Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1931. / The entire thesis text is included in file. Typescript. Illustrated by author. Title from title screen of thesis/dissertation PDF file (viewed February 9, 2010) Includes bibliographical references (p. 53) and index (p. 54).

Greenhouse gases including carbon dioxide are formed by the consumption of carbon anodes during aluminium production, making it a major contributor to global emissions. This consumption necessitates replacement of the anodes in electrolysis cells every 2-3 weeks. A solution to the environmental and economic problems posed may be found in an inert anode which facilitates direct decomposition of alumina to aluminium and oxygen. Finding a material which is stable in the aggressive high temperature electrolyte poses a major materials engineering challenge. In this study, apparatus was designed and constructed to allow cermets to be manufactured in the laboratory, and a method of establishing electrical contact developed. Additionally, apparatus was designed to perform high temperature conductivity measurements on the cermets. Nickel ferrite-nickel oxide-copper-silver cermets were prepared and conductivity measured. No significant change in the activation energy of the conduction process was observed for cermets with 40wt% excess NiO compared to those with no excess. No significant difference in conductivity was observed between the compositions at cell operating temperatures. Voltammetric techniques were used to identify anode processes. High anodic currents associated with oxidation of anode constituents were observed repeatedly, the magnitude of which could not simply explained by oxidation of the metal phase. This suggested the formation of other reduced species during sintering (confirmed by thermodynamic analysis). Gaseous oxidation products were confirmed at the anode at potentials expected for oxygen evolution, and the application of high potentials (>4V vs Al/A13+) was found to passivate the cermets. Voltammetry and chemical microanalysis (using scanning electron microscopy (SEM) with energy dispersive x-ray spectrometry (EDS)) showed that copper in the cermets was depleted at the anode surface, apparently by oxidation then dissolution into the electrolyte. The inclusion of silver powder into the cermets was not found to improve the corrosion resistance of the cermets, existing almost entirely as a discrete phase. Preliminary SEM and EDS results highlighted several areas for further investigation regarding the compounds formed during sintering and electrolysis and the anode corrosion mechanisms. Of particular interest were a copper nickel oxide formed during sintering and complex oxyfluorides containing anode and bath constituents, formed during electrolysis.

Mémoire (M. Sc. A.)-- Université du Québec à Chicoutimi, 1984. / Bibliographie: f. 101-102. Document électronique également accessible en format PDF. CaQCU

Titre de l'écran-titre (visionné le 8 août 2023) / Les anodes de carbone sont des composants essentiels du procédé Hall-Héroult utilisé dans l'industrie de l'aluminium primaire. La mise en forme des anodes par compactage ou vibrocompactage a un impact significatif sur leur qualité et leurs différentes propriétés. La présence de gradients de densité dans les anodes peut causer leur surconsommation dans les cuves d'électrolyse et réduire leur performance. Ce projet vise à étudier le comportement thermomécanique de la pâte d'anode lors de sa mise en forme, à modéliser ce comportement et à examiner l'effet de la géométrie du moule sur la distribution de la densité dans l'anode. L'effet de la température de la pâte d'anode sur son comportement mécanique lors de la compaction a été étudié expérimentalement. Dans ce contexte, des essais de compaction monotones et des essais de friction ont été menés à des températures situées entre 130 °C et 170 °C. Les résultats ont révélé les effets importants de la température sur le comportement non linéaire de la pâte et ont également permis de déterminer les coefficients de friction statique et dynamique de l'interface pâte/acier. Une loi de comportement thermoviscoplastique non linéaire a été développée afin de modéliser le comportement de la pâte d'anode lors de sa compaction. Cette loi est basée sur un cadre thermodynamique, la théorie des grandes déformations et le concept de configuration naturelle. Les paramètres de la loi évoluent durant la compaction en fonction de la densité et de la température. Ils ont été identifiés à l'aide d'une procédure d'identification inverse. La loi de comportement a été implémentée dans le logiciel de simulation par éléments finis Abaqus à travers une sous-routine VUMAT, destinée à l'analyse dynamique explicite. Les simulations par éléments finis portant sur la mise en forme par compaction de géométries complexes ont été en mesure de prédire avec une bonne précision les profils de densité mesurés par tomodensitométrie. L'effet de la température ainsi que de différentes caractéristiques géométriques, telles que des arêtes chanfreinées et arrondies, des tourillons et des rainures de différentes dimensions, ont été étudié à l'aide de simulations par éléments finis. Dans cette optique, de petites anodes ont été compactées par éléments finis afin de déterminer si les paramètres susmentionnés peuvent améliorer l'uniformité de la densité. Par la suite, des simulations par éléments finis ont été réalisées sur une anode industrielle et différentes modifications de la géométrie du moule ont été proposées. Les résultats de ces simulations suggèrent que la réduction de la taille des rainures et la modification de leur géométrie pourraient améliorer de façon significative l'uniformité de la densité des anodes industrielles. / Carbon anodes are essential components of the Hall-Héroult process used in the primary aluminium industry. The anode forming process by compaction or vibrocompaction has a significant impact on their quality and properties. The presence of density gradients in the anode can cause carbon overconsumption in the electrolysis cells and negatively affect their performance. This project aims to study the thermomechanical behavior of the anode paste during compaction, to model this behavior and to examine the effect of the mold geometry on the density distribution in the anode. The effect of the anode paste temperature on its mechanical behavior during compaction was studied experimentally. In this context, monotonic compaction tests and friction tests were conducted at temperatures between 130 °C and 170 °C. The results revealed the significant effect of temperature on the nonlinear behavior of the paste and also allowed the determination of the static and kinetic friction coefficients of the paste/steel interface. A nonlinear thermo-viscoplastic constitutive law was developed to model the behavior of the anode paste during compaction and is based on a thermodynamic framework, the finite strain theory and the concept of natural configuration. The constitutive law's material parameters evolve during compaction as a function of density and temperature and were identified using an inverse identification procedure. The constitutive law was implemented in the finite element simulation software Abaqus through a VUMAT subroutine, intended for explicit dynamic analysis. The finite element simulations of the compaction of complex geometries were able to predict with good accuracy the density profiles measured by X-ray computed tomography. The effect of temperature as well as of different geometrical features, such as chamfered and rounded edges, stub holes and slots of different dimensions, was investigated using finite element analysis. To this end, small anodes were compacted through finite element simulations to determine if the aforementioned parameters can improve the density uniformity. Additional finite element simulations were performed on an industrial anode and different modifications to the mold geometry were proposed. The results of these simulations show that reducing the size of the slots and modifying their geometry could improve the density uniformity of industrial anodes.

