Preparation of nanosized antimony by mechanochemical reduction of antimony sulphide Sb2S3

Article abstract of DOI:10.1016/j.jallcom.2006.08.169

The preparation of nanosized antimony (grain size 19 nm) by high-energy milling of antimony sulphide Sb₂S₃ with elemental Fe as reducing element is reported. The mechanochemical reduction was performed in a planetary ball mill for 10-180 min. The process is rather straightforward with elemental antimony and iron sulphide (pyrrhotite-4H) being the only solid-state products. The process kinetics as described by X-ray diffraction (XRD) and vibrating sample magnetometer (VSM) magnetometry shows that most of the reduction is complete after 60 min of milling.

Full text of DOI:10.1016/j.jallcom.2006.08.169

Journal of Alloys and Compounds 434–435 (2007) 773–775
Preparation of nanosized antimony by mechanochemical
reduction of antimony sulphide Sb2S3
b
a
c
´ˇ a,∗
ˇ´
´
´
ˇ
P. Balaz , L. Takacs , E. Godocıkova , I. Skorvanek ,
´ˇ c
d
J. Kovac , W.S. Choi
a Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 043 53 Kosˇice, Slovakia
b University of Maryland Baltimore County, Department of Physics, Baltimore, MD 21250, USA
c Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 043 53 Kosˇice, Slovakia
d Pusan National University of Korea, Pusan 609 735, South Korea
Available online 2 October 2006
Abstract
The preparation of nanosized antimony (grain size 19 nm) by high-energy milling of antimony sulphide Sb2S3 with elemental Fe as reducing
element is reported. The mechanochemical reduction was performed in a planetary ball mill for 10–180 min. The process is rather straightforward
with elemental antimony and iron sulphide (pyrrhotite-4H) being the only solid-state products. The process kinetics as described by X-ray diffraction
(XRD) and vibrating sample magnetometer (VSM) magnetometry shows that most of the reduction is complete after 60 min of milling.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Metals; Nanostructures; High-energy ball milling; Mechanochemical synthesis
1. Introduction
reduced via high temperature annealing in the presence of reduc-
ing agents such as hydrogen or iron. Torma and Inal [13] have
investigated the reduction with hydrogen at atmospheric pres-
sure and at temperatures between 473 and 873 K. Only 60% of
Sb2S3 was converted to metallic antimony. The reduction with
elemental iron is possible at temperatures 773–823 K but the
process is inefficient because the antimony sulphide dissolves
in the already formed iron sulphide [14]. The yield of both pro-
cesses is low, they need high temperatures and the products have
large grain size.
A wide variety of techniques are being used to synthesize
nanocrystalline materials. One of them is high-energy milling
that has a potential for easy scale-up to large quantities [1–7].
¨
Matteazzi and Le Caer [8] were the first to study high-energy
ball milling in mixtures of a sulphide and a reducing metal
in order to obtain nanostructures. They demonstrated that the
mechanochemical reduction of metal sulphides MeS (Me = Fe,
Cu, Co, Pb, Zn) with suitable reducing metal was feasible using
room temperature vibratory milling. The reduction of CuS with
Ti, Zr and Hf was studied by Takacs [6]. It was shown that these
reactions take place as mechanically induced self propagating
reactions [6], as indicated by a characteristic sudden temperature
increase as a function of milling time.
The aim of the present work is to study the mechanochemical
reduction of antimony sulphide Sb2S3 with elemental iron at
ambient temperature, according to the equation
Sb2S3 + 3Fe → 2Sb + 3FeS
(1)
The kinetics of the mechanochemical reduction of MeS
(Me = Fe, Cu, Pb) with elemental iron and silicon as well as the
magnetic properties of the obtained systems have been studied
The reaction is thermodynamically feasible, as the enthalpy
change is negative, ꢀH◦
= −116.7 kJ mol−1
.
298
´ˇ
by Balaz et al. [9–12].
2. Experimental
The direct reduction of antimony sulphide by milling has
not been studied before. Conventionally, antimony sulphide is
2.1. Synthesis
MechanochemicalreductionofantimonysulphideSb2S3 withelementaliron
as reducing element (1) was performed in a planetary mill Pulverisette 6 (Fritsch,
Germany). Tungsten carbide (WC) grinding chamber of 250 ml volume and 50
∗
Corresponding author. Tel.: +421 55 79 22603; fax: +421 55 79 22604.
E-mail address: balaz@saske.sk (P. Bala´zˇ).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2006.08.169

