Ti-Ni形状記憶合金の表面皮膜のエリプソメトリーによる解析

抄録

In order to investigate the relationship between corrosion resistance and the nature of surface films on a Ti-Ni shape memory alloy in aqueous solutions, ellipsometric measurements have been performed in-situ on the alloy under anodic polarization in 0.5 kmol·m⁻³ H₂SO₄ and 3.0 mass%NaCl at 293 and 363 K. The chemical composition of these films was also analyzed by ESCA.
From the ellipsometric measurements, it was found that both the refractive index and the extinction coefficient of optical constant for the films formed in 0.5 kmol·m⁻³ H₂SO₄ at 363 K were smaller than those formed at 293 K, whereas the films formed at 363 K were considerably thicker than those formed at 293 K. In the case of 3.0 mass%NaCl, both the refractive index and the extinction coefficient of optical constant for the films formed at 363 K were also smaller than those formed at 293 K. The thickness of films was also larger at 363 K. After pitting corrosion occurred in the solution, the optical constant became smaller and the thickness increased abruptly.
The cationic fraction of Ni²⁺ of the films formed at 363 K in 0.5 kmol·m⁻³ H₂SO₄ was larger than that of films formed at 293 K at any potentials examined. The changes in the optical constant and the protective nature of the films with temperature were closely related to that in the cationic fraction of Ni²⁺ of the films.