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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Estudos da copigmentação de compostos análogos às antocianinas / Studies of the copigmentation of compounds analogous to anthocyanins

Held, Bárbara 07 August 2015 (has links)
Foram propostos, no projeto, estudos da interação de compostos modelos de antocianinas (íons hidroxiflavílios e hidroxi/metoxiflavílios sintéticos) com íons metálicos e com copigmentos orgânicos, bem como uma busca de sinergia na complexação ternária destes modelos de antocianinas com íons inorgânicos e copigmentos orgânicos. A partir dos resultados obtidos, pretendeu-se modelar e entender as interações antocianina - íon metálico - copigmento envolvidas na estabilização da cor de antocianinas in natura. Para realizar os estudos, quatro compostos modelos os cloretos dos íons 7,8-diidroxi-4-metilflavílio (DHMF), 8-hidroxi-4-metil-7-metoxiflavílio (HMMF), 3\',4\'-diidroxi-7-metoxiflavílio (B-DHMF) e 7,3\',4\'-trimetoxiflavílio (B-TMF) foram sintetizados. Todas as estruturas apresentam hidroxilas e/ou metoxilas vicinais (estruturas tipo catecol). Além de sua síntese e caracterização, foram estudadas as propriedades fotofísicas e as espécies presentes em solução quantificadas, de acordo com os multiequilíbrios aos quais estes compostos estão submetidos. Nos estudos de complexação por um íon metálico, o Al3+, foram determinadas estequiometrias de 1:1, 2:3 e 1:3 (relação flavílio:Al3+), dependendo da metodologia adotada. As constantes de complexação foram estimadas na ordem de 104 a 105 M-x, onde x depende da estequiometria determinada. A segunda etapa envolveu a interação com copigmentos orgânicos, tais como os ácidos p-cumárico (PCA), ferúlico (FRA), sinápico (SNA), vanílico (VNA) e siríngico (SRA). Utilizando espectroscopia de absorção e de fluorescência, determinaram-se estequiometrias de 1:1 para todos os pares pigmento-copigmento. As constantes dos equilíbrios também foram estimadas sem diferenças significativas entre os pares, embora a afinidade do flavílio pelos derivados de acido cinâmico seja ligeiramente maior. Com relação à base quinonoidal, em pHs em torno de 5,0, foram observadas interações menores, tendo sido concluído que os ácidos fenólicos estabilizam melhor a forma catiônica. A estabilidade do cátion flavílio frente à hidratação na presença destes copigmentos foi avaliada e, em comparação com a estabilidade promovida pelos íons Al3+ ou pela cucurbit[7]urila, é pouco significativa. Finalmente, a terceira etapa envolveu o estudo dos complexos ternários. Observaram-se diferenças na estabilização do cátion flavílio dependendo das concentrações dos dois tipos de copigmento - concentrações maiores de Al3+ foram requeridas para estabilizar o B-DHMF em comparação ao sistema supramolecular formado com DHMF. A partir destes estudos, foi concluído que a presença do copigmento orgânico, embora em pequena extensão, também é responsável pela manutenção da cor, quando envolvido no complexo ternário, evidenciando comportamento sinérgico. Como parte integrante do projeto, um trabalho em colaboração com o grupo da Profa Cornelia Bohne, na University of Victoria (UVic), no Canadá, foi desenvolvido, envolvendo a determinação das constantes de equilíbrio e de velocidade de uma reação do tipo hóspede-hospedeiro, entre um íon flavílio (B-TMF) e um composto orgânico cíclico (hospedeiro), a curcubit[7]urila - CB[7]. A estequiometria da reação foi determinada como 1:2 (B-TMF:CB[7]) sendo que concentrações de CB[7] suficientes para formar o complexo 1:2 promovem uma estabilização da forma catiônica do