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P. Bala´zˇ et al. / Journal of Alloys and Compounds 434–435 (2007) 773–775
Fig. 1. XRD patterns as a function of milling time. 1-Stoichiometric mixture of
Sb2S3 and Fe before milling. The milling times for patterns 2–4 are 20, 60 and
120 min, respectively.
Fig. 2. The conversion degree for precursors (Sb2S3, Fe) and product (Sb) of
reaction (1) calculated from normalized of XRD line intensities.
WC balls of 10 mm diameter (total weight 360 g) were used. Weight of powder
for milling was 3 g. The rotation speed of the planet carrier was 500 rev/min.
Milling times between 10 and 180 min were applied. The atmosphere inside the
milling chamber was argon.
Fig. 3 shows the room temperature magnetization data for the
investigated samples as a function of external magnetic field. It
is evident that the resulting magnetization curves are well satu-
rated after the application of a magnetic field higher than 2 T. The
variation of the saturation magnetization as a function of milling
time, as displayed in the inset of Fig. 3, reflects the amount of
metallic iron, the only ferromagnetic component in the sam-
ples. In good agreement with the XRD results shown in Fig. 2,
the Fe fraction decreases continuously for milling times up to
180 min, with more than 80% being transformed during the first
60 min. After 180 min of milling the saturation magnetization
is negligible, indicating that the constituent phases are almost
entirely paramagnetic and/or antiferromagnetic, i.e. reaction (1)
is practically complete.
2.2. Characterization techniques
X-ray diffraction (XRD) measurements were carried out using a Philips
X’Pert diffractometer, working in the Θ–Θ geometry with Cu K␣ radiation. The
XRD lines were identified by comparing the measured patterns to the JCPDS
data cards. Magnetization data were obtained by employing a vibrating sam-
ple magnetometer (VSM) equipped with a superconducting coil. A maximum
magnetic field of 3 T was applied in order to assure the magnetic saturation of
specimens at room temperature. Transmission electron microscopy was carried
out using a Jeol-2000FX instrument at an acceleration of 200 kV.
3. Results and discussion
The progress of the mechanochemical reduction of anti-
mony sulphide Sb2S3 by elemental iron is illustrated by the
selected XRD patterns in Fig. 1. The process is rather straight-
forward with elemental antimony Sb (JCPDS 05–0562) and
FeS (pyrrhotite-4H, JCPDS 22–1120) being the only solid-
state products. The intensity of the metal iron reflexion (1 1 0)
decreases upon continued milling and only a very small amount
of iron is detectable at 60 min (pattern 4). There is a small hump
at 2Θ = 31–32◦ which originates from tungsten carbide abraded
from the balls during milling. In the starting material (pattern
1) more small peaks are seen which belong to stibnite Sb2S3
(JCPDS 42–1393).
The conversion degree for precursors (Sb2S3, Fe) and prod-
uct (Sb) of reaction (1) as obtained by normalization of the XRD
intensities is shown in Fig. 2. It is clear that most of the reduction
is complete after 60 min with the intensity of Sb2S3 decreas-
ing faster than Fe. There is no reason to expect different phase
ratios here as the content of Fe and Sb2S3 should change parallel
according to Eq. (1). A possible explanation is the partial amor-
phization of stibnite, which is indeed manifested in an increased
background of the XRD patterns.
Fig. 3. Magnetization as a function of external magnetic field for several milling
times. The inset shows the saturation magnetization as a function of milling
time.

P. Bala´zˇ et al. / Journal of Alloys and Compounds 434–435 (2007) 773–775
775
Fig. 4. (A) Dark field TEM image and (B) SAED pattern of (Sb + FeS) nanoparticles formed by mechanochemical reduction of Sb2S3 with Fe during 180 min of
milling.
The XRD line widths of the sample milled for 180 min have
been analyzed in order to confirm the presence of nanometric
particles. The grain size of Sb was found to be 19 nm with 0.35%
residual strain and the particle size of FeS is about 10 nm. Fig. 4A
shows a typical dark field TEM image obtained using beams
from the diffraction rings of the irregular shaped nanoparticles
formed during 180 min of milling. Fig. 4B shows the SAED
pattern of an area containing some nanoparticles. The SAED
pattern shows a set of rings instead of spots due to the random
orientation of the nanoparticles. The TEM image is consistent
with the XRD grain size but also shows the strongly agglomer-
ated nature of the powder. The agglomeration of nanoparticles is
a general phenomenon originating from the tendency to reduce
the surface area.
Acknowledgements
The support through projects VEGA 2/5151/5, Center of
Excellence NANOSMART and Slovak State programme (SP-
26) is gratefully acknowledged.
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ˇ
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