程研究所
99
The study used ultrasonic testing to obtain the attenuation of 99.999% pure aluminum and 6063 aluminum alloy. As the result, the measured attenuation is sensitively in varied dislocation density or dislocation loop, so that would increase the calculation errors. Furthermore, we measure attenuation and separate into two parts for discuss: i) grain boundaries set as ; The grain boundary on attenuation were divided to varied angle boundaries (low angle: 0 o ~ 5o, middle angle: 5 o ~ 15o, high angle: 15 o ~ 65o). The angle of grain boundaries of 5N pure Al was observed by using electron back scatter diffraction (EBSD), and estimated the relation between the grain boundary fractions and attenuation. And ii) matrix set as B value. 　　The subtraction of the ultrasonic attenuation of high frequency and low frequency would increase the sensitivity of the difference of the attenuation. The change of grain size of annealed Al6063 by different cooling rate can observed from the subtraction of the ultrasonic attenuation. There are two stages were observed from the subtraction of the ultrasonic attenuation varying micro-hardness of Al6063 during T4 process (nature aging). One is the nucleation and growth of solute atoms (Mg-cluster、Si-cluster). The subtraction decreases with the increasing of the aging time. The other stage is the steady growth or coalescence of clusters. The changes of the subtraction and micro-hardness are unapparent.

Magnesium is the lightest metal that can be used for structural applications. For the reasons of weight saving, there has been an increasing demand for magnesium from the automotive industry. However, poor formability at room temperature, due to a limited number of slip systems available owing to its hexagonal close packed crystal structure, imposes severe limitations on the application of Mg and its alloys in the wrought form. One possibility for improving formability is to form the components superplastically. For this, it is necessary to refine the grain structure. A fine-grained material is also stronger than its coarse grain counterpart because of grain size strengthening. Moreover, fine-grained magnesium alloys have better ductility as well as a low ductile to brittle transition temperature, thus their formability at room temperature could be improved. In addition to grain refinement, the issues pertaining to poor formability or limited ductility of Mg alloys can be addressed by controlling the crystallographic texture. Recently, it has been shown that warm equal channel angular extrusion (ECAE) of magnesium led to reduction in average grain size and shear texture formation, by virtue of which subsequent room temperature rolling was possible. Based on the literature, it was also certain that, in order to make magnesium alloys amenable for processing, grain refinement needs to be carried out and the role of shear texture needs to be explored. Since processing at higher temperature would lead to relatively coarser grain size, large strain deformation at lower temperatures is desirable. The present thesis is an attempt to address these issues. The thesis has been divided in to eight chapters. The chapters 1 and 2 are dedicated to introduction and literature review on the subject that provides the foundation and motivation to the present work. Subsequent chapters deal with the research methodology, experimental and simulation results, discussion, summary and conclusion. In the present investigation, two single phase alloys were chosen, the commercially pure magnesium and the magnesium alloy AM30. These materials were subjected to suitable processing techniques, detailed posteriori. A systematic analysis of microstructure and texture for each of the as-processed materials was performed by electron backscattered diffraction (EBSD) using a field emission gun scanning electron microscope (FEG-SEM). Bulk texture measurement by X-ray diffraction, neutron diffraction and local texture measurement by synchrotron X-rays were also carried out. In addition, dislocation density was measured using X-Ray diffraction line profile analysis (XRDLPA). The experimental textures were validated by using Visco-Plastic Self Consistent (VPSC) simulation. The details of experimental as well simulation techniques used in the present investigation is described in chapter 3. To understand the philosophy of large strain deformation by shear in magnesium and its alloy, free end torsion tests could provide a guide line. Based on the understanding developed from these tests, further processing strategy could be planned. Therefore, a rigorous study of deformation behaviour under torsion was carried out. In chapter 4, the results of free end torsion tests carried out at different temperatures, 250⁰C, 200⁰C and 150⁰C and strain rates, 0.01 