Homogeneous nucleation in metal tetrachloride vapors: Tin and titanium tetrachlorides

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Abstract
The upward thermal diffusion cloud chamber was used to measure the critical supersaturations for homogeneous nucleation of droplets from the supersaturated vapors of tin and titanium tetrachlorides. The measured supersaturations are in good agreement with the predictions of the classical theory of nucleation. Trends in free energy barrier are correctly predicted by the classical theory for carbon, silicon, tin, and titanium tetrachlorides. However, the classical barrier does not reflect the binding energies in the critical clusters. According to the classical theory, the size of the nucleus of SiCl4 ranges from 60 to 120 molecules while for TiCl4 it varies from 35 to 65 molecules in the temperature range of 240–310 K. The classical theory predicts a linear log J vs 1/T relationship. Corresponding states correlations are used to locate general trends and correlate them with molecular properties. Titanium tetrachloride deviates from the ‘‘simple fluid’’ behavior observed for CCl4, SiCl4, and even SnCl4. This deviation must reflect a modified intermolecular potential for TiCl4 as compared to a simple fluid potential.