EFFECTS OF SO2 DEPOSITION ON PAINTED STEEL SURFACES

The effects of 1 ppm SO2 with high humidity on alkyd‐painted steel was investigated using x‐ray photoelectron spectroscopy (XPS) and adhesion tensile tests. The SO2 caused a spotted discoloration on the specimens on which dew is allowed to dry and accelerated the loss of adhesion between the primer and the steel. The brown spots are characterized by a high S content and form in areas where the condensed dew becomes more concentrated in H2SO3 or H2SO4 as it evaporates. Specimens not exposed to dew also have high S concentration on the surface, but do not discolor. High humidity alone caused a loss of adhesion at the primer–metal interface, but SO2 increased the rate of this de‐adhesion. Such a loss of adhesion decreases the protection provided by the paint system and the presence of Fe on both sides of some failures indicated that the substrate was beginning to corrode. Copyright © 1990 John Wiley & Sons Ltd.