Calc.  SED & PREDOM / PREDOM

A predominance area diagram shows the species formed with a given “main” component as a function of two variables. The following rules are used:

A special type of predominance area diagram is the potential-pH diagram, also called a Pourbaix diagram. The following figure shows a potential-pH diagram for iron:

Eh-pH diagram

This diagram was obtained with the following input file:

 3, 13, 7, 0
H+, e-, Fe 2+
Fe 3+     ,-13.02   0 -1 1, Fe(OH)2   ,-20.8   -2  0 1
Fe(OH)3-  ,-33.4   -3  0 1, Fe(OH)4 2-,-46.35  -4  0 1
FeOH+     ,-10.2   -1  0 1, OH-       ,-14.0   -1  0 0
Fe(OH)2+  ,-18.69  -2 -1 1, Fe(OH)3   ,-25.58  -3 -1 1
Fe(OH)4-  ,-34.62  -4 -1 1, Fe2(OH)2+4,-28.99  -2 -2 2
Fe3(OH)4+5,-45.36  -4 -3 3, FeO4 2-   ,-125.87 -8 -4 1
FeOH 2+   ,-15.21  -1 -1 1,
Fe(c)     ,-16.097  0  2 1, Fe(OH)2(c), -12.996 -2  0 1
Fe3O4(c)  ,-37.077 -8 -2 3, Fe(OH)3(am),-17.911 -3 -1 1
Fe2O3(cr) ,-26.448 -6 -2 2, Fe3(OH)8(c),-46.262 -8 -2 3
FeOOH(cr) ,-14.02  -3 -1 1
EH, e-, H+, Fe 2+,
LAV, 0 -13,  LAV, 16.9034 -18.5937, T, 1E-5