Corrosion behaviour of high-chromium ferritic steels in molten carbonate in cathode environment

The corrosion behaviour of four ferritic steels with a high chromium content and AISI 310 was investigated in (Li-0.60/Na-0.40)(2)CO3 melt in three different cathode gas environments. The electrochemical techniques used were linear polarisation resistance and Tafel extrapolation. The corrosion layers formed on the surface during the tests were analysed by glow discharge optical emission spectroscopy (GDOES), The corrosion layer formed on the Thermax 4762 sample consists of an iron-rich outer layer and a protective aluminium- and chromium-rich inner layer. The corrosion potential increased to a more positive value as the corrosion layer grew on the surface. This supports the supposition that the cathodic reaction in the corrosion process changes gradually from water reduction to oxygen reduction. It was shown that higher temperatures and low concentrations of oxygen and carbon dioxide under so-called outlet cathode gas conditions result in higher corrosion rates. (C) 2001 Elsevier Science Ltd. Ail rights reserved.