Global ETD Search

1	Dégradation chimique de l’interface cathodique carbone-fonte de cellules de production d’aluminium Brassard, Martin January 2017 (has links) Les producteurs d’aluminium sont des acteurs majeurs dans l’économie du Québec. Le métal gris est apprécié pour sa légèreté et sa résistance à la corrosion. Bien qu’il possède des qualités indéniables, sa production consomme une quantité considérable d’électricité. L’amélioration de l’efficacité énergétique du procédé est donc primordiale d’un point de vue économique et environnemental. L’étude du contact électrique entre le carbone et la fonte à l’intérieur de l’ensemble cathodique fait partie de la liste des paramètres pour optimiser la consommation énergétique de la cellule Hall-Héroult. Ce contact doit offrir une résistance minimale au passage du courant nécessaire pour la réaction d’électrolyse. Au cours du temps, la qualité du contact se dégrade en raison de la transformation physique et chimique des matériaux. Cette thèse se concentre sur l’étude de la dégradation chimique de la surface de la fonte. La première partie étudie la pénétration des composés chimiques provenant du bain d’électrolyse à l’intérieur du bloc de carbone. Le gonflement sodique suit généralement la diffusion du sodium, un sous-produit de la réaction cathodique, et du bain. Le gonflement causé par le sodium a été mesuré directement à l’aide de LVDT alors que la diffusion du bain électrolytique a été déterminée par microtomographie à rayons X. La seconde partie évalue le mécanisme de la dégradation du contact électrique entre le carbone et la fonte. Des travaux en laboratoire ont été réalisés pour quantifier l’impact des paramètres d’opération. Les résultats obtenus ont été comparés par la suite à des échantillons industriels provenant de deux technologies pour évaluer leur degré de dégradation. Un modèle numérique a été calibré à partir de ces résultats pour estimer l’effet de la dégradation de la fonte sur la chute de voltage cathodique. Les résultats démontrent que les paramètres d’opération de la cellule d’électrolyse ont des effets sur la vitesse de pénétration des espèces chimiques dans le bloc de carbone. Un bain plus riche en sodium ou une densité de courant cathodique plus élevée augmente la vitesse de pénétration. La présence d’une nappe d’aluminium au démarrage de l’électrolyse au contraire divise le gonflement et la pénétration du bain de moitié. La vitesse de dégradation de la fonte suit la même tendance. De plus, une augmentation de température de 50 °C provoque une fusion partielle de la surface de la fonte. Ces résultats intégrés au modèle numérique montre que la dégradation du contact entre le carbone et la fonte augmente la chute de voltage cathodique mais aussi change la distribution du courant à la surface du bloc de carbone. La détermination du mécanisme de dégradation de la fonte par des essais en laboratoire combinée avec la pénétration des espèces chimiques constitue l’apport original de cette thèse et ceci permet d’éclaircir le processus d’évolution de ce contact électrique sous condition d’opération. Hall-Héroult Aluminium Carbone Fonte Rapoport Cryolite Dégradation Résistance de contact
2	Étude de phénomènes chimiques au contact entre le bloc cathodique et la barre collectrice d'une cellule d'électrolyse d'aluminium Lebeuf, Martin January 2012 (has links) La production d'aluminium est une industrie importante au Québec. Les propriétés de ce métal le vouent à de multiples usages présents et futurs dans le cadre d'une économie moderne durable. Toutefois, le procédé Hall-Héroult est très énergivore et des progrès demeurent donc nécessaires pour en diminuer les coûts financiers et environnementaux. Parmi les améliorations envisageables de la cellule d'électrolyse se trouve le contact entre la cathode et la barre collectrice, qui doit offrir une faible résistivité au passage du courant électrique. En cours d'opération de la cellule, ce contact a tendance à se dégrader, générant des pertes énergétiques significatives. Les causes de cette dégradation, pouvant provenir de phénomènes chimiques, thermiques, mécaniques et/ou électriques, demeurent mal comprises. Le but du présent projet était donc d'étudier les phénomènes chimiques se produisant au contact bloc-barre de la cellule d'électrolyse Hall-Héroult. En premier lieu, un aspect crucial à considérer est la pénétration du bain électrolytique dans la cathode, car des composés de bain atteignent éventuellement la barre collectrice et peuvent y réagir. À cet effet, une méthode novatrice a été développée afin d'étudier les cathodes et la pénétration du bain dans celles-ci à l'aide de la microtomographie à rayons X. Cette méthode rapide et efficace s'est avérée fort utile dans le projet et à un potentiel important pour l'étude future des cathodes et des phénomènes qui s'y produisent. Ensuite, une cellule