Fabrication and photodegradation properties of TiO_2 nanotubes on porous Ti by anodization

Both Ti foil and porous Ti were anodized in 0.5%HF and in ethylene glycol electrolyte containing 0.5%NH4F(mass fraction) separately. The results show that TiO2 nanotubes can be formed on Ti foil by both processes, whereas TiO2 nanotubes can be formed on porous Ti only in the second process. The overhigh current density led to the failure of the formation nanotubes on porous Ti in 0.5%HF electrolyte. TiO2 nanotubes were characterized by SEM and XRD. TiO2 nanotubes on porous Ti were thinner than those on Ti foil. Anatase was formed when TiO2 nanotubes were annealed at 400 °C and fully turned into rutile at 700 °C. To obtain good photodegradation, the optimal heat treatment temperature of TiO2 nanotubes was 450 °C. The porosity of the substrates influenced photodegradation properties. TiO2 nanotubes on porous Ti with 60% porosity had the best photodegradation.

Preparation of gradient wettability surface by anodization depositing copper hydroxide on copper surface

A facile route for preparation of gradient wettability surface on copper substrate with contact angle changing from 90.3°to4.2°was developed.The Cu（OH）2 nanoribbon arrays were electrochemically deposited on copper foil via a modified anodization technology,and the growth degree and density of the Cu（OH）2 arrays may be controlled varying with position along the substrate by slowly adding aqueous solution of KOH into the two-electrode cell of an anodization system to form the gradient surface.The prepared surface was water resistant and thermal stable,which could keep its gradient wetting property after being immersed in water bath at 100℃ for 10 h.The results of scanning electron microscopy（SEM）,X-ray diffraction（XRD） and X-ray photoelectron spectroscopy（XPS） demonstrate that the distribution of Cu（OH）2 nanoribbon arrays on copper surface are responsible for the gradient wettability.

Improving hot corrosion resistance of aluminized TiAl alloy by anodization and pre-oxidation

To shield TiAl alloy from hot corrosion attack,a compact protective coating was fabricated by the combination of aluminizing,anodization and pre-oxidation.The hot corrosion behavior of the coated-TiAl specimen was investigated in the mixture salt consisting of 75 wt.%Na2SO4 and 25 wt.%NaCl at 700°C.Results indicated that the anodization and pre-oxidation were beneficial to the generation of Al2O3 layer,which could act as a diffusion barrier to prevent the molten salts and oxygen from diffusing into the alloy during exposure to a hot corrosion environment while the aluminizing coating could provide sufficient aluminum source to support the continuous formation of Al2O3 layer.Moreover,the internal stress of the coating was reduced due to the formation of a gradient coating consisting of TiAl3 and TiAl2.

Preparation of Porous Alumina Film on Aluminum Substrate by Anodization in Oxalic Acid

Self-ordering of the cell arrangement of the anodic porous alumina was prepared in oxalic acid solution at a constant potential of 40V and at a temperature of 20C. The honeycomb structure made by one step anodization method and two step anodization method is different. Pores in the alumina film prepared by two step anodization method were more ordered than those by one step anodization method.

Corrosion resistance improvement of Ti-6Al-4V alloy by anodization in the presence of inhibitor ions

Colorful thin oxide films were synthesized by galvanostatic anodization on Ti−6Al−4V alloy.Three different aqueous solutions containing corrosion inorganic inhibitors(Na_(2)MoO_(4),NaH_(2)PO_(4) and NH4VO3)were employed for the anodization treatment.The effect of inhibitor anions on the corrosion behavior of the alloy in Ringer solution was studied.Open circuit potential(OCP),Tafel polarization,linear sweep voltammetry(LSV)and chronoamperometry(CA)were performed to evaluate the corrosion performance of the treated electrodes.The incorporation of the inhibitor ions was detected by the release of Mo,V and P through ICP-AES technique.The formed oxides were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The results show that compact,amorphous oxides without pores or cracks were obtained independently of the solution used.The sample anodized in Na_(2)MoO_(4) solution registered the lowest corrosion current density(0.11μA/cm^(2)),and it was able to protect the alloy even after 168 h of immersion in Ringer solution.No cracks or corrosion products were detected.The XPS analysis reveals the incorporation of molybdenum to the oxide film in the form of Mo^(6+) and Mo^(4+).

