Porous Anodic Oxide Films Research Articles

A model for the mechanism of nickel fluoride cold sealing of anodized aluminium

The sealing of porous anodic oxide films on aluminium by the use of nickel fluoride solutions at ambient temperatures has been proposed as an alternative to hydrothermal sealing methods, on energy grounds. The process of cold sealing shows some promise and a mechanism is proposed as to how it may operate. As fluoride ions enter the pores, a place exchange mechanism occurs causing a shift in the local pH which is sufficient to cause nickel ions to precipitate. The nickel hydroxide blocks the pore mouths, effectively sealing the film. A slow step then occurs whereby water from the atmosphere diffuses into the film, effectively hydrating the film and causing general pore blocking. This slow step explains the ageing effect seen with such films. Eventually a film is produced which is effectively sealed.

Characterization of various aluminium oxide layers by means of spectroscopic ellipsometry

This paper reports the characterization of both barrier type and porous type anodic oxide films on aluminium by means of spectroscopic ellipsometry (SE). In order to show the capabilities of the technique for quantitative determination of the layer characteristics, results based on ellipsometric data are correlated with complementary information from the analytical techniques transmission electron microscopy (TEM) and Auger electron spectroscopy (AES). It is concluded that ellipsometry yields an accurate characterization for the thicknesses and the interfacial properties of both the barrier layer and the porous layer. The porosity of the porous layer, determined with SE, is found to be in good agreement with the results obtained from TEM.

Kinetics of growth of porous anodic Al 2O 3 films on A1 metal

The kinetics of growth of porous anodic aluminium oxide films on A1 metal, anodized galvanostatically in a non-stirred bath solution 15%w/v H 2SO 4 at various current densities (5–75 mA/cm 2) and bath temperature (20–40°C), were studied. The kinetic model m = kit - λ 1 t exp (λ 2 t) was found to be valid for all the anodization conditions chosen and for anodization time intervals shorter than those beyond which limiting constant values of film mass and thickness are obtained. The model shows that the true shape of pores is that of a truncated cone, whereas parameters λ 1 and λ 2 are directly related to the surface area of the pore base section (λ 1 = 4 −1 kinπ D 2 0 and the dissolution rate of pore wall oxide (λ 2 = 2 k d D −1 0. With the aid of the model it was proven that, during anodization, oxide dissolution at the depth of pores is essentially a field-assisted process; while pore wall oxide dissolution is a first-order reaction, thermally activated, with an activation energy of 78.6 kJ/mol; electrolyte concentration inside the pores increases linearly with true current density ( C = C 0 + ai t). The open circuit oxide dissolution rate was found to be 0.52–4.1 Å/min for anodization temperatures of 20–40°C. Also, by applying the model, information was obtained on the oxide's main structural characteristics such as concentration of cells and pores, cell mean width, pore base mean diameter, thickness of barrier layer, total and specific real surface, porosity, etc.

Gas permeation through siloxane-anodic aluminum oxide composite membranes at temperatures up to 200°C

Experimental work was carried out aimed at producing composite membranes possessing high permeation rate and high thermal stability. Such composite membranes were prepared by supporting different siloxane polymers on porous anodic aluminum oxide film; they were then subjected to permeation experiments with H 2, He, N 2, O 2 and CO 2 gases at various temperatures. The permeation characteristics of the membranes were found to be controlled by permeation in the polymers. High thermal stability was exhibited by the composite membranes. Poly(methylsiloxane) composite membranes were usable up to 200°C and showed the highest permeation rate, which was at least ten times that of commercial silicone polymer membranes. The permeation characteristics of the composite membranes are discussed in connection with the correlation of gas solubilities in the siloxane polymers.

