Aluminum Foils For Electrolytic Capacitors Research Articles

Effect of sintered aluminum powder layer structure on properties of sintered anode aluminum foil

The effects of the structure characteristics of sintered aluminum powder, such as particle size and thickness of the sintered aluminum layer, on the mechanical properties, electrochemical properties, and specific capacitance of sintered anode aluminum foil for electrolytic capacitors were investigated using scanning electron microscopy, adhesion and anti-bending tests, electrochemical tests, and specific capacitance tests. The results indicate that reducing the particle size while maintaining the same sintered layer thickness can enhance the specific capacitance of anode foils for aluminum electrolytic capacitors. The optimal particle size was found to be 2.25 μm. Increasing the thickness of the sintered layer can increase the specific capacitance, but it also leads to higher interface resistance and decreased anti-bending performance. The optimal comprehensive performance is achieved when the thickness of both sides of the sintered aluminum powder layer is approximately 65 μm. At this thickness, the specific capacitance is 1.1910 μF/cm2, the interface resistance is 511.5 Ω, and the number of bending can reach 85 cycles, satisfying the requirements of aluminum electrolytic capacitors.

Segregation of Lead on High Purity Aluminum Foil for Electrolytic Capacitors

The capacitance of aluminum foil used in electrolytic capacitors is determined by their surface area after etching. Many studies have assessed pit growth using high-purity aluminum foil during DC etching in hot hydrochloric acid solutions with respect to impurity effects. High-purity aluminum foil used for electrolytic capacitors containing small amounts of lead is known to exhibit severe rolling line effects after electrochemical etching. Apparently, the lead atoms distributed on the aluminum foil surface after annealing provide nucleation sites of pitting attacks during DC etching. For this study, lead segregation on aluminum foil surfaces containing 0.6 ppm, 5 ppm and 8.2 ppm Pb annealed at 813 K for 5 h was investigated using ultra-high resolution field emission scanning electron microscopy（FE-SEM）with selective detection of high-angle backscattered electrons （BSE） and transmission electron microscopy （TEM）. High-angle BSE images revealed the presence of Pb as brighter nanoparticles with size on the order of 10 nm at the surface oxidation layer along the rolling lines caused by pick up inclusion during hot rolling. The approximately 0.5-μm-thick surface oxidation layer microstructure resembled that of grain refined surface layer （GRSL） of alloy 8006 characterized by ultra-fine grains of nano-level size. Pitting attacks first occur at the oxidation layer because of the less noble potential for tunnel dissolution during initial DC etching.

Study of a complex of physical, crystallographic and mechanical properties of aluminum foil for electrolytic capacitors

The results of studies of the complex of physical, crystallographic and mechanical properties of aluminum foil for low-voltage and high-voltage electrolytic capacitors made of high-purity aluminum (99.99% Al) are presented. A comparative analysis of technological schemes for the production of foil for lowvoltage and high-voltage applications is given, the main differences in the schemes are shown, and the results are presented for the physical parameter: the value of specific capacitance, crystallographic characteristics (structure and predominant texture), mechanical properties (tensile strength and relative elongation). Low-voltage foil after electrochemical etching has a fine etching relief, which can cause the danger of its smoothing after the next operation of the electronic processing of molding — the creation of an oxide film of the dielectric. The required surface topography can be achieved at high total degrees of cold deformation, amounting to 98.8%, without intermediate annealing, obtaining a structure that is fibrous along the rolling direction with a predominant deformation texture {011} and pole density according to the results obtained (5.2). On the contrary, high-voltage foil after electrochemical etching has a rougher relief, and here the risk of surface smoothing after the molding operation is minimal, since the dielectric oxide film being formed is actually superimposed and duplicated along the trajectory of the resulting relief. The latter can be achieved by using a foil after recrystallization (intermediate) and final annealing to obtain an average grain size of about 72 microns, a predominantly near-cubic texture of the {420} foil, and a pole density of 2.4 obtained results. At the same time, high values of specific capacitance can be observed in the studied range: at forming voltages of 30 and 450 V, the value of specific capacitance is 1750 and 29 μF/dm2 for low-voltage and high-voltage foils, respectively.