d'électrolyse rectangulaire à petite échelle a été développée. Plusieurs phénomènes observés en industrie sur des autopsies de cellules post-opération et rapportés dans la littérature ont été reproduis avec succès à l'aide de cette cellule expérimentale. Puis, des tests sans électrolyse, ciblant l'effet du bain électrolytique sur l'acier, ont aussi été conçus et complétés afin de ségréger l'influence des différents paramètres en jeu. L'analyse des résultats de l'ensemble de ces tests a permis de constater différents phénomènes au contact bloc-barre, dont la présence systématique de NaF et, surtout, de béta-Al[indice inférieur 2]O[indice inférieur 3]. Outre la carburation inévitable de la barre collectrice, la formation d'une couche Fe-Al a aussi été observée, favorisée par une pénétration rapide du bain électrolytique dans la cathode ainsi que par une composition de bain acide en surface de la barre. Cette couche comportait par ailleurs des cristaux de béta-Al[indice inférieur 2]O[indice inférieur 3] pouvant nuire à sa conductivité électrique. Ensuite, à des ratios de bain entre 2.5 et 4.9, une mince couche contenant les éléments Al et N peut se former en surface de la barre. Pour un bain tres basique (> 6.0), c'est plutôt une couche Na [indice inférieur 2] O qui a été observée. En conditions d'électrolyse mais sans une pénétration rapide du bain dans la cathode, du Na a pu carrément pénétrer dans la barre collectrice, préférentiellement avec le carbone. De plus, de la corrosion ainsi que des couches de fer et d'oxyde de fer peuvent se former sur la barre et potentiellement dégrader la qualité du contact électrique. \Pour la suite des travaux, des mesures de résistivité ainsi que l'analyse des échantillons industriels permettraient d'évaluer l'impact de ces phénomènes sur la qualité du contact. Bain électrolytique Interface barre-cathode Hall-Héroult Aluminium Électrolyse
3	Liquidus surface for the high cryolite/low alumina portion of the Na₃AlF₆-AlF₃-CaF₂-Al₂O₃ system Xu, Ming-Wei Paul January 1983 (has links) The purpose of this work was to determine the liquidus surface of the cryolite-rich portion of the ternary system Na₃AlF₆-CaF₂-AlF₃ and to establish the effect of Al₂O₃ on the operation of the Hall cell electrolysis. A series of isotherm of the cryolite-rich portion were graphed. It was shown that pseudo-binary phase diagrams of Al₂O₃ and bulk composition in the cryolite-rich portion of the Na₃AlF₆-CaF₂-AlF₃ system were found to be simple eutectic. The temperatures and the alumina contents of the double solubility limit, two important parameters for the Hall cell, of the joins 95 Na₃AlF₆/5 AlF₃-Na₃AlF₆, 90 Na₃AlF₆/ 10 NaCaAlF₆ and 85 Na₃AlF₃/15 AlF₃-NaCaAlF₆ were determined. The cryolite liquidus temperature of the quaternary system Na₃AlF₆-CaF₂-AlF₃-Al₂O₃ was found to be expressed by: T<sub>Liq.</sub>. (C) = 1009.4 + 4.059(CaF₂) - 1.167(CaF₂)² + 0.968 x (CaF₂)(AlF₃) - 0.105(CaF₂)(AlF₃)² + 0.073 x (CaF₂)²(AlF₃) + 0.002(CaF₂)² (AlF₃)² - 4.165 x (AlF₃) - 0.054(AlF₃)² - 5.33(Al₂O₃) for CaF₂ 3.8~11.25%, AlF₃ 5~20%. / M.S. LD5655.V855 1983.X85 Aluminum -- Electrometallurgy Cryolite Hall Héroult process
4	Phase equilibria in the system Na₃AlF₆-Al₂0₃- NaCaAlF₆ Parks, William P. January 1982 (has links) The NaCaAlF₆-Al₂O₃ and Na₃AlF₆-Al₂O₃-NaCaAlF₆ phase diagrams were determined using DTA, x-ray diffraction, quench analysis, and optical microscopy. The NaCaAlF₆-Al₂O₃ system was a simple eutectic system with the eutectic located below 0.5 weight percent NaCaAlF₆. The ternary system was a eutectic system showing solid solution of NaCaAlF₆ in both polymorphs of Na₃AlF₆. Alumina exhibited no appreciable solubility in Na₃AlF₆ and, in the ternary system, less than 2% solubility above 15% NaCaAlF₆. / Master of Science LD5655.V855 1982.P375 Aluminum -- Electrometallurgy Phase rule and equilibrium Hall Héroult process
5	The Effect of Aluminium Industry Effluents on Sediment Bacterial Communities Gill, Hardeep 19 October 2012 (has links) The goal of this project was to develop novel bacterial biomarkers for use in an industrial context. These biomarkers would be used to determine aluminium industry activity impact on a local ecosystem. Sediment bacterial communities of the Saguenay River are subjected to industrial effluent produced by industry in Jonquière, QC. In-situ responses of these communities to effluent exposure were measured and evaluated as potential biomarker candidates for exposure to past and present effluent discharge. Bacterial community structure and composition between control and affected sites were investigated. Differences observed between the communities were used as indicators of a response to industrial activity through exposure to effluent by-products. Diversity indices were not significantly different between sites with increased effluent exposure. However, differences were observed with the