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Pitting potential repassivation

Like anodic pitting potentials, repassivation potentials Eire significantly lower in bromide and iodide media. Room-temperature Bp values of+1.2 and +0.95 V are measured for grades 2 and 5 titanium, respectively, whereas values of +0.9 V in dilute KBr solutions have been reported. Repassivation potentials for grades 2 and 5 titanium in dilute room-temperature iodide solutions have... [Pg.113]

In the potential range catliodic to one frequently observes so-called metastable pitting. A number of pit growtli events are initiated, but tire pits immediately repassivate (an oxide film is fonned in tire pit) because the conditions witliin tire pit are such that no stable pit growtli can be maintained. This results in a polarization curve witli strong current oscillations iU [Pg.2728]

At the area between the breakdown potential Eb and the critical pitting potential pit local film breakdown occurs, which leads to the creation of pit nuclei. However, these nuclei are immediately repassivated. Consequently, in this potential region it is concluded that breakdown and repair are continuously repeated without creating pit growth. [Pg.233]

Figure II. Schematic anodic polarization curves at a fixed temperature. Determination of either transpassive potential ( ,) or pitting potential ( p and repassivation potential ( ,) at the critical current density (/ ). t rcvis the current density at which the scan is reversed. ... Figure II. Schematic anodic polarization curves at a fixed temperature. Determination of either transpassive potential ( ,) or pitting potential ( p and repassivation potential ( ,) at the critical current density (/ ). t rcvis the current density at which the scan is reversed. ...
Figure 11 shows idealized polarization curves for the cases where the temperature is above the CPT (pitting) and below the CPT (transpassive corrosion). These polarization curves show the pitting potential ( ),), transpassive potential (E,), and repassivation potential (E ). Ep and E, are defined as the potentials at which the current density unambiguously... [Pg.293]

Plotting the repassivation potentials (or the pitting potentials and the transpassive potentials) as a function of the specimen temperature evaluates the CPT. An example of an evaluation is shown in Fig. 20. [Pg.294]

There are those who feel that there are not two distinct potentials. These workers propose that, when measured correctly, Eb6 and Ew are one and the same. In standard testing, the nucleation of pits occurs at Ev, but owing to the time necessary for pits to become established, the probability that pits will repassivate, and the finite potential scan rate used, pits do not cause a dramatic increase in the current until EM. This explanation would rationalize the often-observed effect that increasing the scan rate increases Ebi but not Eip. If I i is properly measured, these workers feel that it can be used as a go-no go potential for applications, i.e., if the potential of the alloy is always below Eip, then pitting cannot occur. [Pg.105]

Figure 6.23 Schematic of a polarization curve showing Ep (pitting potential) R (repassivation potential) relative to Ecorr, critical potentials and metastable region (Frankelf... Figure 6.23 Schematic of a polarization curve showing Ep (pitting potential) R (repassivation potential) relative to Ecorr, critical potentials and metastable region (Frankelf...
The critical pitting potential cpr lies between the breakdown potential and the protection potential and can be determined by the scratch repassivation method. In the scratch repassivation method for localized corrosion, the alloy surface is scratched and exposed to a constant potential. The current change is monitored as a function of time and this will show the influence of potential on the induction time and the repassivation time. A careful choice of the level of potential between the breakdown potential and the critical pitting potential can give the critical pitting potential for a chosen material in given conditions.42 (Scully)14... [Pg.366]

Noise analysis obtained from microelectrochemical investigations of stainless steels under potentiostatic conditions revealed that the current noise, expressed as standard deviation a of the passive current, increases linearly with the size of the exposed area, whereas the pitting potential decreases.47 However, to complete the electrochemical studies and distinguish between repassivating superficial pits and penetrating ones, microscopic studies are highly desirable. The scanning reference electrode technique (SRET) should be an appropriate complementary tool.28... [Pg.369]

Pitting potential increased with increase in chromium contents >20 wt%, and molybdenum of 2-6 wt%. Recent results, applying microelectrochemical techniques, confirmed that even in the superaustenitic stainless steels molybdenum strongly improves the repassivation behavior but has no influence on pit initiation.27 The corrosion resistance of aluminum alloys is totally dependent on metallurgical factors.52, (Frankel)5... [Pg.373]

FIGURE 22.31 Schematic potential-dimension diagrams for localized corrosion of stainless steel in aqueous solution [63] Epit — pitting potential, ER = pit repassivation potential, Ep = passivation potential in the critical pit solution, Emv — crevice protection potential, rj]13 = critical pit radius for pit repassivation, a = pit repassivation, and b = transition from the polishing mode to the active mode of localized corrosion. [Pg.570]

If the passive film cannot be reestablished and active corrosion occurs, a potential drop is established in the occluded region equal to IR where R is the electrical resistance of the electrolyte and any salt film in the restricted region. The IR drop lowers the electrochemical potential at the metal interface in the pit relative to that of the passivated surface. Fluctuations in corrosion current and corrosion potential (electrochemical noise) prior to stable pit initiation indicates that critical local conditions determine whether a flaw in the film will propagate as a pit or repassivate. For stable pit propagation, conditions must be established at the local environment/metal interface that prevents passive film formation. That is, the potential at the metal interface must be forced lower than the passivating potential for the metal in the environment within the pit. Mechanisms of pit initiation and propagation based on these concepts are developed in more detail in the following section. [Pg.285]


See other pages where Pitting potential repassivation is mentioned: [Pg.691]    [Pg.691]    [Pg.143]    [Pg.144]    [Pg.145]    [Pg.145]    [Pg.234]    [Pg.245]    [Pg.215]    [Pg.90]    [Pg.365]    [Pg.365]    [Pg.366]    [Pg.98]    [Pg.169]    [Pg.182]    [Pg.564]    [Pg.564]    [Pg.565]    [Pg.566]    [Pg.567]    [Pg.567]    [Pg.570]    [Pg.294]    [Pg.300]    [Pg.402]    [Pg.308]    [Pg.309]    [Pg.320]    [Pg.328]    [Pg.338]    [Pg.338]    [Pg.339]    [Pg.710]    [Pg.21]    [Pg.21]   
See also in sourсe #XX -- [ Pg.103 , Pg.111 , Pg.239 , Pg.378 ]




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