Teses / dissertações sobre o tema "Ultra high purity oxygen"

Next generation aerospace vehicles require thermal protection system (TPS) materials that are capable of withstanding the extreme aerothermal environment during hypersonic flight (>Mach 5 [>1700 m/s]). Ultra-high temperature ceramics (UHTC) such as zirconium diboride (ZrB₂) are candidate TPS materials due to their high-temperature thermal and mechanical properties and are often the basis for advanced composites for enhanced oxidation resistance. However, ZrB₂ matrix impurities in the form of boron trioxide (B₂O₃) and zirconium dioxide (ZrO₂) limit the high-temperature capabilities. Electric based sintering techniques, such as spark plasma sintering (SPS), that use joule heating have become the preferred densification method to process advanced ceramics due to its ability to produce high density parts with reduced densification times and limit grain growth. This study focuses on a combined experimental and thermodynamic assisted processing approach to enhance powder purity through a carbo- and borocarbo-thermal reduction of oxides using carbon (C) and boron carbide (B₄C). The amount of oxides on the powder surface are measured, the amount of additive required to remove oxides is calculated, and processing conditions (temperature, pressure, environment) are controlled to promote favorable thermodynamic reactions both during thermal processing in a tube furnace and SPS. Untreated ZrB₂ contains 0.18 wt%O after SPS. Additions of 0.75 wt%C is found to reduce powder surface oxides to 0.12 wt%O. A preliminary Zr-C-O computational thermodynamic model shows limited efficiency of carbon additions to completely remove oxygen due to the solubility of oxygen in zirconium carbide (ZrC) forming a zirconium oxycarbide (ZrCₓOᵧ). Scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM) with atomic scale elemental spectroscopy shows reduced oxygen content with amorphous Zr-B oxides and discreet ZrO₂ particle impurities in the microstructure. Processing ZrB₂ with minimal additions of B₄C (0.25 wt%) produces high purity parts after SPS with only 0.06 wt%O. STEM identifies unique “trash collector” oxides composed of manufacturer powder impurities of calcium, silver, and yttrium. A preliminary Zr-B-C-O thermodynamic model is used to show the potential reaction paths using B₄C that promotes oxide removal to produce high-purity ZrB₂ with fine grains (3.3 𝜇m) and superior mechanical properties (flexural strength of 660MPa) than the current state-of-the-art ZrB₂ ceramics. Due to the desirable properties produced using SPS, there is growing interest to advance processing techniques from lab-scale (20 mm discs) to large-scale (>100 mm). The advancement of SPS technologies has been stunted due to the limited power and load delivery of lab-scale furnaces. We use a large scale direct current sintering furnace (DCS) to address the challenges of producing industrially relevant sized parts. However, current-assisted sintering techniques, like SPS and DCS, are highly dependent on tooling resistances and the electrical conductivity of the sample, which influences the part uniformity through localized heating spots that are strongly dependent on the current flow path. We develop a coupled thermal-electrical finite element analysis model to investigate the development and effects of tooling and current density manipulation on an electrical conductor (ZrB₂) and an electrical insulator, silicon nitride (Si₃N₄), at the steady-state where material properties, temperature gradients and current/voltage input are constant. The model is built based on experimentally measured temperature gradients in the tooling for 20 mm discs and validated by producing 30 mm discs with similar temperature gradients and grain size uniformity across the part. The model aids in developing tooling to manipulate localize current density in specific regions to produce uniform 100 mm discs of ZrB₂ and Si₃N₄.

Supplying oxygen to water via the physical process of aeration is the most widely used water treatment technology. It supports microbial growth in water and wastewaters by introducing dissolved oxygen to the water, stabilizing organic matter and providing the necessary oxygen for many other aquatic species to survive. There exists the potential for much improvement in aeration techniques, which can account for 60 percent of the energy required for water treatment. This research aimed to analyze one such technique that has limited research of this magnitude, aerating water under high pressures with high-purity oxygen. Increasing the partial pressure of oxygen in the aeration gas, by way of Henry's law, increases the saturation concentration of the water and, thus, several aeration design parameters. The parameters required for aeration design and sought after in this research are: the mass transfer coefficient (KLa), saturation concentration (C*sat), standard oxygen transfer rate (SOTR), standard aeration efficiency (SAE), and the standard oxygen transfer efficiency (SOTE). This research compared the obtained design values under gauge pressures of 0, 50, 100, 150, and 200 kPa using air and Pressure Swing Adsorption (PSA) oxygen in an 18.5 foot (5.6 meter) aeration column, allowing for comparative analysis of the design parameters for aeration. Results show that, with increasing pressure for both air and PSA oxygen: KLa decreases, C*sat increases; however, at a rate other than predicted by Henry's law, the SOTR remains constant, the SAE decreases, and the SOTE increases. Between air and PSA oxygen, PSA was found to have a slightly larger KLa, larger C*sat, larger SOTR, lower SAE, and a higher SOTE.
Applied Science, Faculty of
Civil Engineering, Department of
Graduate

