The flow behaviour of liquid metals (Sn, Pb and Sn-Pb eutectic) under different shearing conditions is investigated. Experiments were performed with two designs of concentric cylinder viscometers: rotating the inner cylinder (Searle) and rotating the outer cylinder (Couette). The latter technique is uncommon and the equipment was optimised with standard oils. The flow behaviour for the metals differs in the two systems. The curves of 'apparent' viscosity versus shear rate may be divided into two regimes: I. At lower shear rates (<200 s-1): a reduction of 'apparent' viscosity with shear was observed with both viscometers. It is suggested that the high density and high surface tension of the metals and eccentricity between the cylinders at low shear rates, leads to instabilities. Results at low shear rates were therefore discarded and further detailed analysis would be required for a fuller understanding of this behaviour. II. At higher shear rates: a steady, shear-independent behaviour of 'apparent' viscosity with shear rate is observed in the Couette system (upto 600 s-1) whereas in the Searle system the 'apparent' viscosity increases with shear rate (upto 2600 s-1). From hydrodynamic theory about Newtonian fluids, it is suggested that in the Searle type viscometer, the fluid is unstable and Taylor vortices are expected at low shear rates (~80 s-1). This gives rise to an increase in the 'apparent' viscosity with shear rate. Whereas, in the Couette type, the flow is more stable, resulting in a steady 'apparent' viscosity. This interpretation is consistent with liquid metals behaving as Newtonian fluids, but further research is required to confirm this. The author suggests further experiments, with the prime one being the investigation of the fluid with counter and co-rotation of the cylinders in order to observe more complex flows. The results are expected to have implications in the modelling of flow for liquid metal processes, especially the initiation of Taylor vortices under the unstable flow conditions produced by rotating the inner cylinder.

No processo de obtenção de níquel de fontes de minério limonita, a lixiviação ácida do minério resulta na dissolução de íons metálicos em uma solução aquosa. Com o uso da tecnologia apropriada, é possível recuperar esses íons metálicos em vez de descartá-los. O presente estudo tem como objetivo a recuperação de magnésio de uma solução contendo íons magnésio e sulfato utilizando-se a técnica da cristalização a alta temperatura. A aplicação da cristalização a alta temperatura para recuperar o magnésio na forma de sulfato de magnésio hidratado pode ser vantajosa uma vez que sua decomposição térmica resulta em MgO e SO2, produtos que podem ser reutilizados no processo de mineração da limonita. Isso reduz o volume de resíduo formado e custo de reagentes no processo. Foi projetado um sistema de cristalizador acoplado a filtração e foi verificado a influência da temperatura, tempo de residência e pH da solução na quantidade de magnésio cristalizado. A solução residual de cada batelada foi analisada por cromatografia de íons para quantificar o magnésio na solução. Os cristais formados foram analisados utilizando-se a técnica de difração de raios-X (DRX), por microscopia eletrônica de varredura (MEV-EDS) e agitamento de peneiras a fim de avaliar a composição química, morfologia e granulometria dos cristais. A solubilidade do sulfato de magnésio foi determinada experimentalmente com o intuito de ampliar a compreensão da solubilidade do sal e obter valores de Kps. Em 5 horas de tempo de residência o sistema foi estabilizado, indicando que não haverá mais crescimento cristalino em tempos de residência maiores que 5 horas. Em pH 5,7 a 230°C e em 5 horas de tempo de residência ocorreu a maior remoção de magnésio com cerca de 81% cristalizado. Os cristais apresentaram morfologia esférica com exceção do cristal obtido a 230 °C em pH 2, que apresentou formato retangular. A análise por DRX mostrou a presença de um produto constituído majoritariamente por sulfato de magnésio monohidratado. / In the process of obtaining nickel from sources of limonite ore, the acid leaching of the ore results in the dissolution of metallic ions in solution. With the use of appropriate technology, it is possible to recover these metal ions instead of discarding them. The present study aims to recover magnesium from a solution containing magnesium and sulfate ions using high temperature crystallization. The application of high temperature crystallization to recover magnesium in the form of hydrated magnesium sulfate may be advantageous since its thermal decomposition results in MgO and SO2, products which can be reused in the limonite mining process. This reduces the volume of waste formed and the cost of reagents in the process. A crystallizer coupled to a filtration system was designed and the influence of the temperature, residence time and pH of the solution on the amount of crystallized magnesium from solution was investigated. The residual solution was analyzed by ion chromatography to quantify the magnesium in the solution. The crystals formed were analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-EDS) and sieve shakers in order to evaluate the chemical composition, morphology and grain size of the crystals. The solubility of magnesium sulphate was determined experimentally to increase the understanding of the solubility of the salt and obtain values of Kps. In 5 hours of residence time the system was stabilized, indicating that there will be no more crystalline growth at residence times greater than 5 hours. At pH 5.7 at 230 ° C and in 5 hours of residence time 81% of Mg crystallized. The crystals presented spherical morphology except for crystals obtained at 230 °C, at pH 2, which presented a rectangular shape. XRD analysis showed the presence of a product consisting mainly of magnesium sulphate monohydrate.

