Chemical synthesis of tungsten-copper nanocomposite powder

Article abstract of DOI:10.1134/S0036023610020051

In this study homogeneous powders of CuWO₄ and WO₃ was produced from ammonium paratungstate (APT) and copper nitrate. Then, the product was used to prepare nano-sized W-Cu powder. Hence, a mixture of ammonium paratungstate and copper nitrate with predetermined weight proportion was made in distilled water, while the content of the beaker was being stirred at a certain speed to reach the desired composition of W-20 wt % Cu. Mixture was heated to 80-100°C for 6 h. Also, pH range was adjusted at about 3-4. The mixture was then evaporated and dried in the air. To reach W-Cu composite powder, the precursor powders burned out at 520°C for 2 h in the air to form W-Cu oxide powder and then were ball milled and reduced in H2 atmosphere to convert it into W-Cu composite powder. The resulting powders were evaluated using scanning electron microscopy, X-ray diffraction, thermogravimetric analysis and differential thermal analysis techniques. The results showed that homogeneous powders of W-Cu with particle size of around 100 nm and a nearly spherical shape could be obtained by this process. Each particle include smaller parts with size of around 20-30 nm. Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0036023610020051

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 2, pp. 167–173. © Pleiades Publishing, Ltd., 2010.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Chemical Synthesis of Tungsten–Copper Nanocomposite Powder1
M. Babapour Naseri, A. R. Kamali, and S. M. M. Hadavi
Department of Materials, Malek Ashtar University of Technology, Tehran, Iran
eꢀmail: m.babapour.naseri@inbox.com
Received June 17, 2008
Abstract—In this study homogeneous powders of CuWO4 and WO3 was produced from ammonium paraꢀ
tungstate (APT) and copper nitrate. Then, the product was used to prepare nanoꢀsized WꢀCu powder. Hence,
a mixture of ammonium paratungstate and copper nitrate with predetermined weight proportion was made
in distilled water, while the content of the beaker was being stirred at a certain speed to reach the desired comꢀ
position of Wꢀ20 wt % Cu. Mixture was heated to 80–100°C for 6 h. Also, pH range was adjusted at about
3⎯4. The mixture was then evaporated and dried in the air. To reach WꢀCu composite powder, the precursor
powders burned out at 520°C for 2 h in the air to form WꢀCu oxide powder and then were ball milled and
reduced in H2 atmosphere to convert it into WꢀCu composite powder. The resulting powders were evaluated
using scanning electron microscopy, Xꢀray diffraction, thermogravimetric analysis and differential thermal
analysis techniques. The results showed that homogeneous powders of WꢀCu with particle size of around
100 nm and a nearly spherical shape could be obtained by this process. Each particle include smaller parts
with size of around 20ꢀ30 nm.
DOI: 10.1134/S0036023610020051
1
1. INTRODUCTION
order to reduce costs and to produce net shape comꢀ
ponents with homogeneous structure, highꢀdensity
W/Cu parts can be produced by liquidꢀphase sintering
of composite powders characterized by very fine disꢀ
persions of both metals [1–3]. Such composite powꢀ
ders can be obtained by the reduction of copper and
tungsten oxides [4, 5]. The first step in this process
consists in producing cupric tungstate (CuWO4), via
solid state reaction of tungstate trioxide (WO3) or
Tungstenꢀbase electrical contacts exhibit excellent
resistance to mechanical wear and electrical erosion.
Therefore, tungstenꢀcopper (W/Cu) composites,
which benefit from the high thermal conductivity of
copper, have been used for many decades for applicaꢀ
tions such as currentꢀcarrying contacts, vacuum interꢀ
rupter, arcing tips, and electrical discharge machining
electrodes. Moreover, W/Cu composites benefit from
the low coefficient of thermal expansion of tungstate.
For this reason they have been recently used as heat
sinks, manufactured by powder metallurgy (PM) for
microprocessors, microwave modules, wireless teleꢀ
communication devices, as well as other power and
radio frequency packages for the microelectronics
industry. The conventional methods for the fabrication
of W/Cu composites are infiltration of a porous tungꢀ
sten skeleton with liquid copper. Infiltration is a twoꢀ
step process that wicks molten copper into the open
pores of a previously sintered tungsten porous strucꢀ
ture. Since copper and tungsten are mutually insoluꢀ
ble, alloying does not occur in the conditions (i.e.,
pressures and temperatures) usually employed in the
infiltration process. Following infiltration, the parts
are mechanically machined to the final dimensions.
Moreover, the infiltration process does not result in a
homogeneous microstructure and it is not a net shape
process, thus causing high production costs [1]. In
ammonium tungstates (meta,(NH4)6W12O39 ·
with 0.75 1.25 or para,(NH4)10W12O41 · 5H2O) and
copper oxides (CuO or Cu2O) or copper hydroxide
Cu(OH)2) [6]. After the formation of the cupric tungꢀ
xH2O
≤ ≤
x
(
state, powders are reduced in flowing hydrogen at
800°C to yield a fine W/Cu composite powder. If the
stoichiometric ratio of the starting components is
employed, only CuWO4 will be formed, leading to a
W/Cu composite powder containing 25.7 wt % Cu. If
excess of WO3 is present in the starting oxide mixture,
then metallic powders with lower copper process conꢀ
sists in producing cupric tungstate (CuWO4), via solid
state reaction of tungstate trioxide (WO3) or ammoꢀ
nium tungstates (meta,(NH4)6W12O39
0.75 1.25 or para,(NH4)10W12O41 · 5H2O) and copꢀ
per oxides (CuO or Cu2O) or copper hydroxide
Cu(OH)2) [6]. After the formation of the cupric tungꢀ
· xH2O with
≤ ≤
x
(
state, powders are reduced in flowing hydrogen at
800°C to yield a fine W/Cu composite powder. If the
stoichiometric ratio of the starting components is
employed, only CuWO4 will be formed, leading to a
1
The article is published in the original.
167

