About Pourbaix Diagrams in Thermo‑Calc

This guide is for Thermo‑Calc software users who know the basics of thermodynamics and want to know more about Pourbaix Diagrams.

You are introduced to the concept of a Pourbaix diagram and shown how to interpret such diagrams through a series of examples.

Materials corrosion occurs almost everywhere. It may lead to serious material damages, unexpected application failures, tremendous economic costs and environmental degradations.  Consequently, scientists and engineers must often conduct expensive and time-consuming corrosion experiments as part of failure analyses, risk evaluations, quality improvements and application enhancements.

Under certain conditions, when a metal or alloy is exposed to an aqueous solution with a concentration of inorganic/organic mixture, corrosion phenomena occur at a corresponding degree. During corrosion, some metallic phases dissolve, the metal or alloy surface gets damaged and some secondary solid phases form at the solid-liquid interfaces (such as oxides, hydroxides, silicates, sulphides, sulphates, carbonates, nitrates, phosphates, borates, or halides). Such corrosive chemical or electrochemical reactions can be studied by means of the so-called Pourbaix diagrams if the reactions reach their equilibrium states [1973/1974Pou; 2003Cra; 2011Ver; 2011Tho].

GES5 and GES6 Calculation Engine Version

As of Thermo‑Calc version 2019b, the default calculation engine is set to GES6. For POURBAIX module users, you need to use GES5. When you try to enter this module, you are instructed to switch to GES5 using the SET_GES_VERSION command.

About the Gibbs Energy System (GES) Module

To globally set the default from GES6 back to GES5, go to the Options window Global General Settings tab and click Version 5 for the Preferred Gibbs Energy System setting. The SET_GES_VERSION Console Mode command is used to change GES versions for a single Thermo‑Calc session.

Contact Thermo‑Calc Software AB at info@thermocalc.com for more information about the changes or if you encounter any issues you think are related to the new version of the calculation engine.

GES6 is a re-write and new implementation of the Gibbs Energy System module of Thermo‑Calc and it is the default engine. The previous version, GES5, is still available and will continue to work in the background of the program where necessary. The main purpose of GES6 is to support faster development of new features. However, not all GES5 functionality is implemented in GES6. In such cases (except for the POURBAIX module), GES6 falls back silently and uses functionality from GES5 in the background.

References

[1973Pou] M. Pourbaix, Lectures on Electrochemical Corrosion (Plenum Press, New York, 1973).

[1974Pou] M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions (National Association of Corrosion Engineers, Houston, TX, ed. 2, 1974).

[2003Cra] S. D. Cramer, B. S. Covino Jr., Eds., Corrosion: Fundamentals, Testing, and Protection: ASM Handbook, Volume 13A (ASM International, 2003).

[2011Ver] E. D. Verink Jr., "Simplified procedure for constructing Pourbaix diagrams", in Uhlig’s Corrosion Handbook, R. W. Revie, Ed. (John Wiley & Sons, Inc., Hoboken, NJ, USA, ed. 3, 2011), pp. 93–101.

[2011Thom] W. Thompson, M. H. Kaye, C. W. Bale, A. Pelton, "Pourbaix diagrams for multielement systems" in Uhlig’s Corrosion Handbook, Revi, Ed. (John Wiley & Sons, Hoboken, NJ, USA, 2011), pp. 103–109.