Nanosurfaces

Anodizing

Anodic oxidation treatments applied on titanium and its alloys to increase the thickness of the oxide film


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Titanium owes its corrosion resistance to the presence of a protective titanium oxide film, a few nanometres thick, whose thickness, chemical composition and crystal structure can be modified so as to obtain peculiar properties.
The electrochemical technique named anodic oxidation, or anodizing (1), allows to increase the thickness of the oxide layer from few nanometres to hundreds of nanometres, which also enhances the resistance of titanium itself to corrosion and atmospheric agents.
By increasing the film thickness, optical interference phenomena arising from light diffraction at the metal-oxide interface (2) establish, causing the generation of interference colors (3) on titanium whose hue depend on the oxide thickness, which in turn is determined by the anodizing feeding voltage (4).
Since the oxide thickness is not affected by the exposure to “natural” environments, the obtained interference colours are stable in time (5).
This treatment, which was firstly developed by Professor Pietro Pedeferri to produce artworks (not reproducible unique works)(6-10), was also exploited to revisit some design objects (10-12)(Rexite © pencilholder).

Anodic Spark Deposition

High voltage anodizing treatment of titanium and its alloys aimed at modifying the oxide film composition and properties


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Anodic Spark Deposition is a particular anodizing technique which is realized on titanium and its alloys by imposing high feeding voltages (1-2).
The oxide layer generated by anodizing has insulating properties; if the applied tension is raised to high values, the film starts to crack and electric microarcs strike on the surface, which cause the local melting and subsequent quenching of the oxide (3).
This mechanism allows to incorporate into the film chemical species belonging to the anodizing electrolyte, which could possibly improve the corrosion behaviour of the material, or permit a slow release of substances (4-5).
Once the Anodic Spark Deposition treatment is completed, it is possible to perform mechanical treatments (rolling, shot-peening, sifting) in order to obtain a more compact oxide, hence enhancing its corrosion behaviour and decreasing its roughness to extremely low values. This determines an increase in the mechanical properties of treated components due to improved resistance to fatigue, grip, wear and fretting corrosion (6).

Chemical attacks

Electropolishing of stainless steels and chemical attack of stainless steels and titanium



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Chemical and electrochemical treatments applied to metals (in particular, to stainless steels and titanium) are extremely interesting techniques for metallic components surface finishing.
In fact, these treatments lead to the removal of contaminating agents from the metal surface (environmental pollution, oils and residuals due to metal working), and at the same time assure optimum surface finishing (by determining a strictly programmable increase or decrease in surface roughness) and surface cleanliness; furthermore, if the component is subsequently sterilized and packed in clean rooms, the sterility requirements for biomedical applications are met.
While electropolishing generates uniform, mirror-like surfaces, the application of treatments involving chemical attacks on properly masked surfaces can create different surface morphologies and textures depending on the specific application of the component, for example, osseointegrated dental implants and semi-noble jewellery (1-5).
NanoSurfaces has developed a deep know-how allowing the realization of both standard and customized treatments, depending on the clients’ needs.

Sol-gel

Production of "sol" solutions to deposit nanostructured films, focused on titanium dioxide films showing photocatalytic and self-cleaning properties

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Sol-gel technology is based on the use of solutions of metallorganic or inorganic precursors, which are driven through hydrolysis and condensation processes (1) to give colloidal solutions (sol) containing oxides nanoparticles (TiO2, SiO2, etc): under proper conditions, the sol condenses into a gel phase, from which massive ceramics, nanoparticles, nanofibres or thin films can be obtained (2-3).
In particular, once the sol is produced (4-8), it can be easily deposited almost on any substrate (9) so as to obtain nanostructured films by immersion (10), spraying (11), spin-coating (12) or padding (13) for textiles.
By modifying the synthesis conditions, films can be functionalized with several properties, such as photocatalytic activity (14) for outdoor (15) and indoor (16-17) purification, self-cleaning attitude for self-cleaning facades and glass walls (18-21), antibacterial activity (22-23) for hospital surfaces and equipments, as well as for toys.
In the textile field, suitably formulated sols can lead to the achievement of noticeable materials, such as waterproof, stain-proof and oil-proof tissues, or surfaces presenting hydrophilic or hydrophobic characteristics, antibacterial activity, sweat absorption, slow fragrances or drugs release, insect repellents, UV filters (24-26).