Tailoring nanostructured powders for functional and structural applications

Nanostructured powders, i.e. powders with nanoscale primary feature size, offer a host of attractive properties. With the growing number of applications in new as well as existing markets for this new class of powders; several techniques have evolved for the synthesis of metal, ceramic, and composite nanoparticles. At issue in each of these processes is the extent of aggregation, which depends on the technique used to produce the nanopowders. A vapour phase synthesis process is described in which vapours of chemical precursors are pyrolysed in a low pressure flat flame. By controlling the time-temperature history of the particles in the hot zone of the flame, high surface area nanopowders of oxide materials are produced with minimal aggregation. In addition, the structure of the individual nanoparticles is controlled to optimise properties. The use of such powders in the area of energy storage is outlined. On the other side of the spectrum, for some applications, nanoscale particles are deliberately aggregated into a specific morphology to obtain the required functionality, or to facilitate processing. Two examples are described: extrinsic conducting polymers produced by the incorporation of nanoscale silver particles; and sintering of nanocrystalline phase pure tungsten.