HEAT-INSULATING REFRACTORY MATERIAL
BASED ON HOLLOW CORUNDUM MICROSPHERES
B. L. Krasnyi,
V. P. Tarasovskii,
A. B. Krasnyi,
A. L. Galganova,
and A. V. Reznichenko
Translated from Novye Ogneupory, No. 12, pp. 29 – 31, December, 2014.
Original article submitted September 18, 2014.
A study is made of the effect of dispersant additives on the properties of a mix and a fired material containing
hollow corundum microspheres. It is shown tht the addition of CASTAMENT FS10 together with
CASTAMENT FW 10 makes it possible to obtain a green product having an ultimate compressive strength of
at least 2 MPa. The fired material is slightly less porous than the material without dispersant additives.
Heat-insulating ceramics based on hollow corundum microspheres and having an open porosity of at least
50.7% and an ultimate compressive strength of at least 35 MPa are obtained after firing at 1600°C. The mate
rial shrinks no more than 0.2% during the firing operation, which has made it possible to make large products
of complex shape and ship them to customers.
Keywords: ceramics, structure, corundum, hollow microspheres, thermal conductivity, strength, porosity.
The amount of thermal energy lost in the course of
high-temperature processes is often several times greater
than the amount of heat theoretically needed for the given
process. Special materials — high-temperature heat-insulat-
ing materials — are needed to keep heat energy inside the
working space of equipment that operates at high tempera-
tures and prevent it from escaping into the environment.
Thus, modern industrial operations which are performed at
high temperatures would not be possible without efficient
heat-insulating refractories and products made of them.
In connection with the increasing rates at which produc
tion processes are carried out, the temperature inside
high-temperature equipment is also continually rising. To
make the equipment’s operation more efficient, it is neces
sary to develop new high-strength heat-insulating materials
that can perform for long periods of time at temperatures in
the range 1700 – 1800°C. Porous ceramics based on hollow
corundum microspheres might constitute one such type of
Repeated attempts have been made previously to create
heat-insulating materials based on hollow corundum micro
spheres. However, all of the resulting materials lacked ade
quate ultimate strength in compression. For example, semi-
dry pressing was used in  to obtain specimens based on
hollow corundum microspheres. After being fired at 1750°C,
the apparent density of the material was no greater than
and its ultimate compressive strength was 14 MPa.
The authors of [3, 4] proposed the use of a method which in-
volves vibrational compaction in wooden or gypsum molds
to obtain large products and products of complex shape from
mixes based on hollow granules. Surface-active additives are
used in the process. After firing at 1750°C, the large products
which were made had an apparent density no higher than
and an ultimate compressive which ranged up to
The investigation described in this article was performed
to create a highly efficient high-strength heat-insulating ma
terial with an Al
content of at least 99.5 wt.% and a ser
vice temperature of 1700 – 1800°C in reducing atmospheres.
We examined the feasibility of obtaining heat-insulating
refractories from mixes based on hollow corundum
microspheres by subjecting highly concentrated suspensions
Figure 1 shows the microstructure of the corundum
refractories. The microspheres’ impurity content, %: SiO
O 0.3. The bulk density of different frac
tions of the microspheres is shown below:
Fraction, mm ............ 0.5–5.05.0–3.01.0–3.00.1–1.0
Apparent density, g/cm
.... 1.5 0.61* 0.71* 0.93*
* After screening into fractions.
Refractories and Industrial Ceramics Vol. 55, No. 6, March, 2015
1083-4877/15/05506-0559 © 2015 Springer Science+Business Media New York
ZAO “NTTs Bakor,” Shcherbinka, Moscow Oblast, Russia.
Moscow State Industrial University, Moscow, Russia.