REFRACTORIES IN HEAT UNITS
PART 3. PHASE TRANSFORMATIONS WITHIN THE LAYER
OF A DRY BARRIER MIXTURE FOR ALUMINUM ELECTROLYSIS CELLS
V. V. Sharapova,
I. I. Lishchuk,
and D. Yu. Boguslavskii
Translated from Novye Ogneupory, No. 9, pp. 7 – 13, September, 2005.
Original article submitted April 29, 2005.
It has been established that transformations within the layer of a dry barrier mixture (DBM) are selective in
character and are mainly confined to the upper zones of the innermost part (core) of DBM. The DBM layer un
dergoes a solid-liquid sintering in these zones. The glass phase thus formed prevents the electrolysis products
from penetration into the DBM layer. Modifier admixtures — titanium and iron oxides, products of electroly
sis and degradation of the refractory layer AlF, SiF
, and sodium oxide — decrease the viscosity of alumino-
silicate melt. The grains of a disthene-sillimanite concentrate undergo cracking along the cleavage plane. Im-
perfections of the crystal lattice promote transformations in the grains of normal electrofused corundum.
Oxyfluoride AlOF and an oxyfluoride of variable composition AlOF
are formed in the cathode lining of
the electrolysis cell.
In this paper we present the results of a study of the dry
barrier mixture (DBM) sampled for analysis from the bottom
lining of an aluminum electrolysis cell after 45.6 months of
service life. This work is a continuation of our previous stu
dies reported in [1 – 3].
Originally, the DBM was a mixture of granular dis
thene-sillimanite concentrate (GDSC) and normal electro
fused corundum (NEC) of fraction 20 mm. According to
TU U 14-10-017–98 Specifications, GDSC contains, wt.%:
, not less than 57; iron oxides, not higher than 0.8%;
CaO, not higher than 0.4; TiO
, not higher than 2.5. GDSC
consists mainly of aluminum silicates — disthene
]O and sillimanite Al[AlSiO
]. Disthene and
sillimanite are the same in chemical composition, but they
differ structurally. Both minerals are eutomous. The strength
of disthene is emphasized by its name (di + Greek sthene
force) . So, its hardness in the cleavage plane lengthwise
is 4.5; across, it is 6. The hardness of sillimanite (named after
the American chemist and geologist Benjamin Silliman,
1779 – 1864) is 6.5 – 7. Occasionally, quartz grits and glass
with N = 1.54 are found among other impurities in GDSC.
The NEC micropowder consists mainly of a-Al
NEC chemical composition is, wt.%: Al
, not less than 94;
, not higher than 0.6; TiO
, not higher than 2.8; SiO
not higher than 1.3; CaO, not higher than 0.7. A specific fea
ture of NEC is the occurrence of Ti
in it in the form of a
solid solution [5, 6]. Oxides of titanium and iron were also
found in the basal jointing of a crystalline electrocorundum.
These impurities increase the degree of the a-Al
lattice imperfection. In the powdered NEC, rutile TiO
curs as an individual impurity phase. The mentioned features
of constituents GDSC and NEC cannot leave unaffected the
DBM performance characteristics.
Specimens 9-2n, 12-3s, 18-3s, 20-1v, 21-1n, 26-2v,
28-1v, 29-1n, 39-2s, 41-1v, and 44-1n were examined petro
graphically. The sampling scheme and chemical analysis of
the DBM post-service specimens were as described in .
The density of DBM post-service specimens determined by
hydrostatic weighing was 3.06 – 2.66 g/cm
28-1v and 44-1n). Specimens 12-3s, 18-3s, 20-1v, and 21-1n
are powders of bright-gray color; specimens 9-2n, 26-2v,
29-1n, and 39-2s look like bright gray lumps , easily crum
Refractories and Industrial Ceramics Vol. 46, No. 5, 2005
1083-4877/05/4605-0295 © 2005 Springer Science+Business Media, Inc.
For Parts 1 and 2, see Novye Ogneupory, Nos. 3 and 5, 2005.
Ukrainian State Research Institute of Special Steels (USSI),
Zaporozhe, Ukraine; Zaporozhe Aluminum Production Kombinat,