A Capacitance-Resistance Study of Polybutadiene Coatings on Steel

The capacitance and resistance of polybutadiene coatings on steel were determined as a function of time of exposure to air-saturated 3% sodium chloride solution. The results were interpreted in terms of a model in which the solution rapidly penetrates capillaries or defects in the coating followed by solution of water throughout the coating. The model predicted the resistance and the change in resistance of the coating with time. Generalized corrosion of the steel coincided with a departure from linear behavior of the capacitance-time curve and a coating resistance of 50,000 to 100,000 ohms for the 5 cm² sample area.