<p>The development of highly formable aluminum alloy sheets is of great interest to the automotive industry, because they provide a lightweight alternative to steel sheet for structural panels. Finding ways to improve the formability of Al alloys is the main subject of the present investigation. This issue is tackled from two angles. First, a possibility of fabricating a two-phase material containing newly discovered ductile intermetallic compounds is considered. The Al-La-Mg system is thermodynamically optimized accompanied with a differential thermal analysis (DTA) experiment to validate the optimization results. A new approach is introduced to deal with the incompatibility of phase models in binary Al-La and La-Mg systems. This approach is successfully applied to the Laves and B2 phases in the binary La-Mg system. A utilization of the thermodynamic description of the Al-La-Mg system to model solidification at low and high cooling rates shows that it is impossible to fabricate such a two-phase material by casting.</p> <p>Second, the effect of small additions of cerium and lanthanum on Fe-bearing intermetallics in a wrought heat-treatable Al alloy is examined. Fe-containing intermetallics are known to deteriorate the formability of Al alloys by acting as void nucleation sites. It is found that in alloys containing 0.1-0.2 wt. % of lanthanum, the fraction of less harmful Chinese script particles is pronouncedly higher than that in the reference alloy. In addition to this advantage, much smaller grains are seen in the alloy with 0.2 wt. % La. Despite similarities between La and Ce, the latter metal neither modifies the microstructure nor noticeably affects the gram size. Hot rolling and solutionizing nullifies the beneficial effect of small La additions resulting in no improvement in the formability of the alloy.</p> <p>In order to understand how lanthanum affects the phase portrait of the alloy, a socalled direct thermal analysis experiment is performed. Solidification paths are derived for slowly cooled alloys by coupling the results of this investigation with microstructural observations. The likelihood of two modification mechanisms is speculated using these solidification paths.</p> / Thesis / Doctor of Philosophy (PhD)

No description available.

<p>The application aluminum sheet alloy for light vehicle development was limited by the high cost of alloy fabrication. The impurity iron, which is easily picked up during fabrication, deteriorates its formability. The sheet alloy produced by continuous casting techniques was showing lower in-service performance than the one produced with traditional high-cost direct-chill casting technique. Therefore, enhancing the general formability of the aluminum alloy became .the aim of many researchers and engineers in past decades.</p><p>This project was launched to detect a possible modification effect of rare-earth (RE) element on a Al-Mg-Fe alloy, which is a simplified AA5754 alloy. Cerium was chosen as the RE element to test with. The influence of this rare-earth element on the alloy grain microstructure, phase morphology, and corresponding mechanical behavior was investigated.</p><p>It was found that cerium had a modification effect on the phase morphology to some extent. Its addition provided a great grain refinement in as-cast alloys. However, after thermo-mechanical processing, this effect would be eliminated by the small broken particles and recrystallized fine grains. It was found that the mechanical performance of the cerium-containing AA5754 was neither enhanced nor deteriorated. The AA5754 alloy remained non-heat-treatable after the addition of cerium.</p> / Thesis / Master of Applied Science (MASc)

No description available.

Les oxynitrures dopés terre rare présentent des propriétés intéressantes pour un usage en tant que luminophore pour LEDs blanches. Une nouvelle famille de luminophores dopés Eu2+ ou Ce3+ avec un réseau hôte oxynitrure de structure apatite a été étudiée : La8+xSr2-x(Si/Ge)6NyO26+x/2-3/2y. L’ammonolyse d’un précurseur oxyde de structure apatite a été utilisée comme technique générale de nitruration. Elle a permis de diminuer substantiellement la température de nitruration en comparaison avec la méthode classique par réaction à l’état solide sous atmosphère mixte N2/H2. Les différentes luminescences des luminophores obtenus ont été étudiées et corrélées à la structure cristalline à l’aide de différentes techniques de caractérisation.La structure apatite présente notamment la particularité de proposer plusieurs sites anioniques pour l’introduction de l’azote ainsi que deux sites cationiques pour les ions terre rare activateurs. L’utilisation de nombreuses techniques de caractérisation (IR, Raman, RMN, diffraction des neutrons) a permis d’obtenir des informations sur la position de l’azote. En parallèle, la comparaison des propriétés optiques avec celles de composés réduits sous Ar/H2 a permis d’attribuer les émissions aux différents sites cristallins disponibles dans la structure. Des mesures de rendement quantique ainsi que des tentatives d’optimisation des propriétés de luminescence ont été effectuées. / Rare-earth doped oxynitrides have attracted much attention as phosphors for white LEDs. A new family of Ce3+ or Eu2+-doped oxynitride phosphors with the apatite structure has been studied: La8+xSr2-x(Si/Ge)6NyO26+x/2-3/2y. The ammonolysis of an apatite oxide precursor has been used as a general method of synthesis, allowing decreasing the nitriding temperature respective to the classical solid state reaction in N2/H2 atmosphere. The luminescence properties of the obtained phosphors have been studied and relationships with the crystalline structure have been drawn.The apatite structure shows several crystallographic sites available for nitrogen as well as two cationic sites for optically active rare-earth ions. Several structural characterization technique have been used (IR, Raman, NMR, Neutron diffraction) and important information has been obtained concerning the nitrogen distribution in the available positions of the crystal structure. Comparison of the luminescent properties with those of compounds reduced under Ar/H2 allowed attributing emissions to the different crystallographic sites available in the structure.Quantum efficiency measurements have been carried out as well as trials for improving the intensity of the luminescent properties.

