A thesis submitted in ful lment of the requirements for the degree Doctor of Philosophy in Electrical Engineering May 2016 / Modern electrical networks provide an opportunity for inevitable interaction between metal oxide arresters and power system harmonics. Therefore, these arrester devices are continuously exposed to the combined e ect of distorted system voltage and envi- ronmental thermal stresses. Recent studies supported by eld experiments have shown signi cant rise in the leakage current through these surge arrester devices when exposed to ac voltage with harmonics. However, the major shortcoming in the current knowledge and applications of varistor arresters resides on the reliability and the electrical stabil- ity of these overvoltage protection units, when subjected to long-term and continuous distorted ac voltage and thermal stresses from the environment. Commercially-sourced ZnO arresters of similar size and electrical properties are tested using standard ac accelerated degradation procedure or electro-thermal ageing test. The times to degradation, the coe cient of non-linearity, the reference voltages, as well as the clamping voltage measured are used to analyse the reliability and the electrical stability of the metal oxide-based arrester samples. The resistive component of the leakage current is extracted from the measured total leakage current. The three-parameter Weibull probability model is invoked in order to analyze the degradation phenomenon. / MT2016

Hydrothermal synthesis is a widely used technique for the preparation of fine particles. It can be carried out in batch or flow systems, although most studies have used batch reactors below 200 C. More recently, however, continuous hydrothermal synthesis has been employed in near- and supercritical water to obtain metal oxide particles. This technique offers tremendous promise for control of particle characteristics due to the rapidly changing properties of water with temperature and pressure in the critical region. However, the role of temperature in this process is not completely understood. Moreover, agglomeration of particles remains a problem in both batch and continuous hydrothermal techniques. This work is concerned with the use of continuous hydrothermal synthesis at near-critical and supercritical conditions to obtain iron oxide and lithium iron phosphate nanoparticles. Factors that affect size, size-distribution, and morphology of nanoparticles were investigated and the results have been used to resolve differences in the literature concerning the effect of temperature on particle size. It was shown that agglomeration can be minimized by using a protective polymer coating and this appears to be an effective method to control particle size. The continuous hydrothermal technique was also extended to materials other than metal oxides by synthesizing lithium iron phosphate. Differences in the particle sizes obtained using the batch and continuous methods were shown to be due to the different mechanisms of particle formation in the two techniques. Better particle characteristics (size, size distribution and morphology) were obtained using the continuous hydrothermal technique than using the batch hydrothermal method. Iron oxide nanoparticles were also deposited on the surface and in the pores of activated carbon pellets in a batch reactor in order to minimize agglomeration of particles. The resulting iron oxide activated carbon nanocomposites exhibited significant catalytic performance in the oxidation of propanal. Therefore, the use of supercritical water to deposit metal oxide particles on hydrophobic surfaces offers promise for carbon-supported catalyst preparation without the use of toxic or noxious solvents.

Phosphonic acids are known to bind strongly to a variety of metal oxide surfaces. Phosphonic acids were designed in order to impart specific properties to the surface of a range of metal oxides upon formation of a monolayer. A large number of novel phosphonic acids were synthesized and fully characterized. The binding of phosphonic acids to the surface of several metal oxides, such as indium tin oxide (ITO) and barium titanate, was studied in detail and determined to be a mixture of bidentate and tridentate binding modes. The modification of several key surface properties of ITO by phosphonic acid modification was also studied. The work function of ITO could be increased or decreased with respect to unmodified ITO by controlling the dipole of phosphonic acids bound to the surface. Additionally, the surface energy could be substantially lowered by attaching phosphonic acids with non-polar terminal functional groups to the ITO surface. The ability to control these surface properties resulted in organic light-emitting diodes (OLEDs) which showed superior lifetimes and stability with respect to OLEDs incorporating ITO without a phosphonic acid monolayer. In addition, the binding of phosphonic acids to a number of other oxides, such as zinc oxide and zeolites, was also studied.

When a metallic alloy is placed in an oxygen environment, oxide scale may be formed on the metal surface. The continuous growth of such oxide scale is enabled by the diffusion of various ionic species in the scale layer primarily driven by the gradient of chemical potentials of these ionic species. In addition, the molar volume of oxide is typically greater than that of the base metal. Consequently, mechanical stresses are generated in the oxide scale. Such mechanical stress, in return, may affect the diffusion of ionic species resulting in different oxide growth kinetics. Such interaction between ionic diffusion and mechanical stresses and its effect on oxide scale growth have not been studied. The goal of this thesis is to develop a systematic model for oxide scale growth that takes into account the diffusion-stress interaction. To achieve this goal, the coupled equations based on continuum formulas for diffusion and stresses are developed in first part of this study. The chemical potentials are defined as a stress dependent function. The variation of stress can therefore change the diffusion force, which is the gradient of chemical potentials, to affect the ionic species distribution and consequently have effects on the oxidation kinetics. The model is used to investigate several important aspects of oxidation including scale growth kinetics, stress distribution in the oxide scale, void formation near the metal/oxide interface, and initiation of oxide scale spallation. The reactive element effect (REE) during oxidation of reactive element doped alloy is extensively studied in this study using the developed stress-diffusion interaction model. The key information, such as the modification effects of reactive element upon the diffusion properties of ionic species in oxide scale are quantitatively accessed for yttrium doped Cr alloy. Finite element method was used through a User Element subroutine for ABAQUS to solve the fully coupled stress-diffusion equations in 2D domains with accounting for both elastic and inelastic deformations. The REEs are comprehensively investigated by studying the effects of yttrium on interfacial delamination driving force, energy release rate (G), oxide-alloy interface morphology, and defect diffusion. The outcomes of this study give (1) a deeper understanding of how stresses affect the oxidation, (2) a model to simulate oxide scale growth, and (3) design guidelines on rare earth element doping for improving oxidation resistance. The results of this work elucidate the impact and importance of stress-diffusion coupling on oxidation kinetics and mechanical reliability.

