Galvanoluminescence of oxide films during the anodization of titanium (original) (raw)
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ChemInform, 2010
The anodic growth of oxide films on titanium in aqueous electrolytes (phosphoric acid, sodium dihydrogen phosphate and disodium hydrogen phosphate) as well as mixed solutions of aqueous electrolyte with dieth~lene glyco~in the~resence ofUV radiatioqs has been studied. The results indicate higher rates of growth of titanium oxide film In the presence ofUV radiations than those obtained in the absence of radiation. The constants A and B of Guntherschulze-Betz equation. Tafel slopes and half jump distances have been evaluated and their dependence on the nature of composition of electrolyte has been discussed. The breakdown voltages for titanium oxide films in contact with aqueous and mixed solutions have also been obtained and the values are lower in the presence of UV radiation than those in their absence. Breakdown voltage has been found to depend on nature and composition of the electrolyte.
Anodic Titanium Oxide Films: Photoelectrochemical and Tribocorrosion Behavior
Journal of Nanoelectronics and Optoelectronics, 2014
Titanium oxide films are fabricated by Ti anodization in orthophosphoric acid-ammonium fluoride electrolytes. On the mechanically polished semi-bright Ti substrates the continuous TiO 2 films are formed, whereas ordered nanoporosity is formed on the mirror-like surface of Ti substrate at temperatures of 10-20 C in the H 3 PO 4 electrolyte with NH 4 F. The photocurrents and photopotentials are affected by the amount of fluorine in the electrolyte and consequently in the deposit. Tribocorrosion tests were performed in a neutral solution, and changes of open-circuit potential (OCP) as well as electrochemical impedance spectra were recorded with/without 0.4 N load. The rapid changes of OCP can be explained by the passive film abrasion, when oxide film becomes damaged and bare Ti surface is exposed. The wear loss depends on the NH 4 F concentration in the solution used for TiO 2 films fabrication. TiO 2 films destroyed during sliding tend to restore within 300-400 s after unloading.
Effect of Thermal and Mechanical Treatments on the Cathodoluminescence of Tin and Titanium Oxides
MRS Proceedings, 2002
ABSTRACTThe luminescence of titanium oxide and tin oxide has been investigated by cathodoluminescence in the SEM, as a function of the structural changes induced by thermal treatments. The evolution of the luminescence of TiO2 rutile, anatase and mixture phase with the annealing temperature is related to the process of thermal induced grain texture and to transition of metastables phases to the stable rutile. The emission band is peaked at 480 nm for the composite phase and at 580 nm for anatase and rutile phases respectively. A broad band in the 520–560 nm region is present in the spectra of both anatase and rutile phase. Thermal annealing leads to a red shift of the luminescence emission, with the emission band peaked at around 820 nm. In sintered tin oxide the main emission bands appear centered at about 480 nm and 630 nm. The intensity of these bands increases with annealing temperature up to 1200°, whereas for samples annealed at 1500° these emissions are quenched. Mechanical b...
Corrosion Science, 2001
Changes in electronic properties of the anodic oxide ®lms formed on titanium in weakly alkaline borate solution were investigated by using impedance measurements. Analysis of the cyclic voltammogram and capacitance during the cyclic potential sweep suggested that the outer part of the anodic oxide ®lm was converted from an n-type semiconductor to a dielectric above 3 V, and converted to an n-type semiconductor again below 0.5 V. This phenomenon seems to be related to the dissociation of bound water in the ®lm due to very high electric ®eld applied to the oxide ®lm. Formation of OH À in the ®lm may compensate the positive charge of the donor states and form Ti peroxides such as TiO 3. These compounds are reduced below 0.5 V to show a characteristic cathode current peak.
Anodic growth of titanium oxide: Electrochemical behaviour and morphological evolution
Electrochimica Acta, 2012
The mechanism of growth of anodic titanium oxide in sulphuric acid has been investigated by potentiostatic and potentiodynamic anodizing, electrochemical impedance spectroscopy and transmission electron microscopy. It was found that most of the charge passed during growth is consumed in oxygen evolution at the oxide-solution interface and the measured current relates to the electronic conduction properties of the oxide. Further, it was confirmed that an amorphous to crystalline transition takes place during potentiodynamic growth, and the transition triggers the additional generation of oxygen bubbles that occurs within the oxide. Depending on the growth conditions, the oxygen bubbles can rupture with local re-growth of the film then occurring.
