Corrosion of Fe alloys in NaNO₃-KNO₃-NaNO₂ at 823 K

In support of advanced solar central receiver programs, six commercially available, iron-based construction materials were exposed to a molten NaNO₂-NaNO₃-KNO₃ salt mixture at 823 K for periods up to six months. After one month of exposure, oxide coatings formed on each alloy;the amount of oxidation ranged from 10 mg/cm ² for low carbon steel to ∼0.7 mg/cm² for 310 stainless steel. The low-Cr alloys tended to blister and spall but the stainless steels were much more corrosion resistant. Analysis of the oxide surface of a 5 pct chrome alloy clearly indicated a chromium enriched layer was present at the oxide/metal interface and an iron oxide rich layer at the oxide/nitrate interface.