How to Obtain Phase Diagrams

The method for obtaining phase diagrams is to find the required data in books on physical properties. Some examples are International Critical Tables (1924) Beilsteins Handbook of Organic Chemistry (1960) CRC Handbook (1984) D Ans, Lax Handbuch (1967) Ullmann s Encyclopedia of Industrial Chemistry (1988) Kirk-Othmer s Encyclopedia of Chemical Technology (1979) and VDI-Wdrmeatlas (1988). 

If the data required to construct a phase diagram are not available in the literature for the mixture of interest, the data will have to be obtained experimentally. In this case, the determination of the melting points of known compositions of the mixture has to be carried out. Several experimental techniques are described in detail by Sloan and McGhie 1988. 

Another method is to record the temperature curve as a function of time while the temperature increases with a constant tem- 

Many mixtures, however, have a melting zone rather than a melting point. This is due to a number of reasons. One is the error in the detection, another the quality of the specimen. This second point can be caused by an unrepresentative specimen or because of a less than ideal mixture within the specimen. 

If an experiment is performed in which the temperature is recorded to detect the point where crystallization begins, one is more likely to find a zone instead of a point. This is due to the different nucleation conditions in each measurement, which is dependent strongly on the statistical distribution of nucleation incidents (metastabile zone). Thus, a different supercooling will occur in each measurement before nucleation starts, which will then control the crystal growth. This leads, of course, to differently detected crystallization temperatures (hence a zone and not a point). 

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