DC Anodization Research Articles

A new understanding on titanium coloration-variation of external stimuli and in-depth mechanism analysis

Surface coloring technology plays a very unique role in the diversification of Ti applications. We report our new findings using AC polarization to fabricate chromatic passive films on Ti surface. Compared to passivation films formed using DC anodization, brighter and more uniform colors could be generated in a controlled manner by simply varying the waveform of AC polarization. The colored films fabricated by AC polarization were very dense without visible cracks or defects. DC anodization, AC sine polarization, and AC square polarization exhibited high light reflectivity in the wavelength range of 380–450 nm, 500–650 nm, and 400–500 nm, respectively. The composition distribution and formation process of colored films were analyzed in depth, which enabled our further understanding of the electrochemical coloration mechanism on Ti surface. The thickness of DC anodization, AC sine polarization, and AC square polarization were 161 nm, 203 nm, and 165 nm, which corresponded to the colors of oxford blue, pale yellow, and light blue, respectively. In addition, the corrosion resistance measurements further revealed that the films with lower surface roughness prepared by AC polarization presented great protective effect on the Ti matrix.

Fabrication and characterization of transparent Cr-decorated TiO2 nanoporous electrode for enhanced photo-electrocatalytic performance

A Cr-decorated TiO2 nanoporous transparent electrode was fabricated by DC sputtering, anodization, and thermal evaporation methods, respectively. Ti films were deposited on fluorine-doped tin oxide (FTO) coated glass and anodized to obtain a transparent TiO2 nanoporous film (TN). The fabricated electrodes were characterized using a field emission scanning electron microscope (FESEM), atomic force microscope (AFM) and X-Ray diffraction (XRD). Photoelectrochemical activity of prepared films was investigated by photo-electrocatalytic degradation of RhB dye under constant voltage and UVA light irradiation. The Cr-decorated TiO2 nanoporous film (CTN) served as an electrode and exhibited better photo-electrocatalytic performance than a TN electrode. Results show that Cr decoration increased photoelectrochemical activity significantly due to more efficient charge separation and lower recombination rate.

Surface characterization of nanoporous aluminium oxide films synthesized by single-step DC and AC anodization

Nanoporous alumina films were synthesized on commercial grade aluminum substrates using single-step anodization technique in 0.3M phosphoric acid at room temperature. Effect of applied voltage (100–130V) on surface characteristics of anodized aluminum oxide (AAO) film was investigated. Surface topography parameters and regularity ratio of nanopores arrangement were characterized using power spectral density (PSD) and fast Fourier transform (FFT) profiles. While DC anodization suffered from filament-like cavities at 130V owing to thermally enhanced dissolution of oxide, AC anodization produced localized flower-like morphology for all the applied voltages. The intensity of localized flower-like morphology was increased monotonically with applied voltage. Evolution of flower-like morphology was discussed on the basis of Pashchanka-Schneider model.

Synthesis of Aluminum-Doped TiO<sub>2</sub> Nanotubes by Anodization Method

We report the synthesis of Al-doped TiO2 nanotubes (Al-TNT) by DC anodization method at 50 volts. The method is simple, cost effective, environmentally safe and the samples produced are of good quality. The electrolytesolution was composed of ethylene glycol (EG), ammonium fluoride (0.3% wt NH4F), deionized water (2% vol H2O) and varying molar masses of aluminum nitrate - Al (NO3)3. The samples were analyzed XRD before and after annealing at 450 °C for 2 hours. The surface morphology and the elemental analysis of the annealed samples were characterized by SEM and ED-XRF respectively. The results show that phase transformation only occur after annealing. And that the surface organization, uniformity and structure are influenced by the concentration of the dopant element.

Synthesis of TiO<sub>2</sub> Nanotubes and the Effects of Deionized Water on their Surface Morphology and Microstructure

Nanotubes of TiO2 have been synthesized on titanium metal by DC anodization at 50 V in an EG/NH4F/D.I. H2O electrolyte. The anodization apparatus which uses a platinum cathode is unique and designed to allow only for a single-face anodization. The influence of deionized water (D.I. H2O) on the surface morphology of the nanotubes was investigated using the scanning electron microscope (SEM), while the microstructure before and after calcination was studied using X-ray diffraction technique (XRD). Results show that the surface density and uniformity of the TiO2 nanotube arrays varies with the percentage of D.I. H2O in the electrolyte. The best result was obtained at 6% vol D.I. H2O after calcination. This result is useful since, the surface morphology and microstructure play a vital role in the performance of TiO2 nanotubes in various applications.

