A study of formation of nanometric W by room temperature mechanosynthesis

Nanometric particles of elemental tungsten can be produced by solid state room temperature reduction of tungsten (VI) oxide with magnesium metal. The reaction is driven by high-energy ball milling powder mixtures of WO3 and Mg and involves a thermite route that allows for very short reaction times (as small as 8 min) under the proper milling conditions. The evolution of the reaction was followed as a function of time by X-ray diffraction, showing a gradual decrease in crystallite size of the reactant WO3, with formation of intermediate reaction products, until a near-instantaneous reaction takes place leaving only MgO and elemental W as final products. MgO was removed by leaching in diluted HCl and high purity tungsten (purity >99%) was obtained with a typical molar yield of 84%. The W powders are formed of impact welded aggregates of small particles of homogeneous dimension of about 70-100 rim, the typical crystallite size is 19 nm. (C) 2003 Elsevier B.V. All rights reserved.