PROSPECTS OF THE USE OF ALUMINOSILICATE REFRACTORIES
FOR ALUMINUM ELECTROLYZERS. PART 3. THE ROLE OF THE GLASS
PHASE FORMED IN THE OPERATION OF ALUMINUM ELECTROLYZERS
V. V. Sharapova,
B. P. Sereda,
D. Yu. Boguslavskii,
I. P. Malyshev,
V. D. Troyan,
and N. A. Troshenkov
Translated from Novye Ogneupory, No. 12, pp. 10 – 12, December, 2007.
Original article submitted July 5, 2007.
The compositions of glasses formed in the process of operation of an aluminum electrolyzer, the lowest con
tent of aluminum at which the glass is separated into aluminosilicate and oxyfluoride components, and the
temperatures of softening and of formation of drops of titanium-bearing glasses composition close to the glass
in ShPD-45 refractory (with an additive of mullite-corundum chamotte) are determined. It is shown that the
oxyfluoride glasses consist of both a silica skeleton and a corundum skeleton. The titanium-bearing glass
phase can hinder penetration of aggressive gaseous byproducts of electrolysis.
It is reported that the glass phase formed in operation of
an aluminum electrolyzer plays a protective role. In accor-
dance with the data of [1, 2] a high-viscosity vitreous mass
based on albite is capable of hindering the penetration of
electrolyte components into the lower layers of a lining.
The exact chemical composition of the amorphous vitreous
phase has not been determined . It is only known that its
primary component is silicon dioxide. It has been shown
[3 – 6] that the glass phase has a variable composition and is
chiefly represented by oxyfluoride and aluminosilicate
glasses. However, the element composition of the glass
phase has not been determined.
In the present study we made an attempt to decipher the
glasses formed in the process of operation of an aluminum
electrolyzer. We performed the study by the petrographic
method in reflected and transmitted light using MBI-6 and
MIN-8 microscopes. It is known that glass is an amorphous
substance that cannot be deciphered by the method of x-ray
diffraction analysis. For a chemical analysis we took samples
of glasses with various refractive indexes under a binocular lens.
The element composition of the common vitreous phase
in ShA-5 refractories after service is as follows (in mass per
cent): 20.1 Sitot, 16.9 Altot, 8.86 Na, and 12.2 F. The density
of this phase as determined by the method of hydrostatic
weighing amounts to 2.37 g/cm
. It has also been determined
that the prevailing kind of glass in the refractory layer after
operation of an aluminum electrolyzer has an oxyfluoride
composition consisting of (in mass percent) 3.92 Al, 20.65 Si,
and 8.48 F at N = 1.33. Samples with a low total content of
elemental silicon (due to its removal) are characterized by
the presence of oxyfluoride glass with N = 1.362 and the fol-
lowing composition (in mass percent): 17 Al, 18.91 Na,
10.62 F, and traces of Si. Thus, the data of chemical and crys-
tallographic analyses show that the oxyfluoride glasses con-
sist of both a silica skeleton and a corundum skeleton.
The authors of [5, 7] have observed immiscibility of the
oxyfluoride and aluminosilicate glasses. They detected pure
aluminosilicate glass with N = 1.521 (nepheline glass with
N = 1.51) containing 17.15% Al and 31.54% Si in a refrac
tory layer. It was interesting to determine the critical content
of aluminum at which the glasses separate into oxyfluoride
and aluminosilicate components. An analysis of the glass
phase of a heat-insulating layer  has shown the presence
of aluminosilicate glasses with N = 1.464 in it (Le Chatelier
glass with N = 1.458) The content of elemental aluminum in
such glasses is 8.41%, which corresponds to the lowest mass
fraction of Al at which the glass separates into aluminosili
cate and oxyfluoride components. In addition, we should
mention a sodium-fluoride kind of glass. The presence of
such glasses, of glasses with nepheline composition, and of
sodium glasses of type Na
with albite composition [3, 8]
indicates that a part of the sodium vapors penetrating into the
depth of the lining is accumulated in the glass phase.
It is known that the slag resistance of refractory articles
also depends on the susceptibility to loosening. It should also
be noted that in alkaline glasses the spatial lattice has breaks,
because a sodium ion can be bound to only one “foreign”
Refractories and Industrial Ceramics Vol. 48, No. 6, 2007
1083-4877/07/4806-0395 © 2007 Springer Science+Business Media, Inc.
Parts 1 and 2 of the paper appear in “Novye Ogneupory” Nos. 9
and 10 of 2007.
UkrNIIspetsstal, ZGIA, “ZAlK” Company, “Zaporozhogneupor”