Detection of Wet Debonding

In the case of an interfacial layer that completely inhibits electron-transfer reactions at the interface (or in oxygen-free atmospheres), hydrated ions that ingress into the polymer/metal interface lead to a decay of the measured potential, since the interfacial potential is polarized to the defect potential. Moreover, as long as oxygen reduction is inhibited by insulating layers, the potential does not shift when oxygen is added to the gas phase. 

the transport of hydrated ions and chemical debonding processes can be studied by means of the SKP. Fig. 31.6 shows the potential distribution measured with the SKP when a thin electrolyte layer enters the interface between an adhesive and an iron surface covered by a thin (about 6 nm) nonconducting SiOx layer precipitated by a plasma-polymerization process [51, 52]. The SiO layer inhibits the electron-transfer reaction. Consequently, no corrosive degradation of the interface takes place (see Section 31.3.2.1). However, as the adhesion of the epoxy adhesive to the siUca-Uke layer is weak, the polymer is replaced by 

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