Structure Of Anodic Oxide Films Research Articles

Changes in the Structure and Corrosion Protection Ability of Porous Anodic Oxide Films on Pure Al and Al Alloys by Pore Sealing Treatment

It is well known that corrosion protection of pure Al is enormously improved by the formation of porous anodic oxide films and by pore sealing treatment. However, the effects of anodizing and pore sealing on corrosion protection for Al alloys are unclear, because the alloying elements included in Al alloys affect the structure of anodic oxide films. In the present study, porous anodic oxide films are formed on pure Al, 1050-, 3003- and 5052-Al alloys, and pore sealing was carried out in boiling water. Changes in the structure and corrosion protection ability of porous anodic oxide films on pure Al and the Al alloys by pore sealing, were examined by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). SEM observation showed that anodic oxide films formed on pure Al have a smooth surface after pore sealing, and that cracks are formed in anodic oxide films on 1050-, 3003- and 5052-aluminum alloys, after pore sealing. Corrosion protection after pore sealing increased with anodizing time on pure Al, but only slightly increased with anodizing time on the Al alloys.

Influence of the Ti alloy substrate on the anodic oxidation in an environmentally-friendly electrolyte

The influence of the Ti alloy substrate (α, β, α + β) on the anodic oxidation process was studied. The surface morphology, composition and crystalline structure were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). It was shown that the surface morphology and crystalline structure of anodic oxide films were considerably affected by the Ti alloy substrate. The surface morphologies of the oxide films retain their matrix microstructure characteristics. The oxide film on the residual β phase contains a trace amount of V, Zr, Mo element for TA15. Compared to the secondary α phase, the β phase has a higher degree of oxidation for TB6. The oxide film has the higher Al content on the secondary α phase, while the oxide film formed on β-phase has the higher V content. The XPS results show that the Al, Mo, V, Zr alloy elements of TA15 are involved in anodic oxidation and exist as Al2O3, MoO3, V2O5, ZrO2. Likewise, the Al, V alloy elements of TB6 are involved in anodic oxidation and exist as Al2O3, V2O5, but Fe element is not involved in anodic oxidation. The anodic oxide films are partly crystallized and mainly amorphous for the three kinds of titanium alloys. The TA15 anodic oxide film has the highest crystal content, and TB6 has the least.

Surface characteristics of anodic oxide films fabricated in acid and neutral electrolytes on Ti–10V–2Fe–3Al alloy

Anodic oxide films were fabricated on Ti–10V–2Fe–3Al alloy in acid (H2SO4/H3PO4) and neutral environmental friendly (C4H4O6Na2) electrolytes. The morphology, roughness, crystalline structure of the anodic oxide film were characterized by using scanning electron microscopy, atomic force microscopy, Raman spectroscopy and electrochemical impedance spectroscopy (EIS). The results showed that the oxide film fabricated in H2SO4/H3PO4 electrolyte had a porous structure and the thickness of the film was 3.5 µm. The oxide film fabricated in C4H4O6Na2 electrolyte presented a nonporous structure that sustained the evident microstructure of the substrate, and the thickness of the film was 6.0 µm. The surface average roughness values of the two types of films were 245 nm and 166 nm, respectively. The phase of the anodic oxide films consisted mainly of anatase and rutile. EIS results showed that the film fabricated in C4H4O6Na2 electrolyte had higher impedance of the outer layer, while the film fabricated in H2SO4/H3PO4 electrolyte had higher impedance of the inner layer. Moreover, we attempt to explain the differences in the anodizing kinetics, structure and electrochemical impedance of anodic oxide films by the different films growth processes in the two types of electrolytes. Copyright © 2012 John Wiley & Sons, Ltd.