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<p>The performance of negative electrodes based on Si nanoparticles for Li-ion batteries has been investigated. Electrodes consisted of Si nanoparticles, carbon black and Na-CMC. The investigation covered electrode production parameters such as pre-treatment of the Si-powder, different emulsifiers and cycling with two different electrolytes. Testing of the electrodes’ performance was done electrochemically with two different galvanostatic approaches: constant charge rate and stepped-up charge rate. Electrodes’ morphology, stability and surface chemistry were also evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thickness measurements and X-ray photoelectron spectroscopy (XPS).</p><p> </p><p>High electrode capacities were achieved though strong variation depending on electrode thickness has been found. For the best performing electrodes the capacity exceeded 1600 mAh/g with slight fading after 10-15 cycles. The difference in performance could not be assigned to the different production parameters, but had a clear correlation to the thickness of the electrode and the different electrolytes used. Propylene carbonate based electrolyte gives a lower coulombic efficiency and lower capacity retention than an ethylene carbonate-diethyl carbonate based electrolyte. The electrodes could not store any capacity at cycling rates higher than 2C, but were not damaged by cycling rates up to 50C. SEM micrographs revealed that a solid electrolyte interface (SEI) was formed on the electrodes during cycling and their surface analysis by XPS suggested that the SEI was formed by decomposition of electrolyte components.</p>

The performance of negative electrodes based on Si nanoparticles for Li-ion batteries has been investigated. Electrodes consisted of Si nanoparticles, carbon black and Na-CMC. The investigation covered electrode production parameters such as pre-treatment of the Si-powder, different emulsifiers and cycling with two different electrolytes. Testing of the electrodes’ performance was done electrochemically with two different galvanostatic approaches: constant charge rate and stepped-up charge rate. Electrodes’ morphology, stability and surface chemistry were also evaluated by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thickness measurements and X-ray photoelectron spectroscopy (XPS).   High electrode capacities were achieved though strong variation depending on electrode thickness has been found. For the best performing electrodes the capacity exceeded 1600 mAh/g with slight fading after 10-15 cycles. The difference in performance could not be assigned to the different production parameters, but had a clear correlation to the thickness of the electrode and the different electrolytes used. Propylene carbonate based electrolyte gives a lower coulombic efficiency and lower capacity retention than an ethylene carbonate-diethyl carbonate based electrolyte. The electrodes could not store any capacity at cycling rates higher than 2C, but were not damaged by cycling rates up to 50C. SEM micrographs revealed that a solid electrolyte interface (SEI) was formed on the electrodes during cycling and their surface analysis by XPS suggested that the SEI was formed by decomposition of electrolyte components.

One of the major technical challenges towards a viable H2S//Air SOFC is to identify and develop anode materials that are electronically conductive, chemically and electrochemically stable, and catalytically active when exposed to H2S-rich environments. The corrosive nature of H2S renders most traditional state-of-the-art SOFC anode materials (Ni, Pt, Ag) useless for long-term cell performance even at very low sulfur concentrations. In my doctoral thesis work, a new class of perovskite-based anodes was developed for potential use in SOFCs operating with H2S and sulfur-containing fuels. Cermets from this family of materials have shown excellent chemical stability and electrochemical performance at typical SOFC operating conditions. As an added benefit, they appear to preferentially oxidize H2S over hydrogen, as suggested by open circuit voltage, impedance spectra, and cell performance measurements obtained using various H2S-H2-N2 fuel mixtures. Cell power output values were among the highest reported in the literature and showed no significant deterioration during 48-hour testing periods. Impedance measurements indicated overall cell resistances decreased with increasing temperature and H2S content of the fuel. This behavior is starkly different from that of contemporary SOFC anodes, where the presence of H2S usually increases overall polarization resistance and ultimately destroys the cell. Results are promising due to the drastic improvement in sulfur tolerance compared to the current generation of SOFC power systems.

Thesis (M.Eng.(Hons.))--University of Wollongong, 2003. / Typescript. Includes bibliographical references: leaf 99-106.