抄録
Control of diameter of ultrafine particles (UFPs) is an important problem from both scientific and technololgical points of view when they are produced by means of a plasma method. The purpose of this work was to investigate the effects of production conditions on the specific surface area and the morphology of UFPs produced by DC plasma jet using an insulated constrictor plasma torch.
Nickel UFPs were produced by feeding Ni powder of 10μm diameter into Ar or Ar-H2 plasma jet. Specific surface area of UFPs increased with hydrogen contents up to 5%, whereas further increase in hydrogen content did not affect the specific surface area. Increase in hydrogen content changed the morphology of UFPs from isolated particles to coagulated shapes.
Specific surface area of UFPs produced with hydrogen content of 15% increased with increasing plasma gas flow rate to a certain extent; further increase of the flow rate caused a decrease in specific surface area. The morphology of UFPs changed from coagulated shapes to isolated particles as plasma gas flow rate increased.
The relation between specific surface area, Sw, and powder feeding rate, Jp, is described by Sw=fJpn, where f and n are the constants determined experimentally. The value of n determined from the experiments was close to the theoretical value of 0.4. This suggests that the formation mechanism is Brownian coagulation. Control of specific surface area of UFPs is possible by optimizing the powder feeding rate under conditions of low hydrogen content and high flow rate of plasma gas.
