Preparation of Spherical Particles with High Melting Point by Plasma Fusion Technique

Abstract

Highly dense spherical particles of oxides, carbides and metals with high melting point above 2, 000°C were . obtained by means of plasma fusion technique.Each fine raw powder was kneaded and extruded into thin rods. Extruded rods were then sintered to over 70% theoretical density in a suitable atmosphere. Sintered rods were fused and atomized in direct current argon plasma flame. Being collected in a water-jacket cooled chamber filled with argon, these fused particles were separated from small fractions of irregular particles.Major part of these studies consisted of the experiments related to the effects of such variables as feeding method of sintered rod, collecting method of fused particles and operating conditions of plasma-jet generator on the particle size distribution, the density and the yeild of the spherical particles.As the results of these studies, the technique has been developed, in which nearly spherical, highly dense and pure particles (0.1-2mm in diameter, above 95% theoretical density) could be fabricated continuously from fine raw powder of a few microns. Besides, from X-ray diffraction analyses and metallographic observation, it was known that the particles had supercooled structures and that they could be normarized to structures similar to sintered bodies by annealing at adequate temperature.