Encyclopedie de la recherche sur l'aluminium au Quebec - Edition 2014 | Page 41

Modélisation deL’ALUMINIUM // ALUMINIUM PRODUCTION PRODUCTION DE la conductivité électrique des anodes vertes MODÉLISATION DE LA CONDUCTIVITÉ ÉLECTRIQUE DES ANODES VERTES Modelling of electrical MODELLING OF ELECTRICAL conductivity of green anodesCONDUCTIVITY OF GREEN ANODES 39 Geoffroy Rouget1,2, Houshang Alamdari1,2 Javad Mashreghi3, Donald Picard2, Donald Ziegler4. 1 2 Department of Mining, Metallurgical and Materials Engineering, 1065 avenue de la Médecine Université Laval, Québec, QC, G1V 0A6, Canada NSERC/Alcoa Industrial Research Chair MACE3 and Aluminium Research Centre – REGAL Université Laval, Québec, QC, G1V 0A6, Canada 3 Department of Mathematics and statistics 1045, avenue de la Médecine Université Laval, Québec, QC, G1V 0A6, Canada 4 Alcoa Primary Metals, Alcoa Technical Center, 100 Technical Drive, Alcoa Center, PA 15069-0001 USA Introduction Electrical conductivity of green anodes should be defined as a function of electrical conductivities of the different components. Lewis and Nielsen’s [1] model take account of electrical conductivity, shape factor and packing fraction of each phases. (1) Binder matrix. (2) Coke aggregates. (3) Pores. Schematic view of anode paste. Methodology Coke aggregates Electrical conductivity of coke aggregates is measured by impedance spectroscopy and compared to direct current method to provide the most accurate the most accurate value to fill in the model. The actual packing fraction in aggregate sample is measured to estimated the true electrical conductivity, excluding voids. Binder matrix Theoretical binder matrix is pressed representing an average recipe containing pitch and particles smaller than 100 mesh. (150 µm). The sample pressed is cored, top and bottom are removed to obtain an homogeneous sample to study. Material and results Coke aggregates Binder matrix Voltage measurement Plunger + current electrode Insulating Shield Alumina and rubber composite Binder matrix is pressed at 150 C under a 73 MPa pressure. Pressure is maintained as long as the displacement keeps going on. As the displacement reach to an end, we can estimate the density tends to a maxima, as specified by Azari et al. [3] Shot coke and sponge coke will be characterized. Size fraction: 8 to 9, 9 to 10, 10 to 12 and 12 to 14 mesh. Chosen due to good sphericity of shot coke. Resistance (mΩ) Polarisation threshold Polarisation threshold curve shows a minimum 15 mA current must flow through the fixture to provide reliable data. 0.054 0.052 0.05 0.048 0.046 0.044 0.042 0.04 Computed Tomography Scanner used to analyse material structure by X-ray absorption measurement and computation. Layer definition are between 0,6 and 1,3 mm depth. This method allows to represent a 3 dimensional view of the sample. CT Scan Analysis Sample 1 0 10 20 Current (mA) 30 Sample 1 40 Image analysis Hakamada et al. [2] Proposed a model to predict the electrical resistivity of porous aluminium foam. Removal of voids should lead to true electrical conductivity. RP= ρP*(L/S) ρp =(S/L)*ρC*(L-Lv) / (S-Sv) Sample 2 Sample 3 Cm Bottom Axial gradient density Top Edge Radial gradient density Conclusion Center -Preliminary results for impedance spectroscopy tend to show that electrical conductivity can be accurately estimated by the usual DC measurement. -Binder matrix study may give the opportunity to model its electrical conductivity according to its recipe and components. References: [1] : Nielsen L.E. Ind Engng Chem Fund 13 (1974) 17 [2] :Hakamada et al. Mater. Trans., 48, 1 (2007) 32-36 Geoffroy Rouget Houshang Alamdari Département de génie des mines, de la métallurgie et des matériaux, Chaire de recherche industrielle CRSNG/ Alcoa MACE3, Centre de recherch sur l’aluminium - REGAL, Université Laval Donal Picard Chaire de recherche industrielle CRSNG/Alcoa MACE3, Centre de recherche sur l’aluminium REGAL, Université Laval Javad Mashreghi Département de mathématiques et de statistique, Université Lava Donald Ziegler Alcoa Technical Center [3] : Azari et al. Powder Technology 235 (2013) 341-348 Journée des étudiants – REGAL expensive step in anode production. A non-destructive method Baking is a very La cuisson est une étape très coûteuse de la fabrication des anodes. Une méthode 18 cuisson, serait un de caractérisation non destructive des anodes pressées, avant novembre 2014 grand avantage pour l'industrie. L'étude des propriétés électriques des anodes crues est une solution envisageable. Le sujet d'étude proposé est de caractériser indépendamment chaque phase constituant l'anode, afin de les introduire dans un modèle liant leurs propriétés : conductivité électrique, compacité et forme des phases dispersées (agrégats, pores). Le modèle modifié de Nielsen et Lewis tient compte de ces différents aspects. La validation de ce modèle mathématique pourra permettre de l'introduire dans un logiciel de simulation numérique afin de comparer des mesures effectuées in situ aux valeurs obtenues par simulation numérique. of characterization of pressed anodes, before bakin