High-purity Aluminum Foils Research Articles

高純度アルミニウム箔の立方体集合組織に及ぼす部分焼なまし‐軽圧延処理の繰返しの影響

Cube texture formation in high purity aluminum foil for electrolytic capacitor was investigated by X-ray diffraction and optical microscopy. In addition to one step of partial annealing and light rolling process, one or two more steps of the process lead to the formation of the more intense cube texture than by the one step. Simultaneously, as the cycles of partial annealing and light rolling increase, formation of R-orientation grains is suppressed. Optimum condition of second and third partial annealing and light rolling for the formation of strong cube texture was determined. It was confirmed by slip trace experiments that cube grains formed at second partial annealing grow preferentially during final annealing after second light rolling. Strong cube texture formation was ascribed to the ease of recovery in rolled cube grains and their preferential growth at the expense of un-recrystallized region.

高純度アルミニウム薄板における不均質圧延集合組織中の立方体方位領域と再結晶集合組織

For the production of thin high-purity aluminum foils for capacitor, it is essential to develop cube texture in the foils. The foils are produced in the following way: hot-rolled plates are cold-rolled by high reduction, intermediately annealed at a relatively lower temperature to cause primary recrystallization, then cold-rolled by a small amount and finally annealed at a higher temperature to develop cube texture. In this work, a crystallographic orientation distribution of a cold-rolled sheet with high reduction was examined in comparison with that of a primarily recrystallized sheet to study the mechanism of cube texture development in the foils. The orientation on a transverse section of these sheets of 500 μm in thickness were studied by electron back-scatter diffraction pattern measurements. The results are summarized as follows: (1) The cold-rolled sheet showed an elongated layered structure, nearly parallel to the rolling direction. Although there were large misorientation angles between layers, every layer contained many fine regions with small misorientation angles. (2) In the inhomogeneous cold-rolled sheets, fine cube-oriented regions were already present at certain position: 15 μm, 80 μm from the surface and in the central part. They were most frequently observed at about 80 μm. (3) In the primary recrystallization texture, cube grains were frequently observed 80 μm to 200 μm in the depth from the surface. It is considered that fine cube-oriented regions are closely related to the development of cube texture in the annealed sheets for capacitor.

Positron Annihilation Spectroscopy Study of Interfacial Defects Formed by Dissolution of Aluminum in Aqueous Sodium Hydroxide

High-purity aluminum foils were examined using positron annihilation spectroscopy (PAS) after dissolution for various times in 1 M NaOH at room temperature. Measurements of the S and W shape parameters of the annihilation photopeak at 511 keV show the presence of voids of at least nanometer dimension located at the metal-oxide film interface. The large S parameter suggests that the metallic surface of the void is free of oxide. Voids are found in as-received foils and are also produced by dissolution in NaOH, evidently by a solid-state interfacial process. Atomic force microscopy (AFM) images of NaOH-dissolved foils, after stripping the surface oxide film in chromic-phosphoric acid bath, reveal cavities on the order of 100 nm size. The average cavity depth is in quantitative agreement with the PAS-derived thickness of the interfacial void-containing layer, and the dissolution time dependence of the defect layer S parameter closely parallels that of the fractional coverage of the foil surface by cavities; thus, the cavities are believed to be interfacial voids created along with those detected by PAS. The cavity distribution on the surface closely resembles that of corrosion pits formed by anodic etching in 1 M HCl, thereby suggesting that the interfacial voids revealed by AFM serve as sites for pit initiation. © 2001 The Electrochemical Society. All rights reserved.

Atomic Force Microscopy Study of Anodic Etching of Aluminum: Etching Morphology Development and Caustic Pretreatment

Atomic force microscopy (AFM) was used to investigate the topographic characteristics of pitting sites during anodic galvanostatic etching of high-purity aluminum foils in hot baths containing HCl and Pit sites near pre-existing ridges formed by rolling are preferred, and the distribution of sites depends on the foil fabrication process. Etch tunnels are found only within shallow pits formed by surface dissolution, which may be a prerequisite for tunnel formation. Pit sites are more numerous and evenly distributed after pretreatment of foils by immersion in 1 N NaOH. AFM imaging during acid dissolution of NaOH treated foils reveal submicrometer cavities formed as a result of NaOH treatment. Some cavities appear to form near oxide particles or inclusions. It is argued that these cavities are subsurface voids exposed by uniform dissolution in the acid. If the void surface is oxide-free, they may dissolve as pits when exposed by the shallow surface dissolution shown to take place in the etchant bath. © 2001 The Electrochemical Society. All rights reserved.