Oxygen is used for a wide range of applications, with a globally projected production capacity of 1.8 million tonne per day in 2020. Depending on the economic range and the required purity, various methods are used to extract oxygen. Conventionally, cryogenic air separation is used for the large to medium production scale, characterised by high purity oxygen and relatively low energy consumption, whilst pressure swing adsorption (PSA) is widely used for the small-scale production, with lower oxygen purity and higher energy consumption. A high-efficiency system for high purity oxygen production based on the integration of solid oxide- fuel and electrolysis cells (SOFC and SOEC) was first proposed by Iora and Chiesa in 2009. However, the lack of a detailed methodology and the novelty of such a system necessitated a system-level energy analysis with an emphasis on the SOFC and SOEC to understand the nature of thermal and electrical coupling between them. Here, the initial feasibility of the system has been evaluated considering the lumped-parameter modelling of the SOFC, SOEC and balance of plant. A system energy consumption that is significantly less than that of PSA systems was predicted, and a significant contribution of the stack energy consumption to the overall system energy consumption was observed, suggesting the need for a thorough examination of the electrochemical models. Therefore, the parameter estimation technique has been implemented to validate the electrochemical models based on a 5-cell stack and a single repeating unit SOEC experimental data. A good agreement was obtained between the experimental and model-predicted cell potential across all operating conditions, and key electrochemical parameters were estimated with confidence. The validated electrochemical model has then been integrated into a newly-developed onedimensional model of a planar SOFC-SOEC stack to further improve the predictions of the stack and system performance. Significant contributions of experimental validation and distributed modelling on enhancing the predictions of the stack model were observed. The advantages of the system over PSA systems in terms of energy efficiency and oxygen purity were confirmed. A potential design point of the system was selected via a techno-economic study, revealing an extremely low contribution of the electricity cost to the total cost of production. An adequate thermal integration at both the stack and system levels were demonstrated at the design point.

Trends show that the fraction of the world's population with electronic devices using modern integrated circuits is increasing at a rapid rate. To meet consumer demands: less expensive, faster, and smaller electronics; while still making a profit, manufacturers must shrink transistor dimensions while increasing the number of transistors per integrated circuit; a trend predicted by Gorden E. Moore more than 44 years prior. As CMOS transistors scale down in size, new techniques such as atomic-layer deposition (ALD) are used to grow features one atomic layer at a time. ALD and other manufacturing processes are requiring increasingly stringent purities of process gases and liquids in order to minimize circuit killing defects which reduces yield and drives up manufacturing cost. Circuit killing defects caused by impurity incursions into UHP gas distribution system can come from a variety of sources and one of the impurity transport mechanisms investigated was back diffusion; the transport of impurities against convective flow. Once impurity incursions transpire, entire production lines are shut down and purging with UHP gas is initiated; a process that can take months thus resulting in tens of millions of dollars in lost revenue and substantial environment, safety, and health (ESH) impacts associated with high purge gas consumption. A combination of experimental investigation and process simulation was used to analyze the effect of various operational parameters on impurity back diffusion into UHP gas distribution systems. Advanced and highly sensitive analytical equipment, such as the Tiger Optics MTO 1000 H2O cavity ring-down spectrometer (CRDS), was used in experiments to measure real time back diffusing moisture concentrations exiting an electro-polished stainless-steel (EPSS) UHP distribution pipe. Design and operating parameters; main and lateral flow rates, system pressure, restrictive flow orifice (RFO) aperture size, and lateral length were changed to impact the extent of back diffusing impurities from a venting lateral. The process model developed in this work was validated by comparing its predictions with data from the experiment test bed. The process model includes convection, molecular diffusion in the bulk, surface diffusion, boundary layer transport, and all modes of dispersion; applicable in both laminar and turbulent flow regimes. Fluid dynamic properties were directly measured or were obtained by solving Navier-Stokes and continuity equations. Surface diffusion as well as convection and dispersion in the bulk fluid played a strong role in the transport of moisture from vents and lateral branches into the main line. In this analysis, a dimensionless number (Peclet Number) was derived and applied as the key indicator of the relative significance of various transport mechanisms in moisture back-diffusion. Guidelines and critical values of Peclet number were identified for assuring the operating conditions meet the purity requirements at the point of use while minimizing UHP gas usage. These guidelines allowed the determination of lateral lengths, lateral diameters, flow rates, and restrictive flow device configurations to minimize contamination and UHP gas consumption. Once a distribution system is contaminated, a significant amount of purge time is required to recover the system background due to the strong interactions between moisture molecules and the inner surfaces of the components in a gas distribution system. Because of the very high cost of UHP gases and factory downtime, it is critical for high-volume semiconductor manufacturers to reduce purge gas usage as well as purge time during the dry-down process. The removal of moisture contamination in UHP gas distribution systems was approached by using a novel technique dubbed pressure cyclic purge (PCP). EPSS piping was contaminated with moisture, from a controlled source, and then purged using a conventional purge technique or a PCP technique. Moisture removal rates and overall moisture removal was determined by measuring gas phase moisture concentration in real time via a CRDS moisture analyzer. When compared to conventional purge, PCP reduced the time required and purge gas needed to clean the UHP gas distribution systems. However, results indicate that indiscriminately initiating PCP can have less than ideal or even detrimental results. An investigation of purge techniques on the removal of gas phase, chemisorbed, and physisorbed moisture, coupled with the model predictions, led to the testing of hybrid PCP. The hybrid PCP approach proved to be the most adaptable purge technique and was used in next phase of testing and modeling. Experiments and modeling progressed to include testing the effectiveness of hybrid PCP in systems with laterals; more specifically, laterals that are "dead volumes" and results show that hybrid PCP becomes more purge time and purge gas efficient in systems with increasing number and size of dead volumes. The process model was used as a dry-down optimization tool requiring inputs of; geometry and size, temperature, starting contamination level, pressure swing limits of inline equipment, target cleanliness, and optimization goals; such as, minimizing pure time, minimizing purge gas usage, or minimizing total dry-down cost.

