Ni ultrafine-particles (UFP) were produced by direct current thermal plasma under various producing conditions in order to investigate a possibility of controlling the particle size of UFPs. In this study, influence of the gas pressure in reactive chamber in which the plasma flame spouted, and the feed rate of raw material powder on the particle size and size distribution of UFPs were investigated. The particle size distribution of UFPs were measured by analyzing the transmission electron microscope images.
The results obtained were as follows: (1) The size distribution of UFPs produced by thermal plasma conformed to log-normal distribution with 1.7-2.1 geometric standard deviation. (2) Specific surface area (SW) of UFPs decreased as the gas pressure in reactive chamber (PC) increased. There was a good linear relationship between log SW and log PC with a slope of −0.8. (3) Specific surface area (SW) of UFPs decreased as the feed rate of raw material powder (JP) increased. There was a linear relationship between log SW and log JP with a slope of about −0.2. (4) By considering the collision-coalescence mechanism, the dependence of specific surface area on the present producing conditions of UFPs was explained reasonably.
