Determination of the Reactive Area of Organic Coated Metals Using the Breakpoint Method

Experimental results and mathematical considerations were used to investigate the physical meaning and the application limits of the breakpoint method to evaluate the reactive area in organic coatings. The physical meaning of the reactive area values of a metal under an organic coating, obtained using the breakpoint method, were reviewed. Experimental evidence indicated the area was related to coating defects and porosity, rather than to the total reactive or delaminated area. Limits in applying the breakpoint method were reviewed using mathematical considerations that showed the method was not accurate when values of the coating capacitance and double-layer capacitance were too close, which was a possibility during the initial time of degradation and also when two time constants were distinguishable.