Production of Ultrafine Nickel Particles Using an Insulated Constrictor Plasma Torch

Abstract

Ultrafine nickel particles (UFPs) were produced using an Ar-H₂ plasma jet generated by an insulated constrictor plasma torch, and the effects of plasma gas flow rate and hydrogen content on the proportion of UFPs produced were investigated. Since hydrogen supply from the cathode causes erosion of a copper anode, two different methods were proposed to prevent erosion of the anode: use of an anode with a tungsten pipe insert in the nozzle and supply of hydrogen from a feed ring installed under the anode.
The proportion of UFPs produced decreased with increasing plasma gas flow rate. This decrease is due to the reduction in residence time of powders present in the plasma. The proportion of UFPs produced increased with increasing hydrogen content. This is because the recombination energy of dissociation and ionization were added to the plasma. However for a relatively high hydrogen content, the proportion of UFPs saturated or decreased because a melt drop adhesion occurred in the nozzle. Further examination to find more effective powder heating methods and to prevent the melt drop adhesion is required in order to increase the proportion of UFPs.