BARRIER MATERIALS TESTED FOR CRYOLITIC RESISTANCE
METHODOLOGY AND EXPERTISE
I. Yu. Patrakhin,
A. M. Pogodaev,
A. V. Proshkin,
P. V. Polyakov,
I. A. Yarosh,
and R. V. Osipov
Translated from Novye Ogneupory, No. 5, pp. 49 – 54, May, 2006.
Original article submitted November 9, 2005.
A method for testing barrier materials for cryolitic resistance to corrosive attack by molten fluoride and alumi
num has been described. The method allows good reproducibility of measurements; an error analysis is given,
factors affecting the accuracy of experiment are discussed, and ways of its improvement are suggested.
As soon as an aluminum electrolysis cell is put in opera-
tion, its cathode blocks are fed with sodium and electrolyte.
The electrolyte transfer is greatly assisted by sodium, which
is formed by the reactions
Al(liq) + 3NaF = 3Na (in C) + AlF
® Na (in Al). (2)
Sodium penetrates into the bottom block to render it
wettable by molten fluoride; in this process, the front of mol
ten fluoride is followed by a sodium front .
The rate at which sodium penetrates into the bottom
block is controlled by the blocks’s material. Increasing the
degree of graphitization of bottom blocks causes a signifi
cant decrease in sodium penetration rate . A laboratory
study has shown that the rate at which sodium penetrates into
graphite is high enough — from 10 to 30 mm/h at 900°C .
For an amorphous graphite it was still higher, reaching 40 to
60 mm/h . It is seen therefore that the life of a electrolysis
cell is mainly controlled by the resistance to aggressive at
tack of barrier materials of the lining underlying the bottom
blocks. Consequently, the choice of an appropriate barrier
material is a major concern for technologists. Many alumi
num manufacturers rely on the in-house methods of testing
refractory materials for resistance to molten fluorides. Various
testing methods have been described in some detail in .
In this paper we are concerned with a method that has
been in use over more than two years at the RUSAL Co. and
Legkie Metally Research and Technology Center to test re-
fractory materials for cryolitic resistance. The method is
based on the direct attack of molten fluorides on test speci-
men that has formerly been suggested by Allaire and co-
EXPERIMENTAL CELL AND TESTING UNIT
A schematic diagram of the cell for testing refractory ma
terials is shown in Fig. 1. A specimen of refractory material
Refractories and Industrial Ceramics Vol. 47, No. 3, 2006
1083-4877/06/4703-0183 © 2006 Springer Science+Business Media, Inc.
Legkie Metally Research and Technology Center, Krasnoyarsk,
Russia; RUSAL Co. Moscow, Russia.
Fig. 1. Schematic diagram of a cell for testing refractory material
for corrosive attack by electrolyte and aluminum: 1 ) graphite
beaker; 2 ) specimen; 3 ) aluminum; 4 ) electrolyte.