Anodization Duration Research Articles

Structural and characteristic variation of anodic oxide on pure Ti with anodization duration

Change in the structural and characteristic of the anodic oxide on pure Ti with the duration of anodization time was investigated. With the progress of the anodization, the phase of the formed TiO2 successively changed from anatase phase to rutile phase. In the transition process, peak intensities of rutile TiO2 101, 111 and 211 planes of X-ray diffraction characteristically increased. The contact angles of water droplets on the anodize TiO2 were monotonously decreased with the progress of the anodization except on the characteristically oriented rutile surface. In the evaluations of acetaldehyde photocatalysis under UV illumination, the anatase TiO2 anodized for short period exhibited high activities. On the other hand, when illuminated with visible light (>422nm), rutile-structured TiO2 formed by anodization with a long duration exhibited superior photocatalytic activities probably due to high rutile fraction and sulfur incorporation from the electrolyte.

Photoelectrochemical Fabrication of Porous GaN and Their Applications in Ultraviolet and Ammonia Sensing

This article reports the studies of porous GaN fabricated using photo-electrochemical anodization method and their applications in UV and ammonia gas sensing. GaN was anodized under different durations and their fundamental aspects were investigated. Electron micrographs revealed that the porous surface was obtained, however prolonged anodization durations would lead to breakdown of porous layer, forming nanostructures. A plausible pore formation and breakdown mechanism were proposed based on current-transient profile. In Raman spectroscopy, forbidden bands such as E1(TO) and A1(TO) were noted in anodized samples. The intensity of these bands was dependent on the geometrical position of the nanostructures formed on porous surface. In UV and ammonia sensing studies, change in Schottky barrier height was the greatest for anodized samples. Porous GaN in UV sensing was 5 times more sensitive relative to as-grown GaN. In ammonia sensing, porous GaN displayed positive results even in the absence of catalytic metal, Pt.

Porous WO3 formed by anodization in oxalic acid

This work reports the investigation of the anodic growth of porous tungsten oxide (WO3) in oxalic acid. It was found that pore diameter increases from approximately 50 to 90 nm while the layer thickness of porous structures increases from approximately 100 to 400 nm as the voltage varies from 40 to 100 V. Extended anodization duration improves the homogeneity of the porous structure at 40 V but it has no effect on the pore layer thickness. During the pore formation process, nucleation of small pores in the existing pore is observed while several layers of pores with voids underneath the surface layer are formed especially at high anodization voltage. A possible growth mechanism of the pores is proposed.

Electrochemical Self-Assembly of Nanoporous Alumina Templates Title

Porous alumina was fabricated electrochemically through anodic oxidation of aluminum by means of such a self-organized method. Anodic aluminium oxide (AAO) template with nanopores was grown by two-steps anodization processes from a high purity aluminium foil. The anodization process was carried out in a phosphoric acid electrolyte at ambient temperature with a different duration of anodization. The analysis observation by Atomic Force Microscopy (AFM) showed that nanopore size increased with anodization time. The nanopore sizes of porous alumina were (16.04, 26.19 and 37.39 nm) for (1, 2 and 3 hour) respectively.