Effect of azelaic acid on microstructure evolution and electrical properties of anodic aluminum foil for electrolytic capacitor

The effect of azelaic acid on microstructure evolution and electrical properties of anodic aluminum foil for electrolytic capacitor is studied quantitatively. The azelaic acid is selected as formation solution in the multi-step anodization process, and boric acid is applied for comparison. The field-emission scanning electron microscopy and X-ray diffractometer technologies are used for observation of microstructure and detection of crystallinity, respectively. The electrical properties are tested by LCR meter and T–V tester. The microstructure observation shows that the ‘corn-flake’ structures are taken place by ‘cotton-ball’ ones gradually along with the preparation process, and such phenomenon is more obvious when azelaic acid is used. The pores area of anodic aluminum foil formed in azelaic acid is larger because of the stronger acidity. The formation with azelaic acid induces smaller thickness of oxide film, promotes the formation of crystalline oxide, therefore, a barrier film with higher crystallinity and larger grain size is obtained. The barrier film formed in azelaic acid shows larger specific capacitance, lower withstand voltage and larger leakage current, which needs the multi-step anodization for performance improvement.

Effect of mechanical attrition on anodizing of DC-etched aluminum foil for electrolytic capacitor

On tunnel-etched aluminum foil for electrolytic capacitor, the barrier dielectric film, γ-Al2O3, was formed by a mechanical attrition enhanced anodizing process. The anodizing was conducted in a traditional boric acid solution and the mechanical attrition (MA) action was applied by impact of nano-sized α-Al2O3 particles on the sample surface with a special vibrating frequency. The surface morphology of anodized foil was observed with SEM. The morphology and microstructure of the anodized oxide were examined by SEM, TEM and XRD. The capacitance and withstanding voltage of the oxide film were also determined with LCR meter and small-current charging. The results show that MA has significant effects on the microstructure and performance of Al anodic film. The MA-assisted barrier film becomes thinner, more crystallized but with less structure defects than the traditional one without MA, leading to increase in the film capacitance and withstanding voltage.

Production of Ti, La, Pb, Cd, Mn, Zr, and Y oxide thin films on complex surfaces of etched aluminum foils for electrolytic capacitors by the pyrolysis method of salts of organic acids

Experimental results of depositions of thin Ti, La, Pb, Cd, Mn, Zr, and Y oxide films on the surface of a 50-μm-thick aluminum foil, used for manufacturing electrolytic capacitors by the pyrolysis method of salts of carboxylic acids, are presented. The obtained samples are characterized by capacitance values of 40 to 240 μF/cm2 and electric strength values in an interval of 0.5 to 2 V, except for Ti oxides, whose samples have an electric strength of 2 to 8 V. The obtained capacitance and electric strength values are close to the values possessed by commercially produced aluminum foils with thicknesses of 70–107 μm having an aluminum oxide dielectric on the surface.

Effect of cerium addition on microstructure and texture of aluminum foil for electrolytic capacitors

Anode foil of aluminum electrolytic capacitor, which requires large surface area for high capacitance, were prepared by rolling, annealing and electrochemical etching. Effects of cerium addition on the capacitance of aluminum electrolytic capacitors were investigated. Microstructure of the aluminum foil surface was observed by optical microscopy (OM) and scanning electron microscopy (SEM). Electron back scattered diffraction (EBSD) was also employed to reveal texture evolvement of cold-rolled aluminum foil after annealed. The results showed that addition of cerium contributed to higher <100> texture and higher etch pit density as well. Moreover, the distribution of etch tunnels was more uniform compared with that without cerium addition. Perfect specific surface area was obtained with 0.0074% addition of cerium.

Influence of impurity hydrogen on coarse grain evolution in high purity aluminum foils for electrolytic capacitors

Two aluminum plates with 99.99 mass% purity with different hydrogen contents of 0.17 and 0.41 mass ppm were hot-rolled to 10 mm in thickness, cold-rolled by 99% to 130 μm in thickness, annealed at 250°C for 2 h, cold-rolled by 15% to 110 μm in thickness and finally annealed, which is similar to commercial processes of high purity aluminum foils for electrolytic capacitors. The foils were subjected to optical macro- and micro-scopies, thermal desorption spectroscopy (TDS), hydrogen micro-print technique (HMPT) and electron back-scattering diffraction pattern (EBSP) analysis and the effect of impurity hydrogen on the growth of off-cube grains in a recrystallized microstructure with a strong cube texture was investigated. It was confirmed that abnormal grain growth of off-cube grains becomes more conspicuous with the increase in the amount of impurity hydrogen in the original ingot. The HMPT analysis showed that hydrogen concentration in the cube-oriented region was larger than in the off-cube grain. The grain size in the cube-oriented region decreased with decreasing hydrogen content. From these facts and the result of TDS, supersaturated hydrogen atoms were presumed to segregate to low angle grain boundaries, the boundaries between cube-oriented grains, which can provide the driving force for the abnormal grain growth.

