Anodization Bath Research Articles

Effect of Quantum Dot Deposition on the Interfacial Flatband Potential, Depletion Layer in TiO2 Nanotube Electrodes, and Resulting H2 Generation Rates

CdS QD-modified TiO2 nanotube arrays were fabricated using an anodic oxidation-sequential chemical bath deposition process. By means of FESEM, EDS, XRD and XPS, it could be confirmed that the use of an ultrasonication-assisted deposition approach improved the distribution of CdS QDs on the tube walls. The as-prepared CdS-modified TiO2 nanotube arrays exhibited enhanced photoelectrochemical properties and hydrogen production activity, which benefitted from the extended light absorption and the improved interfacial charge-transfer properties of TiO2 nanotube arrays. By analyzing the interfacial properties, the flatband potential, the depletion layer, the capacitance, and the impedance of the CdS/TiO2 photoelectrode, it can be concluded that compared with pure TiO2 nanotube arrays the CdS QD-modified arrays exhibited a more negative flat band potential and a lower energy barrier for interfacial electron transfer. The calculated depletion layer width (dSC) of the sensitized TiO2 nanotube arrays was larger, wh...

Branched titania nanotubes through anodization voltage control

Titania nanotubes are attractive for many applications such as energy generation, storage and delivery, gas sensing, and water purification. Here, we demonstrate branched titania nanotube formation during potentiostatic anodization of titanium films or foils in a single electrochemical bath by stepping down the anodization voltage V anod below a threshold value. The linear dependence on the titanium nanotube diameter with V anod and the lack of nanotube formation for V anod < 20 V constrains homogeneous branching to occur only V 2 ≤ V 1 2 − V 0 , where V 1 and V 2 are the initial and final anodization voltages and V 0 is a voltage offset dependent on the anodization bath chemistry. Our technique circumvents the constraints of multi-bath and multi-temperature methods for branching, and provides a versatile means for creating hierarchically sized and/or interconnected titania nanotubes for applications.

Controlled Growth of TiO2 Nanotubes on Conducting Glass

We report on nanotubular TiO2 on top of a compact TiO2 layer on conducting glass substrates. Highly regular structures were obtained from anodization of DC sputtered Ti films of thicknesses between 0.2 and 2 μm in ammonium fluoride containing ethylene glycol solutions. The influence of different anodization parameters was systematically analyzed revealing that full control over tube length, diameter, spacing, and tube wall thickness is possible. Inner tube diameters and spacing between tubes can be controlled via the anodization field. Tube wall thickness can be tuned using different anodization bath temperatures. Tube length can be adjusted by sputtering appropriate layers of Ti. The resulting TiO2 structures can be readily used in poly(3-hexylthiophene)-TiO2 hybrid solar cells and solid state dye sensitized solar cells. In contrast to anodized Ti foils the presented geometry allows the fabrication of photovoltaic devices which can be frontside-illuminated (through the glass substrate).

Temperature-Dependent Growth of Self-Assembled Hematite (α-Fe2O3) Nanotube Arrays: Rapid Electrochemical Synthesis and Photoelectrochemical Properties

We report on the self-assembled fabrication and photoelectrochemical properties of α-Fe2O3 (hematite) nanotube arrays, prepared by potentiostatic anodization of iron foil in an ethylene glycol electrolyte containing NH4F and deionized water. Vertically oriented nanotube arrays provide a highly ordered material architecture of high surface area that is nearly ideal for efficient transport and separation of photogenerated charges. We have achieved iron oxide nanotube arrays over a potential range of 30−60 V, using an electrolyte comprised of 0.2−0.5 wt % NH4F, and 2−4% DI water. The resulting nanotube arrays have a pore diameter ranging between 30 and 80 nm, with a minimum wall thickness of ∼10 nm. Nanotube formation is strongly dependent on the anodization bath temperature and fluoride concentration, with higher temperatures leading to increased rates of nanotube array growth, and with lower temperatures required in order to obtain identifiable nanotubes arrays for increased F− ion concentration. Crystallization of the as-synthesized, amorphous, iron oxide nanotube arrays to hematite is achieved through annealing in an oxygen-deficient ambient.