Molecular contaminants on the surface of nanoparticles (NPs) are critical in determining the environmental safety and health (ESH) impacts of NPs. In order to characterize the surface properties that relate to adsorption and desorption interactions, a method has been developed for studying the dynamic interactions of adsorbing species on NP samples. The results are analyzed using a process simulator to determine fundamental properties such as capacity, affinity, rate expressions, and activation energies of NP interactions with contaminants. The method is illustrated using moisture as a representative model compound and particles of SiO₂, HfO₂, and CeO₂, which are three oxides used in semiconductor manufacturing. The effect of particle size and temperature on the surface properties of porous oxide NPs was investigated. Infrared spectra peaks corresponding to the stretching vibration of water molecules were monitored by in-site Fourier transform infrared (FTIR) spectroscopy. These are related to the moisture concentration on the surface of NPs. A transient multilayer model was developed to represent the fundamental steps in the process. The thermal stability of adsorbed species and the strength of bonding to the surface were evaluated by determining the activation energies of the various steps. The results indicate that the surface interaction parameters are dependent on species, temperature, and particle size. SiO₂ has the highest adsorption capacity and therefore is most prone to the adsorption of moisture and similar contaminants. However, the affinity of the NPs for H₂O retention is highest for CeO₂ and lowest for SiO₂. As temperature decreases, NPs exhibit a higher saturated moisture concentration and are more prone to the adsorption of moisture and similar contaminants. Furthermore, smaller NPs have a higher saturated surface concentration and a slower response to purging and desorption. Factors contributing to the environmental and health impact of NPs (extent of surface coverage, capacity, and activation energy of retention) have been investigated during this study. The second objective of this study is to develop a method to measure and control the contamination in ultra-high-purity (UHP) gas delivery systems. Modern semiconductor manufacturing plants have very stringent specifications for the moisture content at the point-of-use, usually below several parts per billion (ppb). When the gas delivery system gets contaminated, a significant amount of purge time is required for recovery of the background system. Therefore, it is critical for high-volume semiconductor manufacturers to reduce purge gas usage as well as purge time during the dry-down process. A method consisting of experimental research and process simulations is used to compare steady-state purge (SSP) process of constant pressure and flow rate with the pressure-cycle purge (PCP) process of cyclic pressure and flow rate at a controlled interval. The results show that the PCP process has significant advantages over the SSP process under certain conditions. It can reduce the purge time and gas usage when the gas purity at point-of-use is the major concern. The process model is validated by data congruent with the experimental results under various operating conditions and is useful in conducting parametric studies and optimizing the purge process for industrial applications. The effect of key operational parameters, such as start time of PCP process as well as choice of PCP patterns has been studied.

