Transient behaviour of the anodic oxide film on tantalum

After heating the anodic oxide film on tantalum, a constant current or voltage was applied to the specimen in a diluted phosphoric acid solution, and the transient behaviour was examined according to the Frenkel defect model.Interstitial ions taking part in ionic conduction are captured in the vacant sites by heating. For an expression of this rate, the second term of Dewald's equation (iσm) was found to be valid. By using this equation it was found that the film, once deteriorated by heating, could be repaired by subsequent current flow and no more serious deterioration was observed after a second heating.When a constant voltage was applied to the specimen after heating, transference of ions from the normal lattice sites to interstitial ones was considered to be induced by current flow as well as by field strength, hence the current term i was incorporated in to the first term of Dewald's equation. The amended equation coincided fairly well with the experimental results.     

The behavior of incorporated impurities in tantalum anodic oxide films at the dielectric breakdown

Distribution profiles of incorporated impurities in anodic oxide films of tantalum were investigated before and after the dielectric breakdown of the film as a function of the depth of the film for incorporation of phosphorus, sulfur and chlorine. The in-depth distribution profiles of the incorporated impurities dramatically changed at the breakdown of the oxide films. However, the trend of the change was quite different among the incorporated impurities; chlorine is concentrated in the interior of the film, but phosphorus and especially sulfur showed tendencies to be swept into electrolytes. The ionization of the film seems to be responsible for these phenomena.     

Decay of capacitance on ceasing formation of anodic oxide films on tantalum

The decrease with time in the capacitance of anodic oxide films on tantalum after ceasing film growth by reducing the field in the oxide was investigated. No dependence was observed of the amount and rate of change in relative dielectric permittivity on the initial current density. The kinetics of this effect are therefore different from those for the decay of the latent ionic conductivity.     

The effect of phosphorus incorporation on the dielectric constant and ionic conductivity of anodic tantalum oxide

Weight gain in excess of that expected for the anodic formation of Ta₂O₅ on tantalum in phosphate electrolytes can be accounted for by the incorporation of phosphorus as free phosphoric acid or, more likely, tantalum phosphate.Film thickness measurements show that faster anodization rates caused by phosphorus incorporation cannot be due to the formation of an increased amount of film material per unit of charge compared to solutions where relatively pure Ta₂O₅ is formed. Anodization rates are, however, inversely related to film dielectric constant which, in turn, is negatively proportional to the amount of phosphorus contained in the film.It is quantitatively shown that the use of the Lorentz or effective field in the equation relating anodization current density and field strength results in a constant field coefficient, whereas the Maxwell field produces field coefficients dependent on film dielectric constant.     

Stability of anodic tantalum oxide films in NaOH solutions

The dissolution behaviour of the anodic oxide films formed on tantalum was investigated in NaOH solutions of different concentrations. In solutions of [OH^–]<3.0 M, no pronounced dissolution could be detected. However, in concentrated alkali solutions, [OH]>3 M, the dissolution occurred to different extents depending on the alkali concentration. As observed from capacitance and potential measurements, the barrier film on Ta was found to be defective owing to the incorporation of OH^– ions in the film. The nature of the barrier film and its dependence on formation rate, alkali concentration and solution temperature were investigated. Complex plane analysis illustrates the behaviour of the barrier film of different thickness, i.e. formation voltages, in NaOH solutions. The barrier film cannot be considered accurately as a perfect dielectric.     

Dielectric properties of anodic oxide layers on tantalum

The dielectric properties of the anodically formed oxide layers on tantalum in contact with electrolyte were analysed by measuring the frequency and temperature dependence of the impedance. It has been found that the frequency dependence of the series capacitance and resistance component of the impedance in the audio frequency range are in accordance with Young's relation. In order to explain such behaviour the electrical resistivity is assumed to vary exponentially with distance through the oxide layer. This variation can be ascribed to the occurrence of the exponential change of oxygen vacancies in the anodic layer during the growth of the oxide layer. The activation energy was obtained from the temperature dependence of the series capacitance. In the paper the unsimplified Young's relations have been proved to be K-K transformable.Nomenclature C _s series capacitance (F) - R _s series resistance () - f frequency of applied signal (Hz) - x integration variable of frequency (Hz) - A area (cm²) - K characteristic length (cm^–1) - d oxide layer thickness (cm) - y distance through oxide (cm) - a _C slope of linear part of 1/C _s against logf plot (Equation 5) - a _R slope of linear part ofR _s against 1/f plot (Equation 3) - relative permittivity of oxide layer - (y) resistivity at distancey ( cm) - (0) resistivity on positiony=0 ( cm) - (d) resistivity on positiony=d ( cm) - T absolute temperature (K) - k Boltzmann constant (eV K^–1) - activation energy (eV) - z complex variable,z=x+iy, - Res residue     

