Thickness Of Anodic Oxide Film Research Articles

Galvanic Corrosion Behavior between Aluminum and Iron in Chloride Solutions at Near-Neutral pH and Corrosion Prevention By Anodizing

The joints between steels and aluminum alloys are expected to be used as multi-material structures due to their low cost, high stiffness, and high corrosion resistance. When aluminum alloys are connected to steels, galvanic corrosion is expected to occur because the corrosion potentials of aluminum alloys are lower than those of iron and steels. In the case of the galvanic corrosion in chloride solutions at near-neutral pH, the anodic reaction on aluminum alloys are oxide film formation and/or pitting. For pure Al and aluminum alloys, the generation of localized corrosion is evaluated by the critical potential for localized corrosion, such as pitting potential. In this study, the electrode potential under galvanic coupling and pitting potential were compared. Surface modification is effective methods for improvement on corrosion resistance of aluminum alloys. However, there is little research related to the galvanic corrosion between steels and aluminum alloys. In this research, the galvanic corrosion behavior of pure aluminum coupled to pure iron in chloride containing near-neutral pH solutions and the effect of anodizing on galvanic corrosion were investigated.Pure iron and pure aluminum were prepared as specimens in this research. The specimen surface of aluminum was polished down to 0.25 µm with a diamond paste. The iron surface was also polished down to 1 µm with a diamond paste. Diluted synthetic seawater (200 mg/L Cl-, pH 8.2) was used as the electrolyte for electrochemical measurements. The electrode area was ca. 10 mm2. Ag/AgCl (3.33 M KCl) was used as the reference electrode. Galvanic currents and electrode potentials were measured. The distance between iron and aluminum electrodes was kept at 10 mm. A zero resistance ammeter was used to measure the galvanic currents. The electrode potential of pure aluminum was also measured. Additionally, anodizing in sulfuric acid was conducted to pure aluminum in various voltages and times. Galvanic current measurements were carried out between these anodized specimens and pure iron to evaluate the effect of anodizing on galvanic corrosion prevention.The galvanic currents and electrode potentials of pure aluminum coupled to pure iron were measured. The galvanic currents were anodic currents. The oscillations of galvanic currents and electrode potentials were generated during the measurements. Filiform corrosion was observed on pure aluminum after the measurements. The generation of filiform corrosion was caused by higher electrode potentials of pure aluminum coupled to pure iron compared with the initiate potential for filiform corrosion.The time variation of galvanic currents and electrode potentials of anodized aluminum coupled to pure iron were also measured in the diluted synthetic seawater (pH 8.2). Pure aluminum specimens were anodized at 4, 8 and 16 V at 18 s. The oscillations were observed in the galvanic currents of anodized aluminum (4 and 8V); however, no oscillation was measured on the specimen anodized at 16 V. After the measurements, pitting was observed on anodized aluminum (4 and 8V). However, no pitting was observed on the specimen anodized at 16 V. The thickness of anodic oxide film was measured. It was confirmed that the thickness of the oxide film increased with anodizing voltage. Consequently, it was indicated that the galvanic corrosion resistance of pure aluminum for galvanic corrosion was enhanced by the increase of the thickness of the oxide film.

Influence of stirring conditions on hard anodising of aluminium A6061-T6 shapes

Hard anodising is used to produce relatively thick and adherent coatings in order to improve the hardness, abrasion and corrosion resistance of aluminium components. In typical industrial conditions, the local variation of anodic oxide film thickness is often significant and it affects the dimensional tolerances and reliability of coating thickness. Electrolyte stirring is a simple and effective way to improve the uniformity of the oxide layer thickness. However, very little practical information is available in the literature to guide industry in this regard. In this work, extruded A6061-T6 specimens were anodised in industrial conditions. To reduce the thickness variability of the coating, three methods of electrolyte stirring were studied and compared. Air bubble stirring showed the best coating thickness uniformity and improved control over anodising parameters. However it did not reduce the variability due to metal forming texture.On utilise l’anodisation dure afin de produire un revêtement d’oxyde épais et adhérent à la surface de pièces en alliage d’aluminium. Ce revêtement accroît la dureté, la résistance à l’abrasion et la résistance à la corrosion des composantes. En milieu industriel, l’épaisseur de la couche d’oxyde a tendance à varier en fonction de la position dans la cellule et même d’un endroit à l’autre sur une pièce, ce qui réduit la précision dimensionnelle. L’agitation de l’électrolyte dans la cellule est un moyen simple et efficace d’améliorer l’uniformité de l’épaisseur du revêtement. Toutefois, très peu d’information est disponible dans la littérature pour guider les industriels et déterminer dans quelle mesure l’agitation permet de réduire cette variabilité. Dans ce travail, des composantes extrudées en alliage A6061-T6 ont été anodisées en milieu industriel. Afin de réduire la variabilité de l’épaisseur de la couche anodisée, trois types d’agitation d’électrolyte dans la cellule ont été étudiés et comparés. L’agitation par bulles d’air a permis d’obtenir la meilleure uniformité de l’épaisseur de la couche anodisée et le meilleur contrôle sur les paramètres d’anodisation. Toutefois, les résultats montrent aussi que l’agitation accentue la différence d’épaisseur de la couche anodisée occasionnée par la texture de laminage ou d’extrusion.

