ELECTROCHEMICAL INVESTIGATION ON THE ANTI-CORROSION PROPERTIES OF ZINC-RICH COATING FILM AGAINST THE DEFECTS

Abstract

 The zinc-rich coating film has been used as an anti-corrosion primer of the heavy-duty paint coating for the steel structures exposed to the atmospheric environment. However, there are many unclear points about the corrosion protection properties of zinc-containing paints on those regions in steel structure, where the rainwater accumulated, and wet-dry cycles repeated. Moreover, the electrochemical mechanism of steel substrates between coating defects has not been investigated with elucidating its anti-corrosion properties. The objective of this research is to electrochemically elucidate the anti-corrosion properties of the steel substrate exposed at the adjacent coating defects of the organic and inorganic zinc-rich paints, focusing on the stagnated water and repeated wet-dry cyclic condition. Therefore, the model specimens were fabricated to simulate coating defects, and the time-dependent macrocell currents and AC impedance were monitored. Their test results revealed that for the inorganic zinc paints with relatively small diameters of defects, the anti-corrosion acts effectively due to the sacrificial anodic effects of zinc powder and compounds shielding. Nevertheless, the anti-corrosion effect of the organic zinc-rich coating is difficult to generate against the steel substrate.