by Tang Yeung Shun. / On t.p., "2", u "3", "7-x", and O"3" are subscripts following "growth of" in the title. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 87-89). / Chapter Chapter 1 ： --- Introduction --- p.1 / Chapter Chapter 2 : --- Preparation of Thin Films --- p.10 / Chapter Chapter 3 : --- Structural Analysis / Chapter 3.1 --- Setup of XRD --- p.14 / Chapter 3.2 --- θ-2θ Scan --- p.17 / Chapter 3.3 --- Rocking Curve --- p.27 / Chapter 3.4 --- Pole Figure --- p.29 / Chapter 3.5 --- Off-axis Scan --- p.33 / Chapter 3.6 --- Grazing Incidence X-ray Diffraction --- p.53 / Chapter 3.7 --- Percentage of (110) Phase --- p.59 / Chapter 3.8 --- Lattice Parameters --- p.63 / Chapter Chapter 4 : --- Transport Properties / Chapter 4.1 --- Experimental --- p.66 / Chapter 4.2 --- Results --- p.68 / Chapter Chapter 5 : --- Surface Morphology --- p.75 / Chapter Chapter 6 : --- Discussion --- p.80 / Chapter Chapter 7 : --- Conclusions --- p.85 / References --- p.87 / Appendix A : Powder Diffraction Patterns of YBCO System

by Sou Ka Hou. / On t.p. "2', "3", and "T" are subscript following "deposition of" in the title. / Parallel title in Chinese characters. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1992. / Includes bibliographical references (leaves [88]). / Chapter 1. --- Introduction --- p.1 / Chapter 2. --- Computer-controlled sputtering system for deposition of high Tc thin films --- p.10 / Chapter 2.1 --- Introduction --- p.10 / Chapter 2.2 --- Vacuum system --- p.12 / Chapter 2.3 --- Gas flow control --- p.16 / Chapter 2.3.1 --- Design --- p.16 / Chapter 2.3.2 --- Flow control --- p.18 / Chapter 2.4 --- Gas pressure control --- p.21 / Chapter 2.4.1 --- Gauges --- p.21 / Chapter 2.4.2 --- Control method --- p.21 / Chapter 2.5 --- "Sputtering, guns and deposition control" --- p.24 / Chapter 2.5.1 --- Types --- p.24 / Chapter 2.5.2 --- Orientation of the sputter gun --- p.26 / Chapter 2.5.3 --- Dual magnetron gun system --- p.26 / Chapter 2.5.4 --- Deposition control system --- p.27 / Chapter 2.6 --- Substrate holder and temperature control --- p.30 / Chapter 2.6.1 --- Substrate holder --- p.30 / Chapter 2.6.2 --- Substrate temperature control --- p.31 / Chapter 2.7 --- Interlock protection --- p.34 / Chapter 2.8 --- Control program --- p.35 / Chapter 3. --- The presputtering effect --- p.39 / Chapter 3.1 --- Presputtering effect (a review) --- p.39 / Chapter 3.2 --- Emission spectroscopy on sputtered materials --- p.48 / Chapter 3.3 --- Experimental --- p.49 / Chapter 3.4 --- Emission spectra --- p.53 / Chapter 3.4.1 --- Effect of sputter power source --- p.53 / Chapter 3.4.2 --- Effect of gas ratio --- p.58 / Chapter 3.4.3 --- Effect of gas pressure --- p.64 / Chapter 3.4.4 --- Study of presputtering effect --- p.67 / Chapter 3.4.5 --- Monitoring the evaporation rate by the spectral line intensities --- p.71 / Chapter 4. --- Conclusion and discussion --- p.75 / Chapter Appendix A. --- Motor control --- p.77 / Chapter Appendix B. --- Thin film deposition --- p.82

The Al-Zr system is used to form a thermally stable strengthening phase in high temperature aluminum-base casting alloys. These alloys have good strength at elevated temperature due to the precipitation of coherent metastable Al3Zr particles upon decomposition of the supersaturated Al-Zr solid solution by a carefully designed heat treatment. Formation of the Al3Zr particles occurs by a peritectic reaction, which decrees that once formed, the particles cannot be dissolved by a solid-state homogenization process. Accordingly, melting the alloy must serve as the homogenization step of the precipitation hardening process; and solidification during casting must serve as the quenching step. Unfortunately, a prohibitively fast solidification rate is necessary to obtain a solid solution with as little as 0.4% Zr in Al. It is found that adding Cr to Al-0.4wt%Zr binary alloy makes it easier to form the supersaturated solid solution, and the ternary Al-0.4wt%Zr- 0.8wt%Cr alloy has better room and elevated temperature tensile properties than the binary Al- 0.4wt%Zr alloy. Various one-step and two-step isothermal aging cycles were investigated in