The thermogalvanic corrosion of mild steel in alkaline solution—I. Actively dissolving electrodes

Abstract

Using a simple model it has been shown that both thermodynamic and kinetic factors contribute to the temperature coefficient of the corrosion potential of a freely corroding electrode when the local action processes are under activation control. In the particular case of a 0·21%C steel immersed in deaerated Na 2B 4O 7/HCl buffer solution (pH 7·6) the kinetic factors predominate resulting in a negative coefficient. A thermogalvanic cell with a hot anode is therefore formed when when two such electrodes, maintained at different temperatures, are connected. In the absence of a significant cell internal resistance, a current will flow which reflects a stimulation of corrosion at the anode and a corresponding protection of the cathode, both attributable to thermogalvanic action. When the thermal e.m.f. is small the cell current overestimates the increased corrosion damage; since the individual electrodes are barely polarized it follows that the kinetics of the local action cathodic process at the anode cannot be ignored.