Capacitance characteristics and structure of anodic oxide films grown on rapidly quenched aluminum alloys

Anodic oxide films grown on rapidly quenched aluminum alloys containing 2 at% Ti, Zr, Ta, Nb or Hf were characterized. The capacitance of the film on each alloy was found to be related to the dielectric constant of the alloying metal oxide film. In addition, the capacitance was found to depend on the degree of the exposure of the alloyed metal to the electrolyte, due to aluminum dissolution during the anodic oxidation. Capacitance varied with time, temperature and pH of the electrolyte in the anodic oxidation process. An oxide film of the barrier type was observed on Al3Zr by TEM, whereas the oxidation film of the Al–Ti alloy had a dual structure consisting of an inner layer with lower TiO2 content and an outer one with higher TiO2 content. It is considered that these phenomena were caused by the preferential dissociation of aluminum in the anodic oxidation process.

Electronic structure of anodic oxide films formed on cobalt by cyclic voltammetry

The chemical composition and degrees of oxidation of thin oxides films formed on cobalt by cyclic voltammetry have been investigated by Auger electron spectroscopy and XPS analysis. In addition the electronic properties of the films have been examined by capacitance measurements using the Mott–Schottky method and photoelectrochemistry. The analytical results show that the thickness of the cobalt oxide films increases with the number of cycles and varies from a few tens to a few hundreds of angströms. When observed by transmission electron microscopy and diffraction, the films appear compact and well crystallised (spinel structure). Capacitance measurements show that both very thin and relatively thick films exhibit p-type semiconductivity. The band structure model proposed and the interpretation of the oxidation processes in terms of lattice ionic defects, can explain the film growth mechanism. The study shows how the electric fields created by the development of space charges influence both ionic transport and electronic transfer of charges.

Composition and Structure of Anodic Oxide Films on Titanium–Aluminum Alloys by Fast Electron Reflection Diffraction, Rutherford Backscattering, and Secondary Neutral Particle Mass Spectrometry

Anodic oxide films on some Ti–Al alloys are studied using fast-electron reflection diffraction, Rutherford backscattering, and secondary neutral-particle mass spectrometry. The films are amorphous, with a small amount of crystalline phases, and comprise a mixture of TiO2 and Al2O3. The Ti/Al ratio in an anodic film corresponds to that in the alloy matrix. Constants of anodic oxidation of the alloys are determined.

Surface characteristics and structure of anodic oxide films containing Ca and P on a titanium implant material.

An anodic oxide film that formed on titanium with a mixture of beta-glycerophosphate sodium (beta-GP) and calcium acetate was investigated. The anodic oxide had interconnected pores (ca. 1-2 microm in diameter) and intermediate roughness (0.60-1.50 microm). In addition, it contained a mixture of amorphous, anatase, and rutile oxides. With an increase in the anodizing voltage and/or concentration of calcium incorporated into the oxide, the degree of oxide crystallinity increased. However, with an increase in the concentration of beta-GP, the degree of oxide crystallinity decreased. It was concluded that the surface roughness, oxide crystallinity, and surface composition of the anodic oxide were dependent on the voltage, current density, and concentration of the electrolyte. It was also concluded that the anodized surface could be optimized for maximum osseointegration.

Structure of Anodic Oxide Films on Titanium.

Recent studies of the anodic oxide films on titanium are reviewed. In-situ electrochemical techniques including AC impedance, optical reflection like ellipsometry, photoelectrochemistry, and Raman spectroscopy have been used. The results are summarized as follows: (1) The TiO2 film is amorphous at potentials lower than 5 V but changes to anatase type at potentials higher than 5 V. (2) Thickness of the film is linearly proportional to the anodic potential in the poten-tials range lower than 7 V. However, the ratio of thickness to potential becomes larger if the potential is higher than 7 V probably due to formation of an ionic leakage path accompanied by crystallization of the film. (3) The film behaves as an n-type semiconductive electrode with a high concentration donor density and a bandgap of 3.2 eV.

