document: There have been relatively few attempts to observe and in some cases extract the average current density from video images taken of growing 2D pits. Frankel presented a method to directly measure the average anodic current density from the growing pit boundary velocity in Al [33], an Al alloy [34] and Ni–Fe [35] thin films. Subsequently, Ryan et al. [27,36] determined the anodic current density in pits propagating as 2D disks in stainless steel thin films by measuring the pit edge movement velocity. Ernst and Newman [11,12,37] studied stability of pit growth in detail and measured the kinetics of 2D pit propagation in depth and width and compared the results with kinetics in 1D pencil electrodes. They developed a semi-quantitative model for pit propagation which explained the lacy pit cover formation during the pit growth, although they did not measure current density within the pit. More recently, Tang and Davenport [38] tracked the pit boundary movement and computed the instantaneous but average current density in Fe-Co thin films. However, there have been no previous attempts to quantify the local current density during inhomogeneous growth of pits, although such local variation in current density has long been recognised [7].
extractive_keyphrases: 1d pencil electrodes 2d disks 2d pit 2d pits al anodic current current lacy pit cover pit pits stainless steel thin films video images
abstractive_keyphrases: 2d pit propagation al alloy fe-co thin films lacy pit cover formation measured the kinetics of 2d pit propagation ni–fe [35] thin films pit edge pit growth pit propagation semi-quantitative model