In situ ESTM and ESTS studies of the nanostructure and energetic properties of Fe-20% Cr-40% Ni and Fe-20% Cr-70% Ni alloy surfaces

Abstract

Fe-20% Cr-40% Ni and Fe-20% Cr-70% Ni alloys are studied in air and in 0.01 N HCl and 0.1 N H₂SO₄ solutions at the controlled potentials of the specimen and needle using in situ techniques of electrochemical scanning tunneling microscopy (ESTM) and electrochemical scanning tunneling spectroscopy (ESTS). The changes in the potential of Fe-20% Cr-40% Ni alloy specimen fall in ranges of −0.3 to 1.1 V and 0–0.3 V (N.H.E.) in 0.01 N HCl and 0.1 N H₂SO₄, respectively, and the changes in the potential of Fe-20% Cr-70% Ni specimen, in ranges of 0.09–0.94 V and −0.1 to 0.5 V in 0.01 N HCl and 0.1 N H₂SO₄, respectively. Local spectral dependences of the tunnel current on the tunnel voltage are obtained and processed and the coefficients that characterize the local electrophysical properties of the surfaces are calculated on their basis. It is found that, in the studied acid solutions at the controlled potential, the surfaces are more energetically homogeneous than in air, where a substantially larger dispersion of the properties is observed. It is concluded that the energetic characteristics of separate surface sites of these alloys are determined on the atomic scale by the mutual effects of the neighboring atoms involved in its composition, i.e., by the matrix effect, which was discovered previously in the case of Kh18N10T stainless steel [1].