Characterization of surfaces of amorphous NiFeP alloys

Abstract

The surface of amorphous and crystallized Ni 80− x Fe x P 20 alloys containing 0–80 at.% iron was studied in comparison with crystalline NiFe alloys by X-ray photoelectron spectroscopy after mechanical polishing in cyclohexane at room temperature and after heat treatment of the mechanically polished specimen in hydrogen gas of 1 MPa at 500 K. The binding energies of P 2p, Fe 2 p 3 2 and Ni 2 p 3 2 electrons of the metallic state in the alloys changed linearly with the ratio of the atomic fraction of metallic iron to the sum of atomic fractions of metallic iron and nickel in the alloy surface immediately under the surface film. In the NiFeP alloys, the electron transfer from Fe and Ni to P occurred since the P 2p electron binding energy in the alloys smaller than in red phosphorus and the Ni 2 p 3 2 and Fe 2 p 3 2 electron binding energies in the alloys are larger than those in nickel and iron metals. During polishing in cyclohexane, the iron-concentrated surface films were formed on both the amorphous and crystalline alloys, and the contents of anionic species in the surface films changed with compositions of both alloys. These surfaces were hydrogen-reduced and then shortly exposed to air. The surface films formed on the hydrogen-reduced amorphous alloys contained exclusively iron ions as cations and a large amount of OH − and some phosphate as anions, and were significantly thicker indicating a high reactivity of the hydrogen-reduced amorphous alloy surface, while the hydrogen-reduced crystalline NiFe alloys were covered by thin, protective surface films.