A Facile Route to Tungsten Oxide Nano Materials

Nano-sized materials and products have been used widely in many applications because of their outstanding properties, different from those of the bulk materials. In early investigations into nanotechnology, the arc discharge technique was the first well-developed method used to manufacture nanoproducts.

However, owing to difficulties involved in controlling the manufacturing parameters, the purity and quality of nanoproducts synthesized by arc discharge called for improvement. The inert gas condensation (IGC) system was thus established by Gleiter. Because there are no catalysts or containments, it is considered the cleanest method of producing high quality products. In this system, metals are first placed in a tungsten or graphite boat and evaporated. The metal vapor is then cooled under an inert gas atmosphere (e.g. helium or argon) to condense into clusters or nanoparticles.

Although the arc method has a higher production rate than IGC system, the latter produces larger particles. Hence, a modified technique based on the IGC system was developed, in which blowing gases were introduced to obtain finer particles with better particle size distribution. To retain the benefits of both the arc discharge method and the IGC system, a plasma arc is used as the heat source and blowing gas is applied to quench the evaporated materials in this modified system. A simplified manufacturing process that enhances the purity of the as-prepared products is required. Therefore, an effective method, namely, the modified plasma arc gas condensation technique has been proposed.

A modified plasma arc gas condensation technique was successfully used to synthesize various nano-sized tungsten oxide nano materials with morphologies and structures that may be tuned by controlling the experimental parameters. Various non-stoichiometric WO3−x nano materials could be prepared by tuning the oxygen content during the process. W18O49nanotubes and nanorod bundles were also prepared by He plasma arc with different Ar/O2 ratios. In addition, W18O49/TiO2 core–shell nanoparticles were prepared by evaporating a dual target. In the present study, we addressed the feasibility of the plasma arc gas condensation technique and confirm its potential for nanomaterial fabrication.