Production of Ultrafine Particles of Refractory Materials in the Thermal Plasma Processing

In order to clarify the interaction between the plasma flow and powder materials in the low pressure processing, we have studied the influence of the feed ring length on production of fine particles. In the present reactor, the feed ring works as a mixing plenum after injecting powders and gas mixture into the plasma flow, because it confines the plasma and powders for both efficient mixing and heat transfer from plasma flow. We have confirmed that the number density of the prepared fine particles increases with the increase of the feed ring length. On the other hand, at the feed ring exit, the spectroscopic temperature of the three plasma jets for three different feed rings is nearly equal to each other. From these results we have concluded that it is effective for heating powder materials injected into the plasma flow to increase the feed ring length.