Anodization Temperature Research Articles

Photoelectrochemical Performance of Smooth TiO2Nanotube Arrays: Effect of Anodization Temperature and Cleaning Methods

The formation of self-organized titanium dioxide (TiO2) nanotube arrays without bundling or clustering is essential for their high efficiency in photoelectrochemical (PEC) application. The present paper reports on the use of different temperatures to control the specific architecture of nanotube arrays and effective cleaning techniques to ensure the formation of clean TiO2nanotube surface. The wall thickness of nanotube arrays could be controlled from 12.5 nm to 37.5 nm through different anodization temperature ranging from 10°C to 80°C. Furthermore, ultrasonic cleaning combined with acetone showed the high-ordered TiO2nanotube arrays without morphological disorder, bundling, and microcrack problems. Based on the results obtained, a higher PEC response of 1 mA/cm2and a photoconversion efficiency of 1.3% could be achieved using a wall thickness of 12.5 nm and defect-free TiO2nanotube arrays for low charge transfer resistance.

Synthesis of anodic aluminum oxide (AAO) at relatively high temperatures. Study of the influence of anodization conditions on the alumina structural features

Anodic aluminum oxide (AAO) is a well known template for nanofabrication. Structural features of AAO like pore diameter, interpore distance, porosity, pore density can be fully controlled by operating conditions of anodization. Typically, self-organized two-step anodization is carried out at low temperature (below room temperature) and is a time consuming process. There are individual experiments describing anodization at temperatures close to room temperature. In our study, furthermore, a systematic analysis of the anodization condition influence on the nanoporous alumina structural features was done. The anodization temperature was ranging from 35 to 50°C increasing significantly current density of the processes, which has increased oxide film growth rate. The anodizing potential ranged from 20 to 60V and time of the anodization steps was 30, 60 or 120min. The data obtained has shown that the pore diameter increases with potential, temperature and time of anodization, while the interpore distance is influenced solely by the potential. Temperature and time changes do not affect the interpore distance. Porosity is also influenced by potential, temperature and duration of anodization. Pore density is influenced only by the potential. The synthesis of AAO reported here gives possibilities to obtain the AAO templates in a faster and cheaper way, essential for researchers applying anodic alumina as a template.

Computational simulation and experimental evaluation on anodic flow field structures of micro direct methanol fuel cells

Abstract The flow field structures can have a large influence on both flow velocity and temperature distributions of the direct methanol fuel cells (DMFCs), thus proper flow field constructions are very important for the improvement in DMFC’s performance. In this work, anodic flow velocity and temperature distributions based on four different designs, including double serpentine, parallel, helix and single serpentine, were simulated in three-dimensional models. Computational fluid dynamics (CFD) was used to investigate the effects of flow field structures on the DMFC’s performance. Simulated results indicate that the double-serpentine flow field shows better flow velocity distribution and more uniform temperature distribution, which might lead to a better performance of the DMFC. Further experimental investigation on four types of flow fields also confirmed that the DMFC with double-serpentine flow field structure exhibits a maximal power density at a variety of inlet velocities, which is in good agreement with the simulated results. The maximum power density of the fabricated DMFC with double-serpentine flow field is ca. 34.2 mW cm −2 when the inlet flow velocity was 0.01 m s −1 at room temperature.

Multiple regression analysis of hydrogen sulphide poisoning in molten carbonate fuel cells used for waste-to-energy conversions

Bioenergy addresses three important social concerns: security of energy supply, mitigation of greenhouse gas emissions and development of agriculture. Bioenergy is the energy generated by either direct or indirect combustion of biomass, which is non-fossil organic material of both vegetable and animal origins. Different technologies are currently available for bioenergy production, but fuel cells are one of the most interesting devices because of their environmental benefits and their high efficiency. In particular, molten carbonate fuel cells are suitable devices for waste-to-energy conversion because of their ability to be fed with biogas, which is biomass-derived gas rich in methane and carbon dioxide. Indeed, methane can be internally reformed to hydrogen, carbon dioxide is a safe diluent preventing electrolyte loss, and carbon monoxide acts both as a hydrogen supplier and as an actual fuel. Unfortunately, biogas impurities, such as sulfur, halogen and nitrogen compounds, cause adverse effects on cell performances. The most dangerous impurities are sulfur compounds, among whom hydrogen sulphide is the predominant and the most harmful chemicals. It reacts with nickel-based anode to form nickel sulphides, that block catalytic sites, slowing hydrogen oxidation down, and change the anode wettability in molten carbonates, compromising the optimal electrolyte distribution within cell components. Poisoning mechanism of hydrogen sulphide depends on operating conditions such as current density, anodic gas composition, temperature and pressure. The aim of this work is to study hydrogen sulphide effects on MCFCs by means of multiple regression analysis. The mathematical approach gives us tools to define the main sulfur poisoning mechanism under MCFC operating conditions, quantify the effects of the main parameters affecting poison actions, such as current density, hydrogen and hydrogen sulphide, and identify their mutual interactions. Also it is possible to formulate a multivariate model to predict sulfur poisoning.