阳极氧化法制备医用钛纳米结构表面的工艺研究

采用正交试验法设计出一种阳极氧化技术制备纳米结构医用钛表面的工艺，研究了不同电解液浓度，阳极氧化电压和氧化时间对医用钛表面润湿性能和耐腐蚀性能的影响，得到综合性能最佳的纳米结构医用钛表面。实验采用纯水接触角测试说明纳米结构表面的亲疏水性能，通过测定塔菲尔曲线来表征纳米结构表面的耐腐蚀性能和利用扫描电子显微镜观察纳米结构表面的微观形貌。结果表明：电解液组成为1.0%的HF溶液，阳极氧化电压为20 V和工作时间为60分钟，为最优的工艺参数。此条件下处理得到的医用钛表面具有较小的接触角和较大的腐蚀电位，说明其良好的亲水性能和抗腐蚀性能。扫描电子显微镜结果表明医用钛材料经优化的阳极氧化工艺处理后其表面呈现为规则的纳米管阵列，且材料表征显示处理的医用钛表面为非晶氧化钛薄膜，厚度约为380 nm。 An anodic oxidation approach for preparation of nanostructured titanium surface was developed by orthogonal design. The effects of the concentration of electrolyte, the working voltage and the duration for anodic oxidation on the hydrophobic property and the corrosion resistance of biomedical titanium surface have been systematically studied, and the biomedical titanium surface with the high quality has been achieved. In the study, the contact angle of pure water was utilized to demonstrate the hydrophobic property, the Tafel curve was used to characterize the corrosion resistance, and scan electronic microscope was performed to observe the surface morphology. It was found that the electrolyte composition of HF 1.0% solution, the anodic oxidation voltage set at 20 V and the anodic oxidation duration of 60 minutes were the optimal parameters for the anodic oxidation process. Using the optimal parameters, the obtained titanium surface possessed smaller contact angle and higher corrosion potential, indicating its good hydrophilic property and corrosion resistance. Scanning electron microscope results shown that ordered nanotube arrays were present on biomedical titanium material treated by the optimal anode oxidation process and the materials characterization revealed that the as-prepared surface was amorphous TiO2 film with thickness about 380 nm.

Structural characterizations of Cu3Pt electrocatalyst featuring Pt-rich surface layers synthesized via mechanical alloying and selective dissolution routes

We demonstrate a selective electrochemical dissolution route to prepare Cu3Pt catalysts featuring Pt-rich surface layers (Cu3Pt-Pt rich surface) from mechanically alloyed Cu3Pt. These catalysts were investigated by X-ray diffraction and X-ray absorption spectroscopy, and were subjected to electrochemical analyses to evaluate their catalytic properties. With appropriate anodization, Cu3Pt entered an oxygen-evolving regime where the corrosive dissolution of Cu dominated the reaction. Selective dissolution was carried out to prepare Pt-rich layers at the surface, while Cu3Pt was left unreacted at the core. An increase in the anodization duration modified the sample morphology, with the redistribution of Pt atoms to thicken the surface layers. A charge transfer from Pt to Cu accompanied the structural transition from Cu3Pt to Cu3Pt-Pt rich surface upon selective dissolution, rendering the sample to be electronically similar to a metal Pt. However, compared to the metal Pt and conventional Pt-based catalysts, the proposed structure is a more economical catalyst for direct methanol fuel cell, with less need of Pt in raw material but increased electrochemical surface area by exposing enormous Pt at the surface with an increase in the anodization duration.

Electropolymerization of Ni(salen) on carbon nanotube carrier as a capacitive material by pulse potentiostatic method

The composites of poly[Ni(salen)] and multi-walled carbon nanotube (MWCNT) were synthesized by pulse potentiostatic method. The composites were characterized by field emission scanning electron microscopy, Fourier transform infrared spectra, and electrochemical impedance spectroscopy. The wrapping of carbon nanotubes with poly[Ni(salen)] varied significantly with anodic pulse duration. Variance of structure of poly[Ni(salen)] caused by anodic pulse duration affected the ability of absorption to solvent molecules or solvated ions, which was indicated by ν (C≡N) intensity. The ability to store/release charge of poly[Ni(salen)] caused by redox switching was evaluated in the form of low-frequency capacitance. Correlations of charge-transfer resistance/ionic diffusion resistance with potential and anodic pulse duration were investigated.