電解コンデンサ用高純度アルミニウム箔の立方体集合組織形成過程のＥＢＳＰ法による解析

In this study, to clarify the formation process for electrolytic capacitor, crystal orientations and residual strains in a cold rolled foil, a partially annealed foil and an additionally rolled foil were evaluated by EBSP method. The partially annealed foil and the additionally rolled foil were heat treated at 300°C and the crystal orientation and the grain boundary character were analyzed. The main results are summarized as follows, (1) Additional rolling preferentially introduces strains in off-cube grains. (2) Most of the grain boundaries of cube grains are high angle boundaries. (3) The cube grains in high purity aluminum foils grow by the migration of high angle boundaries due to the lower strain energy.

高純度アルミニウム箔の最終焼なまし過程におけるＣｕｂｅ方位形成過程

The purpose of the present work is to clarify the factors that cause the difference between the 99%–foil and the 98%–foil in volume fraction of cube component in high-purity aluminum foils for electrolytic capacitors. The growth behavior of the cube-oriented grains during the final annealing was investigated in detail using SEM–EBSP technique. A remarkable difference was seen in grain size and distribution of the cube and R components between the two foils at the heating point of 300°C during the final annealing. On the basis of these results, the formation process of the residual non-cube grains that are controlled by the difference in the grain size distribution of cube grains after primary recrystallization is discussed. It was thought that the maximum grain diameter is an influential factor in the process, and it depends on the thickness of the foil. Furthermore, it was discussed that the size distribution of cube-grains after primary recrystallization is affected by the factors that exert influence on the driving force of grain boundary movement. These factors are the heating rate in the final annealing, the reduction rate in light-rolling and particularly the size distributions of cube nuclei formed after the intermediate annealing.

Study on high dose iron ion implantation in aluminum foil

Iron was implanted to different implantation doses (1×10 17–1×10 18 cm −2) at different average beam fluxes (25–76 μA cm −2) in high purity aluminum foil by using a metal vapor vacuum arc ion implanter. The maximum thickness of the implanted layer can range between 350 and 400 nm for the highest dose of 1×10 18 cm −2. Upon implantation dose and average beam flux, the retained concentration of Fe implants ranges between 22 at.% and lower than 10 at.%. Two crystal phases, i.e. Fe 2Al 5 and FeAl 6, are formed in the samples which were implanted to a dose larger than or equal to 5×10 17 cm −2 at an average beam flux of 51 μA cm −2. The ratio of Fe 2Al 5 to FeAl 6 increases with increasing implantation dose and average beam flux. The effect of implantation conditions on Mössbauer parameters is given. Mössbauer measurement reveals that there exists an amorphous state in the specimen implanted to the lowest implantation dose of 1×10 17 cm −2 at the smallest average beam flux of 25 μA cm −2.

Pit nucleation behavior of aluminium foil for electrolytic capacitors during early stage of DC etching

The electrode potential of high purity aluminium foils for electrolytic capacitors moves from a high potential period to a steady period during the early stage of DC etching in a hot HCl solution. In this study, the behavior of pit nucleation was investigated. Pits varied in structure from a hemispherical pit to a half-cubic pit. The difference in the number of initial pits affects the size of the half-cubic pits and the period of pit formation during the early stage up to steady potential period.

電解コンデンサ用高純度アルミニウム箔の直流エッチング挙動に及ぼす表面形態の影響

The pit growth behavior of high purity aluminum foil in electrolytic capacitors used for DC etching in a hot HCl solution has been studied using grained foil. Hemispherical patterns with diameters of about 1∼3μm and cubic patterns with widths and lengths of 7∼15μm were formed by electrolytic grainings in HNO3 and HNO3/HCl solutions, respectively. By using cubic or hemispherical patterns, uniform distributions of pits were obtained for a surface that was untreated and one that was pre-treated during the early stage of DC etching. Tunnel pits were distributed most uniformly on hemispherical patterns grained at 1C/cm2. Surface dissolution occurred as clusters of tunnel pits at the intersection of hemispherical patterns above a graining charge of 10C/cm2. For cubic patterns grained at up to 30C/cm2, the distribution of tunnel pits became uniform with an increase in the charge for graining. As a result, grainings affected the expansion of the surface area as measured by capacitance after DC etching. Cubic patterns are more effective for an increase in capacitance than hemispherical patterns.

