The anodic behaviour of two titanium cast alloys, obtained by fusion in a voltaic arc under argon atmosphere, was analyzed in aeratedaqueous solutions having different pH values. In all solutions the alloys, having nominal compositions Ti–50Zr at.% and Ti–13Zr–13Nb wt.%,displayed a valve-metal behaviour, owing to the formation of barrier-type oxide films. Passive films, grown potentiodynamically up to about9 V, were investigated by photocurrent spectroscopy (PCS) and electrochemical impedance spectroscopy (EIS). These passive layers showphotoactivity under anodic polarizations, with optical gaps close to 3.55 and 3.25 eV for the binary and the ternary alloy, respectively,independent of the anodizing electrolyte. Films grown on the binary alloy present insulating behaviour and anodic impedance spectra with onetime constant; this was interpreted in terms of a single-layer mixed Ti–Zr oxide enriched in Ti with respect to the alloy composition. Also forthe ternary alloy the results are consistent with the formation, upon anodization, of Ti–Nb–Zr mixed oxide films, but they display n-typesemiconducting behaviour, owing to their poor content of ZrO2 groups.
|Numero di pagine||14|
|Stato di pubblicazione||Published - 2004|
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