order to arrive at the optimum aging schedule for the Al-0.4wt%Zr-0.8wt%Cr. It is found that soaking the alloy at 400C for 24 hours is optimum; and employing a two-step aging schedule reduces the aging time without sacrificing strength. The two- step aging schedule includes soaking the alloy at 375C for 3 hours and then at 425C for an additional 12 hours. Examination of the precipitates that form in the Al-0.4wt%Zr-0.8wt%Cr with High Resolution Transmission Electron Microscopy (HRTEM) shows that they have the L12 crystal structure. Energy Dispersive Spectrometry (EDS) shows that the particles contain only aluminum and zirconium whereas the matrix is a solid solution of chromium in aluminum. Hence, it is suggested that zirconium strengthens the Al- 0.4wt%Zr-0.8wt%Cr alloy by a precipitation hardening mechanism and chromium further enhances the strength by solid solution strengthening.

Biocompatible anatase TiO2 single-crystals with 27 % -- 50 % chemically reactive facets were obtained in 90 minutes by using a microwave-assisted method. The preparation involved an aqueous solution of titanium tetrafluoride and an ionic liquid (1-methyl-imidazolium tetrafluoroborate). The as-obtained TiO2 single-crystals exhibited a truncated tetragonal bipyramidal shape. By simply changing the concentration of the ionic liquid, the level of reactive facets can be continuously tuned from 27 % to 50 %. The use of microwave heating is critical as it allows rapid and uniform heating of the reaction mixture. The TiO2 single-crystals were characterized by XRD, TEM, XPS and FESEM. The products exhibited excellent photocatalytic efficiency for both oxidation of nitric oxide in air and degradation of organic compounds in aqueous solution under UV light irradiation. The relationship between the physicochemical properties and the photocatalytic performance of the samples was discussed. The TiO2 single-crystals were found to be nontoxic using Zebrafish (D. rerio) as a model. / Bismuth oxyhalide semiconductors (BiOBr, BiOCl) with marigold-like open architectures were also prepared by a solvothermal method involving imidazolium-based ionic liquids and ethylene glycol. The 3D self-assembled marigold-like materials were effective photocatalysts for degrading organic pollutants and generating hydrogen. The main advantages of the new materials were large surface area, high surface-to-bulk ratio, facile species transportation, and ease of recovery and regeneration. / By using a microwave-assisted hydrothermal method involving titanium tetrafluoride and a tetrafluoroborate-based ionic liquid (1-butyl-3-methyl-imidazolium-tetrafluoroborate), a micro-sheet anatase TiO2 single crystal photocatalyst with remarkable 80 % reactive facets was synthesized. The as-obtained TiO2 single-crystal exhibited a truncated tetragonal bipyramidal shape. The high reactivity of facets made these single crystals highly photocatalytically active. They were easily recyclable and thermally stable up to 800 &deg;C. / Furthermore, a simple and environmentally benign approach for the synthesis of photocatalytically active rutile TiO2 mesocrystals was developed. It was a microwave-assisted hydrothermal method involving titanium(III) chloride as the only reactant. The resulting 1D rutile nanowires could easily assemble into 3D hierarchical architectures without the help of surfactants or additives. The average aspect ratio for the nanowires was 267. The BET specific surface area of the mesocrystal was 16 m2/g. / Part I: Size-tunable monodispersed hierarchical metallic Ni nanocrystals (58-190 nm in diameter) were prepared by the reduction of Ni2+ with hexadecylamine under atmospheric pressure. The diameter of the particles could be tuned by simply changing the reaction time. A reaction mechanism was proposed and the relationships between the size, hierarchical surfaces and the magnetic properties were investigated. The as synthesized Ni crystals exhibited higher coercivities than the bulk metallic material owing to the reduced size and the hierarchical surface structure. The saturation magnetization (Ms) and the ratio of remanence to saturation (Mr/Ms) increased with