Choi Ching Yeung = 鎂和氧化銀粉反應制備鎂基復合材料 / 蔡靜洋. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Choi Ching-Yeung = Mei he yang hua yin fen fan ying zhi bei mei ji fu he cai liao / Cai Jingyang. / Abstract --- p.i / 摘要 --- p.iii / Acknowledgement --- p.iv / List of Figures --- p.xi / List of Tables --- p.xvi / Chapter Chapter 1 --- Introduction --- p.1.1 / Chapter 1.1 --- Metal matrix composites (MMCs) --- p.1.1 / Chapter 1.1.1 --- Introduction --- p.1.1 / Chapter 1.1.2 --- Reinforcement in metal-matrix composites --- p.1.1 / Chapter 1.1.2.1 --- Particle-reinforced composites --- p.1.2 / Chapter 1.1.2.2 --- Laminated composites --- p.1.2 / Chapter 1.1.2.3 --- Fibre-reinforced composites --- p.1.2 / Chapter 1.1.3 --- Conventional fabrication of metal matrix composites --- p.1.6 / Chapter 1.1.3.1 --- Liquid state processes --- p.1.6 / Chapter 1.1.3.1.1 --- Liquid infiltration --- p.1.6 / Chapter 1.1.3.1.2 --- Pressure infiltration --- p.1.8 / Chapter 1.1.3.1.3 --- Spray forming --- p.1.10 / Chapter 1.1.3.2 --- Solid-state process --- p.1.11 / Chapter 1.1.3.2.1 --- Powder consolidation --- p.1.11 / Chapter 1.1.3.2.2 --- Diffusion bonding --- p.1.11 / Chapter 1.1.3.2.3 --- In-Situ processes --- p.1.13 / Chapter 1.1.4 --- Properties of metal matrix composites --- p.1.13 / Chapter 1.2 --- Magnesium based metal matrix composites --- p.1.14 / Chapter 1.2.1 --- Properties of Mg-based metal matrix composites --- p.1.14 / Chapter 1.2.2 --- Application of Mg-based metal matrix composites --- p.1.16 / Chapter 1.3 --- Magnesium and silver (I) oxide --- p.1.16 / Chapter 1.3.1 --- Magnesium --- p.1.16 / Chapter 1.3.2 --- Silver (I) oxide --- p.1.17 / Chapter 1.4 --- Pervious works --- p.1.17 / Chapter 1.5 --- Aims of Current works --- p.1.18 / Chapter 1.6 --- Thesis layout --- p.1.20 / References --- p.1.21 / Chapter Chapter 2 --- Methodology and fabrication --- p.2.1 / Chapter 2.1 --- Introduction --- p.2.1 / Chapter 2.1.1 --- Powder metallurgy --- p.2.1 / Chapter 2.1.1.1 --- Powder production --- p.2.3 / Chapter 2.1.1.2 --- Powder consolidation --- p.2.4 / Chapter 2.1.1.3 --- Sintering process --- p.2.6 / Chapter 2.1.1.4 --- Properties of sintered parts --- p.2.10 / Chapter 2.2 --- Sample preparation --- p.2.12 / Chapter 2.3 --- Characterization methods --- p.2.13 / Chapter 2.3.1 --- Thermal analysis - Differential Thermal Analysis (DTA) --- p.2.13 / Chapter 2.3.2 --- Phase determination - X-ray Powder Diffractometry (XRD) --- p.2.13 / Chapter 2.3.3 --- Microstructure analysis --- p.2.14 / Chapter 2.3.3.1 --- Scanning electron microscopy (SEM) --- p.2.14 / Chapter 2.3.3.1 --- Transmission electron microscopy (TEM and HRTEM) --- p.2.14 / Chapter 2.3.4 --- Physical property - Thermomechanic analyser (TMA) --- p.2.14 / Chapter 2.3.5 --- Mechanical property - Vickers hardness measurement --- p.2.15 / References --- p.2.16 / Chapter Chapter 3 --- Thermal analysis of Mg-Ag20 --- p.3.1 / Chapter 3.1 --- Introduction --- p.3.1 / Chapter 3.2 --- Experiments --- p.3.2 / Chapter 3.3 --- Results --- p.3.2 / Chapter 3.3.1 --- DTA curve of the Mg-30wt%Ag20 --- p.3.5 / Chapter 3.3.2 --- DTA curve of the pure Ag20 powder --- p.3.7 / Chapter 3.4 --- Discussions --- p.3.7 / Chapter 3.5 --- Conclusions --- p.3.10 / References --- p.3.11 / Chapter Chapter 4 --- Fabrication and characterization of Mg-£-AgMg3 MMCs --- p.4.1 / Chapter 4.1 --- Introduction --- p.4.1 / Chapter 4.2 --- Experiments --- p.4.2 / Chapter 4.2.1 --- Sample preparation --- p.4.2 / Chapter 4.2.1.1 --- Effect of temperature --- p.4.2 / Chapter 4.2.1.2 --- Effect of time --- p.4.3 / Chapter 4.2.1.3 --- Effect of composition --- p.4.3 / Chapter 4.2.1.4 --- Effect of cooling rate --- p.4.3 / Chapter 4.3 --- Results --- p.4.4 / Chapter 4.3.1 --- Samples sintered at different temperatures --- p.4.4 / Chapter 4.3.1.1 --- XRD spectra --- p.4.4 / Chapter 4.3.1.2 --- SEM micrographs and EDS analysis --- p.4.7 / Chapter 4.3.1.3 --- Discussions --- p.4.11 / Chapter 4.3.2 --- Sample with different dwelling times --- p.4.13 / Chapter 4.3.2.1 --- SEM micrographs --- p.4.13 / Chapter 4.3.2.2 --- Weight loss against dwelling time --- p.4.16 / Chapter 4.3.2.3 --- Discussions --- p.4.18 / Chapter 4.3.3 --- Samples with varied weight percentage of Ag2O --- p.4.19 / Chapter 4.3.3.1 --- SEM micrographs --- p.4.19 / Chapter 4.3.3.2 --- Discussions --- p.4.22 / Chapter 4.3.4 --- Samples with different cooling rate --- p.4.23 / Chapter 4.3.4.1 --- XRD patterns --- p.4.23 / Chapter 4.3.4.2 --- Optical photographs --- p.4.25 / Chapter 4.3.4.3 --- SEM micrographs --- p.4.28 / Chapter 4.3.4.4 --- TEM micrographs and high-resolution TEM micrographs…… --- p.4.31 / Chapter 4.3.4.5 --- Discussions --- p.4.35 / Chapter 4.3.4.5.1 --- XRD spectra --- p.4.35 / Chapter 4.3.4.5.2 --- Optical photographs --- p.4.35 / Chapter 4.3.4.5.3 --- SEM micrographs --- p.4.35 / Chapter 4.3.4.5.4 --- TEM micrographs --- p.4.36 / Chapter 4.4 --- Conclusions --- p.4.37 / References --- p.4.38 / Chapter Chapter 5 --- Mechanical hardness and thermal expansion of Mg-Ag20 --- p.5.1 / Chapter 5.1 --- Introduction --- p.5.1 / Chapter 5.2 --- Mechanical properties --- p.5.1 / Chapter 5.2.1 --- Experiments --- p.5.1 / Chapter 5.2.2 --- Results --- p.5.2 / Chapter 5.2.3 --- Discussions --- p.5.8 / Chapter 5.3 --- Thermal properties --- p.5.9 / Chapter 5.3.1 --- Experimental details --- p.5.9 / Chapter 5.3.2 --- Results --- p.5.10 / Chapter 5.3.3 --- Discussions --- p.5.12 / Chapter 5.4 --- Conclusions --- p.5.13 / References --- p.5.14 / Chapter Chapter 6 --- Conclusions and future works --- p.6.1 / Chapter 6.1 --- Conclusions --- p.6.1 / Chapter 6.2 --- Further works --- p.6.2

Part I discusses the development of an aluminum-magnesium-silicon alloy that may combine strength, extrudability, favorable corrosion resistance with low cost and scrap compatibility. The first part of the study determined the effects of small composition, heat treatment and mechanical processing changes on the ambient temperature tensile properties of the alloy. A combination of magnesium and silicon of about 2%, 1% copper, 0.2% chromium and 0.1% vanadium can produce a T6 alloy with significant higher strength, fatigue and corrosion fatigue properties for both ingot and extrusion than those of 6061 but with only a modest increase in cost. The new alloy has been designated as AA6069. The second part of the study determined the T6 properties of 6069 alloy. The tensile test results of cold and hot extrusions of hollow, solid bars, and high pressure cylinders indicate that the T6 properties ranged from 55-70 ksi (380-490 MPa) UTS, 50-65 ksi (345-450 MPa) yield strength, and 10-18% elongation. It also appears that the fracture toughness and general corrosion resistance in saline environment are comparable or better than those of 6061 T6. Part II attempted to evaluate the formation, formability, thermal and mechanical properties of semi-solid A356, A357 and modified aluminum silicon semi-solid alloys. The semi-solid alloy microstructure was produced in this study by purely thermal treatment rather than conventional and expensive electromagnetic or mechanical stirring. Three heat-up stages in semi-solid treatment were evaluated. Stage I is related to the heating of the alloy in the solid state. Stage II is related to the eutectic reaction. Stage III is related to the heating of the semi-solid slurry. Stage II requires the longest time of the three heat-up stages due to the endothermic reaction on heating. An increase of furnace temperature can greatly reduce the time of stage II. The atmosphere (vacuum, air, argon) of the semi-solid treatment does not appear to greatly affect the T6 properties of semi-solid alloys. The microstructure and T6 properties of semi-solid A356 do not appear sensitive to the homogenization treatments before semi-solid treatment. The porosity of semi-solid ingots and pressed parts increases as the cooling rate decreases in unformed and subsequent-to-moderate pressure forming. The T6 properties basically appear sensitive to voids, with a degradation of properties as the void concentration increases. The formability of A357 may be improved as the spheroidal particle size decreases. Hence, formability may improve with decreasing ingot grain size. The mechanism of coarsening of the solid phase at isothermal temperatures is related to Ostwald ripening and/or "merging" of particles. The mechanical properties of die-casting parts show that the method of thermal treatment to produce a spheroidal microstructure is an effective method for industrial production of semi-solid aluminum-silicon alloys. / Graduation date: 1997

