Operational characteristics of laboratory scale alumina reduction cells with wettable cathodes

Bubble Evolution and Anode Surface Properties in Aluminium Electrolysis

“…Although not focused on here, as others also observed [12,21], the quality of the measured saw-tooth curve degraded after long periods of electrolysis; Kiss [48] suggests that whilst regular oscillations are observed for single bubbles, when many Reasons for the latter discrepancy are not known, but may relate to more variation within the measurements, as seen in Figure 9. A good correlation between FFT major frequency and bubble release time was similarly obtained by Dorin and Frazer [21] for their horizontal 24 mm diameter graphite anode, although others [19] found a discrepancy between bubble release times and major FFT frequencies, attributed to a lack of periodicity of bubble release possibly due to overlapping bubbles.…”

“…However, larger anodes are thought to sustain several bubbles simultaneously [16]. The magnitude of voltage variation of graphite recorded in other studies at 1 A cm -2 has been lower; for example 0.1 V [22] or 0.3 V [21], but in both cases discrepancies are most likely related to the geometry of the anode. The first used a cup-shaped, slightly inclined anode, and the latter study used 24 mm diameter anodes with a 5° inclination and the lowest 1.5 mm unshielded.…”

“…On small anodes this process is sequential, but with intermediate size or industrial anodes, typical behaviour is less periodic and multiple bubbles are released [13]. Previously, bubbles have been monitored through direct visual/X-ray observation [14][15][16], bath height fluctuation [3], current interruption and/or associated resistance [3,4,17,18] and potential oscillation [19][20][21][22]. Most studies suggest that bubble layer thickness is around 5 mm in both laboratory [3,12,16,23] and industrial [3,14,16,24] cells, although there is some variation reported [25,26].…”

Comparing Anodic Bubble Behavior of Anodes from Anisotropic and Isotropic Cokes in Laboratory Scale Aluminum Electrolysis Cells

“…Current density has also been shown to affect bubble build-up and release. Increasing current density has been shown to increase the bubble frequency and the voltage amplitude (17,20,25), which has also been confirmed by CFD models (21). Increasing current density has also been found to give increasing bubble screening and the same was found for decreasing Al2O3 content (12).…”

“…Several works report a quasi-periodical dynamic pattern of voltage oscillations, related to the additional voltage induced by the gas bubbles e.g. (14,(17)(18)(19)(20)(21)(22)(23)(24)(25). The lowest potential during the voltage oscillations are normally attributed to an anode surface free of bubbles.…”