Blood responses to titanium surface with TiO2 nano‐mesh structure

The goal of this study was to enhance the blood responses to titanium (Ti) surfaces used for dental implant application through the formation of a TiO2 nano-mesh surface layer produced by a fast electrochemical anodization treatment. Electrochemical anodization treatments with different anodization currents and temperatures in an alkaline solution were used to create a nano-mesh oxide layer on polished Ti surface. Surface characterizations of the mesh structure were carried out using thin-film X-ray diffractometer, field-emission scanning electron microscope, and atomic force microscope. The blood responses, including the blood-clotting ability and platelet adhesion morphology, to the test Ti surfaces were evaluated. The blood-clotting ability, in terms of optical density of blood, was statistically analyzed using a nonparametric method, Kruskal-Wallis test, for the factor of anodization treatment. A multilayer TiO2 nano-mesh structure was rapidly formed on the polished Ti surface using a simple electrochemical anodization treatment in an alkaline solution. The TiO2 nano-mesh had an average mesh size between 34 and 93 nm, depending on the anodization current and temperature. The features on the TiO2 nano-mesh structure on the anodized Ti surface were of a similar size scale as blood proteins, giving the material better blood clot ability (P<0.05) and improved platelet activation and aggregation as compared with an untreated polished Ti surface. The formation of TiO2 nano-mesh on the Ti surfaces was shown to enhance blood responses, which we expect to promote cell growth in the application of dental implants.

Ni-doped TiO 2 nanotube arrays on shape memory alloy

Self-organized Ni–Ti–O nanotube arrays were fabricated through a direct anodization of NiTi shape memory alloy in glycerol-based electrolyte. The growth of Ni-doped TiO 2 nanotube arrays was mainly affected by anodization voltage and temperature. Higher anodization voltage facilitated the growth of uniform nanotube arrays. Large-area open-ended Ni–Ti–O nanotube arrays could form on the surface of the shape memory alloy under a higher anodization temperature. The oxide nanotubes had a gradually changed composition along the growth direction of the nanotube and presented a thermal stability up to 400 °C. The nanotubular oxide demonstrated a much better hydrophilic behavior than that of the traditional oxide layer grown on NiTi substrate through air oxidization. The successful fabrication of Ni-doped TiO 2 nanotube arrays here makes it feasible to further explore excellent physical and chemical as well as biomedical properties of the nanotube-modified surfaces of the NiTi shape memory alloy.

Aluminum Anodization in Oxalic Acid: Controlling the Texture of Al2O3/Al Monoliths for Catalytic Aplications

The anodization and postanodization processes of aluminum in order to prepare monoliths for catalytic applications have been studied in this work using oxalic acid as electrolyte. The effect of anodization variables (anodization time, current density, temperature, and electrolyte concentration) and postanodization processes on the surface morphology and textural properties of AAO (anodic aluminum oxide) films is analyzed. The anodization variables affect the two main processes taking part in the Al2O3 layer formation: alumina generation and its dissolution that are controlled by temperature, electrolyte concentration and time. The proper combination of both processes, as a result of the anodization variables choice, produces adherent alumina layers with tailored porosity and surface morphology that show excellent properties to be used as catalyst structured support. Larger pore sizes and the complete absence of sulfur that may poison reduced metal−supported active phases are main differences with the clas...

