Characteristics of Fe/SiO2 nanocomposite powders by the chemical vapor condensation process

Article abstract of DOI:10.1016/j.jallcom.2006.02.085

Fe/SiO₂ nanocomposite powders were produced by the chemical vapor condensation (CVC) process. Characteristics of the as-CVCed powders were investigated by XRD, TEM and VSM, etc. The Fe/SiO₂ powders could be sytheised from 700 °C. With increasing reaction temperature, the a-Fe phase peaks in the XRD became clearer. The size of CVCed powders was about 50 nm at 1100 °C. The powders showed intricate long-stand structure due to their magnetic characteristics. TEM results revealed that the Fe powders were covered by SiO₂ layer fully or partially depending on the experimental condition. The saturation magnetization and the coercive force of the as-CVCed powders were investigated with the decomposition temperature in this study.

Full text of DOI:10.1016/j.jallcom.2006.02.085

Journal of Alloys and Compounds 449 (2008) 258–260
Characteristics of Fe/SiO nanocomposite powders by the chemical
2
vapor condensation process
a,∗
b
b
b
Jin-Chun Kim , Jae-Wook Lee , Byung-Yeon Park , Chul-Jin Choi
a
School of Materials Science and Engineering, University of Ulsan, P.O. Box 18, Ulsan 680-749, Republic of Korea
b
Powder Materials Research Center, Korea Institute of Machinery and Materials,
66 Sangnam-dong, Changwon, Kyungnam 641-010, Republic of Korea
Received 4 November 2005; received in revised form 8 February 2006; accepted 18 February 2006
Available online 11 January 2007
Abstract
Fe/SiO
2
nanocomposite powders were produced by the chemical vapor condensation (CVC) process. Characteristics of the as-CVCed powders
◦
were investigated by XRD, TEM and VSM, etc. The Fe/SiO
a-Fe phase peaks in the XRD became clearer. The size of CVCed powders was about 50 nm at 1100 C. The powders showed intricate long-stand
2
powders could be sytheised from 700 C. With increasing reaction temperature, the
◦
2
structure due to their magnetic characteristics. TEM results revealed that the Fe powders were covered by SiO layer fully or partially depending on
the experimental condition. The saturation magnetization and the coercive force of the as-CVCed powders were investigated with the decomposition
temperature in this study.
©
2006 Elsevier B.V. All rights reserved.
Keywords: Nanocomposite; Chemical vapor condensation; Magnetic property
1
. Introduction
In the present study, we produced Fe/SiO2 nanocomposite
powders by the CVC process using the metal–organic pre-
cursors. The effects of reaction parameters on phases, micro-
structures and magnetic properties of the as-synthesized
nanocomposite powders were systematically investigated.
Recently, nanoparticles or nanocomposite powders with the
size of 1–100 nm have been intensively investigated because
of their wide range of potential applications in areas such as
electronics, optics, catalysis, ferrofluids and magnetic data stor-
age [1–3]. The nanocomposite powders could be fabricated by
various methods such as inert gas condensation process (IGC),
plasma arc discharge (PAD)[4] and chemical vapor conden-
sation (CVC)[5]. Each fabrication technique has its own set
of advantages and disadvantages and some limitations. How-
ever, as compared with other methods, the CVC process has
been developed for preparation of almost all kinds of mate-
rials because a wide range of precursors are commercially
available, and it can easily produce the nanocomposite or
coating powders with high purity and non-agglomeration prop-
erties.
2
. Experimental
The basic setup for CVC is similar to that described in literature elsewhere
[
(
6]. Fe/SiO2 nanocompositepowderswerepreparedusingtheironpentacarbonyl
IP, Fe(CO)5) and the tetraethyl-orthosilicate (TEOS, C8H20O4Si) as precursors
under flowing Ar atmosphere at different temperatures. Two bubblers were used
in this work because the IP and TEOS have different physical and thermochem-
3
ical properties. Flow rate of Ar carrier gas was fixed at the level of 600 cm .
Feeding ratio of IP to TEOS was kept with 9:1. A tubular furnace provided
a heat source for the decomposition of precursors. The flow of the carrier gas
entrained precursor vapor and passed through the heated tubular furnace in which
the precursor is decomposed and condensed into clusters or powders. The syn-
thesized powders were scraped off and collected from the chiller cooled by cold
◦
water. The CVC experiments were conducted at 700–1100 C.
X-ray diffraction (XRD) with monochromatic Cu K␣ radiation (λ = 0.1542)
was performed to identify the phases existing in as-prepared CVC powders.
The morphology, size and lattices images of the powders were analyzed by
high-resolution transmission electron microscopy (HR-TEM, JEOL) operated
at 200 kV. Magnetic properties were measured using a vibrating sample magne-
tometer (VSM) at room temperature in a field up to 20 kOe.
∗
Corresponding author at: School of Materials Science and Engineering, Uni-
versity of Ulsan, P.O. Box 18, Ulsan 680-749, Republic of Korea.
Tel.: +82 52 2592231; fax: +82 52 2591688.
E-mail address: jckimpml@ulsan.ac.kr (J.-C. Kim).
0
925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2006.02.085

