special - ALUMINIUM-Nachrichten – ALU-WEB.DE

PATENTE
obvious that more than one mechanism must
be involved. Solheim presented and discussed
three models concerning cathode wear [17].
Only one model, the so-called ‘carbon pump’-
hypothesis, provides a direct link between local
current densities at the cathode surface and
the wear rate [17, 18]. It is based on the assumption
that a solid aluminium carbide layer
covers the cathode surface during cell operation,
at least in spots or intermittently. This carbide
layer contains pores filled with electrolyte
which originates either from sludge or from a
bath film present between aluminium pad and
cathode. A possible pathway for the current is
then either through metal-filled areas/pores,
or more likely, around the carbide spots, leaving
a high local current density at the edges and
a smaller density above and below the centre
of the ‘islands’.
This current-shielding effect generates
a potential gradient along electrolyte-filled
pores, which might lead to electrochemical
crystallisation of Al 4 C 3 at the bottom of the
pore and dissolution of Al 4 C 3 at the top of the
pore. The scenario is sketched in Fig. 5 [18]
and can explain rapid wear leading to a W-
shaped cross-section of a used cathode. However,
other mechanisms exist that may increase
the wear rate; e.g. the metal flow velocity
and / or abrasion caused by the movement of
alumina particles. This has not yet been considered
in the modelling context described
here. More work is certainly needed to clarify
these issues. As a helpful tool, the commercial
FEM simulation software COMSOL Multiphysics
version 4.3 was used in the present
work in order to evaluate and support experimental
findings [14, 16, 18].
Conclusions
Laboratory tests indicate similar wear for all
tested carbon cathode grades under standardised
conditions, showing the independency on
the material type, but a strong effect of local
current density and metal flow velocity was
identified.
Acknowledgement
The present work was carried out in the competence-building
project ‘Durable Materials
in Primary Aluminium Production’ (KMB,
DuraMat), financed by the Research Council
of Norway, Hydro Primary Metal Technology,
Sør-Norge Aluminium, and Elkem Carbon.
The authors gratefully acknowledge permission
to publish the results.
References
[1] A. Tabereaux, JOM 52 (2000)2, pp. 23-29.
[2] H.A. Øye and B.J Welch, JOM 50(1998)2, pp.
18-23.
[3] E. Skybakmoen, S. Rørvik, A. Solheim, K. R.
Holm, P. Tiefenbach, and Ø. Østrem, Light Metals
2011, pp. 1061-1066.
[4] D. Lombard, T. Béhérégaray, B. Fève, and J. M.
Jolas, Light Metals 1998, pp. 653-658.
[5] M. Sørlie and H.A. Øye, Cathodes in Aluminum
Electrolysis, Düsseldorf, Germany: Aluminum Verlag,
2nd ed., 1994.
[6] M.A. Coulombe, M. Lebeuf, P. Chartrand, B. Allard
and G. Soucy, Light Metals 2010, pp. 811-816.
[7] R.C. Dorward, Met. Trans 4(1973), pp. 386-
388.
[8] P. Reny and S. Wilkening, Light Metals 2000,
pp. 399-404.
[9] J. Rødseth, B. Rasch, Ole Lund, and J. Thonstad,
Light Metals 2002, pp. 883-887.
[10] R. Ødegård, Å. Sterten, and J. Thonstad, Light
Metals 1987, pp. 295-302.
[11] B. Novak, K. Tschöpe, A.P. Ratvik and T.
Grande, Light Metals 2012, pp. 1343-1348.
[12] B. Novak, K. Tschöpe, A.P. Ratvik and T.
Grande, to be published in Light Metals 2013.
[13] K. Tschöpe, A. Støre, S. Rørvik, A. Solheim,
T. Grande, and A. P. Ratvik, Light Metals (COM)
2011, pp. 143-153
[14] K. Tschöpe, A. Støre, S. Rørvik, A. Solheim,
E. Skybakmoen, T. Grande, and A. P. Ratvik, Light
Metals 2012, pp. 1349-1354.
[15] K. Tschöpe, A. Støre, E. Skybakmoen, A. Solheim,
T. Grande, and A. P. Ratvik, to be published
in Light Metals 2013.
[16] K. Tschöpe, A. Støre, A. Solheim, E. Skybakmoen,
T. Grande and A.P. Ratvik, to be published
in JOM.
[17] A. Solheim, Loght Metals (COM ) 2011, pp.
135-142.
