GENERALIZED ELECTROCHEMICAL POTENTIAL DIAGRAMS FOR COMPLEX AQUEOUS (M-X-H-O-E-) SYSTEMS

A simple convex-polygon approach has been adopted to construct generalized electrochemical potential diagrams for metal-nonmetal-H2O systems. When one species is selected among aqueous, gaseous species or condensed phases so as to have a constant chemical potential (in addition to a(H2O) = 1), the following diagrams can be drawn: (i) a stability area of any condensed phase can be projected on a pE-pH plane when the activity of the condensed phase is fixed at unity; (ii) a vertical intersection of the Pourbaix diagram can be drawn as a pE vs. log a(M)/a(X) plot when the chemical potential of H+ (pH) is fixed; (iii) the Pourbaix diagram under a constant partial pressure of gaseous species also can be set up. These diagrams have been compared with the chemical potential diagrams for the corresponding dry or hydrated systems. This makes clear how the presence of water affects equilibria among phases in the dry systems. © 1990, The Electrochemical Society, Inc. All rights reserved.