flavílio nunca vista antes, em pHs em que a reação de hidratação ocorre. / The proposal of this project was to study the reactions of model compounds of anthocyanins (synthetic hydroxyl- and hydroxyl/methoxyflavylium ions), with metal ions, as well as organic copigments or both, in a ternary complex. With results obtained from these systems, it was intended to propose mechanisms and understand how this structure - flavylium ion-metal ion-organic copigment - enables maintenance of the color of anthocyanins in natura. This study would provide information to investigate and search for evidence of synergic effect in the stabilization of these model compounds. Four model compounds were synthesized for the study - chloride salts of 7,8-dihydroxy-4-methylflavylium (DHMF), 8-hydroxy-4-methyl-7-methoxyflavylium (HMMF), 3\',4\'-dihydroxy-7-methoxyflavylium (B-DHMF) and 7,3\',4\'-trimethoxyflavylium (B-TMF). Each one of those compounds presents a catechol-like structure, with bounded hydroxyl and/or methoxy in vicinal positions. The main aims were to synthesize, characterize and study photophysical properties, with a view to determine the concentration of multiequilibria species according to the pH of the medium. The first step was an investigation of metallic complexes produced with Al3+ ions. The stoichiometries were determined as 1:1, 2:3 and 1:3 (flavylium:Al3+), depending on the methodology adopted. Complexation constants were estimated between 104 and 105 M-x, where x represents stoichiometry. A second step was the study of interaction of flavylium ions and organic copigments, such as the following phenolic acids: para-coumaric acid (PCA), ferulic acid (FRA), sinapic acid (SNA), vanilic acid (VNA) and siryngic acid (SRA). Using absorption and fluorescence spectroscopy, a stoichiometry of 1:1 for each of the pigment:copigment pairs was found. Equilibrium constants were determined, and there was no significant differences considering the structures of flavylium ions, although for cinnamic acid derivatives the constants found are slightly larger. The same reactions studied in pH of about 5.0, showed that affinities between the cationic forms and the phenolic acids are larger in comparison to the bases. The stability of the cation regarding the hydration reaction is much smaller in the presence of these organic acids than in the presence of Al3+ or cucurbit[7]uril. At last, the third step involved both types of copigment - metal ions and organic acids - in a supramolecular assembly with flavylium ions. It was observed that different concentrations of the two types of copigments studied are required for B-DHMF and DHMF to stabilize the cationic form; much larger concentrations of Al3+ in the complex in which B-DHMF are involved. It was also concluded that the presence of organic copigments, less representatively, are necessary for the maintenance of the color, an evidence of synergic behaviour. An additional study, which was not in the scope of the project, but did provide another source of flavylium stabilization, was the reaction inclusion of B-TMF with CB[7] cucurbit[7]uril. This step was developed in collaboration with Prof. Cornelia Bohne, at the University of Victoria (UVic), Canada. It consisted of the determination of the equilibrium and kinetic constants of this host-guest system, in which the flavylium cation interacts as the guest for the macrocyclic host. It was proposed a sequential 1:2 (B-TMF:CB[7]) mechanism that provides an alternative to avoid the hydration reaction of B-TMF, where CB[7] must be present in concentrations large enough to form the 1:2 complex.
2