Metal oxide nanoparticles constitute an important class of nanomaterials which has have received tremendous attention due to their distinct, specific activities comparison to their bulk. Among these, cerium oxide nanoparticles (CeNPs) have displayed outstanding promise across a wide range of applications owing to their unique redox properties. Given that the physical and chemical characteristics of nanomaterials are significantly influenced by their morphologies and sizes, the development of well-controlled synthesis methods for CeNPs holds great importance in both scientific research and industrial applications. This dissertation seeks to peer into the formation of CeNPs in solution through wet chemical synthesis. Additionally, antioxidant properties of CeNPs were examined to explore the potential use of facet CeNPs in gene delivery and promoting wound healing for diabetic. The beginning of this work provides introduction and summary of some common concepts widely used in understanding of nanoparticles formation. In chapter two and three, the spontaneous hydrolysis behavior of tetravalent cerium salts in aqueous systems were studied in detail to understand the influence of synthesis condition on the nucleation kinetic and morphology evolution in the course of growth of nanoparticle. The results obtained from these studies offer constructive insights into designing a straightforward and controlled synthesis strategy for producing nanoclusters and faceted nanoparticles through wet chemical methods. Furthermore, in chapter five, we examine the impact of faceted CeNPs on biomolecule conjugation and their performance in gene delivery for the regulation of abnormal diabetic wound healing. Overall, by taking advantage of the intrinsic properties of tetravalence cerium salt, this work highlights how manipulation of spontaneous hydrolysis could lead to formation of particles with different nanostructure and physicochemical properties.

ITC/USA 2011 Conference Proceedings / The Forty-Seventh Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2011 / Bally's Las Vegas, Las Vegas, Nevada / The National Aeronautics and Space Administration's (NASA) Remote Imaging System Acquisition (RISA) camera will integrate the functionalities of existing space cameras. The system operates between 350nm and 1050nm wavelengths, with a MATLAB user interface, uses a CS-mount standard with a CMOS detector, and has a fixed focal plane. The implementation of a liquid lens uses electrical focus adjustments to image from infinity down to one foot. This will allow wireless operation and reduces mechanical failure. All images and video captured will be transmitted wirelessly to a MATLAB program. This data is then processed and stored, allowing for remote imaging.

Metal ions and complexes utilized as cleavage agents have influenced many synthetic approaches of scientists to assist in the cleavage and transformation of biomolecules. These metal-based synthetic cleavage agents have potential applications in biotechnology or as molecular therapeutic agents. Herein, we have examined Ce(IV) metal ion and complexes as acidic hydrolytic agents in lipid hydrolysis reactions (Chapter 2 and 3), and a copper(II) complex that photo-oxidizes DNA upon exposure to ultraviolet light (Chapter 4). In Chapter 2 we examined the hydrolysis of sphingomyelin vesicles by Ce(NH4)2(NO3)6 (Ce(IV)) and compared the results to twelve d- and f-block metal salts, hydrolysis of mixed lipid vesicles and mixed micelles of sphingomyelin by Ce(IV), and hydrolysis of phosphatidylcholine vesicles by Ce(IV), using either MALDI-TOF mass spectrometry or colorimetric assays. In Chapter 3, we described the study of a Ce(IV) complex based on 1,3-bis[tris(hydroxymethyl)methylamino]propane as a potential acidic hydrolytic agent of phospholipids using colorimetric assays and NMR spectroscopy. The hydrolytic agent provided markedly enhance hydrolysis at lysosomal pH (~ 4.8), but suppress hydrolysis when pH was raised to near-neutral pH (~ 7.2). This was due to the pKa values of the donor atoms of the ligand, in which the metal’s electrophilicity was reduced to a greater extent at ~ pH 7.2 compared to ~ pH 4.8. Chapter 4 describes the synthesis and study of a Cu(II) complex based on a hexaazatriphenylene derivative for photo-assisted cleavage of double-helical DNA. Scavenger and chemical assays suggested the formation of DNA damaging reactive oxygen species, hydroxyl and superoxide radicals, and hydrogen peroxide, in the photocleavage reactions. Thermal denaturation and UV-vis absorption studies suggested that the Cu(II) complex binds in a non-intercalative fashion to duplex DNA.

