Titanium dioxide (TiO 2 ) coatings have potential applications in biomedical implants or as photo-catalytic functional systems. Cold spraying is a well-established method for metal on metal coatings. In cold spraying, the required heat for bonding is provided by plastic deformation of the impacting ductile particles. In contrast, few authors have investigated the impact phenomena and layer formation process for spraying brittle ceramic materials on ductile metal surfaces. In this study, the formation of TiO 2 coatings on aluminum, copper, titanium, and steel substrates was investigated by SEM, TEM, XRD, and Raman spectroscopy. The results show that the deposition efficiency depends on spray temperature, powder properties, and in particular on substrate ductility, even for impact of ceramic particles during a second pass over already coated areas. Ceramic particles bond to metallic substrates showing evidence of shear instabilities. High-resolution TEM images revealed no crystal growth or phase transitions at the ceramic/metal interfaces.
Electronic
properties and charge transfer processes were studied
in an n-Si(n++)/TiO2(ALD) system at an amorphous
TiO2/anatase transition by transient surface photovoltage
spectroscopy at constant photon flux. The TiO2 layers were
deposited by atomic layer deposition (ALD) onto highly doped silicon
(c-Si(n++)), and the phase composition of the TiO2 layers changed with increasing thickness from amorphous to the anatase
polymorph as anatase crystallites started to grow at the surface.
Depending on phase composition, the band gap of TiO2 correlated
with the characteristic energy of exponential tails. In most cases,
photogenerated electrons were separated toward the back contact. For
photogeneration in c-Si(n++), electron back transfer was
limited by Auger recombination with holes in the surface space charge
region of c-Si(n++), and by electron transfer across the
interface, either via exponentially distributed states near the conduction
band edge of amorphous TiO2 or via distance-dependent recombination
with holes trapped in anatase. For photogeneration in TiO2, electron back transfer was limited by trapping in TiO2. Under strong light absorption in amorphous TiO2 with
anatase crystallites on top, electrons were preferentially separated
toward the TiO2 surface.
Films prepared by cold spray have potential applications as photoanodes in electrochemical water splitting and waste water purification. In the present study cold sprayed photoelectrodes produced with WO 3 (active under visible light illumination) and TiO 2 (active under UV illumination) on titanium metal substrates were investigated as photoanodes for the oxidation of water and methanol, respectively. Methanol was chosen as organic model pollutant in acidic electrolytes. Main advantages of the cold sprayed photoelectrodes are the improved metal-semiconductor junctions and the superior mechanical stability.Additionally, the cold spray method can be utilized as a large-scale electrode fabrication technique for photoelectrochemical applications. Incident photon to current efficiencies reveal that cold sprayed TiO 2 / WO 3 photoanodes exhibit the best photoelectrochemical properties with regard to the water and methanol oxidation reactions in comparison with the benchmark photocatalyst Aeroxide TiO 2 P25 due to more efficient harvesting of the total solar light irradiation related to their smaller band gap energies.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.