rad.s-1, 0.1 rad.s-1, 1 rad.s-1 are presented for both the alloys. In addition to the analysis of stress-strain behaviour, a thorough microstructural characterization including texture analyses pertaining to deformation and dynamic recrystallization was performed. Both pure Mg and the AM30 alloy exhibit similar ductility under the same deformation condition, while the strength of AM30 was more. The strain hardening rate decreased with temperature and increased with strain rate for both the materials. However, the strain hardening rate was always higher in case of the alloy AM30. Large amount of dynamic recrystallization (DRX) was observed for both the alloys. The initial texture had an influence on the deformation behaviour under torsion and the resulting final texture. The initial non-axisymmetric texture of pure Mg samples led to nonaxisymmetric deformation producing ear and faces along the axial direction, and the final texture was also non-axisymmetric. An examination of the texture heterogeneity was carried out in one of the pure Mg torsion tested samples by subjecting it to EBSD examination at different locations of the surface along the axial direction. The strain induced on the ear portion was maximum, and in the face was lower. This has been attributed to the orientation of basal planes in the two regions. The axisymmetric initial texture in case of the alloy AM30 led to the formation of axisymmetric texture with no change in the shape of the material. Owing to this simplicity, the occurrence of dynamic recrystallization (DRX) was studied in more detail for this alloy. The mechanism of texture development due to deformation as well as dynamic recrystallization could be tracked at every stage of deformation. A typical shear texture was observed with respect to the strain in each case. Very low fraction of twins was observed for all the cases indicating slip dominated deformation, which was validated by VPSC simulation. It was found that with the increase in strain during torsion, the fraction of dynamically recrystallized grains increased. The recrystallization mechanism was classified as “continuous dynamic recovery and recrystallization” (CDRR) and is characterized by a rotation of the deformed grains by ~30⁰ along c-axis. After developing an understanding of large strain deformation behaviour of pure Mg and the alloy AM30 through torsion tests, the possibility of low temperature severe plastic deformation for both the materials by equal channel angular extrusion (ECAE) was explored. The outcome of this investigation has been presented in chapter 5. At first, ECAE of pure magnesium was conducted at 250⁰C up to 4 passes and then the temperature was reduced by 50⁰C in each subsequent pass. In this way, ECAE could be carried out successfully up to 8th pass with the last pass at room temperature. A grain size ~250 nm and characteristic ECAE texture with the fibres B and C2 were achieved. The AM30 alloy subjected to similar processing schedule as pure Mg, however, could be deformed only up to 6th pass (TECAE=150⁰C) without fracture. An average grain size ~ 420 nm and a texture similar to ECAE processed pure Mg was observed for this alloy. The difference in the deformation behaviour of the two alloys has been explained on the basis of the anisotropy in the stacking fault energy (SFE) in the case of pure Mg. Neutron diffraction was carried out to confirm and validate the microtexture results obtained from the EBSD data, while the local texture measurement by synchrotron radiation was carried out at different locations of the ECAE samples to give a proper account of the heterogeneity in texture. The effect of grain refinement was examined, deconvoluting the effect of shear in improving the strength and ductility using another severe plastic deformation technique, namely multi axial forging (MAF). In this process, the material was plastically deformed by a combination of uniaxial compression and plane strain compression subsequently along all the three axes. The details of this investigation has been presented in chapter 6. By this method, the alloy AM30 could be deformed without fracture up to a minimum temperature of 150⁰C leading to ultra-fine grain size (~400 nm) with very weak texture. A room temperature ductility ~55% was observed for this material. Finally, a comparison of room temperature mechanical properties of the alloy AM30 was carried out for the ECAE and MAF processed conditions having similar grain size in order to observe the effect of texture formed during both the processes. A similar strength and ductility for both the cases was attributed to the orientation obtained from both the ECAE and MAF, which is away from the ideal end orientation for tensile tests. The final outcomes of the thesis has been summarized in chapter 7.

