MECHANOCHEMICAL REDUCTION OF A COPPER OXIDE
T.F.Grigorieva, S.A.Petrova, I.A.Vorsina, A.P.Barinov, A.I.Ancharov, R.G.Zakharov,
L.E.Bodrova, E.A.Pastukhov, N.Z.Lyakhov
Institute of Solid State Chemistry and Mechanochemistry SD RAS, Novosibirsk,
Russia
Institute of Metallurgy, UD RAS, Ekaterinburg, Russia
Abstract
A possibility to obtain mechanochemically the Cu/oxide nanocomposites
through copper reduction by different metal reducing agents under mechanical
activation conditions has been studied.
Introduction
Metal matrix composites surpass essentially general cast alloys in their
performance attributes. The most commonly used method to produce cast composite
materials consists in mechanical kneading of disperse particles into a melt. The main
problem for this technique is low wetting of reinforcing phases with melted metal,
especially when dealing with oxide phases. One of the possible solutions is cladding
an oxide phase with a metal.
In the paper a possibility to obtain mechanochemically the Cu/oxide
nanocomposites appropriate to further use for precipitation strengthening of cast
copper alloys was studied.
To produce nanocomposites of this kind chemical reactions of oxide copper
reduction by different metal reducing agents under mechanical activation conditions
were used:
3CuO+2Al→Al2O3+3Cu
CuO +Cu(Al) -solid solution→ Al2O3+Cu
CuO +Cu →Cu2O.
Mechanical activation was performed in argon atmosphere in a planetary ball
mill AGO-2 with a crushing cylinders volume of 250cm3, 200g loading balls of 5mm
in diameter and a treating powder batch of 10g. X-ray phase analysis was carried out
on DRON-3M and URD-63 diffractometers in CuKα and CoKα radiation. For a
whole-pattern analysis patterns were taken on URD-63 with a graphite
monochromator in a step scan mode in the 20≤ 2Θ ≤ 70 interval, with a step of 0.05
and exposition time of 10s per step. An efficient size of a coherent scattering domain
was detected by a formula
D

2 cos 
.
Diffraction studies was also performed at the 4th Synchrotron Station. A fine
beam (0.4x0.4mm) of monochromized radiation (λ=0.3686Å) passed through a thin
film of the sample and produced a diffraction pattern recording by a two-dimensional
flat detector. To register the diffracted beam a detecting system based on the
Marresearch MAR345 Image Plate was used.
194
Absorption IR-spectra of the samples in the form of pellets with well annealed
KBr were recorded by the Specord 75IR spectrometer.
Distribution of a mechanocomposite in a melt was realized with the help of
low-frequency oscillations.
I. CuO+Al
It is known, a reduction reaction for a copper oxide with an aluminum is
highly exothermic and can proceed in SHS mode, but achievable high temperatures
bring about coarse crystals of resulting phases. As it was shown previously [1-4],
preliminary mechanical activation of a reacting mixture decreases essentially its
combustion temperature, which in turn alters a phase composition of products and
their size specifications. Analogous regularities were observed for mechanically
stimulated highly exothermic reactions proceeding under mechanical activation [5].
a
b
12
10
8
6
4
-2
 x 10 , см
-1
Fig. 1. IR-spectra of the CuO + Al mixture: initially (a) and after 40s activation (b)
The chemical reaction 3CuO+ 2Al→Al2O3+3Cu under mechanical activation
conditions has been studied. On the IR-spectra of the sample treated mechanically
during 40s (fig.1b) valence and deformation absorption bands corresponding to
α-Al2O3 appeared [6].
195
Cu
Cu2O
-Al2O3
-Al2O3
Cu
-Al2O3
CuO
Cu2O
-Al2O3
Cu
-Al2O3
-Al2O3
20
30
40
50
60
70
80
2Theta, degrees
Fig. 2. XRD pattern of the CuO+Al mixture after 40s of mechanoactivation
While the IR-spectrum of the initial sample contains a band with two maxima
at 575 and 520 cm-1 corresponding to stretching vibrations of the Cu(II)-O bond [7],
after mechanical activation during 40s, bands with maxima at 650 and 615cm-1 and
shoulders at 790 and 455cm-1 pertaining to the Al-O stretching vibrations and
distinctive to the alumina in octahedral environment are shown up.
Diffraction studies also prove the formation of α-Al2O3 and the copper
reduction after 40s of mechanical activation (fig.2).
Upon kneading the composite obtained into a copper melt the oxide phase
became partly agglomerated and thereafter was inhomogeneously distributed in the
cast copper. A lack of the copper on the surface of the Al2O3 crystals may be one of
the possible reasons for this behavior.
II. CuO+Cu(Al)
To increase a copper content in the composite, mechanically obtained solid
solution of the aluminum in the copper containing 20% of the aluminum:
CuO+Cu(Al)→Al2O3+Cu was used as a reducing agent. IR-spectroscopic
investigations of interactions between the copper oxide and the Cu(Al) solid solution
shown a process started by the end of the second minute of mechanical activation. By
this, the intensity of the Cu-O stretching vibration band decreases and the band itself
becomes diffused pointing out possible abnormalities in the copper oxide structure
(fig.3a).