An increase in nanotechnology has seen an associated rise in nanoparticles released into the environment. Their potential toxicity and exposure to humans and the environment, the field of nanoecotoxicology, is not yet well understood. The interactions at the nanoparticle surface will play a fundamental role in the nanoparticle behaviour once released into the environment. This study aims to characterise the particle surface interaction, determining key parameters influential in the nanoparticle fate. Evanescent Wave Cavity Ring Down Spectroscopy techniques have been applied to study molecular interactions at the silica-water charged interface. The adsorption of the electronic spectrum of Crystal Violet has demonstrated the formation of a monolayer with different binding site orientation at the interface. The binding affinity for the chromophore was calculated as 29.15 ± 0.02 kJmol-1 at pH 9 and this was compared with other interface structures involving both inorganic and organic components. The study of the model interface was extended to the properties of CeO2 nanoparticles, where the surface charge density was determined to be 1.6 ± 0.3 e- nm-2.The nanoparticle surface charge controls the suspension stability which was measured for CeO2 nanoparticles giving a stability half-life of 330 ± 60 hours in pure water, and 3.6 ± 0.6 hours in ISOFish water. Studies were extended to the toxicity of ZnO nanoparticles. An assay was developed to quantify the photo-electron production for nanoparticles exposed to UV light both in deionised water and soil suspensions with a photo-radical production yield of 19 ± 2 % and an electron production of 709 e-s-1np-1 for a 100 mgL-1 suspension. The species-specific photo-radical assay was subsequently used to determine the rate of ZnO nanoparticle dissolution in water and soil suspensions. Comparable dissolution rates in complex cell growth media were also measured, detecting total zinc by Inductively Coupled Plasma Atomic Emission Spectroscopy, with comparable dissolution rates derived.

M.Sc. / Aspects of electron-electron correlations have for the past few decades been at the forefront of research in Solid State Physics. More traditional concepts under this topic have been phenomena such as superconductivity, and magnetic ordering in its many forms including long-range ordering and spin-glass freezing. The class of so-called strongly correlated electron systems has been a particularly active field of study, as witnessed by for instance the series of annual international conferences held under this topic since 1992. Compounds and alloys of strong electronic correlations have proved a very rich field of new and anomalous physical behaviours in metallic and semiconducting compounds and alloys of especially 4f- and 5f-electron systems, together with ceramics characterized as the so-called ¡§high-TC¡¨ superconductors. The f-electron systems have revealed a variety of behaviours such as ~ 1000-fold enhanced effective electron masses at low temperature, coexistence of superconductivity and magnetic ordering in systems where the magnetic interactions are far too strong to allow for Cooper-pair formation within the well-established BCS-interpretation, and electron transport and thermodynamic behaviour at low temperatures that completely defy our conventional Fermi-liquid paradigm of understanding the ground states of metals. The series of pseudo-ternary compounds Ce1-xLaxRu4Sn6 that were synthesized and characterized in this work for the first time are formed by substituting La for Ce in CeRu4Sn6, the parent compound. CeRu4Sn6 exhibits a number of properties which have been associated with a special class, the Kondo semiconductors of strongly correlated electron systems. CeRu4Sn6 has very recently been shown [A. M. Strydom et al. (2004)] to comprise an intriguing combination of characteristics that are thus far unique among the Kondo semiconductors: At low temperature (T 10 K) the specific heat proves the development of very strong electronic correlation out of an already low density of charge carriers (as shown by Hall-effect, resistivity, and the Sommerfeld coefficient of the specific heat). Furthermore, the specific heat follows a logarithmic increase as temperature is decreased below ~ 2 K, in a range where thermal transport shows the presence of an energy gap in the electronic density of states. The aim of this work was to investigate the intermediate and higher temperature (4.01 K „T T „T 300 K) behaviour of the electrical resistivity of the Ce1-xLaxRu4Sn6 series of compounds in which the concentration of the 4f-electron magnetic ion Ce is progressively being reduced. A steady but slow decrease of the energy gap with increasing La concentration was found in this work in contrast with what is usually the case in Kondo semiconductors. Both the presence of an energy gap and the low density of charge carriers are found to be connected to the presence of Ce in the unit cell, and are therefore not an artefact of the peculiar filledƒ{cageƒ{like tetragonal crystal structure of these compounds. An interesting strong anisotropy was found in the way in which the tetragonal unit cell expands preferentially within the aƒ{b plane, compared to the elongation along the cƒ{axis, upon moving from CeRu4Sn6 to LaRu4Sn6. / Prof. A.M. Strydom