Formation and Breakdown of Anodic Oxide Films on Aluminum in Boric Acid/Borate Solutions

Highly pure aluminum was anodized at a constant current density of at 293 Kin 0.5 M boric acid/0, 0.005, or 0.05 M sodium tetraborate solutions, to examine the effect of sodium tetraborate concentration on the formation and breakdown characteristics of barrier oxide films by using inductively coupled plasma atomic emission spectrometry, electroluminescence/photoluminescence measurements, scanning electron microscopy, transmission electron microscopy, and electrochemical impedance spectroscopy. In boric acid/borate solutions, a crystalline alumina formed locally in the middle of the amorphous oxide film. Above the crystalline alumina, a void is formed and may lead to a breakdown of the oxide film at 420 to 540 V. In boric acid solution, an amorphous oxide film grew until 1180 V with the formation and development of imperfections and with enhancement of electroluminescence and gas evolution. At imperfections, the oxide/solution interface was convex and the oxide/metal interface curved in the opposite direction. This deformation is attributed to high‐pressure evolved in the pores of imperfections and to the local formation and dissolution of oxide. The breakdown of the oxide film started when the evolution and oxide dissolution at imperfections become predominant. The mechanism of formation and breakdown of the anodic film in the boric acid/borate solutions is discussed in terms of pH buffering of the anodizing solution, and the electronic structure of anodic oxide films is correlated with electroluminescence and photoluminescence spectrum results.

バルブ金属のアノード酸化と皮膜構造

バルブ金属のアノード酸化と皮膜構造

Photographic Evidence of Delamination of Two‐Layer Structure of Anodic Oxide Films on Tantalum Formed in Electrolytes Containing Phosphate

Direct photographic evidence of delamination of the two‐layer film structure for anodic tantalum oxide films formed in phosphate‐containing electrolytes has been discovered in scanning electron microscopy photomicrographs of flaws in the anodic oxide. The amorphous dielectric oxide, whose bi‐layer structure was suggested by Vermilyea et al., appears to have been displaced from the site of crystalline oxide growth and to have undergone layer delamination as a result of the large mechanical stresses present.

高分解能電子顕微鏡によるアルミニウムアノード酸化皮膜の構造

高分解能電子顕微鏡によるアルミニウムアノード酸化皮膜の構造

Direct observation of the two-layer structure of anodic oxide films on tantalum

Abstract Transmission electron microscopy of ultra-microtomed sections of anodic oxide films formed on sputtered tantalum substrates in phosphoric acid electrolyte reveals immediately that the films consist of two distinct layers of differing contrast. Elemental analysis of the film sections by energy-dispersive analysis of X-rays indicates the presence of phosphorus in the outer layer of lighter appearance, with phosphorus detected in the inner film layer of darker appearance. Direct interpretation of the data implies that the atomic density of tantalum in the outer layer is less than that within the inner layer owing to the incorporation of phosphate anions at the film-electrolyte interface during film growth. Furthermore, using the direct observation procedure, allowing precise film thickness measurements and revelation of differently contrasted film regions, it is possible to quantify the distribution of the field during anodic oxidation.

急冷Al-Ti合金の陽極酸化皮膜の構造

急冷Al-Ti合金の陽極酸化皮膜の構造

Composition and Structure of Anodic Oxide Film on Iron in Neutral Phosphate Solution

The composition and structure of anodically-formed iron oxide film in nearly neutral phosphate solution was examined by means of ESCA, electron diffraction and FT-IR spectroscopy. In the active region and in deaerated phosphate solution at pH 6.0 or lower, ferrous phosphate –Fe3(PO4)2·8H2O– was formed. In the presence of air, a small amount of ferric phosphate was found. On the other hand, in the passive region at high pH, for example at pH 9.1, the iron was covered with a multiple oxide film. The structure of the film was found to consist of an inner “Fe3O4” layer and an outer “γ-Fe2O3, FePO4·nH2O or γ-FeOOH” layer, the outermost part of the film containing a small quantity of reaction products or contaminations such as Na+, Ca2+, PO3-4. The most passive films were estimated to be 30–50 Å.

