Nanoparticle production by UV irradiation of combustion generated soot particles Page: 4 of 28
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We found that there are significant differences in the laser-material interactions when the
particles are in the submicron range - the particles do not exhibit incandescence, and the
broadband background emission is virtually absent (Stipe, Lucas et al. 2003; Stipe, Higgins et al.
2002). Here, we modify soot particles from a laboratory diffusion flame using UV photons. The
initial soot agglomerates irradiated by 193 nm laser pulses produce spherical, unagglomerated
nanoparticles of a controlled diameter. This technique shows promise for producing a high
concentration of nanoparticles for use in advanced engineering applications and for better
understanding laser-particle interactions.
Experimental Apparatus
The experimental apparatus is shown in Figure 1. Combustion generated particles are
created by an inverted, co-flow, non-premixed burner described previously (Stipe, Higgins et al.
2002). Methane flows at 1.27 liters per minute (lpm) through a 2 cm diameter center jet
surrounded by a shroud of 19 lpm of co-flow air enclosed in a 5 cm diameter quartz tube. The
methane and air were at atmospheric pressure and 293 K. The flame is roughly 30 cm in length.
Air injected 4 cm downstream of the flame tip at 25 lpm dilutes and cools the soot and exhaust
gases exiting the quartz tube. The soot and exhaust gases then flow through a 140 cm stainless
steel tube to enhance mixing. An ejector pump further upstream extracts 2 lpm of flow from the
stainless steel tube and further dilutes the flow by a factor of 11. The flow passes through a
diffusion dryer to remove water and through a diffusion denuder to remove unburned gas phase
hydrocarbons.
Of the 22 lpm exiting the ejector pump, half flows to a mixing chamber, where the
number particles drops and the mean particle diameter increases through collisions. The flow
then travels through a BGI cyclone (model KTL GK2.05), which removes particles larger than4
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Stipe, Christopher B.; Choi, Jong Hyun; Lucas, Donald; Koshland, Catherine P. & Sawyer, Robert F. Nanoparticle production by UV irradiation of combustion generated soot particles, article, July 1, 2004; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc783243/m1/4/: accessed April 19, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.