Thesis (Ph. D.)--University of Queensland, 2002. / Includes bibliographical references.

The effect of Li additions to Mg on the texture and mechanical properties in both the hot and cold rolled condition has been examined. It was found that using the texture goniometer (Schulz technique) only the surface texture is obtained. As a result average textures were prepared for each alloy. Lithium additions to Mg causes a loss in sharpness of the (0001) texture. No indication of a <1120> directional texture was found. The change in texture was explained successfully on the basis of deformation systems active during rolling. Cold rolling of the alloys caused a loss in sharpness of the (0001) texture for low Li alloys. In the high Li alloys (6 at. % and 12.4 at. %) a pronounced split occurred. A definite <1120> directional texture was observed on the surface of the cold-rolled low Li alloys but this disappeared in the "average" pole figure. Again the change in texture was explained on the basis of deformation systems active during rolling. Tensile tests of hot-rolled Mg-Li alloys agreed completely with those of Yoshinaga & Horiuchi (9) but showed some variance with those of Hauser, Landon, and Dorn (8). Tensile tests of cold-rolled Mg-Li alloys showed appreciable strain hardening and a loss of ductility due to the cold work. The higher the Li content the higher the rate of strain hardening observed for large increments of strain. The ratio of the transverse to longitudinal tensile properties decreased with increasing Li content. A qualitative explanation of the above was made on the basis of active deformation systems. Limited success was obtained in attempts to correlate mechanical properties and texture in low Li alloys. No attempt was made for high Li alloys. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references. Also available via the World Wide Web.

Magnox, a magnesium alloy, was specifically developed in early 1950s for use as a fuel cladding in the British first generation nuclear civilian reactors. Magnesium metal demonstrates outstanding properties for use as a nuclear fuel cladding; however, it has an intrinsic ability to undergo oxidation. This introduces significant limitations during aqueous storage required prior to reprocessing of the spent fuel. A possibility exists for a failure of the dated reprocessing facilities, and therefore this may require for the spent fuel to be kept in the aqueous storage for an extended period of time. In a most extreme case, the corrosion of the fuel cladding may lead to a contamination of the storage facilities with hazardous radioactive fission species and corrosion products. A comprehensive study of chemical behaviour of the Magnox alloy may allow a deeper understanding of the reactivity of the cladding and lead to improvements in management of storage of spent Magnox fuel, thus preventing corrosion induced leakage of hazardous products. The understanding of chemistry of the Magnox alloy during storage may be improved by the development of a novel approach to study corrosion reactions. Infrared spectroscopy and Raman spectroscopy are widely used to study properties of surfaces. In addition, electron microscopy provides with information on the structure and physical appearance of materials. The results show clear evidence for reactivity of the alloy to be greatly influenced by changes induced by nature of cooling processes upon simulated discharge of spent Magnox fuel from a reactor. It is evident that the fast cooling process using water introduces the most deleterious change to the properties of the material. It is understood that presence of water provides with favourable conditions for oxidation of the metal to take place. Opposite effect is observed with slow cooling under an atmosphere of carbon dioxide gas. Further studies using X-ray diffraction suggest that crystallinity of the alloy is increased during simulated reactor exposure and phase segregation takes place during cooling. The latter appears to be dependent on the nature of the cooling process, and thus as a result different strains are applied. Through the studies it is shown that the pond conditions also contribute to control of the behaviour of the fuel cladding. A series of experiments demonstrated that sodium carbonate offers paramount corrosion protection when compared to sodium hydroxide. Systematic investigations allowed for a complete corrosion mechanism of the Magnox cladding to be drawn. It is demonstrated that the effects of present as well past conditions should be assessed and taken into consideration when establishing chemical behaviour of a material.

In fracture management with open reduction and internal fixation with metallic implant, secondary procedure of removal of implant is often required. Such procedure causes additional surgical risks to patients, including anaesthetic risks, wound infection, bone infection, soft tissue adhesion and joint stiffness. The procedure is also costly to the patient and society. If the fixation implant is self-resorbable, the need for secondary surgery will be completely eliminated and the social resources can be saved. Making use of the corrosion process, metals can be developed into new generation of resorbable (or biocorrodible, biodegradable) implants. An ideal bioresorbable orthopaedic implant should provide adequate mechanical support that matches the bone healing process. The implant should resorb progressively as the bone heals. Many current resorbable materials are biomechanically inferior to conventional metallic implants. Magnesium based alloys are popularly studied because of their mechanical properties and biocompatibility. Implants made of magnesium based alloy are expected to resorb in the human body with no harmful effect. The major research challenge is to identify an alloy that performs satisfactorily in the following aspects: biocompatibility, degradation rate, hydrogen gas formation (gas product from the reaction between Mg and water), and mechanical strength. In addition, there is no standard evaluation method for the biodegradable alloys. It is because the interaction between the degradable implants and the physiological environment is too complicated to mimic. The in vitro and the in vivo results often mismatch. This research involved the design and the tests of three Mg based alloys. Zinc (Zn) and manganese (Mn) were chosen as the alloying elements for corrosion resistance and mechanical enhancement. Mg-1Zn-1Mn, Mg-3Zn-1Mn, Mg-5Zn-1Mn (in wt.%) were developed and compared. The study was divided into three parts: material characterization, in vitro studies, and in vivo (animal) studies. The SEM/EDX confirmed that the surface properties of the alloys were consistent after the surface treatment. From the mechanical test, the yield strengths and the densities of the alloys were found to be close to that of the natural bones. The theoretical calculation showed that the amount of Mn determined the threshold implant mass of the test alloys. The hydrogen evolution test showed that the Mg-1Zn-1Mn was the least corrodible. The elution test showed that the Mg-1Zn-1Mn was the least cytotoxic and the cytotoxicity was affected by the pH changes brought by the alloys. The live cell imaging captured the interaction between the alloys and the cells. The subcutaneous implantation showed that the Mg-3Zn-1Mn formed the smallest gas pocket. In the six-month femoral implantation study (Mg-3Zn-1Mn excluded), the Mg-1Zn-1Mn showed the least volume loss and the steadiest degradation behaviour. It was also found to associate with better bone responses. Concluding from all the results, the Mg-1Zn-1Mn demonstrated better potential to become biodegradable orthopaedic products. This work evaluated the potentials of the new alloys and proposed some suggestions for the mismatch results. Moreover, quantitative investigation of biomechanical properties, long term degradation behaviour, and toxicity are recommended to be carried out in the future. / published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

No description available.

No description available.

Thesis (Ph.D.)--Université Laval, Québec, 2000. / Includes bibliographical references (leaves 187-205).

Thesis--University of Wisconsin--Madison. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 250-257).

Thesis (Ph.D.)--City University of Hong Kong, 2010. / "Submitted to Department of Physics and Materials Science in partial fulfillment of the requirements for the degree of Doctor of Philosophy." Includes bibliographical references.