Calcareous microfossils are not always present in marine or lacustrine sediments owing to unfavourable ecological or post-depositional conditions. These non-carbonated sediments sometimes contain abundant biogenic silica, rendering them suitable for studies of stable isotopes. For this reason, considerable progress has been made in the study of biogenic silica using isotopes in recent years. Diatom isotopes are increasingly being used for palaeoenvironmental reconstructions in lacustrine sedimentary records. Tropical proxy records offer valuable insights into past climate and environmental changes of the Earth and into possible future climate change scenarios. Research into tropical regions has therefore become a key issue among palaeoclimatologists. Influenced by the tropical circulation in the north, and by the mid-latitude westerlies in the south, the Central Andes are an ideal site to study past variations of atmospheric circulation systems. Thus, the Andean Altiplano has become a key region for the study of late Quaternary climate change in South America. Sedimentary records of high-altitude Andean Altiplano lakes usually preserve an excellent centennial- to millennial-scale record of effective moisture fluctuations and source changes during the Late Glacial and Holocene despite the fact that the interpretation is not always straightforward. Oxygen and carbon isotope analyses in carbonates (δ18Ocarbonate and δ13Ccarbonate) and δ13Cbulk have been successfully used to reconstruct the hydrological responses to climate change in different Andean lacustrine systems to date. No attempt, however, has been made to use δ18Odiatom and δ13Cdiatom despite the fact that they are usually the best preserved fossils in the sedimentary record of the Andean Altiplano lakes. For this reason, the aims of the PhD Thesis are twofold: a) to explore the possibilities that the study of δ18Odiatom and δ13Cdiatom can offer in palaeoenvironmental reconstructions, and b) to carry out high- and ultra-high resolution environmental and climate reconstructions in the Andean Altiplano during the Late Glacial- Early Holocene transition using these stable isotopes. The thesis focuses on new and poorly documented fields where δ18Odiatom and δ13Cdiatom can successfully be applied to lacustrine sediments. It shows how stable isotopes from diatom silica may be used a) to highlight the importance of reconstructing the different evolutionary stages of lake ontogeny given that climate derived palaeohydrological signals can be distorted by changes in lake morphology b) as a main proxy in ultra-high resolution moisture balance reconstructions forced by fluctuations in the intensity of the ENSO and solar activities c) to reveal the major biogeochemical processes that give rise to the formation of rhythmites, and finally d) to reconstruct the regional environmental evolution at centennial-to-millenial time scales.
La tesis está basada en la reconstrucción ambiental y climática a muy alta resolución mediante los sedimentos laminados y ricos en diatomeas de un lago tropical situado en los Andes Centrales. Para la reconstrucción se ha utilizado la novedosa técnica del análisis de isótopos estables (δ18Odiat y δ13Cdiat) de la sílice de las diatomeas. Los principales resultados y conclusiones son: Diversos factores ambientales pueden influir en los valores de δ18Odiat. Los registros de δ18Odiat en sistemas lacustres cerrados no pueden ser simplemente interpretados en términos de seco o húmedo, sino que es imperativo entender la hidrología y geomorfología de cada sistema antes de hacer una interpretación de tipo estrictamente climático como se había hecho hasta la fecha. Por su parte, los análisis de δ13Cdiat han demostrado que esta técnica es una herramienta válida para realizar reconstrucciones del ciclo del carbono en los lagos, así como para dar un mejor punto de vista del ciclo del carbono a nivel global. La unidad sedimentaria laminada del Lago Chungará está formada por ritmitas multianuales compuestas por láminas de color blanco y verde. Estás láminas son ricas en diatomeas y son el resultado de diferentes procesos lacustres. Las láminas de claras se formaron como consecuencia de «blooms» extraordinarios de muy corta duración (días o semanas). Las láminas oscuras se depositaron a lo largo de diversos años bajo diferentes condiciones de la columna de agua y por tanto representan las condiciones de base del lago. Los valores de δ18Odiat muestran que los «blooms» extraordinarios fueron más intensos con condiciones de bajo nivel del lago, mientras que la formación de láminas oscuras se vio especialmente inducida por subidas del nivel. Al mismo tiempo, los valores de δ13Cdiat indican que la disponibilidad de carbono fue superior durante los «blooms» extraordinarios de diatomeas. La combinación de los dos registros ha destacado les complejas relaciones entre los procesos limnológicos, los procesos de la cuenca de drenaje, la hidrología y los forzamientos climáticos. El registro de isotopía expone claramente que, según la escala temporal, un tipo de proceso puede dominar sobre los otros en la interpretación de la isotopía.

The ozone formation reaction O+O2+M→O3+M is a unique example of a chemical reaction that leads to an anomalous isotopic composition of the products, most likely due to symmetry - breaking effects. So far, results on other chemical systems that might show similar effects are spurious, even though such claims concerning reactions other than the formation of ozone have been made repeatedly.This applies in particular to the spin forbidden O+CO+M→CO2+M reaction, where two studies report a mass-independent fractionation of about 8%. Nevertheless, the presence of ozone in these experiments raises questions as to the validity of this assertion. We thus make a new attempt to study the O+CO+M reaction in the photoreactor at CCAR (University of Copenhagen) where reagents and contaminants are monitored on-line by FTIR spectroscopy. This study combined with the analysis of the spectral distribution of the employed lamps and isotope kinetic modeling lead to a complete re-interpretation of previous experiments. We conclude that available measurements are more compatible with the hypothesis that there is no mass-independent isotope fractionation in the O+CO reaction. We propose that all observations can be completely explained by an isotope transfer from ozone, involving photolytic production of O(1D) that in turn leads to OH radicals, which then rapidly form CO2 from reaction with CO. We also present a method to produce pure ozone samples and derive an upper limit on nitrogen oxide contaminations based on mass spectrometer measurements. These values will serve as benchmarks values for future studies of ozone absorption cross sections in the IR and UV.