Micro/nanostructure evolution of zircaloy surface using anodization technique: Application to nuclear fuel cladding modification

Zircaloy with nano-scale and micro/nano-scale (dual-scale) surface structures was fabricated using an anodic oxidation fabrication technique. The surface structure evolved as a function of duration of anodization. The resulting nanotubes and dual-scale surface structure were characterized by scanning electron microscopy (SEM) to analyze the evolution of the structures. The current density curve during the anodization was closely related to morphology of surface structure. Thus, surface structures can be selectively fabricated by watching the current density and controlling the duration of anodization. Control of surface structure formation resulted in change of wettabilities in the range of 0°–50° contact angle. The modified surfaces significantly enhanced critical heat flux, meaning this simple yet effective surface modification method can enhance the thermodynamic performance of the surface, especially in the case of the nuclear fuel cladding application. This technique would greatly contribute to the safety of nuclear reactors.

Growth and Morphology of Highly Ordered TiO2 Nanotube Arrays via Electrochemical Anodization

In this paper, highly ordered titania nanotube arrays (TNTs) were prepared by anodization of Ti foils in ethylene glycol electrolyte. The morphology of the TNTs under different voltage and duration has been studied by Scanning Electron Microscopy (SEM). The constituent elements of the TNTs are mapped by energy dispersive X-ray (EDX). Immobilized TNTs were formed in the voltage range of 20~80V. High anodic voltage (>80V) induced detachable nanotube arrays on Ti foils. The nanotube diameter increases with increasing the applied voltage and without dependence on the anodic duration. The concentration of element oxygen is rich at top and bottom sections of the nanotube arrays. Meanwhile, the oxygen concentration on top surface decreases with increasing the anodization voltage.

Effects of geometric and crystal structures on the photoelectrical properties of highly ordered TiO2 nanotube arrays

Abstract

X-ray photoelectron spectroscopic studies of anodically synthesized self aligned TiO2 nanotube arrays and the effect of electrochemical parameters on tube morphology

Self aligned TiO2 nanotube arrays, compared to other TiO2 nanostructures, have better electron transport properties that will enhance the efficiency of photo catalysis, hydrogen generation by photo-electrolysis and dye sensitized solar cells. Optimization of process parameters by tuning of electrochemical parameters allows the synthesis of TiO2 nanotube arrays of desired aspect ratio, wall thickness and morphology. In this study TiO2 nanotube arrays were synthesized at various electrochemical parameters and characterized using field emission scanning electron microscopy (FESEM), Fourier transform infra-red (FTIR) and X-ray photoelectron spectroscopy (XPS). From the results of the study optimum potential range, electrolyte compositions and duration of anodization for the fabrication of smooth walled nanotube arrays of desired aspect ratio are delineated. Presence of surface hydroxyl groups and non-stochiometry in the as prepared and annealed TiO2 nanotubes were found from FTIR and XPS studies respectively, thus providing rationalization for the enhanced photo catalytic activity of TiO2 nanotube arrays.

TiO 2 nanorods branched on fast-synthesized large clearance TiO 2 nanotube arrays for dye-sensitized solar cells

A large clearance TiO 2 nanotube arrays (LTAs) has been synthesized by a not more than 12 h anodization duration and based on this a branched TiO 2 nanotube arrays (BLTs) has been achieved through TiO 2 nanorods branch-like grown on the LTAs. Some key factors and probable mechanisms of the fabrication processes on two novel nanoarchitectures are discussed. Exhilaratingly, it is found that the obtained LTAs has demonstrated large pore diameter and void spaces (pore diameter ∼350 nm; void spaces ∼160 nm; and tube length ∼3.5 μm), and the synthesized hierarchical BLTs, compared with conventional TiO 2 nanotube arrays, has shown a much stronger dye absorption performance and an approximately double of the solar cell efficiency (in our case from 1.62% to 3.18% under simulated AM 1.5 conditions).

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.