inclusion of algae and cyanobacteria. UniFrac analyses indicated that a control (NNB) and an affected site (Site 2) were more similar to one another with regard to community structure than either was to a medially affected site (Site 5) (Figure 2.4). We did not observe a signature of the microbial community structure that could be predicted with effluent exposure. Microbial community function in relation to bacterial mercury resistance (HgR) was also evaluated as a specific response to the mercury component present in sediments. Novel PCR primers and amplification conditions were developed to amplify merP, merT and merA genes belonging to the mer-operon which confers HgR (Table 5.6). To our knowledge, the roles of merP and merT have not been explored as possible tools to confirm the presence of the operon. HgR gene abundance in sediment microbial communities was significantly correlated (p < 0.05) to total mercury levels (Figure 3.4) but gene expression was not measurable. We could not solely attribute the release of Hg0 from sediments in bioreactor experiments to a biogenic origin. However, there was a 1000 fold difference in measured Hg0 release between control and affected sites suggesting that processes of natural remediation may be taking place at contaminated sites (Figure 3.7). Abundance measurements of HgR related genes represent a strong response target to the mercury immobilized in sediments. Biomarkers built on this response can be used by industry to measure long term effects of industrially derived mercury on local ecosystems. The abundance of mer-operon genes in affected sites indicates the presence of a thriving bacterial community harbouring HgR potential. These communities have the capacity to naturally remediate the sites they occupy. This remediation could be further investigated. Additional studies will be required to develop biomarkers that are more responsive to contemporary industrial activity such as those based on the integrative oxidative stress response. bacteria heavy metal resistance mercury mer operon sediment biomarker community diversity mercuric reductase sediment metagenome environmental microbiology industry bauxite alumina red mud Saguenay River, QC PCR qPCR bioreactor gene merT merP merA rpoB katG glnA river system environmental DNA aluminum industry Bayer Process Hall–Héroult Process 16S rRNA UniFrac sediment wash buffer community richness mothur ribosomal database project DNA sequencing aluminum aluminium RNA metatranscriptome ecotoxicology environmental contaminants industrial effluent
6	The Effect of Aluminium Industry Effluents on Sediment Bacterial Communities Gill, Hardeep 19 October 2012 (has links) The goal of this project was to develop novel bacterial biomarkers for use in an industrial context. These biomarkers would be used to determine aluminium industry activity impact on a local ecosystem. Sediment bacterial communities of the Saguenay River are subjected to industrial effluent produced by industry in Jonquière, QC. In-situ responses of these communities to effluent exposure were measured and evaluated as potential biomarker candidates for exposure to past and present effluent discharge. Bacterial community structure and composition between control and affected sites were investigated. Differences observed between the communities were used as indicators of a response to industrial activity through exposure to effluent by-products. Diversity indices were not significantly different between sites with increased effluent exposure. However, differences were observed with the inclusion of algae and cyanobacteria. UniFrac analyses indicated that a control (NNB) and an affected site (Site 2) were more similar to one another with regard to community structure than either was to a medially affected site (Site 5) (Figure 2.4). We did not observe a signature of the microbial community structure that could be predicted with effluent exposure. Microbial community function in relation to bacterial mercury resistance (HgR) was also evaluated as a specific response to the mercury component present in sediments. Novel PCR primers and amplification conditions were developed to amplify merP, merT and merA genes belonging to the mer-operon which confers HgR (Table 5.6). To our knowledge, the roles of merP and merT have not been explored as possible tools to confirm the presence of the operon. HgR gene abundance in sediment microbial communities was significantly correlated (p < 0.05) to total mercury levels (Figure 3.4) but gene expression was not measurable. We could not solely attribute the release of Hg0 from sediments in bioreactor experiments to a biogenic origin. However, there was a 1000 fold difference in measured Hg0 release between control and affected sites suggesting that processes of natural remediation may be taking place at contaminated sites (Figure 3.7). Abundance