Binary systems immiscibility

The principal point of interest to be discussed in this section is the manner in which the surface tension of a binary system varies with composition. The effects of other variables such as pressure and temperature are similar to those for pure substances, and the more elaborate treatment for two-component systems is not considered here. Also, the case of immiscible liquids is taken up in Section IV-2. 

Eutectics melting at about —30, —47, and —40° C are formed in the binary systems, cesium—sodium at about 9% sodium, cesium—potassium at about 25% potassium, and cesium—mbidium at about 14% mbidium (34). A ternary eutectic with a melting point of about —72°C has the composition 73% cesium, 24% potassium, and 3% sodium. Cesium and lithium are essentially completely immiscible in all proportions. 

All the phase diagrams reported above show a complete mutual solubility in the liquid state. The formation of a single phase in the liquid state corresponds to behaviour frequently observed in intermetallic (binary and complex) systems. Examples, however, of a degree of immiscibility in the liquid state are also found in selected intermetallic systems. Fig. 2.16 shows a few binary systems in which such immiscibility can be observed (existence of miscibility gaps in the liquid state). All the three... 

Figure 2.27. Isothermal section at 307°C of the Al-Zn-Si diagram. The boundary binary systems are shown. The isothermal section at 307°C is marked on the binary Al-Zn diagram. The corresponding single-phase (thick segment) and two-phase regions are indicated in the base edge of the triangle. By additions of Si (immiscible in the solid state in the other two elements) two- and three-phase fields are formed. ( ) = three-phase region. In the two-phase region on the left examples of tie-lines are presented.

Other uranium binary systems de-mixing in the liquid state are U-Pb and U-Bi and several uranium-lanthanides systems which are characterized by nearly complete immiscibility in the liquid and solid state. 

Figure 7.2 G-X and T-X plots for a binary system with a molten phase with complete miscibility of components at all T conditions and a solid phase in which components are totally immiscible at all proportions (mechanical mixture, 7 = 7 + V )-...

Ohno T (2002) Morphology of composite nanoparticles of immiscible binary systems prepared by gas-evaporation technique and subsequent vapor condensation. J Nanoparticle Res 4 255-260... 

Three-Phase Transformations in Binary Systems. Although this chapter focuses on the equilibrium between phases in binary component systems, we have already seen that in the case of a entectic point, phase transformations that occur over minute temperature fluctuations can be represented on phase diagrams as well. These transformations are known as three-phase transformations, becanse they involve three distinct phases that coexist at the transformation temperature. Then-characteristic shapes as they occnr in binary component phase diagrams are summarized in Table 2.3. Here, the Greek letters a, f), y, and so on, designate solid phases, and L designates the liquid phase. Subscripts differentiate between immiscible phases of different compositions. For example, Lj and Ljj are immiscible liquids, and a and a are allotropic solid phases (different crystal structures). 

The Class I binary diagram is the simplest case (see Fig. 6a). The P—T diagram consists of a vapor—pressure curve (solid line) for each pure component, ending at the pure component critical point. The loci of critical points for the binary mixtures (shown by the dashed curve) are continuous from the critical point of component one, Ca , to the critical point of component two,Cp . Additional binary mixtures that exhibit Class I behavior are C02 -hexane and C02 benzene. More complicated behavior exists for other classes, including the appearance of upper critical solution temperature (UCST) lines, two-phase (liquid—liquid) immiscibility lines, and even three-phase (liquid—liquid—gas) immiscibility lines. More complete discussions are available (1,4,22). Additional simple binary system examples for Class III include C02—hexadecane and C02 H20 Class IV, C02 nitrobenzene Class V, ethane— -propanol and Class VI, H20— -butanol. 

Eutectic diagrams (from Greek svtt]ktoo- easily melted ) represent the T-x melting behavior for binary systems with completely immiscible solid phases a, /3. The solid a, /3 phases often correspond to (virtually) pure components A, B, respectively, so we may treat phase and component labels (rather loosely) as interchangeable in this limit. 

For binary systems, a variety of phase behaviours possible when partial immiscibility of liquids and gases, and the occurrence of solid phases is considered. Phase-behaviours are classified into six basic types, and transitions between them are possible. 

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. 

Similar to Equation (3.115), the equation for an immiscible binary system, in which the weak acid in the oil phase exists as a dimer, is in terms of volume ratio ... 

Figure 13.20 Temperature/composition diagram for a binary system of immiscible liquids.

Two early studies of the phase equilibrium in the system hydrogen sulfide + carbon dioxide were Bierlein and Kay (1953) and Sobocinski and Kurata (1959). Bierlein and Kay (1953) measured vapor-liquid equilibrium (VLE) in the range of temperature from 0° to 100°C and pressures to 9 MPa, and they established the critical locus for the binary mixture. For this binary system, the critical locus is continuous between the two pure component critical points. Sobocinski and Kurata (1959) confirmed much of the work of Bierlein and Kay (1953) and extended it to temperatures as low as -95°C, the temperature at which solids are formed. Furthermore, liquid phase immiscibility was not observed in this system. Liquid H2S and C02 are completely miscible. 

The Krause (37,39) method involves the comparison of the calculated values of Xj9, the interaction parameter between the two polymers and ( X 2)cr interaction parameter at the critical point on a phase diagram mr that particular binary system. Krause (37,39) stated that if Xj2 12 r polymers should be immiscible at... 

The phase diagram of the Fe-0 binary system at ambient pressure exhibits a large liquid immiscibility gap (Baker, 1992 Figure 5(b)). 

Figure 14.20 Binary system of immiscible liquids, (a) Txy diagram (b) Pxy diagram...

For the binary systems, only the P-T trace extending to the UCEP is sought in this work. The LCEP is typically very near the critical temperature and pressure for the pure supercritical fluid. Similarly, for the ternary systems, only the q point branch of the four phase line is sought in this work. Systems studied here exhibit solid-solid immiscibility. 

Using the information in the previous example, calculate iVmin- The binary system is H2S and N2. The water is essentially an immiscible liquid since it is in low concentration in the gas phase and there is no net mass transfer of water. 

The interphase thickness depends on the miscibility of the polymeric component as well as on the compatibilization. For uncompatibilized binary, strongly immiscible systems, the interphase thickness Al - 2 nm. The thickest interphase has been observed for reactively compatibilized polymer alloys Al = 65 nm. For most blends, the interphase thickness is in between these two limits. The importance on the interphase can be appreciated noting that its volume will be the same as that of the dispersed phase when the drop diameter (without interphase) is about 500 nm. It is noteworthy that in most commercial polymer alloys the drop diameter is about five times smaller, making the importance of the interphase much greater. 

Departures from Raoult s law occur for systems in which there are differing interactions between the constituents in the liquid phase. Sometimes the interaction takes the form of a strong repulsion, such as exists between hydrocarbons and water. In a liquid binary system of components A and B, if these repulsions lead to essentially complete immiscibility, the total pressure P over the two liquid phases is the sum of the vapor pressures of the individual components, and... 

---