No description available.

No description available.

Les formes multiparticulaires injectables présentent l’inconvénient d’une libération initiale prématurée dont les conséquences sont une toxicité systémique si les concentrations sanguines du principe actif deviennent importantes ainsi qu’une modification de la libération. Pour résoudre ce problème, des microparticules composites ont été mises au point : il s’agit de microparticules encapsulant des nanoparticules. Le concept a d’abord été démontré in vitro en encapsulant des nanoparticules de poly(epsilon-caprolactone) dans un polymère non biodégradable en choisissant comme modèles une molécule de faible masse moléculaire (ibuprofène) et un peptide (acétate de triptoréline). L’originalité du travail réside dans le choix des polymères et des solvants retenus pour la fabrication des microparticules. Le solvant utilisé pour fabriquer les microparticules doit être un non-solvant du polymère des nanoparticules. L’acétate d’éthyle répondait à ces conditions puisqu’il ne dissout pas la poly(epsilon-caprolactone) mais que c’est un excellent solvant de l’éthylcellulose ou du polymère polycationique utilisé dans la première partie du travail. Sur la base d’études de libération in vitro, il a ainsi été démontré que les microparticules composites permettaient effectivement de fortement réduire cette libération précoce tout en continuant d’assurer une libération prolongée. Dans un deuxième temps, la réduction de la libération initiale a été confirmée par une étude in vivo chez le rat avec 2 principes actifs modèles : ibuprofène et insuline. Toutefois, le polymère de la matrice des microparticules a été remplacé par un copolymère biodégradable constitué d’acides lactique et glycolique. Il a été démontré que le nouveau concept de microparticules composites permettait de proposer une forme originale limitant la libération initiale des principes actifs suite à leur administration sous-cutanée ou intramusculaire tout en assurant une libération prolongée / Multiparticular injectable dosage forms present a burst effect known to lead to i) a systemic toxicoligal critical issue if blood concentrations of the drug are too high and ii) a change in the release profile due to a lower loading charge in microparticles. In order to solve this problem, composite microparticles have been developed: they consist in nanoparticles encapsulated in microparticles. Such a concept has been demonstrated in vitro by encapsulating poly(epsiloncaprolactone) nanoparticles in a non-biodegradable polymeric matrix with two model drugs: a small molecular weight drug (ibuprofene) and a peptide (triptorelin acetate). The novelty of the research work lies on the adequate choice of polymers and solvents used for microparticles manufacturing. Indeed, the solvent used to manufacture microparticles has to be a non-solvent of the nanoparticles polymer. Ethyl acetate was a good candidate since it does not dissolve poly(epsilon-caprolactone) nanoparticles but is an excellent solvent for ethylcellulose and the polycationic polymer used in the first part of the work. Based on in vitro release studies, it was demonstrated that composite microparticles allowed the initial release to be strongly reduced together with a prolonged release. In a second part, the burst release reduction has been confirmed in vivo in rats with 2 drug models: ibuprofen and insulin. However, the microparticles polymer matrix was replaced by a biodegradable copolymer made of lactic and glycolic acids. It has been demonstrated that the novel composite microparticles were an innovative dosage form able to control the initial burst release often associated to microparticles after sub-cutaneous or intramuscular administration while still maintaining the prolonged release of the encapsulated drugs. Such a result can be associated with the more difficult diffusion of the drug through the two consecutive polymeric barriers of nanoparticles and microparticles.

