| Potential-pH diagrams also known as Pourbaix, Eh-pH, and predominance diagrams, graphically depict the equilibrium phases of a metal, its oxides or hydroxides, and its ions. They are useful because they summarize, in a condensed form, the thermodynamically spontaneous solution reactions for a given element. Potential-pH diagrams have long been used to describe phase stability in aqueous systems. Since they were introduced by Pourbaix, potential-pH diagrams have found widespread use in many areas of chemistry such as corrosion chemistry, geochemistry and teaching descriptive inorganic chemistry.; An expert system-based computer program was developed to draw and interpret potential-pH diagrams in the pH range of 0 to 14 and the potential or Eh range of {dollar}-{dollar}2.0 V to +2.0 V. The output of the program is a diagram for any element at any given ion concentration. The range of 1.0 M to 1.0 {dollar}times{dollar} 10{dollar}sp{lcub}-30{rcub}{dollar} M has been tested. Each predominance area is labeled in the center of the area with the species formula. The user has the choice of graphing the solid, solution, or solid/solution diagrams for each element chosen. Different colors and appearance (solid or dashed) are assigned to the lines depending on which graphing choice is chosen and which phases are present in the reaction. Two diagrams, either of distinct elements or of the same element at different concentrations, can be overlaid in any combination of the graphing choices. The colors of the lines change for the overlaid diagram so that the two diagrams can be distinguished. |
