Geometry of Metastable State Volume for Vapor-Gas System and Experimental Data on Nucleation Rates in Critical Line Vicinity, страница 2

A vapor-gas as binary system has metastable volume which is bounded by surfaces of phase equilibria and spinodal conditions. These surfaces are jointed along the critical line of binary system.  Conditions for critical line can be calculated using correlations published by Reid et al. [7].  Fig. 5 illustrates the critical pressure and temperature variations in relation with mole fraction of 1, 2-propanediol.

	Fig. 5. Critical pressure, P, and temperature, T, variations on mole fraction for a sulfur hexafluoride – 1, 2- propanediol system.

 

A volume of metastable states for a vapor-gas system under investigation can be presented schematically  such  as  in  Fig. 6.   Profiles,  colored  by  grey in Fig. 6, at mole fraction X₁ and

Fig. 6. A schematic presentation of volume of metastable states for a vapor-gas system. T is temperature of system; P is total pressure; letter A is attributed to gas; X is mole fraction of substance B; lines MN  and EF represent an equilibria and spinodal conditions for binary vapor-gas system respectively; ECA & FCB are spinodals and MCA & NCB are binodals for the single components A and B; the dotted contour is presenting schematically the area of the just found phase transitions of the first order; CA and CB are critical points of the single components;  lines ab and cd are representing a level of the constant nucleation rates for each profile at mole fraction X1 and temperature T1 respectively.

 

Fig. 7.  The vapor activities, a, on nucleation temperatures, T, at two levels of nucleation rates, J, for a sulfur hexafluoride – 1,2- propanediol system at pressure, P=0.30 MPa and a sulfur hexafluoride – 1,3- propanediol mixture at pressure, P=0.10 MPa.

temperature T₁ respectively are illustrating schematically the volume sections for A-B system. Lines ab and cd are representing a constant nucleation rate conditions.  These lines are similar (except some details, which are a subject for the future investigations) to the experimental sections of the vapor activities on nucleation temperatures which are shown in Fig. 7.

It can be concluded that a conceptual problem in vapor-gas to liquid (or solid phase) nucleation is its treatment of the nucleation as a single component problem instead of a two component system. Results of the present research illustrate clearly that gases can generate a phase transitions in a condensed state of matter in the critical line vicinity.  Gas can be involved in the critical embryos and any vapor-gas system nucleation should be considered in an approximation of binary solutions. A direct mass spectrometric measurements show the presence of the carrier gas in the critical cluster under some nucleation conditions, for example, in a monosilane-argon system [8].    

 Acknowledgements

Prof. M.P. Anisimov is acknowledged for the useful and stimulating discussions of problem. The present study was conducted under Basic Research Russian Foundation support through grant numbers of 07-08-13529-ofi and 07-03-00587-а. 

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