PHOTOLUMINESCENCE OF NON-CRYSTALLINE ALUMINA NANOWIRES SYNTHESIZED BY DIRECT ANODIZATION OF ALUMINUM

Alumina nanowires have been synthesized by a simple electrochemical route, by tailoring the anodization process of aluminum. Two-stage anodization of pure aluminum foils were carried out in 0.3 M oxalic acid electrolyte by maintaining a constant current density of 250 A/m2 and suitably controlling the other anodization parameters: anodization voltage, bath temperature and anodization time. The fabricated alumina nanowires were investigated by field-emission scanning electron microscope (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Moreover, the X-ray diffraction (XRD) study on the prepared nanowires shows that they are non-crystalline in nature. The photoluminescence (PL) spectra of alumina nanowires exhibit two stable emission bands at 438 and 581 nm. The blue luminescence behavior of the alumina nanowires are attributed to the oxygen-deficient defect centers. PL study of alumina nanowires shows that they have potential applications in light emission devices.

Effect of Substrate on Electroless Co-Base Deposited Films

The deposition behavior and structural and magnetic properties of electroless Co-B and Co-Fe-B deposits, as well as the amorphous ribbon substrates, were investigated. These Co-based alloy deposits exhibited characteristic polycrystalline structures and surface morphology and magnetic properties that were dependent on the type of amorphous substrates. The catalytic activity sequence of the amorphous ribbon electrodes for anodic oxidation of DMAB was estimated from the current density-potential curve in the anodic partial electrolytic bath that did not contain the metal ions. Both the deposition rate and potential in the initial region were obtained in order of the catalytic activity, depending on the alloy compositions of the substrates. The deposition rate linearly varied against the deposition time. The initial deposition potential may have also determined the structural and magnetic properties of the deposit based on the thickness of <TEX>${\mu}m$</TEX> order. Furthermore, a basic study of the electroless deposition processes on an amorphous ribbon substrate has been carried out in connection with the structural and magnetic properties of the deposits.

Porosity Tailored Growth of Black Anodic Layers on Magnesium in an Organic Electrolyte

Thick anodic layers on pure Mg were produced by anodization in a nonaqueous electrolyte. The most promising systems for growth of thick, uniform anodic layers were nominally water-free methanol or ethanol electrolytes containing nitrate ions. The layer thickness shows a linear dependence on the applied voltage and on the anodization time. This nonlimited layer growth, leading to a very high thickness with time (e.g., up to with at for the methanol system), suggests a porous nature of the layer. Scanning electron microscopy examination of the surface morphology indeed reveals nanopores/flakes in the layer. In addition, the porosity of the layer can be tuned by the use of ethanol and methanol mixtures as an anodization bath. The chemical composition of the films was examined by using X-ray photoelectron spectroscopy and energy-dispersive X-ray analysis, which reveals that the anodic layer consists of mainly Mg, O, and C (without toxic or environmentally hazardous species). Furthermore, the layers can be converted into crystalline MgO upon annealing without significant loss in morphology. This type of thick nanoporous layer is a promising candidate for the functionalization of Mg surfaces for different applications.

Corrosion properties of AZ31 magnesium alloy and protective effects of chemical conversion layers and anodized coatings

The corrosion properties of AZ31 magnesium alloys were studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy(EIS) techniques, meanwhile, the protective properties of two environmentally protective types of chemical conversion layers and anodized coatings of AZ31 magnesium alloys were also discussed. The component of chemical conversion bath is NaH 2O 4 12H 2O 20 g/L, H 3PO 4 7.4 mL/L, NaNO 2 3 g/L, Zn(NO 3) 2·6H 2O 5 g/L and NaF 1g L, and components of the anodization bath is Na 2SiO 3 60 g/L, C 6H 5Na 3O 72H 2O 50 g/L, KOH 100 g/L and Na 2B 4O 7·2H 2O 20 g L. The results show that the corrosion resistance of AZ3 1 magnesium increases with the increase of pH value of the corrosive medium. For the chemical conversion layer acquired at 80 °C, 10 min is the best processing time and the charge transfer resistance of the chemical conversion layer is enhanced nearly by 10 times. The optimum processing time for the anodization of AZ31 is 60 min, the charge transfer resistance value of the anodized sample at the early immersion stage is nearly 26 times of that of the blank sample and the corrosion type of the anodized samples is pitting.

