Kinetics of mechanochemical synthesis of Me/FeS (Me = Cu, Pb, Sb) nanoparticles

Article abstract of DOI:10.1016/j.jallcom.2008.07.151

The mechanochemical synthesis of Cu/FeS, Pb/FeS and Sb/FeS nanoparticles was investigated with the regard to solid-state kinetics. Experiments were performed in a planetary mill and in an eccentric vibratory mill by a high-energy milling of Cu₂

Full text of DOI:10.1016/j.jallcom.2008.07.151

Journal of Alloys and Compounds 483 (2009) 484–487
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Journal of Alloys and Compounds
journal homepage: www.elsevier.com/locate/jallcom
Kinetics of mechanochemical synthesis of Me/FeS (Me = Cu, Pb, Sb) nanoparticles
a
b
c
d
d
P. Balázˇ a,∗, E. Dutková , I. Skorvánek , E. Gock , J. Kovac , A. Satka
ˇ
a Institute of Geotechnics, Slovak Academy of Sciences, Watsonova 45, 043 53 Kosˇice, Slovakia
b Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 043 53 Kosˇice, Slovakia
c Institute of Mineral and Waste Processing and Dumping Technology, Technical University Clausthal, Walther-Nernst Strasse 9, 38678 Clausthal-Zellerfeld, Germany
d Department of Microelectronics, Slovak University of Technology and International Laser Centre, 812 19 Bratislava, Slovakia
a r t i c l e i n f o
a b s t r a c t
Article history:
The mechanochemical synthesis of Cu/FeS, Pb/FeS and Sb/FeS nanoparticles was investigated with the
regard to solid-state kinetics. Experiments were performed in a planetary mill and in an eccentric vibratory
mill by a high-energy milling of Cu2S, PbS and Sb2S3, respectively with elemental iron under protective
atmosphere. Cu, Pb and Sb nanometals were obtained due to the reducing power of iron. The reduction
processes are very straightforward and fast and can be carried out at ambient temperature. Nanometals
are embedded into FeS matrix forming metal/ceramics nanocomposites. XRD, SEM and magnetometry
methods were used to characterize the ball-milled products. Solid-state kinetics has been evaluated based
on magnetometry data.
Received 30 August 2007
Received in revised form 24 July 2008
Accepted 26 July 2008
Available online 18 December 2008
Keywords:
Metals
Nanostructures
High-energy ball milling
Mechanochemical synthesis
Solid-state kinetics
© 2008 Elsevier B.V. All rights reserved.
1. Introduction
sulphides by applying solid-state kinetics approach based on pro-
cessing of magnetometry data.
Recently, mechanochemical processing via high-energy milling
has been reviewed as means of the synthesis of a wide variety of
nanocrystalline materials [1–3]. The chemical reactions occur at
the interfaces of the nanometer size grains that are continually
regenerated during milling. As a consequence, reactions that would
normally require high temperatures to occur due to the separation
of the reacting phases by the products phases, can proceed at low
temperature in a ball mill.
2. Experimental
2.1. Synthesis
Mechanochemical reduction of metal sulphides Cu2S, PbS and Sb2S3 with ele-
mental iron as reducing element in a ratio corresponding to Eqs. (2)–(4) was
performed in a Pulverisette 6 laboratory planetary mill (Fritsch, Germany). A 250-
ml tungsten carbide (WC) grinding chamber and 50 WC balls of 10 mm diameter
(total weight 360 g) were used. The weight of the milled powder charge was 3 g.
The speed of the planet carrier was set to 500 rpm. Milling times between 1 and
180 min were applied. The atmosphere inside the milling chamber was argon. The
same reactions were also performed in an industrial eccentric vibratory mill ESM
654 (Siebtechnik, Germany). Milling was carried out in air for durations between
30 and 120 min. The milling chamber was filled with tungsten carbide balls and
the weight of milled powder mixture was 100 g. The speed of the mill eccenter was
960 rpm.
Mechanochemical solid-state reduction of sulphides to prepare
nanocrystallineproductscanbeschematicallyexpressedbygeneral
equation
Me1S + Me2 → Me1 + Me2S
(1)
where Me1 is reduced metal and Me2 is reducing metal. Several
papers have been published using iron metal as reducing element
[4–10]. The reactions are thermodynamically feasible at ambient
temperature, as the enthalpy change ꢀH2◦98 is negative (Table 1).
Various nanostructures have been identified in products of reac-
tions (2)–(6) by XRD, Mössbauer, SEM and TEM methods.
2.2. Characterization
X-ray diffraction measurements were carried out using a Philips X’Pert diffrac-
tometer (the Netherlands), working in ꢁ–ꢁ geometry with CuK␣ radiation. The
XRD lines were identified by comparing the measured patterns to the JCPDS data
cards. The morphology of samples was analyzed using FE-SEM LEO 1550 scanning
microscope (Germany). The samples were not covered with any conductive mate-
rial in order to avoid artefacts. Magnetization data were obtained by employing a
vibrating sample magnetometer (VSM) equipped with a superconducting coil. The
magnetic field was increased up to 3 T in order to assure the magnetic saturation of
the specimens at room temperature.
The aim of this paper is to illustrate the progress in the
mechanochemical preparation of nanometals from corresponding
∗
Corresponding author. Tel.: +421 55 7922603; fax: +421 55 7922604.
E-mail address: balaz@saske.sk (P. Balázˇ).
0925-8388/$ – see front matter © 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2008.07.151

