STUDY OF THE INTERCONNECTION
OF ALUMINUM ELECTROLYZER LIFE WITH CORROSION
OF ITS CASING
V. V. Sharapova
Translated from Novye Ogneupory, No. 1, pp. 39 – 42, January 2009.
Original article submitted March 5, 2008.
It is confirmed that an aluminum electrolyzer casing is subject to electrochemical corrosion. It is established
that on reaction of electrolyzer associated gaseous products with the electrolyzer casing there is formation of
fluorides of bi- and trivalent iron, and also iron fluorides of non-stoichiometric composition. It is shown that
the fluoride layer formed does not protect the casing surface from further corrosion. In order to protect the
electrolyzer casing it is necessary to fasten a refractory barrier layer. More reliable heat insulation should be
used in order to maintain the optimum casing heating temperature.
Keywords: aluminum electrolyzer, corrosion, heat insulating layer, vermiculite, haematite, iron fluorides,
Apart from the properties of materials in cathode units,
the service life of aluminum electrolyzers depends to a con-
siderable extent on the state of the casing. The state of the
casings of electrolyzers after service are analyzed in a num-
ber of publications and strength predictions are given for the
properties of cathode casings for aluminum electrolyzers .
There is information about electrocorrosion of a casing in
. Phase changes that occur with casing materials under
conditions of an actual electrolyzer have not been studied
sufficiently. Due to the lack of standard specimens and infor
mation about the optical properties of iron fluorides it has not
been possible to identify by a crystal-optical method the sub
stances analyzed by the author of publication .
The aim of the present work is determination of the rea
sons for the short life of aluminum electrolyzer casing based
on studying phase transformations that occur with the casing
material during aluminum production by the Hall – Heroult
method. Petrographic, x-ray structural and chemical methods
of analysis were used during the studies. Petrographic studies
were carried out in reflected and transmitted light in micro
scopes MBI-6 and MIM-8, x-ray analysis was performed in a
DRON-3 unit in CuK
According to solid deformation theory a cathode casing
is a complex structural system of joined thin plates. The cas
ing material (St3) is considered to be uniform and isotropic.
In steel sheet of an electrolyzer casing after 3.5 years of ser
vice according to chemical analysis data provided by the au-
thor of this article there is an increased amount total fluorine.
In a number of casing specimens the total fluorine content
was at the level of 15.96 – 22.23%. Haematite in an amount
of 10.0 – 56.62% has also been detected in steel sheet. The
content of elemental sodium detected in the specimens in
question was 5.37%, the overall aluminum was 3.55%, and
the silicon was 0.371%. In addition, casing deformation is
observed in the form of areas of eroded steel sheet. Sheet
failure is noted from within the casing. The typical size of the
corrosion products formed exceeds the original sheet thick
ness by almost a factor of three.
It should be noted that a number of samples of the heat
insulation layer made of vermiculite after service acquire a
red color of different intensity. In these specimens an in
creased amount of iron and haematite is revealed, i.e. 7.28
and 5.59% respectively. In samples of the heat insulation
glass and fluorides are detected containing haematite in the
form of a solid solution and microlites.
There is information [3, 4] for the existence of iron fluo
, and iron fluorosilicate
O; there is also a lower gaseous compound, i.e.
FeF ; iron fluoride complexes are known . There are no
published data for the optical properties of iron fluorides .
For the first time the author of the present work has de
termined the refractive index of iron fluorides for which
standard specimens of FeF
were prepared using
Refractories and Industrial Ceramics Vol. 50, No. 1, 2009
1083-4877/09/5001-0049 © 2009 Springer Science+Business Media, Inc.
GP UkrNIIspetsstal’, Zaporozh’e, Ukraine.