WEB Aging of carbon materials for Aluminium electrolysis at alternating temperaturesWednesday (23.09.2020) 17:20 - 17:35 P: Processing and Synthesis 1 Part of:
For many years ongoing efforts have been made to optimize the manufacturing route for primary aluminium. Nowadays, the Hall-Héroult process is established as the worldwide standardized method to decompose alumina. Global action to increase the amount of renewable energy has created new ideas in terms of industrial resources management. One of the latest developments in the aluminium industry has focused on the implementation of controlled power modulation. During operation the bottom lining of an electrolysis cell, usually called the cathode, is subject to a continuous wear process. Thus, the carbon cathode can be expected as a key component, determining the operational life span of a cell. While standard cells are basically designed for constant power supply, alternating power loads might boost this degradation process with respect to the alternating thermal loads. Since in situ measurements are costly and time-consuming, laboratory experiments are taken into account. In order to investigate the influence of alternating temperature on the electrochemical wear behaviour of the cathode material, a laboratory electrolysis cell was used for all experiments. A typical feature of this cell type is given by the arrangement of the electrodes in a reverse fashion. A graphite crucible serves as electrolyte container which is polarized anodically while a cathodically polarized cylindrical graphitic rod, the sample, which is dipped into the liquid bath from the top of the cell. The cell is placed inside a muffle furnace under inert gas atmosphere and heated up to a temperature slightly above the liquidus temperature of the bath. A constant current was applied to the system as the resulting voltage was recorded by a high precision voltmeter. All tests were carried out for a total time of 24 hours at different current densities. Reference samples were examined at 940 and 960 °C under isothermal conditions. In comparison, cyclic thermal loads with different temperature amplitudes were applied to the specimens, representing alternating (960 ± 40 °C) and negative modulation (960 - 40 °C). The diameters of the samples were determined before and after each experiment at each millimeter in longitudinal direction with a laser micrometer. The electrochemical wear rates were calculated from the wear profiles. The present research is part of the EFRE project Aluminiumelektrolyse 4.0.