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Repassivation potential geometry

A pending question is still to know whether this repassivation potential has a unique value or depends on corrosion damages and crevice geometry. The following arguments are in favor of such a unique value ... [Pg.376]

However, the Fig. 29 shows that the effect of chloride content is low on the repassivation potential, particularly when looking at the lower bound of the scatter b and of the measured value which is almost constant for chloride contents in excess of 10 M. This is consistent with the presence of a nearly saturated solution and/or precipitated salt film in well developed crevice corrosion, and indeed such environments should be almost independent on the bulk solution chemistry. Thus, a repassivation potential which, according Pourbaix [36], is close to the local potential of an actively corroding crevice should be poorly or no dependent on the bulk environment and crevice geometry. [Pg.377]

Nevertheless, this point still requires more work, particularly regarding the exact meaning of the high values of the repassivation potentials measured in low chloride and/or low temperature environments (left side of the Fig. 10,11 and 29). In this case, the local environment inside the crevice is likely to be controlled by mass transport and thus the repassivation potential could be dependent on the crevice geometry. [Pg.377]

As already discussed, the main difficulty of this techruque, beside the problem of the crevice former geometry and reproducibility, is that the results are strongly dependent on the potential scan rate both because of the time-dependent stability of the passive films and because of the time-dependent evolution of the environment inside a crevice. In particular, the repassivation potential may be overestimated if corrosion is not well developed in the crevice and it can be underestimated if the potential backscan is too fest to allow the evolution of the local environment to be in quasi-steady conditions. It is generally admitted that the scan rate has to be very low, which causes the two critical potentials to become closer. But the appropriate scan rate must be determined on each system because it may depend on the alloy and on the environment. [Pg.389]

A pit stops growing only if the surface within the pit is again passivated, bringing the pit and the adjacent alloy to the same potential. Extraneous anions, such as SO4, have no effect on the other hand, dissolved oxygen or passivator ions (e.g., NO3) reinitiate passivity on entering a pit. Successful repassivation depends on factors such as pit geometry and stirring rate. [Pg.352]

For a given crevice geometry, the critical potentials for crevice initiation and repassivation decrease with increasing chloride content (Fig. 10) and increasing temperature (Fig. 11) of the bulk solution. This means that the susceptibility to crevice corrosion of passivated alloys increases with the chloride content and the temperature. For example, titanium alloys become sensitive to crevice corrosion only in hot concentrated chloride solutions around 100/150°C [9,10]. Propagation rates also increase with temperature. [Pg.357]


See other pages where Repassivation potential geometry is mentioned: [Pg.269]    [Pg.377]    [Pg.297]    [Pg.339]    [Pg.536]    [Pg.2029]    [Pg.226]    [Pg.60]    [Pg.60]    [Pg.377]    [Pg.294]    [Pg.301]    [Pg.301]   
See also in sourсe #XX -- [ Pg.478 ]




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