Synthesis and properties of magnetic fluid based on iron nanoparticles prepared by a vapor-phase condensation process

Article abstract of DOI:10.1016/j.jmmm.2006.02.027

Magnetic fluid containing metallic iron nanoparticles was successfully fabricated in this work. The iron nanoparticles were synthesized by chemical vapor condensation process and then dispersed in water-base solution (pH 11) with oleic acid as surfactant. More than 80% of iron nanoparticles were fully dispersed in the fluid and remained stable without any further oxidation over 200 h. Both the iron nanoparticles and the subsequent magnetic fluid exhibited typical ferromagnetic behavior.

Full text of DOI:10.1016/j.jmmm.2006.02.027

ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 304 (2006) e16–e18
www.elsevier.com/locate/jmmm
Synthesis and properties of magnetic fluid based on iron nanoparticles
prepared by a vapor-phase condensation process
a
Ji-Hun Yu , Dong-Won Lee , Byoung-Kee Kim , Taesuk Jang
a
a
b,
Ã
a
Powder Materials Research Center, Korea Institute of Machinery and Mateials, Changwon, Kyungnam 641-010, Korea
b
Department of Electronic Materials Engineering, Sunmoon University, Asan, Choongnam 336-708, Korea
Available online 28 February 2006
Abstract
Magnetic fluid containing metallic iron nanoparticles was successfully fabricated in this work. The iron nanoparticles were synthesized
by chemical vapor condensation process and then dispersed in water-base solution (pH 11) with oleic acid as surfactant. More than 80%
of iron nanoparticles were fully dispersed in the fluid and remained stable without any further oxidation over 200 h. Both the iron
nanoparticles and the subsequent magnetic fluid exhibited typical ferromagnetic behavior.
r 2006 Elsevier B.V. All rights reserved.
PACS: 75.50.Mm; 75.50.Tt; 81.07.Wx
Keywords: Iron nanoparticles; Chemical vapor condensation; Magnetic fluid; Dispersion
1
. Introduction
vaporized in evaporator. The vapor was then transferred
with high-purity Ar (0.01 Torr) into tubular reactor kept at
600 1C so that the precursor decomposed and condensed to
nanoparticles. The condensed particles were then carried to
collection chamber held at room temperature under high-
purity Ar, in which the particles were deposited on the
surface of the chamber. Finally, the particles were
Magnetic fluid has a great potential for magnetic seal,
speaker damper, aerospace fuel injector as well as magnetic
resonance imaging (MRI) agent [1]. So far, iron-oxide
nanoparticles have been used in most magnetic fluids and
some metallic iron particles whose size is somewhat larger
than that of the iron oxides have also been tried [2].
However, relatively lower magnetization of the iron oxides
and strong adhesion of the iron particles have limited
practical application of such magnetic fluids. In this study,
a feasibility of metallic iron nanopowder, fabricated by a
vapor-phase condensation, as medium of magnetic fluid
was investigated by examining dispersity and magnetic
properties of both the iron nanopowder and the subsequent
magnetic fluid.
passivated with a mixed gas of Ar and O before collection.
2
The synthesized iron nanoparticles were dispersed in DI
3
water (10 g/L) with oleic acid (5 cm ) to make a magnetic
fluid. The solution was subsequently ultra-sonicated for
30 min at 80 1C while NH OH was added to control pH of
4
the solution. After the magnetic fluid was made, it was left
alone in air and a fixed amount of the fluid was taken and
weighted periodically to examine dispersity of the iron
nanoparticles. Both the iron nanoparticles and the fluid
were characterized by using Cu Ka X-ray diffraction,
TEM, and VSM.
2
. Experimental
Iron nanoparticles were fabricated by chemical vapor-
condensation(CVC) process using iron pentacarbonyl
3. Results and discussion
(
Fe(CO) ) as precursor [3,4]. The liquid precursor was
5
Microstructures of iron nanoparticles synthesized at
Ã
6
00 1C are shown in Fig. 1. These spherical particles with
Corresponding author. Tel.: +82 41 530 2341; fax: +82 41 544 1857.
E-mail address: tsjang@sunmoon.ac.kr (T. Jang).
the average size of about 20 nm were dispersed pretty well,
0304-8853/$ - see front matter r 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2006.02.027

ARTICLE IN PRESS
J.-H. Yu et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e16–e18
e17
Fig. 1. TEM micrographs of iron nanoparticles synthesized at 600 1C by
chemical vapor condensation (CVC) process.
Fig. 3. X-ray diffraction patterns of iron nanoparticles synthesized at
6
00 1C by CVC process and of those in a magnetic fluid (pH 11).
Fig. 2. Dispersity vs. standing time and pH, for the iron nanoparticles
shown in Fig. 1 in water-base magnetic fluids.
without forming big cluster. As shown in the right-hand
figure, each particle had a typical core–shell structure: The
metal iron core was enclosed with a layer of iron oxide, i.e.,
Fe O [4].
3
4
Fig. 4. Magnetization curve of a magnetic fluid (pH 11) made with iron
nanoparticles synthesized at 600 1C by CVC process. Inset: M vs. H, for
the iron nanoparticles themselves.
In order to measure the dispersity of iron nanoparticles
in the water-base fluid, a fixed amount of the fluid was
taken from the equivalent upper position of the standing
fluid, and subsequently dried and weighted. The dispersity
was then expressed as the ratio of the weight, measured as a
function of time, to the initial weight. As shown in Fig. 2,
partially agglomerated or large iron particles were rapidly
settled within 10 min. However, finer particles were
suspended well in all fluids, resulting in slight decrease of
dispersity with the increase of standing time. Furthermore,
the dispersity of iron nanoparticles tended to increase with
the increase of pH in the fluids, showing the optimum value
at pH 11. But it decreased abruptly at pH 12. In general,
the electric double layer on the surface of iron nanoparticle
increases as pH of the fluid increases. It causes higher
repulsive reaction between each electrically charged iron
nanoparticle, thereby providing better dispersion of the
particles in the fluid. The reason of the abrupt decrease in
dispersity at pH 12 is uncertain. Nevertheless, it was found
that the dispersity exceeding 80% could be obtained at pH
11.
As can be seen in X-ray diffraction patterns in Fig. 3,
strong (1 1 0) peak of crystalline a-Fe was still detected,
without showing any visible change in iron-oxide peaks,
from the water-base magnetic fluid left alone for 200 h. It
indicates that the iron nanoparticles suspended in the fluid
can remain stable for a long time, obviously due to the
oxide layer that encloses metal iron core, as shown in Fig.
1, and is stable enough to prevent further oxidation into
the interior of the nanoparticles.
Fig. 4 shows magnetization curves measured from the
iron nanoparticles shown in Fig. 1 and the magnetic fluid
of pH 11 containing these particles. Comparing with the
saturation magnetization of bulk Fe (220 emu/g), M of the
s

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J.-H. Yu et al. / Journal of Magnetism and Magnetic Materials 304 (2006) e16–e18
e18
iron nanoparticles was considerably low (ꢀ125 emu/g). It is
mainly due to the surface oxide layer that has much lower
saturation magnetization and the surface anisotropy of the
iron nanoparticles [5]. Because of the strong dilution of the
iron nanoparticles in the fluid and, moreover, the removal
of larger particles that were rapidly settled down in the
fluid, H and M of the fluid were significantly low, i.e.,
and remained stable without any further oxidation for a
long time.
Acknowledgment
This work has been supported by the Korean Ministry of
Science and Technology through the National R&D
Project for Nano Science and Technology.
i
c
s
2
7.4 Oe and 3.9 emu/g, respectively.
References
4
. Conclusions
[
1] E.X. Wu, H.Y. Tang, J.H. Jensen, NMR Biomed. 17 (2004) 478.
[2] C. Pochler-Schoniger, J. Kopke, F. Guckel, J. Sturm, M. Georgi, Mag.
Reson. Imag. 17 (1999) 383.
Magnetic fluid based on metal powder has been
¨
¨
¨
¨
successfully made with iron nanoparticles synthesized by
CVC process. The iron nanoparticles were about 20 nm in
size and had core–shell type structure, i.e., metal iron core
[
[
3] C.J. Choi, O. Tolochko, B.K. Kim, Mater. Lett. 56 (2002) 289.
4] D.H. Lee, T.S. Jang, D.W. Lee, B.K. Kim, Phys. Status Solidi A 201
(
8) (2004) 1930.
enclosed with thin layer of Fe O . More than 80% of these
3
particles were fully dispersed in the magnetic fluid of pH 11
4
[5] B.D. Cullity, Introduction to Magnetic Materials, Addison-Wesley
Publishing Co., Massachusetts, 1972, p. 383