168
BABAPOUR NASERI et al.
W/Cu composite powder containing 25.7 wt % Cu. If highꢀenergy ball mill (Fritsch pulverisetteꢀ5 model)
excess of WO3 is present in the starting oxide mixture, with the selected rotation velocity of 250 rpm. The ballꢀ
then metallic powders with lower copper contents can milled oxide powder was reduced in an H2 atmosphere
be obtained after the highꢀtemperature reduction step through a twoꢀstage reduction, the first being at the
[6]. Currently, ammonium paratungstate (APT) is the 400°C for 30 min and the second stage of reduction was
dominating raw material used for the manufacture of performed at 650, 700, 750, and 800°C at different
tungstenꢀbased products. The thermal decomposition times, respectively. The fixed parameter quantities such
of crystalline APT and amorphous ammonium metaꢀ as stirring speed were selected according to our experiꢀ
tungstate (AMT) has been investigated [7, 8]. AMT is ences during the preliminary tests. Notice that since no
a material with good waterꢀsoluble tungsten chemicals process which might change the copper content was
and larger molecular weight.
made, the composition of the powder after synthesis
practically remained unchanged and the copper conꢀ
tent was identical to its initial content, which was conꢀ
sidered stoichiometrically 20 wt %.
At 25°C, the solubility of AMT is 30 g/100 g water,
while that quantity for ammonium paratungstate is
1.5 g/100 g water [9]. The decomposition of APT
showed that there are two transformations between
amorphous and crystalline phases from room temperꢀ
ature to 450°C, that is, precursor (crystalline)
2.2. Characterization of the Powders
The thermal decomposition of the precursor powꢀ
der was studied by measuring the weight loss as a funcꢀ
tion of temperature in the air using TGA and DTA
instruments. The heating rate was 5 K min–1 from
room temperature to 800°C. The dried precipitates,
the calcined precipitates, and the last WꢀCu powder
were characterized by Xꢀray diffraction. Particle size
and microstructure of the precipitates, calcined,
milled, and reduced powders were observed by scanꢀ
ning electron microscope (SEM).
amorphous powder
oxides (crystalline) [7, 8]. The
aim of the present study is to produce homogeneous
powders of CuWO4 and WO3 from APT and copper
nitrate to prepare nanoꢀsized WꢀCu powders.
2. EXPERIMENTAL
2.1. Materials and Precursor Synthesis
Experiments were carried out in a glass beaker of
300 ml volume equipped with a mechanical stirrer subꢀ
merged in a thermostatic bath. Mechanical stirrer
(Heidolf RZR 2020) had a controller unit and the bath
temperature was controlled using digital controller
(within 0.5°C). Firstly, 150 ml of double distilled
water was put into the beaker and when the desired temꢀ
perature of the beaker content was reached, a predeterꢀ
mined amount of powder with defined size distribution
was added into the solution, while the content of the
beaker was being stirred at a certain speed of 250 rpm.
To fabricate Wꢀ20 wt % Cu composite powders, white
colored ammonium paratungstate (NH4)10W12O41 ·
3. RESULTS AND DISCUSSION
3.1. Synthesis of W/Cu Oxide Composite Powder
Mixing ammonium paratungstate and aqueous
solution of copper was observed to form some colorful
precipitate, which once more resulted in the formaꢀ
tion of a green precipitate at the end of the reaction.
The existence of ammonia was observed in the precipꢀ
itation, and resulted in the formation of a complex
compound. However, when the precipitate is heated to
about 100°C, some of the ammonia evaporates. Figure 1
shows diffractogram of the dried precipitates. It indiꢀ
cates that the powder with W/Cu ratio of 4 has a genꢀ
x
H2O powder (>99% purity, Merck, Germany) with
mean particle size of 150 m and blue colored copper
μ
eral composition of (NH4)4Cu3(NH3)3H2W12O42
·
nitrate (Cu(NO3)2 · 3H2O, >99% purity, Merck, Gerꢀ
many) were used as raw materials. The beginning mixꢀ
tures were prepared by mixing APT in an aqueous soluꢀ
tion of copper nitrate in distilled water to achieve
desired composition of Wꢀ20 wt %Cu. APT was slightly
soluble and suspended in a stirred reactor containing
water. The mixture was heated to 90–100°C for 6 h at
relatively constant volume, while maintaining the pH of
xH2O, in which paratungstate anions are surrounded
by copper and ammonium ions, as well as water and
possibly ammonia molecules. According to SEM
micrograph of the dried precipitates (Fig. 2), it was
seen that the precipitates have granular shape with very
fine particle size (50–200 nm).
Figures 3 and 4 show TGA and DTA curves of dried
the slurry at about 3–4 by adding ammonia solution. precipitates in the air. It is evident from the curves that
The volume was maintained constant by adding disꢀ there are three reaction points for precursor powders
tilled water. At the end of the reaction, the slurry was in the air atmosphere, which are: 100, 260, and 500°C
,
evaporated in the air to form a solid powder. The respectively. In four steps, different amounts of water
obtained precursor powders were calcined at different and ammonia were released, and different weight
temperatures varying between 150 and 750°C for 2 h in losses were obtained. As the first weight loss correꢀ
the air with a heating rate of 5 K min–1, forming WꢀCu sponded to endothermic peaks at 100°C, the weight
oxide powder. The WꢀCu oxide composite powder was loss accompanying this step suggests that it can be
ball milled for 6 h in the air with a ball/powder weight attributed to loss of physisorbed water. The second
ratio of 15 : 1. The milling process was carried out in a decomposition step takes place between 110 and
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

