Generation of submicron metal particles

Abstract

A low inductance circuit was designed, built and employed for the evaporation of metal wires with subsequent condensation of the metal vapor into small particles. The metal vapor was produced by the fast transfer of energy stored in a capacitor. A single pulse discharge with current and voltage going to zero simultaneously without the usual oscillation or dwell and restrike, was employed for each measurement of actual energy transferred to the wire (rather than energy stored). Silver, cadmium, and zinc wire were used in ambient atmospheres of air, of helium or of argon. The particles generated were measured by actual count employing enlarged photographs taken from electron microscope pictures of shadowed samples.The particles generated were spherical in shape and in the submicron range (50-1,000 A), with roughly a log normal distribution of diameters. The mean diameter decreased with an increase in the characteristic length for the expansion based on the energy transferred. The kind of ambient gas appears to have at most a minor effect on the particle size generated (when there is no chemical reaction).