Electrochemical Phase Diagrams for Aqueous Redox Systems.

摘要

A completely new phase diagram, the electron number diagram, has been developed for aqueous redox systems. The electron number diagram is a transformed potential-pH diagram in which potential is replaced by its thermodynamic conjugate, the number of electrons. The relationship between electron number diagrams and potential-pH diagrams, which provide complementary information, is explained in thermodynamic and geometric terms. Electron number diagrams show any similarities to metallurgical T-x diagrams. Because electron number is a conserved quantity, material balances can be performed on electron number diagrams, and process trajectories can be followed. The mass and electron balance equations are derived, and electron number diagrams are used to illustrate a variety of process trajectories. The diagrams are of particular value in describing the complex phase chemistry involved in aqueous corrosion, hydrometallurgical ore processing, nuclear waste disposal, geochemical processes and some fuel sulfur removal processes. A detailed thermodynamic analysis of complex aqueous redox systems was the basis for algorithms for construction of generalized chemical potential diagrams, potential-pH diagrams and electron number diagrams. Extremely efficient computer programs based on the algorithms were used to construct diagrams for a variety of systems, including the following which include two active redox elements: the aqueous U-C, Cd-Te and Ga-As systems. Extension of these algorithms to systems of arbitrary complexity is also discussed. (aw)