Ternary systems immiscibility regions

Emulsions formed from immiscible organic liquids in aqueous peroxide mixtures may behave in the same way as miscible organic liquids, but if the emulsion breaks and separation of the organic phase occurs, passage into an explosive region of the peroxide-water-organic liquid ternary system may occur, and this is potentially very dangerous. 

To explain the behavior of a polymeric multicomponent system, the polymer is considered as a mixture of two polymer species, PI and P2. By doing this, the polymer-solvent system can be illustrated using a ternary Gibbs triangular diagram. It is assumed that one species of the polymer, PI, has a lower molecular mass than P2 and is completely miscible with the solvent, whereas P2 exhibits an immiscibility region (Figure 15.5). 

The spinodal boundary is rarely shown on ternary immiscibility diagrams. Since this boundary is also represented by a dome, similar contour lines could be drawn. However, since the spinodal boundary is rarely known for these systems, it is usually neglected in the presentation of ternary immiscibility regions. 

The tie-lines shown in Figure 4.10 display a fan-shaped pattern, with the base of the fan in the silica corner of the composition diagram. This pattern is typical of ternary systems where both modifier oxides exhibit immiscibility with the network oxide. These systems include the Li20-R0, Na20-R0, and BaO-RO silicate systems, where RO is any alkaline earth oxide. A different pattern occurs for systems where immiscibility occurs for only one of the modifier oxides in its binary system with the network oxide. In this case, the immiscibility region is restricted to the area near the binary where immiscibility does occur, and the tie-lines do not extend to the network oxide corner of the diagram. 

The calculated metastable miscibility gap (see above) in the liquid-phase region of the Cu-Fe-Nb system is shown in Fig. 4 [2000Wan]. A miscibihty gap island exists inside the ternary system. The tie-lines in the immiscible region he along the radial hnes fiom the Cu comer to die Fe-Nb side. In Fig. 4 they are shown by dashed lines for different temperatures at different Fe/Nb ratios. Sohd hnes in Fig. 4 show the tie-lines at 1827°C. 

The immiscibility regions of type b and d spreading from the binary subsystems are terminated by one nonvariant point in ternary systems (the double critical endpoint HN (Li = L2-G) and the tricritical point RN (Li = L2 = G), respectively). Disappearance of the immiscibility region of type c takes place only after transformation (through the tricritical or double critical points) into immiscibility region of type b or d. 

An existence of immiscibility region in any binary subsystem leads to an appearance of immiscibility phenomena in ternary mixtures and the second critical surfaces with the equilibrium Li = L2. The available experimental data on ternary aqueous systems with volatile (inorganic gas or organic compound) and salt component show the influence of added salts on the mutual miscibility of water and the volatile component. 

An influence of salt addition on the immiscibility region of type d was studied in ternary systems CO2 - H2O - NaCl (Gehrig et al., 1986), CH4 - H2O - NaCl, CH4 - H2O -CaCl2 (Krader and Franck, 1987), C2H6 - H2O - NaCl, C6H14 - H2O - NaCl (Michelberger and Franck, 1990), CF4... 

There is only one binary subsystem (H2O - Na2B407) with the immiscibility region of type d in the first ternary system. The phase diagram demonstrates disappearance of immiscibility phenomena in ternary solution as a result of nonvariant tricritical equilibria (Li = L2 = G) (point NR in Figure 1.44a). 

Figure 1.44 T-X projections of ternary immiscibility regions bounded by the critical curves Li = L2-G and Li = G-L2 in the systems (a) H2O - Na2B40y - NaCl (ternary class la-la-ld) [Urusova and Valyashko, 1998], (b) H2O - Hgl2 - Pbl2 (ternary class la-lb -ld ) [Valyashko and Urusova, 1996] and (c) CO2 - tetradecane (C13H28) -pentanol (C5H12O) (ternary class la-lc -ld ) (Peters and Gauter, 1999).

As one can see the experimental phase diagram in Figure 44a is the same as the left-hand parts of topological schemes IIIa-1, IIIa-2 or IIIa-3 (see Figure 37). The right-hand parts of these schemes are complicated with the another immiscibility regions which spread from binary subsystems A-C. The immiscibility phenomenon is absent in the binary subsystem H2O - NaCl as well as in intermediate quasibinary cross-sections of ternary systems A - B - C in Illa-1, IIIa-2 or IIIa-3 topological schemes. 

Experimental studies of ternary water-salt systems of type 2d -ld-la, with both binary water-salt subsystems being complicated by three-phase immiscibility regions in stable (type Id) and metastable (type 2A ) conditions, show that a transition of metastable immiscibility into stable one occurs through the immiscibility phenomena in sohd saturated solutions. At first it was shown for the system H2O -Na3P04 -Na2HP04 (Urusova and Valyashko, 2001a,b), then... 

Ternary systems with two binary subsystems of types 2. The experimental data on phase equiUbria in the systems H2O - K2SO4 - KLiS04 (Ravich and Valyashko, 1969 Valyashko, 1975) and H2O - Si02 - Na2Si20s (Valyashko and Kravchuk, 1977, 1978 etc.) provided the most direct evidence of a transition of metastable immiscibility region, extending from the binary subsystems of type 2d, into stable equihbria in ternary solutions. All binary subsystems with water belong to type 2d and there is no three-phase equilibrium L1-L2-G in stable equilibria. 

Figure 1.49 Two versions of p-T projection of phase diagram for the system H2O - KCl - K2SO4 (ternary class la-la-2d ). Version (a) shows a continuous transition of the ternary critical curve L = G-S into the critical curve L, = L2-S through a temperature maximum. Version (b) shows an appearance of metastable immiscibility region in stable equilibrium L1-L2-G-S (curve pR-QN) and a termination of critical curves L = G-S and L, = L2-S in the nonvariant critical points pR (L, = G-L2-S) and QN (L, = L2-G-S), respectively (Urusova, M.A., Valyashko, V.M. and Grigoriev, l.M. (2007) Zh. Neorgan. Khimii, 52, pp. 456-470 Russ. J. Inorg. Chem. 52, with permission from Academizdatcenter Nauka , Russian Academy of Sciences).

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