Estudos da copigmentação de compostos análogos às antocianinas / Studies of the copigmentation of compounds analogous to anthocyanins

Bárbara Held 07 August 2015 (has links)
Foram propostos, no projeto, estudos da interação de compostos modelos de antocianinas (íons hidroxiflavílios e hidroxi/metoxiflavílios sintéticos) com íons metálicos e com copigmentos orgânicos, bem como uma busca de sinergia na complexação ternária destes modelos de antocianinas com íons inorgânicos e copigmentos orgânicos. A partir dos resultados obtidos, pretendeu-se modelar e entender as interações antocianina - íon metálico - copigmento envolvidas na estabilização da cor de antocianinas in natura. Para realizar os estudos, quatro compostos modelos os cloretos dos íons 7,8-diidroxi-4-metilflavílio (DHMF), 8-hidroxi-4-metil-7-metoxiflavílio (HMMF), 3\',4\'-diidroxi-7-metoxiflavílio (B-DHMF) e 7,3\',4\'-trimetoxiflavílio (B-TMF) foram sintetizados. Todas as estruturas apresentam hidroxilas e/ou metoxilas vicinais (estruturas tipo catecol). Além de sua síntese e caracterização, foram estudadas as propriedades fotofísicas e as espécies presentes em solução quantificadas, de acordo com os multiequilíbrios aos quais estes compostos estão submetidos. Nos estudos de complexação por um íon metálico, o Al3+, foram determinadas estequiometrias de 1:1, 2:3 e 1:3 (relação flavílio:Al3+), dependendo da metodologia adotada. As constantes de complexação foram estimadas na ordem de 104 a 105 M-x, onde x depende da estequiometria determinada. A segunda etapa envolveu a interação com copigmentos orgânicos, tais como os ácidos p-cumárico (PCA), ferúlico (FRA), sinápico (SNA), vanílico (VNA) e siríngico (SRA). Utilizando espectroscopia de absorção e de fluorescência, determinaram-se estequiometrias de 1:1 para todos os pares pigmento-copigmento. As constantes dos equilíbrios também foram estimadas sem diferenças significativas entre os pares, embora a afinidade do flavílio pelos derivados de acido cinâmico seja ligeiramente maior. Com relação à base quinonoidal, em pHs em torno de 5,0, foram observadas interações menores, tendo sido concluído que os ácidos fenólicos estabilizam melhor a forma catiônica. A estabilidade do cátion flavílio frente à hidratação na presença destes copigmentos foi avaliada e, em comparação com a estabilidade promovida pelos íons Al3+ ou pela cucurbit[7]urila, é pouco significativa. Finalmente, a terceira etapa envolveu o estudo dos complexos ternários. Observaram-se diferenças na estabilização do cátion flavílio dependendo das concentrações dos dois tipos de copigmento - concentrações maiores de Al3+ foram requeridas para estabilizar o B-DHMF em comparação ao sistema supramolecular formado com DHMF. A partir destes estudos, foi concluído que a presença do copigmento orgânico, embora em pequena extensão, também é responsável pela manutenção da cor, quando envolvido no complexo ternário, evidenciando comportamento sinérgico. Como parte integrante do projeto, um trabalho em colaboração com o grupo da Profa Cornelia Bohne, na University of Victoria (UVic), no Canadá, foi desenvolvido, envolvendo a determinação das constantes de equilíbrio e de velocidade de uma reação do tipo hóspede-hospedeiro, entre um íon flavílio (B-TMF) e um composto orgânico cíclico (hospedeiro), a curcubit[7]urila - CB[7]. A estequiometria da reação foi determinada como 1:2 (B-TMF:CB[7]) sendo que concentrações de CB[7] suficientes para formar o complexo 1:2 promovem uma estabilização da forma catiônica do flavílio nunca vista antes, em pHs em que a reação de hidratação ocorre. / The proposal of this project was to study the reactions of model compounds of anthocyanins (synthetic hydroxyl- and hydroxyl/methoxyflavylium ions), with metal ions, as well as organic copigments or both, in a ternary complex. With results obtained from these systems, it was intended to propose mechanisms and understand how this structure - flavylium ion-metal ion-organic copigment - enables maintenance of the color of anthocyanins in natura. This study would provide information to investigate and search for evidence of synergic effect in the stabilization of these model compounds. Four model compounds were synthesized for the study - chloride salts of 7,8-dihydroxy-4-methylflavylium (DHMF), 8-hydroxy-4-methyl-7-methoxyflavylium (HMMF), 3\',4\'-dihydroxy-7-methoxyflavylium (B-DHMF) and 7,3\',4\'-trimethoxyflavylium (B-TMF). Each one of those compounds presents a catechol-like structure, with bounded hydroxyl and/or methoxy in vicinal positions. The main aims were to synthesize, characterize and study photophysical properties, with a view to determine the concentration of multiequilibria species according to the pH of the medium. The first step was an investigation of metallic complexes produced with Al3+ ions. The stoichiometries were determined as 1:1, 2:3 and 1:3 (flavylium:Al3+), depending on the methodology adopted. Complexation constants were estimated between 104 and 105 M-x, where x represents stoichiometry. A second step was the study of interaction of flavylium ions and organic copigments, such as the following phenolic acids: para-coumaric acid (PCA), ferulic acid (FRA), sinapic acid (SNA), vanilic acid (VNA) and siryngic acid (SRA). Using absorption and fluorescence spectroscopy, a stoichiometry of 1:1 for each of the pigment:copigment pairs was found. Equilibrium constants were determined, and there was no significant differences considering the structures of flavylium ions, although for cinnamic acid derivatives the constants found are slightly larger. The same reactions studied in pH of about 5.0, showed that affinities between the cationic forms and the phenolic acids are larger in comparison to the bases. The stability of the cation regarding the hydration reaction is much smaller in the presence of these organic acids than in the presence of Al3+ or cucurbit[7]uril. At last, the third step involved both types of copigment - metal ions and organic acids - in a supramolecular assembly with flavylium ions. It was observed that different concentrations of the two types of copigments studied are required for B-DHMF and DHMF to stabilize the cationic form; much larger concentrations of Al3+ in the complex in which B-DHMF are involved. It was also concluded that the presence of organic copigments, less representatively, are necessary for the maintenance of the color, an evidence of synergic behaviour. An additional study, which was not in the scope of the project, but did provide another source of flavylium stabilization, was the reaction inclusion of B-TMF with CB[7] cucurbit[7]uril. This step was developed in collaboration with Prof. Cornelia Bohne, at the University of Victoria (UVic), Canada. It consisted of the determination of the equilibrium and kinetic constants of this host-guest system, in which the flavylium cation interacts as the guest for the macrocyclic host. It was proposed a sequential 1:2 (B-TMF:CB[7]) mechanism that provides an alternative to avoid the hydration reaction of B-TMF, where CB[7] must be present in concentrations large enough to form the 1:2 complex.
3

