No / Nucleation and condensation of mercury vapor has been investigated in various divergent angle and operating condition. Divergent angle has a great effect on droplet size at the end of nozzle. Influence of operating condition such as pressure and temperature on the size of droplet has been investigated. A one-dimensional mathematical model based on classical nucleation and growth has been developed to calculate the nucleation and condensation of mercury vapor. A mercury vapour turbine has been used in conjunction with a steam turbine for generating electricity. The mercury cycle offers an efficiency increase compared to a steam-only cycle because energy can be injected into the Rankine Cycle at higher temperature. The target of modeling is predicting the droplet size of mercury nano-particles during rapid expansion. The results are verified by accurate experimental data available in the literature. The governing equations were solved using Runge-Kutta third-order numerical method in MATLAB software.

A principal limitação do uso de MgO em refratários é a facilidade com que reage com água formando hidróxido de magnésio (Mg(OH)2) que, devido à sua menor densidade, causa tensões destrutivas nesses materiais. Para outras aplicações, no entanto, a reação de hidroxilação do MgO é necessária, como em produção de agentes antichamas, em compósitos poliméricos e na correção de pH de solos. Observações empíricas na literatura demonstraram que diferentes fontes de MgO possuem reatividades e sensibilidades à hidroxilação distintas. Este estudo analisou o impacto de variáveis externas (por exemplo, a liberação de calor que ocorre durante a reação ou o volume das amostras) que ainda não foi completamente compreendido. O impacto auto-catalítico da temperatura reacional e da exotermia da reação foi avaliado. Por meio de medidas de temperatura in situ e de grau de hidroxilação termogravimétrico, também foram estudados os impactos do volume das amostras testadas e da concentração de sólidos nas suspensões, por meio de medidas de temperatura in situ e termogravimetria. Analisou-se também as principais diferenças estruturais entre duas principais fontes de MgO (sínter de MgO e magnésia cáustica): morfologia de partículas, densidade e área superficial específica. Em seguida, os mecanismos de hidroxilação em suspensões aquosas e seus efeitos foram avaliados por meio de testes de hidroxilação seguidos de termogravimetria, difração de raios-X, medidas de condutividade iônica, densidade, área superficial específica e microscopia eletrônica, e relacionado com as características físico-químicas e morfológicas das respectivas fontes de MgO. Pôde-se constatar que diferenças significativas entre a temperatura nominal do meio reacional e no interior da amostra podem afetar a cinética de hidroxilação do material. O volume e a concentração de sólidos variáveis também podem acentuar consideravelmente os efeitos da exotermia e gerar gradientes de hidroxilação. Também se verificou que a morfologia e a quantidade do Mg(OH)2 formado mudam significativamente dependendo do precursor e em função das condições de tempo-temperatura. / The use of MgO in refractories is restrict due to the easy reaction with water forming magnesium hydroxide (Mg(OH)2). Its lower density causes compressive stresses that can crack their structure. On the other hand, for applications such as the production of flame retardant agents for polymer composites and pH correcting of contaminated soil, this reaction is necessary. Empirical observations in the literature have shown that different sources of MgO have district levels of chemical reactiveness. The present study analyzed the main structural differences between the two main sources of MgO (magnesia sinter and caustic magnesia): particle morphology, density and specific surface area. The mechanisms of hydroxylation of these raw materials in aqueous suspensions and their effects were followed by hydroxylation tests, X-ray diffraction, ionic conductivity, density, specific surface area and scanning electron microscopy. They were associated with the physical characteristics morphological, chemical of these MgO sources. The impact of external variables (e.g., heat release during the reaction or the sample volume), that was not yet completely understood, was also evaluated through temperature measurements carried out in situ and hydroxylation degree accessed by thermogravimetry. The effects of samples volume and solid concentration in aqueous suspension were also investigated. The results showed that differences between the ambient temperature and reaction inside sample temperature can affect the kinetics of hydroxylation of the material. The samples volume and solids concentration can also enhance significantly the effects of heat release and generate gradients of hydroxylation. It was also found out that the morphology and the amount of Mg(OH)2 formed can change depending on the precursor and on the time-temperature conditions.

