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<p> An investigation is reported of oxygen diffusion in monoclinic zirconia at elevated temperatures. </p> <p> A method was developed for production of solid zirconia spheres of a quality suitable for diffusion measurements. The spheres, 60μ and 90μ diameter were subsequently used for the determination of the coefficient of self-diffusion of oxygen in stoichiometric zirconia at 800°C, 850°C, 900°C, 950°C and 1000°C. Oxygen O18 isotope exchange using mass spectrometry for the gas analysis was employed for this investigation. </p> <p> The oxygen self-diffusion coefficent was found to conform to the Arrhenius equation (see online text for equation) Theoretical considerations indicate that this diffusivity represents virtually the lattice diffusion of oxygen in zirconia. </p> <p> Diffusivities of oxygen in zirconia scale calculated from zirconium oxidation studies are 104 times higher and are believed to be due to short-circuit diffusion through line defects. To substantiate this hypothesis, "slabs" of stoichiometric zirconia scale and irregular, but equiaxed particles of the same material were used for oxygen diffusion experiments employing the same method. The diffusivities for the slabs were 10^3 times higher than those for spheres, supporting the validity of the short-circuit diffusion theory for zirconia scale. </p> <p> Oxygen concentration drop across zirconia scale on metal, during its formation by parabolic kinetics was calculated for 600°C and 850°C, and was found to be 0.04 g/cm3 approximately, while the concentration drop across the interface between the oxide and the oxygen-saturated metal was about 1.07 g/cm3. </p> / Thesis / Doctor of Philosophy (PhD)

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The range of applications and versatility of NMR diffusion measurements [1,2] increase with the speed, accuracy, and the practical lower concentration limits that can be used. For example, faster measurements expand the horizons of diffusion measurements to study reaction kinetics [3,4], as well as simply increasing throughput. Our group has been investigating various approaches for improving the performance of NMR diffusion measurements. Here we present some of our recent advances.

Approved for public release, distribution is unlimited / In this thesis, a series of experiments were performed to characterize the material properties of InGaAs/GaAs for use in a two-color quantum-well IR photodetector (QWIP) design. Results from room temperature studies using cathodoluminescence and photoluminescence indicated light emission at 858 nm and 1019 nm from GaAs and InGaAs, respectively. Using a direct transport imaging technique, an edge dislocation pattern was observed and shown to be confined to the InGaAs layer of the material. A dislocation density measurement was performed and was shown to be less than 2000 lines/cm. Quantitative intensity level measurements indicated fluctuation in the region of dislocations to be less than 30% of the signal to background level. Finally, a spot mode study using the direct transport imaging method was performed to evaluate the feasibility of using this technique for contact-less diffusion length measurements. / Civilian, Department of Air Force

Les verres du système binaire Ag₂S-As₂S₃ sont connus pour être de très bons conducteurs ioniques et l’ajout de HgI₂ permet d’envisager une application des verres du pseudo-ternaire HgI₂-Ag₂S-As₂S₃ en tant que membrane ionique spécifique dédiée au dosage du mercure en solution aqueuse. Les limites de son domaine vitreux ont été vérifiées à l’aide de la diffraction des rayons X. Les évolutions des propriétés macroscopiques des verres, incluant les densités et les températures caractéristiques (Tg, Tc et Tf) ont été analysées de façon systématique. Les propriétés de conduction des verres HgI₂-Ag₂S-As₂S₃ ont été évaluées à l’aide de la spectroscopie d’impédance complexe et de la diffusion du traceur radioactif 108mAg. Un des résultats les plus marquants dans ces verres conducteurs ioniques est l’augmentation de la conductivité lorsque Ag₂S est substitué par HgI₂. Afin de comprendre les mécanismes de conduction mis en jeu, des études structurales ont été menées par spectroscopie Raman, diffusion de neutrons et diffraction des rayons X haute énergie. Pour appréhender la structure de ces verres complexes, des études préalables sur les deux systèmes pseudo-binaires Ag₂S-As₂S₃ et HgI₂-As₂S₃ ont aussi été menées. Les différentes techniques utilisées ont notamment permis de montrer que des réactions d’échanges se produisaient lors de la synthèse. Enfin, la dernière partie de cette thèse est entièrement consacrée à la caractérisation de nouveaux capteurs chimiques pour la détection des ions Hg²+ en solution. Différentes compositions sont testées afin de définir la sensibilité, la limite de détection et les coefficients de sélectivité en présence d’ions interférents. / Glasses of the pseudo-binary system Ag₂S-As₂S₃ are well known to be good ionic conductors and the addition of HgI₂ allows considering the glasses of the pseudo-ternary system HgI₂-Ag₂S-As₂S₃ as ion-membrane dedicated to mercury sensing in aqueous solution. The limits of its vitreous domain were verified by X-ray diffraction. Changes in macroscopic properties of glasses, including density and characteristic temperatures (Tg, Tc et Tm) were systematically investigated. Conduction properties of HgI₂-Ag₂S-As₂S₃ glasses were evaluated using the complex impedance spectroscopy and 108mAg tracer diffusion measurements. One of the most interesting results concerns the conductivity increase if Ag₂S is substituted by HgI₂. To understand the conduction mechanisms involved, structural studies were carried out by Raman spectroscopy, neutron scattering and high-energy X-ray diffraction. To understand the structure of these complex glasses, preliminary studies on the two pseudo-binary systems Ag₂S-As₂S₃ and HgI₂-As₂S₃ were also undertaken. These techniques have underlined exchange reactions that occur during the synthesis. The last part of this research work is entirely devoted to the characterization of new chemical sensors for the detection of Hg²+ ions in solution. Different compositions were tested to determine the sensitivity, detection limit and selectivity coefficients in the presence of interfering ions.