PERGAMON
Carbon 38 (2000) 1917–1923
Formation of nodulated vapor grown carbon fiber
*
Jyh-Ming Ting , B.C. Lan
Department of Materials Science and Engineering
,
National Cheng Kung University
,
Tainan
,
Taiwan
Received 22 October 1999; accepted 4 January 2000
Abstract
A very unusual form of carbon fibers is reported. While preparing vapor grown carbon fiber at temperatures exceeding
12008C, formation of nodulated carbon fibers were found in addition to normal vapor grown carbon fibers. The growth
temperature was found to be the primary, if not only, factor influencing the formation of nodules and the frequency of
occurrence. The formation of such an unusual structure is related to the defect microstructures found in the fiber during the
growth, and explained in terms of a three-dimensional nucleation model. 2000 Published by Elsevier Science Ltd. All
rights reserved.
Keywords
:
A. Carbon beads; B. Chemical vapor deposition; C. Scanning electron microscopy; D. Microstructure
1. Introduction synthesized at a temperature of 11008C under different
gaseous compositions and growth times [7]. Although
Polymeric precursor, such as polyacrylonitrile and pitch effects of temperature on the growth and characteristics of
derived carbon fiber and vapor phase grown carbon fiber VGCF have been investigated, these studies primarily
represent two different types of carbon fibers currently focused on temperatures below 12008C [8]. A recent report
available. They differ not only in synthesis, but also the indicates the formation of beaded carbon obtained at
microstructure and therefore in properties. Synthesis of 14008C while growing VGCF [9]. The report shows
polymeric precursor derived carbon fiber is a melt-spun micrographs of the beaded carbon and briefly discusses the
process and involves many processing steps [1,2]. On the microstructure. However, the formation mechanism was
other hand, the vapor phase process is a single-step process not reported. In this paper, we report the formation of
involving the use of a metal catalyst [3]. Fibers thus another very unusual nodulated VGCF at growth tempera-
produced are often called catalytic chemical vapor de- tures greater than 12008C, and discuss the formation
posited fiber (CCVD fiber) or vapor grown carbon fiber mechanism. The formation and frequency of nodules
(VGCF). Due to the differences in preparing these two occurrence were both influenced by the growth conditions.
groups of carbon fibers, the resulting fibers have very The formation of such an unusual structure is related to the
different microstructure and properties [4,5]. For example, defect microstructures found in the fiber during growth and
VGCF exhibits a tree annual ring type of structure and has explained in terms of a three-dimensional nucleation
a hollow core whose diameter is influenced by the size of model.
the catalyst particle used [6]. As the diameter of VGCF is
reduced, its tubular nature becomes more apparent. This is
shown in Fig. 1A where a tubular VGCF with an outer
2. Experimental
diameter and inner diameter of 220 and 170 nm, respec-
tively, is seen [7]. The tubular VGCF exhibits a constant
Growth of VGCF was performed using a technique
diameter and a smooth surface with the hollow passing
similar to that described elsewhere [10,11]. Briefly, the
through the entire tube. However, a bamboo-like structure
carbon fibers were grown through the pyrolysis of methane
where the hollow is sectioned is occasionally observed, as
in the presence of iron catalyst particles using a 1-inch
shown in Fig. 1B. The fibers shown in Fig. 1 were all
horizontal tube furnace.Various concentrations of methane,
diluted by hydrogen, were used. The methane concen-
tration ranges from 10 to 83.3%. The growth temperatures
*Corresponding author. Tel.: 1886-6275-7575 ext. 62949;
fax: 1886-06-238-5613.
were 1000, 1100, 1200, 1300, and 14008C, which were
0008-6223/00/$ – see front matter 2000 Published by Elsevier Science Ltd. All rights reserved.
PII: S0008-6223(00)00021-X