Improvement of film boiling chemical vapor infiltration process
for fabrication of large size C/C composite
Ji-ping Wang⁎, Jun-min Qian, Guan-jun Qiao, Zhi-hao Jin
State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China
Received 21 June 2005; accepted 5 November 2005
Available online 28 November 2005
An improved film boiling chemical vapor infiltration process was developed to fabricate a large size C/C composite with homogeneous density
and microstructure. The C/C composite was prepared by processing a disc-shaped carbon felt preform, whose upper and lower sides were fixed
and heated simultaneously by two flat surfaces of two heat sources, with kerosene as a precursor at 1050 °C for 3 h at an atmospheric pressure.
The in-situ temperature distribution along the radial direction of the preform upper surface was analyzed to get better information and control of
the process. Experimental results show that the average density of the composite of Φ 110×10 mm3size is about 1.72 g/cm3and its maximal
difference along radial direction is 0.05 g/cm3. Polarized light microscopy (PLM) and scanning electron microscopy (SEM) reveal that the carbon
fibers of the composite are surrounded by ring-shaped pyrocarbons with a thickness of ∼20 μm, and that pyrocarbons are delaminated to 4–6
layers. A schematic model is proposed to analyze the process by dividing the reactor into different regions associated with specific functions.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Carbon/carbon composite; Chemical vapor infiltration; Rapid densification; Microstructure
Carbon/carbon (C/C) composites are widely applied in many
fields for their low density, excellent thermal and mechanical
properties with smooth frictional behavior and good biocom-
patibility . Currently, the main method for fabricating C/C
composites in industry is the isothermal chemical vapor
infiltration (CVI) technique. However, it has a major intrinsic
drawback, namely, a long processing period is inevitable to
obtain desired density [2,3]. Fortunately, another method called
as film boiling chemical vapor infiltration (FBCVI) or chemical
liquid-vaporized infiltration (CLVI) [4–7] has been developed
to increase the deposition efficiency. It appears very attractive to
prepare C/C composite in a short processing time with a high
carbon yield which is about one order of magnitude larger than
by classic isothermal CVI.
It is known that the FBCVI method involves a strong thermal
gradient inside cold wall reactor. A mobile densification front is
created in a porous preform which is directly immersed into a
liquid hydrocarbon precursor. The principle, the experimental
device, and the influences of some basic parameters (temper-
ature, pressure, precursors, etc.) have already been well studied
[3,5,6]. Further investigations are carried out experimentally or
theoretically to reveal the complex chemical reactions leading to
the pyrocarbon matrix in a confined place and the role of the
heat and mass transfers inside porous preform [8–11].
Nevertheless, these studies were mainly carried out in
laboratory reactors. The prepared C/C composites are usually of
thin-walled tubular shape with small dimensions (the wall
thickness is below 35 mm). Moreover, spatial density gradients
exist in the composites, where the density at the interior regions
near the heat source is the highest and that at the outer surfaces
near the liquid precursor is the lowest [11,12]. Therefore, further
improvement of this process is necessary for preparing large
bulk C/C composite of more regular shape with homogeneous
density distribution and uniform microstructure.
For this purpose, a double heat source design is firstly
developed in the present work. A large size C/C composite disc
was fabricated by this improved FBCVI method. To get better
information and control of the whole process, the in-situ
temperature distribution in the preform was recorded and
Materials Letters 60 (2006) 1269–1272
⁎Corresponding author. Tel.: +86 29 82667942; fax: +86 29 82665443.
E-mail address: firstname.lastname@example.org (J. Wang).
0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved.