Mechanistic study of moisture
corrosion of FeCr alloys in molten
salts by ab-initio molecular dynamics
simulations
Molten salts are promising for various energy applications including
fuel and solar cells and nuclear energy. These applications face a
common challenge: corrosion of structural materials by impurities such
as H2O. This work employs ab-initio molecular dynamics simulations to
study H2O induced corrosion of FeCr alloys in molten NaF and NaCl
salts. H2O is found highly stable in both salts, with infrequent, reversible
dissociation into OH− and H+ along with HF or HCl formation. The
dissociation tendency correlates positively with the electronegativity
and negatively with the size of halogen atoms. Accordingly, H2O
reaches the salt/metal interface as a molecule before reacting with
metal. Reduction of H+ is found to occur without simultaneous
oxidation of specific metal atoms such as Cr, suggesting sequential
instead of the commonly proposed concurrent reduction and
oxidation. The reduced H atoms prefer to stay at the interface and may
re-enter NaF but not NaCl, highlighting the influence of salt chemistry.