A brief review on fabrication and applications of auto-organized TiO2 nanotube arrays

Fabrication and applications of self-organized TiO2 nanotube arrays is briefly reviewed. This nanoscale material has attracted considerable attention owing to its potential in gas sensing, photo-thermal and photovoltaic conversion devices, photoelectrolysis and photocatalysis, etc. TiO2 in nanowire form, nanotube form and other nanoporous structures is desirable because of its high surface–volume ratio, high surface activity and superior sensitivity. TiO2 nanotubes and nanofibers have been developed by diverse techniques such as sol-gel, electrodeposition and anodization. In recent years, there has been significant progress in nano-structured TiO2 fabrication using the anodization method. This consists of oxidation (corrosion) of titanium foils or titanium thin films deposited onto substrates (e.g., silicon), immersed in acid or neutral F-containing solutions. Significant interest has arisen in anodization parameters, such as applied potential, concentration and type of corrosive solutions, anodization time length and temperature. This parameters influence mechanical-structural, chemical and electrical features of porous TiO2. Recent work concerning fabrication, applications and growth models is described in this review paper.

Uniform and Pitting Corrosion Processes of Al, Al-6061, Al-Zn and Al-Cu Alloys Exposed to SCN- Solutions and the Effect of Some Inorganic Anions

Abstract The effect of the alloying elements and some inorganic inhibitors (WO4 2-, MoO4 2-, SiO3 2- and CrO4 2- anions) on the uniform and pitting corrosion characteristics of Al-6061, Al-4.5% Cu, Al-7.5% Cu, Al-6% Zn and Al-12% Zn alloys were studied in 0.04M KSCN solution. Susceptibility of the tested alloys towards pitting corrosion was investigated using transient (potentiostatic and galvanostatic) measurements. An independent method of chemical analysis, namely ICP-AES (inductively coupled plasma atomic emission spectroscopy) was also used to study the effect of the alloying elements and the tested inorganic anions on the uniform corrosion of these materials. Results obtained were compared with pure Al. ICP measurements revealed that the alloyed Cu and alloyed Zn enhance uniform corrosion of the Al samples, while WO4 2-, MoO4 2-, SiO3 2- and CrO4 2- anions suppressed it. Transient measurements showed that nucleation of pit takes place after an incubation time (t i). The rate of pit initiation and growth (t i -1 ) increased with increase in SCN- concentration, applied anodic current, applied anodic potential and solution temperature. This rate of pit initiation and growth decreased in presence of inorganic inhibitors to an extent depending on the concentration and type of the introduced inhibitor. Alloyed Zn was found to accelerate pitting attack, while alloyed Cu suppressed it. Among the tested Al alloys, Al-6061 presented the highest resistance towards uniform and pitting corrosion processes. SiO3 2- and CrO4 2- were the most efficient anions in inhibiting uniform and pitting corrosion processes of Al in these solutions.

Effects of anodization parameters on the formation of titania nanotubes in ethylene glycol

The effects of fluoride concentration, anodization temperature, and anodization applied potential difference on the formation and dimensions of the titania nanotubes in ethylene glycol/water systems were investigated. It was found that fluoride concentration and anodization temperature were the two critical parameters for controlling the nanotube formation whilst anodization applied potential difference mainly contributes to tuning the dimension of the nanotubes. Electrolytes containing a low fluoride concentration are beneficial for initiating nanotube formation, whilst a higher anodization temperature is helpful to the rapid growth of the nanotubes. It is shown that the current–time curve obtained during the anodization can be used as an effective tool to predict the morphology of titania nanotubes. A model based on the competition between electrochemical oxidation of the titanium and chemical dissolution by fluoride ions is developed to explain the experimental observations.

양극산화법에 의한 TiO2나노튜브 어레이의 제조 및 광전기화학적 특성에 관한 연구

Self-standing <TEX>$TiO_2$</TEX> nanotube arrays were fabricated by potentiostatic anodic oxidation method using pure Ti foil as a working electrode and ethylene glycol solution as electrolytes with small addition of <TEX>$NH_4F$</TEX> and <TEX>$H_2O$</TEX>. The influences of anodization temperature and time on the morphology and formation of <TEX>$TiO_2$</TEX> nanotube arrays were investigated. The fabricated <TEX>$TiO_2$</TEX> nanotube arrays were applied as a photoelectrode to dye-sensitized solar cells. Regardless of anodizing temperature and time, the average diameter and wall thickness of <TEX>$TiO_2$</TEX> nanotube show a similar value, whereas the thickness show a different trend with reaction temperature. The thickness of <TEX>$TiO_2$</TEX> nanotube arrays anodized at <TEX>$20^{\circ}C$</TEX> and <TEX>$30^{\circ}C$</TEX> was time-dependent, but on the other hand its at <TEX>$10^{\circ}C$</TEX> are independent of anodization time. The conversion efficiency is low, which is due to a morphology breaking of the <TEX>$TiO_2$</TEX> nanotube arrays in manufacturing process of photoelectrode.

