ELECTRONIC-STRUCTURE CALCULATIONAL STUDIES ON CORROSION OF STAINLESS-STEEL IN LIQUID-METAL

The mechanism of element-selective corrosion of austenitic stainless steel in liquid sodium has been investigated using the molecular orbital method. Electronic states were calculated for the elements Cr and Ni substituted for an atom at the Fe(001) surface. The energy differences between the 3d orbitals for Fe, Cr and Ni cause charge transfers from Cr to Fe and from Fe to Ni. These charge transfers indicate that the charged element is apt to be attacked selectively by an oppositely charged atom. Following this, a calculation was carried out for an oxygen impurity associated with an Na atom on top of Cr, and for an Na atom coupled with an O atom on top of Ni at the Fe(001) surface exposed to sodium. The result indicates that an O anion will bring about selective Cr release, and that a positively charged Na will cause Ni to transfer selectively into sodium.