Three phase region

Figure A2.5.31. Calculated TIT, 0 2 phase diagram in the vicmity of the tricritical point for binary mixtures of ethane n = 2) witii a higher hydrocarbon of contmuous n. The system is in a sealed tube at fixed tricritical density and composition. The tricritical point is at the confluence of the four lines. Because of the fixing of the density and the composition, the system does not pass tiirough critical end points if the critical end-point lines were shown, the three-phase region would be larger. An experiment increasing the temperature in a closed tube would be represented by a vertical line on this diagram. Reproduced from [40], figure 8, by pennission of the American Institute of Physics.

The three-phase region of D2—DT—T2 has been studied (12). Relative volatilities for the isotopic system deuterium—deuterium tritide—tritium have been found (13) to be 5—6% below the values predicted for ideal mixtures. 

P. C. Souers and co-workers, Three-Phase Region of D -DT-T, Eawrence Eipermore Eaboratoy Report UCRE-79036, 1977. 

Liquid-Fluid Equilibria Nearly all binary liquid-fluid phase diagrams can be conveniently placed in one of six classes (Prausnitz, Licntenthaler, and de Azevedo, Molecular Thermodynamics of Fluid Phase Blquilibria, 3d ed., Prentice-Hall, Upper Saddle River, N.J., 1998). Two-phase regions are represented by an area and three-phase regions by a line. In class I, the two components are completely miscible, and a single critical mixture curve connects their criticsu points. Other classes may include intersections between three phase lines and critical curves. For a ternary wstem, the slopes of the tie lines (distribution coefficients) and the size of the two-phase region can vary significantly with pressure as well as temperature due to the compressibility of the solvent. 

The equilibrium composition of the n-butane - water binary in the three-phase region are illustrated in Figure 8. 

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.

Fig. 8.9 Coulometric titration curve for the ternary system Li-In-Sb. Plateaux correspond to three-phase regions. The phases are indicated.

The phase condition for concentrations in the range close to the cmc are found in Fig. 4A. For the lowest soap concentrations, a liquid isotropic alcohol solution separated, when the solubility limit of the alcohol was exceeded. This was changed at concentrations approximately one half the cmc, when a lamellar liquid crystalline phase appeared Instead. After the relatively narrow three-phase region had been transversed, this liquid crystalline phase was the only phase in equilibrium with the aqueous solution. Solubilization of the long chain alcohol Increased at the cmc, as expected. 

Figure 5,25 Phase stability relations for natural pyroxenes in the quadrilateral. (A) Magmatic pyroxenes (not reequilibrated at low 7). (B) Three-phase region for pyroxenes of stratihed complexes and magmatic series. (C) Pyroxenes reequilibrated in subsolidus conditions. = Pbca orthopyroxene V = augite C2lc) A = pigeonite (P2jlc) 0 = olivine. From Huebner (1982). Reprinted with permission of The Mineralogical Society of America.

On the left-hand side of Fig. 4 we have the normal phase diagram of the binary BE-H2O system. The addition of DEC shifts the two phase equilibria to higher BE concentrations and to lower temperatures. If the addition of a third component is continued beyond the cloud point, eventually three distinct phases appear. Unfortunately the cloud point technique gives us the initial concentration or temperature where unmixing begins but is not suitable to distinguish between the coexistence of two phases and three phases. Also the three phase region depends quite critically on temperature. 

The amount of oxygen adsorbed in the three-phase region has been found to depend linearly on the exchange current density for different catalyst-electrodes under similar conditions.31,32 This indicates that the electrocatalytic reaction takes place at the three-phase boundary. Vayenas and co-workers pointed out that for less porous electrodes the charge-transfer reaction at the two-phase boundary might become important and that under some conditions oxygen on the electrolyte surface itself might play a role. 

Since the micellar phase changes from water-continuous to oil-continuous with increasing temperature, it is an intriguing question how to describe the micelles in the three-phase region that exists at intermediate temperatures. 

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