Fluids are an essential component of tectonic and metamorphic processes such as subduction and crustal anatexis. Fluids are elusive to trace as they commonly escape high-pressure rocks. This study uses oxygen isotopes to identify fluid influxes in metamorphic rocks and tie them to geologic events, measuring δ18O in situ by ion microprobe in garnet, zircon, apatite, monazite and lawsonite. New method developments are presented for δ18O analyses by Sensitive High Resolution Ion MicroProbe: (i) in apatite, a precision of 0.2‰ (1σ) is achieved; diffusion modelling shows that apatite is expected to preserve oxygen isotope signatures from 400-450°C and below; (ii) a matrix correction scheme is derived for monazite oxygen isotope measurement, allowing a precision of 0.35‰ (1σ); (iii) rutile oxygen isotope measurements yield major orientation effects. Fluid pulses generated by prograde dehydration reactions are investigated in the ultra-high-pressure Dora Maira whiteschists, Italy. Rare-earth-element abundances indicate prograde monazite and zircon growth (pre-garnet 34.5±0.7 Ma, 6.4‰ and syn-garnet at 34.9±0.4 Ma, 6.2 to 6.7‰), which are linked to dehydration reactions using thermodynamic modelling. This allows drawing a P-T-time-fluid path that implies that (i) prograde subduction from 25 to 45 kbar occurred within a couple of My (minimum burial rate of 2 cm/yr); (ii) high-pressure fluids were of internal origin and metasomatism likely have occurred at a rifting phase before subduction. Four phases of fluid circulations are identified in the high-pressure low-temperature lawsonite eclogites and blueschists of the Tavşanlı zone, Turkey. The Halilbağı unit is an oceanic complex containing various sediments and serpentinite together with 222±5 Ma MORB and 123±3 Ma OIB lithologies (zircon U-Pb, whole-rock major and trace elements). The sequence was thoroughly altered and mechanically mixed at the seafloor and in the accretionary prism, leading to overall high whole-rock δ18O of 11.0-17.0‰ for metabasites. Garnet, apatite and lawsonite are zoned in δ18O in samples across the unit, with contrasts of 7‰ in a MORB eclogite (garnet core: 6.3‰, rim: 13‰) and 3‰ in an impure quartzite (apatite core: 19.5‰, rim: 17‰). Petrographic and trace element evidence allow identifying localised prograde-peak fluid influx, and homogenisation of oxygen isotopes and Sr/Pb at the start of retrogression by pervasive fluid circulation across the unit. Heavy δ18O signatures (WR: 11.8 to 13.6‰) were measured in Eoarchaean metasediments from the Isua supracrustal belt, Greenland. The sources of the sediments were mantle-derived boninites (mafic component) and andesites (felsic component, detrital/volcanic zircons dated at 3709 Ma,δ18O 5.3‰). Three garnet growth zones record high δ18O (9 to 10‰), in equilibrium with the whole-rock. Rare-earth-element and petrographic evidence allow identifying a higher-pressure signature in the high- δ18O garnet, which can be linked to a 3690-3660 Ma tectonic event. The elevated δ18O signature in the metasediments thus originated from surficial processes (e.g. weathering) before 3690Ma. Melting of such heavy-δ18O amphibolite-facies sediments could represent a source for early Archean high-δ18O magmas and zircons. The combination of oxygen isotope and trace element microanalysis in zoned minerals proves a powerful tool for uncovering multistage minor and major fluid infiltration events in metamorphic rocks.

Thesis submitted in fulfilment of the requirements for the degree Master of Technology: Biomedical Technology in the Faculty Health and Wellness Sciences at the Cape Peninsula University of Technology, 2013
The accurate and consistent measurement of antioxidants is crucial to evaluating their biological role in the prevention and delay of cancer and other pathological conditions. Hence, the performance of the analytical method utilized should be evaluated for acceptable levels of accuracy, precision and other performance parameters according to internationally accepted standards. Additionally, the measure and influence of existing errors should be evaluated and the method optimized to reduce such errors. In furtherance of this vital aim, this research project sought out to optimize and validate two bio-analytical assays for the measurement of total antioxidant capacity and L-ascorbic acid (L-AA), respectively in food commodities. The validation procedure was performed in accordance with ISO 17025 international standard. The first study in this thesis evaluated, optimized and validated the hydrophilic oxygen radical absorbance capacity (H-ORACFL) assay using fluorescein for total antioxidant capacity in various food and beverage products. The assay demonstrated good results with regard to accuracy, precision, linearity, specificity, limits of detection (LOD) and quantification (LOQ) and robustness. The extraction solvent (60% ethanol) recovered excellent antioxidant yields for most samples tested. The optimization of the method in terms of temperature and sample usage on the micro-plate significantly (p<0.05) reduced errors and subsequently improved precision substantially.