In Situ EBSP Analysis of Grain Boundary Migration during Recrystallization in Pure Aluminum Foils

Grain boundary mobility in preferential growth of cube grains ({100}&lt;001&gt;) was evaluated by in-situ electron back scattering diffraction pattern (EBSP) analysis in order to clarify the fundamental mechanism of primary recrystallization in pure aluminum foils of 99.9% purity thermo-mechanically processed in the industrial production route for aluminum foils for electrolytic capacitors. We have carried out the continuous EBSP measurements during recrystallization of the aluminum foils heated to various temperatures in the chamber of scanning electron microscopy (SEM). We have succeeded in dynamic observation of the preferential growth of cube grains by the in-situ EBSP analysis. The in-situ EBSP analysis could reveal the migration rate of grain boundaries surrounding the cube grains. It was clarified that the proportional relation between migration rate and annealing time was satisfied. The stored energy providing the driving force for the grain boundary migration during primary recrystallization could be estimated from the misorientation within the deformed grains. The mobility of the grain boundary could be evaluated using the measured grain boundary migration rate and stored energy. Then the activation energy could be estimated by the in-situ EBSP analysis at various temperatures ranging from 270°C to 310°C. The obtained activation energy was 124 kJ/mol, which approximately corresponded to that for the diffusion of impurity such as iron or silicon in aluminum. This suggested that the rate-determining process of the grain boundary migration of cube grains was impurity diffusion in the pure aluminum foils.

(Ba 0.5Sr 0.5)TiO 3 modification on etched aluminum foil for electrolytic capacitor

A new method was proposed to form (Ba 0.5Sr 0.5)TiO 3–Al 2O 3 composite oxide film on etched aluminum foils. The specimens were covered with (Ba 0.5Sr 0.5)TiO 3 (BST) layer by dip-coating in citrate solution and subsequent heat-treatment under 400–650 °C, finally by anodizing in a hot boracic acid and borate solution. The BST powders heated under different temperatures were characterized by X-ray diffraction (XRD) and the specific capacitance of the coated specimens heat-treated under different temperatures and times was measured. It is found that the specific capacitance increases initially with enhancing the temperature and reaches to maximum at 550 °C, but slightly decreases with the heat-treatment time. The capacitance was increased by about 35% after BST coating.

Electrochemical Etching of Aluminum Foil for Electrolytic Capacitors

The increase of capacitance on dielectric layer is associated with enlargement of etched surface area of electrodes for aluminum electrolytic capacitors. Etched tunnels extending along [100] directions are formed by crystallographic dissolution of aluminum in a chloride solution. This study has been focused primarily on the effects of addition of inhibitors to hydrochloric acid solution on the increase of the surface area by Electrochemical Impedance Spectroscopy (EIS). The addition of 3 % ethylene glycol was more effective for the enlargement of the surface area comparing with those of 1M sulfuric acid and no additive. And it was observed by TEM that the tunnels were grown straight and parallel to [100] directions.

Abnormal Grain Growth of Off-Cube Grains in High Purity Aluminum Foils with Cube Texture