Several research efforts have been directed towards in-situ fabrication of titanium matrix composites (TMCs) from Ti and B4C powder mixtures as one of the ways to improve the physical and mechanical properties of titanium and its alloys. In this perspective, the present study reports the development of in-situ particulate reinforced titanium matrix composites from TiH2-B4C and Ti-B6O powder mixtures The relationship between densification and microstructure and mechanical properties (hardness and fracture toughness) of pure Ti and in-situ reinforced titanium matrix composites have been studied in detail using pressureless and hot-pressing techniques. Titanium hydride powder was compacted into cylindrical pellets that were used to produce pure Ti through dehydrogenation and pressureless sintering technique. Various composition of TiH2-B4C powder mixtures were initially milled using alumina balls in a planetary mill. The milling was to achieve homogeneous mixing and distribution of the ceramic partially in the TiH2 powder, as well as uniform distribution of reinforcing phases on the resulting Ti matrix. Dehydrogenation and conversion of loose powder and compacts of TiH2 powder was carried out in argon atmosphere and complete removal of hydrogen was achieved at 680 and 715oC for loose and compacted powder respectively. Pressureless sintering of pure Ti from TiH2 was carried out between 750-1400oC, while pressureless sintering and hot pressing of TiH2-B4C was carried out in the temperature range1100-1400oC using 30MPa for hot pressed samples in argon atmosphere. Different sintering times were considered. The microstructure and phase composition of the sintered and hot-pressed materials were characterized using scanning electron microscopy (SEM) and X-ray diffractometry (XRD). Densities of the sintered and hotpressed materials were measured to determine the extent of densification, while Vickers hardness and indentation fracture toughness were used to measure the mechanical properties of the sintered and hot-pressed materials. Pure Ti from TiH2 showed higher densification of above 99% of theoretical density compared to literature where lower densification and swelling was observed. Its Vickers hardness is higher than that of commercial Ti sintered under the same conditions. Titanium matrix composites (TMCs) with different volume content of in-situ formed reinforcements (TiB + TiC) were successfully produced. The amount of reinforcements formed increases with increased amount of B4C used in the starting powder mixtures, while the amount of needle-type TiB decrease and size and amount of blocky-type TiB increase with increasing volume fraction of TiB. Dense materials and improved Vickers hardness were achieved by the hot-pressed composites especially at 1400oC compared to the pressureless sintered composites under the same conditions and to the relevant literature. TMCs produced in this study show higher Vickers hardness compared to available data in the literature. The hardness was found to depend on the volume content of the reinforcing phases. However, the fracture toughness obtained is low (5.3MPa.m1/2) in comparison to pure Ti but is comparable with reported data in the literature. The mechanisms leading to the achievement of improved densification and higher hardness and the reasons for lower fracture toughness with different sintering temperature and composition of reinforcements in the composites are critically analysed. It has been shown that pure Ti can be pressureless sintered using TiH2 and reinforced Ti matrix composites with improved densification and mechanical properties can be produced from TiH2-B4C powder mixtures. Further work on the comprehensive study of the mechanical properties of these composites would enhance the industrial potential of using these materials and the processing route to produce economically feasible titanium matrix composites

