What is the difference between predominance area diagrams calculated by Predom and those calculated by Phase Diagram?
For some systems, for example the one-metal Fe-SO2(g)-O2(g) system with compound data, the diagrams are the same. In Predom a two- (three-) metal system always generates domains that have 2 (3) species. In Phase Diagram, if you select a composition variable that lies on a stoichiometric compound line then one of the species in a two- or three-metal system may not appear on the figure since it has zero moles. If you calculate the equilibrium within such a domain (figure ‘phase equilibrium mode’) then you will see the missing species has 0 moles but unit activity. There are fundamental differences between the programs. Predom can only access the compound databases. Unlike Phase Diagram, Predom offers some options useful in predominance-type diagrams. These include • simple input tailor-made for predominance area diagrams • list of invariant points • total pressure isobar • provision to set activities to a common value On the other hand Phase Diagram offers some powerful features, includi
For some systems, for example the one-metal Fe-SO2(g)-O2(g) system with compound data, the diagrams are the same. In Predom a two- (three-) metal system always generates domains that have 2 (3) species. In Phase Diagram, if you select a composition variable that lies on a stoichiometric compound line then one of the species in a two- or three-metal system may not appear on the figure since it has zero moles. If you calculate the equilibrium within such a domain (figure ‘phase equilibrium mode’) then you will see the missing species has 0 moles but unit activity.
