Heterogeneous nucleation characteristics of mixed vapor of benzene and cyclohexane on a cold substrate.

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The heterogeneous phase transition of mixed benzene and cydohexane vapors on a cold copper substrate was observed by slowly cooling the substrate under reduced pressure conditions. In the conversion of the vapor to the condensed phase, vapor-to-liquid or vapor-to-solid phase transitions occurred depending on the mixing ratio of both vapors. By measuring the critical vapor pressure and temperature, corresponding critical supersaturation ratios were determined for various mixing ratios of both vapors. The critical pressure for the formation of solid benzene from mixed vapor agreed closely with that of pure vapor having higher composition. The critical pressure for the formation of solid cyclohexane from mixed vapor decreased from 6 to 9% compared with that from pure vapor. Liquid condensate was formed at critical supersaturation ratios of almost unity. A phase diagram was constructed by solving a non-linear simultaneous equation derived from vapor-liquid equilibrium and critical pressure-temperature relationships. It agreed in a practical sense with the observed results.