Epoxy cathodic delamination

Figure 4. Cathodic delamination of pigmented epoxy coatings on steel. A defect was placed in the coating and the coated metal was maintained at a potential of - 0.8 v vs. SCE while immersed in NaCl solutions of different concentrations.

Fig. 17. Cathodic delamination rates of galvanized steel/epoxy-polyamide coating systems when a 0.1 M CoCl2 dipping pretreatment was applied to the metal substrate prior to the application of the coating 91K (Reprinted with permission from Ref. 91Copyright (1981) American Chemical Society)...

Fig. 31.3 Cathodic delamination potential profiles of an unmodified epoxy adhesive layer (adhesive as in Fig. 31.2, about 50 pm thick) on an iron substrate (purity 99.99%) with 0.5 M NaCI as electrolyte measured (a) 20 h after the addition of the electrolyte (b) 50 h after the addition, x increases positively with distance from the electrolyte-filled defect.

Plasma polymers with a special surface structure suitable to bond to an epoxy amine primer were used as interfecial coupling layers on iron and galvanized steel and led to even better results [122]. However, in all cases the system always showed cathodic delamination at the polymer/metal oxide interface, indicating the importance of oxygen reduction on the oxide surface. For verification, after the delamination of the sample, the delaminated polymer was pulled off and the underside of the polymer and the iron surface were investigated by XPS to reveal whether the system delaminated at the plasma polymer/metal interface or at the... 

Figure 6. Cr 2p XPS spectra from the chromated steel/epoxy system, (a) Metal surface following chromate treatment (b) interfacial metal surface following cathodic delamination. Note the reduction in the Cr component when compared with the as-received substrate prior to coating. The underside of the polymer coating, (c), shows a very low concentration of Cr . (From Ref. 42.)...

Figure 10. SIMS positive secondary ion images of the interfacial substrate surface of zinc phosphated steel after adhesion failure of epoxy-ester coating in cathodic polarization testing. Images obtained at the intact coating edge of the delaminated zone. Image diameter 400 fm. Image a mass 55 Fe+ image b mass 54 Zn+ image c mass 31 P+.

Filiform corrosion on epoxy-coated 1045 carbon steel was investigated with SKPFM [111]. Under coatings of 150 and 300 nm thickness at 93% relative humidity, samples were studied under air. Separation of active anode and cathode locations in the head of the filament could be identified. Microscopic and even submicroscopic aspects of electrochemical delamination have been studied with SKPFM [99]. 

Sloan and Talbot [113] cathodically coupled 26-ply quasi-isotropic T300/ 934 carbon/epoxy laminate coupons to magnesium in natural Pacific sea water at 40°C for 140 days. In the uncoupled state in tapwater or natural sea water, the moisture uptake was -0.85% and calcerous deposit was 0.14% and 0.36%, respectively. For the coupled materials, the moisture uptake was -1.3% and the calcerous deposit was 16%. There was some leaching loss from the coupled material. The shear strengths in four point bend tests showed negligible degradation for the soaked samples, but a 30% reduction was measured for electrically coupled materials. This reduction was correlated to delaminations, reducing the effective specimen width by 20-40%. 

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