196
Fig.3 IR-spectra of the activated mixture CuO + Cu(Al) solid solution.
Activation time: a – 1 min 40 s; b – 1 min 50 s
Further activation within 10s leads to significant changes and clear bands of
stretching and deformation vibrations of the [AlO6] octahedra special for α-Al2O3
appeared in IR-spectra.
XRD analysis revealed after 10s treatment the mixture additionally contained
the Cu2O oxide (fig.4 a). Further mechanical activation within one minute and a half
brings no serious changes into the system besides decreasing coherent domain sizes
which is testified by intensity decreasing and reflection broadening at the diffraction
pattern (fig.4b). One may suppose the formation of an advanced interface among
components proceeding at this stage. As a result next 10s of mechanical treatment
arises in dramatic changes of the phase composition (fig.4c): the reduction of the
copper and the formation of the Al2O3 oxide. At that, effective domain sizes of newlyarisen phases grown up distinctively, as it was confirmed by electron microscopy
data.
197
Fig.4 XRD pattern of the CuO+Cu(Al) mixture after 40s of mechanoactivation
Thus, the investigations undertaken revealed the mechanical activation of the
copper oxide and aluminum solid solution in the copper led to the formation of the
Cu/Al2O3 composite. This composite material was totally kneaded into a copper melt.
Electron microscopy confirms the oxide phase crystallites are distributed along the
copper grain boundaries (fig.5).
198
Fig.5. Microphotograph of the cast copper sample
III. CuO+Cu
To estimate a copper effect on mechanochemical reduction of the copper oxide
by the solid solution of the aluminum in the copper, a study of mechanochemical
interactions between the copper and its oxide has been carried out.
IR-spectroscopy analysis of the interaction products in the CuO + Cu mixture
upon various activation times shown the appearance of the Cu2O lower oxide became
noticeable already after 40s of activation (fig.6b): on the band with two maxima of
520 and 575 cm-1, devoting to the Cu-O bond stretching vibrations of the CuO copper
oxide, a shoulder appears at 635 cm-1 and during further activation transforms into a
band corresponding to the Cu-O bond stretching vibrations in the Cu2O copper oxide.
Thereafter the amount of Cu2O increases and towards the end of 12 minutes of
activation nearly all CuO oxide is over (fig.6c).
Fig 6. IR-spectra of the mixture CuO + Cu after activation during (a) 20 s.; (b) 40 s.;
(с) 12 min
199
XRD phase analysis undoubtedly evidences the presence of the Cu2O phase
after one minute activation (fig.7) with an efficient coherent domain size for this
phase of approximately 7nm. Coherent domain sizes for CuO are approx. 15nm, and
for the copper ~ 40nm. After 12 minutes activation on the diffraction patterns there
are reflections of two phases: Cu and Cu2O, and their efficient coherent domain sizes
are around 10nm.
Fig.7 XRD pattern of the Cu+CuO mixture after mechanical activation
The investigations carried out shown the Cu2O lower oxide could be
synthesized mechanochemically from the mixture of CuO and Cu, it means the copper
can contribute to a copper reduction, but lightly as a reduction with the aluminum
proceeds at significantly higher rate.
The work has been carried out in the frame of the integration project of
Siberian Division of the Russian Academy of Science No.98 'Mechanocomposites –
precursors for producing materials with novel properties'.
References
1. Korchagin M.A., Grigorieva T.F., Barinova A.P., Lyakhov N.Z.: ‘Solid phase
mode of self-spreading high-temperature synthesis’. Doklady Academii Nauk
2000 372 (1) 40-42 (in Russian)
2. Grigorieva T.F., Korchagin M.A., Barinova A.P., Lyakhov N.Z.: ‘Selfspreading high-temperature synthesis and mechanical alloying for producing
monophase fine intermetallic compounds’. Material Science 2000 (5) 49-53(in
Russian)
3. Korchagin M.A., Grigorieva T.F., Bokhonov B.B., Sharaphutdinov M.R.,
Barinova A.P., Lyakhov N.Z.: ‘Combustion solid phase mode in
mechanoactivated SHS-systems. Part I. Influence of mechanical activation
time on process characteristics and composite of combustion products’.
Physics of combustion and detonation 2003 39 (1) 51-59 (in Russian)
4. Korchagin M.A., Grigorieva T.F., Bokhonov B.B., Sharaphutdinov M.R.,
Barinova A.P., Lyakhov N.Z.: ‘Combustion solid phase mode in
200
mechanoactivated SHS-systems. Part II. Influence of mechanical activation
modes on process characteristics and composite of combustion products’.
Physics of combustion and detonation 2003 39 (1) 60-68 (in Russian)
5. Merzhanov A.G.: Combustion processes and material synthesis.
Chernogolovka. ISMAN Publ., 1998. (in Russian)
6. Plyusnina I.I.: IR spectra for minerals. Moscow, MSU Publ., 1977
7. Batsanov S.S., Bokarev V.P., Lazareva E.V. et al. Zhurnal Neorganicheskoi
Khimii, 1977 22 (4) 888. (in Russian)
201