Pitting probability

The difference between pitting and protective potential is used to estimate pitting corrosion susceptibility for materials [6,7,15]. If protection is more negative than the pitting potential, as shown in Fig. 7.1, the pitting probability is greater [6,7]. When the open circuit or corrosion potential is above the pitting potential, the material spontaneously pits at the corrosion potential. 

The time derivative g = dm/dt of the elementary pitting probability is referred to as the pit generation rate. The intrinsic pitting potential (if it really exists) is given by g = 0 and can be deduced from the transition from P = 1 to P = 0 for infinite surface areas 5. This condition is not easily fiilfilled in laboratory experiments, and it is often more convenient to use small surface areas and to characterize the pitting resistance by the probabifistic function or g. 

Potentiostatic measurements on a sufficient number of samples, or simultaneous measurements using a multicharmel device [2,3ab], given the survival probability P and then the elementary pitting probability (F, t) as a function of the polarization time t (Fig. 2a). The probability density for the random function x is -dP/Pdt = Sg(y, t). Figure 2a and b show the pit generation rate time dependence... 

Figure 2 (a) Elementaiy pitting probability in NaCl (0.5 M) for an AISI 304 type... 

Figure 9 Effect of sulfate ions on the pitting probability in 0.1 M NaCl (pH 6.6). / is the sodium sulfate molarity and V the electrode potential, (a) Steel A (b) steel B.

Figure 15 Effect of a 16-h aging at constant potential (steel A, 150 mV steel B, 200 mV) on the elemenlaiy pitting probabilities NaCl 0.02 M, pH 6.6.

Zinc. Up to 1.0% zinc can be added to AA 1099 without increasing the pitting probability. At higher levels, its influence would depend upon other constituents, such as Mg and Cu, and the microstructure produced. 

Pitting frequency The number of pits per unit area. Pitting probability P = N /N x 100, where Np is the number of specimens in the pit, and N is the total number of specimens. 

A large number of specimens are required for the reliable assessment of this parameter. Pitting probability and penetration rate are two concepts that characterise the durability of aluminium in water. They are not related to each other a given aluminium can have a high pitting probability and a low penetration rate, and vice versa. The former is of course... 

The question arises however to know whether the whole initiation process is Poissonian in time and space, nearly Poissonian or not Poissonian at all. ° As concerns spatial correlations, it is expected that the probability of new pitting events in the vicinity of an existing pit i may be different from the pitting probability in a not pitted region. 

Sulfate additions in 0.1 M NaCl were found to decrease the pitting probability for the two steels steels A and B but this effect is more pronounced for steel A than for steel B, even when this difference becomes smaller when the chloride concentration increases. Furthermore sufficient sulfate additions result in a deviation from the standard exponential (x) V) law, which tends to become bimodal (two different exponential co(V) laws for high and low electrode potentials), for high enough sulfate amounts on steel B. MnS containing steels are then clearly less sensitive to the inhibitive action of sulfate ions than MnS free ones. 

Effect of a 16h aging at constant potential (steel A 150mV, steel B 200mV) on the elementary pitting probabilities 05(V). NaO 0.02M, pH 6.6. 

Snowidowo SNOW/ob74/16/2009 Animal bone/ 2.4%N 7.4%C Poz-43123 the Przewoisk culture, pre-Roman period 2nd century BC - BC/AD) rubbish pit probably two development phases... 

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