In the present work we investigate compact anodic oxides formed on titanium by a broad range of anodizing parameters (electrolyte, applied voltage, substrate pre-treatment) and their influence on the performance of such oxides in photocurrent response and photocatalytic properties (photodegradation of AO7). In general, crystallinity and ion inclusion from the electrolyte are crucial. As-grown compact layers of partial crystallinity show increased efficiencies in both applications; interestingly, phosphate ions have a detrimental effect, whereas sulfate ions do not. After thermal annealing (crystallization) the photoresponse significantly increases: except for a crystallization of the anodic layer, annealing causes a rutile oxide layer growth at the oxide/metal interface - this is found to additionally affect the photoresponse. Results overall demonstrate that higher anodization voltage, exclusion of phosphates from the electrolyte, substrate pre-treatment and annealing are of major importance for achieving an enhanced photoresponse on compact anodic layers. © The Author(s) 2015. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse, please email: oa@electrochem.org. [DOI: 10.1149/2.0891602jes] All rights reserved.
1988
The data obtained during the growth of anodic oxide films on tantalum indicate higher values of rates of growth, constant A (of Guntherschulze-8etz equation) and Tafel slopes in the presence of UV radiations than those in the absence of radiations. However, the values of constant B (of Guntherscbultze-Betz equation), haIfjump distances and breakdown voltages are lower in the presence of UV light. Faster rate in the presence of UV is probably due to increased number of mobile ions per unit volume and decreased width of potential energy barrier. Stimulated ionic movements due to UV radiations cause breakdown of films at lower voltages. Heat treatment of the oxide films in air makes these more conducting. This effect depends on the time period and temperature of heat treatment but is independent of film thickness and nature of electrolyte. The conductivity patterns before and after heating show similar trends and are of two types: One is associated with high conductance and lower rate of change of capacitance with increase in temperature and the other is associated with low conductances and changes cllpacitance more rapidly with increase in temperature. The hypothetical break temperature is independent of the nature of electrolyte or treatment.
The Photoelectrochemical Response of Various Surface Morphologies of Titanium Anodic Oxide Films
2013
Anodic oxide films of Titanium (Ti) with different surface morphologies were investigated by controlling the content of NH4F in EG electrolyte. When Ti was anodised in the low content of NH4F (1 wt%), a thin TiO2 compact oxide layer was formed. However, TiO2 nanoporous structure appeared on the surface of Ti when 3 wt% of NH4F was added. When NH4F was further increased to 5 wt%, a self-ordered nanotubular oxide structure was observed. TiO2 nanotubular structure exhibited higher photocurrent density (~0.45 mA cm -2 ) as compared to the nanoporous and compact oxide layer.
Surface Engineering and Applied Electrochemistry, 2013
It is shown that films of titanium dioxide obtained by anodic plasma electrolytic processing of commercial titanium in an aqueous solution of ammonium chloride are photosensitive. Incident photon to charge carrier efficiency (IPCE) in the near ultraviolet (366 nm) reached 8.5%. Magnitude of the photocur rent generated by the films obtained under optimum processing conditions decreases no more than 20% at the transition from the ultraviolet to the mixed light.
A photoelectrochemical and ac impedance study of anodic titanium oxide films
Electrochimica Acta, 1998
ÐThe electrochemical behavior of sulphuric acid anodised titanium prepared galvanostatically under high ®eld conditions over a wide range of maximum potentials (V max) was examined using photoelectrochemistry (PEC) and ac impedance spectroscopy (EIS). Film structure and morphology were examined by transmission electron microscopy (TEM). The variation in reciprocal capacitance against V max obtained from EIS was evaluated using a constant phase element model. For V max = 0±10 V a straight line relationship was observed, enabling evaluation in terms of a parallel plate capacitor. This was followed by a region of decreasing reciprocal capacitance, indicating a substantial change in the nature of the material. Finally a slow rise occurred beyond 30 V. Large changes in the band structure of the anodic oxide were observed by PEC near the optical band edge for 0±10 V and in the sub-band gap region for 10±20 V. A defective TiO 2 structure with impurity bands located deeply inside the band gap was still observed for 60 V and 84 V, where microcrystals of anatase are present. Strong correlation between the reciprocal capacitance, optical band gap, sub-band gap photoresponse and changes in crystallinity and degree of order within the anodic ®lms were established.