Thesis (Ph.D.) - University of St Andrews, June 2009. / Restricted until 1st December 2009.

Thesis (Ph. D.)--Florida State University, 2004. / Advisor: Dr. Jim P. Zheng, Florida State University, College of Engineering, Dept. of Electrical and Computer Engineering. Title and description from dissertation home page (viewed Jan. 13, 2005). Includes bibliographical references.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18445号 / 理博第4005号 / 新制||理||1577(附属図書館) / 31323 / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)教授 前野 悦輝, 教授 石田 憲二, 教授 田中 耕一郎 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

Le ruthénium, issu du retraitement des combustibles usés de type Uranium-Oxyde a une très faible solubilité dans les verres de conditionnement de déchets radioactifs. Il précipite dans ces verres à l'état liquide sous forme de particules de RuO2 polyédrique ou aciculaire. Parce que leurs morphologies et leurs dispersions peuvent influencer les propriétés physico-chimiques des verres, la connaissance et le contrôle de leur mécanisme de formation sont d'extrême importance. Tout l'enjeu de cette thèse est de déterminer les différents chemins réactionnels de transformation du ruthénium, présent au sein du déchet calciné, lors de l'élaboration des verres. Par une approche de simplification progressive nous étudions les interactions entre la fritte de verre et des composés simples (NaNO3-RuO2) et plus complexes (calcinat NaNO3-RuO2- Al2O3). Grâce à l'apport de la microscopie et du XANES in situ en température nous suivons l'évolution de la composition, la spéciation et la morphologie des phases intermédiaires contenant du ruthénium. Ces composés sont caractérisés à l'état solide par MEB, DRX, HRTEM et spectroscopie d'absorption X au seuil K du ruthénium. Cette approche combinée nous permet de montrer que la modification de la spéciation du ruthénium au cours de l'élaboration du verre est à l'origine du contrôle de la morphologie des particules de RuO2 dans le verre. En particulier, la formation d'un intermédiaire réactionnel (Na3RuO4) est une des étapes fondamentales à l'origine de la précipitation de RuO2 de morphologie aciculaire. La formation de polyèdres dans le verre résulte au contraire de l'interaction directe de particules de RuO2 avec le verre à l'état liquide. / Ruthenium, arising from the reprocessing of spent uranium oxide fuel, has a low solubility in glass melt. It crystallizes in the form of particles of RuO2 of acicular or polyhedral morphology dispersed in fission product and actinides waste containment glass. Since the morphology of these particles strongly influences the physico-chemical properties, the knowledge and the control of their mechanism of formation are of major importance. The goal of this work is to determine the chemical reactions responsible for the formation of RuO2 particles of acicular or polyhedral shape during glass synthesis. Using a simplification approach, the reactions between RuO2-NaNO3, and more complex calcine RuO2-Al2O3-Na2O and a sodium borosilicate glass are studied. In situ scanning electron microscopy and XANES at increasing temperatures are used to follow changes in composition, speciation and morphology of the ruthenium intermediate species. Those compounds are thoroughly characterised by SEM, XRD, HRTEM, and ruthenium K-edge X-ray absorption spectroscopy. This combined approach allows us to show that the ruthenium speciation modification during vitrification is the key of control of the morphology of RuO2 particles in the glass. In particular, the formation of a specific intermediate compound (Na3RuO4) is one of the main steps that lead to the precipitation of needle-shaped RuO2 particles in the melt. The formation of polyhedral particles, on the contrary, results from the direct incorporation of RuO2 crystals in the melt followed by an Ostwald ripening mechanism.

