Melting point diagrams, composition

Molten cryohte dissolves many salts and oxides, forming solutions of melting point lower than the components. Figure 1 combines the melting point diagrams for cryolite—A1F. and for cryohte—NaF. Cryohte systems ate of great importance in the HaH-Heroult electrolysis process for the manufacture of aluminum (see Aluminumand ALUMINUM alloys). Table 5 Hsts the additional examples of cryohte as a component in minimum melting compositions. 

Associations within the bulk crystalline phase. The physical property of enantiomeric solids and their mixtures which is cited most often is melting point. Figure 18 gives the melting point versus composition diagram for mixtures of S( + )- and R( — )-SSME. The solid-liquid coexistence line of... 

Fig. 18 Melting point versus composition diagram for stearoylserine methyl ester crystals. Reprinted with permission from Harvey et al., 1989. Copyright 1989 American Chemical Society.

For systems of more than one chemical component, the concentrations of each are additional variables. A typical two-component phase diagram displays the variation of vapor pressure or melting point with composition at a fixed pressure, for example. 

As the alumina content is increased from 5% to 72%, the melting points of compositions in this range increase as shown in Fig. 1. As mentioned earlier, maximum use temperature of fireclay (25% to 45% A1203) and low alumina (45% to 65% A1203) compositions is shown approximately by the dashed line in the diagram. Compositions in this range can tolerate limited amounts of liquid during service due to the viscous nature of the melt. 

A liquid-solid phase diagram established for blends of iPP/POE by means of DSC and LS is presented at the top left of Fig. 7.12, displaying four distinct regions isotropic (I), coexistence of crystal-isotropic (Ci +1), coexistence of crystal-crystal-isotropic (C1+C2 + I), and crystal-crystal (Ci + C2- -C3). Cj and C2 represent the a- and y-form crystals of iPP, respectively, while C3 is designated for POE crystals (31). The blend preparation is identical to the procedure conducted for sPP/POE blend specimens. These iPP/POE blends are found to be completely miscible in the melt state, showing little or no depression of the melting point with composition. 

Figure 2 Typical phase diagrams of melting point against composition for (a-c) three types of racemic species, (a) racemic conglomerate, C, (b) racemic compound, R, (c) pseudoracemates, P (d-e) terminal solid solutions involving opposite enantiomers, (d) solid solution rich in an enantiomer, (e) solid solution rich in an enantiomer or rich in the racemic compound (f) a pair of diastereomers. (From Ref. 13. Reproduced by permission of John Wiley and Sons.)...

Fig. 2. The composition of enantiomeric mixtures obtained by crystallization (ee) in fimction of starting enantiomeric purity (eeo). a), conglomerate melting point diagram b). racemate melting point diagram The diagrams of expected results of c). conglomerate crystallization, d). racemate crystallization, e) kinetic-conglomerate like crystallization...

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 freezing point diagram for the hydrazine—water system (Eig. 1) shows two low melting eutectics and a compound at 64 wt % hydrazine having a melting point of —51.6°C. The latter corresponds to hydrazine hydrate [7803-57-8] which has a 1 1 molar ratio of hydrazine to water. The anomalous behavior of certain physical properties such as viscosity and density at the hydrate composition indicates that the hydrate exists both in the Hquid as well as in the soHd phase. In the vapor phase, hydrazine hydrate partially dissociates. 

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