Synthesis, characterization and densification of W\Cu nanocomposite powders Prasanta Kumar Sahoo a,c, ⁎, Sarika Srinivas Kalyan Kamal a,c , M. Premkumar a , Bojja Sreedhar b , Suneel Kumar Srivastava c , Loganathan Durai a a Defence Metallurgical Research Laboratory (DMRL), Kanchanbagh, Hyderabad 500 058, India b Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology (IICT), Tarnaka, Hyderabad 500 007, India c Department of Chemistry, Indian Institute of Technology Kharagpur (IIT Kharagpur), Kharagpur 721 302, India abstract article info Article history: Received 3 March 2011 Accepted 23 March 2011 Keywords: Chemical synthesis W\Cu Nanocomposite Sintering In the present investigation, W\20–40wt.% Cu nanocomposite powders with average sizes ranging between 25 and 30 nm were synthesized by a soft chemical approach using tungsten hexacarbonyl [W(CO) 6 ] and copper acetonyl acetonate [Cu(acac) 2 ] as metal precursors. Particle size, morphology and distribution were measured using transmission electron microscope (TEM) and small angle X-ray scattering (SAXS). Surfactant coating on W\Cu composite powders was removed on heat treatment of powders at 450 °C in hydrogen atmosphere for 1 h. Elemental analyses of as-synthesized and annealed (at 450 °C) W\Cu nanocomposite powders were carried out using inductively coupled plasma-optical emission spectrometer (ICP-OES) and Leco gas analyzers. X-ray diffraction studies showed that the tungsten phase is amorphous while the crystal structure of copper phase is fcc in as-synthesized W\Cu nanocomposite powders. After annealing at 700 °C peaks corresponding to bcc tungsten are observed and peaks corresponding to fcc copper become sharper. Relative densities of 98.2%, 98.8% and 99.2% were achieved for W\20wt.% Cu, W\30wt.% Cu, and W\40wt.% Cu composite powders respectively when sintered at 1000 °C. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction Metal–metal nanocomposites are new generation materials in the growing field of nanoscience and nanotechnology. These nanocomposites are synthesized by the co-transformation and co- aggregation of two or more different metallic precursors [1–3]; for example, gold–silver binary nanoalloys have been produced by reduction of aurochloric acid (AuCl 4 ) and silver chloride (AgCl) in the presence of thiol molecules [4]. W\Cu nanocomposites have been fabricated mostly by mechanical alloying of metallic (W/Cu) and metal oxide (WO 3 /CuO) powder [5–7]. Properties of these nanocomposites are unlike those of individual types of clusters or of bulk composites of constituent metals [8,9]. Tungsten and copper are two immiscible elements under equilib- rium conditions and even immiscible in liquid state to a large extent as all the three Hume-Rothery rules are violated. First of all copper is fcc and tungsten is bcc, secondly the atomic radii difference between tungsten and copper is N 20% and lastly the electronegativities are also far apart (Cu = 1.9 and W = 2.36). The immiscibility of tungsten and copper is also reflected in their heat of mixing, which is positive (35 kJ/mol) [10,11]. The W\Cu nanocomposites are promising materials for manufac- ture of electrical contacts and electrodes, heavy duty electronic contacts, welding and electro-forging dies, heat sinks, packaging materials, arcing resistance electrodes and thermal management devices [12–23]. Preparations of W\Cu nanocomposites have been extensively pursued through mechanical alloying [24–43]. However, only few reports are available for the synthesis of W\Cu composite powders through chemical routes [44–48]. Chemical synthetic approaches have the advantage of better control on particle size, shape and distribution by adjusting the reaction parameters, when compared to mechanical alloying processes [49]. Polyol and thermal decomposition processes are considered as better processes among the chemical synthetic approaches, because these are simple, one-step, cost effective and give better control over particle size, shape and distribution. In addition, hydrolysis and oxidation of nanostructures, which quite often occur in aqueous synthesis, are prevented by surface adsorbed capping agents and stabilizers. In this work we address the synthesis of W\Cu nanocomposites by a multivariate route, comprising of polyol and thermal decompo- sition processes. W\Cu nanocomposite powders were synthesized by simultaneous reduction of Cu(acac) 2 by polyethyleneglycol (PEG- 200) and decomposition of W(CO) 6 in diphenyl ether. Composition of the resultant W\Cu nanocomposites could be easily tuned by adjusting the ratio of metal precursors as both are solid powders. The properties of W\Cu nanocomposites depend on their chemical composition, particle size, shape and distribution [50,51]. Powders Int. Journal of Refractory Metals and Hard Materials 29 (2011) 547–554 ⁎ Corresponding author at: Defence Metallurgical Research Laboratory (DMRL), Kanchanbagh, Hyderabad 500 058, India. Fax: + 91 040 2434 0884. E-mail address: prasantchem@dmrl.drdo.in (P.K. Sahoo). 0263-4368/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ijrmhm.2011.03.011 Contents lists available at ScienceDirect Int. Journal of Refractory Metals and Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM