Mechanosynthesis and process characterization of some nanostructured intermetallics-ceramics composites

Article abstract of DOI:10.1016/j.jallcom.2006.08.125

In situ formation of nanostructured composite materials consisting of intermetallic phases and ceramic oxide starting from two different mixtures of Cu₂(OH)₂CO₃ or CuO with Al was performed. Composites were synthesized by high-energy ball milling in a laboratory planetary mill. Formation of Cu(Al) solid solution and Al₂O₃ composite was followed by X-ray diffraction and thermal analysis of milling products.

Full text of DOI:10.1016/j.jallcom.2006.08.125

Journal of Alloys and Compounds 434–435 (2007) 501–504
Mechanosynthesis and process characterization of some
nanostructured intermetallics–ceramics composites
K. Wieczorek-Ciurowaa,∗, D. Oleszakb, K. Gamrata
a Institute of Inorganic Chemistry and Technology, Cracow University of Technology,
Warszawska 24, 31-155 Cracow, Poland
b Faculty of Materials Engineering, Warsaw University of Technology, Wołoska 141,
02-507 Warsaw, Poland
Available online 11 October 2006
Abstract
In situ formation of nanostructured composite materials consisting of intermetallic phases and ceramic oxide starting from two different mixtures
of Cu2(OH)2CO3 or CuO with Al was performed. Composites were synthesized by high-energy ball milling in a laboratory planetary mill. Formation
of Cu(Al) solid solution and Al2O3 composite was followed by X-ray diffraction and thermal analysis of milling products.
© 2006 Elsevier B.V. All rights reserved.
Keywords: Mechanochemical processing; Metal matrix composites; Oxide materials; Thermal analysis; X-ray diffraction
1. Introduction
other simultaneously evolving water and/or other volatile com-
pounds. These compounds are characterized by 3–4-fold lower
hardness than their anhydrous oxides. It probably provides the
mechanochemical process with lower mechanical loading. Pro-
cesses taking place with such type of substances are known as
soft mechanochemical reactions [7].
In our previous study successful attempts were made apply-
ing the hydroxycarbonate of transition metals as “a source”
of metal to provide in situ SHS reactions that resulted in
intermetallics–ceramic oxide composites [8–10].
Large number of mechanically driven SHS reactions occurs
in anhydrous metal oxide and active metal systems [1–3]. The
literature data show some examples of Cu–Al alloy formation
either by reactive milling of Cu and Al or copper oxide with alu-
minium [4–6]. Thus, Ying and Zhang [5] have observed that in
Cu and Al mixture with low aluminium concentration, the first
phase formed by the reaction is ␥-Cu9Al4, while with higher
Al concentration it is ␪-CuAl2. Milling of the CuO and Al
mixture realized by Wu and Li [6] involved the formation of
metastable Cu9Al4 phase, while CuAl2 phase was observed only
after subsequent thermal treatment of mechanically synthesized
composite.
In this study in situ formation of intermetallic phase and
ceramic oxide from systems containing aluminium and Cu
hydroxycarbonate or Cu anhydrous oxide is compared.
2. Experimental
It is obvious that oxide materials are important in many fields
of technology but a low level of reactivity due to its thermody-
namic stability characterise them. Therefore it seems that their
use in mechanosyntheses is not necessary efficient. The alter-
native method is application of compounds containing groups
of atoms with oxygen or hydrogen. Such substances are, for
example, acidic and basic salts, crystal hydrates, etc. Their
certain feature in common is the fact that they react to each
2.1. Materials
Cu-hydroxycarbonate (Cu2(OH)2CO3), CuO and Al in a powdered form
(99.9% purity) were used as commercial reagents. Two-component systems,
Cu2(OH)2CO3–Al and CuO–Al, were prepared as physical mixtures in which
the amount of aluminium was calculated assuming the Cu9Al4 and Al2O3 for-
mation as components of the milling products.
2.2. Instrumentation and milling procedure
∗
Corresponding author. Tel.: +48 126282036; fax: +48 126282036.
E-mail address: kwc@usk.pk.edu.pl (K. Wieczorek-Ciurowa).
For mechanochemical syntheses laboratory planetary mills Pulverisette 5
and 6 GmbH Fritsch with vials and balls made of hardened steel were used. The
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2006.08.125