博士
國立中央大學
機械工程學系
101
In recent years, aluminum alloys are widely used for making 3C products due to their lightweight, good mechanical properties and superior cosmetic appearance after anodizing. The purpose of this study is to introduce the anodization behavior of high purity aluminum and the qualities of anodized Al-Mg-Si and Al-Zn-Mg-Cu aluminum alloy with different matrix structures. The individual brief are as following: Gas bubbles formed during anodization of aluminum in sulfuric acid solution but no precise computation of bubbles size have been presented and discussed in literatures. In this study, we utilized X-ray photoelectron spectroscopy (XPS) to investigate the constituent phases of anodic alumina oxide that formed in a short anodization time. Amorphous alumina prevailed in the films together with a certain amount of hydrated alumina (Al(OH)3), oxyhydroxide (AlOOH) and alumina sulfate (Al2(SO4)3). A hydrophone was applied to measure the acoustic pressure field in the electrolyte during anodization. Experimental results indicated that acoustic pressure oscillated with appropriate frequency ranging from 50 Hz up to 500 Hz. A power spectrum density function (PSD) and cepstrum was adopted to analyze the signal of sound spectrum. The collapse and rebirth of gas bubbles on the surface of anodic aluminum oxide (AAO) film and/or at the pore bases oscillated the measured acoustic pressure. We found that the size of gas bubbles could range from 8 nm to 16 nm in diameter to corresponding to the detected oscillated frequency 400 to 50 Hz, respectively. A series of reactions occurred during anodization to yield SO3 gas and O2 gas, which collapsed and rebirth during the early-growth of AAO film. This study also intends to investigate the effect of deformation on varying the matrix of 6063 and 7075 alloy and on the quality of anodized aluminum oxide film.The Al-Mg-Si alloy and Al-Zn-Mg-Cu contains about 0.6 %Mg and 0.4%Si and Al- 5.4 wt% Zn- 2.5 wt% Mg- 1.5 wt% Cu are a heat treatable alloy with precipitation hardening. Different degree of deformation would be introduced to simulate the forming process in making parts resulting in varying effects on the precipitation hardening of matrix. The highest dislocation density was observed in the SCRT6 sample which also showed the lowest inclusion particle numbers among the three Al-Mg-Si samples. The sample that has been subject to the cryo-rolling process prior to rolling and heat treatment showed few subgrains and smaller amounts of second phase particles in the matrix than was the case with the other two sets of Al-Zn-Mg-Cu samples. Subsequently, all samples were anodized in a 15 wt % sulfuric acid solution for different time spans to obtain different state of AAO films. The anodized samples were further analyzed and observed with Field emission scanning electron microscope (FE-SEM), Transmission electron microscopy (TEM), Atomic force microscopy (AFM) and Electrochemical impedance spectroscopy (EIS) and potential-dynamic polarization curve (PD-curve) analysis. We determined that the constituent phases in the AAO film were composed of hydrated amorphous alumina, hydrated oxide (Al(OH)3) and oxyhydroxide (AlOOH) phases together with some silicon-containing particles trapped in the films on Al-Mg-Si samples. The matrix of Al-Zn-Mg-Cu alloy contained the disc-like precipitates of Mg2Zn and Al2Cu and dissolved from the matrix during anodizatione and remained tiny air-pockets in the AAO film. In the potential-dynamic polarization test, the silicon-containing particles and tiny air-pockets that existed in the AAO films were found to inversely influence the corrosion resistance of the anodized samples.

碩士
逢甲大學
材料科學與工程學系
104
The hydrogen storage capacity of pure magnesium with adding various amounts of active carbon by ball milling was investigated in this study. To compare with the hydrogen storage performance of ZK60 alloy, the related properties of pure magnesium with adding 5 wt% active carbon and various amounts of Ag、Pd、Pt、Zr and Nb by ball-milling for 20 hours were also studied. Experimental results showed that the pure magnesium with 15wt% C has the best hydrogen storage capacity of 6.62 wt%. Then it decreases with increasing the amount of active carbon. For pure magnesium with 5 wt% C, the hydrogen storage capacity can reach 5.00 wt%. In the study of pure magnesium with adding various kinds of catalyst elements, the hydrogen storage capacity of Mg with 5C and 0.5Ag can reach 5.71 wt% at 360℃, and it becomes 6.81 wt% for Mg with 5C and 0.5Pd at the same absorption/desorption temperature. The hydrogen storage capacities of Mg5C0.7Zr and Mg5C0.7Pt are 5.83 wt% and 5.59 wt%, respectively, at 360℃. It is noted that the catalytic effect is obvious for Mg with adding Pd, and the hydrogen storage speed is significant for Mg with adding Zr. In the study of Mg with adding 5C and various amounts of Nb, the hydrogen storage capacity of Mg with 5C and 0.5Nb reaches the maximum value of 5.78 at 360℃, and it exhibits excellent cyclic stability for Mg with 5C0.5Nb. However, the hydrogen storage capacity of Mg with 5C0.5Nb is not so good at 320℃ and 340℃, and it becomes less than 2 wt% after the first cycle at these temperatures. The hydrogen storage performance of Mg5C1Nb and Mg5C1.5Nb is worse than that of Mg5C0.5Nb. For comparison between Mg and ZK60 with adding 5C and various amounts of Ag、Pd and Zr, the hydrogen storage capacity of Mg 5C0.5Pd is 6.81 wt% at 360℃, which is higher than 6.33 wt% for ZK605C0.5Pd at the same temperature, due to the significant catalytic effect for Mg with adding Pd. The effect of adding Ag、Pd and Zr on the hydrogen storage speed is more obvious for ZK60 than that for Mg. The hydrogen storage capacity of ZK60 for absorbing hydrogen at the first five minutes is about 95% of that for 60 minutes, and it is about 90% for Mg at the same conditions.