UNMOLDED REFRACTORIES WITH A SILICA SOL BINDER
S. S. Gordeeva,
A. G. Kozlovskii,
Yu. V. Askinazi,
and S. A. Suvorov
Translated from Novye Ogneupory, No. 7, pp. 26 – 28, July 2010.
Original article submitted March 3, 2010.
Results are provided for a study of unmolded refractories based on silica sol binder, and comparison of them
with unmolded refractories with a binder based on high-alumina cement. It is shown that with respect to
strength and thermal shock resistance unmolded refractories with a silica sol binder surpass those with a ce
ment binder. Refractories with a silica sol binder make it possible to use them for drying up to 110°C, and this
reduces considerably the preparation time to use for a molded refractory.
Keywords: unmolded refractories, concrete mixes, silica sol, corundum, silicon carbide, sol-gel transition, ul
timate strength in compression, density, ultimate strength in compression.
In the metallurgical industry there is extensive use of
unmolded refractories. As experience of their use has shown,
they are high technology materials and make it possible to
prepare refractory objects complex in shape directly for the
user. Most widespread are refractory concretes based on co-
rundum, within which the binder used is high-alumina ce-
ment (HAC) [1 – 3].
In order to prepare high quality refractories from con-
crete mixes based on HAC-binders structure control of the
temperature is necessary for concrete hardening in order to
provide strength and exclude lining defects. In heat treating
products of HAC hydration in the range 200 – 600°C chemi-
cally bonded water is released, that is accompanied by a re-
duction in material strength. Rapid evaporation of water may
lead to breaking of the refractory structure (explosive effect).
These features of unmolded refractory behavior based on
HAC are complicated in the winter period of performing
The aim of this work was to study the production fea
tures and properties of unmolded refractories of concrete
mixes based on a silica sol binder. A feature of silica sol and
transitions typical for their sol-gel is the fact that in contrast
to a cement binder, entering into chemical bonding with wa
ter, a binder based on silica-sol releases chemically bonded
water with a sol-gel transition. Sol viscosity increases with a
change-over to a gel state. Joining of colloidal sol particles
develops in time, strengthening the matrix formed all the
more. A considerable part of the water in gel is liberated and
evaporated at temperatures close to 100°C. with an increase
in temperature a small amount of water, that remains in the
form of bonded hydrated gel groups, is also liberated, but is
accompanied by material strengthening.
Studies were performed on specimens molded from a
mix based on silica-sol and cement binders. Refractories
with HAC binder were prepared from a dry refractory mix of
the following composition, wt.%: corundum filler fraction
0.6 mm, 60, silicon carbide, 15, binder based on HAC, 25.
the dry mix was mixed with 5 wt.% water above 100%.
Within the concrete mix composition based on silica sol
binder HAC was replaced by alumina and mixed with sil-
ica-sol in an amount of 5 wt.%.
Determination of the ultimate strength in compression
was carried out in a IP-500 test machine according to GOST
4071.1 and GOST 7875.0 in cubic specimens with an edge
size of 50 mm. The ultimate strength in compression and ap
parent density were determined in specimens after drying at
100°C for 24 h and also after heat treatment at 1000 and
1500°C for 3 h. Linear specimen dimensions after drying and
heat treatment were measured with an accuracy of 0.1 mm.
The change in linear dimensions Dl was calculated by the
is specimen size before firing; l
is specimens size
after firing. Testing of cubic specimens with an edge size of
50 mm for thermal shock resistance was carried out in accor
dance with GOST 2405 by the regime 950°C – water.
RESULTS AND DISCUSSION
The strength of refractories based on silica gel and ce
ment binder after drying at 100°C and also after heat treat
ment at 1000 and 1500°C are shown in Fig. 1. The ultimate
strength in compression after drying a refractory based on
cement binder is higher by a factor of two than for silica sol
Refractories and Industrial Ceramics Vol. 51, No. 4, 2010
1083-4877/10/5104-0272 © 2010 Springer Science+Business Media, Inc.
OOO Refractory Technologies, St Petersburg, Russia.
GOUVPO St Petersburg State Technological Institute (Technical
University), St. Petersburg, Russia.