De nombreux organismes marins précipitent des squelettes en calcite magnésienne. Depuis près d’un siècle, il est connu que les concentrations en magnésium de ces squelettes sont influencées par les conditions environnementales, telle la température, régnant au moment de leur dépôt. Dans le contexte actuel de changement climatique, cette propriété a promu l’usage de plusieurs taxons en tant qu’archive naturelle des conditions environnementales du passé. Cependant, les squelettes d’espèces sympatriques, voire d’individus de la même espèce, peuvent présenter des concentrations en magnésium très différentes, attestant de l’influence de facteurs biologiques sur la détermination de la concentration squelettique en cet élément. Une parfaite compréhension des mécanismes d’incorporation du magnésium dans les squelettes est donc requise pour valider l’usage de ce paléotraceur. De plus, la solubilité des calcites augmentant avec leur concentration en magnésium, l’incorporation de cet élément conditionne en partie la stabilité des squelettes calcitiques dans un océan en cours d’acidification. Le présent travail contribue à l’étude des différents facteurs, tant environnementaux que physiologiques et minéralogiques, susceptibles d’affecter l’incorporation du magnésium dans les squelettes en calcite de trois taxons présentant des concentrations en cet élément particulièrement élevées, une éponge hypercalcifiée, Petrobiona massiliana, et deux échinodermes, Paracentrotus lividus et Asterias rubens. Dans une première partie, les effets de plusieurs facteurs environnementaux ont été étudiés, en milieu naturel dans le cas de l’éponge, étant donné son incapacité à survivre en aquarium, et en conditions contrôlées d’aquarium dans le cas des deux échinodermes. Une influence environnementale prépondérante de la température sur la concentration en magnésium squelettique a été mise en évidence dans les 3 modèles biologiques étudiés. Une fois les facteurs génétiques (espèce) et structurels (élément squelettique) fixés, une relation positive liant la température à la concentration en magnésium squelettique a été caractérisée en milieu naturel chez l’éponge hypercalcifiée P. massiliana et en conditions contrôlées chez l’oursin P. lividus. Chez ce dernier, cette relation, non linéaire, se stabilise aux plus hautes températures envisagées, probablement suite à la saturation d’un processus biologique intervenant dans l’incorporation de cet élément. La salinité, un autre facteur environnemental majeur en milieu marin, influence elle aussi positivement la concentration en magnésium dans le squelette de l’étoile de mer A. rubens. A nouveau, il est proposé que cette influence de l’environnement soit modulée par un processus biologique: chez les échinodermes, la concentration en magnésium, contrairement à celle du calcium, n’est pas régulée dans le liquide coelomique. Elle est donc directement influencée par la salinité, et affecte probablement la concentration en cet élément dans le squelette formé. La diffusion depuis l’eau de mer jusqu’au site de calcification par l’intermédiaire des fluides internes a en effet été suggérée sur base du fait que le rapport Mg/Ca de l’eau de mer influence celui des squelettes calcaires Une fois l’influence, directe ou indirecte, des facteurs environnementaux exclue, 44% de la variabilité du rapport Mg/Ca du squelette des échinodermes restent à expliquer. Les expériences de croissance d’échinodermes réalisées en conditions contrôlées indiquent que ce rapport est indépendant de la vitesse de croissance dans ce groupe, contrairement aux hypothèses émises dans la littérature. Dans la seconde partie, la modulation des facteurs minéralogiques par les facteurs biologiques a été investiguée. Pour ce faire, d’une part, les interactions entre rapport Mg/Ca en solution et matrice organique de minéralisation ont été étudiées dans un modèle in vitro. D’autre part, les relations entre soufre et magnésium dans le squelette ont été décryptées. Le rapport Mg/Ca de la solution de précipitation a une influence prépondérante sur la concentration en magnésium du carbonate de calcium précipité in vitro, attestant de l’importance de la régulation de la composition du fluide de calcification et des mécanismes de transport la contrôlant. Deux mécanismes biologiques complémentaires permettent de favoriser l’incorporation, dans les calcites biogéniques, de quantités de magnésium largement supérieures à celles observées dans les calcites inorganiques, et ce, malgré la forte hydratation de ce cation : l’intervention d’agents chélateurs du magnésium et le passage par une phase de carbonate de calcium amorphe (CCA). Les molécules de la matrice organique de minéralisation jouent entre autres le rôle de chélateur du magnésium, réduisant son état d’hydratation et facilitant ainsi son incorporation dans le minéral. Un rôle similaire a été suggéré pour les sulfates en solution, au vu de la corrélation observée dans ce travail entre les rapports Mg/Ca et S/Ca dans la phase minérale des calcites biogéniques