J.-C. Kim et al. / Journal of Alloys and Compounds 449 (2008) 258–260
259
◦
Fig. 2. SEM micrographs of powder prepared at 1100 C.
Fig. 1. XRD patterns of the as-prepared the CVC powders.
3
. Results and discussions
netic properties of Fe and agglomeration of the nanopowders
itself.
By TGA analyses, the iron pentacarbonyl (Fe(CO )) was
The size of the as-CVCed powders was increased with
increasing the reaction temperature as shown in Fig. 3. The
5
decomposed from Fe(CO) to Fe + 5CO in the temperature
5
◦
◦
range of 140–300 C. Therefore, the liquid Fe(CO) precursor
was kept at the 140 C to vaporize in evaporator. And the TEOS
was vaporized from its liquid state at 103 C in evaporator and
size of the powders produced at 1100 C was about 50 nm. In
5
◦
◦
Fig. 3(a) shows that the CVC powders produced at 700 C had
◦
amorphous phase. However, in Fig. 3(b), the image reveals that
◦
fed into reaction furnace.
the Fe/SiO2 nanopowders produced at 1100 C had crystalline
By the analysis of XRD patterns as shown in Fig. 1, we
phase and were composed of core and shell. The shell thickness
of the CVC powders was about ∼5 nm.
◦
knew the nanopowders could be produced above 700 C. No
◦
powders were obtained under 700 C in this experiment. Fully
In Fig. 4, TEM results revealed that the shell thickness of the
◦
◦
amorphous halo pattern was found at 700 C. With increas-
Fe composite powders produced at 1100 C was different with
ing reaction temperature, the XRD peaks became clearer. At
the surface position. As indicated by the point 2, the thickness
of this part was about only 5 nm. The layer was composed with
Si, O and C as shown in the micro-EDS (point 2), which was
well matched with XRD results. In this figure, the shell showed
random structure, i.e., amorphous phase. In fact, carbon or car-
bide was not detected in the XRD results. However, in point 2,
we could find the crystalline carbon layer. The core phase was
pure iron as shown in micro-EDS result of the point 1.
◦
1
100 C, very sharp bcc Fe (a-Fe) peaks were detected, and
week Fe2SiO4 peaks were also traced, that means Fe and Si ele-
ments were reacted at this temperature. Amorphous SiO2 phase
◦
was confirmed at near 22 of 2θ. No visual Fe oxide peaks
were observed in this study. Fig. 2 showed the SEM micro-
◦
graphs of the CVC powder produced at 1100 C. It showed
the intricate long stand structure because of intrinsic mag-
◦
◦
Fig. 3. TEM micrographs of the as-prepared powders: (a) 700 C and (b) 1100 C.

2
60
J.-C. Kim et al. / Journal of Alloys and Compounds 449 (2008) 258–260
◦
Fig. 4. (a) HR-TEM images and (b) micro-EDS results of the CVC powders produced at 1100 C.
In this study, the CVC was performed under noble Ar atmo-
respectively. The existence of pure Fe leads to increase in
the saturation magnetization and coercivity of the Fe/SiO2
nanocomposites.
sphere. As mentioned above, however, the carbon layer was
found by the micro-EDS results. Carbon coating of Fe powders
could occur during CVC process by the dissociation reaction of
CO from precursors, Fe(CO) . Generally, under the high tem-
4. Conclusions
5
perature conditions and in the presence of metallic catalyst (Fe,
Ni, Co, etc.), 2CO gas could be decomposed into CO2 + C and
react with metallic catalysis [7]. The chemical reaction, which
is expected to take place, is as follows with increasing reaction
temperature.
In conclusion, the Fe/SiO2 nanocomposite powders were suc-
cessfully fabricated by the chemical vapor condensation process
carried out in Ar atmospheres. The phase in the Fe nanocapsules
was affected by the decomposition temperatures. The Fe/SiO2
nanocomposite powders consisted of SiO2 shell and Fe metal
Pyrolysis of Fe(CO)5:
core. The size of the Fe nanocomposite was about 50 nm at
◦
1100 C, and it showed intricate long stands structure because
◦
Fe(CO) → Fe + 5CO, T = 140–300 C
(1)
(2)
5
of intrinsic magnetic properties of Fe. The saturation magnetiza-
tion of the Fe/SiO2 nanocomposite powders were increased with
the increasing the reaction temperature because of the existence
of Fe phase.
CO gas dissociation:
5
2
5
2
◦
Fe + 5CO → Fe + C + CO2, T = 500–1100 C
Pure iron formation or carbon coating:
References
Fe + C + CO2 → Fe + Fe(C)
T = 1100 C
+ CO2↑,
coating
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[
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◦
(4)
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influences the saturation magnetization of the Fe nanocompos-
ites. Although the particles size increased with the reaction
temperatures, the phase composition is the main reason for the
increasing in the saturation magnetization. With the increase of
reaction temperature, the saturation magnetization and coerciv-
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