A deposition - precipitation method was developed to produce magnesium hydroxide / zeolite 4A (Mg(OH)₂ - Z4A) nanocomposites at mild conditions and the effect of processing variables such as precursor concentration, type of base added, and synthesis time on the composition, size, and morphology of the nanocomposite were studied. It was determined that the precursor concentration, basicity, and synthesis time had a significant effect on the composition, size, and morphology of the deposited magnesium hydroxide (Mg(OH)₂) nanostructures. The properties of the Mg(OH)₂ - Z4A such as surface area, pore volume and composition were characterized. Mg(OH)₂ - Z4A samples and bare zeolite 4A were dispersed in Ultem® polymer to form a mixed matrix membrane. The thermal and mechanical properties of the resulting films were investigated. It was found that the addition of rigid bare zeolites into the polymer decreased the mechanical properties of the polymer composite. However, some of these adverse effects were mitigated in the polymer composite loaded with Mg(OH)₂ - Z4A samples. Isotherms for the adsorption of Mg(OH)₂ petals on zeolite 4A were measured in order to determine the optimum conditions for the formation of magnesium hydroxide / zeolite 4A nanocomposites at ambient conditions. The loading of the Mg(OH)₂ can be determined from the adsorption isotherms and it was also found that the adsorption of Mg(OH)₂ on zeolite A occurs via 3 mechanisms: ion exchange, surface adsorption of Mg²⁺ ions, and surface precipitation of Mg(OH)₂. Without the addition of ammonium hydroxide, the predominant processes are ion exchange and surface adsorption of Mg²⁺ ions. In the presence of ammonium hydroxide, Mg(OH)₂ crystals are precipitated on the surface of zeolite 4A at moderate Mg²⁺ ions concentration and the loading of Mg(OH)₂ was found to increase with increasing Mg²⁺ ions concentration. A detailed examination of the interactions between Mg(OH)₂ and functional groups on the zeolite surface was conducted. Solid-state 29Si, 27Al, and 1H NMR spectra were coupled with FTIR measurements, pH and adsorption studies, and thermogravimetric analyses to determine the interactions of Mg(OH)₂ with surface functional groups and to characterize structural changes in the resulting zeolite after Mg(OH)₂ deposition. It was discovered that acid - base interactions between the weakly basic Mg(OH)₂ and the acidic bridging hydroxyl protons on zeolite surface represent the dominant mechanism for the growth of Mg(OH)₂ nanostructures on the zeolite surface.

Metal organic frameworks (MOFs) and metal oxide-MOF composites were investigated for adsorption and oxidation of carbon monoxide. Metal oxides were successfully included in MOFs via both impregnation and encapsulation. UiO-66, a zirconium-based MOF, was impregnated with magnesium or cobalt oxide. Cobalt oxide in UiO-66 increases the room temperature CO capacity and shows increased adsorption at 65°C due to strong cobalt-CO interactions. Titania and magnetic nanoparticles were encapsulated in HKUST-1, a copper-based MOF. Including titania in HKUST-1 lowers the CO oxidation onset temperature by over 100°C compared with HKUST-1, and the composite reaches complete conversion by 250°C. HKUST-1 with magnetic nanoparticles shows enhanced structural stability and increased room temperature adsorption of CO and hexane. MOF-74, an isostructural family with coordinatively unsaturated metal centers of cobalt, magnesium, nickel, or zinc, was investigated for the metal center’s impact on stability and adsorption. Pre-treatment conditions to optimize accessibility were found that maximize solvent removal while retaining structural integrity. The impact of air exposure on equilibrium CO capacity was investigated, and these predictions were compared to dynamic conditions, separating CO from nitrogen or air at room temperature. The cobalt analog loses only 25% of its CO capacity with air exposure, retaining higher capacity than the other analogs under ideal conditions. Unlike cobalt, the magnesium analog does not follow the predicted trends with air exposure, having higher dynamic capacities with pre-exposed samples. Under all dynamic conditions, the nickel analog oxidized a portion of the carbon monoxide feed.