Fabrication of thick nanoporous oxide films on stainless steel via DC anodization and subsequent biofunctionalization

Abstract Remarkably thick nanoporous anodic films have been formed through simple DC anodization by adding hydrogen peroxide as an oxidant to a sulfuric acid electrolyte. This result was not possible when using the previously reported pulsed polarization technique. While this anodic film's growth was significantly promoted by DC anodization, having only sulfuric acid resulted in the preferential anodic dissolution of the substrate material. Transmission electron microscopy of the anodic film's cross-section confirmed that the film has numerous fine pores with a size distribution ranging from 5 nm to 20 nm. Energy-dispersive x-ray spectroscopic analysis of the anodized specimens revealed that the films were composed of a complex chromium-rich oxide. In addition, coating stainless steel with thick nanoporous oxide films through anodization in the optimized conditions confirmed that it could act as a highly suitable host for synthetic hydroxyapatite coating, resulting in the enhanced growth of natural apatite in a simulated body environment. The enhancement of the apatite deposition is attributed to the availability of the empty pore volume in the thick anodic porous films, formed on stainless steel surfaces. These findings suggest a novel functionality to stainless-steel surface modification.

The Effect of Ultrasonic Treatment on the Morphology and Microstructure of TiO<sub>2 </sub>Nanotubes Prepared by DC Anodization

This paper presents the effect of ultrasonic treatment on the morphology and microstructure of TiO2 nanotubes prepared by DC anodization method. The TiO2 nanotubes were grown by one-face anodization at room temperature on titanium sheets of 0.25 mm thickness and 99.7% purity. The electrolyte was composed of ethylene glycol (EG), ammonium fluoride (0.3% wt NH4F) and deionized water (2% V H2O). A constant DC voltage of 50 V was applied during anodization for 2 hours. The samples were ultrasonically cleansed in ethanol for different extended periods of time: 0, 10, 30 and 50 minutes respectively. The samples were annealed at 450 °C for 2 hours. The surface morphology and microstructure of the TiO2 nanotubes formed were studied by XRD and SEM. The best result was obtained when the sampleswere ultrasonicated for 30 minutes.

The Control of Nanotube Morphology Using Various Factors for Dental Implant.

The purpose of this study was to investigate the control of nanotube morphology using various factors for dental implant. TiO2 nanotube formation on biomedical grade α+β type Ti-6Al-4V alloy was investigated using anodization technique as a function of applied DC potential (10 V to 30 V and 30 V to 10 V) and anodization time for 60 min in 1 M H3PO4 with small additions of NaF (0.5 wt.%, and 0.8 wt.%). The microstructure and phase characteristics of surface were examined by optical microscopy, field emission scanning electron microscopy and X-ray diffraction. Also, in order to observe the biocompatibility and surface roughness, wettability and atomic force microscopy of alloy was measured.

Rugated porous Fe3O4 thin films as stable binder-free anode materials for lithium ion batteries

Rugated porous Fe3O4 thin films were synthesized by a facile multi-pulse electrochemical anodization method. The fabricated Fe3O4 films are directly grown on Fe, featuring nano-channels with periodically rugated channel walls running throughout the film thickness direction. Electrochemical measurements show that the as-prepared Fe3O4 films readily serve as high-performance anode materials for lithium ion batteries with a specific capacity of 1100, 880 and 660 mA h g−1 at 0.1, 0.2, and 0.5 C, respectively, which compared favorably with the conventional straight-channel counterparts fabricated by DC anodization. Moreover, the cycling capability test of the novel electrode at 0.1 C for 100 cycles shows a steady charge/discharge platform, indicating a high cycling stability and structural robustness. The observed improvements of the rugated Fe3O4 films as lithium ion battery anode materials are attributed to their special periodic rugated nanostructures.