Evolution of the cube texture in high purity aluminum capacitor foils by continuous recrystallization and subsequent grain growth

The evolution of the cube-texture in high purity aluminum foils which were produced with a high level of cold reduction and a low finishing temperature is tracked by analysis of microstructure and crystallographic texture. The formation of the cube-texture proceeds in two consecutive steps. (1) During the first stages of annealing, the deformed substructure is transformed into a very fine grained recrystallized microstructure through extended recovery reactions (continuous recrystallization); the rolling texture is retained. (2) Subsequently, the cube-orientation becomes prominent by discontinuous grain growth under consumption of the continuously recrystallized microstructure.

電解コンデンサ用アルミニウム箔の交流エッチング時の初期ピット形成に及ぼすＴｉの影響

Pit initiation and propagation in high-purity aluminum foils during etching with 5Hz rectangular alternating current (AC) in 1mol/dm3 hydrochloric acid solution at 30°C were studied based on potential changes and TEM observation of pit structures. High-purity aluminum foils containing 1 and 6 wt-ppm titanium were used, and titanium effects on pit propagation were discussed. Films stripped from etched foils by immersion in I2/methanol solution and samples prepared by jet electropolishing were used for TEM observation. Cubic pits formed at subgrain boundaries after one AC cycle. Pits varied from hemispherical to cubic during the first anodic half cycle, and a hydrous oxide etch film formed during the next cathodic half cycle. The cyclic voltammogram obtained through polarization in hydrochloric acid solution showed that titanium in high-purity aluminum foil accelerated hydrogen evolution in pits.

電解コンデンサ用高純度アルミニウム箔のピット形成に及ぼす電解液浸漬時間の影響

電解コンデンサ用高純度アルミニウム箔のピット形成に及ぼす電解液浸漬時間の影響

電解コンデンサ用アルミニウム箔の直流エッチング挙動に及ぼす結晶性酸化物の影響

The electrode potential of high-purity aluminum foils for electrolytic capacitors moves from a high potential period to a stability period during early DC etching in hot hydrochloric acid. We observed changes in pit structures in transmission electron micrographs of films stripped from etched foils, and measured a potential change using a digital oscilloscope. Pitting attacks occurred around MgAl2O4 spinel or γ-Al2O3. Pits varied from hemispherical to half-cubic, and the etch tunnel growth was promoted by crystallographic dissolutions of the (100) faces. Pit wall surfaces of a half-cubic pit and part of the tips of etch tunnels were passivated. Both MgAl2O4 spinel and γ-Al2O3 crystals were observed at the metal ridges on the aluminum substrate by transmission electron micrographs of ultramicrotomed sections. Pits are considered to be initiated at cracks associated with oxide film crystallizations. MgAl2O4 spinel crystals were observed in a foil containing 123 wt-ppm magnesium after annealing at 445°C for 5h in an Ar gas atmosphere. At 575°C, γ-Al2O3 crystals were only observed in a foil containing 1 wt-ppm magnesium. The growth of MgAl2O4 crystals was accelerated above 1 wt-ppm magnesium.

高純度アルミニウム箔における立方体集合組織形成

The recrystallization texture in high purity aluminum foils for electrolytic condenser varies extensively with the conditions of cold rolling and heat treatment. The formation behavior of cube texture has been found to depend distinctly on the iron content less than 0.01 mass%, using hot rolled plates containing 7 ppm (4N) and 35 ppm Fe (3N). It has been elucidated that sharp cube texture can be developed in the 4N foils easily by high reduction cold rolling and high temperature final annealing, the combined process of an intermediate annealing at 260°C and a low reduction rolling prior to final annealing is indispensable to develop the cube texture and use of small diameter rolls in the final stage of rolling is effective to suppress the R component in the 3N foils, and the intermediate annealing temperature at 260°C is too high for the 4N foils.

The effect of indium impurity on the DC-etching behaviour of aluminum foil for electrolytic capacitor usage

The effects of indium impurity on the etched morphology of high purity aluminium foils for electrolytic capacitor usage were investigated. The indium impurity was present either in as-received aluminium foils or deposited purposely on the foil surface through immersion-reduction reaction. The rolling line effect can be improved through introducing deposited indium on foil surfaces by immersion of the foil into In(NO 3) 3 solution prior to DC-etching. Under a high immersion temperature and more concentrated In(NO 3) 3 condition, surface etching competes with tunnel etching, and the foil thickness clearly decreases. Under low temperature and dilute In(NO 3) 3 condition, surface etching is inhibited and tunnel etching prevails. The different DC-etching behaviour under the two In-deposition conditions is explained through the energy state difference between the two deposited-In and the activation energy difference between surface etching and tunnel etching. The modification of etchability by indium on aluminium surface is stronger than that of lead. This facilitates employing lower temperature and dilute In(NO 3) 3 condition in the immersion-reduction process to optimize the etchability.

