Treatment of metallurgical silicon powder by thermal RF plasma

This work focusses on the purification of metallurgical grade silicon powde r during its treatment in a thermal RF plasma. The first step consists of studying the mechanisms of heat and mass transfe r during the interaction between silicon particles and an argon plasma. The refore we use two particle sizes (50 - 80 mu m and 80 - 125 mu m) in order to qualify the influence of the surface area on the evaporation effect. The measurements of the spheroidised particle diameters after their treatment give the opportunity to define the best residence time of the particles in the plasma. At the same time for each experimental condition both velocity and particle evaporation are measured by Laser Doppler Anemometry (LDA) and Optical Emission Spectroscopy (OES). The second step proposes a modeling for the heat and mass transfer between plasma and particle taking into account the cold gas channel in the plasma torch. It has been estimated that the silicon particle could be melted if t he initial diameter does not exceed 140 mu m. The correlation between model and experimental data will permit in the future to control the melting of the particle, the evaporation phenomenon for different plasma gases and the ir viscosity.