Enhanced Capacitance of Composite Anodic ZrO2 Films Comprising High Permittivity Oxide Nanocrystals and Highly Resistive Amorphous Oxide Matrix

Anodic oxide films with nanocrystalline tetragonal ZrO(2) precipitated in an amorphous oxide matrix were formed on Zr-Si and Zr-Al alloys and had significantly enhanced capacitance in comparison with those formed on zirconium metal. The capacitance enhancement was associated with the formation of a high-temperature stable tetragonal ZrO(2) phase with high relative permittivity as well as increased ionic resistivity, which reduces the thickness of anodic oxide films at a certain formation voltage. However, there is a general empirical trend that single-phase materials with higher permittivity have lower ionic resistivity. This study presents a novel material design based on a nanocrystalline-amorphous composite anodic oxide film for capacitor applications.

Structural and dielectric properties of anodic oxide film on Nb–Ti alloy

The structural and dielectric properties of anodic oxide films on Nb and Nb–Ti alloys containing 1, 3, 5, 7, 10 and 15 at.% Ti were investigated. Anodized Nb–Ti alloys were covered with an anodic oxide film containing amorphous and partly crystalline Nb 2O 5 and TiO 2. Increase of the Ti content in the alloy resulted in the increase of the anodic oxide film thickness and the amount of TiO 2 in the oxide film, which led to an enhancement of the permittivity and a suppression of the leak current of the anodic oxide film. Therefore, both the capacitance and the leak current of anodized Nb–Ti alloys can be improved by controlling the composition of the alloy.

Growth of anodic oxide films on titanium-nickel alloys and breakdown of alloy passivity with halide ions

Some characteristics of anodic oxide films growth on titanium-nickel alloys in the borate buffer solution and local breakdown of alloy passivity in the chloride and bromide solutions were determined from the experimental results. In particular, the dependences of anodic oxide film thickness at a given formation potential, anodizing constant, and potential of passivity breakdown (anodic-anionic activation) on the nickel content in the alloys are obtained.

Impedance Characterization of Anodic Barrier Al Oxide Film Beneath Porous Oxide Layer

Electrochemical impedance spectroscopy (EIS) is a common technique used in the assessment of the thickness of anodic oxide films formed on Al and its alloys. However, it is shown here that the resistance values obtained from EIS data are highly dependent on the solution in which the measurements are made, while the capacitance values are independent of the solution conditions and are therefore a much more reliable means of determining oxide film thickness and other properties. We also show that the experimental EIS data for unsealed porous anodic oxides formed on top of a barrier Al oxide film in acidic solutions exhibit only a single time constant, with very little influence seen from the overlying porous oxide layer on the apparent and values. The reason for this is demonstrated by utilizing the Laplace equation to calculate the electric field induced in the oxide, which confirms that the EIS response of these films can generally be assumed to reflect the properties and coverage of the underlying barrier oxide film.