Aneurysmal subarachnoid haemorrhage (SAH) accounts for only 3-5% of all strokes but has the highest morbidity and mortality rates among all types of stroke. Experimental studies have confirmed that magnesium inhibits excitatory amino acid (EAA) release, blocks N-methyl-D-aspartate (NMDA) receptors and prevents calcium from entering cells. These changes may minimise neuronal injury during episodes of cerebral vasospasm. / Based on the aforementioned biological evidence, a pilot study of magnesium sulphate (MgSO4) infusion for aneurysmal SAH was conducted. This pilot study indicated that MgSO4 infusion for aneurysmal SAH is safe and has the potential to improve clinical outcomes. The pilot study results are supported by the findings of other research groups. / In summary, our results do not support a clinical benefit of intravenous magnesium sulphate infusion in patients with acute aneurysmal SAN. / Studies were carried out to investigate the distribution of magnesium in the cerebrospinal fluid (CSF) and the brain after intravenous magnesium sulphate infusion. We found that magnesium sulphate infusion resulted in an 11% to 21% increase in CSF magnesium, which was sustained for at least nine days. We further investigated intracellular free magnesium using 31 P-MRS, in aneurysmal SAH patients receiving and not receiving intravenous magnesium sulphate infusion. Intravenous magnesium sulphate infusion was found to produce a significant increase (15.6%) in the level of intracellular free magnesium during the first week, which covered the time frame required for neuroprotection, to improve outcomes in patients with aneurysmal SAH. / Three hundred and twenty-seven patients with aneurysmal SAH were recruited and randomly assigned to receive magnesium sulphate infusion or a saline placebo for 10 to 14 days. In the primary outcome analysis, the proportions of patients with a favourable outcome at six months (Extended Glasgow Outcome Scale [GOSE] score of 5-8) were similar, 64% in the MgSO4 group and 63% in the saline group (OR 1.0, 0.7-1.6). In the secondary outcome analyses, there were also no significant differences between the two groups. Analysis of the plasma magnesium concentration levels did not suggest that higher levels of plasma magnesium concentration result in better clinical outcomes. / Wong Kwok Chu. / Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 132-152). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web.

Thesis (M.Sc. (Physics)) --University of Limpopo, 2005 / Self-consistent electronic structure calculations have been performed on ordered cubic-based magnesium-lithium (Mgx-Li1−x) alloys spanning the concentration range 0 ≤ x ≤ 1, using an ab initio plane wave pseudopotential (PWP) method. The first principle pseudopotential planewave approach is used within the local density approximation (LDA) and generalized-gradient approximation (GGA)of the density functional theory (DFT) framework. We have calculated the binding energy curves and the systematic trends in various cohesive and elastic properties at zero temperature, as a function of Li concentration. The calculated equilibrium lattice parameters show a large deviation from Vegard’s rule in the Li-rich region whilst the bulk moduli decrease monotonically with increase in Li concentration. The heats of formation for different ground state superstructures predict that the DO3, B2 and DO22 structures would be the most stable at absolute zero amongst various phases having the Mg3Li, MgLi and MgLi3 compositions, respectively. This stability is reflected in the electronic density of states (DOS). Because of the special significance of the isotropic bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio for technological and engineering applications, we have also calculated these quantities from the elastic constants. The elastic constants indicate the softness of the material as more Li is added with the bcc-based phases becoming mechanically less stable for Li concentration less than 50%. Our results show good agreement within the estimated uncertainty with both experimental and previous theoretical results. / The National Research Foundation (NRF), South Africa-Royal Society (RS), Great Britain collaboration and Council for the Scientific and Industrial Research (CSIR)