increasing particle size. / Part II: A facile microwave-assisted solvothermal method was developed for the controlled synthesis of novel 3D CdS structures. Dendrite-, star-, popcorn- and hollow sphere-like CdS structures could be obtained by changing the reaction conditions including the reaction temperature and the amounts of reagents and solvents. The results revealed that the final structures were related to the solvent properties such as surface tension and viscosity. The degree of supersaturation was also responsible for the morphology variation and it could be adjusted by the reaction temperature. The CdS products with different morphologies exhibited interesting shape-dependent optical properties and photocatalytic activities. / The optical band energy of the product exhibited an obvious red-shift of 0.2 eV with aspect to that of pure rutile TiO2. This red-shift effect may be ascribed to the high aspect ratio of the rutile nanowires. The products showed excellent photocatalytic activity for NO removal in air and the activity was well maintained after three cycles. Gold modification on the rutile TiO2 resulted in a 50 % improvement in the photocatalytic performance. / This thesis focuses primarily on the preparation of various functional materials with controllable structures and properties. The first part describes the synthesis of materials by solvothermal methods. The second part describes the rapid fabrication of novel semiconductor materials by microwave-assisted methods. / Zhang, Dieqing. / Source: Dissertation Abstracts International, Volume: 72-04, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 189-190). / 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 Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The gradual increase in global warming and environmental pollution has made low-carbon technologies an urgent need for the whole world. Superconducting technology, which is known for its extremely high conductivity and high power density, is capable enough to provide novel solutions, contributing to the future smart grid, thus aiding the power industry towards the realisation of a low-carbon and green planet. In recent decades, several industrial applications using superconducting technology have been developed. Of them, particularly in the power industry, a range of superconducting applications including superconducting magnetic energy storage (SMES), superconducting motors/generators, superconducting cables and superconducting fault current limiters (SFCLs) have been developed. Among them, SFCLs are one of the most promising and are successfully being implemented in power distribution networks. SFCLs exhibit low impedance during normal operation and gain considerable impedance under a fault condition, providing a new solution to the increasingly high fault current levels. However, most of the SFCL projects are limited to low-voltage and medium-voltage levels, there are very few successful operational trials of high voltage SFCLs. This thesis, for the first time, studies the comprehensive characteristics of solenoid type SFCLs based on second generation (2G) high temperature superconductors (HTS), which may be successfully implemented in power grids with high voltage levels. The main contributions of this work include three aspects: 1) proposing an innovative method for simulating the AC losses of the solenoid coils and an electro-magneto-thermal model for simulating the SFCL’s current limiting property; 2) comprehensive and in-depth comparison study concerning the application of the two types of non-inductive solenoid coils (braid type and non-intersecting type) in SFCLs both experimentally and numerically; and 3) the first and thorough discussion of the impact of different parameters such as pitch and radius of coils to the overall performance of braid type SFCLs and the validation of the braid type SFCL concept with a 220 V/300 A SFCL prototype. Based on these experimental and simulation works, the thesis provide strong guidance for the development of future non-inductive solenoid type SFCLs based on 2G HTS, which are promising for high voltage level power grid applications.