Propylene epoxidation reaction was investigated on catalytic surfaces of chlorinated copper(I) oxide and ruthenium(IV) oxide using periodic density functional theory (DFT). Cu2O(001) and (110) surface of RuO2 was selected to generate chlorinated surfaces to be used in the study. Besides epoxidation, other reactions that compete with epoxidation were also studied such as formations of allyl-radical, acrolein, acetone on chlorinated Cu2O(001) and formations of propionaldehyde, allyl-radical and acetone on chlorinated RuO2(110) surface. Path of each reaction was determined by CI-NEB method and transition state analyses. Generally accepted stable surface intermediate mechanism was utilized in reactions to final products. The surface intermediate favorable on the surfaces in this study was determined to be the intermediate that is not preferable on metallic surfaces under low oxygen. On chlorinated Cu2O(001) surface, formation of propylene oxide, acetone and acrolein have higher probability than gas phase allyl-radical since the desorption energy of allyl-radical was calculated to be 70kcal/mol which is a relatively high value. In fact it is desirable since gas phase allyl-radical is known to be the precursor of combustion products. On chlorinated RuO2(110) surface, desorption Propylene epoxidation reaction was investigated on catalytic surfaces of chlorinated copper(I) oxide and ruthenium(IV) oxide using periodic density functional theory (DFT). Cu2O(001) and (110) surface of RuO2 was selected to generate chlorinated surfaces to be used in the study. Besides epoxidation, other reactions that compete with epoxidation were also studied such as formations of allyl-radical, acrolein, acetone on chlorinated Cu2O(001) and formations of propionaldehyde, allyl-radical and acetone on chlorinated RuO2(110) surface. Path of each reaction was determined by CI-NEB method and transition state analyses. Generally accepted stable surface intermediate mechanism was utilized in reactions to final products. The surface intermediate favorable on the surfaces in this study was determined to be the intermediate that is not preferable on metallic surfaces under low oxygen. On chlorinated Cu2O(001) surface, formation of propylene oxide, acetone and acrolein have higher probability than gas phase allyl-radical since the desorption energy of allyl-radical was calculated to be 70kcal/mol which is a relatively high value. In fact it is desirable since gas phase allyl-radical is known to be the precursor of combustion products. On chlorinated RuO2(110) surface, desorption observed to be possible on chlorinated RuO2(110) surface but not possible on chlorinated Cu2O(001). When activation barriers and desorption energies of all possible reactions are compared on chlorinated RuO2(110) surface / gas phase propylene oxide generated directly seems as the preferable product with allylradical although it was computed to have high desorption energy. Comparison of activation barriers obtained in this study on chlorinated Cu2O(001) with the barriers of nonchlorinated surface revealed chlorine slightly increases the activation barrier of unwanted allylic hydrogen stripping and hence slightly decreases the probability of occurance. When chlorine is placed closer to reaction site, activation barrier of allylic hydrogen stripping reaction increases further. The effect of chlorine might be electronic since the charge of oxygen at reaction site slightly becomes less negative when the place of chlorine gets closer to the reaction site on the surface. Similar comparison between chlorinated and nonchlorinated RuO2(110) surfaces revealed that chlorine addition does not improve the surface toward propylene oxide formation, rather it is detrimental as chlorine addition caused a decrease in unwanted allylic hydrogen stripping reaction.

Hydrogen production is dependent on natural gas, 90% in the U.S. and 48% of the world's production. Natural gas supply is dwindling and it's price is increasing. Greenhouse gases and air pollutants are emitted when natural gas is used. In a single product production facility, coal is not competitive with natural gas for hydrogen production at current prices. Hydrogen production by direct electrochemical dissociation of water requires a relatively high voltage.Techniques have been developed for manufacturing hydrogen as a lucrative byproduct of IGCC electric power generation, refinery sulfur production and sulfuric acid production for fertilizer production. Laboratory experiments have been conducted on small systems to advance the technology and full size commercial plants have been conceptualized and analyzed to establish economic viability.In this thesis, a low voltage electrochemical hydrogen production technique has been developed that entails scavenging of the anode with sulfur dioxide. In an electrochemical cell hydrogen is produced at the negative electrode while the positive electrode is bathed in sulfur dioxide which is oxidized with water to sulfuric acid. The presence of SO2 substantially reduces the equilibrium voltage relative to that required for the direct dissociation of water into hydrogen and oxygen. Also sulfuric acid is a more valuable byproduct than oxygen. More sulfuric acid is produced than any other chemical commodity in the U.S. and is a major economic indicator. Hydrogen produced by the electrochemical route being discussed in this thesis illustrates industrial possibilities for large scale-up, economical hydrogen production.In an electrochemical cell, an equilibrium voltage of 1.23 volts is required to decompose water into hydrogen and oxygen. The presence of sulfur dioxide to scavenge the anode can reduce the equilibrium voltage from 1.23 volts to 0.17 volts. The equations shown below are reactions showing the energy requirements.2H2Oâ?? 2H2 + O2 - 4 Faradays @ 1.2Vâ?? 2SO2 + 4H2O 2H2SO4 + 2H2 - 4 Faradays @ 0.17V The thermochemical free energy is reduced from 113kcal/mole to 15kcal/mole if sulfur dioxide is used as a scavenger.In this work, extensive studies to determine the most effective electrodes and catalysts have been carried out. The possibilities for photo electrochemical implementation have been investigated and cell design optimization has been performed Experimental methods and results will be presented and discussed.

