Abstract
Sputter-deposited amorphous Cr-Nb and Cr-Ta alloys possessing higher corrosion resistance than that of alloy constituents were spontaneously passivated in 12 M HCl solution. Their open circuit potentials were higher than those of alloy constituents in 12 M HCl solution, and the passive current densities of amorphous Cr-Nb and Cr-Ta alloys were lower than those of niobium and tantalum metals, respectively, and decreased with increasing chromium concentration. XPS analysis revealed that air-formed films and passive films on the amorphous Cr-Nb and Cr-Ta alloys were composed of double oxyhydroxides of chromium and niobium or tantalum. The higher corrosion resistance of the amorphous Cr-Nb and Cr-Ta alloys in comparison with their constituent elements is attributed not only to the uniformity and homogeneity of the amorphous alloys but also to the formation of the double oxyhydroxide film of chromium and niobium or tantalum, both of which act synergistically in improving the corrosion resistance, partly because the double oxyhydroxide films possess high activity for cathodic oxygen reduction with a consequent ennoblement of the open circuit potential.
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