Breakdown of passivity in Al-Ta and Al-Nb amorphous alloys

Artur Jaśkiewicz 3Maria Janik-Czachor 1Piotr Kędzierzawski 1Zbigniew Werner 2

1. Polish Academy of Sciences, Institute of Physical Chemistry, Kasprzaka 44/52, Warszawa 01-224, Poland
2. Andrzej Sołtan Institute for Nuclear Studies (IPJ), Świerk, Otwock-Świerk 05-400, Poland
3. Warsaw University of Technology, Faculty of Materials Science and Engineering (InMat), Wołoska 141, Warszawa 02-507, Poland

Abstract

The effect of Cl (minus) ions (0-1M NaCl) on the anodic behaviour of two series of sputter-deposited Al-Ta (11-46 at %) and Al-Nb (13-46 at %) amorphous alloys was investigated in neutral electrolytes by using electrochemical and in-situ microscopic methods.
The samples were characterized by AES; a thin alumina film was found to cover the surface of the substrate, whereas transition metal was not detected therein. In solutions containing Cl (minus) the alloys broke down at and above the pit nucleation potential Enp. The alloys exhibited a stable passivity within a much wider (Δ E> 1V) potential range than crystalline Al. In-situ microscopic investigations revealed that for Al-Ta and Al-Nb amorphous alloys the local current density within the pits was ~106 higher than the c.d. from the remaining passive surface. The results are compared with those for Al-Mo and Al-W alloys and the mechanism of restrained passivity breakdown is discussed.

This work was supported by the State Committee for Scientific Research under grant
7T08C0 1220

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Presentation: poster at E-MRS Fall Meeting 2003, Symposium B, by Artur Jaśkiewicz
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-08-28 13:38
Revised:   2009-06-08 12:55
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