CHEMICAL SYNTHESIS OF TUNGSTEN–COPPER NANOCOMPOSITE POWDER
169
Cu nitrate powder
APT powder
Coꢀprecipitation powder
5
15
25
35
2θ, deg
45
55
65
Fig. 1. Xꢀray diffraction of raw materials (APT and Cu nitrate coprecipitation powder).
5 μm
500 nm
(а)
(b)
Fig. 2. SEM micrograph of the dried precipitates: (a) 5000×, (b) 30 000×.
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
20 60 100 140 180 220 260 300 340 380 420 460 500 540 580 620 660 700 740 780
Temperature,
°
C
Fig. 3. TGA curve of dried precipitates.
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170
BABAPOUR NASERI et al.
115
DTA Signal [W_02]
105
95
85
75
65
55
45
35
25
15
5
–5
50
150
250
350 450
Temperature,
550
650
750
°
C
Fig. 4. DTA curve of dried precipitates.
a: WO3
b: CuWO4 –
c: CuWO4
x
750°C
cc
a
c
c
c
c
c
a
a
c
520°C
c
a
c
c
c
c
c
c
a
a
c
c
a
a
c
c
c
a
a
a
c
c
c
a
c
b
a
a
a
c
c
a
a
c
b
c
c
a
b
b
a
a
b
b
b
b
b
b
a
350°C
b
a
b
b
a
a
b
a
a
b
a
a
a
b
150°C
5
15
25
35
, deg
45
55
65
2θ
Fig. 5. XRD spectra of the powders calcined at different temperatures.
260°C, and amorphous powder starts to form in this mic nature. The combustion processes of NH3 have
occurred in exothermic processes at 260°C, producing
H2O, dinitrogen oxide (N2O), and nitrogen monoxide
(NO). The decomposition product obtained at temꢀ
perature 305°C between second and third reaction
step.
XRD pattern (Fig. 5) of the decomposition product
obtained at 150°C, just after the first reaction point,
suggests the formation of (NH4)2WO4 · H2O and
Cu(NO2)2(NH3)4. The third decomposition step (Fig. 3),
x
points exhibits the diffractogram of CuWO4
x
and WO3. It is seen that (NH4)2WO4
⋅
x
H2O a–nd
reached to its maximum at 260°C, is also of exotherꢀ Cu(NO2)2(NH3)4 phases disappeared and new phases
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

