P-T-x diagram

Figure 3 gives the P-T-x diagram for the binary system hydroquinone-argon and shows that at ordinary temperatures the three-... 

Fig. 3. P-T-x diagram of the system hydroquinone - argon x — mole fraction of hydroquinone, = fraction of cavities filled by argon [yA =. 3(l — x)/x). The pressures of the triple points A and B of the a and ft modifications of hydroquinone have been exaggerated in order to make these points visible.

The occurrence of solid clathrate solutions is clearly seen in Fig. 4, which gives a cross section of the P-T-x diagram at 60°C according to recent results.28 The two two-phase equilibria clath-rate-gas and clathrate-hydroquinone are separated by a one-phase... 

Fig. 4. Cross section through the P-T-x diagram of the system hydro -quinone-argon at 60°C (cf. Fig. 3).

The composition of the hydrates varies with temperature along the three-phase lines H ice G and HL2G in a way similar to that described for the system hydroquinone-argon. But as already noted in Section II.D this variation is smaller than for the hydroquinone clathrates. Accordingly, a cross section through the P-T-x diagram at constant temperature below 0°C would reveal a two-phase area G+H in which the composition of the latter is less sensitive to pressure than found in the corresponding case for the hydroquinone clathrates (cf. Fig. 4). 

Figure 2.31. Schematic representation of the P/T equilibria in a simple two-component system (forming continuous solid and liquid solutions). In (a) a perspective view of the P-T-X diagram is shown in (b) its projection on the P/T plane. Notice the two single-component systems represented, for instance, for the component B by the three lines SB/G (sublimation line of B representing the gas/so lid equilibrium), SB/LB (melting equilibrium of B) and the boiling line LB/G. The solid solution is indicated by a. Notice in (a) the isobaric and isothermal sections of the diagrams (compare with Fig. 2.1).

Because there is an added term, the composition, binary systems are inherently more complex than unary systems. In order to completely represent the phase diagram of a binary system a three dimensional pressure-temperature-composition (P-T-x) diagram can be constructed. However, it is a more common... 

Now let us progress to the construction of the general three-dimensional P-T-x diagram for type-I binary mixtures, shown in figure 3.2. The P-T-x... 

As the pressure is further increased at this fixed overall composition, the amount of the liquid phase increases while the amount of the vapor phase shrinks until only a small bubble of vapor remains. If the pressure is still further increased, the bubble of vapor finally disappears, then a single liquid phase exists. The locus of points that separates the two-phase vapor-liquid region from the one-phase liquid region is called the bubble point curve. This vapor-liquid envelope can now be inserted into the three-dimensional P-T-x diagram in figure 3.2a. 

Figure 3.4 P-T-x diagram for the three-phase liquid-liquid-vapor region of a binary mixture.

If the temperature is raised to Tj, the phase behavior shown in figure 3.7e occurs. This temperature is greater than the UCEP temperature, therefore two phases exist as the pressure is increased as long as the critical mixture curve is not intersected. The two branches of the vapor-liquid phase envelope approach each other in composition at an intermediate pressure and it appears that a mixture critical point may occur. But as the pressure is further increased, a mixture critical point is not observed and the two curves begin to diverge. To avoid confusion, the phase behavior shown in figure 3.7e is not included in the P-T-x diagram. 

Shown in figure 3.12a is the P-T-x diagram for the type of solid-SCF system described in the previous paragraph. The phase behavior depicted in figure 3.12c is observed if a P-x diagram is experimentally determined at Ti, a temperature below the critical temperature of the lighter component Tc,- At low pressure solid-vapor equilibria are observed until the three-phase SLV line is intersected. Three equilibrium phases exist at this pressure a pure solid, a liquid, and a gas. 

P-T-X diagram A three-dimensional graphic representation of the phase relationships in a binary system by means of the pressure, temperature, and concentration variables. 

In this section noteworthy features are reported which are not described in preceding paragraphs. These include graphical data not covered by the general report format, such as lattice spacing - composition data, p-T-x diagrams, etc. 

Binary fluid mixture phase diagrams are usually represented as two-dimensional projections of the three-dimensional P-T-x diagram onto the P-T plane, or as two-dimensional sections of the P-T-x diagram, with variables T-x at constant P, P-x at constant r, or P-T at constant x. Here x is the mole fraction of the second component (solute). 

The known p-T-x diagrams can be constructed for some simple and mixed oxides using this gas coulometric method. Closed systems... 

T and K - triple and critical points of component A and B f - eutectic equilibrium (L-G-Sa-Sb). Open circles - nonvariant points in one-component systems. Solid circles - nonvariant points in binary systems (p-T projection) and compositions of fluid (liquid, gas and critical) phases in binary nonvariant equilibria (p-T-x, T-x and p-x schemes). Diamonds - compositions of solid phases in binary nonvariant equilibria. Heavy lines - monovariant curves in one-component systems (A, B) solid lines - compositions of Uquid phases in monovariant equilibria of binary systems dashed lines - compositions of vapor (gas) phases in monovariant equUibria of binary systems dash-dotted lines - critical curves thin lines - isothermal cross-sections of the p-T-x diagram and tie-lines in T-x and p-x projections. For clarity, only tie-lines between fluid phases are shown in monovariant equilibria. 

On the basis of the results obtained clathrate formation evolution in the water-iodides binary systems can be represented by the summarized P,T,X-diagram, whose P,T-projection and a mmiber of characteristic isobaric sections are shown in figure 6. 

Measurements of the dependence of partial pressures on temperature along the liquidus (two phase equilibrium between liquid and solid phases) and solidus (solid-solid) lines and partial pressure dependences on system composition at constant temperature give the total pressure and vapour brutto composition as function of temperature and system composition. After these data are obtained, a T X diagram can be transposed to a P T X diagram. Such diagrams are used in applied science e.g. the growth of crystals and films by the vapour deposition method. 

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