In present study, abnormally coarsened grains in high purity aluminum foils with cube texture (f100gh001i) after a final annealing was investigated using SEM/EBSP method. Most of abnormally coarsened grains had Goss (f110gh001i )o r S( f123gh634i) orientations. The coarsened grains with Goss and S-orientations were surrounded by �5 and �7 coincidence boundaries, respectively. This result clarified that these coincidence boundaries would enhance the abnormal grain growth of Goss and S oriented grains. Grain boundary energy of sub-boundaries between cube-oriented grains provided the driving force for the abnormal grain growth. The distribution of Goss oriented grains in the partially annealed foils was characterized by SEM/EBSP method. This characterization revealed that many Goss-oriented grains were distributed in the transition band on the central layer of the sheets. aluminum and its alloys, which is closely related to forming or etching property. Several thermo-mechanical processes have been developed for the control of cube texture in commercially pure aluminum and its alloys. A thermo- mechanical process through a cold rolling, a partial annealing (the annealing temperature is 240-260 � C), an additional rolling (the reduction in thickness is approximately 20%) and a final annealing has been developed for the formation of sharp cube texture in a high purity aluminum and an Al-Mn- Mg alloy, 2) which are referred to as Pechiney process. 3) This process is the production process for aluminum foils for electrolytic capacitors. The mechanism of preferential growth of cube-oriented grains (cube grains) by the Pechiney process has been investigated using SEM/EBSP method. 4,5) The previous investigations have clarified that the difference of accumu- lated strains between cube grains and off-cube grains induced by an additional rolling could provide the driving force for the preferential growth of cube grains during the final annealing. This mechanism is expected to have come from the property that cube grains have less accumulated strains than off-cube grains. 6) Hence Controlling the formation of substructure accelerated the preferential growth of cube grains and inhibited growth of off-cube grains, leading to the production of higher volume fraction of cube texture more than 95%. 7) However, in some cases, off-cube grains abnormally grow to over 10 cm in grain size in high purity aluminum sheets through the Pechiney process, and bring about decline of a volume fraction of cube texture. Most of recent studies 8-14) are concerned to the preferential growth of cube grains, so that there are few studies on the character of residual off-cube grains in aluminum sheets with cube texture. Accordingly, establishing the mechanism of the formation and growth of off-cube grains in aluminum sheets with cube texture is important for not only the development of processes for control of cube texture but also under- standing the fundamental mechanism of cube texture devel- opment in aluminum and its alloy. In the present study, off-cube grains in high purity aluminum foils with cube texture were analyzed by SEM/ EBSP method. From the results, the mechanism of abnormal growth of off-cube grains is discussed focusing an attention to mobility and driving force of grain boundary migration between cube grains and off-cube grains. A distribution of orientation in aluminum foils before the final annealing was characterized by SEM/EBSP method. Comparing the dis- tribution of off-cube grains in the foils before and after the final annealing, we discuss the mechanism of the formation of off-cube grains during the thermo-mechanical process. 2. Experimental

Influence of Purity on the Formation of Cube Texture in Aluminum Foils for Electrolytic Capacitors

In the present study, the crystal orientation and residual strains in hot rolled sheets, cold rolled foils, partially annealed foils, and additionally rolled foils of aluminum of 99.9% (3NAl) and 99.99% (4NAl) purity used for the fabrication of electrolytic capacitors, were evaluated by the SEM/EBSP method. The additionally rolled foils were annealed at 573 K and the behavior of the growth of cube-oriented grains and the grain boundary character were analyzed. In the hot rolled sheets and the partially annealed foils, cube-oriented grains in 4NAl were larger in number and size than those of 3NAl. From the result, it was clarified that purity of the aluminum affected the growth of cubeoriented grains during the thermo-mechanical treatment. In the additionally rolled foils annealed at 573 K, the growth of the cube-oriented grains in 4NAl was faster than that in 3NAl. In both 3NAl and 4NAl, the residual strains and the grain boundary character were similar. Accordingly, it is concluded that impurity in 3NAl could have segregated at the grain boundaries around cube-oriented grains and supressed the growth of cube-oriented grains.

電解コンデンサ用アルミニウム箔材におけるＭＣシミュレーションによる粒界移動予測

In order to control orientation distributions or texture in polycrystalline materials, it is important to study microstructural evolution, such as recrystallization and grain growth. In this study, microstructures have been observed in detail by using the SEM/EBSP orientation analyzing system before and after annealing during grain growth in an aluminum foil for electrolytic capacitor. The foil sample after the first annealing had a columnar structure with a few R-orientation grains in a cube texture. It was found that some grains disappeared after the second annealing. We carried out Monte Carlo simulation of grain growth in the Potts model applying orientations image data before the second annealing to an initial microstructure to predict microstructural evolution. Dependence of grain-boundary energy on misorientation was given on the basis of previous experimental knowledge in the simulation model. The simulation reproduced migrations in high angle grain-boundaries with disappearing of R-orientation grains and stable topological features in low angle grain-boundaries.

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.

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.

Application of IrO&lt;sub&gt;2&lt;/sub&gt;/Ti Anodes and Stability of Electrolyte in the Liquid-contact Forming Process of Aluminum Foil for Electrolytic Capacitor

Application of IrO&lt;sub&gt;2&lt;/sub&gt;/Ti Anodes and Stability of Electrolyte in the Liquid-contact Forming Process of Aluminum Foil for Electrolytic Capacitor

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.