Pit generation rate

The influence of varying temperature or electrolyte concentration can be simulated by tuning wq which is the maximum pit generation rate. The graph of eq. (8.2) is displayed in Fig. 8.2. Below Mo = 50 the rate is small, increases then rapidly and finally saturates. The width of the transition regime is specified by the parameter H. 

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 3 Effect of the Cr content on the pit generation rate in NaCl (0.02 M) for some Ti-bearing (Ti=0.4%) FeCr industrial alloys with different Cr contents. V is the electrode potential. (From Ref 3c.)...

Nucleation and repassivation are now considered as the two steps of a birth and death initiation process. It was proposed that the repassivation probability (per unit of time) p is constant up to a critical time then nullifies (which means that a sufficiently developed pit can no longer repassivate). The pit generation rate writes then g=G exp(-pxe). 

The Zone 2A canyon eievator pit and Room 109 are the only two areas in the HCF where waste will be accumulated. By the time that the waste is moved into Room 109, the hydrogen generation rate is sufficiently low as to preclude accumulation to flammable levels (Mitchell and Naegeli 1999). The normal Zone 2A ventilation flow of 1800 cfm (which Includes flow into the SCB s) will preclude any appreciable hydrogen concentrations in Room 109 or the Zone 2A canyon. 

The conditional event generation rate r t) was calculated as a function of TEL thickness by inserting the values of the shape and scale parameter m and n into Eq. 4.17. The result of r t) was illustrated as a function of time t in Fig. 4.18. The value of r t) represents the formation rate of pit initiation in the next unit time for the specimens, in which pit initiation has not yet been generated when t has elapsed. It was observed that the value of r t) under TEL was remarkably lowered compared with that in the bulk solution at a given time t. This indicated that pit initiation was inhibited under TEL. 

Production of differential aeration cell. A scatter of individual barnacles on a stainless steel surface creates oxygen concentration cells. The formation of biofilm generates several critical conditions for corrosion initiation. Uncovered areas will have free access to oxygen and act as cathodes, while the covered zones act as anodes. Underdeposit corrosion (crevice corrosion) or pitting can occur. Depending on the oxidizing capacity of the bacteria and the chloride ion concentration, the corrosion rate can be accelerated. However, the presence of a biofilm does not necessarily mean that there will always be a significant effect on corrosion. (Dexter)5... 

Collapse of bubbles generated in the proximity of the soiid surface produces high-speed microjets which can raise transport rates and increase the surface area through surface pitting. 

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