RAW MATERIALS
A STUDY OF THE CRYSTALLINE STRUCTURE
OF VERMICULITE FROM THE TEBINBULAK DEPOSIT
V. I. Andronova
1
Translated from Novye Ogneupory, No. 5, pp. 24 – 29, May, 2007.
Original article submitted March 3, 2007.
The results of studies of vermiculite rock from the Tebinbulak deposit are given. It is established that this ver
-
miculite rock consists of biotite mica minerals. The crystalline lattice of these minerals contains interpack wa
-
ter known as zeolite water, which is responsible for swelling of the rock in heating. Vermiculite rock fired at
200 – 900°C is capable of absorbing water, i.e., of rehydration. This is important in using swelled vermiculite
in the production of fire-retardant paints. The compositions of fire-retardant paints and the results of their test
-
ing for heat resistance according to GOST 30402 are given. It is established that all the developed mixtures
impart fired-retardant properties to timber.
The development of new technologies and promising
materials make it necessary to expand the list of available
raw materials. Among the promising products are fire-retar-
dant paints that are used in different sectors of industry.
Swelled vermiculite is widely used as a filler in fire-retardant
paints. Such paints are not produced in the Republic of Uzbe-
kistan and have to be imported from other countries. The de-
velopment of a large deposit of vermiculite ore in Tebinbulak
will make it possible to start the production of fire-retardant
paints in Uzbekistan.
The vermiculite ore from the Tebinbulak deposit belong
to biotite mica. It should be noted that very few varieties of
vermiculite rocks belong to biotite mica. For instance, the
large Kovdor deposit in Russia mainly consists of phlogopite
mica; therefore, all previous studies of vermiculite have been
performed on these phlogopite rocks. The present study has
been carried out on the biotite vermiculite rock in order to
determine its applicability for the production of fireproof
paints. Vermiculite samples taken from the Tebinbulak de
-
posit have a dark gray color and comprise mainly biotite,
hydrobiotite, and vermiculite minerals. The chemical com
-
position of vermiculite samples is given in Table 1.
The crystal-optical properties of vermiculite ore were de
-
termined using a microscope in immersion liquids for the bi
-
otite — vermiculite series (and for rehydrated vermiculite as
well); the refraction index N*m and its variation under firing
samples to 1000°C was estimated as well. As the degree of
hydration grows, we observe a decrease in the refraction in-
dex from biotite to vermiculite (Table 2), which was earlier
reported in studies performed on phlogopite — vermiculite
minerals [1]. The refraction index presumably decreases due
to the increasing content of water in mica, which is typical of
many other minerals as well [2, 3]. As the firing temperature
grows, the refraction index perceptibly increases. Thus, N
m
in biotite slightly grows when fired to 800°C and then
abruptly grows from 1.595 to 1.645 when fired to 1000°C. A
possible reason for the increasing refractive index in biotite
is the transition of Fe
2+
to Fe
3+
, which is corroborated by the
color of biotite changing from dark gray to gray-brown,
which is caused by oxide iron above 800°C [4].
The refractive index N
m
of vermiculite perceptibly grows
(from 1.558 to 1.650) under a firing temperature above
400°C, which corresponds to the dehydration process, in par
-
ticular, to the removal of zeolite water. These data indicate
that the refractive index in the interval from 400 to 800°C in
-
creases as a consequence of removal of zeolite water, which
can be restored under dehydration. The restoration of zeolite
water is accompanied by a substantial heat release with a
maximum at the temperature of vermiculite firing equal to
600 – 700°C, which agrees well with the trend in refraction
index variations in rehydrated samples. Firing vermiculite
above 700°C produces irreversible changes in the vermicu
-
lite structure, which, according to the existent notions [5],
Refractories and Industrial Ceramics Vol. 48, No. 2, 2007
91
1083-4877/07/4802-00091 © 2007 Springer Science+Business Media, Inc.
1
Institute of General and Inorganic Chemistry of the Academy of
Sciences of the Republic of Uzbekistan.
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