MAKING HOLLOW CYLINDRICAL PRODUCTS
OF HIGH-POROSITY SILICON NITRIDE BY THE CENTRIFUGAL FORMING
OF GRANULES OF A THIXOTROPIC THERMOPLASTIC SLIP
V. G. Gilev
Translated from Novye Ogneupory, No. 10, pp. 44 – 49, October, 2015.
Original article submitted March 25, 2015.
This article describes features of the manufacture of high-porosity silicon semifinished products in the form of
hollow cylinders by the warm centrifugal casting of elements obtained from cutting up castings of a sili
con-based thermoplastic slip. Silicon nitride obtained by plasmochemical synthesis is added to the slip to im
part the necessary rheological properties. Products in the form of hollow cylinders with walls made of a highly
porous silicon nitride material are obtained from the semifinished products by removing the binder through
sublimation and then subjecting the semifinished products to reaction sintering in nitrogen. The areas of appli-
cation proposed for the material and the hollow products obtained from it: porous partitions for the filtration
and combustion of natural fuels in power plants; porous inserts for the local reinforcement of die-cast products
made of light metals.
Keywords: reaction-sintered silicon nitride, RSSN, porosity, thermoplastic slip, centrifugal forming,
Materials that are based reaction-sintered silicon nitride
(RSSN) and are made with a wide range of porosities are re
sistant to thermal shock and thermal cycling, in addition to
being very resistant to oxidation up to at least 700 – 800°C.
Such materials are promising for use in power plants as po
rous partitions which allow natural fuels to be fed through a
porous medium and burned. These partitions can withstand
extreme service conditions.
Most of the silicon-nitride-based materials that are made
by the established technologies are insufficiently uniform in
their porosity and permeability. High-porosity cellular mate
rials (HPCMs) based on heat-resistant metallic materials
similar to Chromal are used instead for the application de
scribed above. However, conventional HPCMs are com
posed of hollow thin-walled tubes, which limits their service
life in oxidizing media.
In this investigation, an attempt was made to obtain
products in the form of hollow cylinders with a wall com
posed of a high-porosity RSSN-based ceramic. The goal is to
have such products eventually compete with similar products
made of HPCM Chromal. The article examines methods
used for the centrifugal forming of hollow cylinders and
more complex shapes with a highly porous wall that is ini
tially made of silicon and is then converted to RSSN by
Many studies have been devoted to developing a technol
ogy for obtaining porous ceramics based on silicon nitride
[1 – 20]. Among the methods that are being employed are
carbothermic reduction of silicon oxide and simultaneous
nitriding [1, 2], sintering powders of Si
at reduced tem
peratures, sintering with additives that undergo combustion,
partial hot pressing [3, 6,8–9,11–18], extrusion with or
ganic binders , sol-gel methods [5, 19], casting and freez
ing of aqueous suspensions (freeze-casting) , sintering of
granules based on Si powder obtained by spray drying ,
and the production of decomposed precursors .
In earlier studies, researchers attempted to achieve a state
of high porosity by resorting to suspension swelling, the in
troduction of ceramic powders into a pre-prepared organic
foam, or the application of a suspension to a cellular polyure
thane-foam substrate which was subsequently decomposed
Refractories and Industrial Ceramics Vol. 56, No. 5, January, 2016
1083-4877/16/05605-0538 © 2016 Springer Science+Business Media New York
Perm National Research Polytechnic University, Perm, Russia.