NEW DEVELOPMENTS IN CORROSION AND BLISTER FORMATION IN COATINGS

Many polymers take up more water at equilibrium at higher temperatures than they do at lower temperatures. Water exposure with cycling tempe ratures can lead to excess free water when films saturated with water at a higher temperature are quenched or rapidly cooled. This mechanism has been called microfogging with soluble water exuded at lowered tem peratures (SWEAT) being the undesired result. The water freed by this process can cause microcavities, blisters, and even total delamination . Means to counteract these failures include increasing permeation coe fficients using micaceous iron oxide or other void-containing filler, for example. The intended incorporation of microvoids (microsponges) a lso allows the SWEAT water to collect in the coating without causing e xcess damage. A polymeric binder which dissolves the same amount of wa ter at all temperatures would eliminate this effect at its source.