Complex dielectric functions of anodic bi-layer tantalum oxide

The optical properties and structure of anodic oxides are dependent on the anodization conditions. For tantalum oxide formed in dilute phosphoric acid, the anodic oxide forms as two chemically distinct layers, referred to as a bi-layer, where the inner layer is pure tantalum oxide and the outer layer contains incorporated phosphate. The complex dielectric functions of the individual inner and outer layers are determined using spectroscopic ellipsometry. The dielectric functions of the bi-layers are compared to mono-layer oxides formed in sodium sulfate, and the effects of hydrothermal sealing are explored. For bi-layer oxides formed to 70 V in phosphoric acid, the inner layer band gap is 4.37 ± 0.02 eV and the outer layer band gap is 3.86 ± 0.06 eV. Thin anodic oxides (∼6-15 nm) are best described by a mono-layer oxide model and exhibit higher optical absorption with a band gap of 3.98 ± 0.08 eV. This study shows that spectroscopic ellipsometry is a valuable tool in assessing processing-property relationships of multi-layer anodic films.     

The anodic oxide film on iron in neutral solution

The composition of the anodic passive oxide film on iron in neutral solution has been investigated by cathodic reduction, chemical analysis and ellipsometry. The cathodic reduction using a borate solution of pH 6·35 containing arsenic trioxide as inhibitor estimates iron in the film to be all iron (III), indicating that no magnetite layer is present. Oxygen in the film is estimated from the ellipsometric thickness to be in excess of the stoichiometric ferric oxide, suggesting the presence of bound water. The average composition is represented as Fe₂O₃.0·4H₂O, in which hydrogen may be replaced partly with iron-ion vacancy. The anodic oxide film is composed of an inner anhydrous ferric oxide layer, which thickens with the potential and an outer layer of hydrous ferric oxide whose thickness depends on the condition of passivation and environment.     

多孔铝阳极氧化膜在催化中的研究进展

利用基体铝的优良热传导性、表面铝阳极氧化膜具有的大的内表面积及材料的可加工性,可以开发出既具有高的热传导性又具有良好催化特性的薄膜.介绍了多孔铝阳极氧化膜在甲醇分解、环境保护、催化精馏、化学热泵用催化剂等方面的应用研究进展,并对其在催化中的应用前景进行了展望.     

Micro-patterning in anodic oxide film on aluminium by laser irradiation

Microstructures such as microchannels and microchambers were fabricated on anodic oxide film of aluminium with laser direct patterning technique. The aluminium substrate covered with porous type anodic oxide film was dyed with organic dyes followed by hydrothermal treatment. The coloured and pore sealed film shows much higher absorption then as-formed porous film, that makes possible to pattern various types of microstructures on the film by removing the upper part of the film surface by laser irradiation. Structure of the crystallized hydroxide layer on the surface of the anodic oxide film, formed during pore sealing, as well as the partial removal of anodic oxide film from the surface is described. Microstructures with depth lower than 1-27 μm were patterned successfully on 16 and 32 μm thick anodic oxide film surfaces, using various combinations of laser power and laser scanning speed. The affect of the laser scanning speed and laser power density on the shape of the microstructures is also explained.     

Mechanism of the cathodic reduction of a bismuth oxide anodic film

The electroreduction of a bismuth anodic oxide film is shown to involve electron migration in the film with reaction at the film-solution interface.     

Effect of hydrogen on stresses in anodic oxide film on titanium

Stresses in anodic oxide film on titanium thin film/glass electrode in pH 8.4 borate solution were investigated by a bending beam method. The increases in compressive stress observed with cathodic potential sweeps after formation of anodic oxide film were attributed to the volume expansion due to the compositional change of anodic oxide film from TiO₂ to TiO_2−x(OH)_x. The instantaneous responses of changes in stress, Δσ, in the anodic oxide film to potential steps demonstrated the reversible characteristic of the TiO_2−x(OH)_x formation reaction. In contrast, the transient feature of Δσ for the titanium without anodic oxide film represented the irreversible formation of TiH_x at the metal/oxide interphase. The large difference in stress between with and without the oxide film, has suggested that most of stresses generated during the hydrogen absorption/desorption reside in the anodic oxide film. A linear relationship between changes in stress, Δ(Δσ)_des, and electric charge, ΔQ_des, during hydrogen desorption was found from the current and stress transients, manifesting that the stress changes were crucially determined by the amount of hydrogen desorbed from the oxide film. The increasing tendency of −Δ(Δσ)_des with increasing number of potential steps and film formation potential were discussed in connection with the increase in desorption amount of hydrogen in the oxide film with increasing absorption/desorption cycles and oxide film thickness.     

