Heating of Powders in the Fire Ball of an Induction Plasma

A theoretical model has been developed for the calculation of the trajectories and temperature histories of particles injected in the fire-ball of an inductively coupled plasma. Calculations were made for alumina particles of different diameters ranging between 10 and 250 μm. The particles were injected through a water cooled probe upstream of the fire-ball. The results shows that the internal plasma recirculation in the coil region is responsable for the bouncing of the particles on the fire-ball. Particles of the order of 10 μm and smaler are entrained in the fire-ball by the inward radial flow caused by the electromagnetic pumping, and are subsequently completely evaporated. Larger particles, depending on their initial position and velocity of injection, could by-pass the plasma fire-ball, and in some cases, end up deposited on the wall of the plasma confining tube. Particles with diameters larger than 100 μm were found to pass straight through the fire-ball when injected close to the center line of the torch.