Production of ultrafine metal particles (UFPs) using an RF plasma method is a promising one, but the effects of experimental conditions on the production of UFPs are not well understood yet. In this paper, we produced nickel UFPs by means of an Ar-H₂ RF plasma and investigated the effect of mean diameter of raw powder on the evaporation ratio in the plasma, the relationship between the generation ratio of UFPs and the collection sites in the apparatus, the effects of hydrogen content in plasma and the pressure in the apparatus on the specific surface area of UFPs.
The evaporation ratio of raw powder is reduced with increasing the particle diameter and decreasing the pressure in the apparatus. The generation ratio of UFPs was the highest at the collection site near the tail of plasma. Specific surface area of UFPs increased with hydrogen content in the plasma when the pressure in the apparatus was low, whereas it is not dependent on hydrogen content when the pressure was high. The mean particle diameter of UFPs calculated from the specific surface area had a good correlation with that measured from TEM photomicrographs.