Partial pressure as a variable

1 Partial pressure as a variable. As mentioned in 2.1, many types of thermodynamic variables may be used in the construction of phase diagrams. The various rules of construction, based on the laws of chemical thermodynamics, which apply to the different types of phase diagrams have been discussed in several books and papers (for instance, Pelton and Schmalzried 1973, Okamoto 1991, Pelton 1991). Following a classification proposed by Pelton, the various, bidimensional, phase diagrams may be subdivided into three types as follows  

Type 1 are potential/potential phase diagrams. The potentials considered in chemical thermodynamics are temperature (thermal potential), pressure (mechanical potential) and the chemical potentials of the N components pj, i2, ig,. .., 

Type 3 are composition/composition phase diagrams, such as the isobarothermal sections of ternary systems shown in Figs. 2.25-2.27. 

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