JOURNAL OF MATERIALS SCIENCE 36 (2001) 4259 – 4266
Carbon/carbon composites derived from
phenolic resin/silica hybrid ceramers
Part I Oxidation resistance and morphological properties
JIA-MIN LIN, CHEN-CHI M. MA
∗
Department of Chemical Engineering, National Tsing-Hua University, HsinChu, Taiwan 300
E-mail: ccma@che.nthu.edu.tw
WEN-CHI CHANG
Materials Science Center, National Tsing-Hua University, HsinChu, Taiwan 300
A novel phenolic resin/silica hybrid ceramer fabricated via the sol-gel method was
prepared. Hybrid systems with different inorganic contents were used as the matrix
precursors to fabricate the silica containing carbon/carbon composites. Isothermal
oxidation tests at temperatures ranging between 650
◦
C and 750
◦
C were employed to
investigate how the oxidation resistance of the derived carbon/carbon composites is
improved. Furthermore, the isothermal oxidation test results between 550
◦
C and 615
◦
C
were used to calculate the activation energy of oxidation. Experimental results demonstrate
that the silica containing carbon/carbon composites have a better oxidation resistance than
those derived from pure phenolic resins. Meanwhile, morphological observations
indicate that the oxidation of carbon fibers is retarded in the phenolic resin/silica hybrid
derived carbon/carbon composites.
C
2001
Kluwer Academic Publishers
1. Introduction
Organic/inorganic hybrid material fabricated through
sol-gel technology represents a new class of mate-
rials developed in the recent decade [1]. Incompat-
ible organic and inorganic components are mixed at
the nanoscale to form molecular composites. The fab-
ricated materials possess the advantages of both or-
ganic polymers and inorganic ceramics. These materi-
als are termed “Ceramers” by Wilkes [2] or “Ormosils”
by Schmidt [3]. Several polymers have been investi-
gated as the organic phase of the hybrids such as poly-
imides [4, 5], polybutadiene and polydimethylsiloxane
[6], phenolic resins [7], and so on.
Carbon fiber reinforced carbon matrix (C/C) com-
posites are unique materials that possess excellent pro-
perties such as high specific strength, high toughness
and light weight. Particularly, they can retain me-
chanical properties at temperatures above 2000
◦
C and,
hence, the C/C composites are attractive materials for
use in rocket nozzles, disk brakes and thermal insulating
elements [8, 9]. However, C/C composites are limited
in that the carbon will rapidly oxidize under an oxy-
gen environment at temperatures as low as 500
◦
C [10].
Thus, a good oxidation protecting system is crucial in
the development of C/C composites.
Two main classes of oxidation protection techniques
exist for C/C composites. The first method involves
coating a protective layer on the outer surface of C/C
∗
Author to whom all correspondence should be addressed.
composites. The microstructure and oxidation resis-
tance of SiC coated C/C composites have been de-
scribed in our previous study [11]. The other method for
improving the oxidation resistance of C/C composites is
adding oxidation inhibitors. Mckee [12, 13] conducted
a series of investigations on the inhibitors for modifying
the oxidation resistance of C/C composites. Mun [14]
also investigated the effects of combining various in-
hibitors in C/C composites. The above studies proved
that adding inhibitors improves the oxidation resistance
of C/C composites in certain temperature regions.
In our previous study [15], sol-gel method derived
phenolic resin/silica hybrid ceramers have been em-
ployed as the matrix to prepare carbon fiber reinforced
composites and to study the mechanical and thermal
properties of the fabricated composites. According to
those results, the phenolic resin/silica hybrid provides
better thermal properties and higher stiffness than neat
phenolic resins, furthermore, only microphase separa-
tion occurred between the organic and inorganic phases.
Generally, phenolic resins are often used as the precur-
sors of C/C composites and silica is a kind of oxidation
inhibitor. The phenolic resin/silica hybrid contains both
components and it should be possible to use the hybrids
as the precursors to fabricate the novel silica containing
C/C composites in one-step. Additionally, good com-
patibility between organic phenolic resin and inorganic
silica ensures improved distribution of silica inside the
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2001 Kluwer Academic Publishers
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