[18] A. Solheim and K. Tschöpe, to be published in
Light Metals 2013
[19] E. Skybakmoen, A. P. Ratvik, A. Solheim, S.
Rolseth, and H. Gudbrandsen, Light Metals 2007,
pp. 815-820.
[20] P. Rafiei, F. Hiltmann, M. Hyland, B. James, and
B. Welch, Light Metals 2001, pp. 747-752.
[21] P. Patel, M. Hyland, and F. Hiltmann, Light
Metals 2005, pp. 757-762.
[22] P. Patel, M. Hyland, and F. Hiltmann, Light
Metals 2006, pp. 633-638.
[23] Y. Sato, P. Patel, and P. Lavoie, Light Metals
2010, pp. 817-822.
[24] P. Patel. Y. Sato, and P. Lavoie, Light Metals
2011, pp. 1073-1078.
[25] K. Vasshaug, T. Foosnæs, G. M. Haarberg, A.
P. Ratvik, and E. Skybakmoen, Light Metals 2007,
pp. 821-826.
[26] K. Vasshaug, T. Foosnæs, G. M. Haarberg, A.
P. Ratvik, and E. Skybakmoen, Light Metals 2009,
pp. 1111-1115.
Authors
Dr. Kati Tschöpe is research scientist at the electrolysis
research team at SINTEF Materials and Chemistry
since 2012. She has been working on cathode
wear and degradation of bottom linings during her
PhD and Postdoc position at the Norwegian University
of Science and Technology (NTNU).
Egil Skybakmoen is research manager at the electrolysis
research team since 2004. He has 28 years
of experience within aluminium electrolysis and
his main fields of research have been fluoride bath
chemistry and lining materials.
Asbjørn Solheim, chief scientist, has conducted research
within aluminium electrolysis at SINTEF for
more than 30 years, particularly within bath chemistry
and modelling.
Dr. Tor Grande has been a professor at NTNU since
1997 and has a broad experience in materials science
and engineering with focus on both oxide and
none-oxide materials.
Patentblatt Oktober 2012
Fortsetzung aus ALUMINIUM 12/2012
Verfahren zum waagerechten Gießen und
Schneiden von Metallknüppeln. Novelis, Inc.,
Toronto, Ontario, CA. (B22D 11/126, EP 2 286
940, AT: 09.12.2004, EP-AT: 09.12.2004)
Gussaluminiumlegierung und Zylinderkopf
eines Verbrennungsmotors. Nippon Light Metal
Co. Ltd., Tokio, JP; Nissan Motor Co., Ltd., Yokohama-shi,
Kanagawa-ken, JP. (C22C 21/04, PS
60 2008 009 916, EP 2014780, AT: 04.07.2008,
EP-AT: 04.07.2008)
Verfahren zur Herstellung eines Titanschweißdrahtes.
Norsk Titanium Components AS, 0255
Oslo, NO. (C22C 14/00, EPA 2491155, WO
2011/049465, EP-AT: 21.10.2010, WO-AT:
21.10.2010)
Aluminiummaterial für eine Elektrode eines
elektrolytischen Kondensators, Verfahren zur
Herstellung von Elektrodenmaterial für einen
elektrolyt. Kondensator, Anodenmaterial für
einen elektrolyt. Aluminiumkondensator und
elektrolyt. Aluminiumkondensator. Showa
Denko K.K., Tokio, JP. (C22C 21/00, EP 1 841
892, WO 2006/068300, AT: 21.12.2005, EP-AT:
21.12.2005, WO-AT: 21.12.2005)
Aluminiumbandmaterial für lithographische
Druckplatten. Fujifilm Corp., Tokio, JP; Sumitomo
Light Metal Industries, Ltd., Tokio, JP. (C22B 9/02,
EP 2 284 288, AT: 24.07.2010, EP-AT: 24.07.2010)
Magnesiumlegierungsplatte und Verfahren
zur Herstellung derselben. Sumitomo Electric
Industries, Ltd., Osaka, JP. (B21B 3/00, PS 603 08
023, EP 1510265, WO 2003/103868, AT: 03.06.
2003, EP-AT: 03.06.2003, WO-AT: 03.06.2003)
Verfahren zum Druckgießen von gegliederten
Metallgussstücken. Trimet Aluminium AG,
45356 Essen, DE. (B22D 17/22, EP 2 008 740,
AT: 21.06.2008, EP-AT: 21.06.2008)
98 ALUMINIUM · 1-2/2013