The PhD project has been performed in the Surfaces and Catalysts group active in the Department of Chemical Sciences, within the frame of the grant “A rational approach to the optimization of efficient electrocatalysts for the next generation Fuel Cells”, funded by CARIPARO foundation. The project has been focused on the preparation and characterization of new carbon-based materials for applications in Polymer Electrolyte Membrane Fuel Cells (PEMFCs), also known as oxygen-hydrogen FCs. The preparation of the materials has been performed using different techniques, depending on the type of the target material and on the possible applications that these materials can offer. With reference to the studied model systems (Highly Oriented Pyrolytic Graphite (HOPG) and Glassy Carbon (GC)), the introduction of doping heteroatoms has been performed by ion implantation, while the study of new chemical functionalities has been allowed by the use of Wet Chemistry techniques, in particular derived from the electrochemical synthesis. The deposition of thin films or nanoparticles (metal or oxides of transition metals) on the ion-modified materials has been carried out in-situ by using advanced techniques under Ultra High Vacuum conditions (UHV), such as Physical Vapor Deposition (PVD). Within the study of the model systems, PVD was chosen because of its ability to provide an atomic scale control of the metal deposition. In a second time, conventional deposition techniques such as chemical or electrochemical reduction of suitable metal precursors have been performed, in a synergistic combination between Surface Science and Electrochemistry-derived techniques. The characterization of these materials has been performed using the facilities of the Surface Science group, such as the X-ray and Ultraviolet Photoelectron Spectroscopy (XPS - UPS), Scanning Tunneling and Atomic Force Microscopy (STM - AFM), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDX) and Low Energy Electron Diffraction (LEED). To get a deeper insight in the chemistry/structure/properties of the prepared systems, synchrotron light-based techniques such as HR-XPS, NEXAFS, ARPES, ResPES and PEEM have been extensively used. The study of the electro-catalytic activity has been performed using conventional Electrochemistry techniques, in particular Cyclic and Linear Sweep Voltammetry (CV - LSV), as well as electro-dynamic techniques such as Rotating Disk Electrode (RDE). Finally, in order to support the experimental data or to bring their understanding at a deeper level, simulations using Density Functional Theory (DFT) have been performed in collaboration with the group coordinated by Prof. Cristiana Di Valentin (University of Milano Bicocca). During the course of the doctorate, several collaborations have been pursued with other research groups operating in the Department of Chemical Sciences or abroad, such as the "Interfaces and Energy Conversion E19" research unit, Technical University of Munich (TUM, Germany), coordinated by Profs. O. Schneider and J. Kunze-Liebhäuser.
Il progetto di dottorato nasce all’interno del gruppo di ricerca di Superfici e Catalizzatori operante nel dipartimento di Scienze Chimiche, nell’ambito della borsa a titolo vincolato “Un approccio razionale alla ottimizzazione di elettrocatalizzatori efficienti per le celle a combustibile di nuova generazione”, finanziata da fondazione CARIPARO. Le tematica è stata focalizzata sulla preparazione e caratterizzazione di nuovi materiali a base di carbonio utilizzabili per applicazioni in celle a combustibile di tipo PEMFCs (Polymer Electrolyte Membrane Fuel Cells) ad ossigeno-idrogeno. La preparazione dei materiali è avvenuta facendo uso di differenti tecniche, in relazione al tipo di materiale oggetto di studio ed alle applicazioni che tali materiali possono offrire. Con riferimento allo studio dei sistemi modello (grafite pirolitica altamente orientata, HOPG, e carbonio vetroso, GC), il drogaggio degli stessi mediante l’introduzione di eteroatomi (in particolare azoto) è avvenuto ricorrendo alla tecnica dell’impiantazione ionica, mentre lo studio di nuove funzionalità chimiche è stato permesso dall’utilizzo di tecniche di Wet Chemistry, in particolare mutuate dalla sintesi elettrochimica. La deposizione di film sottili o di nanoparticelle (metalliche o a base di ossidi di metalli di transizione) su tali materiali modificati è stata effettuata facendo uso di tecniche avanzate come la deposizione fisica da fase vapore (PVD) in condizioni controllate di Ultra Alto Vuoto (UHV), in grado di offrire un controllo su scala atomica della deposizione di tali film. Sono state utilizzate anche tecniche di deposizione tradizionali quali la riduzione chimica o elettrochimica di opportuni precursori metallici: l‘utilizzazione di una siffatta combinazione sinergica tra tali differenti tecniche di preparazione ha permesso di ottenere materiali caratterizzati da strutture e proprietà peculiari. La caratterizzazione di tali materiali è svolta utilizzando le facilities del gruppo di Scienza delle Superfici, come la spettroscopia di fotoelettroni (XPS) o della banda di valenza (UPS), la microscopia ad effetto tunnel o a forza atomica (STM - AFM), la microscopia elettronica e la dispersione energetica dei raggi X indotta dagli elettroni (SEM-EDX), la diffrazione di elettroni lenti (LEED). Allo scopo di caratterizzare maggiormente in dettaglio la struttura e le proprietà chimiche dei materiali preparati sono state usate estensivamente le tecniche di indagine offerte dalla luce di sincrotrone (HR-XPS, NEXAFS, ARPES, ResPES, PEEM), mentre lo studio della reattività catalitica si basa su tecniche derivate dall’analisi elettrochimica, in particolare la voltammetria ciclica ed a scansione lineare del potenziale applicato, nonchè tecniche elettro-dinamiche come la voltammetria su elettrodo rotante. Infine, allo scopo di supportare i dati sperimentali o portare la comprensione delle proprietà dei materiali ad un livello più profondo, simulazioni mediante teoria del funzionale densità (DFT) sono state adottate per un approccio critico allo studio dei materiali preparati (in collaborazione con il gruppo coordinato dalla prof. Cristiana Di Valentin, Università di Milano Bicocca). Durante il corso del dottorato, diverse collaborazioni sono state perseguite con gruppi interni al Dipartimento di Scienze Chimiche o anche Esteri, come l’unità di ricerca “Interfaces and Energy Conversion E19”, dell’università tecnica di Monaco di Baviera (TUM, Technische Universität München, Germania), coordinata dai proff. O. Schneider e J. Kunze-Liebhäuser.