Thickness dependence of refractive index for anodic aluminium oxide films

Anodic oxide films on aluminium have been employed in a variety of devices such as solar cell [1], sensors [2] and thin film transistor liquid crystal display (TFT/LCD) [3]. It was reported [3, 4] that anodic aluminium oxide film is a solution to depress hillock formation. Thin film transistors with Al gates and anodic Al2O3 ‡ Si3N4 double layer gate insulators have been successfully fabricated in an 10.4inch diagonal multicolour LCD display panel [3]. Consequently, much progress has been made in understanding the structure [5, 6], composition [7– 10] and electrical properties [6, 7] of anodic aluminium oxide. In previous work it has been shown that an anodic oxide layer formed on pure Al without any prior heat treatment exhibits better dielectric properties, uniformity, and stability than oxide layers formed on Al pre-annealed at 410 8C [6]. Si or Cu doping of Al film was also found to reduce the quality of the anodic oxide layer [5]. For device application, the control of anodic film thickness and uniformity is very important. There are many methods to evaluate the thickness of an anodic oxide film, such as coulometry [11], transmission electron microscopy (TEM), ellipsometry [12], impedance [11], spectrophotometry [13], photoluminescence [14] etc. Coulometry is most convenient for anodic oxide film thickness determination, the thickness being calculated from the charge consumption based on Faraday’s law. The calculated thickness, however, is subjected to uncertainties due to non-ideal current efficiency, roughness of the electrode, film non-stoichiometry, and error in the presumed film density. TEM offers a direct and absolute measurement of film thickness, but is time consuming and destructive. Ellipsometry can determine not only the thickness but also the refractive index of the film [12, 15]. For a top surface layer on a substrate with given optical properties the evaluation of both thickness and refractive index requires the numerical solution of two complex simultaneous equations, and the accuracy of the thickness results depends sensitively on the calculated refractive index [12]. If, however, either the thickness or the refractive index of the top film is known precisely then the numerical solution of the other quantity can be greatly simplified and its accuracy significantly increased. The purpose of this study is to measure the thickness of anodic Al2O3 films precisely by cross-sectional TEM techniques and then use the thickness value to fit the ellipsometry data for the unique solution of refractive index as a function of film thickness. This calculation is made possible by the assumption that the extinction index of the Al2O3 film is zero, or in other words, the film is non-absorbing. Dell’oca [16] has carefully studied anodic Al2O3 films formed on evaporated Al films ellipsometrically and showed that the non-absorbing model fits his experimental data the best. He estimated the extinction index of anodic Al2O3 film to be 0.002. The error in the calculated refractive index is about 0.01 if the extinction index is 0.002 instead of zero. The effect of absorption may be neglected since it affects the refractive index by less than 0.6%. We hope that the refractive index data obtained in the present study can be used in device applications for quick and precise thickness measurement by ellipsometry. Sample preparation is similar to that described previously [5–6]. A 300 nm thick pure Al film was sputtered by DC magnetron on BPSG(borophosphosilicate glass)/SiO2/Si substrates. The substrates were 4-inch diameter, p-type, k1 0 0l Si wafers. Wafers were anodized after the metal deposition without any heat treatment, and the anodization was conducted at room temperature in an AGW electrolyte [6] (AGW electrolyte is a mixture of 3% aqueous solution of taitaric acid and propylene glycol at a volume ratio of 2:8). The wafers were anodized, one at at time, at constant current mode (current density ˆ 0.4 mA/cm2) initially until reaching 100 V, then the anodizing was automatically switched to constant voltage mode until a preset time was reached. To monitor the anodic oxide growth, specimens were anodized for different durations varying from 3.5 to 30 min. TEM samples were prepared for film thickness measurement by ion milling in the usual fashion [17] and examined with a Philips CM20 microscope operating at 200 kV. Using the thickness data obtained from the TEM analysis the refractive index of the anodic oxide film was evaluated by ellipsometry. A Rudolph Research Auto EL-ILL ellipsometer using an He–Ne laser at a wavelength of 632.8 nm was employed for ellipsometry with an incident angle of 708. The refractive index (n) and extinction coefficient (k) for the substrate aluminium are presumed to be 1.3 and 6.5, respectively [16]. Fig. 1a, b, c and d show the morphology of Al2O3

In situ determination of the optical constants of titanium surface films formed in higher voltage anodization

The optical constants and thickness of anodic oxide films formed on titanium surface, during the polarization, have been determined in 0.5 M H 2SO 4 by in situ ellipsometric measurements. The anodic titanium films are formed in the voltage region from 0 to 100 V. The possibility of determining the real part film refractive index without direct utilization of the metal substrate refractive index has been shown.

