Spherical submicron-size copper powders coagulated from a vapor phase in RF induction thermal plasma

Spherical submicron-sized powder of copper was synthesized through condensation from a vapor phase with a significantly high degree of supersaturation in thermal plasma. The degree of supersaturation was increased by the relatively high feed rate of raw copper powder. A high concentration of metal vapor was attained by using copper powder in Ar-H2 plasma, and relatively large particles of up to 0.1 μm in diameter were prepared. The powder feed rate, reactor pressure and gas flow rate of hydrogen were varied to examine their effects on the evaporation of the raw powder. Particle size and its distribution in the powder sample were evaluated by image analysis. The total amount of evaporated raw powder depended on the powder feed rate, the reactor pressure and hydrogen flow rate. The copper vapor concentration increased in proportion to the total amount of evaporation. Particle growth subsequently took place through heterogeneous condensation to form submicron-sized particles.