P. Balázˇ et al. / Journal of Alloys and Compounds 483 (2009) 484–487
485
Table 1
Fe while Cu metal and FeS are formed – is clearly seen, particularly
by inspecting the relative intensities of the diffraction lines of Cu
and Fe metal. With increase time of milling cubic FeS changes to its
hexagonal modification troilite FeS [5]. This phase is considered to
be the stable modification of stoichiometric iron sulphide.
The reaction between galena PbS and elemental Fe has been
appliedtoobtainnanocrystallinelead(grainsize13–21 nm)accord-
ing to Eq. (3) in Table 1 [6]. The XRD patterns are given in Fig. 1B.
The process of mechanochemical reduction of PbS is evident. The
significant line broadening suggests dramatical grain size reduc-
tion. After 60 min of milling, the reflection of well crystallized
lead metal and cubic FeS can be observed with a relative high
conversion.
Mechanochemically induced solid-state reactions of metal sulphides with iron.
Reaction
ꢀH2◦98 (kJ mol−1
)
Cu2S + Fe → 2Cu + FeS
PbS + Fe → Pb + FeS
(2)
(3)
−21.0
−1.3
Sb2S3 + 3Fe → 2Sb + 3FeS(4)
−116.7
−13.3
−160.7
FeS2 + Fe → 2FeS
(5)
As2S3 + 3Fe → 2As + 3FeS(6)
2.3. Kinetics processing
Avrami–Erofeev equation [11,12] in the form
−ln(1 − x) = ktn
(7)
The preparation of the nanoantimony by milling antimony sul-
phide with elemental iron as described by Eq. (3) in Table 1 has been
performed in an industrial mill. XRD patterns are given in Fig. 1C.
The most reduction is complete after 60 min of milling in a plane-
tary mill. The grain size of antimony was found to be 19 nm with
0.35% residual strain [9,10].
has been applied for processing of kinetic data. In Eq. (7) n is the order of reaction
and k is the reaction rate constant. The conversion parameter x can be taken from
the magnetometry data. Mathematical transformation of Eq. (7) leads to Eq. (8)
ln(− ln(1 − x)) = n ln k + n ln t
(8)
allowed to calculate the order of the reaction n from the slope of the ln(−ln(1 − x))
as a function of ln t.
Fig. 2A–C shows the room temperature magnetization data
for investigated samples as a function of external magnetic
field. It is evident that the resulting magnetization curves are
well saturated after an application of higher magnetic fields.
The difference in the saturation magnetization of the samples
milled for different times is mainly caused by a various amount
of the ferromagnetic component in these samples which is
bcc-Fe.
3. Results and discussion
3.1. Mechanochemical synthesis and product characterization
The progress of the nanocopper (grain size 20–30 nm) formation
from copper sulphide (see Eq. (2) in Table 1) is illustrated by XRD
patterns in Fig. 1A. The primary process – the reduction of Cu2S by
Fig. 1. (A) XRD patterns in the copper/iron sulphide system. A: starting Cu2S. The milling times for patterns B–D are 30, 60 and 120 min, respectively (1: copper sulphide,
2: iron, 3: copper, 4: pyrrhotite, 5: quartz). (B) XRD patterns in the lead/iron sulphide system. A: starting PbS. The milling times for patterns B–D are 30, 60 and 120 min,
respectively (1: lead sulphide, 2: iron, 3: lead, 4: pyrrhotite, 5: quartz, 6: pyrite). (C) XRD patterns in the antimony/iron sulphide system. A: starting Sb2S3. The milling times
for patterns B–D are 30, 60 and 120 min, respectively (1: antimony sulphide, 2: iron, 3: antimony, 4: pyrrhotite, 5: tungsten carbide, 6: quartz).
Fig. 2. (A) Magnetization as a function of external magnetic field in the copper/iron sulphide system. The milling times for patterns (1–6) are: 1: 0 min, 2: 1 min, 3: 4 min, 4:
6 min, 5: 10 min, 6: 20 min, 7: 25 min, 8: 30 min, 9: 35 min, 10: 40 min. (B) Magnetization as a function of external magnetic field in the lead/iron sulphide system. The milling
times for patterns (1–9) are: 1: 0 min, 2: 10 min, 3: 20 min, 4: 30 min, 5: 40 min, 6: 50 min, 7: 90 min, 8: 120 min, 9: 180 min. (C) Magnetization as a function of external
magnetic field in the antimony/iron sulphide system. The milling times for patterns (1–10) are: 1: 0 min, 2: 10 min, 3: 20 min, 4: 30 min, 5: 40 min, 6: 50 min, 7: 60 min, 8:
90 min, 9: 120 min, 10: 180 min.

