Understanding ac-dc-ac accelerated test results

The ac-dc-ac accelerated testing method is an unconventional method that involves subjecting organic coatings on metallic substrates to cycles of cathodic potential. The ac-dc-ac degradation associated with a standard Army epoxy primer on a steel substrate is reported. The ac-dc-ac procedure was modified to include wetting and drying stages. Experimental results demonstrated the influence that the method had on the barrier property, the diffusion of water, and saturated condition of the primer. A quantitative analysis of the transient potential profile that followed the cathodic potential was performed to address processes of charge transfer, transport, and coating relaxation during this step. (C) 2009 Elsevier Ltd. All rights reserved.