DFT studies of the effect of sulfur impurities on the structural, electronic and magnetic properties of iron (100).

Understanding the factors influencing the surface properties and corrosion tendencies of iron is a step toward corrosion insights and prevention. The effect of sulfur impurities on the surface properties of Fe (100) has been investigated at monolayer (1 ML) concentration. The structural, electronic, optical and magnetic properties of the Fe (100) surface have been investigated using the spin polarized-density functional theory method. The results indicate that at 1 ML, sulfur migration and grain boundary formation on iron is most favored. However, iron absorption and deposition are both thermodynamically favored. S at the sub-surface causing pitting due to the preferred lower coordination of sulfur compared to iron at the subsurface sites. This phenomenon could explain the exposure of more bulk iron atoms and pit corrosion experienced as a result of the presence of sulfur in steel. Sulfur is seen to act as a corrosion promoter (an electronegative species) as it lowers the work function of Fe (100), making the surface more electropositive. S lowers the magnetic properties of iron, providing an antimagnetic spin to iron. The projected density of states plot shows the localization of electronic states below the Fermi level and the lowering of the conductivity of iron. The magnetic effect of iron is reduced in the presence of sulfur impurity as well as its corrosion resistance which is undesirable. Trapping S, however, at the bulk site under 4 coordination constraints, where sulfur is immobile could help reduce corrosion of the (100), the predominant face of iron crystals, as the work function of Fe (100) increases by 0.58 eV. [ABSTRACT FROM AUTHOR]