La réparation des composants en alliages légers est un processus clés dans le domaine de l’aéronautique. Ces alliages sont abondamment utilisés dans les constructions aéronautiques notamment pour des composants à forte valeur ajoutée. Leur utilisation combinée à une optimisation de la conception des pièces permet de disposer de produits satisfaisants aux exigences de masse, de coût et de performances. Cependant l’utilisation de ces pièces est limitée dans le temps car divers endommagements peuvent survenir aussi bien lors de leurs manipulations que lors de leurs utilisations en service. Des solutions de retouches existent mais ne permettent pas toujours de redonner leur intégrité aux zones affectées. Ces limitations sont à l’origine d’un fort taux de rebut parmi les pièces à forte valeur ajoutée.Les multiples avantages du procédé Cold Spray en font un candidat idéal pour la projection de revêtements adaptés aux composants en alliages légers mis en oeuvre en aéronautique, que ce soit dans une logique de protection, de retouche ou de réparation. Il s’agit de reconstruire la pièce par un revêtement aux caractéristiques les plus proches possibles de celles du matériau de base. Ce travail de thèse consiste à optimiser l’ensemble des paramètres du procédé de projection dynamique à froid (Cold Spray) pour plusieurs couples substrat-revêtement combinant différents alliages d'aluminium, de magnésium et des composites à matrice métallique à base aluminium.La première étape a consisté à optimiser les paramètres principaux du procédé Cold Spray afin de s’affranchir du phénomène de colmatage pouvant intervenir au sein de la section divergente de la buse de projection. Ce phénomène a pour effet de diminuer la vitesse des particules, les revêtements obtenus devenant alors assez poreux. Une étude s’est ensuite focalisée sur l’optimisation de l’adhérence des couples substrats-revêtements. Il a été démontré le rôle primordial de la préparation de surface dans l’adhérence des revêtements où l’ancrage mécanique apparaît prépondérant. Enfin, une étude originale a été conduite pour mettre au point une méthodologie pour recharger localement une zone défectueuse sans avoir à recouvrir toute la surface du substrat. Une programmation hors ligne du robot a été employée afin de recouvrir deux types de défaut pré-usinés sur des blocs d’alliage d'aluminium. Les résultats sont satisfaisants avec des gains en temps de projection et des dépôts sans défaut après usinage. / The repair of light alloy parts is a major issue in aeronautics. Aluminum alloy and magnesium alloy are widely used in aircraft parts, especially for high value-added components. Their use combined to optimizing design allows to have satisfactory products meeting mass, cost and performance requirements. However, like any other life-limited components, various damages can occur not only during handling procedure but also while operating. Rectification solutions exist but do not always comply with requirements. These limitations entail high scrap rates among high value-added parts.The various advantages of the cold spray process make it an ideal candidate for suitable coatings for light alloy aircraft components as protective, retouching or repair methods. The aim is to rebuild the damaged part by a coating whose characteristics are closest to those of primary materials. This thesis proposes to optimize different cold spray parameters for several substrate-coating pairs combining different aluminum alloys, magnesium alloys and aluminum alloy-based metal matrix composites.The first step was to optimize the main parameters of cold spray process to prevent clogging phenomenon that may occur in the expansion part of the nozzle. It decreases particle kinetics and promotes porous coating. Then, adhesion optimization of substrate-coating couples was investigated. The substrate surface preparation is a key factor on coating adhesion, where the mechanical anchoring appears essential. Finally, an innovative study was conducted to develop a method to cover locally surface defects. Offline programming trajectories were used to fill up two kinds of pre-machined defaults on aluminum alloy blocks. Results are in good agreement with spray time savings and defect free coatings after machining.

Main reason for the current losses in electrolytic magnesium production is the reaction between electrode products. Present study was devoted to effective separation of chlorine gas from the electrolysis environment by a new cell design and thus reducing the extent of back reaction between magnesium and chlorine to decrease energy consumption values. The new cell design was tested by changing temperature, cathode surface, current density, anode cathode distance and electrolyte composition. Both the voltages and the current efficiencies were considered to be influenced by the amount and hydrodynamics of chlorine bubbles in inter-electrode region. Cell voltages were also found to be affected from the nucleation of magnesium droplets and changes in electrolyte composition that took place during the electrolysis. A hydrodynamic model was used to calculate net cell voltage by including the resistance of chlorine bubbles on anode surface to theoretical decomposition voltage during electrolysis. Good correlations were obtained between experimental and calculated voltages. The same model was used to calculate current efficiencies by considering chlorine diffusion from bubble surfaces. A general agreement was obtained between calculated and experimental current efficiencies. Desired magnesium deposition morphology and detachment characteristics from cathode were obtained when MgCl2-NaCl-KCl-CaCl2 electrolytes were employed. Current efficiencies higher than 90% could be achieved using the above electrolyte. The cell consumes around 8 kWh&amp / #903 / kg-1 Mg at 0.43 A&amp / #903 / cm-2 as a result of high chlorine removal efficiency and capability of working at low inter-electrode distances. Furthermore, the cell was capable of producing magnesium with less than the lowest energy consumption industrially obtained, at about double the commonly practiced industrial current density levels.

