REFRACTORIES IN HEATING UNITS
PROTECTION OF AN ALUMINUM ELECTROLYZER
CARBON-GRAPHITE LINING BY A LITHIUM INTERCALATION LAYER
V. Yu. Bazhin,
R. Yu. Feshchenko,
A. V. Saitov,
and E. A. Kuznetsova
Translated from Novye Ogneupory, No. 3, pp. 87 – 90, March, 2014.
Original article submitted December 11, 2013.
The problem of improving the life of carbon-graphite lining material used in aluminium electrolyzers under
conditions of a high-temperature molten cryolite-alumina medium is discussed. An active effect is established
for lithium on the change in graphite structural layers due to their growth as a result of intercalation. An im
provement in electrolyzer carbon-graphite lining properties is confirmed by a series of experiments performed
with different carbon materials.
Keywords: carbon-graphite material (CGM), lithium intercalation, electrolyte, lining.
Improvement of refractory resistance is an important
problem for increasing aluminium electrolyzer service life.
During electrolyzer operation component reaction com-
mences with penetration of cryolite-alumina melt into open
pores and cracks of carbon-graphite material (CGM), which
is accompanied by breakdown of a cathode unit lining. The
main reason for worsening of block properties is introduction
of sodium into the carbon material layer boundary with melt.
This leads to swelling, loosening, formation of breaks and
microcracks, and also worsens conditions for subsequent
electrolyte absorption and formation of aluminum carbide in
It is well known  that with action of sodium there is
expansion and deformation of many carbon materials, since
the atomic radius of sodium is greater than the distance be
tween graphite structural elements. Under action of sorption
and carbide formation there is a significant change in
physicochemical properties in the carbon-graphite block
working layer. The bond of the working layer with the main
mass of blocks is weakened and it breaks down, which be
comes more pronounced due to the high temperature gradi
ent through the thickness of a lining, and also temperature
variations and shock effects .
On the other hand, graphite may react actively with al
kali metals, and is converted into a form of intercalated alkali
metal-graphite compounds . Sodium does not form com
pounds of a lower order NaC
and is converted into readily
soluble forms of intercalates with high order numbers. These
reactions with a carbon lining are also inherent for other al-
kali metals, in particular lithium and potassium.
In spite of an adequate study and considerable experi-
ence of practical operation of aluminium electrolyzers in
lithium electrolytes , the question of reaction of lithium
with CGM has not been aired adequately in publications.
Questions have been studied in  connected with formation
of lithium compounds with carbon, but the mechanism of
lithium introduction and nature of its reaction with carbon
block layers has not been revealed.
There is scientific and practical interest in performing re
search connected with behavior of lithium, since small lith
ium atom dimensions make it possible for easy penetration
into a carbon layer. Lithium atoms, in contrast to other alkali
metal atoms, are capable of introduction into a layer and
pores of a block without distorting the carbon crystal lattice.
Since CGM have the property to form interstitial phases with
lithium, in spaces between layers at certain temperatures
there is an intercalation reaction of lithium at a high rate .
A shaft furnace was used in order to perform tests. Speci
mens cut from industrial graphite cathode blocks were
placed in a suspended condition in a sealed steel container.
The temperature was controlled by means of a thermocouple
pressed to the container lid. A prescribed lithium vapour
pressure was established by a control valve. The experimen
tal layout of the device is shown in Fig. 1. Lithium carbonate
Refractories and Industrial Ceramics Vol. 55, No. 2, July, 2014
1083-4877/14/05502-0081 © 2014 Springer Science+Business Media New York
FGBOU VPO National Mineral Raw Material University Gornyi,
St. Petersburg, Russia.