Effect of Anodization Parameters on Morphologies of TiO2 Nanotube Arrays and Their Surface Properties

This work presents the potentiostatic anodization study of titania nanotube array films fabricated in fluoride-based organic electrolytes including DEG （diethylene glycol） and EG （ethylene glycol）. The work focuses on the effect of important anodization parameters such as applied voltage, anodization time, and electrolyte type on nanotube morphologies and corresponding surface properties. Depending upon unique nanotube formation structures obtained from each anodizing electrolyte, wettability of the nanotube array layer has been determined by means of the contact angle measurement. The EG nanotube array films with close-packing cell orientation are found to show hydrophilic behavior. While the well separated DEG nanotube array films are found to exhibit hydrophobic behavior, with the characteristics of more discrete, wider cell separation obtained through manipulating the electrolyte conditions and the fabrication techniques offering considerable prospects for developing the superhydrophobic sample surface. Such formation structures observed for the DEG fabricated nanotube is believed to play a prominent role in determining the surface wettability of the anodized nanotube array film. The achieved result in this work is anticipated to pave the way to other relevant applications, where interfacial properties are critically concerned.

Nanotube array-like WO_3/W photoanode fabricated by electrochemical anodization for photoelectrocatalytic overall water splitting

Photoactive WO3is attractive as a photocatalyst for green energy evolution through water splitting.In the present work,an electrochemical anodic oxidation method was used to fabricate a photo‐responsive nanotube array‐like WO3/W(NA‐WO3/W)photoanode from W foil as a precursor.Compared with a reference commercial WO3/W electrode,the NA‐WO3/W photoanode exhibited enhanced and stable photoelectrocatalytic(PEC)activity for visible‐light‐driven water splitting with a typical H2/O2stoichiometric ratio of2:1and quantum efficiency of approximately5.23%under visible‐light irradiation from a light‐emitting diode(λ=420nm,15mW/cm2).The greatly enhanced PEC performance of the NA‐WO3/Wphotoanode was attributed to its fast electron–hole separation rate,which resulted from the one‐dimensional nanotube array‐like structure,high crystallinity of monoclinic WO3,and strong interaction between WO3and W foil.This work paves the way to a facile route to prepare highly active photoelectrodes for solar light transfer to chemical energy.

Effect of Anodization on the Graphitization of PAN-based Carbon Fibers of PAN-based Carbon Fibers

One-step pretreatment,anodization,is used to activate the polyacrylonitrile （PAN）-based carbon fibers instead of the routine two-step pretreatment,sensitization with SnCl2 and activation with PdCl2.The effect of the anodization pretreatment on the graphitization of PAN-based carbon fibers is investigated as a function of Ni-P catalyst.The PAN-based carbon fibers are anodized in H3PO4 electrolyte resulting in the formation of active sites,which thereby facilitates the following electroless Ni-P coating.Carbon fibers in the presence and absence of Ni-P coatings are heat treated and the structural changes are characterized by X-ray diffraction and Raman spectroscopy,both of which indicate that the graphitization of PAN-based carbon fibers are accelerated by both the anodization treatment and the catalysts Ni-P.Using the anodized carbon fibers,the routine two-step pretreatment,sensitization and activation,is not needed.

Fast Growth of Highly Ordered TiO2 Nanotube Arrays on Si Substrate under High-Field Anodization

Highly ordered TiO_2 nanotube arrays(NTAs) on Si substrate possess broad applications due to its high surfaceto-volume ratio and novel functionalities, however, there are still some challenges on facile synthesis. Here, we report a simple and cost-effective high-field(90–180V) anodization method to grow highly ordered TiO_2 NTAs on Si substrate,and investigate the effect of anodization time, voltage, and fluoride content on the formation of TiO_2 NTAs. The current density–time curves, recorded during anodization processes, can be used to determine the optimum anodization time. It is found that the growth rate of TiO_2 NTAs is improved significantly under high field, which is nearly 8 times faster than that under low fields(40–60 V). The length and growth rate of the nanotubes are further increased with the increase of fluoride content in the electrolyte.

