Metamorphosis from LCEP to UCEP in the Metastable Three-Phase Region

The behavior of the phase lines in binary gas−liquid systems was classified by van Konynenburg and Scott according to the various connectivities of the critical lines and the three-phase lines, occurring in the pressure temperature diagrams of such systems. The three-phase line in type IV starts at a (LL)V point and ends at a L(LV) point. Somewhere near this line a transition takes place which determines the outcome at the end of the line. At this changeover point, called the plait-point transformation, two binodal cusps meet each other on the spinodal and at the same time, on the other end of the tieline, two binodals will cross each other and osculate. This phenomenon is described and analyzed in detail and a mathematical description of this behavior is given.