The Anodic Passivity of the Sputter-Deposited W-Ti Alloys in Hydrochloric Solutions
AbstractA beneficial effect of titanium in the anodic passivity of the sputter-deposited amorphous or nanocrystalline W-Ti alloys has been studied after immersion or potentiostatic polarization for 1 h in hydrochloric acids at 30°C, open to air by electrochemical measurements and X-ray photoelectron spectroscopy (XPS) analysis.The protectiveness of the anodic passive films formed on the W-Ti alloys is better than that of tungsten. Titanium element acts synegistically with tungsten in enhancing the anodic passivity of the W-Ti alloys. XPS analysis shows that the formation of new anodic passive double oxyhydroxide films composed of W6+ and Ti4+ ions are responsible for enhancing anodic passivity of the W-Ti alloys. These films have higher protectiveness and stability than those of anodic passive oxyhydroxide films of alloying elements.The anodic polarization at about 0.4V to 1.2 V (SCE) leads to thickening of the anodic passive films for the W-Ti alloys in hydrochloric acids, mainly due to an increase in hexavalent tungsten in addition to the cations of the alloying elements.
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