Formation of TiO_(2) Nanotube Layer by Anodization of Titanium in Ethylene Glycol-H_(2)O Electrolyte

In orthopaedics and orthodontics, the growth of nanotubes of titanium oxide on titanium implants is a promising route for improving the osseointegration. Among the fabrication routes to produce nanotubes, anodization was generally preferred due to its simplicity and low cost. TiO2 nanotubes are formed by the simultaneous anodic reaction and chemical dissolution due to the fluoride species present in the anodization bath. In this work, the formation of TiO2 nanotubes was studied in stirred ethylene glycol-H2O electrolyte (90 - 10 v/v) containing NH4F at room temperature. In order to study the effect of NH4F concentration, voltage and anodization time, and to reduce the number of experiments, a design of experiments (DOE) based on a 2k factorial design with four replicates at the center point was used. The analysis of variance (ANOVA) was used to evaluate the effects of the factors of control and their interactions on the percentage of the titanium surface coated by nanotubes. The dimensions of nanotubes (length and diameter) were also evaluated using field emission gun scanning electron microscopy. The cristallinity and phase composition of the oxide layers was investigated by X-ray diffractometry. The electrochemical behavior of as-received and anodized titanium specimens was studied in Ringer’s solution. The statistical analysis showed that fluoride concentration is the most significant factor. The best condition according to the response surface analysis is the center point (1% NH4F, 20 V, 2 h). The nanotubular oxide layers presented an amorphous structure. Electrochemical tests showed that TiO2 nanotubes coated titanium is less corrosion resistant than as-received titanium.

STUDY OF THE ANODIZATION OF Al FILM ON InP SUBSTRATE AND ITS PROPERTIES

The anodization of Al film on InP substrate and properties of anodic Al2O33/InPhave been investigated by AES,DLTS,I-V,C-V and ellipsometer.The results show that theanodic oxide Al2O3 has a permittivity of 11～12 and a resistivity of 1.3×1013 ohm-cm.Interfacestate density at Al2O3/InP is about 1011 cm-2·eV-1.DLTS reveals that there is a continuouslydistributed interface electron traps at Al2O3/InP interface.Anodic Al2O3 exhibits good stabilityand electrical properties and could be used for passivation,diffusion mask and gate insulator,etc.

Two-Step Anodization of Maltilayer TiO_2 Nanotube and Its Photocatalytic Activity under UV Light

A double-layer TiO2 nanotube arrays were formed by two-step anodization of Ti foils in different electrolytes. First, Ti in 0.5 wt% HF was anodized to form thin nanotube layer. Afterwards a second anodization was conducted in a formamide based electrolyte, which allowed the second layer of nanotube growing directly underneath the first one. From FESEM investigation we found that the thickness of second layer corresponded to the anodization time, the increasing of which would lead to the excessive etching on the first layer. The first layer protected the lower one from fluoride corrosion during anodization process. The double layer TiO2 nanotube arrays showed no benefit to photodegradation effect in methyl orange degradation experiments.

Temporal Evolution of Anodization Current of Porous Silicon Samples

Temporal evolution of the anodization current of porous silicon samples was studied by means of a model of resistances connected in series that represented the temporal changes of the substrate and of the interface between the substrate and the electrolyte during the porous sample formation process. The porous samples were obtained by means of photoelectrochemical etching of (100) n-type silicon wafers with different resistivity values, all in the range of 1 - 25 Wcm. The samples were formed at room temperature in an electrolytic bath composed by a mixture of hydrofluoric acid (48%) and ethanol having a composition ratio of 1:1 in volume under potentiostatic condition (10 V and 20 V) and an etching time of 2 minutes using back illumination provided by a laser beam with a wavelength of 808 nm.