Recent studies have demonstrated the omnipresence of antibacterial agents in the aquatic environment due to high usage and widespread applications of these compounds in medicine and agriculture, raising concerns over proliferation of antibiotic-resistant bacteria and other adverse health effects. Tetracyclines (TCs) are among the most widely used antibiotics and their fate and transformation in the soil-water environment are not yet well understood. Based on TCs' strong tendency to interact with metals, their environmental fate and transport are expected to be greatly influenced by metal species commonly present in waters and soils and thus the focus of this study. The study results show that TCs are highly susceptible to oxidative transformation mediated by dissolved Mn(II) and Cu(II) ions and manganese dioxide under environmentally relevant conditions. The oxidative transformation can occur via different TC structural moieties and reaction pathways when different metal species are involved, leading to complicated product formation patterns. It was also found that Al oxide surfaces can promote the acid-catalyzed isomeration and dehydration of TCs. To better evaluate the surface reactions of Mn oxide with TCs and other compounds, a new kinetic model was successfully developed to describe the complex reaction kinetics based on the experimental results with TCs and three other classes of antibacterial agents. Overall, this work significantly advances the fundamental understanding of the reaction mechanisms of TC compounds and provides the knowledge basis for better risk assessment of these compounds in the environment.

Thesis (M.S.)--Mississippi State University. Department of Chemistry. / Title from title screen. Includes bibliographical references.

Thesis (M.S.) -- Mississippi State University. Dave C. Swalm School of Chemical Engineering. / Title from title screen. Includes bibliographical references.

Ce travail de thèse a été réalisé grâce à une collaboration entre le laboratoire IMS (Université Bordeaux 1, CNRS) et la société STANTUM dans le cadre d’une bourse CIFRE.La thématique étudiée se positionne dans le domaine en pleine expansion des interfaces tactiles intégrées dans les écrans. La mise en production ces dernières années des systèmes multi-touches a permis l’arrivée sur le marché grand public de nombreux dispositifs tels que les GPS, les Smartphones ou encore les tablettes. Malgré tout, de nombreux problèmes sont encore à résoudre, en particulier la possibilité d’avoir une écriture naturelle via un stylet, en posant la main sur la tablette comme sur une feuille de papier. Après un rappel sur l’historique et sur l’intérêt des dalles tactiles comme interface homme/machine, le premier chapitre présente les principales technologies actuelles et la technologie iVSM développée par STANTUM. La structure des dalles tactiles et les différentes étapes de fabrication de ces dernières sont abordées dans le deuxième chapitre. Nous avons ensuite développé un modèle théorique permettant de décrire le fonctionnement et les limitations de la technologie. Ces dernières peuvent survenir lorsque l’utilisateur écrit sur la dalle tactile et peuvent empêcher, dans certaines configurations, une bonne reconnaissance d’écriture. Deux approches sont proposées dans le quatrième chapitre pour corriger ces phénomènes inhérents : la couche résistive et les diodes intercalées. Le dernier chapitre est dévolu à la partie expérimentale. Tout d’abord, les différentes approches dédiées à la réalisation d’une couche résistive, que ce soit par enduction par sol-gel ou encore par pulvérisation cathodique, sont présentées. Pour la caractérisation des dalles tactiles, nous avons mis en place des facteurs de qualité permettant de juger efficacement de l’amélioration des performances et avons également pris en compte les paramètres de dureté, d’adhésion et surtout d’état de surface des couches intermédiaires. La seconde partie de ce chapitre se focalise sur la réalisation des diodes par les approches couches minces (jonction tunnel par PVD, diode organique et jonction PN en silicium amorphe). / This work comes from close collaboration between IMS laboratory (University of Bordeaux 1, CNRS) and STANTUM. This thesis is focused on tactile interface integrated on display. Recently multitouch systems became compatible for consumer electronic market which led to incoming devices such as GPS, Smartphones and tablet PC. However troubles still remained. Performing the discrimination between finger, palm and stylus was still an insuperable technology step to provide natural handwriting input on a display. After reminding a brief historic and the interest as human to machine interface, the first chapter presents the dominating touch screen technologies at the moment and the iVSM STANTUM technology. Touch screen structure and fabrication processes are approached, including industrial step as laser patterning or stencil printing. Then a theoretical model is detailed to explain the iVSM scanning engine and the inherent phenomena. These latter can occur when user is writing on the display with stylus in certain configurations. Two approaches are discussed in the third chapter in order to cut off or at least decrease those phenomena amplitude: the resistive layer and the embedded matrix diodes. The last chapter is dedicated to experimental results. Firstly, several processes, as doctor-blade and physical vapor deposition, are explained. Characterization is performed in using quality factors, to specifically evaluate inherent phenomena decreasing. Hardness, roughness and surface morphology are also discussed in this chapter. The second part is focused on embedded matrix diodes using thin film technologies (tunnel junction, organic diode and a-Si PN junction).