Melting Point of the System

Differences in microstructure between 20%SSS/80%000 can be observed upon interesterification (Figure 17.8). Chemical interesterification caused a severe decrease in the melting point of the system as no crystals were observed above 30°C. Chemical interesterification also caused an increase in nucleation rate with a concomitant... 

If we project the lines Kk, Kk and Kk in fig. 13.10 on to the base of the diagram we obtain the triangular diagram shown in fig. 13.11. Suppose we consider what happens when a solution of composition P is cooled from a temperature above the melting point of the system. Crystallization... 

In the polymerization of cetylvinylether (l ) the polymer formed remained isomorphous with the monomer and the melting point of the system increased. This isomorphism was destroyed, however, when the system reached its melting point. After cooling it formed a two-phase system. 

The attachment probability can be influenced by several parameters. For example, one can control the attachment probability and consequently the growth rate via temperature. Crystallization is only possible below the melting point of the system. Exactly at the melting temperature, the probabihty for attaching a molecule to the crystal is so low that the molecule will not stay attached. Thus, the crystal will not grow. Attachment may also be in competition with the displacement of other molecules like solvent molecules, additives or impurities. For example, if an additive is strongly adsorbed onto the crystal surface the crystal will not grow as fast as in cases when these additional molecules are not present. 

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 phase diagram for aluminum/silicon (Fig. 4.5) is a typical example of a system of two components that form neither solid solutions (except for very low concentrations) nor a compound with one another, but are miscible in the liquid state. As a special feature an acute minimum is observed in the diagram, the eutectic point. It marks the melting point of the eutectic mixture, which is the mixture which has a lower melting point than either of the pure components or any other mixture. The eutectic line is the horizontal line that passes through the eutectic point. The area underneath is a region in which both components coexist as solids, i.e. in two phases. 

A different situation exists if the compound exists as form I and form III. This is referred to as a monotropic system, and here III is unstable relative to I over the whole solid range. In this case, however, the melting point of the unstable polymorph is lower than that of the stable (Tis lower than T ). 

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