Chemical states of 3d transition metal impurities in a liquid lead-bismuth eutectic analyzed using first principles calculations.

Abstract

Steels are easily corroded in a liquid lead-bismuth eutectic (LBE) because their components, such as Fe, Cr and Ni, exhibit a high solubility in the liquid LBE. To understand the reason for such a high solubility of these 3d transition metals, we have performed first-principles molecular dynamics calculations and analyzed the pair-correlation functions, electronic densities of states, and Bader charges and volumes of the 3d transition metals dissolved in the liquid LBE as impurities. The calculations show that the 4s and 3d orbitals of the 3d impurity atoms largely interact with the 6p band of the LBE, which generates bonding orbitals. We suggest that the high stability of 3d metals in the liquid LBE is caused by the interactions of the 4s and 3d orbitals with the 6p band. Spin polarization is induced by V, Cr, Mn, Fe and Co impurity atoms in a similar manner to the Slater-Pauling curve of solid transition metals, which exhibits a downward shift in the atomic number by approximately two. Based on the degree of spin polarization and the shifted trend of the Slater-Pauling curve, we suggest that Ni exhibits a higher solubility than Cr and Fe because of the differences in their interaction strengths between their 3d orbitals and the 6p band. In addition, the 4s and 3d orbitals of the 3d impurity atoms were found to interact more favorably with the Bi 6p band than the Pb 6p band, which is consistent with the fact that liquid Bi is more corrosive to steels than is liquid Pb.