Pourbaix Diagram Examples
tcex40
This is the first in a series of examples to demonstrate the advanced POURBAIX module calculations and plotting. This example automatically calculates and plots a Pourbaix diagram for 0.001 m Fe in a 0.1 m NaCl aqueous solution at 25 °C and 1 bar. Other diagrams, along various phase boundaries for the same interactions resulted from the same Pourbaix module calculation, are also plotted.
It is recommended you read the text file TCEX40-README.txt, which is located in the Extended subfolder.
About Pourbaix Diagrams in Thermo‑Calc
A so-called Pourbaix diagram is actually a phase diagram with independently-varied acidity (pH) and electropotential (Eh), for a heterogeneous interaction system at a certain bulk composition (that is by default always set as 1 kg of water dissolving a specified amount of metals and other solutes), under a defined temperature and pressure condition.
The PAQ2 Database
The example uses the PAQ2 (TCS Public Aqueous Solution Database using the SIT aqueous solution model) included with your installation. The database contains an AQUEOUS solution phase and REF_ELECTRODE phase (as a reference for electron in aqueous electrolyte systems), as well as some data for various solid phases (solution or stoichiometric) and gaseous mixture phase. The PAQ2 is specially designed for these example calculations of the so-called Pourbaix diagrams (i.e., pH-Eh plots) and other types of phase diagrams or property diagrams in some aqueous-bearing multicomponent heterogeneous interaction systems within the limited chemical framework of Fe-Co-Cr-Ni-C-N-S-H2O-NaCl, via the Single-Database Option in the advanced POURBAIX module or through the normal TDB-GES-POLY-POST routine.
Additional Examples in this Series
Additional examples (TCEX40A, TCEX40B, TCEX40C, and TCEX40E) are provided to demonstrate options and features in the Pourbaix module and to show more advanced applications of the TCAQ and AQS aqueous solution databases [in the Multiple-Database Option, i.e., with appended data from the SSOL and SSUB databases]. See Pourbaix Examples TCEX40A, 40B, 40C, and 40E.
Example TCEX40D is deprecated as of version 2022a.
tcex53 - Pourbaix Diagram Calculations for a Heterogeneous Interaction System
About Pourbaix Diagrams in Thermo‑Calc
This example uses the PAQ2 database to calculate some Pourbaix diagrams. The DATABASE_RETRIEVAL (TDB), GIBBS_ENERGY_SYSTEM (GES), POLY3, and POST modules are used for the Fe-X-H2O-NaCl heterogeneous interaction system, where X = Cr-Ni-Co.
The initial bulk composition of Fe-based alloy in this calculation is just preliminarily assigned, in which the BCC_A2 and/or FCC_A1 solution phase(s) are considered as of primarily interest. For practical calculations, one shall have more precise inputs for the initial bulk compositions of alloys.
Step 1: Single-Point Calculations for H2O-NaCl system
To demonstrate how to define the molality of NaCl in an aqueous-bearing heterogeneous interaction system.
Step 2: Single-Point Calculations for Fe-X (X = Cr-Ni-Co) system
To demonstrate how to define the initial amount of alloy in an aqueous-bearing heterogeneous interaction system. In this example, we are interested in only the BCC_A2 and FCC_A1 phases in the Fe-based alloy.
Step 3: Single-Point Calculations for Fe-Cr-Ni-Co + H2O-NaCl system
Step 4: Pourbaix Diagram Mapping for Fe-Cr-Ni-Co + H2O-NaCl system - define the variables
From the same mapping calculations you arrive at by the end of the example, you can plot more diagrams using a variety of X-Y axis variables.
For a list of pre-defined symbols, go to the end of the tcex53.TCM macro file (open it in a text editor).