Electrochemical behaviour and structure of anodic oxide films formed on aluminium in a neutral borate solution

99.99% Al specimens were anodically oxidized in a boric acid-borate solution (pH = 7.4) at temperatures of 20, 40 and 60, by applying a constant potential of 50V ( vs sce). The anodic current and the amount of dissolved Al ions were measured as a function of the anodizing time. Observations of sections of the oxide films were made by electron microscopy using an ultra-microtome for sample preparation. The current was found to decrease exponentially with time to a steady value which increases with increasing temperature. The current efficiency for the formation of oxide decreases gradually with decreasing current and is less than 70% in the period with steady current. The low efficiency of the reaction is exclusively due to the field-assisted dissolution of the oxide. In general, the oxide film is composed of two layers. The inner layer next to the metal is compact and is responsible for the polarization behaviour, its thickness being almost constant during anodizing but increasing with decreasing solution temperature. The outer layer, on the other hand, has many vertical pores and continues to grow even in the period with steady current. The porosity of the outer layer is estimated to be 22% for 40 and 60° films and the 60° film contains 4.5% bound water. The current-potential relationships measured for the anodized specimens in a 20° solution indicate that the protective ability of the inner layer increases with increasing anodizing time and temperature.

Multilayer structure of tantalum anodic oxide films formed in dilute phosphoric acid

An investigation has been made of the multilayer structure of anodic oxide films on pure tantalum, formed up to various voltages with a constant current density of 1.0 mA cm -2 in 1.0 × 10 -2 N H 3PO 4 at 20°C. For the study, infrared reflectance spectra (IRRS) were recorded and the optical thickness measuring method was successfully applied using the wavelengths of optical interference maxima and a chemical film stripper (concentrated ammonium hydrogen difluoride aqueous solution). The conclusions are that: (1) tantalum anodic oxide films anodized in dilute phosphoric acid consist of three layers, irrespective of the formation voltage; (2) the innermost layer is uniform whatever the anodization voltage; (3) phosphate anions are incorporated in both the outermost and middle layers but not in the innermost layer; (4) all three layers grow from the initial formation stage and the growth rates are nearly equal; (5) for formation voltages below 100 V the middle layer has an unchanging chemical structure, but above 100 V its chemical structure changes with the voltage; (6) the outermost layer appears to vary in chemical structure over all anodization voltages.

クロム酸水溶液中で生成されたアルミニウムアノード酸化皮膜の構造について

The structure of anodic oxide films on aluminum formed in chromic acid solution at constant voltage, and under various electrical or electrolytic conditions, has been studied by electron microscopy. Electron micrographs of film section replica showed that pore branching and subsequent colony structure was formed during anodizing. With film growth, pore colony took hemispherical shape, which resembles to that of barrier layer bottom in typical porous type oxide film, at metal-oxide interface. These film structures were not in accord with vertical structure model proposed by Keller et al. A form of branching pore structure depended on anodizing voltage, the higher the applied voltage, the sooner the initiation of pore branching and colonial structure. The formation of branching colonial structure was strongly favored by following conditions. (1) Sudden voltage drop during anodizing (that is colled Recovery Effect). (2) Anodizing after formation of preliminary thick barrier layer, for instance, primary anodization was done in ammonium tartarate solution. The second anodizing voltage in chromic acid solution was lower than that of preliminary one. The facts suggest that the cause of pore branching is due to the film growth through thick barrier layer.

Electromigration in Aluminum Film Stripes Coated with Anodic Aluminum Oxide Films

The effect of an anodic-Al2O3-coating on the electromigration lifetime of Al stripes is investigated. Experiments show that the mean time to failure (MTF) of Al stripes is significantly increased by the presence of the anodic Al2O3 on stripe-surfaces. In particular the most effective structure of anodic oxide film for MTF is constructed by double layers of porous and composite oxides. It is also observed that coating with the double layers of alumina films has an effect greater than that with chemical-vapor deposited SiO2 films, and that the Al stripes coated with either alumina or SiO2 films have the same activation energy as Al stripes without coating. The observed difference in MTF-improvement can be explained by the difference of mechanical characteristics of the coating films.

The structure of anodic oxide films formed on pre-hydrated Al

The structure of anodic oxide films formed on pre-hydrated Al