An electrochemical study on self-ordered nanoporous and nanotubular oxide on Ti–35Nb–5Ta–7Zr alloy for biomedical applications

Highly ordered nanoporous and nanotubular oxide layers were developed on low-rigidity β Ti–35Nb–5Ta–7Zr alloy by controlled DC anodization in electrolyte containing 1 M H 3PO 4 and 0.5 wt.% NaF at room temperature. The as-formed and crystallized nanotubes were characterized by electron microscopy, energy-dispersive X-ray spectrometry and X-ray diffraction. The electrochemical passivation behavior of the nanoporous and nanotubular oxide surfaces were investigated in Ringer’s solution at 37 ± 1 °C employing a potentiodynamic polarization technique and impedance spectroscopy. The diameters of the as-formed nanotubes were in the range of 30–80 nm. The nanotubular surface exhibited passivation behavior similar to that of the nanoporous surface. However, the corrosion current density was considerably higher for the nanotubular alloy. The surface after nanotube formation seemed to favor an immediate and effective passivation. Electrochemical impedance spectra were simulated by equivalent circuits and the results were discussed with regard to biomedical applications.

Comparison of corrosion resistance and apatite-forming ability of NiTi treated by different low-temperature methods

Abstract A number of low-temperature soft methods recently attempted by the authors for preparing TiO2 coating on NiTi intermetallic are described. These methods include hydrothermal oxidation in water, sol–gel coating with steam post-treatment, low-voltage DC anodization in acetic acid, AC anodization in a calcium and phosphate containing medium, and electrodeposition. In all these methods, the temperature reached by the bulk of the substrate did not exceed 200 °C. The characteristics of the coatings acquired using various techniques are summarized. The increases in corrosion resistance for various samples in Hanks’ solution (a simulated body fluid commonly used to assess in vitro corrosion resistance) obtained from polarization study and electrochemical impedance spectroscopy are compared and discussed. The apatite-forming ability of the treated samples was also studied.

Pattern Formation in Nanoporous Titania Templates

We have carried out a systematic investigation into the formation of nanoscaled patterns in titania (TiO2) templates under dc anodization of Ti in HF acid. At lower acid concentrations (around 0.5 wt% HF) either pores or tubes form at the surface of anodized titanium foil. The pores or nanotubes are separated from the bottom Ti layer by a thin barrier layer of TiO2. The critical voltage where the transition from pores to tubes occurs has been determined. It is observed that the transition voltage shift towards higher voltages as acid concentration is increased, with pore formation disappearing altogether at high acid concentrations. We have also carried out a systematic investigation into the dependence of pore and tube parameters on the applied dc anodization voltage. Our results indicate that the barrier layer thickness, pore and tube length increase as a function of applied voltage.

Fabrication of head-flyable nanohole patterned media and dynamic write/read measurement with GMR head

A method to fabricate head-flyable alumina nanohole patterned media is reported. Alumina nanoholes are formed by DC anodization of Al layer (500 nm) with anodizing voltage of 25 V. The pore diameter is widened by dilute phosphoric acid in order for Co to fill easily into these holes by AC electrodeposition. Surface polishing of the media is done to smooth the surface and carbon is used as a protective coating layer which is lubricated and tape burnished to assure head flying. The write-read characteristics are measured by Guzik system with latest merge type magnetic head. Results show that detailed GMR readback signals show correlation with the nanohole array location.

Tin plating

Remarkably thick nanoporous anodic films have been formed through simple DC anodization by adding hydrogen peroxide as an oxidant to a sulfuric acid electrolyte. This result was not possible when using the previously reported pulsed polarization technique. While this anodic film's growth was significantly promoted by DC anodization, having only sulfuric acid resulted in the preferential anodic dissolution of the substrate material. Transmission electron microscopy of the anodic film's cross-section confirmed that the film has numerous fine pores with a size distribution ranging from 5 nm to 20 nm. Energy-dispersive x-ray spectroscopic analysis of the anodized specimens revealed that the films were composed of a complex chromium-rich oxide. In addition, coating stainless steel with thick nanoporous oxide films through anodization in the optimized conditions confirmed that it could act as a highly suitable host for synthetic hydroxyapatite coating, resulting in the enhanced growth of natural apatite in a simulated body environment. The enhancement of the apatite deposition is attributed to the availability of the empty pore volume in the thick anodic porous films, formed on stainless steel surfaces. These findings suggest a novel functionality to stainless-steel surface modification.

