HEAT-INSULATING CERAMICS WHICH HAVE A NANOPOROUS
STRUCTURE AND ARE MADE WITH THE USE OF ASH-BEARING
WASTES FROM POWER PLANTS
T. V. Vakalova,
T. A. Khabas,
I. B. Revva,
and I. A. Pavlova
Translated from Novye Ogneupory,No.12,pp.6–11,December, 2014.
Original article submitted August 4, 2014.
It is determined that the pore-forming effect exhibited by ash and ash microspheres in compositions with
clayey rocks is due not only to certain structural features (the presence of spherical hollow particles) and the
makeup of the ash components (the presence of residual fuel in the ash) but also to physico-chemical pro
cesses (the synthesis of anorthite and mullite) which take place in clay – ash-and-clay – ash- microsphere sys-
tems and prevent shrinkage during sintering.
Keywords: technogenic wastes, ash-slag wastes, ash-soot, ash microspheres, structure formation, pore forma-
tion, pore distribution, strength.
The high rates of growth of industrial and civil construc-
tion are creating a need for larger quantities of competitive,
environmentally green, low-priced heat-insulating ceramics.
Given the diminishing reserves of natural raw materials and
the need to make use of industrial waste products, it is impor
tant to create ceramic materials that make use of secondary
resources. Included among these resources: solid ash-bearing
waste products from the burning of coal at electric power
plants and heat and power plants (ash-slag wastes, ash
microspheres, and wastes consisting of ash-soot), rice husks
and other vegetable residues, biomasses, and textile wastes.
The sources of the ash depend on the nature of the local re
sources. In international practice, ash-bearing wastes are
most often used to make porous lightweight concrete. A less
frequent application of these wastes is in the production of
heat-insulating ceramics [1 – 4].
Wastes composed of ash-soot from the combustion of
coal are considered environmentally clean and are used to
make construction materials. New types of heat-insulating
materials are being developed with the use of ash-soot as a
component. Here, the refractory products are shaped by vari
ous technologies — from extrusion to casting. Sintered heat-
insulating materials with a porosity from 86.3 to 94.5 vol.%
have a very low thermal conductivity (0.0511 W/(m·K) but
are also low in strength — ultimate compressive strength
ranges from 0.43 to 1.10 MPa [5 – 7].
When coal from a certain basin is used, the ash-soot is
characterized by a fairly stable chemical composition. This
makes it possible to predict the quality of the ceramic materi
als that will be obtained from them.
Another waste product formed in the combustion of coal
at heat and power plants consists of ash microspheres - a
lightweight fraction formed from molten alumosilicates
filled with a mixture of gases. In the removal of ash by wet
methods, the low density of the microspheres causes them to
form a floating layer of ash on the watery surface of the sedi
ment. The ash can easily be collected and removed in this
Abroad, ash microspheres from solid wastes formed by
the combustion of coal are extracted in volumes totaling
thousands of tons a year. The microspheres can be used in
place of such minerals as clay, talc, calcium carbonate, and
silica. It is also possible to use artificially produced spheres,
which is a more costly undertaking [8, 9]. It has been estab
lished that ash microspheres can be successfully used in heat
engineering, construction, plastics manufacturing, metal
Refractories and Industrial Ceramics Vol. 55, No. 6, March, 2015
1083-4877/15/05506-0505 © 2015 Springer Science+Business Media New York
Tomsk National Polytechnic Research University, Tomsk, Russia.
Ural Federal University, Ekaterinburg, Russia.