SCIENTIFIC RESEARCH AND DEVELOPMENT
LOW-TEMPERATURE PRODUCTION OF POROUS SILICON-CARBIDE
CERAMICS BY THE SELF-BINDING METHOD
and Jun Ma
Translated from Novye Ogneupory, No. 5, pp. 26 – 30, May, 2012.
Original article submitted November 29, 2011.
Polycarbosilane (PCS) heat-treated (preheated) at low temperatures (500 – 600°C) was chosen as the raw ma
terial for the production of porous SiC ceramics. The PCS was ground in a ball mill, shaped by slip casting,
and sintered at 1000°C. Due to the semi-organic structure of the preheated PCS, the milled powders can be
shaped and then sintered at 1000°C without the use of other binders; this made possible to create the
above-mentioned porous SiC ceramics. The pore size, open porosity, and ultimate flexural strength of the SiC
ceramics that were obtained were studied. It was found that an increase in the temperature at which the PCS is
heat-treated impedes its shaping and reduces the open porosity and ultimate flexural strength of the resulting
SiC ceramics. Information is also presented from a study of the fracture surface of the porous SiC ceramic.
Keywords: porous SiC ceramics, polycarbosilane (PCS), PDC method, ultimate flexural strength.
One advantage of membranes and filters made of porous
SiC is their ability to perform at high temperatures. They can
do so because of their low density, low coefficient of thermal
expansion, chemical stability, and resistance to oxidation
[1 – 5]. However, due to the covalent nature of the Si-C
bonds, it is usually necessary to sinter SiC ceramics at high
temperatures and/or to add sintering agents. These require
ments have limited the application of such ceramics. There
has recently been an increasing amount of interest in a
method used to obtain ceramics from polymers — the PDC
(polymer-derived ceramic) method — and its application to
the production of porous SiC at low temperatures; poly
carbosilane (PCS) is the most important precursor for prepar
ing porous SiC by the PDC process [6 – 9].
The ultimate flexural strength of porous SiC ceramics
obtained by the PDC method is relatively low due to the
large amount of weight lost during the heating of PCS
(50 – 60 wt. %). In this study, porous SiC ceramics were
made by preheating PCS at a low temperature (500 – 600°C),
this operation then being followed by milling, slip casting,
and sintering at 1000°C. It was found that the semi-organic
structure of the preheated PCS allows the milled powder to
be shaped and sintered at 1000°C without any other binders.
This in turn made it possible to increase the ultimate flexural
strength of the resulting porous SiC ceramics.
Polycarbosilane (melting point 180°C, molecular weight
1800, C/Si = 1.6; synthesized in our laboratory ) was
preheated at low temperature (500 – 600°C) in a flow of N
(the corresponding specimens were given the designations
PCS500, PCS550, and PCS600). The PCS500, PCS550, and
PCS600 specimens were then ball-milled for 2 h with the use
of xylene as a solvent. The jars were filled with N
milled powders were then passed through a 100-mesh sieve
and pressed into wafers at a pressure of 20 MPa. The wafers
were subjected to pyrolysis at 1000°C for 1 h in an N
Figure 1 presents a flow chart depicting the synthesis of the
porous SiC ceramic.
FTIR spectra (obtained with a Nexus 670 spectrometer)
and TG analysis (performed on a Netzsch STA 499C thermal
analyzer) were used to determine the differences between the
initial PCS and the PCS500, PCS550, and PCS600 speci
mens. The structure of the SiC ceramics that were obtained
was studied by XRD (performed on a Siemens D500 diffrac
tometer in Cu K
-radiation). The open porosity of the speci
Refractories and Industrial Ceramics Vol. 53, No. 3, September, 2012
1083-4877/12/05303-0157 © 2012 Springer Science+Business Media New York
National University of Defense Technology (Changsha, China).