Effects of Synthesis Parameters on Controllable Growth of Highly-Ordered TiO<sub>2</sub> Nanotube Arrays

Titania nanotube arrays were fabricated in deionize water and glycerol mixed electrolyte containing a certain amount of NH4F. Three different polishing methods were used for pretreatment of Ti substrates: polished by hand with abrasive paper, by polishing machine, or by chemical polishing fluid (HF:HNO3=1:4, in volumetric ratio). The morphology of three different samples were imaged by scanning electron microscopy, and their photoelectrical properties were studied as well. Experimental results showed that Titania nanotube arrays grown on the Ti substrate and polished by polishing fluid has highly-ordered and well-defined nanotube structure. The effects of anodization potential and duration on synthesis of highly-ordered TiO2 nanotubes were also studied in this paper. Both the layer thickness and nanotube diameter linearly increase with the increasing potential. The layer thickness also increases with prolongation of anodization time. By optimizing the preparation conditions, we can successfully control the geometrical structure of TiO2 nanotube arrays with diameters in the range between 50 and 200 nm and the layer thickness between 800 and 2000 nm.

Fabrication of Highly Ordered TiO2 Nanotubes from Fluoride Containing Aqueous Electrolyte by Anodic Oxidation and Their Photoelectrochemical Response

The fabrication of TiO2 nanotubes (TNT) was carried out by electrochemical anodization of Ti in aqueous electrolyte containing NH4F. The effect of electrolyte pH, applied voltage, fluoride concentration and anodization duration on the formation of TNT was investigated. It was observed that self-organized TNT can be formed by adjusting the electrolyte to pH 2-4 whereby applied voltage of 10-20 V can be performed to produce highly ordered, well-organized TNT. At 20 V, TNT can be fabricated in the concentration range of 0.07 M to 0.20 M NH4F. Higher fluoride concentration leads to etching of Ti surface and reveals the Ti grain boundaries. The prepared TNT films also show an increase in depth and in size with time and the growth of TNT films reach a steady state after 120 minutes. The morphology and geometrical aspect of the TNT would be an important factor influencing the photoelectrochemical response, with higher photocurrent response is generally associated with thicker layer of TNT. Consequently, one can tailor the resulting TNT to desired surface morphologies by simply manipulating the electrochemical parameters for wide applications such as solar energy conversion and photoelectrocatalysis.

Synthesis and characterization of highly ordered TiO 2 nanotube arrays for hydrogen generation via water splitting

Highly ordered TiO 2 nanotube arrays (TNA) have been synthesized by anodization of Ti foils using an established electrochemical process. The parameters such as anodization potentials and durations have been varied to fabricate the specific morphology of TNA. In addition, Pt nanoparticles were deposited on these TNA via microwave irradiation. The photocurrent density–voltage ( J– V) properties induced by the standard AM 1.5 solar simulator have been characterized using a potentiostat meter. The efficiency of photoelectrocatalytic effect of the large-pore-sized TNA (=120 nm) is found to be higher than those of the TNA in smaller pore sizes (≤100 nm). TNA with smaller pore sizes exhibit lower surface areas, and therefore, inferior photo-current efficiency to those of TNA with larger pore sizes. The low surface area of smaller-pore-sized TNA was resulted from the shorter tube length obtained at smaller anodizing voltages. Deposition of Pt nanoparticles on TNA was successfully accomplished using microwave irradiation technique. An enhanced hydrogen generation rate of 0.613 ml h −1 cm −2 (≅25.0 μmol h −1 cm −2) was obtained on these Pt-deposited TNA compared to the 0.313 ml h −1 cm −2 (≅12.8 μmol h −1 cm −2) of pristine TNA in a solution of methanol and water (1:1 ratio).

Modified TiO2 nanotube arrays (TNTAs): progressive strategies towards visible light responsive photoanode, a review

Since first introduced by Zwilling and co-workers in 1999, titania nanotube arrays (TNTAs) fabricated by simple electrochemical anodization method have attracted great interest due to their outstanding photoelectrochemical properties which render them the most promising candidate for many solar energy harvesting applications. In this contribution, the fabrication, properties, and applications of TiO2 nanotube arrays have been reviewed, with special focus on synthesis by anodization in fluoride-containing electrolytes. The effect of anodization process parameters such as electric potential, pH, anodization duration and electrolyte composition on the size, and morphology of TNTAs has been discussed in detail. Electronic property modification strategies of the wide band gap TNTAs to enhance the material responsiveness to visible light irradiation have also been reviewed. Modification strategies include nonmetal doping such as nitrogen, carbon, boron and sulfur; metal ion doping such as Fe, Zn, Zr and Cr; surface decoration with precious metal nanoparticles such as Pt, Ag, Au; and sensitization with CdS nanoparticles.

