Corrosion immune

Eig. 2. The thermodynamic regions of corrosion, immunity, and passivation of iron in an iron—water system assuming passivation by a film of Ee202 (H)-... 

It should be noted that Fig. 1.15 (top) is based entirely on thermodynamic data and is therefore correctly described as an equilibrium diagram, since it shows the phases (nature and activity) that exist at equilibrium. However, the concepts implicit in the terms corrosion, immunity and passivity lie outside the realm of thermodynamics, and, for example, passivity involves both thermodynamic and kinetic concepts it follows that Fig. 1.15 (bottom) cannot be regarded as a true equilibrium diagram, although it is based on one that has been constructed entirely from thermodynamic data. 

Although the zones of corrosion, immunity and passivity are clearly of fundamental importance in corrosion science it must be emphasised again that they have serious limitations in the solution of practical problems, and can lead to unfortunate misconceptions unless they are interpreted with caution. Nevertheless, Pourbaix and his co-workers, and others, have shown that these diagrams used in conjunction with E-i curves for the systems under consideration can provide diagrams that are of direct practical use to the corrosion engineer. It is therefore relevant to consider the advantages and limitations of the equilibrium potential-pH diagrams. 

Fig. 6.1 Theoretical domains of corrosion, immunity and passivation of silver, at 25°C...

Fig. 3.11 Theoretical condition of corrosion, immunity, and passivation of CulnSe2, Cu Se, and Se phases in an aqueous solution. Concentrations of Cu, In, and Se species in the aqueous solution at 25 °C were assumed to be 10 M. (Reproduced from [179], Copyright 2009, with permission from Elsevier)...

Marcel Pourbaix 1940 Pourbaix diagrams involving pH and potential give regions of corrosion, immunity and passivity... 

Fig. 2.16 Pourbaix diagrams for the iron/water system, (a) Reproduction of Fig. 2.11 showing regions of corrosion, immunity, and possible passivation, (b) Form of the diagram frequently employed. Source Ref 9, 10...

Fig. 2.17 Pourbaix diagrams for selected metals showing regions of corrosion, immunity, and possible passivation. Source Ref 9...

In Fig. 20.1, the theoretical potential-pH domains of corrosion, immunity, and passivation of copper at 25°C are shown, considering that passivation occurs by formation of the oxides CU2O and CuO [2]. 

Titanium is very active in the F.mf Series, about 1.2 V more active than iron (Table 3.2, Section 3.8). The theoretical potential-pH domains of corrosion, immunity, and passivation of titanium in aqueous solution are presented in Fig. 25.1 [1]. In this figure, passivation is attributed to a film of Ti02. The excellent corrosion resistance of titanium in many environments results from a hard, tightly adherent oxide film that forms instantaneously in the presence of an oxygen source [2]. This film, typically less than 10 nm thick, is very chemically resistant and is attacked by very few substances, including hot concentrated HCl, H2SO4, NaOH, and HF [3]. 

Figure 26.1. Theoretical conditions of corrosion, immunity, and passivation of zirconium at 25°C, assuming passivation by Zr02-2H20 [1], (M. Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions, 2nd English edition, p. 227. Copyright NACE International 1974 and...

The theoretical potential-pH domains for corrosion, immunity, and passivation are shown in Figure 28.1 [1]. As shown in the diagram, in acid or neutral solution, lead can be cathodicaUy protected by controlling the potential to less than -0.3 V. In alkaline solution, potential control for cathodic protection is below -0.4 to -0.8 V, depending on the pH [1]. 

Fig. l.lS(top) Equilibrium potemial-pH diagram for the Fe-HjO system showing the zones of stability of cations, anions and solid hydroxides (after Deltombe and Pourbaix ) and (bottom) simplified version showing zones of corrosion, immunity and passivity (curve / is the HjO/Hj equilibrium at Phj= 1 and cur s the Oj/HjO equilibrium at Poj = )... 

Potential-pH (Pourbaix) diagram shows the thermodynamic stability of a metal. A region of corrosion immunity can be defined using this diagram. The Pourbaix diagram of A1 is discussed in detail. 

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