A Statistics-Based Approach to Studying Aluminum Pit Initiation

Abstract

A statistical description of pit initiation in high-purity aluminum ͑99.99͒ is developed based on the statistical frameworks established by Baroux ͓Corros. Sci., 28, 969 ͑1988͔͒ and Shibata and Takeyama ͓Corrosion, 33, 243 ͑1977͒ and 52, 813 ͑1996͔͒. The statistical treatment is used to examine the dependency of pitting behavior on electrode area, scan rate, and chloride concentration. It is shown that the average pitting potential is proportional to the log of the scan rate and the log of one over electrode area, implying an exponential dependence of pit germination rate on applied potential. The constants that describe pit germination rate are independent of area for electrodes of diameter 125 m and smaller. However, the constants are area-dependent for larger electrodes. Based on these results a homogeneous pit nucleation process is proposed to account for pit initiation on 125 m diam and smaller electrodes, while a heterogeneous process is proposed to control the behavior of 500 m diam electrodes. The results from these studies also demonstrate the importance of correctly choosing experimental conditions when studying pitting behavior. The dependencies of pitting potential on scan rate and area are found to be sensitive to electrode size, scan rate, and aggressiveness of the electrolyte.

Composition Profiles around Solute-Lean, Spherical Nanocrystalline Precipitates in an Amorphous Matrix: Implications for Corrosion Resistance

“…The results in Figure 9 provide the foundation for a possible tradeoff in the corrosion resistance of partially devitrified glasses based on precipitate radius. The probability of pit nucleation at a nanocrystal might increase with an increase in its size, [34] but, because the surrounding amorphous matrix collects the beneficial solutes, it becomes more difficult for that pit to propagate beyond the precipitate and into the amorphous matrix. [32] However, the decrease in the distance of separation between the precipitates with an increasing precipitate radius means that less amorphous matrix would need to be penetrated for the pitting attack to reach another susceptible precipitate.…”

Effect of alloyed Cu on localized corrosion susceptibility of Al–Cu solid solution alloys—Surface characterization by XPS and STEM

“…The effect of electrode area on the extent of ennoblement observed in pitting potential measurements can be understood in the context of arguments presented by Wall and Martinez [20], who distinguish homogeneous and heterogeneous forms of pit initiation. According to their arguments, heterogeneous pit initiation refers to pitting at specific sites that possess a high probability of pitting.…”

“…Generally, as electrode area is decreased, the measured pitting potential increases, all other factors being equal [20]. This behavior is attributed to the idea that the probability of an electrode containing a particularly weak site that initiates pitting at low potentials decreases as the exposed area decreases.…”

Relationship Between Induction Time for Pitting and Pitting Potential for High-Purity Aluminum

“…Recently, we reviewed the derivation of such a model; the details can be found elsewhere. 3 Here we briefly summarize the equations necessary to calculate the pitting potential distribution from parameters that can be extracted from induction time data.In the mid-1970s, Shibata developed a statistical treatment of pit nucleation in stainless steel which expressed both E pit and in terms of a germination rate, ͑s Ϫ1 ͒. 4 More recently, we applied this treatment to the pitting behavior of aluminum and found that could best be described by an exponential dependence on potential 3…”