by Man-Ling Wong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / by Man-Ling Wong. / Acknowledgments --- p.i / Abstract --- p.ii / 摘要 --- p.iv / Table of contents --- p.v / Chapter Chapter 1 --- Introduction --- p.1-1 / Chapter 1.1 --- Overview of metal matrix composites --- p.1 -1 / Chapter 1.1.1 --- Types of MMCs --- p.1-1 / Chapter 1.1.2 --- The matrices --- p.1 -2 / Chapter 1.1.2.1 --- Mg-based matrix --- p.1 -2 / Chapter 1.1.2.2 --- Al-based matrix --- p.1-2 / Chapter 1.1.2.3 --- Ti-based matrix --- p.1 -3 / Chapter 1.2 --- Fabrication methods of MMCs --- p.1 -3 / Chapter 1.2.1 --- Solid-liquid reaction --- p.1-4 / Chapter 1.2.2 --- Vapor-liquid-solid (VLS) reaction --- p.1 -4 / Chapter 1.2.3 --- Solid-Solid reaction --- p.1-5 / Chapter 1.2.4 --- Liquid-liquid reaction --- p.1-5 / Chapter 1.3 --- Applications of MMCs --- p.1 -6 / Chapter 1.4 --- Previous works versus our work --- p.1 -7 / Chapter 1.5 --- Layout of the thesis --- p.1 -8 / Figures --- p.1-9 / References --- p.1-10 / Chapter Chapter 2 --- Methodology and Instrumentation --- p.2-1 / Chapter 2.1 --- Introduction --- p.2-1 / Chapter 2.2 --- Powder metallurgy --- p.2-1 / Chapter 2.3 --- Sample preparation --- p.2-2 / Chapter 2.3.1 --- Cold pressing --- p.2-2 / Chapter 2.3.2 --- Sintering --- p.2-3 / Chapter 2.4 --- Characterization methods --- p.2-4 / Chapter 2.4.1 --- Differential Thermal Analyzer (DTA) for thermal analysis --- p.2-4 / Chapter 2.4.2 --- X-Ray powder Diffractometry (XRD) for phase determination --- p.2-5 / Chapter 2.4.3 --- Scanning Electron Microscopy (SEM) and Electron Dispersive X-ray analysis (EDX) for structural analysis --- p.2-6 / Chapter 2.4.4 --- Mechanical properties --- p.2-7 / Chapter 2.4.4.1 --- Relative density --- p.2-7 / Chapter 2.4.4.2 --- Porosity --- p.2-9 / Chapter 2.4.4.3 --- Tensile strength --- p.2-10 / Chapter 2.4.4.4 --- Hardness test --- p.2-10 / Figures --- p.2-12 / References --- p.2-18 / Chapter Chapter 3 --- Formation of the Mg-ZnO MMCs --- p.3-1 / Chapter 3.1 --- Thermal analysis on the reactions between Mg and ZnO --- p.3-1 / Chapter 3.1.1 --- Introduction --- p.3-1 / Chapter 3.1.2 --- Experiments --- p.3-1 / Chapter 3.1.3 --- Results and Discussions --- p.3-1 / Chapter 3.2 --- Characterization of the Mg-ZnO MMCs --- p.3-2 / Chapter 3.2.1 --- Introduction --- p.3-2 / Chapter 3.2.2 --- Experiments --- p.3-3 / Chapter 3.2.3 --- Results and Discussions --- p.3-3 / Chapter 3.2.3.1 --- Scanning electron microscopy (SEM) and Electron dispersive X-ray analysis (EDX) --- p.3-3 / Chapter 3.2.3.2 --- X-ray Diffraction (XRD) --- p.3-4 / Chapter 3.2.3.3 --- Mg-Zn intermetallics Phases --- p.3-5 / Chapter 3.2.4 --- Model of formation of Mg-ZnO MMCs --- p.3-5 / Chapter 3.2.4.1 --- Chemical reactions --- p.3-5 / Chapter 3.2.4.2. --- Order of priority of reactions --- p.3-6 / Chapter 3.2.4.3 --- Diffusion during sintering --- p.3-7 / Chapter 3.2.4.4 --- Reaction Model --- p.3-8 / Chapter 3.2.5 --- Conclusions --- p.3-8 / Figures --- p.3-10 / References --- p.3-18 / Chapter Chapter 4 --- Mechanical properties of the Mg-ZnO MMCs --- p.4-1 / Chapter 4.1 --- Introduction --- p.4-1 / Chapter 4.2 --- Experiments --- p.4-1 / Chapter 4.3 --- Results and Discussions --- p.4-2 / Chapter 4.3.1 --- Relative density --- p.4-2 / Chapter 4.3.2 --- Porosity --- p.4-3 / Chapter 4.3.3 --- Tensile strength --- p.4-4 / Chapter 4.3.4 --- Hardness --- p.4-6 / Chapter 4.4 --- Conclusions --- p.4-7 / Figures --- p.4-9 / References --- p.4-23 / Chapter Chapter 5 --- Reinforcement in Mg-ZnO MMCs --- p.5-1 / Chapter 5.1 --- Introduction --- p.5-1 / Chapter 5.2 --- Experiments --- p.5-1 / Chapter 5.3 --- Results and Discussions --- p.5-1 / Chapter 5.3.1 --- Microstructure of the Mg-ZnO MMCs --- p.5-2 / Chapter 5.3.2 --- Fracture of Mg-ZnO MMCs --- p.5-5 / Chapter 5.3.2.1 --- Fracture surface --- p.5-5 / Chapter 5.3.2.2 --- Fracture mode --- p.5-7 / Chapter 5.4 --- Conclusions --- p.5-8 / Figures --- p.5-9 / References --- p.5-18 / Chapter Chapter 6 --- Conclusions and Future Works --- p.6-1 / Chapter 6.1 --- Conclusions --- p.6-1 / Chapter 6.2 --- Future Works --- p.6-2 / References --- p.6-4

