Thermal diffusion cloud chamber studies of homogeneous nucleation

Abstract

The critical supersaturations required for the homogeneous nucleation of 12 different substances have been measured using an upward thermal diffusion cloud chamber. The technique used is the steady-state diffusion of vapour upward from a warm liquid pool, through a low molecular weight “carrier” gas, to a cooled upper plate. The supersaturations at which nucleation was observed to occur for all these substances, i.e., n-hexane, n-heptane, n-octane, n-nonane, benzene, toluene, o-xylene, n-butylbenzene, carbon tetrachloride, chloroform, trichloro-fluoromethane, and 1,1,2,2-tetrachloroethane, over the temperature range of these measurements, 220 to 380 K, were found to be in good agreement with the predictions of the classical (Volmer, Becker, Doering, Zeldovich) theory of nucleation. The Lothe-Pound theory does not fit any of these results. It is shown that the assumption that surface tension is independent of radius even for clusters of molecules as small as 10 Å radius is consistent with these results.