Application of DC plasma torches for spheroidization processes of irregularly shaped powders

The article presents a review of modern designs of direct current arc plasma torches and the technological configurations used for plasma spheroidization of irregularly shaped powders. The study examines plasma torch designs employing both 'hot' thermionic tungsten electrodes and 'cold' autoemissive copper electrodes, demonstrating their ability to operate with various types of plasma-forming gas mixtures. The influence of the plasma-forming gas's composition on the electrode erosion intensity is analyzed, and approaches to improving the electrode's lifetime and overall torch reliability are outlined. The processes of particle heating, melting, and spheroidization are examined, along with the key parameters determining spheroidization efficiency: Plasma enthalpy and velocity, particle size, residence time in the high-temperature zone, and the powder feeding scheme. It is shown that radial feeding provides 70%–82% spherical particles, and up to 86%–97% under high-power operating conditions. Axial feeding achieves more than 95% spheroidized particles. Promising technological solutions aimed at increasing the productivity of the spheroidization of ceramic and metallic materials are also discussed.