The enhancement of adhesive joint strength by extending the surface of anodized aluminium

The initial joint strengths and durabilities of adhesively bonded 5251 aluminium alloy lap shear joints were determined after the surface of anodized aluminium was extended by etching. The post-anodizing etching solutions investigated were sodium hydroxide and, for comparison purposes, phosphoric acid. Durability was assessed by measuring joint strength after immersion in water at 50°C for 1500 hours. Improvement in initial joint strength and durability occurred when wetting of the surface by the adhesive was good. The improvement was ascribed to an increased contact area between oxide and adhesive. Good wetting was obtained with acrylic adhesives. The difficulty of wetting the surface with epoxy adhesives was eased by using a primer or by preheating the surface before bonding. Etching conditions were critical: temperature, immersion time and dissolved aluminium content of the sodium hydroxide solution all affected the rate of dissolution. The strongest joints were obtained after approximately 8 μm of the anodic oxide film thickness had been dissolved and left about 4–6 μm of unetched inner oxide beneath 5–6 μm of etched outer oxide.

分光光度計を用いたアルミニウム表面処理皮膜の膜厚測定

Recently, the need has increasingly been felt for a non-destructive, rapid and precise method of testing, which can be used to measure the thickness of functional film. Use of the microscope and eddy-current instrument recommended by JIS H8680, however, produces unsatisfactory test results for thicknesses below 2μm.Thickness of anodic oxide films and chromate coatings was therefore measured using interference fringes obtained by spectrophotometer, and the results obtained were compared with those obtained by microscope and TEM in terms of precision and measurement limits. The thickness test results obtained for sulfuric film and chromate coating using the spectrophotometer were good, with mimits for the thickness test of 0.14μm on sulfuric film (n=1.6) and 0.11μm on chromate coating (n=2.0) at wavelengths from 200 to 2500nm, where n is the refractive index.

ChemInform Abstract: ELLIPSOMETRIC STUDY OF ANODIC OXIDE FILMS ON TITANIUM IN HYDROCHLORIC ACID, SULFURIC ACID, AND PHOSPHATE SOLUTION

AbstractDie Dicke des anodisch gebildeten Oxid‐ ?lms auf der Ti‐Oberfläche steigt im Bereich ‐ 0.55 bis 7.5 V (RH E) linear mit der Spannung; die Wachstumsgeschwindigkeiten werden für die einzelnen Elektrolyten angegeben.

Ellipsometric Study of Anodic Oxide Films on Titanium in Hydrochloric Acid, Sulfuric Acid, and Phosphate Solution

The anodic oxide film on titanium has been studied by ellipsometry and SEM observation. Ex situ multiple‐angle‐of‐incidence and in situ ellipsometric measurements allow the complex refractive index to be estimated at for the titanium substrate and at for the anodic oxide film at wavelength 546.1 nm. The anodic oxide film thickness increases linearly with potential in a range from −0.55 to 7.5V (RHE) at the rate of 2.8 nm V−1 in phosphate solutions of pH 1.6–12.1, 2.5 nm V−1 in solution, and 2.4 nm V−1 in solution. At potentials more positive than 7.5V, the film breaks down, leading to the formation of a thick oxide film probably due to an increased ionic current through the breakdown sites. The film composition is estimated to be or , which suggests the presence of hydroxyl bridge in its bonding structure.

アルミニウム陽極酸化皮膜の限界膜厚

It is well known that the thickness of anodic oxide films on Al formed at low current densities is limited by chemical dissolution of the films in the bath during anodization. On the other hand, when anodizing at high current densities, the occurrance of burning limits the film thickness, which decreases with increasing current density.Based on the above facts, the maximum film thickness obtained under galvanostatic anodization was analyzed and calculated using both the chemical dissolving rate for oxide films and the burning occurrance curve. It is theoretically and experimentally demonstrated that the critical thickness of oxide film can be formed on Al only by using a high speed anodizing process, in which, after initial galvanostatic anodization at high current density, current density decreases with time along the burning occurrance curve.

Comparison of spectrophotometric and ellipsometric methods of measuring the thickness of anodic oxide films on tantalum

Two optical methods of determining film thickness were applied to the same set of films in order to obtain a calibration. The methods are ellipsometry and the so-called spectrophotometric method in which the wavelengths of minimum reflectivity due to interference are determined. The calibration was necessary in order to compare kinetic data on the ionic conductivity obtained with thicknesses determined by the two methods. In addition it was confirmed that films grown in dilute sulphuric acid, unlike those grown in dilute phosphoric acid, show no signs of a two-layer structure at this wavelength and are isotropic at zero field.

Determination of anodic oxide film thickness by a luminescence method

In this work we use the previously referred to interference effect [1] which takes place in electroluminescence of thin anodic oxide films, in order to determine film thickness, refraction index of anodic alumina and optical constants of aluminium. In contrast to ref. [1], in this work an interference of Lummer-Gehrke type has been used which offers new application possibilities. The results are in very good agreement with the data obtained by other methods.