étudiées. La matrice organique affecte elle aussi la concentration en magnésium dans le cristal, probablement via la stabilisation de la phase de CCA nécessaire à l’incorporation de concentrations élevées de cet élément: ainsi, les macromolécules de la matrice organique du test d’oursin induisent in vitro la formation de calcites plus riches en magnésium que celles formées en présence de matrice de piquant, un résultat concordant avec le fait que, in vivo, le test contient des concentrations en magnésium plus élevées que les piquants. Cette thèse de doctorat a donc soulevé l’importance des effets biologiques dans la détermination du rapport Mg/Ca dans les calcites biogéniques. Les résultats obtenus montrent que le décryptage des mécanismes impliqués dans l’incorporation du magnésium se doit de considérer la phase amorphe transitoire qui précède la cristallisation. Des effets environnementaux affectent eux aussi la concentration squelettique en magnésium, mais nos résultats suggèrent qu’ils agissent au travers d’une modulation des effets biologiques, et non par une influence thermodynamique directe. Cette hypothèse, si elle est confirmée, impose la plus grande prudence lors de l’utilisation des squelettes en calcite en tant que paléotraceurs. SUMMARY The magnesium concentration in calcite skeletons produced by marine invertebrates is known to be dependent on several environmental parameters, including temperature, salinity and seawater Mg/Ca ratio. This property prompted the use of this concentration as a proxy of the considered parameters. However, skeletal magnesium contents in sympatric species and even in individuals of the same species may be rather different. These inter and intra-individual variabilities indicate that biological factors also affect magnesium incorporation into biogenic calcites. Magnesium incorporation mechanisms are still unknown in calcifying invertebrates, a fact that questions the validity of this element as a paleoproxy. Moreover, higher magnesium contents increase calcite solubility and could therefore worsen the case of calcifying organisms facing ocean acidification linked to global change. The present thesis is a contribution to the study of the environmental, biological and mineralogical factors affecting magnesium incorporation into the calcitic skeletons of 3 taxa, i.e. one hypercalcified sponge, Petrobiona massiliana, and two echinoderms, Paracentrotus lividus and Asterias rubens. The first part of this work was dedicated to the study of several environmental factors affecting the magnesium concentration in the calcite skeleton of the 3 studied organisms. Consequently to its low survival in aquarium, the sponge was studied using field specimens collected along an environmental gradient. Echinoderms were grown in controlled conditions in aquarium. Once the genetic (species) and structural (skeletal element) factors were fixed, skeletal magnesium concentration was positively related to temperature in the 3 studied species. The Mg/Ca ratio of the test of aquarium-grown P. lividus increased with temperature until a plateau which was probably due to the saturation of a biological process involved in magnesium incorporation. A positive effect of salinity, an other major environmental parameter, on skeletal Mg/Ca was demonstrated in aquarium-grown A. rubens. This influence can also be linked to a biological process: contrary to magnesium, calcium concentration is controlled in the coelomic fluid, from which ions probably diffuse through the living tissues to the calcification site. Thus, the observed positive relation can be explained by the fact that a salinity increase raises the coelomic Mg/Ca ratio, which, according to previous studies, affected the Mg/Ca ratio of the precipitated skeleton. In addition to the reported environmental influences, 44% of the skeletal Mg/Ca ratio variation remained unexplained in echinoderms. The absence of growth rate effect on magnesium incorporation into the echinoderm skeleton was demonstrated in aquarium experiments, contrary to previous literature statements. Other biological factors must therefore affect the incorporation of this element. In the second part of this work, the modulation of mineralogical factors by biological factors was investigated. The interaction between Mg/Ca ratio in the precipitation solution and organic matrix was studied in an in vitro precipitation experiment. In addition, the relation between skeletal Mg/Ca and S/Ca ratios was investigated. A major influence of the precipitation solution