Materials Sciences and Applicatio n, 2011, 2, 936-939
doi:10.4236/msa.2011.27124 Published Online July 2011 (http://www.SciRP.org/journal/msa)
Si-N-C Nanowires Derived by
Polyhydridomethylsilazane Pyrolysis
Gongjin Qi
Beijing Aeronautical Technology Research Center, Beijing, China.
Received November 10th, 2010; revised January 24th, 2010; accepted May 19th, 2011.
ABSTRACT
The preceramic polymer, polyhydridomethylsilazane, was synthesized and pyrolyzed at 1873 K in nitrogen atmosphere
to prepare Si-N-C nanowires without using any catalysts. The diameters of the nanowires were from tens of nanometers
to several microns, and the maximum length of the nanowires reached several hundred microns. The nanowires had no
bulbs or droplets on the tips. However, two different bulbs with diameters of several microns were observed, and one
bulb was covered by nanowires all around, while the other bulb had nanowires just covered on its han dle.
Keywords: Si-N-C Nanowires, Polyhydridomethylsilazane, Pyrolysis
1. Introduction
Silicon nitride possesses excellent thermal and mechani-
cal properties and is one of the most important engineer-
ing ceramics. Synthesis of one-dimensional nanostruc-
tured silicon nitrides has attracted tremendous interest in
recent years [1-8], because of their potential in applica-
tions where mechanical strength and high-temperature/
corrosive durability are required. What’s more, it has been
demonstrated that wide-band-gap single-crystalline sili-
con nitride can be excellent hos material with high doping
levels similar to GaN and AlN. The synthesis methods for
one-dimensional silicon nitride include chemical vapor
deposition process, nitridation of silicon/silica powders or
silicon substrates, combustion synthesis, and polymeric
precursor pyrolysis method, etc. However, most of the
synthesis methods utilize catalysts such as iron, gallium,
gallium nitride, and FeCl2.
In our previous paper [9], a preceramic polymer, per-
hydropolysilazane (PHPS), was used to prepare silicon
nitride powders by thermal decomposition. A novel phe-
nomenon was found that silicon nitride-based nanowires
appeared on the surface of the polymer-derived ceramic
powders although there were no catalysts at all. No bulbs
or droplets were observed on the tips of the nanowires,
and two gas-solid mechanisms were proposed to explain
their growth.
In this paper, we present Si-N-C nanowires derived by
another preceramic polymer, polyhydridomethylsilazane
(PHMS). The diameters of the nanowires were from tens
of nanometers to several microns, and the maximum
length reached several hundred microns. The nanowires
had no bulbs or droplets on the tips. However, a novel
phenomenon was observed that different bulbs with di-
ameters of several microns appeared in addition to the
nanowires.
2. Experimental
The precursor methylhydridocyclosilazane (MHS) [10],
with the structure unit of [CH3SiHNH]n, was synthesized
and crosslinked into polyhydridomethylsilazane (PHMS).
The polymer PHMS was pyrolyzed at 1873K in nitrogen
atmosphere (99.99%) for 2 hours to obtain ceramic nano-
wires.
The morphology of polymer-derived ceramic powders
and nanowires were characterized using field emission
scanning electron microscope (FESEM, Sirion 200, FEI
Company, Netherlands) equipped with energy dispersive
X-ray (EDX) spectrometer (Genesis 60S, EDAX Com-
pany, USA).
3. Results and Discussion
FESEM micrographs of the PHMS-derived ceramic
products are shown in Figure 1. After pyrolysis at 1873
K in nitrogen atmosphere, the PHMS-derived products
were irregular powders with the maximum size of about
500 microns (Figure 1(a)). Among the ceramic products,
the surfaces of some powders showed hair-like mor-
phology (Figures 1(b,c)). Magnification of the Fig-

Si-N-C Nanowires Derived by Polyhydridomethylsilazane Pyrolysis 937
Figure 1. FESEM micrographs of the PHMS-derived ceramic products. (a) micrographs of ceramic powders; (b)(c)
nanowires on some powders; (d)(e)(f) magnification of the one-dimensional nanostructures in (c).
ure 1(c) exhibited one-dimensional nanostructures at
different sites with different sizes and shapes (Figures
1(d)-( f) ). The diameters of the nanowires were from tens
of nanometers to several microns, and the maximum
length reached several hundred microns. There were no
bulbs or droplets on the tips of the nanowires.
In order to determine the composition of the nanowires,
EDX spectrum was conducted on the nanowires in Fig-
ure 1(c). The composition of the nanowires was silicon,
nitrogen and carbon, suggesting that the nanowires were
Si-N-C (see Figure 2).
As was seen in Figure 1, the nanowires appeared
without bulbs on the tips. In addition to these nanostruc-
tures, however, a novel phenomenon arised that few
ball-like structures were observed (Figure 3). As shown
in Figure 3(a), there was a ball with the diameter of
about five microns. Magnification of the ball indicated
that the ball was covered by nanowires all around (see
Figure 3(b)). Different from Figure 3(a), another bulb
structure like a football was found in Figure 3(c), which
was a little smaller with the diameter of about three mi-
crons. Although there was no nanowires covered on its
surface, yet magnification of the bulb indicated that the
handle was covered by nanowires in parallel circles (Fig-
ure 3(d)).
In Ref. [8], silicon nitride nanowires have been syn-
thesized using a polysilazane pyrolysis method, and
FeCl2 catalyst must be used during the process otherwise
no nanowires could be obtained. However, in our study,
the nanowires were obtained without any catalysts.
Several mechanisms have been proposed for the
growth of silicon nitride nanowires, including vapor-
liquid-solid (VLS), solid-liquid-gas-solid (SLGS), and
vapor-solid (VS) mechanisms. As shown in Figure 1, the
nanowires had no bulbs or droplets at the tips, suggesting
a growth mechanism different from the VLS mechanism.
As for the bulbs in Figure 3, it was a just special case.
What’s more, the sizes of the bulbs were several microns,
which had exceeded the size of NANO-wires. The two
bulbs in Figure 3 showed different morphology, and they
probably had different compositions and different growth
mechanisms. In a word, this paper is still a preliminary
investigation, and further study on TEM observation and
growth mechanism are in progress.

Si-N-C Nanowires Derived by Polyhydridomethylsilazane Pyrolysis 938
Figure 2. EDX spectrum of the nanowires derived by PHMS pyrolysis.
Figure 3. FESEM micrographs of the ball-like structures in PHMS-derived products. (a)(b)ball-like structure covered by
nanowires ; (c)(d) football-like structures with the handle covered by nanowires.
4. Conclusions
In summary, we have synthesized Si-N-C nanowires by
polymeric precursor pyrolysis method using polyhydric-
domethylsilazane without any catalysts. The diameters of
the nanowires were from tens of nanometers to several
microns, and the maximum length reached several hun-
dred microns. There were no bulbs or droplets on the tips

Si-N-C Nanowires Derived by Polyhydridomethylsilazane Pyrolysis939
of the nanowires. In addition to the nanowires, few ball-
like structures appeared with the diameters of several
microns. One bulb was covered by nanowires all around,
while the other bulb just had nanowires covered on its
handle.
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