(198a) Plasma Torch Production of Novel Materials

A low power (<1200 W), atmospheric pressure, microwave plasma torch was successfully employed to make a host of potentially useful materials including supported metal catalysts, micron scale spherical ceramics (solid and hollow), spherical nano-metal and nano-oxide particles, core-shell complex nano-oxide particles, single wall carbon nano-tubes and spherical boron nitride (2004 R & D 100 winner). Each material fabrication required understanding of the mechanism of formation in order to arrange the plasma system. For example, in order to generate spherical BN particles in a nitrogen plasma was employed. This generated a sufficient N atom concentration to prevent decomposition, and allowed the heretofore theoretical melting temperature of BN to be reached. Nanotube formation required the generation of a unique precursor stream. Specifically, carbon monoxide was flowed over a bed of iron to create a mixed gas that upon decomposition in the plasma created the gas composition that empirical evidence indicates leads to the formation of nanotubes: nanoscale iron particles and C-atoms. Some general considerations of particle formation in a plasma, such as the influence of particle charging, as well as some (surprising) results of spectroscopic studies of the influence of particles on atmospheric pressure plasmas will be presented as well.