NUCLEATION LABORATORY
EFFECTS
OF BACKGROUND GASES ON THE
HOMOGENEOUS NUCLEATION OF VAPORS II.
J.
Phys. Chem. 99, 4443 (1995)
Richard H. Heist, J. Ahmed, and M. Janjua
RESEARCH SUMMARY
Using a specially designed high pressure diffusion cloud chamber (HPCC),
we observed a strong dependence of the homogeneous nucleation of methanol,
ethanol, and 2-propanol vapors on total pressure.
We find this dependence to be manifested by increasing values of the
measured Scrit (critical supersaturation) for each of the three alcohols with
increasing total pressure (Ptot). The
increase in total pressure is accomplished by increasing the amount of a
background (or carrier) gas in the diffusion cloud chamber.
The observed increase in measured Scrit implies that the homogeneous
nucleation rate of each of these alcohols decreases as the total pressure
increases.
We observed a significant dependence of the nucleation on the nature of
the background gas. The effect of increasing total pressure on the nucleation of
each of these alcohols is greater using helium as the background gas than using
hydrogen. We also observed that the
dependence of Scrit on total pressure (as manifested by the slope of the Scrit
vs Ptot data at constant temperature) is temperature dependent for each of these
alcohols. The measured slope of the
Scrit vs Ptot dependence increases as the temperature decreases.
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