PRODUCTION OF PERMEABLE FIBROUS MATERIALS
COMPOSED OF SILICON NITRIDE
V. G. Gilev
and L. M. Grevnov
Translated from Novye Ogneupory, No. 6, pp. 24 – 26, June, 2015.
Original article submitted December 15, 2014.
A technology which involves spraying a silicon-based thixotropic thermoplastic slip with a paraffin-based
binder onto a rotating substrate-target is used to obtain a material that based on reaction-sintered silicon nitride
and has a porous, permeable, fibrous framework-like structure. The fibers are distributed evenly over the sur
face of the substrate and are deposited on it in varying directions at low rates allow heat to be removed from
the product. This results in the formation of fibrous framework-like structures that retain their original poros
ity as they subsequently undergo heating and a certain amount of contraction in the height direction. They can
be used as porous partitions for the delivery and combustion of natural fuels in power plants and as filters for
removing slag inclusions and oxide films from melts.
Keywords: reaction-sintered silicon nitride, porosity, thermoplastic slip, thixotropy.
Porous materials can be obtained from silicon nitride by
a variety of methods [1 – 6], including methods that employ
reaction sintering [7 – 18]. Over a wide range of viscosities,
materials based on reaction-sintered refractories (RSSN) are
highly resistant to thermal shock and thermocyclic loading
[19, 20] and to oxidation at temperatures up to 700 – 800°C.
They are promising for use as porous partitions for the deliv
ery and combustion of natural fuels in power plants, and they
are capable of withstanding extreme conditions.
The porosity and permeability of most of the silicon-
nitride-based materials obtained by the established technolo
gies [1 – 18] are not uniform enough for use in the above-in
dicated applications. Thus, these functions are currently per
formed by high-porosity cellular materials based on heat-re
sistant metallic materials (HRMMs) of the chromal type.
However, the service life of traditional HRMMs is limited in
oxidizing media because they are constructed from elements
in the form of thin-walled hollow tubes. We have attempted
to obtain highly porous RSSN-based fibrous ceramics that
can eventually compete with chromal-type HRMMs.
The thermoplastic slip that we developed earlier to make
materials composed of thin-walled ele
ments [12 – 18] has properties that allow the slip to be used
to produce elements in the form of 0.5 – 1.5-mm-thick fibers.
The fibers are formed from the molten slip as it is being at-
In forming a material or product having a structure in the
form of a porous, permeable fibrous framework, an impor-
tant role is played by the quality with which the fibers are ar
ranged and the strength of the bonds between them. The fi
bers are laid in different directions and are spaced uniformly
over the area of the material, with the low rate of fiber place
ment allowing heat to be removed from the product. This
process results in the formation of framework-like fibrous
structures that retain their original porosity as they subse
quently undergo heating and some contraction in the height
direction. These structures can be used to filter melts of met
als in order to remove slag inclusions, oxide films, etc. The
advantages of silicon carbide in this case are obvious: high
heat resistance, good refractoriness, and chemical stability.
Tests were conducted using different types of atomizing
equipment operating on the principle of the atomization of a
molten bath by a submerged rotating tool. The melt did not
adhere to disk-type tools, but better results were obtained
when pins that are periodically submerged in the melt were
attached to the disk. The use of such an instrument resulted
in atomization of the melt in the form of fibers, but the
viscoelastic properties of the slip led to the formation of cav
ities on the surface of the melt and thus made it more diffi
cult to control the atomization process.
Refractories and Industrial Ceramics Vol. 56, No. 3, September, 2015
1083-4877/15/05603-0254 © 2015 Springer Science+Business Media New York
Perm National Research Polytechnic University, Perm, Russia.