Ultrasonic Corrosion-Anodization: Electrochemical Cell Design and Process Range Testing

Titanium was used in the present work as the test metal for the first ultrasonic corrosion anodization (UCA) study, because of its important photonics and biomedical applications. The electrochemical cell design was implemented and tested under various experimental conditions combinations (e.g. electrolyte concentration, duration, temperature, ultra-sound presence or absence, oxygen presence, etc) in order to investigate the effect of those parameters in the cracks propagation in Ti-foils. It was found that an increase of cracks takes place when oxygen is provided in the electrolyte solution and when ultrasound is applied. The results presented in the current study could be exploitable towards design of materials having dendritic morphologies, applicable in a wide range of processes from photovoltaics to biocompatible materials.

Electrochemical anodization of cast titanium alloys in oxalic acid for biomedical applications

Titanium and its alloys have numerous biomedical applications thanks to the composition and morphology of their oxide film.In this study,the colorful oxide films were formed by anodizing cast Ti-6Al-4V and Ti-6Al-7Nb alloys in a 10%oxalic acid solution for 30 s at different voltages(20–80 V)of a direct current power supply.Atomic force microscopy was used as an accurate tool to measure the surface roughness of thin films on the nanometer scale.Scanning electron microscopy and X-ray diffraction were performed to analyze surface morphology and phase structure.According to the results,the produced titanium oxide layer showed high surface roughness,which increased with increasing anodizing voltage.The impact of anodizing voltages on the color and roughness of anodized layers was surveyed.The corrosion resistance of the anodized samples was studied in simulated body fluid at pH 7.4 and a temperature of 37℃ utilizing electrochemical impedance spectroscopy and the potentiodynamic polarization method.The anodized samples for both alloys at 40 V were at the optimal voltage,leading to a TiO_(2) layer formation with the best compromise between oxide thickness and corrosion resistance.Also,findings showed that TiO_(2) films produced on Ti-6Al-7Nb alloys had superior surface roughness properties compared to those of Ti-6Al-4V alloys,making them more appropriate for orthopedic applications.From the obtained data and the fruitful discussion,it was found that the utilized procedure is simple,low-cost,and repeatable.Therefore,anodization in 10%oxalic acid proved a viable alternative for the surface finishing of titanium alloys for biomedical applications.

Influence of anodization conditions on deposition of hydroxyapatite onα/βTi alloys for osseointegration:Atomic force microscopy analysis

Integrating titanium-based implants with the surrounding bone tissue remains challenging.This study aims to explore the impact of different anodization voltages(20−80 V)on the surface topography of two-phase(α/β)Ti alloys and to produce TiO_(2) films with enhanced bone formation abilities.Scanning electron microscopy coupled with energy dispersive spectroscopy(SEM−EDS)and atomic force microscopy(AFM)were applied to investigate the morphological,chemical,and surface topography of the prepared alloys and to confirm the growth of hydroxyapatite(HA)on their surfaces.Results disclosed that the surface roughness of TiO_(2) films formed on Ti−6Al−7Nb alloys was superior to that of Ti−6Al−4V alloys.Ti−6Al−7Nb alloy anodized at 80 V had the highest yields of HA after immersion in simulated body fluid with enhanced HA surface coverage.The developed HA layer had a mean thickness of(128.38±18.13)μm,suggesting its potential use as an orthopedic implantable material due to its promising bone integration and,hence,remarkable stability inside the human body.

Single-step nano-engineering of multiple micro-rough metals via anodization

Anodization is a cost-effective technique to nano-engineer various metals,however,optimizations have been mostly restricted to Al and Ti,and for easy to manage polished and flat substrates,limiting industrial translation.Here,we aim at standardizing and simplifying anodization of ten metals,attempting to make metal nano-engineering more accessible.In a world-first attempt,we synthesize a standard electrolyte to fabricate controlled nanostructures on various metals,taking a close look at the influence of the substrate topography,electrolyte composition,and electrolyte aging(repeated use of same electrolyte)towards designing a standard nano-engineering strategy.Anodization of curved substrates(metal wires)with micro-roughness allows for ease of industrial translation across various applications.This study is a step closer to standardizing anodization and fabrication of controlled nanotopography on various metallic surfaces,while maintaining scalability and ease of use.

