Abstract
Carbon anodes are used in the electrolytic production of aluminum. The quality of anodes is directly related to the production cost, carbon and energy consumption, and environmental emissions. It is desired that the anodes have high density, low porosity/cracks, low electrical resistivity as well as low air and CO2 reactivities. Low resistivity of anodes reduces energy required to produce aluminum during electrolysis. The presence of cracks and pores increases the anode electrical resistivity. Therefore, it is important to know how and when the pores and cracks form during the anode production so that the necessary actions could be taken to prevent their formation. A study was carried out to investigate the effect of different anode production parameters such as anode composition, type of raw material used, time and top-former bellow pressure of vibro-compactor, green anode cooling medium, and heating rate used during baking on the crack formation. The anodes are fabricated at the carbon laboratory of University of Quebec at Chicoutimi (UQAC) and characterized by measuring their properties (density, electrical resistivity, and surface crack density). The anode properties, hence the anode quality, were correlated with the anode production parameters. Also, their tomographic analysis was carried out to visualize and quantify the internal cracks.Graphical abstract
Highlights
Aluminum is produced by electrolysis using the HallHéroult process according to the reaction: (1)The carbon required for aluminum production via electrolytic alumina (Al2O3) reduction is supplied by the carbon anodes which are consumed during electrolysis
The presence of excessive cracks/pores is considered a sign of poor anode quality since they increase the electrical resistivity of anodes, the energy needed for electrolysis
The current study was carried out to investigate the effect of the different parameters to determine the influence of production conditions on anode cracking
Summary
Aluminum is produced by electrolysis using the HallHéroult process according to the reaction: 2Al2O3 + 3C → 4Al + 3CO2. The presence of excessive cracks/pores is considered a sign of poor anode quality since they increase the electrical resistivity of anodes, the energy needed for electrolysis The current study was carried out to investigate the effect of the different parameters (anode composition, raw materials, time and top-former bellow pressure of vibrocompactor, medium used to cool the green anodes, and heating rate used during baking) to determine the influence of production conditions on anode cracking. Homogeneous anode paste reduces the pitch consumption and high local volatile release leading to lower internal pressure and cracking rate during anode baking [12, 13]. In addition to compaction time, compaction force (load and vibro-compactor top-former bellow pressure), vibration frequency, and the utilization of vacuum are the parameters which can affect the anode quality [14]. Ash at 900 °C (% m/m) β Resin (% m/m) Density at 20 °C (g/cm3) Quinoline insolubles (% m/m) Toluene insolubles (% m/m) Coking Value (% m/m) Softening Point (°C) Dynamic Viscosity 170 °C (mPa.s) Surface Tensiona (dyne/cm) at 170 °C
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