Philosophiae Doctor - PhD / Supercapacitors are charge-storage devices. Compared to batteries, they have higher power density, more excellent reversibility and longer cycle life. Therefore, supercapacitors have played an increasingly important role in the fields of power source especially in automotive applications, such as electric and hybrid electric vehicles. The higher power density of supercapacitors offers improved vehicle acceleration and the ability to recover more energy from regenerative breaking, since they can be charged and discharged at high current. Generally, the key for supercapacitors to achieve high specific power depends on the inherent properties and the surface areas of their electrode materials. Therefore, current research in the field of supercapacitors has been carried out with increased emphasis on the development of new electrode materials. Optimal novel synthesis of electrode materials for supercapacitor application in hybrid vehicles was accomplished with polypyrrole nanowires, manganese oxide and its carbon composites, ruthenium oxide and its carbon composites being the products. A set of structural and chemical parameters influencing the performance of synthesized electrode materials were identified. Parameters included crystallinity, particle size, particle size distribution, surface area, electrochemical activity. A large range of analytical tools were employed in characterizing the electrode materials of interest. High accuracy and precision in the quantitative and qualitative structural characterization of electrode materials collected by x-ray diffractometry, transmission electron microscopy, scanning electron microscopy and Fourier transform infra-red spectroscopy was demonstrated. N₂-physisorption produced surface area and pore size distribution data of high quality. Cyclic voltammetry, charge and discharge cycling, electron impedance spectroscopy were employed in the electrochemical characterization of the synthesized electrode materials and both qualitative and quantitative information obtained. The techniques were able to discriminate between various synthesized electrode materials and identify the highly electroactive materials. Preparation variables could be critically evaluated for the synthesis of electrode materials. The techniques were deemed to be applicable in discriminating high and low activity electrode materials based on their structural and chemical properties.

As a very promising material of copper diffusion barrier for next generation microelectronics, Ru has already obtained a considerable attention recently. In this dissertation, we investigated ruthenium and ruthenium oxide electrochemical properties and the application as a copper diffusion barrier. Cu under potential deposition (UPD) on the RuOx formed electrochemically was first observed. Strong binding interaction, manifesting by the observed Cu UPD process, exists between Cu and Ru as well as its conductive ruthenium oxide. Since UPD can be conformally formed on the electrode surface, which enable Ru and RuOx has a potential application in the next generation anode. The [Cl-] and pH dependent experiment were conducted, both of them will affect UPD Cu on Ru oxide. We also found the Cu deposition is thermodynamically favored on RuOx formed electrochemically. We have studied the Ru thin film (5nm) as a copper diffusion barrier. It can successfully block Cu diffusion annealed at 300 oC for 10min under vacuum, and fail at 450 oC. We think the silicidation process at the interface between Ru and Si. PVD Cu/Ru/Si and ECP Cu/Ru/Si were compared each other during copper diffusion study. It was observed that ECP Cu is easy to diffuse through Ru barrier. The function of RuOx in diffusion study on Cu/Ru/Si stack was discussed. In pH 5 Cu2+ solution, Ru and Pt electrochemical behavior were investigated. A sharp difference was observed compared to low pH value. The mechanism in pH 5 Cu2+ solution was interpreted. An interesting compound (posnjakite) was obtained during the electrochemical process. An appropriate formation mechanism was proposed. Also Cu2O was formed in the process. We found oxygen reduction reaction is a key factor to cause this phenomenon.

No description available.

Strongly correlated metals are known to give rise to a variety of exotic states. In particular, if a system is tuned towards a quantum critical point, new ordered phases may arise. Sr₃Ru₂O₇ is a quasi-two dimensional metal in which field-tuned quantum criticality has been observed. In very pure single crystals of this material, a phase with unusual transport properties forms in the vicinity of its quantum critical point. Upon the application of a small in-plane field, electrical resistivity becomes anisotropic, a phenomenon which has led to the naming of this phase as an `electron nematic'. The subject of this thesis is a study of the electrical transport in high purity crystals of Sr₃Ru₂O₇. We modified an adiabatic demagnetisation refrigerator to create the conditions by which the entire temperature-field phase diagram can be explored. In particular, this allowed us to access the crossover between the low-temperature Fermi liquid and the quantum critical region. We also installed a triple axis `vector magnet' with which the applied magnetic field vector can be continuously rotated within the anisotropic phase. We conclude that the low- and high-field Fermi liquid properties have a complex dependence on magnetic field and temperature, but that a simple multiple band model can account for some of these effects, and reconcile the measured specific heat, dHvA quasiparticle masses and transport co-efficients. At high temperatures, we observe similarities between the apparent resistive scattering rate at critical tuning and those observed in other quantum critical systems and in elemental metals. Finally, the anisotropic phase measurements confirm previous reports and demonstrate behaviour consistent with an Ising-nematic, with the anisotropy aligned along either of the principal crystal axes. Our observations are consistent with the presence of a large number of domains within the anisotropic phase, and conclude that scattering from domain walls is likely to contribute strongly to the large measured anisotropy.