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Bojja Sreedhar Indian Institute of Chemical Technology, Tarnaka, Hyderabad 500 007, India (Received 19 August 2010; accepted 9 November 2010)

Tungsten nanoparticles (W-NPs) with average sizes ranging between 30 and 80 nm were prepared by thermolytic decomposition of tungsten hexacarbonyl in presence of a mixture of surfactants, oleic acid and oleyl amine. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy (XPS) results reveal that the surfactants oleic acid and oleyl amine bonded to the surface of W-NP through their functional groups, which in turn render stability to the nanopowders with respect to coarsening or aggregation. XPS results also confirm that carbon is present only at the surface of the W-NPs. The as-synthesized W-NPs were amorphous, and on heat treatment at 600 °C for 1 h, the amorphous powders transform into a body-centered cubic crystalline form (a-W).

I. INTRODUCTION

Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2010.76

Present commercial routes for the production of tungsten depend on conversion of two main natural resources wolframite and scheelite ores to ammonium paratungstate, which is subsequently calcinated in oxygen-bearing atmosphere between 600 and 850 °C and is followed by reduction of tungsten oxides with H2. Though these procedures are cheaper, it is difficult to produce tungsten nanopowders by using conventional methods because of high temperature during processing steps.13 Various methods have been explored to obtain tungsten nanoparticles (W-NPs), such as electrical explosion of wires,14 high-energy ball milling,15 molten salt–assisted self-propagating high-temperature synthesis,16 physical vapor deposition,17 gas-phase combustion synthesis,18 sealed tube synthesis,19 chemical reduction process,20,21 and solvothermal decomposition method.22 Chemical methods have been widely used to synthesize nanomaterials because of their easy operational procedure and potential for scaling-up. There are several chemical synthesis procedures for synthesizing nanoparticles, of which thermolytic decomposition is well known.23 Chemically synthesized W-NPs have the advantage of uniform particle size and desired crystal structure (a-W). Size and shape of W-NPs can be controlled by adjusting the reaction parameters such as reaction time and temperature.22 Success of any material development program depends on the analytical results obtained from various characterization techniques. Chemical, structural, and morphological characterizations are the first and foremost steps carried out while developing a new material. Hence, the analytical results obtained from various characterization tools play a crucial role in the development of strategic materials. Therefore, this study focuses on spectral, compositional, structural, and morphological

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Ó Materials Research Society 2011

Tungsten (W) plays a pivotal role in many hightemperature applications ranging from filaments in light bulbs, cathodes in high-power lamps to rocket nozzles i