Electrolytic coloring of anodic aluminum for selective solar absorbing films: use of additives promoting color depth and rate

An optically black coating on aluminum substrate having improved solar absorption is disclosed along with an enhanced process for formation. The two-step electrolytic coloring process has been used. Porous anodic films have been formed by dc anodization of aluminum samples in 16% sulfuric acid. It is followed by black coloration via ac electrolysis in nickel sulfate solution. In this step, we have investigated the effect of chloride and magnesium as additives. Evaluation of the test samples has been carried out by spectral reflectance and nickel content measurements. Choride existance verifies two aspects: the promotion of the coloring process and higher black tones shades are attained. However, magnesium has a minor effect.

SnO 2:Sb dip coated films on anodized aluminum selective absorber plates

In this paper solar selective coatings have been prepared on aluminum substrates using a two phase eloxal technique. Porous anodic films were formed by dc anodization in phosphoric acid and followed by black coloration via ac electrolysis in nickel sulfate electrolyte. To increase the thermal, chemical and mechanical stability, and also to provide low emissivity, a protective layer of tin oxide was coated on the surface by the sol-gel process. Conditions required to produce good quality coatings having the best spectral selectivity and thermal stability were determined from spectral reflectance measurements and temperature tests. Microstructure and chemical composition of the best samples were investigated using SEM, EDX, AAS. The resulting technology has been formed into a process which suits the facilities and skills of Turkish industry.

アルミニウム合金ダイカストのアノード酸化挙動に及ぼす合金元素の影響

Aluminum alloy die castings and plates were anodized by applying direct current or a constant pulse voltage in a sulfuric acid solution.In DC anodization, castings containing large amounts of silicon and copper, there was a tendency for electrolytic voltage to rise and for the thickness of oxide coatings to decrease.Electrochemical parameters-ionic current density, zenar leading edge angle and zenar time were measured by analyzing the pulse current waveform.The ionic current density and zenar time for 99.99% aluminum were taken as the reference standard. Ionic current densities were lower for Al-Si and Al-Cu based alloys and higher values for Al-Mg based alloys, while zenar times were longer for Al-Si and Al-Cu based alloys, and shorter for Al-Mg based alloys.The pulse current waveforms for AC 4C, ADC 1 and DM 2 die castings were characteristic of porous film formation.ADC 10 and ADC 12 castings, on the other hand showed a borderline type between barrier film formation and porous film formation, since ionic current was relatively high. This seemed to be caused by imperfect barrier layer formation, based on the relatively high ionic resistance of silicon, trapping of electrons by cuprous oxide and the anodic dissolution of CuAl2.

Bond lengths between aluminium and different complex ions

Using crystal field theory and experimental data for maxima in photoexcitation spectra in anodic alumina formed by dc anodization in different electrolytes, it is shown that the bond length between Al 3+ and complex ions (SO 4 2−, PO 4 3−, CrO 4 2−, etc. incorporated into the alumina during the anodizing process, depends on the charge or dipole moment of the ligand and the symmetry of the environment.

Design of variable phase velocity kinetic inductance delay lines and their measured characteristics when fabricated by a simple Nb based process

A simple design for superconducting kinetic inductance delay lines is presented. Delay lines were fabricated with a thin-film process involving only DC magnetron deposition and anodization of Nb. Phase-velocity measurements demonstrated wave slowing to less than 1/150 of the velocity of light in free space with associated impedances in the ohm range. Phase velocity changes on lines which were in physical proximity to long Josephson junctions and normal conducting lines were investigated. Variations larger than 10% of the equilibrium value were observed with junction-coupled lines under bias application. Locally heated lines exhibited changes exceeding a factor of two. Loss and phase velocity were determined as a function of bias conditions in both cases. Measured line loss was within expectations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Excitation processes at the electrolyte-electrode interface

This work is concerned with the investigation of galvanoluminescence at the interface metal-oxide-electrolyte during DC anodization of very pure aluminum foils in boric acid-borax solution at constant current. The rate of anodic film formation, the quantitative relations between anode voltage and luminescence intensity as well as the shape of optical emission spectra at different voltages are obtained for annealed and unannealed Al samples. It is found that the previous thermal treatment has great influence on anodization and luminescence processes.