NiTiHf alloys have emerged as potential materials for applications requiring high transformation temperatures (> 100 °C) with high strength and work output. Although they have high transformation temperatures, their low damping capacity, brittleness and poor superelastic responses (of Ti-rich NiTiHf) impedes their wider usage in many industrial applications. In this study, the quaternary alloying element of Pd has been added to NiTiHf alloys to improve and tailor their shape memory behavior,. NiTiHfPd alloys were systematically examined regarding the composition and heat treatments effects. Effects of substituting Hf with Ti on the shape memory behavior of NiTHfPd alloys were investigated. There compositions were selected as Ni40.3Ti34Hf20Pd5 Ni40.3Ti39.7Hf15Pd5 and Ni40.3Ti44.7Hf10Pd5 (at.%). Their transformation temperatures, microstructure and shape memory properties were revealed and compared with conventional shape memory alloys. It was revealed that their transformation temperatures increases but transformation strain decreases with the increment of Hf content. Additionally, superelastic responses of Ni45.3Ti29.7Hf20Pd5 andNi45.3Ti39.7Hf10Pd5 alloys were investigated. Transformation temperatures of polycrystalline Ni45.3Ti29.7Hf20Pd5are highly dependent on aging temperatures and they can be altered widely from room temperature to 250 oC. Finally, the damping capacity of the Ni45.3Ti39.7Hf10Pd5 polycrystal and [111]-oriented Ni45.3Ti29.7Hf20Pd5 single crystal were investigated. The damping capacities were found to be 16-25 J.cm-3, and 10-23 J.cm-3 for the Ni45.3Ti39.7Hf10Pd5 and [111]-oriented Ni45.3Ti29.7Hf20Pd5 alloys, respectively.

This research concerns the effects on samples of nominal composition Bil.8Pb0.2Sr2Ca2cu30y which were exposed to hot, dense argon in a ballistic compressor. The investigations were concentrated on two specimens which were exposed to hot, dense argon at about 1800 K (peak pressure 330 atm) and 1500 K (peak pressure 230 atm), respectively. Sample Bi #1 showed a completely melted surface structure after triple exposure in the ballistic compressor at 1800 K while the surface of sample Bi #7 was just partly melted after double exposure at 1500 K. Changes in flux trapping capability and qualitative Meissner effect were investigated in addition to the properties described by Duan, et al. ( 17, 18, 3 2] , who reported changes in critical temperature, crystal structure, surface morphology and composition after exposure of samples to hot, dense argon. After triple exposure in the ballistic compressor at a temperature of approximately 1800 K, sample Bi #1 showed an enhanced Meissner effect on the exposed side compared to the unexposed side of the pellet, while no difference in Meissner effect was found between the exposed and the unexposed side of sample Bi #7. EDS analysis showed that both samples are inhomogeneous in chemical surface composition. Oxygen loss due to exposure to hot, dense argon could not be demonstrated. X-ray analysis indicated that the melted surface layer of sample Bi # 1 after triple exposure to hot, dense argon contains smaller crystals than before exposure in the ballistic compressor. Tc measurements gave varying results which are explainable by the chemical inhomogeneity of the specimens. An increase in the amount of trapped flux due to exposure of the samples to hot, dense argon could not be demonstrated

Graduation date: 1997