碩士
逢甲大學
工業工程學所
92
Ultra High Purity (UHP) components are highly required in semi-conductor and bio-medical industries for the characteristic of ultra smooth inner surface. As a result, the Abrasive Flow Machining (AFM) becomes one of the key techniques under such requirement for manufacturing UHP components. Not only the AFM increases the inner surface quality of products, but it decreases the labor cost effectively. At the same time, the index of roughness, rate of roughness improvement, and working time can also be concurrently concerned to keep the design requirement and reduce the production cost when AFM applies. The Semiconductor valve’s components that are also called ultra-high purity components can be produced by Abrasive Flow Machining (AFM) process The AFM process can help deburring 、surface finishing and chaffering. This research especially builds up a set of methodology, while having another the consideration of the target claim, by the pioneer experiment designs and analyzes, with build up the valid regression mode, and set up the manufacturing process parameter database, the decision that then build up the manufacturing process parameter's choosing to use supports the mechanism, to provide to make to turn in the guest under the surface accuracy request, can search the manufacturing process control parameter quickly or the type announce, the test that choose to use with the economical parameter with look for to find time, and the decrease try the manpower of the mistake method waste, and the ability is processing time and reaching an improvement of surface rate effectively under, insure the quality of a request of surface. This research with the particular mold equipment design, whets the material, shape and the surface conditions of anticipating the category, and the work pieces for the case example, by the study processes the pressure(Bar) and processes the discharge(in3) and processes circulating three kinds of manufacturing process parameters of number(Cycles), identify the feasibility of the methodology. Through the pioneer experiment design and analysis, build up the regression mode of single target in advance, and be the basis of setting up the manufacturing process parameter database, choosing by the manufacturing process parameter with the mechanism, can find out the best combination of manufacturing process parameter of matching many target claim indeed.

碩士
國立臺灣大學
機械工程學研究所
94
Valve is an important device which controls the flow rate, pressure, and flow direction. The selection of valves depends on the purpose, environment, and design of the usage. Because of the development of science and technology, the valve products become more accurate, so its performance and characteristic have already been the important research projects. The objective of this paper is to study two different types of the ultra high purity valves. In the analysis of flow field, the velocity, pressure, temperature distribution and the valve flow coefficient (Cv) were studied in details with a CFD-RC code. In the stress analysis, the stress distribution and deformation of diaphragms which were oppressed by the mandrel when shutoff were discussed with a ANSYS code. The results can be used as the optimum design basis of the ultra high purity valve.

碩士
國立陽明大學
醫學工程研究所
96
Abstract On the subject of artificial joint improvement, sequential heating process has been used to improve the crosslink ratio of UHMWPE and eliminate free radicals produced by γ-ray irradiation, ex: X3. However, the free radical decay mechanism(with or without oxygen) is still unclear and it takes two different reaction mechanisms to describe the free radical decay mechanisms in two regions; i.e. the crystalline region and amorphous region of UHMWPE. In the present study, a thin-film mass transfer apparatus is constructed to measure the perameability and diffusivity of oxygen in UHMWPE. We discuss the effect of crystallinity and crosslink ratio on the mass transfer behavior in UHMWPE. Also, thermal conductivity, diffusivity and heat capicity of UHMWPE are measured to help establish a heat conduction model. With this model, the dynamic temperature distributions under different heating sequences are analyzed. The results show that crosslink has little effect on oxygen diffusivity, and the permeability increases with crosslink ratio. As for crystalline effect, both permeability and diffusivity decrease with crystallinity. Crystalline laminar has greater effect than crosslink. From the heat conduction model result, under convensional heating process, it takes more than three hours for a cubic of 8cm in length to reach uniform temperature distribution. With heat conduction model and theoretical dynamic uniform temperature profile, we proposed a heating sequence to achieve a uniform crosslink of UHMWPE.

