Corrosion of Commercial Alloys in Ternary Carbonate Melt at 700 and 750 °C -Role of LiFeO₂ Formation

The use of ternary molten carbonate mixtures Li₂CO₃—K₂CO₃—Na₂CO₃ as heat transfer systems for the CSP technology as well as for heat storage for the chemical industry is widely under consideration. Experiments were carried out on austenitic steels DMV310N compared to nickel alloys in order to evaluate the corrosion properties in a molten 33 wt.% Li₂CO₃—33 wt.% K₂CO₃—34 wt.% Na₂CO₃ mixture at 700 and 750 °C for 1000 h in closed crucibles. The austenitic steel DMV 310N passivates by the formation of an outer LiFeO₂ scale due to its iron content. If the iron content is low (< 5 wt.%), as in Alloy 625 the alloy forms NiO, which obviously does not passivate the material and leads to a strong internal corrosive attack. It has been shown by short-term experiments (3, 30, 300 and 1000 h) that a quick formation of LiFeO₂ is necessary to avoid chromium dissolution and NiO formation. If LiFeO₂ is formed quickly, the growth of the internal corrosion front by chromium dissolution is retarded.