Abstract
In this study, we explored the feasibility of WO3 surface layer formation on electrodeposited Al–W alloy coatings by selective dissolution and heat treatment, with the aim of providing corrosion-resistant Al–W alloy coatings with photocatalytic self-cleaning properties under visible light illumination. The selective dissolution of Al and oxidation of residual W was carried out by immersing Al–W alloy films in an aqueous solution of nitric acid. A nanostructured H2WO4·H2O surface layer was formed on the alloy film by this process. The H2WO4·H2O layer was dehydrated to WO3 by heat treatment, yielding a multilayered WO3/Al–W alloy film with an approximately 300 nm thick WO3 layer. The WO3/Al–W alloy film exhibited photocatalytic self-cleaning, as demonstrated by the photodegradation of stearic acid and methylene blue. We also confirmed that selective dissolution and heat treatment did not significantly diminish the corrosion resistance of the Al–W alloy films.
Highlights
Aluminum and its alloys are highly resistant to corrosion and oxidation
The typical energy-dispersive X-ray spectroscopy (EDX) spectrum of an electrodeposited Al–W alloy film in Fig. 1a indicates that only Al and W are present in the film
A photocatalytic WO3 surface layer was formed on electrodeposited Al–W alloy films by selective dissolution and heat treatment
Summary
Aluminum and its alloys are highly resistant to corrosion and oxidation. They have attracted attention as corrosion-protective coatings for reactive materials, such as Mg alloys and steels[1,2,3]. Self-cleaning coatings have been developed extensively, owing to the practical advantages of energy savings and environmental compatibility[20,21,22,23] Such coatings can be obtained by forming a hydrophilic surface layer with a photocatalytic material, such as titanium dioxide (TiO2), which catalyzes the photodecomposition of adsorbed organic compounds[20,21,23,24,25,26]. We describe a new process for imparting corrosion-resistant Al–W alloy films with self-cleaning properties through the formation of a WO3 surface layer. This process is comprised of a chemical dissolution step and heat treatment. Subsequent heat treatment in air converts the W-enriched surface layer to photocatalytic WO3 Through this process, a corrosion-resistant Al–W coating with self-cleaning ability under visible light illumination is obtained. The corrosion resistance of the WO3/Al–W alloy films was confirmed
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