铝阳极化染黑工艺中的故障处理

1　前言　　某电镀厂新增铝阳极化染黑工艺生产线 ,出现不少质量问题。如工件颜色有深有浅 ,有黑中显青 ,有黑中显红 ,有黑中留白 ,有灰黑混一等等。经细细辨别 ,笔者很快找出了故障起因并提出了解决方法。现将其整理如下 ,有误之处请广大同行批评指正。2　故障原因分析及解决方法2 1　颜色黑中显青　　通常是由如下 4种原因引起的 :　　①阳极氧化溶液温度过低　　②阳极氧化时间过短　　③电压过低　　④染色溶液ｐＨ值接近中性　　经分析 ,该厂所出现的质量问题是由于阳极氧化溶液温度过低而没有相应地延长阳极化时间和提高电压而引起的…     

铝基氧化膜内粒子电沉积及其功能膜的研究进展

由于铝阳极氧化膜的特殊结构,再加上其制备的功能膜具有一系列独特性能。因此,近年来受到国内外广大科研工作者的广泛关注。本文从溶液组成综述铝基膜内单一粒子和复合粒子电沉积工艺,从电源波形介绍直流、交流和脉冲电沉积工艺,另外也叙述了溶胶凝胶和超声波电沉积工艺。列举了用电沉积方法制备功能性薄膜在催化、光学、太阳能吸收膜以及磁学领域的应用,并对制备功能性氧化膜存在问题与发展方向进行阐述。     

Electrochemical reactions by tunnel current through thin insulating anodic oxide films on tantalum

Tantalum electrodes covered with oxide films, the thickness of which ranged from 40–90 Å, were investigated. Indium or gold was deposited on the oxide film by the vacuum deposition technique to prevent any change of oxide film properties by polarization. Polarization curves of In¦oxide film¦Ta diodes in a chloride buffer solution of pH 2.3 almost coincided with theI/V curves of them in the solid state. A redox reaction of a ferricyanide/ferrocyanide couple at Au ¦oxide film¦Ta was also perfectly controlled by electron transfer through the insulating oxide layer. Electron conduction with anodic polarization was mainly brought about by the electron tunnelling, while the Schottky emission possibly predominated in the conduction with cathodic polarization. Actual rates of corrosion of indium deposited on the films did not accord with those predicted by extrapolation of polarization curves to the open circuit potential, owing to the high electric resistance of the oxide films.     

Kinetics of anodic oxide film growth on indium in alkaline solution

Data are presented which describe the kinetics of repassivation of freshly generated indium surfaces of pH 14. The process is controlled by ion conduction through the growing oxide film under high electric field. The associated kinetic parameters are tabulated. At high potentials an excess anodic charge is observed; it is attributed to conversion of some of the barrier film into an non-barrier layer. Some kinetic data associated with this process are presented.     

Metallurgical aspects on the formation of self-organized anodic oxide nanotube layers

The present work reports how metallurgical factors such as grain size and chemical composition of substrate affect the current behavior during anodization and the morphology of resulting formed oxide layers. The grain size of pure Ti sheet is controlled by the accumulative roll-bonding (ARB) process. Tubular oxide layers are formed on the ARB-processed Ti sheets with different grain sizes, but grain size does not affect the length, diameter of tubes and the degree of tube arrangement. The effect of chemical composition is examined using Ti-Zr alloys (Ti-20Zr, Ti-50Zr, Ti-80Zr) that can consist of a single phase, meaning that homogeneous tube formation can be achieved. With increasing Zr content in the alloys, tube diameter decreases while tube length increases. For the Ti-50Zr and Ti-80Zr, self-organization is achieved on two size scales, that is, nanotube arrays with two distinct diameters are observed. TEM observation revealed that anodic oxide layers are in crystalline state only in the case of pure Zr.     

Mono- and multilayer formation studies on silver anodic film formation of silver bromide

The mono- and multilayer formation of silver bromide on silver was investigated by cyclic voltammetric and single potential step current-time transient experiments at different concentrations of bromide. A monolayer peak was noticed at potentials more negative than the Ag/AgBr reversible potential. The electrodeposition of AgBr was shown to occur by adorption-desorption and nucleation-growth kinetic processes during mono- and multilayer formation, respectively.     

Influence of the hydrogen evolution reaction on the anodic titanium oxide film properties

The influence on the physico-chemical properties of electroformed titanium oxide film produced by the hydrogen evolution reaction (HER) was studied. The relation between the cathodic treatment in the HER potential range and the modifications produced in the oxide film was established from current density and differential capacitance measurements, as a function of potential.The products of the oxide film dissolution were identified when this was subject to a prolonged cathodic treatment. The formation of Ti(III) species was found. Depending on the kind of applied cathodic treatment, these species precipitated on the electrode surface or diffused to the bulk of the solution.     

Effect of crystal orientation on anodic oxide film growth of Al

During galvanostatic anodisation of a high purity aluminium sheet of randomly orientated single crystals, the formation of the barrier-type oxide film is accompanied by a bluish white luminescence, whose intensity is different on each crystal grain. The oxide film morphology and film growth kinetics were studied by electron microscopic observation. It was found that the surface of the oxide film with intense luminescent pattern was remarkably rugged, while that with weak luminescent pattern was entirely uniform. The film thickness at each crystal plane was nearly the same (330 nm) at forming voltage (V_f) of 250 V, except that the surface with intense luminescent film had a random fluctuation by ca 20 nm. The oxide film formed on an Al polycrystal grew uniformly and the film thickness increased linearly with the forming voltage up to the final breakdown voltage; then the film grew scarcely, with accompanying surface irregularities. The film breakdown voltage was influenced by the crystal orientation.