Passivity and passivity breakdown of Al and Al–Zn alloys in SCN− solutions and the effect of some inorganic inhibitors – Galvanostatic, potentiostatic and ICP-AES studies

The susceptibility of Al and Al–Zn alloys, containing 6% and 12% (in weight) Zn, towards pitting in KSCN solutions was studied using glavanostatic and potentiostatic techniques. Potentiostatic results showed that the pitting process was categorized into the three stages, i.e., the first passivation stage, the second pit formation and growth stage and the final steady-state stage. Galvanostatic measurements allowed the pitting and repassivation potentials to be determined. The rate of pit initiation and growth was found to increase with increase in SCN− concentration, applied anodic current, applied anodic potential and solution temperature. Alloyed Zn was found to enhance pitting attack. ICP-AES method of chemical analysis confirmed results obtained from electrochemical measurements. The inhibiting effects of MoO42−, WO42−, SiO32− or CrO42− anions were also investigated based on polarization and potentiostatic measurements, complemented with SEM and EDX examinations of the electrode surface. The pitting potential (Epit) and the incubation time (ti) were increased, while the pit growth current density (jpit) was decreased with increase in inhibitor concentration. These inorganic anions therefore inhibited pit nucleation and growth of Al in these solutions. SiO32− and MoO42 anions inhibited pitting corrosion more effectively than MoO42− and WO42− anions.

A newly synthesized glycine derivative to control uniform and pitting corrosion processes of Al induced by SCN − anions – Chemical, electrochemical and morphological studies

A newly synthesized glycine derivative (termed GlyD), 2-(4-(dimethylamino)benzylamino)acetic acid hydrochloride, was used to inhibit uniform and pitting corrosion processes of Al in 0.50 M KSCN solutions (pH 6.8) at 25 °C. For uniform corrosion inhibition study, Tafel extrapolation, linear polarization resistance and impedance methods were used, complemented with SEM examinations. An independent method of chemical analysis, namely ICP-AES (inductively coupled plasma atomic emission spectrometry) was also used to test validity of corrosion rate measured by Tafel extrapolation method. GlyD inhibited uniform corrosion, even at low concentrations, reaching a value of inhibition efficiency up to 97% at a concentration of 5 × 10 −3 M. Results obtained from the different corrosion evaluation techniques were in good agreement. This new synthesized glycine derivative was also used to control pit nucleation and growth on the pitted Al surface based on cyclic polarization, potentiostatic and galvanostatic measurements. The pitting potential ( E pit) and the repassivation potential ( E rp) increased by the addition of GlyD. Thus GlyD suppressed pit nucleation and propagation. Nucleation of pit was found to take place after an incubation time ( t i). The rate of pit nucleation and growth decreased with increase in inhibitor concentration. Morphology of pitting was also studied as a function of the applied anodic potential and solution temperature. Cross-sectional view of pitted surface revealed the formation of large distorted hemispherical and narrow deep pits. GlyD was much better than Gly in controlling uniform and pitting corrosion processes of Al in these solutions.

Structure and dye-sensitized solar cell application of TiO2 nanotube arrays fabricated by the anodic oxidation method

Well-ordered TiO2 nanotube arrays were fabricated by the potentiostatic anodic oxidation method using pure Ti foil as a working electrode and ethylene glycol solution as an electrolyte with the small addition of NH4F and H2O. The influence of anodization temperature and time on the morphology and formation of TiO2 nanotube arrays was examined. The TiO2 nanotube arrays were applied as a photoelectrode to dye-sensitized solar cells. Regardless of anodizing temperature and time, the average diameter and wall thickness of TiO2 nanotube arrays show a similar value, whereas the length increases with decreasing reaction temperature. The conversion efficiency is very low, which is due to a morphology breaking of the TiO2 nanotube arrays in the manufacturing process of a photoelectrode.