Characterization of heavy metal tolerant bacterial plasmids isolated from a platinum mine tailings dam / by Tladi Abram Mahlatsi.

Mahlatsi, Tladi Abram January 2012 (has links)
The development of metal-tolerance and antibiotic resistance in bacteria may be caused by metals polluting a particular environment. During mining and mineral processing activities, large quantities of metals are deposited into the soil. These high concentrations of metals are evolutionary pressures selecting for microorganisms tolerant to these metals. Metaltolerance maybe conferred to these organisms by mobile genetic elements such as plasmids. This study describes the characteristics of plasmids isolated from various bacteria that displayed an ability to withstand high metal concentrations. The isolated plasmids were individually transformed into Escherichia coli JM109. Transformants were then evaluated for metal-tolerant capabilities using a microdilution approach. Plasmids were then isolated from the transformants and the concentration of the plasmid DNA ranged between 11.75 – 118.06 ng/μl. These plasmids were of the same size as the original ones. This demonstrated that successful transformations with plasmid DNA were conducted. In order to determine the compatibility group, plasmids were subjected to PCR amplification using IncQ, IncP-9 and IncW specific primers. Only the IncW provided positive results. To demonstrate that the plasmids were free of genomic DNA, a 16S rDNA PCR test was included. The plasmids that were positive for IncW PCRs were all negative for the rDNA PCRs. Plasmids were stably inherited and at least three, isolated from three different Gram positive species, belonged to the Inc W group of plasmids. These were originally isolated from Paenibacillus ginsingari, Paenibacillus lautus and Bacillus cereus. Minimum inhibition concentrations (MICs) were carried out to determine the ability of transformed E. coli JM109 to tolerate metals at varying concentrations. Results indicated that transformed E. coli JM109 developed ability to grow in the presence of several heavy metals. Some strains were resistant to high concentrations (+10 mM) of Ni2+/Al3+, Pb2+ and Ba2+. The order of metal resistance was Ni/Al=Pb>Ba>Mn>Cr>Cu>Co=Hg. All the x transformants were sensitive to 1 mM of Co2+ and Hg2+. Moreover, protein profiling was used to determine the impact of plasmids on E. coli JM109. Proteins were extracted from both transformed and un-transformed E. coli JM109 using acetone-SDS protocol and subjected to one-dimensional (1D) and two-dimensional (2D) Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS- PAGE). Transformed E. coli JM109 were grown under the metal stress. One dimension SDS-PAGE illustrated general similarity of the profiles except for two banding positions in the 30 to 35 kDa region where bands were present in the transformants that were grown in the Ni/Al alloy containing media. Twodimensional electrophoresis PAGE analysis showed that some of the proteins were upregulated while others were down-regulated. The largest numbers of proteins were from 15 – 75 kDa. The majority of these proteins had isoelectric points (pI) between 5 and 6. It was concluded that plasmids isolated from various heavy metal-tolerant bacterial species were successfully transformed into E. coli JM109 rendering various new metal-tolerant E. coli JM109 strains. Furthermore, the study showed that metal resistance was due to the presence of the plasmids. Two-dimensional SDS-PAGE resolved more differences in the protein expression profiles. Since the plasmids rendered the E. coli JM109 tolerant to metals tested, it also can be concluded that the change in the protein profiles was due to the effects of the plasmids. Furthermore, plasmids were also re-isolated from the transformants and these plasmids were of the same size as the original ones.. All the plasmids in this study were also stably inherited, a feature associated with IncW plasmids. More detailed genetic characterization of these plasmids is required. Plasmids isolated and characterized in this study may hold biotechnology potential. Such features should be exploited in follow-up experiments. / Thesis (Master of Environmental Sciences)--North-West University, Potchefstroom Campus, 2013.
4