Kinetics of the electrolytic coloring process on anodized aluminum

The kinetics of tin electrodeposition during the electrolytic coloring of porous anodic oxide films on aluminum is studied as a function of the oxide properties, e.g., the thickness of the porous oxide layer, and the surface resistance offered by the barrier oxide layer. While the thickness of the porous oxide layer is controlled by the anodization time, the surface resistance is controlled by the anodization voltage, and the anodization bath temperature. Steady-state polarization measurements are employed to characterize the dependence of the coloring kinetics on the oxide properties. Measurements indicate that the kinetics of the electrolytic coloring process can be accelerated by: (i) reducing the surface resistance of the oxide film (primarily offered by the barrier oxide layer) by growing the oxide at a lower anodization voltage, and/or a higher bath temperature, or (ii) growing a thinner porous oxide layer by decreasing the anodization time. The electrochemical measurements are supported by gravimetric analysis of electrolytically colored alumina samples (using calibrated wavelength-dispersive X-ray fluorescence spectroscopy), and by optical spectrophotometry.

Corrosion resistance of phosphate coatings obtained by cathodic electrochemical treatment: Role of anode–graphite versus steel

The formation of phosphate coatings by cathodic electrochemical treatment using graphite and steel anodes and evaluation of their corrosion resistance is addressed in this paper. The type of anode used, graphite/steel, has an obvious influence on the composition of the coating, resulting in zinc–zinc phosphate composite coating with graphite anode and zinc–iron alloy–zinc phosphate–zinc–iron phosphate composite coating with steel anode. The corrosion resistance of the coating is found to be a function of the composition of the coating. The deposition of zinc/zinc–iron alloy along with the zinc phosphate/zinc and zinc–iron phosphate using graphite/steel anodes has caused a cathodic shift in the Ecorr compared to uncoated mild steel substrates. The icorr values of these coatings is very high. EIS studies reveal that zinc/zinc–iron alloy dissolution is the predominant reaction during the initial stages of immersion. Subsequently, the formation of zinc and iron corrosion products imparts resistance to the charge transfer process and increases the corrosion resistance with increase in immersion time. The corrosion products formed might consist of oxides and hydroxychlorides of zinc and iron. The study suggests that cathodic electrochemical treatment could be effectively utilized to impart the desirable characteristics of the coating by choosing appropriate anode materials, bath composition and operating conditions.

Fabrication of hydrogen sensors with transparent titanium oxide nanotube-array thin films as sensing elements

Transparent thin films comprised of highly ordered titania nanotube-arrays were grown from titanium thin films using an anodization technique, from which highly sensitive and selective hydrogen sensors that can operate at room temperature were fabricated. Titanium films sputter deposited on glass at 500 °C were anodized in a fluorine-containing electrolyte to obtain nanotube-array films. Precise monitoring of current during the anodization enabled removal of the samples from the anodization bath at a point where the remaining metal layer became discontinuous, without destroying the nanotube architecture. The samples were then annealed in oxygen at 420 °C to crystallize the nanotube-arrays as well as oxidize any un-anodized metallic regions, yielding transparent films comprised of titanium oxide nanotube-arrays. Herein, we discuss the morphology, structure and optical characterization of these films. When coated with a 10-nm discontinuous palladium layer, the optically transparent nanotube-array films serve as excellent hydrogen sensors, exhibiting a four-order magnitude drop in resistance with exposure to 1000 ppm hydrogen at room temperature.