Corrosion protection of magnesium alloys anode by cerium-based anodization coating in magnesium-ait battery

CeN_(3)O_(9)·6H_(2)O(0.5,1.0,1.5,and 2.0 g/L)was added into an 8.0%NaCl electrolyte solution to investigate this electrolyte for use in a Mg-air battery.The effects of the amount of CeN_(3)O_(9)-6H_(2)O on the corrosion resistance of an AZ31 Mg alloy anode and battery performance were investigated using microstructure,electrochemical(dynamic potential polarization method and electrochemical impedance spectroscopy),and battery measurements.The re sults show that the addition of CeN_(3)O_(9)·6H_(2)O to the electrolyte leads to the formation of a Ce(OH)_(3)protective film on the surface of the AZ31 Mg alloy that improves the corrosion resistance of the Mg alloy.An increase in the concentration of CeN_(3)O_(9)·6H_(2)O results in a denser Ce(OH)_(3)protective film and decreases corrosion rate of the AZ31 Mg alloy.When the concentration of CeN_(3)O_(9)·6H_(2)O is 1.0 g/L,the corrosion rate of the Mg alloy is the lowest with a corrosion inhibition rate of70.4%.However,the corrosion rate increases due to the dissolution of the Ce(OH)_(3)protective film when the concentration of CeN_(3)O_(9)-6H_(2)O is greater than 1.0 g/L.Immersing the Mg alloy in the electrolyte solution containing CeN_(3)O_(9)-6H_(2)O for 50 h leads to the formation of the Ce(HO)_(3)protective film on its surface,which was confirmed by scanning electron microscopy of the AZ31 alloy.The Mg^(2+)charge transfer resistance increases by 69.5Ωfrom the equivalent circuit diagram,which improves the corrosion resistance of the Mg alloy.The discharge performance of CeN_(3)O_(9)·6H_(2)O improves according to a discharge test,and the discharge time increases by 40 min.

Facile anodization approach derived low-crystalline NiCoeOH/NiCoOOH composite films for ultra-high areal capacity and mass loading supercapacitors

The design of supercapacitor materials with both high areal capacity(C)and high mass loading is vitally important for enhancing energy density(E).Herein,we prepared a NiCosingle bondOH/NiCoOOH composite film consisting of NiCosingle bondOH/NiCoOOH nanosheets on an expanded graphite paper(EGP)by using a facial anodization method.The as-prepared NiCosingle bondOH/NiCoOOH film exhibits ultra-high C of 11 mA·h·cm^(-2)at a mass loading of 165 mg·cm^(-2),high rate capability of 71%and excellent cycling stability of 95%after 12000 cycles.The outstanding performance is ascribed to the low-crystalline feature of the NiCosingle bondOH/NiCoOOH nanosheets,and the synergistic effect of the NiCosingle bondOH and NiCoOOH phases and high conductive porous EGP.An aqueous asymmetric supercapacitor,assembled with the NiCosingle bondOH/NiCoOOH on EGP and Fe_(2)O_(3)on EGP as positive-and negative-electrode,respectively,shows a highest E of 3.8 mW·h·cm^(-2)at a power density(P)of 4 mW·cm^(-2)and a maximum P of 107 mW·cm^(-2)at an E of 2.7 mW·h·cm^(-2).

Morphology Control of TiO_(2)Nanotubes towards High-Efficient Electrodes for Supercapacitor

This article studies the role of electrochemical parameters in controlling the morphology of oxidized TiO_(2)nanotubes and the electrochemical performance of modified TiO_(2)nanotubes.Humidity is a key factor for fabricating TiO_(2)nanotubes.When the relative humidity belows 70%,the TiO_(2)nanotubes can be successfully prepared.What's more,by changing the anodization voltage and time,the diameter and the length of TiO_(2)nanotubes can be adjusted.In addition,the TiO_(2)nanotubes are modified through electrochemical self-doping and loading Pt metal particles on the surface of the nanotubes,which promotes the performance of the supercapacitor.The sample anodized at 100 V for 3 h has a specific capacity of up to 2.576 mF/cm~2 at a scan rate of 100 mV/s after self-doping,and its capacity retention rate still remains at 89.55%after 5000 cycles,demonstrating excellent cycling stability.The Pt-modified sample has a specific capacity of up to 3.486 mF/cm~2 at the same scan rate,exhibiting more outstanding electrochemical performance.