整流，コンデンサ両作用をもつ電極による交流電着塗装

A. C. electropainting has not been commercially applied because of the following reasons due paimarily to the presence of reverse direction current: (1) low paint deposition rate, (2) low coulombic yield, and (3) high electric power loss. The present work is concerned with the development of a new electropainting process utilizing a specially made electrode which has a function of both rectifier and condenser of high capacity. The features of this new electropainting process may be summarized as follows: (1) A special electrode is prepared by forming anodic oxide film of certain thickness on either Ta, Nb, Zr, Ti, Al or their alloys so that it warks as both condenser and rectifier. (2) Percentage of reverse direction current is kept within 20% of right direction current by controlling the area ratio of the electrodes or the thickness of anodic oxide film. (3) Phase angle (φ) of bath current under reverse direction voltage is kept at π/3≤φ≤π/2.

Effect of the Thickness of Anodic Oxide Films on the Rate of the Oxygen Evolution Reaction at Pt in H 2 SO 4 Solution: I . Growth at Constant Current

Ellipsometry and standard electrochemical techniques are used to determine whether, and if so, how the thickness of an anodic oxide film affects the catalysis of the oxygen evolution reaction at platinum. A prereduced electrode is first polarized in sulfuric acid solution with a constant current density, for a given time and then the thickness, , of the anodic film and the electrode potential, , are determined for various current densities . It is found that the thickness of the oxide film affects the catalytic activity in an exponential way, i.e. where and δ are constants. For the same time of polarization both the oxide thickness and the electrode potential increase with the logarithm of the polarization current density, . The potential dependence is . This is in contrast with the value of about 115 mV usually reported for the oxygen evolution reaction. The latter value can be obtained only when the electrode is anodically treated at a current density, , and the relationship is subsequently determined at current densities . Ellipsometry shows that under these conditions the anodic film thickness remains essentially constant at the value achieved during the initial polarization at a higher current density.

水酸化ナトリウム浴によるアルミニウムの陽極酸化および皮膜の性質について

Anodizing of aluminum in the electrolyte of alkaline solution was studied. This paper describes the relation between the anodizing conditions and thickness of oxide film, and the properties of the film.The following results were obtained:(1) In the anodizing of aluminum in alkaline solution, the thickness of anodic oxide film was, increased with the drop of bath temperature and it reached a maximum of 28μ at 1°C.(2) As long as brown smuts did not adhere to the surface, the thickness of oxide film was linearly increased with increasing current density and anodizing time.(3) It was shown by electron and optical microscopy that the cell size was larger than that of usual oxide films obtained from acid baths and a number of large pores appeared on the surface.(4) Anodic oxide films from alkaline baths passed CASS test for 70hrs, and showed a corrosion resistance of 20sec/μ by alkaline drop test.

中性溶液中のニッケルの不働態化挙動

The anodic passivity of nickel in neutral solutions has been investigated by means of potentiostatic oxidation, galvanostatic reduction and chemical analysis techniques, and the thickness of anodic oxide film and the effect of solution pH and of anion species on the passivation behaviour are examined. It is shown that the oxide film formed by anodic oxidation is difficult to be removed by cathodic reduction in neutral solution. To obtain a bare surface, cathodic reduction has to be carried out in sulphuric acid for oxidized surfaces and either in acid or in neutral solution for electropolished surfaces.In the passivity region, where NiO film is assumed to be formed, nickel dissolution is still observed during oxidation and the amount of nickel dissolved is dependent on the oxidation potential, the solution pH, and the anion species present. The film thickness estimated from coulometry in the pH range 5.5 to 9.5, however, is not practically affected by the solution pH and the anion species but increases linearly with rise of the potential from 6 to 16 Å.Above the potential of passivity region, the secondary passivation occurs where nickel dissolution is not detected. It is also shown that the secondary passivation is due to the formation of a higher valence nickel oxide, probably Ni2O3, which may be electrodeposited from dissolved Ni2+ ion in solution. The thickness, estimated from the potential decay curve of galvanostatic reduction, increases rapidly with rise of the potential and then decreases through a maximum. Further rise of potential results again in the dissolution of nickel independent of the solution pH and the anion species.The growth kinetics of both the passivation film and the secondary passivation film is concluded to obey the inverse logarithmic rate law.

Measurement of Anodic Oxide Film Thickness by Electroreflectance Interferometry

not Available.