Enhanced Photocleavage of Water Using Titania Nanotube Arrays

In this study highly ordered titania nanotube arrays of variable wall thickness are used to photocleave water under ultraviolet irradiation. We demonstrate that the wall thickness and length of the nanotubes can be controlled via anodization bath temperature. We find that the nanotube wall thickness is a key parameter influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. For 22 nm inner pore diameter nanotube arrays, those fabricated in a 5 degrees C anodization bath, 224 nm length and 34 nm wall thickness produced a photoanodic response that was thrice that of a nanotube array fabricated in a 50 degrees C anodization bath, 120 nm length and 9 nm wall-thickness. At high anodic polarization, above 1 V, the quantum efficiency under 337 nm illumination was greater than 90%. For the 5 degrees C anodization bath samples (22 nm pore-diameter, 34 nm wall thickness), upon 320-400 nm illumination at an intensity of 100 mW/cm(2), hydrogen gas was generated at the power-time normalized rate of 960 micromol/h W (24 mL/h W) at an overall conversion efficiency of 6.8%. To the best of our knowledge, this hydrogen generation rate is the highest reported for a titania-based photoelectrochemical cell.

Modeling of the Current Distribution in Aluminum Anodization

The growth of porous anodic Al2O3 films, formed potentiostatically in continuously stirred 15 wt.% H2SO4 electrolyte was studied as a function of the anodization voltage (14–18 V), bath temperature (15–25 °C) and anodization time (15–35 min). The variation of the anodic surface overpotential with the current density was measured experimentally. The film thickness at the more accessible portions of the anode was observed to increase with the anodization voltage and the bath temperature. However, the film thickness on the less accessible portions of the anode did not significantly change with the voltage or the bath temperature. This indicates that the anodization process at the more accessible regions is more strongly influenced by the surface processes than by the electric migration within the electrolyte. Furthermore, analysis confirms that the major portion of the film resistivity resides within a thin sub-layer that does not vary with the anodization time, and the growing anodic layer contributes only marginally to the overall film resistance. Computer aided design software was employed to simulate the current density distribution. For the range of process parameters studied, the electrochemical CAD software predicts accurately the measured thickness distribution along the anode.

Effect of Anodization Bath Chemistry on Photochemical Water Splitting Using Titania Nanotubes

ABSTRACTIn this study highly-ordered titania nanotube arrays of variable wall-thickness and length are used to photocleave water under ultraviolet irradiation. We demonstrate that the wall thickness, and length, of the nanotubes can be controlled via anodization bath composition and temperature. The nanotube length and wall thickness are key parameters influencing the magnitude of the photoanodic response and the overall efficiency of the water-splitting reaction. For 22 nm inner-pore diameter nanotube-arrays 6 μm in length, with 9 nm wall thickness, upon 320–400 nm illumination at an intensity of 100 mW/cm2, hydrogen gas was generated at the power-time normalized rate of 51 mL/hr•W at an overall conversion efficiency of 12.5%. To the best of our knowledge, this hydrogen generation rate is the highest reported for a titania-based photoelectrochemical cell.

Understanding and improving the uniformity of electrodeposition

A new method namely the wire beam electrode (WBE) has been employed as a means of characterising electrodeposition uniformity. The influences of several electroplating parameters including the geometry of bath, the concentration and movement of electrolyte, and bath temperature on the uniformity of electroplated coatings have been investigated by mapping local electrodeposition currents and by analysing characteristic patterns in these current distribution maps. With the Watts nickel bath, the general current distribution pattern is such that higher currents were recorded along the edges with the magnitude decreasing in a contour-like manner towards the center of the WBE surface. Lower offset voltages, suitable amount of bath agitation, elevated temperatures, appropriate cathode–anode separation and bath concentration were found to contribute to the enhancement of current distribution uniformity when they were assessed individually. However, combining these plating parameters did not produce the expected synergistic effect in uniformity improvement.

