Pourbaix diagrams copper-water system

FIGURE 7.1 Pourbaix diagram of copper-water system (from Ref. 1). 

The Pourbaix diagram for the copper/water system is shown in Fig. 2.15. The more positive standard electrode potential of copper (+337 mV (SHE)) as compared to iron (-440 mV (SHE)) is evident. This greater nobility results in copper being thermodynamically stable in water that is, line 14 (-6) representing aCu2+ = 10-6 lies above line a. 

Fig- 7.36 Pourbaix diagram for the system copper-water. Source Ref 7... 

A Pourbaix diagram for copper/water system is shown in Fig. 2.22. Copper (E° = 0.337 V) is more noble than iron ( p = —0.444V), however, it is more stable in water (SHE) than iron. Copper is not passive in acid electrolytes. The oxide of copper, Cu+ and Cu " " are only... 

Figure 2.22 Pourbaix diagram for the copper-water system at 25° C...

It is important to recognize some of the limitations of the Pourbaix diagrams. One factor which has an important bearing on the thermodynamics of metal ions in aqueous solutions is the presence of complex ions. For example, in ammoniacal solutions, nickel, cobalt, and copper are present as complex ions which are characterized by their different stabilities from hydrated ions. Thus, the potential-pH diagrams for simple metal-water systems are not directly applicable in these cases. The Pourbaix diagrams relate to 25 °C but, as is known, it is often necessary to implement operation at elevated temperatures to improve reaction rates, and at elevated temperatures used in practice the thermodynamic equilibria calculated at 25 °C are no longer valid. 

FIGURE 56.7 Pourbaix diagram of the copper-chlorine-water system. 

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