CC BY
47iSHS 2019
Moscow, Russia
PREPARATION OF Mo-Cu PSEUDOALLOY FROM CuMoO4 PRECURSOR
BY COMBINING SOL-GEL METHOD AND SHS
H. Kirakosyan*" and K. Nazaretyan"
aNalbandyan Institute of Chemical Physics NAS RA, Yerevan, 0014 Armenia
*e-mail: hasmik-kirakosyan@list.ru
DOI: 10.24411/9999-0014A-2019-10060
Mo-Cu pseudoalloys successfully combine the both metal's properties, such as high thermal and electrical conductivity, low and alterable thermal expansion coefficient, low weight and well high-temperature behavior rendering their widespread application in heavy-duty electronic contacts, welding electrodes, vacuum technology, military fields, aeronautics and some other advanced fields [1]. The Mo-Cu alloy has lower density than other Cu-refractory metal alloys and more suitable for spaceflight and navigation industries. Mo-Cu alloys are also easy to machine. Due to the controllable expansion of composite matrix, superior material stability and uniform thermal expansion characteristics, Mo-Cu alloys may withstand to critical thermal conditions as heat sink materials and spreaders, portable apparatus, rocket parts, etc. [2].
There are many methods for the synthesis of Mo-Cu pseudoalloys (mechanical alloying, mechano-chemical synthesis, electroless plating of appropriate salts, gel reduction, reduction with hydrogen from oxygenous compounds of copper and molybdenum, etc). The energy and time consumption, low efficiency and low productivity, the complexity of regulation of homogeneity, microstructure and porosity necessitates to bring a new and reliable pathway for powder synthesis.
In this work it was suggested a new simple and effective approach based on energy-saving combustion synthesis processes for the preparation of Mo-Cu pseudoalloys [3, 4]. The advantage of the method to prepare Mo-Cu is that firstly copper molybdate was obtained as a result of sol-gel process. In CuMoO4 molybdenum and copper are chemically bonded in the same crystal structure. The formation of a homogeneous composite is more preferable when salt is reduced, rather than metal oxides. By changing the ratios of the reducers (Mg, C) at stage II will provide the ability to control the thermal regime of the combustion process and therefore, the phase composition and microstructure of the product. For preparation of CuMoO4 precursor (NH4)6MC7O24-4H2O and Cu(NO3)2 were used as initial reagents, and citric acid (CA) as complexing and reducing agent. A citric acid solution was added to a stoicimetric solution of ammonium molybdate and copper salt (Mo/Cu = 1) in a proportion CA/Cu2+ = 3. Stoichiometric quantities of these substances were initially dissolved in deionized water to obtain saturated solutions and then the solutions were mixed. The obtained blue transparent solution was evaporated in a glassy beaker on the electric fryer at 80oC up to the gel state. The gel was dried at 120oC for 24 h, then pre-calcined at 420oC for 2 h. The procedure is shown in schematic diagram (Fig. 1). The composition of the sol-gel product was ascertained by the XRD and FT-IR analyses (Fig. 2). After the drying process, the sol-gel product was mixed with magnesium and carbon in a ceramic mortar and prepared cylindrical samples were ignited with an electrically heated tungsten coil in nitrogen atmosphere. Combustion parameters were measured by thermocouples: the results are presented in Fig. 3. Based on our previous experience with similar system [5], magnesium amount was changed from 1.2 to 1.4 mol. The addition of even 0.5 mol amount of carbon (2.3 wt %) in the CuMoO4 + 1.2Mg green mixture, causes combustion velocity to decrease more than 5 times. The further increase of carbon amount continues to reduce the combustion velocity. In the entire range of change of carbon amount, the temperature decreases gradually.
Fig. 1. Schematic diagram for preparation of CuMoO4 by sol-gel method.
Fig. 2. (a) XRD pattern and (b) FT-IR spectrum of CuMoO4 obtained by sol-gel method.
Fig. 3. Combustion temperature and velocity vs carbon amount for the CuMoO4-1.2Mg-xC system, P = 0.3 MPa.
Combustion products were subjected to XRD examinations (Fig. 4). It was revealed that at small amount of carbon only the reduction of copper occurs (MoO2MgO, Cu). The increase in carbon amount leads to reduction of molybdenum. However, 1.2 mol of magnesium was insufficient for the complete reduction of the both metals in whole range of change of carbon amount. Further experiments were conducted with the mixtures containing 1.4 mol Mg. Based
ÏSHS2019
Moscow, Russia
on the results of combustion experiments and XRD analysis of the combustion products the mixture containing 1.4 moles magnesium and 2.7 moles carbon was sufficient for the complete reduction of metals and were selected as optimal to obtain Mo-Cu composite powders.
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1-Mo, 2-Cu, 3-MgO, 4-MgO*MoO2, 5-Mo2C 2 1 1,2
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x=1.5 4 4 1 2 1 1,2
x=1 4 44 4 4 132 2 1,2
x=0.5 4 4 4 44 2 2 2
x=0 4 44 2 2 4
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Fig. 4. XRD patterns of combustion products of the CuMoO4-1.2Mg-xC mixtures.
After acid treatment (10% HCl) and removal of magnesia, the XRD pattern comprises only characteristic lines of molybdenum and copper (Fig. 5).
The presented approach outlines a pathway for the preparation of Mo-Cu nanocomposite by the combining energy-efficient sol-gel method and self-propagating high-temperature synthesis.
Fig. 5. XRD pattern of combustion products of the CuMoO4-1.4Mg-2.7C mixture.
This work was supported by the Enterprise Incubator Foundation PhD Support Program
(Hasmik Kirakosyan).
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