Numerical Modelling of an Anodic Metal Bath Heated with an Argon Transferred Arc

A new 3-D model has been developed to describe the interaction between a transferred electric arc and a liquid metal bath, and has been used to simulate a pilot axisymmetrical transferred arc furnace operating in the EDF Research and Development laboratory. This model enables calculations of the flow patterns, temperature distribution and electromagnetic fields in both the arc and the bath. The Navier-Stokes equation coupled with the electromagnetic relations are solved in each domain using a finite volume method. The source term in the radiative energy equation is modeled using the radiative transfer method in order to take into account the strong temperature variations in the electric arc. The transport and condensation of metal vapour in the arc domain are considered by solving a conservation equation for the vapour mass fraction. The arc flow calculation at the bath surface uses a one-dimensional sheath model taking account of the metal vapour, in order to ensure the coupling between the plasma and the bath by evaluating the boundary conditions at the arc/bath interface. The calculations were performed for an arc length of 0.25 m. Realistic predictions are obtained for the electrical, dynamic and thermal behaviour of the plasma and liquid metal, and also for the arc voltage. The results indicate that the effects of the arc impact and Lorentz forces are not sufficient to induce effective mixing throughout the metal bath, leading to a marked thermal stratification in the liquid metal. In the bath, the liquid/solid interface has been determined by calculations. Keywords

非晶質薄帯上への無電解Ｃｏ‐Ｆｅ合金析出の電気化学的特性

Electroless Co-Fe alloy deposition on the substrate of amorphous ribbon in a bath containing DMAB as a reducing agent was studied using an electrochemical polarization curve. The deposition rate was predicted by anodic and cathodic polarization curves for electrolessly-deposited Co-Fe alloy electrodes in the plating bath. The catalytic activity sequence of Co-Fe alloy electrode for anodic oxidation of DMAB was estimated from the current density-potential curve in an anodic partial bath not containing metal ions, and led to clarification of the relationship between the deposition rate of Co-Fe and the alloy composition of the deposit. The catalytic activity sequence of amorphous ribbon electrode depending on its alloy composition for anodic oxidation of DMAB was itself found to significantly affect the deposition rate in the initial stage.

Silver Complex Dependence of Superadditivity in Physical Development

AbstractThe mechanism of the silver complex dependence of superadditivity in physical development was studied by physical development on an evaporated gold layer and current measurement using a comparable model cell to the development. The development rate of the thiocyanate developer including Phenidone/hydroquinone or Phenidone/ascorbic acid agreed with that calculated from the theoretical equation for the catalytic current, while the development rate of the thiosulphate developer was much smaller than the theoretical value. The current flowing through the external circuit of the cell is governed by the silver complex used in the anodic bath. It was concluded that thiocyanate has no influence upon the anodic process of Phenidone, while thiosulphate inhibits it.

Anodic Oxidation of Carbon Fibres in Diammonium Hydrogen Phosphate Solution

Abstract Anodic surface treatment of high tensile-carbon fibres under galvanostatic conditions has been performed in diammonium hydrogen phosphate solution, containing an addition of ammonium rhodanide. The oxidized fibres have been characterized by monofilament tensile strength, XPS measurements and surface energetic analysis. Additionally, the acid-base interactions have been evaluated by wetting with aqueous solutions of different pH values. An addition of ammonium rhodanide to the diammonium hydrogen phosphate anodization bath affects the oxidation of carbon fibres in terms of decreasing both the amounts of the surface oxides as well as that of degradation by-products. At the optimal treatment conditions (I = 100 mA) no changes in the tensile strength or BET-surface area of the fibre have been observed. The rise in ILSS values of amine cured epoxy composites is not dependent on Ols/Cls ratio or surface free energy of the reinforcing fibres, but on the acidic as well as nitrogen functional groups on th...

Effect of anode material and bath composition on bubble layer resistivity and gaseous volume fraction in an aluminium electrolysis cell with sloping anode and cathode

Two carbon anodes of different formulation were employed to study the effect of varying anodecathode distance (ACD) on the effective bath resistivity in a laboratory cell that utilized a sloping inert-wettable TiB2-carbon composite cathode and sloping anode. The bubble layer resistivity and gaseous volume fraction values were also determined and were employed to verify the observed changes in the bubble contribution to the effective bath resistivity. Results associated with the addition of excess AlF3 and NaCl to the bath are also included and discussed.