measurements of HgR related genes represent a strong response target to the mercury immobilized in sediments. Biomarkers built on this response can be used by industry to measure long term effects of industrially derived mercury on local ecosystems. The abundance of mer-operon genes in affected sites indicates the presence of a thriving bacterial community harbouring HgR potential. These communities have the capacity to naturally remediate the sites they occupy. This remediation could be further investigated. Additional studies will be required to develop biomarkers that are more responsive to contemporary industrial activity such as those based on the integrative oxidative stress response. bacteria heavy metal resistance mercury mer operon sediment biomarker community diversity mercuric reductase sediment metagenome environmental microbiology industry bauxite alumina red mud Saguenay River, QC PCR qPCR bioreactor gene merT merP merA rpoB katG glnA river system environmental DNA aluminum industry Bayer Process Hall–Héroult Process 16S rRNA UniFrac sediment wash buffer community richness mothur ribosomal database project DNA sequencing aluminum aluminium RNA metatranscriptome ecotoxicology environmental contaminants industrial effluent
7	The Effect of Aluminium Industry Effluents on Sediment Bacterial Communities Gill, Hardeep January 2012 (has links) The goal of this project was to develop novel bacterial biomarkers for use in an industrial context. These biomarkers would be used to determine aluminium industry activity impact on a local ecosystem. Sediment bacterial communities of the Saguenay River are subjected to industrial effluent produced by industry in Jonquière, QC. In-situ responses of these communities to effluent exposure were measured and evaluated as potential biomarker candidates for exposure to past and present effluent discharge. Bacterial community structure and composition between control and affected sites were investigated. Differences observed between the communities were used as indicators of a response to industrial activity through exposure to effluent by-products. Diversity indices were not significantly different between sites with increased effluent exposure. However, differences were observed with the inclusion of algae and cyanobacteria. UniFrac analyses indicated that a control (NNB) and an affected site (Site 2) were more similar to one another with regard to community structure than either was to a medially affected site (Site 5) (Figure 2.4). We did not observe a signature of the microbial community structure that could be predicted with effluent exposure. Microbial community function in relation to bacterial mercury resistance (HgR) was also evaluated as a specific response to the mercury component present in sediments. Novel PCR primers and amplification conditions were developed to amplify merP, merT and merA genes belonging to the mer-operon which confers HgR (Table 5.6). To our knowledge, the roles of merP and merT have not been explored as possible tools to confirm the presence of the operon. HgR gene abundance in sediment microbial communities was significantly correlated (p < 0.05) to total mercury levels (Figure 3.4) but gene expression was not measurable. We could not solely attribute the release of Hg0 from sediments in bioreactor experiments to a biogenic origin. However, there was a 1000 fold difference in measured Hg0 release between control and affected sites suggesting that processes of natural remediation may be taking place at contaminated sites (Figure 3.7). Abundance measurements of HgR related genes represent a strong response target to the mercury immobilized in sediments. Biomarkers built on this response can be used by industry to measure long term effects of industrially derived mercury on local ecosystems. The abundance of mer-operon genes in affected sites indicates the presence of a thriving bacterial community harbouring HgR potential. These communities have the capacity to naturally remediate the sites they occupy. This remediation could be further investigated. Additional studies will be required to develop biomarkers that are more responsive to contemporary industrial activity such as those based on the integrative oxidative stress response. bacteria heavy metal resistance mercury mer operon sediment biomarker community diversity mercuric reductase sediment metagenome environmental microbiology industry bauxite alumina red mud Saguenay River, QC PCR qPCR bioreactor gene merT merP merA rpoB katG glnA river system environmental DNA aluminum industry Bayer Process Hall–Héroult Process 16S rRNA UniFrac sediment wash buffer community richness mothur ribosomal database project DNA sequencing aluminum aluminium RNA metatranscriptome ecotoxicology environmental contaminants industrial effluent

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