In-Flight Size Focusing of Aerosols by a Low Temperature Plasma

Abstract

Thermodynamics dictate the direction of all chemical and physical processes. In the case of aerosols, maximization of entropy leads to a broadening of the size distribution as the system proceeds toward equilibrium. The expectation is that as an aerosol ages, the size distribution will broaden. Contrary to this expectation, in this work we demonstrate that the unique nonequilibrium environment in a low temperature plasma can modify particulate materials to make the size distribution narrower. Submicrometer aerosols composed of bismuth particles with a polydispersed size distribution were prepared and passed through a low temperature argon plasma. For lower powers at which the plasma operated near room temperature, the incoming polydispersed aerosol was converted into a monodispersed aerosol of geometric standard deviation approximately 1.1 with 65% mass yield. The mechanism by which the process took place involved the particles vaporizing in the plasma operating at near room temperature, which resulted in very large supersaturation of metal vapor. Particle heating and sputtering by ion bombardment are discussed as possible mechanisms leading to vaporization that causes the change in the size distribution to make it narrower.

Phase mixing in GaSb nanocrystals synthesized by nonequilibrium plasma aerotaxy

“…[ 15 ] Increasing ion bombardment rate can lead to higher particle temperatures, [ 15,19 ] and/or higher vaporization rates. [ 20 ] In contrast to the I GaI / I ArI ratio, the I SbI / I ArI ratio decreased when power was increased (Figure 4c inset). Although the Ga vapor is monoatomic, Sb primarily forms tetramers in the vapor phase.…”

“…At this stage, condensation–vaporization in the plasma was balanced, and such aerosol dynamics are known to be capable of narrowing the size distribution. [ 20 ] Above the 80 W threshold, the widths of the size distributions further decreased at constant mean size. The uniformity of particle size across the whole powder was verified by scraping the powder off the filter, and imaging it under a scanning electron microscope (Figure S5).…”

Entropy production and chemical reactions in nonequilibrium plasma

“…Tubular nonequilibrium plasma reactors are often conceived of as two‐zone systems (Figure 2). 8,13,40,41 The first zone is the nonequilibrium plasma, and the second zone is a recombination zone in which there is no plasma. The reactions proceed in different directions in these two zones.…”

Characterization of a non-thermal plasma source for use as a mass specrometric calibration tool and non-radioactive aerosol charger

“…If a high ion concentration and residence time are reached, a charge equilibrium inside the charger leads to a well-known size-dependent charging probability (Fuchs et al, 1965). This stationary-state charge distribution is of importance for the use of differential or scanning mobility particle spectrometers, which rely on accurate knowledge of the size-dependent charge fractions (Wang and Flagan, 1990;Jiang et al, 2014).…”