Mg/Ca ratio on the magnesium concentration of in vitro precipitated minerals was evidenced, highlighting the importance of transport mechanisms which determine the composition of the calcifying solution. The higher magnesium concentrations presented in some biogenic calcites in comparison to inorganic calcites can be attributed to the action of chelating molecules and to the transition trough an amorphous phase. The strong tendency of magnesium towards hydration can be overcome by the involvement of molecules that can function as magnesium chelators and, therefore, favour the formation of calcite with a high magnesium content. Organic matrix macromolecules have been suggested to proceed as magnesium chelators, reducing the hydration of this ion and facilitating its incorporation into calcite. A similar function was suggested for sulphates that were measured in the echinoderm skeleton. This would explain the positive correlation between skeletal Mg/Ca and S/Ca ratios observed in the studied species. Organic matrix macromolecules also increased the magnesium concentration of minerals precipitated in vitro, probably stabilizing the transient phase of amorphous calcium carbonate, which can incorporate high quantities of magnesium in its structure. The enhancement of magnesium incorporation was more pronounced with the organic matrix extracted from the test of sea urchin than with that extracted from their spines. This result was in agreement with the in vivo skeletal Mg/Ca ratios in P. lividus skeleton that were higher in the test than in the spines. This study demonstrated the importance of the biological effects in the determination of Mg/Ca ratios in biogenic calcites. According to the suggested hypotheses, the understanding of mechanisms involved in magnesium incorporation should take the transient amorphous phase into account. Magnesium concentration in biogenic calcite was also affected by environmental parameters, but these influences could proceed through the indirect modulation of biological rather than a direct thermodynamic control. This hypothesis, if proved correct, would have deep implications for the use of magnesium in calcite skeletons as a paleoproxy.

Numerical modeling of failure was performed for magnesium alloys with circular and square cross-sections under axial compression. The failure criterion was employed using material model 124, where failure was simulated using the element deletion method. LS-DYNA material model 124 (MAT_124) was calibrated using stress-strain curves in compression and tension. This approach, combined with MAT_124, captures the material asymmetry. Comparisons with experiments showed that the failure criterion accurately predicted the stress-strain behavior during axial compression tests of the round tubes of magnesium alloy, AZ31. A parametric study was also performed to investigate the effects of various phenomena on simulated results. Numerical modeling of square magnesium tubes during bending was also simulated for extruded magnesium alloys AZ31, AM30 and AM60. The failure criterion, based on element erosion, was used in these models to simulate fracture for all three alloys. Comparisons with experiments, for all three alloys, showed that the proposed numerical model accurately predicted the force-displacement curves during bending. Engineering strain at failure was found from the tensile test curves for the three magnesium alloys (AZ31, AM30 and AM60). Simulations were done to predict local strain at the necking region at this engineering strain. The necking strain was incorporated in the failure criterion, which considerably improved results for the bending simulations. Numerical modeling of slow and fast axial compression tests were also performed for AM30, AM60 and AZ31 magnesium tubes with square cross-section. Comparisons with experiments, for all three alloys, showed that the proposed numerical model accurately predicted the force-displacement curves during quasi-static and high-speed crush tests. Furthermore, the predicted fracture locations and patterns were in good agreement with experimental observations. Finally, new failure criteria was employed to improve the crashworthiness behavior of magnesium alloys by several tube design variations. Magnesium tubes cladded with aluminum and magnesium tubes with alternating strips of aluminum were simulated. Magnesium tubes with thinned sections and spirals were also simulated. Results showed that most of the design modifications increased the crashworthiness of magnesium alloys tubes.

