Pitting corrosion, active, imaging

Etching of metals by the direct mode has been rather scarce. Schuhmann and cowoikers studied the pitting corrosion of steel by combining shear force-based constant-distance mode SECM with the alternating current mode of this technique (AC-SECM). A very small corrosion pit was generated by inducing active corrosion underneath an accurately positioned 5 pm diameter Pt tip that served as counter electrode in the direct mode. Before and after pit initiation, constant-distance mode AC-SECM images were recorded and subsequently used to identily the area of broken passivity. 

Wipf used the SECM to initiate and image active corrosion pits on stainless steel and aluminum samples [58]. Chloride ions were produced at a tip through the reduction of trichloroacetic... 

Intermetallic particles in aluminum alloys may be either anodic or cathodic relative to the matrix. As a result, two main types of pit morphologies are typically observed. Circumferential pits appear as a ring around a more or less intact particle or particle colony and the corrosion attack is mainly in the matrix phase. This type of morphology arises from localized galvanic attack of the more active matrix promoted by the more noble (cathodic) particle as is shown in Figure 16.6, which also shows the phenomenon with an image collected via optical profilometry. 

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