Inhibitory Effects of Uric Acid on Cathodic Reactions of Steels in Saturated Ca(OH)₂ Solutions

Abstract

Severe localized corrosion of buried steel pipes, called macro-cell corrosion in concrete/soil systems, is induced by cathodic reactions on steel surfaces in concrete accompanied by anodic reactions (i.e., corrosion) on those in soil. The addition of cathodic inhibitors to concrete is believed to be one of the effective means of suppressing this phenomenon. In order to evaluate the role of uric acid as an inhibitor for macro-cell corrosion, the inhibitory effects of uric acid on cathodic reaction of steels were investigated in saturated Ca(OH)₂ solution to simulate the environment in pores in concrete. Polarization measurements showed that uric acid effectively inhibited these cathodic reactions, indicating that uric acid worked as an cathodic inhibitor for macro-cell corrosion. The relation between the inhibition ratio and the concentration indicated that uric acid was adsorbed on the steel with a Langmuir adsorption isotherm. Uric acid was suggested to be adsorbed onto cathodic areas of the steel through coordination of nitrogen atoms at positions 7 and 9, and oxygen in the carbonyl group at position 8 to the iron cations on the steel.