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The precipitation of thorium with certain organic reagents has been shown to afford a basis for polarographic methods for the determination of thorium. Appropriate conditions for the precipitation of thorium by certain reagents have been determined, and the advantages of a homogeneous precipitation of thorium 8-quitnolinate have been demonstrated. The precipitate that thorium forms with m-nitrobenzoic acid has been found to be the tetra-m-nitrobenzoate. The new polarographic methods tor thorium have been proven to be directly applicable to zirconium-free magnesium-base alloys . When zirconium is present, a simple anion exchange procedure will eliminate the interference of zirconium, and allow it's subsequent determination.The satisfactory nature of the precision and accuracy of the proposed methods, and their applicability to substances other than magnesium-base alloys, have been demonstrated. / Thesis / Master of Science (MS)

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Mechanical Engineering / Magnesium (Mg) alloys provide material properties that make them attractive for structural components. In particular Mg alloys can be used to produce components with lighter weight than most alloy sheets currently used. However, the insufficient ductility of Mg alloy sheet materials at room temperature can require these to be formed at elevated temperatures to achieve suitable formability. In this research, wrought Mg alloy ZEK100 is studied at 300 °C and lower temperatures. Behavior at these lower temperatures is compared to behavior of 450 °C and 350 °C. A goal of this study is to determine the possibilities for future forming technologies at these lower temperatures. The deformation mechanisms at these temperatures are examined, including their relation to plastic anisotropy. Knowledge of the active deformation mechanisms is used to formulate descriptive models of plastic deformation. Material constitutive models are constructed and used in finite element method (FEM) simulations of gas pressure bulge tests. Finally, results of FEM simulations are compared with experimental results, and the accuracies of the material constitutive models are validated. / text

Eight adolescent males (14 to 18 years old) were evaluated before and after 50 minutes of exercise on a bicycle ergometer at 60 percent of their maximal heart rate to investigate the relationship between blood magnesium status and the derangement of other serum electrolytes in the etiology of "sports anemia." Criteria of assessment included changes in serum concentration and total serum content of magnesium, sodium, potassium, calcium, and red blood cell magnesium concentration, urinary magnesium excretion, hematocrit, hemoglobin, mean corpuscular volume, red blood cell count, osmotic fragility, reticulocytosis, and spherocytosis. A significant reduction in serum sodium concentration was found at post-exercise, whereas, serum calcium and potassium concentrations rose 3.8 percent and 7.7 percent, respectively. Total serum content of magnesium and sodium was significantly reduced by 4.9 percent and 9.0 percent, respectively, at post-exercise. Red blood cell magnesium dropped 3.1 percent at post-exercise. Following a one-hour recovery, serum magnesium concentration had fallen significantly (10.3 percent) and red blood cell magnesium concentration was 2.6 percent higher than the pre-exercise concentration. Although there was no evidence of red blood cell hemolysis, red cells did show spherocytosis and a tendency toward increased osmotic fragility. In addition, the changes observed in total serum magnesium content were significantly correlated to changes in total serum calcium at post-exercise and to total serum potassium content at recovery. The spherocytosis and decreased osmotic resistance appear to result from the impairment of magnesium-dependent adenosine triphosphatase, which is responsible for the active transport of sodium and potassium across the erythrocyte membrane. / Graduation date: 1984

Magnesium (Mg) and its alloys offer potential as a new class of degradable metallic orthopaedic biomaterials. In comparison with current metallic orthopaedic implant materials, Mg offers advantages such as, high specific strength, closer-to-bone stiffness and biodegradability, thereby eliminating the need for a second surgery to remove hardware. The use of porous metal foams as biomaterial scaffolds has been widely adopted, however, many of these porous structures are manufactured with pore architectures that are inherently random. This makes structural optimisation for a specific purpose challenging. Scaffolds containing ordered pore architectures can be fabricated to meet design criteria, such as porosity, stiffness, and volume fraction. Currently there are few methods described in the literature to manufacture ordered porous Mg. The main aim of this thesis was to determine the resolution of a novel indirect solid free-form fabrication (SFF) process for producing topologically-ordered porous Mg (TOPM) structures from pure Mg and commercial Mg alloys. The produced structures were examined for properties such as dimensional accuracy, microstructure, surface properties, mechanical properties and corrosion behaviour. The capability of the process was further examined in manufacturing structures with complex architecture for potential application as degradable metallic orthopaedic devices, namely a spinal fusion device (SFD) and screw. With the produced structures aimed at load-bearing applications in bone, the mechanical properties and behaviour of the TOPM and SFD made from Mg alloys were investigated using finite element analysis (FEA) and compression testing. The relationship between surface roughness and degradation behaviour in Mg biomaterials has received limited interest and is still a controversial issue. Therefore, it was necessary to accurately determine the effect of surface roughness on corrosion rate of Mg, especially samples manufactured from SFF and casting of molten Mg. Given the well-established need for improved corrosion resistance of Mg, two coating techniques, including biomimetic calcium phosphates and electrochemically-assisted deposition coating, were applied on Mg substrates cast via the SFF process. Corrosion testing was employed to investigate the effectiveness of the coating layers in improving corrosion resistance. In this thesis, the capability of the SFF manufacturing process and properties of the produced structures were thoroughly investigated. Results and findings contribute to the development of topology optimised, degradable Mg devices for biomedical applications.

We report here the observation of non-ohmic behavior in the dominant oscillatory component (the cigar component) of ρ('H) in ultrapure magnesium when the magnetic field, 'H, is parallel to [0001] and the current density, 'J, lies in the basal plane. In order to study this new phenomenon systematically, we had to overcome two experimental problems. The first was the design of an experimental probe which could reproducibly control, at low temperatures, the contact resistance at one of the points where current is injected into the sample without disturbing the sample's orientation with respect to 'H. Special micromanipulators, controlled by helium gas pressure, were designed into the probe for this purpose. The second problem was the construction of a detector which had the sensitivity to measure small signals from the magnesium samples in an effort to investigate the low current regime where the oscillations appear to satisfy Ohm's Law. A superconducting chopper amplifier was built which had the sensitivity to measure 10⁻¹¹ volt signals. We present evidence which directly relates this non-ohmic behavior to the long-range influence of a relatively large contact resistance at a point where current is injected into the sample. Data are presented which indicate that when this non-ohmic behavior is present, the corresponding oscillation amplitudes are proportional to the contact resistance. Measurements are also presented which show that the effects of this local current injection are so nonlocal that they extend over distances which are comparable to the dimensions of the sample.