An XPS study of the fluorination of carbon anodes in molten NaF–AlF3–CaF2
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In the Hall–Héroult process for aluminum production electrolysis takes place in molten cryolite (NaF–AlF3–CaF2) with carbon electrodes. Dewetting of the anode leads to operational instability. A surface energy change due to surface fluorocarbon formation during electrolysis is suggested as a contributing factor to diminishing the wettability of the anode. In this work the surface composition of graphite anodes after electrolysis in molten NaF–AlF3–CaF2 is investigated by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) for evidence of fluorination. Fluorocarbon is identified on an electropolished region of an anode surface resulting from anode effect. The discovery of surface fluorination provides an insight into high temperature electrochemical reactions of carbon with molten fluoride salts and informs aluminum smelter cell operation.
KeywordsFluorocarbon Cryolite Anode Surface AlF3 Carbon Anode
This research was undertaken on the Soft X-ray beamline at the Australian Synchrotron, Victoria, Australia. The NZ Synchrotron Group Ltd provided travel funding. Melissa Basil-Jones and Isabel Beattie assisted with XPS data collection and Doug Hopcroft, Manawatu Microscopy Centre, collected the SEM images.
- 1.Thonstad J, Fellner P, Haarberg GM, Híveš J, Kvande H, Sterten Å (2001) Aluminium electrolysis. Aluminium-Verlag, DüsseldorfGoogle Scholar
- 7.Metson JB, Haverkamp RG, Hyland MM, Chen JX (2002) Light Met 239Google Scholar
- 8.Tabereaux AT, Richards NE, Satchel CE (1995) Light Met 325Google Scholar
- 9.Dorreen MMR, Chin DL, Lee JKC, Hyland MM, Welch BJ (1998) Light Met 311Google Scholar
- 10.Utigard T, Toguri JM, Ip SW (1988) Light Met 703Google Scholar
- 11.Zhuxian Q, Liman F, Grjotheim K (1986) Light Met 483Google Scholar
- 14.Vogt H, Thonstad J (2002) Light Met 495Google Scholar
- 18.Nakajima T (ed) (1995) Fluorine-carbon and fluoride-carbon materials: chemistry, physics, and applications. Marcel Dekker, New YorkGoogle Scholar
- 22.Fairley N, Carrick A (2005) The casa cookbook. Part 1: recipes for XPS data processing. Acolyte Science, KnutsfordGoogle Scholar
- 24.Moulder JF, Stickle WF, Sobol PE, Bomben KD (1992) Handbook of X-ray photoelectron spectroscopy. Perkin-Elmer Corporation, Eden PrairieGoogle Scholar