Film thickness change due to grain boundary migration in stressed thin films at elevated temperatures

A recent effort in modeling grain boundary migration seeks to link atomic fluxes in the grain boundaries of stressed, thin films at elevated temperatures with the boundary step mechanism of grain boundary migration. In this article the experimental film thickness in the vicinity of two migrated grain boundaries is determined and any change in thickness of the region swept out by the migrated grain boundary reported. Observed thickness changes are discussed with relation to the grain boundary step mechanism of migration. Discs three millimeters in diameter were punched from well-annealed (500 C for 24 hours), high purity aluminum (99.999%) foil and electropolished to perforation using an ethanol-20% perchloric acid solution at 0 C. The polished foils were then loaded into a Philips 301 transmission electron microscope heating stage and held in intimate contact with the heating holder cup by a platinum conduction ring. Measurements of film thickness at points near the migrated grain boundary in the diminished grain provided a reasonable approximation to the film thickness prior to migration. Subtracting the film thickness in this area from the film thickness in the swept region yielded the extent of the film thickness change caused by grain boundary migration.

The effect of lead impurity on the DC-etching behaviour of aluminum foil for electrolytic capacitor usage

The effects of lead impurity on the etched morphology of high purity aluminum foils for electrolytic capacitor applications were investigated in this work. The lead impurity was either present in as-received aluminum foils or deposited purposely on the foil surface through an immersion-reduction reaction. The amount and distribution of deposited lead varies with the lead content in as-received foil. The as-received foil with higher lead content gave a higher concentration and a more uniform distribution of deposited lead. Uniformly distributed vertical tunnel etchings were obtained when high lead foil, formed by immersion as-received high lead foil in Pb(NO3)2 solution, was subject to DC-etching. For the as-received lower lead foils, the deposited lead was concentrated in rolling lines which resulted in surface etching along rolling lines. Both the surfacial and cross-sectional etching morphologies are presented in this study, together with the etching mechanism discussed.

A model for the ?100? crystallographic tunnel etching of aluminium

When high purity aluminium foil is subjected to DC electrochemical etching in hot aqueous chloride solution at temperatures above 60 °C, the 〈100〉 crystallographic tunnel growth of an etch pit is achieved. This crystallographic tunnel growth behaviour arises due to the following reason. The tunnel tip region where the active corrosion reaction takes place tends to be made of {111} planes which minimize the surface energy, whilst the subsequent tunnel wall is made of {100} planes, because the passive oxide film formed on the {100} planes, along which the biaxial elastic modulus is the smallest, would be least attacked by corrosion.

界面インピーダンス法による電解コンデンサ用アルミニウム箔のエッチング特性の検討

A high density of etch pits on high purity aluminum foil for electrolytic capacitors is produced by anodic dissolution in hot hydrochloric acid solution.Pit morphology and AC impedance characteristics were investigated under potentiostatic conditions for aluminum foil with (100) crystal orientation in 1mol/dm-3 hydrochloric acid solution at 363K, and the charge transfer resistance Rct, time constant τ0 and reaction uniformity parameter θ were estimated.Increase of anodic potential led to an increase in pit density and tunnel length, and to a decrease in pit size. The value of τ0 has a tendency to increase with time until becoming constant value at 0.4ms, and is independent of etching potential. In the steady state, when regular pits with small size and long tunnel length are made and large surface area are got, the value of τ0 is less than 0.4ms. When τ0 has a large constant value, pits proceed circumferentially around the walls of the pits without any preferred direction. This means that the change in τ0 value corresponds to the change in the morphology of pits formed at various potentials.

Ion scattering and Auger electron spectroscopy analysis of alumina-supported rhodium model catalysts

Model systems for Rh/Al 2O 3 catalysts were prepared by anodic oxidation of high-purity aluminium foils followed by subsequent vapor deposition of the noble metal. The alumina layer with a thickness of some hundred Å can be altered by a calcination procedure which leads to a strong increase of the layer thickness. The elemental depth distribution of the model catalysts is characterized by low-energy ion scattering spectroscopy and sputter-etching (ISS) with different primary energies. With Auger electron spectroscopy (AES), the sample composition is determined qualitatively as well as quantitatively. The noble metal loading found with AES is in agreement with the layer thickness measured by Rutherford backscattering spectroscopy (RBS). For the quantification of the metal layer thickness by AES, a layer-by-layer attenuation model is applied. The stoichiometry of the Al 2O 3 layer is monitored with AES and RBS, showing an oxygen gradient from stoichiometric alumina to metallic Al, starting in a depth of only a few monolayers.