Chong, Kam Cheong. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references. / Text in English; abstract also in Chinese. / Chong, Kam Cheong. / ACKNOWLEDGMENT --- p.i / ABSTRACT --- p.ii / 摘要 --- p.iv / Table of contents --- p.v / Chapter 1 --- Introduction / Chapter 1.1 --- Metal Matrix Composites / Chapter 1.1.1 --- Background --- p.1-1 / Chapter 1.1.2 --- Some metallic matrix materials --- p.1-2 / Chapter 1.1.2.1 --- Aluminum alloys --- p.1-2 / Chapter 1.1.2.2 --- Titanium alloys --- p.1-3 / Chapter 1.1.3 --- Different kinds of reinforcements --- p.1-3 / Chapter 1.2 --- Conventional fabrication Methods --- p.1-5 / Chapter 1.2.1 --- Primary liquid phase processing --- p.1-5 / Chapter 1.2.1.1 --- Squeeze casting --- p.1-5 / Chapter 1.2.1.2 --- Spray deposition --- p.1-5 / Chapter 1.2.1.3 --- Slurry casting --- p.1-5 / Chapter 1.2.1.4 --- In Situ processing --- p.1-6 / Chapter 1.2.2 --- Primary solid state processing --- p.1-6 / Chapter 1.2.2.1 --- Physical vapour deposition (PVD) --- p.1-6 / Chapter 1.2.2.2 --- Powder blending and sintering --- p.1-7 / Figures for chapter 1 --- p.1-9 / Tables for chapter 1 --- p.1-14 / References --- p.1-15 / Chapter 2 --- Powder metallurgy --- p.2-1 / Chapter 2.1 --- Introduction --- p.2-1 / Chapter 2.2 --- Fabrication of metal matrix-particulate composites --- p.2-2 / Chapter 2.3 --- Our motivation --- p.2-4 / Figures for chapter 2 --- p.2-5 / References --- p.2-7 / Chapter 3 --- Effects of sintering in processing of metal matrix composites --- p.3-1 / Chapter 3.1 --- Introduction of sintering processing --- p.3-1 / Chapter 3.1.1 --- Solid state sintering --- p.3-2 / Chapter 3.1.2 --- Liquid state sintering --- p.3-5 / Chapter 3.1.3 --- Sintering in metal matrix composites(reactive sintering) --- p.3-7 / Figures for chapter 3 --- p.3-11 / Reference --- p.3-14 / Chapter 4 --- Experiments --- p.4-1 / Chapter 4.1 --- Introduction --- p.4-1 / Chapter 4.2 --- Methodology --- p.4-3 / Chapter 4.2.1 --- High temperature furnace experiment --- p.4.3 / Chapter 4.2.2 --- Arc-melting furnace experiment --- p.4-4 / Chapter 4.3 --- Sample preparations --- p.4-4 / Chapter 4.3.1 --- Sample requirements --- p.4-4 / Chapter 4.3.2 --- Sample milling --- p.4-6 / Chapter 4.3.3 --- Cold pressing --- p.4-6 / Chapter 4.3.4 --- Annealing conditions for high-temperature furnace --- p.4-7 / Chapter 4.3.4.1 --- Different sintering temperatures --- p.4-7 / Chapter 4.3.4.2 --- Different sintering duration --- p.4-8 / Chapter 4.3.5 --- Sample conditions in arc-melting furnace --- p.4-8 / Chapter 4.4 --- Instrumentation --- p.4-10 / Chapter 4.4.1 --- Arc-melting furnace --- p.4-10 / Chapter 4.4.2 --- Vickers hardness tester --- p.4-11 / Chapter 4.4.3 --- X-Ray powder diffractometer (XPD) --- p.4-13 / Chapter 4.4.4 --- Scanning electron microscopy & energy dispersive x-ray analysis --- p.4-15 / References --- p.4-18 / Chapter 5 --- Results / Chapter 5.1 --- High-temperature furnace --- p.5-1 / Chapter 5.1.1 --- XPD results --- p.5-1 / Chapter 5.1.2 --- Different sintering temperatures in 10 weight percent of Cr203 - A1 samples with 1 hour sintering time --- p.5-2 / Chapter 5.1.3 --- Different sintering temperatures in 15 weight percent of Cr203 一 A1 samples with 1 hour sintering time --- p.5-6 / Chapter 5.1.4 --- Different sintering temperatures in 20 weight percent of Cr203 ´ؤ A1 samples with 1 hour sintering time --- p.5-10 / Chapter 5.1.5 --- Different sintering temperatures in 30 weight percent of Cr203 ´ؤ A1 samples with 1 hour sintering time --- p.5-13 / Chapter 5.1.6 --- Different sintering time for 10 weight percent of Cr203 ´ؤ A1 samples at 1100°C sintering temperature --- p.5-19 / Chapter 5.1.7 --- Different sintering time for 15 weight percent of Cr203 ´ؤ A1 samples at 1100°C sintering temperature --- p.5-21 / Chapter 5.2 --- Arc-melting furnace --- p.5-24 / Chapter 5.2.1 --- XPD results --- p.5-24 / Chapter 5.2.2 --- Samples that were melted in arc-melting furnace --- p.5-25 / Chapter 5.2.3 --- Powder samples that were melted in arc-melting furnace --- p.5-28 / Figures for chapter 5 --- p.5-30 / References --- p.5-55 / Chapter 6 --- Discussions --- p.6-1 / Chapter 6.1 --- Chemical reactions --- p.6-1 / Chapter 6.2 --- Sintering --- p.6-6 / Chapter 6.2.1 --- Conditions for having larger Al13Cr2 intermetallic compound --- p.5-7 / Chapter 6.3 --- Vickers hardness results --- p.6-10 / Chapter 6.4 --- Comparisons between the two furnace results --- p.6-12 / Chapter 6.4.1 --- Cooling rates --- p.6-12 / Chapter 6.4.2 --- Volume fraction of all the intermetallic compounds --- p.6-14 / Chapter 6.4.3 --- Pore sizes --- p.6-15 / Chapter 6.4.4 --- Vickers hardness --- p.6-16 / References --- p.6-17 / Chapter 7 --- Conclusions and suggestions for further studies --- p.7-1 / BIBLIOGRAPHY