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K. Wieczorek-Ciurowa et al. / Journal of Alloys and Compounds 434–435 (2007) 501–504
milling processes were performed under protective atmosphere of argon. The
total mass of powders was 5 g and BPR equals 10:1.
In the case of Cu2(OH)2CO3–Al system the gas pressure and temperature
in the milling vial were monitored using GTM system with radio transmission
of data to receiver remote from the mill.
time intervals are presented in Fig. 1. Results indicate that the
initial components of the studied mixture still exist in the system
up to 10 h of mechanical treatment. However, their intensities
decreased significantly in comparison to the untreated mixture.
Peaks of CuO as well as Cu2O phases appeared in products in
the fourth hour of milling. This indicates that Cu2(OH)2CO3
started to decompose and metallothermic reduction of CuO by
Al proceeded gradually with formation of Cu. Furthermore,
the broad diffraction peak appeared in the range of 2θ = 42–45◦
after 10 h of milling. Its intensity increases significantly with
elongation of milling time. The shape of this X-ray reflex
indicates its complexity and the deconvolution confirmed the
presence of copper beside Al2O3 phase. After 15 h and 20 h of
milling the position of Cu(1 1 1) peak shifted from 2θ = 43.32◦
to 43.25◦, respectively, while Al peaks completely disappeared.
This may suggest that solid solution of Cu(Al) has formed
as a result of mechanical alloying of two metals, Cu and Al.
Confirmation is done by the increasing the lattice parameter
3. Results and discussion
The solid products identification of reactive ball milling of
both tested systems, i.e. Cu2(OH)2CO3–Al and CuO–Al, reveals
the formation of materials which are composed of Cu(Al)/Al2O3
phases. This is a consequence of complex chemical reactions
occurring during milling process described in details below.
3.1. The effects of mechanosynthesis in the
Cu2(OH)2CO3–Al system
The XRD patterns (Philips X’Pert diffractometer-Cu K␣) of
the Cu2(OH)2CO3–Al system mechanically treated at different
˚
˚
of metallic copper from 3.615 A to 3.620 A [11]. According
to Vegard’s law which states that the lattice parameter of the
solid solution is a function of the amount of solute and using
parameters of pure Cu and Al, the contents of Al solute in Cu
matrix for the mechanically treated Cu2(OH)2CO3–Al system
can be estimated on the level of about 5%.
From thermodynamic point of view the reactions occurring in
the tested system are highly exothermic, e.g. the enthalpy of alu-
Fig. 1. X-ray diffraction patterns for Cu2(OH)2CO3–Al system after different
time of mechanical alloying (intensities with the same scale).
Fig. 2. GTM curves for Cu2(OH)2CO3–Al system: (a) beginning of mechanical
treatment and (b) final steps of mechanosynthesis.

K. Wieczorek-Ciurowa et al. / Journal of Alloys and Compounds 434–435 (2007) 501–504
503
minothermic reduction of CuO with Al is equal—1179 kJ/mol.
3.2. The effects of mechanosynthesis in the CuO–Al system
However, in the studied system of hydroxysalt–active metal the
processes in mill occur in a control manner. From Fig. 2a and b
illustrating the changes of temperature and pressure in vial dur-
ing milling process one can see that in the first hours of milling
the temperature and pressure increase simultaneously. The rise
in pressure is due to the decomposition of Cu2(OH)2CO3 with
evolving of H2O and CO2, while the temperature increase is
involved (caused) by the friction and impact of balls. But when
Cu-hydroxycarbonate is decomposed completely to CuO any
rise of pressure is observed. Instead one can see the transi-
tory rise in temperature (Fig. 2b). The duration of this tem-
perature rise corresponds to locally induced aluminothermic
reduction. Based on these data one can postulate that in our
case mechanosynthesis takes place in a controlled way, i.e.
CuO is reduced by Al in many steps proceeding locally, in
isolated part of treated powders. Such run of aluminothermic
reduction may be explained by the fact that the occurrence of
a highly exothermic reaction in combustive way depends not
only thermodynamic but on other factors such as mechanical
properties of reactants, their crystalline structures, stability dur-
ing milling [7,12]. In our case reaction does not proceed in
an explosive manner probably due to ductility of Al. Ductile
materials tend to form large particles which cover the surface
of the milling tools, and therefore decreases the efficiency of
treatment.
Fig. 3 shows X-ray diffraction patterns for mechanically
treated mixture of CuO with Al during different time intervals.
It can be observed that initial components disappeared com-
pletely within 4 h of milling. This time is considerably shorter
than in the case of the Cu2(OH)2CO3–Al system, where they
still exist until 10 h of milling. It may suggest that the kinetics
of mechanochemical reactions in the CuO–Al system is higher
than in the Cu2(OH)2CO3–Al one. The presence of reflexes from
Al2O3 confirmed that the aluminothermic reduction in CuO–Al
system occurred within 4 h of milling. After this time a broad
peak, similar to the system of Cu2(OH)2CO3–Al after 10 h of
milling, is detected in the range of 2θ = 42–45◦. The shape of this
peak indicates its multiphase character. However, the strongest
line located inside this reflex is related to copper. The calculated
˚
latticeparameterofthisphaseisequalto3.656 A. Comparisonof
this parameter with its value of pure Cu suggests the expansion
of the copper lattice by aluminium forming the solid solution
of Al into Cu matrix. It is indirectly confirmed by the lack of
Al peaks on X-ray diffraction patterns. In fact the content of Al
solute was estimated on the level near to 10%. Conventionally Al
dissolves in Cu at the temperature of eutectoidal transformation
(565 ◦C) in 9.4%.
4. Conclusions
Mechanosynthesis in both systems, the copper hydroxy-
carbonate–Al and copper oxide–Al, brings about the formation
of composite material consisting of Al2O3, Cu(Al) solid solution
and Cu. The amount of Al dissolved into Cu matrix is consider-
ably higher for the CuO–Al system than for Cu2(OH)2CO3–Al
one. This is probably caused by the different kinetics of
mechanochemical reactions in these two systems.
It is worth to notice that the expected Cu9Al4 phase formation
is not observable although in both systems the stoichiomet-
ric amounts of components were prepared. Deficiency of Al is
probably due to its sticking onto milling tools. It is typical for
ductile substances such as aluminium which easily adheres to
the milling media [12].
Acknowledgements
The authors would like to thank Prof. Yu.G. Shirokov from
the Ivanovo State University of Chemistry and Technology
(Russia) for a valuable discussion. The Polish State Com-
mittee for Scientific Research (KBN) supported this work
(C-1/DS/65/05).
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