The 1:1 reaction between MgR2 and diphenylamine gave heteroleptic alkyl -magnesium amide monomeric compounds [RMgNPh2(THF)2] [R=Et (1) and iPr (2)]. Subsequently, addition of stronger donor solvent HMPA to compound 1 results in the disproportionation reaction to give a bisamidomagnesium crystal [Mg(NPh2)2(HMPA)2] (3). The different size secondary amine HNEt2 or HN(SiMe3)2 reacting with Grignard reagent EtMgBr produced diethylamino-bridging and bromo-bridging Hauser base [(Me3Si)2NMg(£g-Br)(OEt2)]2 (4) and [BrMg(£g-NEt2)(HMPA)]2(5) respectively. Unexpectedly, [(Me3Si)NMg (£g-OEt)(THF)]2 (6) was obtained from the reaction of MgEt2 and HN(SiMe3)2 in the refluxing THF solution. Additionally, iPrMgBr and MgY2 (Y = iPr, C

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.

This investigation involved the experimental study of molten salt solutions containing magnesium chloride, sodium chloride and calcium chloride--an electrolyte of importance in magnesium production. Emf measurements were made on an electrochemical formation cell with pure chlorine gas and magnesium-bismuth alloy electrodes. Good agreement was obtained with the existing data on the thermodynamic properties of pure MgCl(,2) and MgCl(,2) - NaCl binary melts. Nearly ideal (Raoultian) solution behaviour was observed in the binary MgCl(,2) - CaCl(,2) melts. Although the thermodynamic data in this system was different than the reported vapour pressure data it was found to be in accord with the reported phase diagram measurements. The properties of MgCl(,2) in the ternary melts were measured for the first time. / A multiple discrete complex anion (MDCA) model was proposed to correlate all thermodynamic findings in MgCl(,2) - NaCl - CaCl(,2) molten salt solutions. Successful interrelations were obtained when both MgCl(,4)('=) and CaCl(,4)('=) were assumed to coexist in a state of equilibrium with the elementary ions Cl('-), Na('+), Mg('2+) and Ca('2+).

No description available.

Magnesium and its alloys have been considered as alternatives to aluminum alloys and steels for structural applications in automotive and aerospace applications due to their superior specific strength and light-weight. However, they have hexagonal-close packed (hcp) structure, and thus have a small number of deformation systems resulting in low ductility and formability near room temperature, anisotropic thermo-mechanical response and strong deformation textures. The aim of this work is to investigate experimentally the effect of crystallographic texture generated during severe plastic deformation (SPD), on the subsequent formability and mechanical flow anisotropy in AZ31B Mg alloy. The proper control of grain size and texture through SPD is expected to result in better low temperature formability and better control of mechanical flow anisotropy. AZ31B Mg alloy has been successfully processed using equal channel angular extrusion (ECAE) following different processing routes, multiple passes, and different processing temperatures, in order to obtain samples with a wide variety of grain sizes, ranging from ~370 nm up to few microns, and crystallographic textures. Low temperature processing of the AZ31B Mg alloy was successful after initial high temperature processing. Smaller grain sizes were achieved using the temperature step-down method leading to incremental reduction in grain size at each ECAE pass. The temperature step-down method was utilized to develop hybrid ECAE routes to obtain specific crystallographic textures. Optimized hybrid ECAE routes were developed which resulted in a high strength/high ductility material with the average grain size of ~370 nm. The ECAE processed alloy showed a high tensile yield strength of ~380 MPa that has never been reported so far in AZ31 ingot metallurgy Mg alloys. The influence of grain size on the critical stress for the activation of individual deformation mechanisms was also investigated by systematically controlling the texture and grain size, and assuming the activation of mainly a single deformation mechanism through the careful selection of the loading direction on the processed samples. It was revealed that the Hall-Petch slope for the basal slip was much smaller than those of prismatic slip and tensile twinning.