Self-Ordered Anodic Alumina with Continuously Tunable Pore Intervals from 410 to 530 nm

We report a "mild anodization" (MA) process using aluminum oxalate (Alox) as an additive to suppress breakdown of porous anodic alumina (PAA) in the electrolyte of phosphoric acid at high potentials and comparatively high temperatures. It is shown for the first time that continuously tunable pore intervals (D(int)) from 410 to 530 nm with ordered hexagonal pore arrangement can be controlled by varying the concentrations of phosphoric acid and Alox at anodization voltages (U(a)) from 180 to 230 V, far beyond the U(a) in the single electrolyte of phosphoric acid or oxalic acid. The fabricated PAA films are uniform without any burning spots, and the anodization temperature can be increased to 10-20 degrees C with a much higher growth rate of PAA films than that at a low temperature. Meanwhile, a typical two-step anodization process could also be performed under our conditions. Our results could not only extend the applications of PAA templates but also facilitate understanding of the effects of anions in the process of anodic oxidation.

Self‐Assembled TiO2 Nanotube Arrays with U‐Shaped Profile by Controlling Anodization Temperature

TiO2 nanotube arrays with uniform diameter from top to bottom were fabricated. The synthesizing approach is based on the investigation of the influence of electrolyte temperature on the tube diameter. We found that the inner diameter of the tubes increased with the electrolyte temperature. Accordingly, we improved the tube profile from the general V shape to U shape by raising the electrolyte temperature gradually. This is a simple and fast approach to fabricate uniform TiO2 nanotubes in diameter. The improved TiO2 nanotube arrays may show better properties and have broad potential applications.

Electrochemical Preparation of Overlapped Porous Layers on Anodic Alumina

In this paper, we report the development of a new architecture on porous anodic alumina using the conventional two-step anodization method. The samples prepared in two identical steps using galvanostatic anodization exhibited two porous layers overlapped with distinct pore area distributions. The effects from the first anodization time and temperature on this different morphology were assessed using Factorial Design. The chemical removal time of the oxide formed during the first anodization was not relevant for the overlapped porous structure. The most important factor was the time of the first anodization required for formation of stable patterns on the substrate, which would be reproduced in the second anodization. A pore mismatch appeared because under galvanostatic control the changes in the actual area become important, which is not the case for sample preparation under potentiostatic control where the current density is adjusted according to the new boundary condition. The new architecture with mismatching layers may open the way for further applications of porous alumina as template for nanomaterial.

Anodic Current and Temperature Dependence of Light-Emitting Properties of Porous Si

A comprehensive study has been performed on the light-emitting properties of porous silicon (PSi) films formed by anodic etching. PSi films are investigated using photoluminescence (PL), PL excitation, and X-ray photoelectron spectroscopy (XPS). The PL emission features are strongly dependent on the anodic current density. Analysis of the PL spectrum suggests the existence of two different emission mechanisms in the PSi layers: An efficient mechanism that is usually observed at higher temperatures and one that exhibits a multiple-peak structure and appears only at low temperatures , even at an excitation energy far from the PL resonance band (1.5–2.4 eV). The high temperature emission can be interpreted as being due to the quantum-confinement effect, i.e., relaxation of the momentum conservation at and above the indirect absorption edge (supra- emission), while the lower temperature PL emission is explained by the classical configurational-coordinate model with a lattice vibronic quantum of . The XPS data indicate that the short-range order is important in understanding the optical spectra not only for the amorphous substance but also for the nanocrystalline substance.

THE MANUFACTURE OF PERCHLORATE BY DIRECT METHOD USING GRAPHITE SUBSTRATE LEAD DIOXIDE (GSLD) ANODE

Sodium perchlorate has been prepared electrochemically from sodium chloride solutions in one step by passing a direct current through the solution , in the presence of certain addition agents (like sodium fluoride). A laboratory electrolytic cell has been designed to obtain experimental results for the preparation of sodium perchlorate. A solution of sodium chloride (290 g/l ) and sodium fluoride (2 g/l ) is electrolyzed in a batch wise. A stainless steel cathode and Graphite substrate lead dioxide (GSLD) anode are satisfactory . The influence of anodic current density , temperature ,and pH of electrolyte on current efficiency of sodium perchlorate formation were studied. The current efficiency of about 68% was obtained by using (GSLD) anode

OPTICAL TRANSITION OF POROUS SILICON PREPARED AT DIFFERENT ANODIZATION TEMPERATURES

Photoluminescence, photoabsorption, and X-ray photoelectron spectroscopic study revealed that an optical transition of porous silicon from red-shift to blue-shift, and Si -2p binding energy transition from low to high at a critical anodization temperature, 343 K. Possible origin for the reverse variations happening at temperature below and above the critical temperature is discussed.