CONSOLIDATION OF SLIP THIN-WALLED ELEMENTS
BASED ON THIXOTROPIC DISPERSED SYSTEMS FOR PREPARING
HIGHLY POROUS RSSN
V. N. Antsiferov
and V. G. Gilev
Translated from Novye Ogneupory, No. 8, pp. 39 – 43, August 2015.
Original article submitted December 15, 2014.
Features are considered for preparing highly porous workpieces of silica by warm molding of elements pre-
pared by cutting castings from thermoplastic slip based on silica with addition of plasma chemical synthesis
silicon nitride and appropriate highly porous silicon nitride materials, and also methods by means of which a
molded workpiece or sintered object may be given additional channel porosity for improving permeability.
Material is suggested for use in power generation installations as a porous barrier for feeding natural fuel
through porous material and combustion, capable of withstanding extreme situations.
Keywords: reaction-sintered silicon nitride, RSSN, porosity, thermoplastic slip, thixotropy.
Materials based on reaction-sintered silicon nitride
(RSSN) over a wide range of porosity exhibit good resis-
tance to thermal shock and thermal cycling, to oxidation up
to a minimum temperature of 700 – 800°C, and capacity to
withstand extreme situations. These materials may be con-
sidered promising for use in power generation installations
as porous barriers for supply of natural fuel though a porous
medium and combustion.
The majority of materials based on silicon nitride, pre-
pared by well-known technology, do not have adequate uni-
form porosity and permeability, required for this application,
and therefore currently for this purpose highly porous cellu-
lar materials (HPCM) based on metallic heat-resistant mate-
rials of the chromal type are used. Traditional metal HPCM
are made up from elements of the hollow thin-walled tube
type, and therefore their life in an oxidizing atmosphere is
limited. We have attempted to prepare ceramic highly porous
material based on RSSN capable of competing in the future
with chromal type HPCM.
In this work methods are considered for preparing highly
porous workpieces made of silica and corresponding materi-
als based on RSSN, and also methods by means of which
workpieces or sintered objects are formed may be given ad-
ditional channel porosity in order to increase permeability.
Much work has been devoted to technology for preparing
porous ceramic materials [1 – 10]. Carbothermal reduction
of silicon oxide and simultaneous nitriding [1, 2], sintering
powder at reduced temperature, sintering with burn-
ing-off additions, partial hot pressing [3, 6, 8, 9], extrusion
with organic binder , sol-gel methods , casting and
freezing of aqueous suspensions (freeze casting) , and
sintering of granules based on Si powder, prepared by spray
drying , are used. In earlier work in order to achieve a
highly porous condition suspension swelling methods or in-
troduction of ceramic powders into a prepared organic foam,
and application of a suspension to a cellular foam polyure-
thane substrate, followed by substrate destruction , have
also been used.
We have proposed a method for controlling porosity of
silicon nitride material by consolidation of slip thin-walled
elements made of thermoplastic slip based on silicon with
special additions [12 – 21], which is possible if the slip in a
heated condition is a thixotropically dispersed system. The
role of special additives includes increasing slip thixotropic
properties. Different dispersed powders have been tried: sili
con, silicon oxide, and plasma chemical synthesis silicon
nitride (PCS). Only PCS Si
powder gave a thermoplastic
slip based on silicon powder with a paraffin binder with 15
Refractories and Industrial Ceramics Vol. 56, No. 4, November, 2015
1083-4877/15/05604-0413 © 2015 Springer Science+Business Media New York
Powder Materials Science Scientific Center FGBOU VPO Perm’
National Research Polytechnic University, Perm’, Russia.