碩士
淡江大學
水資源及環境工程所
83
Chemical Oxygen Demand (COD) for determination by the dichromate reflux method cannot be accurately measured in water containing more than 2,000mg/l of Cl-. Though the procedure 〝 remove chloride─dichromate reflux〞 is developed currently to measure COD in water containing high chloride concentration that the interference may be overcome, the disadvantage is time consuming and waste generation of hazardous mercury. Therefor,in this study adopt procedure of Ultra-Violet spectroscopy and remove chloride-dichromate reflux simultaneously to measure COD in water containing high chloride concentration. Furthermore, comparing result of measuring COD with deferent operation procedure. To assess reasonableness the COD are measured in water containing high chloride by Ultra-Violet spectroscopy. Otherwise,the objective for rapid determination of COD,real- time monitoring in water,and overcome interference for chloride that also simulated model of monitoring for COD to mill water, which relative between multiwavelength absorption and COD value for suitable reference material(RM) of COD with regressive method. The result have shown that: (1) The use of Ultra-Violet Spectroscopy measure COD in water containing high chloride concentration not only rapidly but also simply;moreover it is applied to measure COD of low concentration as Method Detection Limit(MDL) = 0.4mg/l. (2)Ultra-Violet spectroscopy is a suitable method for monitoring COD in water containing high chloride concentration if the water will not contain organic SS and similar to Ultra-Violet absorptive character of reference material. (3) The use of referf ence material for potassium acid phthalate、 sodium oxalate, and that mixing solution measured COD in water by Ultra-Violet spectroscopy,it is quite accuracy for result to predict by 〝standard type model〞 with 250-300nm wavelength.

碩士
國立交通大學
管理學院工業工程與管理學程
107
The gas tungsten arc welding process is commonly used to do ultra-high purity tube for passing high purity gas into semiconductor devices. Nowadays most of welding machine can set the welding parameters according to the manual. However there’re still several of deviations due to many unexpected interference factors. Factors are such as temperature, material variation, welding environment,…etc. On the other hand, the welding specifications from different customers are with different requirements. To be qualified by customer of the stable welding quality, how to quickly find the GTAW welding parameters that is in accordance with the required specification of the new customer, and shorten the verification period all become important challenges. Hence, to use Taguchi method as theoretical basis, analyzing the potential factors through cause & effect analysis, the design of experiment on GTAW welding can figure out the optimized welding parameters by using Minitab 17 software. Minitab 17 can create Taguchi design via orthogonal arrays, Signal-to-Noise Ratio verification which can easily come out the optimum parameters. In this case the welding requirement of the new customers can be quickly verified and satisfied. The production can then start to manufacture all GTAW tubes with the standard which will in the end creating more revenue to company.

碩士
大同大學
材料工程學系(所)
104
In this study, Hexamethyldisilazane (HMDSZ) plasma (PD-HMDSZ) was used to deposit hydrophobic film on polymers such as polyethylene terephthalate (PET), TPU nonwoven and glass substrates. Plasma system is use a bell-type reactor with internal electrode, 13.56MHz, electrode spacing 5 cm, and 10 cm diameter electrodes, power of 150W. The specimen was put into the chamber after cleaning. The chamber was evacuated to 30mtorr and introduce HMDSZ monomer gas for plasma deposition 5 minutes. Then, oxygen plasma etching technique was employed to produce porous structure and to increasing surface roughness of the specimen. Finally, it was treated again with hydrophobic coating by PD-HMDSZ. The result of water contact angle (WCA) reveals that it is more hydrophobic as compared to the one without oxygen plasma post treatment. The surface properties of TPU non-woven can be controlled its hydrophilic and hydrophobic property by plasma treatment. After using oxygen plasma to etch the oxide, it becomes super-hydrophilic and stable even after 20 days. Roughness of surface are dependent on the time of oxygen plasma treatment. A more hydrophobic surface was obtained retreated by PD-HMDSZ, and water contact angle of non-woven TPU increases from 0 degree to 149.8 degree. Porous Ultra High Molecular Weight Polyethylene (UHMWPE) has excellent biocompatibility. It is widely applied in the field of medicine as a biomaterial. It can be used in medical polymer devices, such as heart valves, artificial joints and surgical correction, etc. In this study, HMDSZ monomer was deposited on UHMWPE surface by cold plasma deposition and the change of surface hydrophobicity were investigated after modification. It could be found that the WCA was very stable about thirty days after HMDSZ plasma treatment on UHMWPE. The WCA of oxygen plasma treatment was also stable after ninety days. Using scanning electron microscopy (SEM) the dendritic structures on the surface of 1 minute oxygen plasma treatment could be observed. Over 5 minutes HMDSZ plasma treatment, the surface of substrate became smooth and the hole is disappear. It would be found the creaks on the film. Higher power of oxygen plasma treatment, the deposited film on the surface would be decomposed causing clogging pores. In this study, the effect of the plasma treatment times on the holding holes.