THE MECHANISM OF CATHODIC DISBONDING OF HYDROXY-TERMINATED POLYBUTADIENE ON STEEL FROM ACOUSTIC MICROSCOPY AND SURFACE-ENERGY ANALYSIS

Scanning acoustic microscopy (SAM) has allowed observation of the microscopic details of the attack by cathodic alkaline corrosion products on a model organic coating on steel. Attack of the polymer by the alkaline corrosion products occurs at numerous localized regions resulting in mechanical degradation of the coating/metal interface. Acoustic microscopy has also provided a rapid determination of the kinetics of the disbonding process. The disbond distance away from a cathodically polarized scribe increases with the square root of time. The corresponding rate parameter Kd increases with decreasing potential for applied potentials below -750 mV vs. Ag/AgCl, The cathodic disbonding rates have been compared to potential dependent wetting of the steel surface as determined using a modified Wilhelmy balance. The results suggest sodium hydroxide generated at the surface under cathodic polarization lowers the surface tension to promote advancing contact by the electrolyte. copyright. © 1990, The Electrochemical Society, Inc. All rights reserved.