Electrochemical impedance spectroscopy etching

The fine control over the ablation process makes another feature possible. If the etching is intermpted just before file metal is reached, a defect with a thin (several im) residual layer on the bottom can be produced, as illustrated schematically in Figure 21. It is this defect that proved to have ideal characteristics for broad characterization of organic coatings, including electrochemical impedance spectroscopy. 

Although the evolution of surface chemistry depicts the hydration of bare surfaces, the same process occurs for buried interfaces within an adhesive bond. This was first demonstrated by using electrochemical impedance spectroscopy (EIS) on an adhesive-covered Forest Products Laboratory (FPL, a sodium dichromate + sulfuric acid etch) aluminum adherend immersed in hot water for several months (Davis et al. 1995b). EIS, which is commonly used to study paint degradation and substrate corrosion, showed absorption of moisture by the epoxy adhesive and subsequent hydration of the underlying aluminum oxide after 100 days (O Fig. 8.5). At the end of the experiment, aluminum hydroxide had erupted through the adhesive. Later, cross-section micrographs of bonded tapered double-cantilever beam... 

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