Pure and palladium&amp / #8208 / covered 350 nm thick magnesium thin films were deposited on glass substrates via thermal evaporation. In the as&amp / #8208 / deposited state, films were highly textured with Mg (001) parallel to the substrate. Hydrogen loading experiments were carried out in two different conditions / namely isothermal and isochronal. Hydrogenation behaviors of the thin films were followed by twopoint probe electrical resistance and optical transmittance measurements, as well as x&amp / #8208 / ray diffraction studies. Isothermal hydrogenation experiments conducted on Pd&amp / #8208 / covered Mg thin films have revealed that these films can absorb hydrogen at temperatures starting from 333 K, producing MgH2 with a random texture. When the films were heated slowly starting from the room temperature, on the other hand, hydrogenation gives rise to a textured MgH2, where (110) parallel to the substrate with a minor (101) component. Formation of the textured hydride in isochronal loading was discussed within the context of lattice mismatch in Mg to MgH2 transformation. It was further shown that formation of such a textured hydride in Mg thin films minimizes in&amp / #8208 / plane lattice distortion.

Abstract The purpose of the thesis is the research of metallurgical properties , mechanical properties and texture analyses of four magnesium-based materials during E-beam welding process. After rapid solidification, the welding properties of fusion zone of four materials are very well without obvious defects and hot cracking. The Surface and depth of the weld of three Mg alloys has stable performance without sputter with Al content increasing.

No description available.

Magnesium alloys have a great potential in automotive industries, compared to steel and aluminium (Al), Magnesium (Mg) is much lighter and this weight reduction improves fuel efficiency and lowers green gas emission. Due to its hexagonal crystal structure, magnesium has poor ductility at room temperature. Magnesium's ductility improves significantly above about 200°C due to thermal activation of additional slip systems. This has lead to efforts to form auto-body panels with commercial AZ31 magnesium sheet at elevated temperatures. In this work, various AZ31 magnesium alloy materials were used to investigate the influence of deformation conditions on texture and microstructure. Moreover, it is to define the correlation between formability and different deformation mechanisms. / It was observed that only basal slip and twinning contributed to room temperature deformation. As deformation temperature increased, an increase in ductility in Mg contributed to dynamic recrystallization occurring readily at elevated temperatures (≥300°C). Even coarse grain material experienced significant tensile elongation due grain refinement. Depending on temperature and strain rate, different deformation mechanisms were activated and lead to different failure modes (moderate necking, cavity, strong necking). More specifically, deformation at elevated temperature in the low-strain-rate regime with stress exponent n about 2-3 and activation energy close to grain-boundary diffusion of Mg (Q = 92 kJ/mol) is characteristic of GBS. Deformation at elevated temperature in the high strain rate regime showed that the stress exponent increased to a value close to 5 and that the activation energy was consistent with the one for Mg self-diffusion (135 kJ/mol) and for diffusion of Al in Mg (143 kJ/mol). This was indicative of a dislocation creep deformation mechanism. Plus the six-fold symmetric patterns of the {1 100} and {1120} pole figures and the splitting of basal plane distribution are another indication of slip mechanism or of dislocation creep mechanism. / The optimum deformation behavior for AZ31 sheet was found to be for the material with fine grain microstructure. The highest elongation of 265% was obtained with the material having initial grain size of 8 mum. In addition, strain-rate sensitivity, which is a good indication of material's ductility, also was the highest in material with 8 mum grain size. As a common trend, the strain-rate sensitivity increased with decreasing strain rate, increasing temperature and decreasing grain size. / In terms of drawability of AZ31 sheet, the deformation controlled by GBS resulted in a fair drawability/formability property with r-value about 1 whereas a deformation mechanism controlled by dislocation creep showed a good drawability with r-value above 1.5. Due to activation of additional slip systems (non-basal <a> and <c+a>), the thinning of the sheet was prevented, in particular at deformation conditions of 450°C with 0.1s-1 where r-value was highest. This deformation condition might suggest good forming process parameters, especially for deep drawing, for the commercial AZ31 sheet under investigation. A preliminary study of Forming Limit Diagram for AZ31 sheet was performed by the Limit Dome Height test method at 300°C. The FLD0 of AZ31 was found to be 67%; the part depth of biaxial forming was 1.86 in; and the maximum LDH varied from 2.4 to 2.6 in.