THERMOSILICATE MATERIALS BASED ON LIME-SILICA BINDER
AND NATIVE WOLLASTONITE
V. I. Vereshchagin,
V. N. Smirenskaya,
S. A. Antipina,
Yu. P. Kostyrev,
and V. G. Kalugin
Translated from Novye Ogneupory, No. 10, pp. 93 – 98, October, 2004.
Original article submitted July 29, 2004.
Results of an experimental study of thermosilicate heat-insulating materials for the aluminum-smelting indus
try based on microsilica and wollastonite (an alternative to anthophyllite asbestos) are reported. The newly de
veloped materials display an apparent density of 1000 – 1200 kg/m
, compressive strength 10 – 15 MPa, and
a high thermal stability.
Heat-treated silicate (thermosilicate) products, owing to
their superior thermal and chemical resistance, strength, and
refractory properties, have found wide use as efficient heat
insulators in aluminum smelting technology and in civil and
industrial engineering. Currently, thermosilicate components
are fabricated from lime-silica binding materials and
anthophyllite asbestos by a technology involving operations
such as lime slaking, diatomite milling, filter-press molding,
autoclaving, and sintering of green performs. Major short-
comings of such asbestos thermosilicate components are the
rather low thermal stability and low durability.
Throughout the world, the recovery of asbestos and its
industrial uses are either limited or prohibited because of the
presumed hazard of asbestos for human health. In the U.S.
and West European countries, the replacement of asbestos by
alternative fibrous materials has been supported by legisla
tion; however, in Russia, such stringent limitations have
never been imposed.
At present, the problems of emerging concern are, in our
opinion, associated, first, with the decline in asbestos reco
very because of the natural exhaustion of existing asbestos
deposits and the lack of explored commercially profitable re
serves and, second, development of the raw materials base
and advanced thermosilicate products, in particular, using
wollastonite as an alternative to asbestos.
Materials based on wollastonite are of practical interest:
adding wollastonite to the silicate mixture improves the per
formance characteristics of the end product. Advantageous
features of wollastonite are its high chemical affinity to pro-
ducts of hydrothermal synthesis of lime-silica binders and
high resistance to molten aluminum; furthermore, wollasto-
nite crystals, owing to their acicular habit, can serve as a
good reinforcing material.
A prototype for the new thermosilicate product was the
heat-insulating material known under the trade name
“Asbotermosilikat” which is currently used in the aluminum
industry. Its properties are compressive strength, 10 – 25 MPa;
apparent density, 700 – 800 kg/m
; open porosity, 55 – 75%,
and moisture content, not higher than 8 g/g.
Tests carried out on pilot-batch specimens prepared us
ing wollastonite and a lime-diatomite binder gave the follow
ing results: compressive strength, 26.90 – 29.40 MPa; appa
rent density, 1530 – 1580 kg/m
; open porosity, 41.59 –
In strength characteristics, the wollastonite-based com
ponents conform to requirements placed on the thermo
silicate; however, their heat-insulating properties (conse
quently, density and porosity), are below standard.
Our goal in this study was to develop thermosilicate ma
terials based on wollastonite (as an alternative to asbestos)
and a lime-microsilica binder.
RAW MATERIALS CHARACTERIZATION
Microsilica (occasionally named “silica fume”) used as a
component for the binder was a waste in the production of
crystalline silicon and ferrosilicon (available from Novo
kuznetsk Ferroalloy Factory and Bratsk Aluminum Smelting
Refractories and Industrial Ceramics Vol. 46, No. 1, 2005
1083-4877/05/4601-0058 © 2005 Springer Science+Business Media, Inc.
Tomsk Polytechnical University, Tomsk, Russia; Mining and
Chemical Engineering Kombinat, Zheleznogorsk, Russia.