"Conventional manufacturing methods are sub-optimal for nano-composites fabrication. Inhomogeneous dispersion of the secondary phase and scalability issues are the main issues. This work focuses on an innovative method where the reinforcement is formed in-situ in the melt. It involves the reaction of the molten aluminum with a nitrogen- bearing gas injected through the melt at around 1273 K. AlN particles are expected to form through this in situ reaction. A model has been developed to predict the amount of reinforced phase. Experiments have been carried out to confirm the feasibility of the process and the mechanism of AlN formation discussed. The detrimental effect of oxygen in the melt which hinders the nitridation reaction has been proved. The effect of process times and the addition of alloying elements (Mg and Si) have also been investigated."

This thesis presents the results of an investigation into the effects of hygrothermal conditioning on the mechanical properties, and fatigue properties of epoxy based composites reinforced with carbon, glass and Kevlar 49 fibres. Cross-plied laminates (0/90) of these materials of nominal volume o fraction 60% were conditioned by drying at 60°C, by exposure to a 65% RH atmosphere at room temperature and by boiling in water. The effects of conditioning on the tensile and shear strengths and on the tensile fatigue response are discussed. The effects of exposure to an extreme diurnal cycle and to the ultra violet in isolation on the tensile properties are also discussed. The 0/90 tensile properties of the three laminates are relatively little affected by the environmental conditioning except for the case of GRP exposed to boiling water, when corrosion damage to the glass fibres significantly reduces the composite strength, and in the KFRP in which the strength is reduced by complete drying. The +/-45 strengths are more sensitive to the effects of moisture, however, it appears that the optimum strength is obtained after conditioning in the 65% RH environment. Acoustic emission monitoring of the tensile tests shows distinctive differences between KFRP and the two other types of composite and permits the identification of characteristic effects of moisture on the tensile failure mechanisms of all three materials. Tensile fatigue tests have been carried out on the laminates in the 0/90 orientation. The CFRP shows no effect of conditioning on the fatigue behaviour, and in the GRP only the boiling water conditioning affects the results. The tensile fatigue of the KFRP is affected both by boiling and by drying, the latter being the most severe. The fatigue response of the KFRP shows a dramatic down turn at lives in excess of 105 cycles. This effect appears to reflect the ease with which mechanical damage is sustained by the aromatic polyamide fibres. The residual strengths of the laminates after fatiguing is discussed and possible mechanisms for the damage accumulation in the materials during fatiguing are given.

The static and fatigue properties of advanced epoxy-based composites reinforced with carbon, glass or aromatic polyamide (Kevlar-49) fibres have been measured for a range of different loading and environmental conditions. Cross-plied laminates were tested in tension in the 0/90 and +/-45° orientations and also under flexural loading. The laminates were similar, except for the type of fibre. The effects of environmental exposure were assessed by preconditioning test specimens to equilibrium by either drying at 60°C, storage at 65%RH at ambient temperature or boiling in water. Moisture absorption was through the resin alone for CFRP and GRP and by additional absorption by the fibres for KFRP. Fatigue testing revealed that the tensile performance in the 0/90 orientation is strongly dependent on the level of cyclic strain. 0/90 CFRP has excellent fatigue and environmental resistance but GRP exhibits a steep fatigue curve and the static and low cycle fatigue strengths are both reduced by boiling. The fatigue strength of 0/90 KFRP is reduced by drying, more so than by boiling, and in all conditions the stress/log-life curves are characterised by a downward curvature or 'knee'. Tensile preloads do not significantly affect the residual fatigue properties or the equilibrium levels of moisture uptake, although extensive damage involving cracking in both longitudinal and transverse plies may lead to increased absorption rates. A tendency for Kevlar fibres to split or 'defibrillate' plays an important role in most failures of KFRP. It limits the shear strength and causes flexural failures to occur at the compression surface at low stress levels. 0/90 CFRP also fails at the compression surface in flexure but GRP fails at the tensile surface, the environmental fatigue performance resembling that under axial tensile loading. The +/-45° tensile and low cycle fatigue strengths are sensitive to the effects of conditioning, all laminates exhibiting optimum performance after conditioning at 65%RH, although generally these effects become insignificant at long lives.

No description available.