Anode Effect Phenomena during Conventional AEs, Low Voltage Propagating AEs & Non‐Propagating AEs

Prediction of Low-Voltage Tetrafluoromethane Emissions Based on the Operating Conditions of an Aluminium Electrolysis Cell

“…For this reason, a local AE is less likely to propagate towards the other anodes and thus probably can last longer. 7 Moreover, as each anode are connected in parallel electrically, the effect of + a correlation was observed, À no correlation was observed, ? the relationship was unclear, empty cells indicate that this variable was not mentioned by the authors gas passivation under a single anode will be less significant on the global cell voltage if the total number of anodes increases.…”

“…Most authors 5,7,[10][11][12][16][17][18][19] agree that alumina concentration, anode current density and anodic overvoltage have a significant impact on the onset of low-voltage PFC emissions. All of these parameters are interrelated and will dictate if the localised overvoltage eventually exceeds the threshold necessary to generate PFC.…”

“…However, a generally accepted value is when the cell voltage exceeds 8 V. 6 For this reason, generalized AE, or high-voltage anode effects (HVAE), are easily identifiable and are very well documented in the literature. [6][7][8] However, if the AE phenomenon occurs only locally in the cell without propagating to all the other anodes, it can lead to a continuous generation of PFC while the cell voltage still remains under the AE detection limit. This makes the detection of lowvoltage emissions difficult without continuous monitoring of the output gas composition.…”

Influence of Heat Transfer on Anode Reactions When Electrowinning Metal from Its Oxides Dissolved in Molten Fluorides

“…Any of these can bring about changes in both the electrode overpotential and the current distribution between individual anodes and the metal pad. Equation 5 is therefore modified as follows for each anode to metal pad pair V anode to metal pad = E Nernst + η anode + i anode i (R anode i +R (electrolye+bubble layer) i + R anode surface film i ) [6] with the constraints that I cell = I line = I i [7] The cell voltage (V cell ) used for alumina feeding and cell heat balance control (directly or indirectly) is given by the relationship V cell = V anode to metal pad + I cell (R cathode + R external circuit ) [8] Consequently it becomes extremely difficult, if not impossible, to know the potential gradient existing at any individual anode. Cell voltage changes are a consequence of changes in individual condition for each anode to metal pad pathway.…”

“…Interest in the anode reaction mechanisms has been revived during the last decades following the development of more sensitive gas analysis instrumentation that can detect low levels of co-evolved perfluorocarbons (PFC's) which have exceptionally high global warming potential. 5,6 These have been found to occur at substantially lower anode potentials than expected from the conventionally assumed PFC formation reaction 4Na 3 AlF 6 (l) + 3C = 3CF 4 (g) + 4Al + 12NaF(l) [1] Because of the established low polarization of the metal deposition reactions, it has become the convention to arbitrarily set the reversible potential for the cathode process at zero, and this is done in subsequent discussion making the anode potential under reversible conditions equal to the reaction Nernst potential.…”