Phase diagrams immiscibility regions

FIGURE 11-21 Schematic phase diagram showing the single phase (miscible) and phase-separated (immiscible) regions. 

A microemulsion is a thermodynamically stable isotropic dispersion of two relatively immiscible liquids, consisting of microdomains of one or both liquids stabilized by a interfacial film of surface-active molecules. In practice, one often identifies the microemulsion by the formation of a clear isotropic mixture of the two immiscible liquids in the presence of appropriate emulsifiers. In a phase diagram, such region is referred as the microemulsion phase. It has been shown that microemulsion regions consist of different microstructures (1,2), e.g., water-in-oil (W/0), oil-in-water (0/W),... 

Figure 7.13 Continuous changes of solid-liquid phase-diagram type from (a) ideal to (f) eutectic, showing (b) positive nonideality that progressively results in (c) a low-melting minimum, (d) a region of solid-solid immiscibility, or (e) complete closing of the solubility gap, culminating in (f) complete eutectic immiscibility.

Figure 7.17 Ternary A/B/C phase diagram (at 25°C, 1 atm) for A = acetic acid, B = vinyl acetate, C = water, showing nonhorizontal tie-lines in the immiscible two-phase region (organic liquid + aqueous liquid), culminating at a plait point (x). Concentration grid values (dotted lines) are in wt% at 10% intervals.

A number of additional DTA experiments were undertaken with various compositions within the binary system up to 66.6 at. % S (= MoS2 composition). In Fig. 7 a phase diagram is shown in which all results are incorporated. With respect to the above-mentioned classification of sulfide systems14), the Mo—S system, as well as the Cr—S system, exhibits Type 1 two regions of immiscible liquids one field of liquid immiscibility in the metal-rich portion at high temperatures, and a second two-liquid field in the sulfur-rich region beyond MoS2 which is not shown in Fig. 7. 

In some systems there is a total miscibility between metal and salt, in others, the metal solubility. All the phase diagrams are characterized by the lowering of the melting point of the salt when the metal is added. This phenomenon is indicative of true solutions. Several systems exhibit a region with two immiscible liquid phases, i.e. the miscibility gap . Systems with miscibility gap show positive deviation from Raoult s law, i.e. the activity coefficient of the salt is larger than unity. Above a certain temperature, which is called the critical temperature of miscibility or above the consolute temperature , salt and metal are completely miscible at all compositions. 

Finally, in Figure 2.36, the phase diagrams of the system BiCls-Bi according to Yosim et al. (1959, 1962) and of the system CeCls-Ce according to Mellors and Senderoff (1959) are shown. Wide regions of immiscibility are characteristic for these systems, which are due to the very strong repulsive forces between Bi + and Ce + cations, respectively. 

The phase diagram for a mixture of acetone, methyl isobutyl ketone (MIK) and water at 25°C is shown at right. The shaded region (below the curve) represents compositions for which two immiscible liquid phases form, while the unshaded region (above the curve) are compositions for which only one phase forms. The nearly horizontal lines with the shaded region represent tie lies connecting the compositions of two liquid phases that co-exist at equilibrium. 

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