THERMAL PLASMA SYNTHESIS OF ULTRAFINE IRON PARTICLES

Ultrafine iron powder was synthesized in an atmospheric-pressure radio -frequency plasma reactor by injecting relatively course iron powder i nto the plasma, where it evaporated. The renucleated iron particles we re characterized by means of a sampling capillary and dilution system interfaced to an electrical aerosol analyzer, a condensation nucleus c ounter and an electrostatic aerosol sampler. Volume-mean particle diam eters for samples obtained near the downstream end of the reactor rang ed from about 20 to 70 nm, with particle size increasing as the feed r ate of injected iron powder was increased. A two-dimensional numerical model was developed, which solved the plasma conservation equations t o predict temperature and velocity distributions, heating and evaporat ion of the injected iron powder, nucleation and growth of iron particl es, and particle transport by convection, diffusion and thermophoresis . Mean particle diameters predicted by the model were in good agreemen t with the experimental data, although the data indicated broader size distributions and flatter radial profiles of particle concentration t han predicted by the model.