Pourbaix’s diagram

Pourbaix s pioneering work on the graphical presentation of gas-metal equilibria and the concept of stability zones and their boundaries between the various stable compounds lead to the second type of diagrams. Figure 7.65 shows a Pourbaix plot of the log P02 system against the reciprocal... 

Streicher s work indicates how useful the potentiostat has been in studying intergranular corrosion. Ideally, future data would be expanded to provide Pourbaix-type diagrams that also contain kinetic information showing various rates of attack within the general domain of intergranular corrosion. (Similar data for cases other than intergranular attack would be equally valuable.)... 

The idea that the cathode potential with respect to ]lt(H20)/Pt-0Hads determines the value of the pre-exponential factor in the ORR rate expression was inspired by a comment by Andy Gewirth (Urbana) in his talk in Leiden, pointing to the value of Pourbaix diagrams for understanding ORR electrocatalysis. Indeed, the information on these ORR-mediating and facilitating M/M-OH surface redox systems is to be found in Pourbaix s Atlas. 

This potential-acidity diagram (Pourbaix s type) has been determined for a large series of alkanes.79 All of these results indicate two types of oxidation mechanism of the C—H bond (i) oxidation of alkanes into carbenium ion at high acidity levels and (ii) oxidation of alkanes into radicals at low acidity levels. 

All of the diagrams in Pourbaix s original atlas were calculated for room temperature. To develop Pourbaix diagrams under higher temperature conditions, several aspects need to be considered. Not only does the temperature affect the logarith-... 

Another type of the facilitated transfer is that involving molecules with acid-base properties. A construction of ion partition diagram of the solute, which is analogous to Pourbaix s -> potential-pH diagrams widely used in electrochemistry of corrosion, has been proposed as a convenient tool that makes it possible to relate the voltammetric behavior to the partition of the neutral and the ionic species, as well as to acid-base equilibria in the adjacent liquid phases [xi]. 

Pourbaix has evaluated all possible equilibria between a metal M and HjO (see Table 1.7) and has consolidated the data into a single potential-pH diagram, which provides a pictorial summary of the anions and cations (nature and activity) and solid oxides (hydroxides, hydrated oxides and oxides) that are at equilibrium at any given pH and potential a similar approach has been adopted for certain M-H2O-X systems where A" is a non-metal, e.g. Cr, CN , CO, SOj , POj", etc. at a defined concentration. These diagrams give the activities of the metal cations and anions at any specified E and pH, and in order to define corrosion in terms of an equilibrium activity, Pourbaix has selected the arbitrary value of 10 ° g ion/1, i.e. corrosion of a metal is defined in terms of the pH and potential that give an equilibrium activity of metal cations or anions > 10 g ion/1 conversely, passivity and immunity are defined in terms of an equilibrium activity of < 10 g ion/1. (Note that g ion/1 is used here because this is the unit used by Pourbaix in the S.I, the relative activity is dimensionless.)... 

Pourbaix diagrams for the aqueous Cd-S, Cd-Te, Cd-Se, Cu-In-Se, and Sb-S systems have been compiled and discussed by Savadogo [26] in his review regarding chemically and electrochemically deposited thin Aims for solar energy materials. Dremlyuzhenko et al. [27] analyzed theoretically the mechanisms of redox reactions in the Cdi xMn , Te and Cdi- , Zn i Te aqueous systems and evaluated the physicochemical properties of the semiconductor surfaces as a function of pH. 

Lead sulfide films have been prepared by various deposition processes like vacuum evaporation and chemical bath deposition. Electrochemical preparation techniques have been used in a few instances. Pourbaix diagrams for all three aqueous lead-chalcogen Pb-S, Pb-Se, and Pb-Te systems, along with experimental results and cited discussion on the chemical etching and electrolytic polishing of lead chalcogenide crystals and films, have been presented by Robozerov et al. [201]. 

Table 8.16 Standard molal Gibbs free energies of formation from the elements for aqueous ions and complexes and condensed phases, partly adopted in constructing the Eh-pH diagrams in figure 8.21. Data in kcal/mole. Values in parentheses Shock and Helgeson s (1988) tabulation. Sources of data (1) Wagman et al. (1982) (2) Garrels and Christ (1965) (3) Pourbaix (1966) (4) Berner (1971)...

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