Design of porous silicon/PECVD SiOx antireflection coatings for silicon solar cells

Abstract The meso-porous silicon (PS) has become an interesting material owing to its potential applications in many fields, including optoelectronics and photovoltaics. PS layers were grown on the front surface of the n + emitter of n + –p mono-crystalline Silicon junction. The thickness and the porosity of the PS layer were determined by an ellipsometer, as a function of time duration of anodization, and the variation law of the PS growth kinetics is established. Single layers PS antireflection coating (ARC) achieved around 9% of effective reflectivity in the wavelength range between 400 and 1000 nm on junction n + –p solar cells. To reduce the reflectivity and improve the stability and passivation properties of PS ARC, silicon oxide layers were deposited by PECVD on PS ARC. SiO x layers of thickness of 105 nm combined with PS layer led to 3.8% effective reflectivity. V oc measurements were carried out on all the samples by suns- V oc method and showed an improvement of the quality of the passivation brought by the oxide layer. Using the experimental reflectivity results and taking into account the passivation quality of the samples, the PC1D simulations predict an enhancement of the photogenerated current exceeding 44%.

Fabrication of titanium dioxide nanotube array and effects of its osteoblast proliferation and alkaline phosphatase activity

To investigate preparation parameters of TiO2 nanotube layer with anodization, and to evaluate the osteoblast activity on TiO2 nanotube layer in vitro. Titanium dioxide nanotube layer was grown using anodization method. TiO2 nanotube layers with different structure were obtained by controlling the voltage and time of anodization and rinsing process after anodization. Pure titanium without anodization was used as control. Osteoblasts were cultivated on the anodizated TiO2 nanotube, and the growth of osteoblasts was then evaluated and analyzed. The voltage, duration of anodization and rinsing process following anodization were key factors to affect morphology of TiO2 nanotube layer. The area of osteoblast cultured on TiO2 nanotube layer was larger than that on pure titanium. Results from methylthiazol tetrazolium (MTT) test showed that the proliferation of osteoblasts after 96 h cultivation on TiO2 nanotube layer (0.62 +/- 0.02) was significantly higher than that on unanodizated titanium (0.55 +/- 0.03, P < 0.05). Three weeks later, the alkaline phosphatase (ALP) activity on TiO2 nanotube layer [(130.8 +/- 5.1) A(405)/mg] was significantly higher than that on unanodizated titanium [(109.6 +/- 4.5) A(405)/mg, P < 0.05]. The structure of TiO2 nanotube layer was greatly associated with anodization voltage. The TiO2 nanotube layer had a positive effect on osteoblast behavior.

Effect of oxalic acid concentration on the formation of anodic aluminum oxide using pulse anodization at room temperature

Most anodic aluminum oxide (AAO) or porous anodic aluminum (PAA) films were fabricated using the potentiostatic method from high-purity (99.999%) aluminum films at low temperatures of 0–10°C to avoid dissolution effects at room temperature (RT). In this article, the fabrication of AAO or PAA film from commercial purity (99%) aluminum at RT has been investigated using hybrid pulse anodization under different oxalic acid concentration and process duration. The effect of acid concentration and anodization duration on the formation of AAO size and morphology has been studied. Both pore diameter and oxide layer thickness of AAO films were examined via SEM images and found that both increased with increasing oxalic concentration and anodization duration. In addition, the pore distribution was more concentrated at high electrolytic concentration and anodization duration.