PASSIVITY OF AMORPHOUS AND CRYSTALLINE NI-TI ALLOYS

In dilute sulphuric solution, amorphous and crystalline Ni-Ti alloys with titanium content greater-than-or-equal-to 40 at.% had almost the same anodic behavior and photoelectrochemical properties in so far as they had the same composition, i.e. they were spontaneously passivated and showed a positive photocurrent. Band-gap energies of the surface film on amorphous and crystalline Ni-Ti alloys were all about 3.3 eV although they were dependent on the applied potential. The thickness of the surface film formed on amorphous and crystalline Ni-40Ti alloys was, in the range of several nanometers, within the potential region examined. It increased with potential. In the surface film Ti4+ ions were concentrated relative to the bulk alloy composition.