CHEMICAL SYNTHESIS OF TUNGSTEN–COPPER NANOCOMPOSITE POWDER
171
500 nm
5 μm
(b)
(а)
Fig. 6. SEM micrograph of the powder calcined at 520°C (a) 5000×, (b) 30 000×.
5 μm
Fig. 7. SEM micrograph of the powder calcined at 750°C.
of CuWO4 – x and WO3 appeared when heated above the pockets in sintered specimen. To avoid this problem,
temperature of 260°C. In this step, the product was the shell structure was crushed by milling of the oxide
mainly composed of a crystalline powder. The appearꢀ powders. Figure 8 shows morphologies of the powders
ance of an amorphous phase has also been identified milled in dry condition.
by XRD. However, very small amount of amorphous
phase existed up to 50°C. The peaks of CuWO4 and
3.2. Preparation of Reduced W/Cu Composite Powder
WO3 were observed in XRD pattern of the powders calꢀ
cined at 520°C. At higher temperatures, growing of the
crystallites takes place.
The ball milled WꢀCu oxide powder was effectively
reduced in hydrogen atmosphere in a twoꢀstage proꢀ
cess minimizing the compositional segregation.
Figure 9 shows the XRD patterns of Wꢀ20 wt % Cu
powders which were fabricated by two stage reduction
process at 400°C for 30 min and 650, 700, 750, and
800°C for several times in H2 (the weight of initial
powder was 5 g, and the height of powder bed was
Figure 6 shows the SEM micrograph of calcined
powders at 520°C, from which could not be seen that
the precursor particle has broken into many small parꢀ
ticles. The specific surface area decreased due to the
agglomeration of small particles during calcinations of
the samples at high temperatures and the particles still
maintained the shape of the precursor, as shown in
Fig. 7. Moreover, as shown in Fig. 6a, the oxidized
2 mm). Cu oxide completely reduced at 400°C
.
As shows in Fig. 10 the optimum temperature for
powders of about
1 m diameter have a highly porous reduction is 750°C in 90 min. Figure 11 shows the
μ
structure owing to removal of organic salt compoꢀ microstructure of reduced powders produced from
nents and oxidation, and still maintained the shell preliminary milled and unmilled oxide powders. As
structure of the precursor. It was expected that this the spherical shell structure was fragmented during
shell structure might cause residual pores or Cu ball milling, the reduced powders had a less agglomerꢀ
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

172
BABAPOUR NASERI et al.
5 μm
500 nm
(а)
(b)
Fig. 8. SEM micrograph of W/Cu oxide powders milled for 6 h in dry conditions.
WO2.9, WO2.7, WO2
Cu
W
800
750
°
°
C
C
700
°
°
C
C
650
5
25
45
65
, deg
85
105
2θ
Fig. 9. Xꢀray diffraction patterns of Wꢀ20 wt % Cu powders reduced at different temperatures.
100
800
750
700
650
°
°
°
°
C
C
C
C
80
60
2
X(800) = –0.0172t + 2.6293t + 0.8527
2
R
= 0.9959
2
X(750) = –0.0139t + 2.388t + 0.3342
= 0.9992
2
40
20
R
2
X(700) = –0.0098t + 1.8703t + 0.622
2
R
= 0.997
2
X(650) = –0.0078t + 1.5316t – 0.7887
R
2
= 0.9906
0
10 20 30 40 50 60 70 80 90 100
Time, min
Fig. 10. The fractional conversion, X, as a function of time during the isothermal reduction of oxide powders.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

CHEMICAL SYNTHESIS OF TUNGSTEN–COPPER NANOCOMPOSITE POWDER
173
500 nm
500 nm
(b)
(а)
100 nm
(с)
Fig. 11. SEM micrographs of W/Cu composite powders at (a) milled, (b) unmilled conditions, and (c) TEM micrographs of
milled sample.
ated structure than those powders without a prior millꢀ
ing. The microstructure of this sample includes partiꢀ
cles with size of around 100 nm. As shows in Fig. 11c,
each particle include smaller parts with size of around
20–30 nm.
REFERENCES
1. D. L. Houck, L. P. Dorfman, and M. Paliwal, Proceedꢀ
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4. CONCLUSION
3. J. S. Lee and T.H. Kim, Nanostruct. Mater.
(1995).
6, 691
Based on the investigation made for the fabrication
of Wꢀ20 wt % Cu composite powder using coprecipiꢀ
tation method, the following points may be highꢀ
lighted. The W/Cu oxide ultrafine powder with a shell
structure could be produced by coprecipitation
method from APT and Cu nitrate. Particle sizes of
around 80–200 nm have been obtained in the powder
calcined at 520°C.The shell structure of oxide powder
could be destroyed by ball milling. Ball milling caused
reduced agglomerations and better dispersion of the
powder. Wꢀ20 wt % Cu composite powder with nanoꢀ
sized tungsten particles could be synthesized by reducꢀ
tion of the milled oxide powder.
4. L.P. Dorfman, M. J. Scheithauer, D. L. Houck, and
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010