PT-system, TX-system, PX-system: Three programs which calculate pressure-temperature-composition phase diagrams

Abstract

PT-SYSTEM, TX-SYSTEM, and PX-SYSTEM are three FORTRAN 77 programs that calculate complete pressure-temperature ( P-T), temperature-composition ( T- X H 2 O- CO 2), and pressure-composition ( P- X H 2 O- CO 2) diagrams. The output of these programs can be plotted for visual representation of phase relations, or inspected from tables. The programs initially generate all possible reactions in the user-specified compositional and PTX space. At the user's option, each point of every reaction is tested for stability with respect to all other phases in the system, and metastable extensions are erased. If a curve is metastable completely, the list of remaining reactions is pruned of those which are metastable entirely within the specified PTX limits of the diagram. Finally, all curves are labeled with stable assemblages. The software is distributed with a recommended thermodynamic database, but a variety of equations of state are provided so that the programs can be used with different data sets. Functions are provided for temperature-dependent disordering, polymorphic transitions, and solid solutions. Run-time options include setting the P, T, X limits of the diagram, the selection of different routines for calculating gas properties, and the specification of fixed phase activities. The user also can specify that only curves stable in the presence of a given phase or assemblage be computed, so that the stability fields of particular phases or assemblages can be identified readily. Copies of the programs (written in ANSI standard FORTRAN 77), the database, and accompanying documentation are available from the senior author.