Characterization of heavy metal tolerant bacterial plasmids isolated from a platinum mine tailings dam / by Tladi Abram Mahlatsi.

Mahlatsi, Tladi Abram January 2012 (has links)
The development of metal-tolerance and antibiotic resistance in bacteria may be caused by metals polluting a particular environment. During mining and mineral processing activities, large quantities of metals are deposited into the soil. These high concentrations of metals are evolutionary pressures selecting for microorganisms tolerant to these metals. Metaltolerance maybe conferred to these organisms by mobile genetic elements such as plasmids. This study describes the characteristics of plasmids isolated from various bacteria that displayed an ability to withstand high metal concentrations. The isolated plasmids were individually transformed into Escherichia coli JM109. Transformants were then evaluated for metal-tolerant capabilities using a microdilution approach. Plasmids were then isolated from the transformants and the concentration of the plasmid DNA ranged between 11.75 – 118.06 ng/μl. These plasmids were of the same size as the original ones. This demonstrated that successful transformations with plasmid DNA were conducted. In order to determine the compatibility group, plasmids were subjected to PCR amplification using IncQ, IncP-9 and IncW specific primers. Only the IncW provided positive results. To demonstrate that the plasmids were free of genomic DNA, a 16S rDNA PCR test was included. The plasmids that were positive for IncW PCRs were all negative for the rDNA PCRs. Plasmids were stably inherited and at least three, isolated from three different Gram positive species, belonged to the Inc W group of plasmids. These were originally isolated from Paenibacillus ginsingari, Paenibacillus lautus and Bacillus cereus. Minimum inhibition concentrations (MICs) were carried out to determine the ability of transformed E. coli JM109 to tolerate metals at varying concentrations. Results indicated that transformed E. coli JM109 developed ability to grow in the presence of several heavy metals. Some strains were resistant to high concentrations (+10 mM) of Ni2+/Al3+, Pb2+ and Ba2+. The order of metal resistance was Ni/Al=Pb>Ba>Mn>Cr>Cu>Co=Hg. All the x transformants were sensitive to 1 mM of Co2+ and Hg2+. Moreover, protein profiling was used to determine the impact of plasmids on E. coli JM109. Proteins were extracted from both transformed and un-transformed E. coli JM109 using acetone-SDS protocol and subjected to one-dimensional (1D) and two-dimensional (2D) Sodium Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS- PAGE). Transformed E. coli JM109 were grown under the metal stress. One dimension SDS-PAGE illustrated general similarity of the profiles except for two banding positions in the 30 to 35 kDa region where bands were present in the transformants that were grown in the Ni/Al alloy containing media. Twodimensional electrophoresis PAGE analysis showed that some of the proteins were upregulated while others were down-regulated. The largest numbers of proteins were from 15 – 75 kDa. The majority of these proteins had isoelectric points (pI) between 5 and 6. It was concluded that plasmids isolated from various heavy metal-tolerant bacterial species were successfully transformed into E. coli JM109 rendering various new metal-tolerant E. coli JM109 strains. Furthermore, the study showed that metal resistance was due to the presence of the plasmids. Two-dimensional SDS-PAGE resolved more differences in the protein expression profiles. Since the plasmids rendered the E. coli JM109 tolerant to metals tested, it also can be concluded that the change in the protein profiles was due to the effects of the plasmids. Furthermore, plasmids were also re-isolated from the transformants and these plasmids were of the same size as the original ones.. All the plasmids in this study were also stably inherited, a feature associated with IncW plasmids. More detailed genetic characterization of these plasmids is required. Plasmids isolated and characterized in this study may hold biotechnology potential. Such features should be exploited in follow-up experiments. / Thesis (Master of Environmental Sciences)--North-West University, Potchefstroom Campus, 2013.
5

