MEMBRANE POROUS MATERIALS FROM SIALON
V. N. Antsiferov
and V. G. Gilev
Translated from Ogneupory i Tekhnicheskaya Keramika, No. 2, pp.2–8,February, 2001.
Carbothermal reduction and simultaneous nitriding of kaolin in pressings from a mixture with graphite are
used to fabricate a ceramics based on b-sialon with a porosity of 50 – 60%, a pore size of about 1 mm, and a
gas permeability of about 0.04 mm
. Mercury porosimetry of one of the specimens shows a narrow size distri
bution of the pores with a maximum at 0.7 mm. The method used for fabricating the porous sialon is classified
as reaction sintering, and the elevated permeability of the obtained sialon materials is associated with the neg
ative volume effect of the reaction of carbonitriding of kaolin.
Today researchers pay much attention to the develop-
ment and use of porous and membrane materials based on
various ceramics including silicon nitride and sialons [1 – 6].
Sialon ceramic materials have a low thermal conductivity
and a high resistance to thermal shocks, and can serve as
heat-insulating, structural, and filtering materials under the
conditions of heat cycles, high temperatures, and corrosive
media [7 – 9].
Fabrication of highly porous preforms from silicon with
sialon-forming additives is connected with some difficul
The pore space is a specific phase component the config
uration of which determines to a considerable degree the
level of physicomechanical, thermophysical, gas dynamic,
and other characteristics of porous materials. The require
ments with respect to the pore size and other parameters of
the porous structure are determined by the purpose of the
material and can differ. Ceramic membranes are produced
from materials with channel pores £ 1 mm in size.
The methods for fabricating microporous materials are
reviewed in .
It is known, for example, that channel pores can be
formed in a material due to phase transformations and che
mical interaction between the components of the charge, if
the forming products have a higher density than the initial
According to I. Ya. Guzman , the method of reaction
sintering presents much interest for fabrication of micro
porous materials. This interest is connected with the fact that
reaction sintering involves mass transfer between the sin-
tered porous body and the gas reagent as a necessary ele-
ment, which a priori requires a connected pore system that
penetrates the entire volume of the material up to the last
sintering stage. However, the materials from reaction-sin-
tered silicon nitride (RSSN) have a limited permeability, and
the use of burning-out additives for enhancing their porosity
and permeability causes a considerable increase in the dia-
meter of the obtained pores .
We tried to fabricate microporous sialon materials by the
method of carbothermal reduction with simultaneous nitrid
ing of kaolin commonly used for the production of sialon
powders [14 – 18]. When the process is performed on pres
sings fabricated from a mixture of kaolin and a carbon reduc
ing agent, it can be treated as reaction sintering.
In classical examples, reaction sintering provides prod
ucts with a stable size with no shrinkage, which in our pro
cess is not observed in all of the stages. However, the con
cepts on the volume and mass effects of the reactions can be
used for explaining the observed phenomena in this case too.
Quite a number of sialon phases can form in the Si – Al –
O – N system, the data on which are scarce and contradictory
Table 1 presents data from the ASTM x-ray diffractomet
ry file on the structure of sialon phases that can form due to
interaction between Si
, AlN or due to carbo
thermal reduction of alumosilicates in a nitrogen medium.
The x-ray densities have been calculated for some of the
phases. The base phases are b-sialon and the X-phase, which
have close densities (about 3.1 g/cm
Refractories and Industrial Ceramics Vol. 42, Nos.1–2, 2001
1083-4877/01/0102-0057$25.00 © 2001 Plenum Publishing Corporation
Scientific Center for Powder Materials Research, Perm, Russia.