Phase diagrams melting-point curve

Fig. 3.16.6. Derivation of a phase diagram from the temperature change of free energy curves of a miscible liquid and two partially miscible solid phases. The melting points of A and B are widely different.

Figure 3.1 is a schematic one-component, three-phase equilibrium diagram. The three different phase regions are separated by lines D-TP (solid vapor pressure, or sublimation curve), F-TP (melting point curve), and TP-C (liquid vapor pressure or boiling-point curve). Point C is the critical point where the vapor and liquid phases become indistinguishable and TP is the triple point where solid, liquid, and vapor phases can coexist. There are only two in-... 

Figure 4.7a shows the temperature-concentration phase diagram for the system naphthalene-/ -naphthol, which forms a continuous series of solid solutions. The melting points of pure naphthalene and -naphthol are 80 and 120 °C, respectively. The upper curve is the liquidus or freezing point curve, the lower the solidus or melting point curve. Any system represented by a point above the liquidus is completely molten, and any point below the solidus represents a completely solidified mass. A point within the area enclosed by the liquidus and solidus curves indicates an equilibrium mixture of liquid and solid solution. Point X, for instance, denotes a liquid of composition L in equilibrium with a solid solution of composition S, and point Y a liquid F in equilibrium with a solid S. ... 

Since the mechanisms of intermolecular interaction are independent, they apparently have different physical nature and cannot be combined into a single mechanism at the triple point of phase diagram. So the curves of melting and vaporization do not merge but intersect at the triple point. 

The phase diagrams (for a diagram see Chapter 3) give the melting point curve or plane for the full range of concentrations possible of a binary or more component system. 

System in which the solid phases consist of the pure components and the components are completely miscible in the liquid phase. We may now conveniently consider the general case of a system in which the two components A and B are completely miscible in the liquid state and the solid phases consist of the pure components. The equilibrium diagram is shown in Fig. 1,12, 1. Here the points A and B are the melting points of the pure components A and B respectively. If the freezing points of a series of liquid mixtures, varying in composition from pure A to pure B, are determined, the two curves represented by AC and BC will be obtained. The curve AC expresses the compositions of solutions which are in equilibrium, at different temperatures, with the solid component A, and, likewise, the curve BC denotes the compositions... 

The general case of two compounds forming a continuous series of solid solutions may now be considered. The components are completely miscible in the sohd state and also in the hquid state. Three different types of curves are known. The most important is that in which the freezing points (or melting points) of all mixtures lie between the freezing points (or melting points) of the pure components. The equilibrium diagram is shown in Fig. 7, 76, 1. The hquidus curve portrays the composition of the hquid phase in equihbrium with sohd, the composition of... 

The normal melting, boiling, and triple points give three points on the phase boundary curves. To construct the curves from knowledge of these three points, use the common features of phase diagrams the vapor-liquid and vapor-solid boundaries of phase diagrams slope upward, the liquid-solid line is nearly vertical, and the vapor-solid line begins at P = 0 and P = 0 atm. 

The recourse to the above-described procedure permitted the derivation [74] of an exact expression for function G(pi,p2). It is of utmost importance for the construction of a phase diagram of a melt or solution of interphase copolymerization products, since this function enters in the equations for the cloud point curve [82]. 

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