Growth Morphology And Coarsening Of Metastable Al3Zr In Melt Spun Al-Ni-Zr Alloys

Srinivasan, Dheepa 01 1900 (has links) (PDF)
No description available.
6

Equilibrium studies of ternary aluminium(III) hydroxo complexes with ligands related to conditions in natural waters

Öhman, Lars-Olof January 1983 (has links)
The thesis is a summary and discussion of eight papers. During the last decades, precipitation has become increasingly acidic due to the extensive use of fossil fuels. In areas of poorly buffered bedrocks, e.g. Scandinavia, northeastern United States, this phenomenon has resulted in elevated amounts of Al(III) being leached into streams and lakes. Recent findings reveal that these elevated Al-concentrations could cause fish death and decreasing forest production. In the present thesis, the importance of taking naturally occurring substances into consideration when discussing Al(III) in natural waters, is emphasized. On the basis of a chemical characterization of relevant ligand classes in a natural water, the complex formation between Al^+, hydroxide ions and the inorganic ligand carbonic acid, the low-molecular weight organic ligand citric acid and the high-molecular weight model substances gallic acid, 1,2-dihydroxynaphtha-lene-4-sulfonate, 1,2-naphthoquinone-4-sulfonate, pyrocatechol and salicylic acid were investigated. The investigations were performed as series of Potentiometrie titrations and data were processed by means of the least-squares computer program LETAGROPVRID using a technique called pqr-analysis, permitting an unbiased search for complex model (and corresponding equilibrium constants) to be made. In most systems studied, the complexation at high ligand excesses can be described by a series of mononuclear complexes AIL-AIL^. Tentatively, the whole series consists of octahedrally coordinated (water and ligand oxygens) AI(III). At lower ligand excesses, the significance and in some cases even predominance of ternary mono- and polynuclear hydroxo complexes is demonstrated. In two of the systems, binary aluminium hydroxo species are evaluated. The potential importance of the substances with respect to Al-com-plexation in natural waters are indicated in a number of model calculations. The solubility of the clay mineral kaolinite is calculated as a function of -lg[H+] and ligand concentration. It is shown that citric acid, gallic acid, 1,2-dihydroxynaphthalene-4-sulfonate, pyrocatechol and salicylic acid contribute quite significant to the total solubilities, even at very low concentrations. As a complement and background to the equilibrium studies, the corrosion rate for one of the naturally occurring Al-bearing minerals, corundum, is reported. In this investigation, performed with a leach-ant solution of ground-water composition, an experimental technique was employed which made it possible to divide the corrosion into chemical and mechanical losses. / <p>Diss. (sammanfattning) Umeå : Umeå universitet, 1983</p> / digitalisering@umu
7

Struktura a únavové vlastnosti vybrané titanové slitiny / Structure and fatigue properties of selected titanium alloy