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P. Balázˇ et al. / Journal of Alloys and Compounds 483 (2009) 484–487
Fig. 3. SEM images in Me/FeS systems: (A) Cu/FeS, (B) Pb/FeS, (C) Sb/FeS.
Fig. 4. (A) Kinetics of the mechanochemical synthesis of Me/FeS nanoparticles, Me = 1 – Cu, 2 – Pb, 3 – Sb. (B) ln(−ln x) vs. ln t plots showing the application of Avrami–Erofeev
equation.
Table 2
tion of our processes. The parameter k with some approximation
has meaning of the overall rate constant [14]. The parameter n is
function of nuclei number and their shape, composition of initial
reactants and products as well as gives information about reaction
mechanismus [15]. The value of this parameter enables to resolve
kinetic (n ≥ 1) and diffusion (n ∼ 0.5) regimes of solid-state reac-
tions [16]. According to this statement, our experimental data in
Table 2 show that the kinetic regime is the rate-determining step
for all the systems under study.
Calculated parameters of Avrami–Erofeev Eq. (7) for mechanochemically induced
solid-state reactions of metal sulphides with iron.
Reaction
Parameter
k (s−1
)
n
Cu2S + Fe → 2Cu + FeS (2)
0.0014
0.0002
0.0004
1.1885
1.5787
1.3650
PbS + Fe → Pb + FeS
(3)
Sb2S3 + 3Fe → 2Sb + 3FeS(4)
SEM images of synthesized nanocomposites are seen in
Fig. 3A–C. According to the observed surface morphology individ-
ual nanoparticles have tendency to form nanoparticle agglomerates
during milling process. The solid-state recombination of nanopar-
ticles into agglomerates is a general phenomenon which reflects
a tendency of nanoparticulate systems to compensate unsaturated
surface forces via surface reconstruction.
4. Conclusions
1. Nanocrystalline copper, lead and antimony metals were pre-
pared by mechanochemical reduction of the corresponding
metal sulphides.
2. Elemental iron has been proven as an effective reducing agent
for sulphide reduction.
3. Magnetization data were utilized for a rate of solid-state kinetics
calculation.
3.2. Solid-state kinetics
The kinetics of the solid-state reactions (2), (3) and (4) in Table 1
has been studied assuming the nucleation and crystal growth take
place at nanostructures formation. The Avrami–Erofeev Eq. (7) has
been applied for the kinetics description. The same procedure has
been applied in paper [13] for single-step displacement reduction
of hematite with magnesium.
The kinetic data for calculation of parameters k and n of Eq. (7)
have been obtained from the magnetometry data presented for all
three systems under study in Fig. 4. The calculated parameters are
given in Table 2.
Acknowledgements
The support through the Slovak Research and Developing
Agency (project APVV 0347-06, VVCE-0049-07), the Slovak Grant
Agency VEGA (project 2/0035/08, 1/689/09), Center of Excellence of
the Slovak Academy of Sciences (project NANOSMART), DAAD-PPT
project and International Laser Center in Bratislava (SEM measure-
ments) is gratefully acknowledged.
The rate of the nanometals preparation is in the order
Cu > Sb > Pb. Kinetic Eq. (7) has been derived on assumption of
three-dimensional growth of nuclei and is well suited for descrip-
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