Prudíková, Alena January 2014 (has links)
Main topic of the thesis was to evaluate fatigue properties of the titanium alloy Ti-A13-V2,5, labelled by ASTM as Grade 9. Most attention was focused on fatigue behaviour of the alloy in the range of high cycle fatigue. Fatigue testing was realised to detect the fatigue properties and consequently to generate the Wöhler curve and the Haigh diagram. In addition to this, tension and bending tests were performed. Metallographic and fractographic analyses of fatigue fracture form part of the overview about material properties, which was accomplished by use of REM. Experimental part of the thesis was backed by the literature research. The first half of it contains a short summary of basic information about the titanium and its alloys, so as some chapters about the history and properties of titanium, the way of its production, classification of titanium alloys and its thermic treatment. The fatigue is thoroughly scrutinised in the second half of the background research. Here can also be found the information about the fatigue process, its stages, the fatigue life and the most significant attributes of the fatigue fracture. The last chapters of the thesis are dedicated to the alloy Ti-A13-V2,5 - being examined in the experimental part - so as to its fatigue properties. The main benefit of this thesis is the completion of the missing information concerning the fatigue behaviour of the alloy, which is – according to the literature research - generally not available.
8

Surfaces d'alliages métalliques complexes : structure, propriétés et nanostructuration / Complexe metallic alloys surfaces : structure, properties and nanostructuration

Addou, Rafik 29 March 2010 (has links)
Ce travail a permis de déterminer les structures atomique et électronique de deux surfaces d'alliages métalliques complexes à l'aide d'une approche multi-techniques supportée par des calculs ab intio de structure électronique. Les surfaces de ces cristaux ont pu être corrélées à certains plans présents dans les modèles structuraux disponibles. La terminaison dominante de la surface (100) d'Al13Co4 est identifiée comme un plan corrugué incomplet du volume. La surface (010) de Al3(Mn, Pd) présente un nombre conséquent d'imperfections structurales. À l'exception de certains sites lacunaires, elle est identique au plan corrugué complet du massif. Dans une seconde étape, ces échantillons ont été utilisés comme substrat pour la croissance de films minces métalliques. Les atomes de Pb déposés sur ces deux surfaces suivent un mode de croissance pseudomorphique jusqu'à la formation de la monocouche. Dans le cas de l'Al13Co4, le coefficient de collage du Pb s'annule une fois cette monocouche formée. Sur la surface Al3(Mn, Pd), le croissance de couches additionnelles de Pb est observée. L'adsorption du Cu sur Al13Co4 mène de nouveau à un mode de croissance pseudomorphique jusqu'à la monocouche. Au-delà de ce dépôt, la phase ß-Al(Cu, Co) apparaît en surface. Pour des dépôts à des températures plus élevées, la phase- ß est suivie par la formation de la phase ?-Al4Cu9. Les phases ß et ? croissent suivant deux domaines (110) orientés l'un par rapport à l'autre avec un angle de 72° / We report the investigation of pseudo-ten-fold surfaces on two complex metallic alloys considered as approximants to the decagonal quasicristal. The atomic and electronic structure of the both samples is investigated by means of a multi-technique approach supported by ab initio electronic structure calculations. The main termination of the (100) surface of Al13Co4 is attributed to an incomplete puckered layer. The (010) surface of Al3(Mn, Pd) exhibits an important amount of structural imperfections. With the exception of several vacancies, this surface is identical to the complete puckered layer. In a second stage, both surfaces have been used as templates for the growth of metallic thin films. On both surfaces, Pb adatoms adopt a pseudomorphic growth mode up to one monolayer. For the Al13Co4 surface, the sticking coefficient of Pb vanishes upon the completion of the monolayer. However, it remains sufficient for the growth of additional layers on the Al3(Mn, Pd) (010) surface. The adsorption of Cu on the Al13Co4 surface follows also a pseudomorphic growth mode up to one monolayer. The ß-Al(Cu, Co) phase appears for coverages greater than one monolayer. For higher temperature deposition, the ß-phase is followed by the formation of the ?-Al4Cu9 phase. Both ß and ? phases grow as two (110) domains rotated by 72° from each other

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