特集 アルミニウムアノード酸化皮膜の構造と機能化 多孔質型陽極酸化皮膜

特集 アルミニウムアノード酸化皮膜の構造と機能化 多孔質型陽極酸化皮膜

アルミニウムのアノード酸化法により作成したイオン透過用メンブレンについて

Porous anodic oxide films on Al with a small diameter were formed in (a) 15% sulfuric acid at 20V and the films with a large one were obtained in (b) Kalcolor solution at 80V. Then the specimens were cathodically electrolyzed in the same solution and the films (membranes) were detached from Al metalic substrate by hydrogen gas evoluted at the bottom of the pores.Scanning Electron Micrographic observation revealed no barrir layer for either of the films produced from (a) or (b). Pores in the films formed from (a) were linked together due to irregular dissolution, while for films formed in solution (b), the film structure was almost regular, with much less pore-linkage. The permeation behavior of ions in the prepared membranes was examined with Fe3+ -sulfosalicylate and Ni2+ -sulfate solutions by applying a constant voltage of 30V. To avoid hydration of the membranes in the humid atmosphere, it was neccessary to keep the membranes in a desicator before the experiment. With the membranes prepared, anions were easier to permeated more easily than cations because the alumina membranes in acidic solutions have positive zeta potential, with the result that only anions adsorb on the inner surfaces of the pores and migrate towards the anode during the electrodialysis.

アルミニウムのアノード酸化皮膜のゾルーゲル法による孔径制御と複合化

In order to modify the properties of porous anodic oxide films on aluminum, much work has been done to introduce metals, organic and inorganic materials into the film pores by various processes We know that while the pores are successfully filled by electrolytic depositing for metals, but it is difficult to fill the pores by dipping Specifically, no one has yet succeeded in pore filling or the modification of pore walls by dipping for organic and inorganic materials In this work, we have tried to control film pore size by a sol-gel dip-coating process using metal alkoxide For this purpose, porous films which were formed in an oxalic acid solution were dip-coated in sols consisting of mixed solutions of silicon ethoxide [Si(OC2H5)4 TEOS], ethyl alcohol, water and additives SEM observation were made of the influence of sol composition and aging time on oxide formation in the pores The SEM results, showed that the sol penetrated along the pore walls filling the pores, and a method of controlling pore size was found The inorganic oxide formed in the pores seemed to consist almost entirely of SiO2 These results suggest that this sol-gel process can give a new usefulness to porous films

アルミニウムアノード酸化皮膜の電解着色

アルミニウムアノード酸化皮膜の電解着色

Microstructure of porous anodic oxide films on aluminium

Microstructure of porous anodic oxide films on aluminium

Microstructure of porous anodic oxide films on aluminium

Microstructure of porous anodized films of aluminium prepared in sulphuric acid solution are different from those prepared in an oxalic or phosphoric acid solution. Transmission electron microscopy reveals a multilayer or higher order structure in the former films. Infrared spectra and specific surface area were also studied for these films and new functional properties of the films suitable for new materials were found. In contrast to the fibrous colloidal structure in the cells and barrier layer in the conventional films anodized in a sulphuric acid solution at d.c. 15 V, a network structure is formed in the cells and barrier layer in the hard films prepared at higher voltage of d.c. 25 V. The microstructure changes according to the anodizing conditions. A new model for these sulphuric acid films is presented, i.e. the cell walls are constructed from five layers and the fracture of the films occurs at the centre of the cell walls. Centre barrier layer (4 to 6 nm in thickness) composed of aluminium oxide of high crystallinity was found in a barrier layer at the bottom of the pore, and the thickness is independent on the applied voltage of the anodizing. Increase in thickness of the barrier layer due to applied voltage is governed by that of the outer barrier layer.

Determination of the refractive index of porous anodic oxide films on aluminium by a photoluminescence method

It is shown that previously described photoluminescence (PL) methods can be used for simultaneous determination of the refractive index n and thickness d of porous anodic oxide films formed on aluminium. The measurement of n and d is based on the determination of the positions of interference maxima which appear in emission PL spectra. For anodic alumina formed in 0.1M oxalic acid at T = 25 ± 1 °C and j = 2.5–12.5 mA cm -2 we obtained n = 1.68 ± 0.02 in agreement with the result of Huber and Gaugler (1.65±0.02) obtained by another measurement method.

多孔質アルミニウムアノード酸化皮膜と熱水との反応 Ｖ 水和挙動に対する熱水中の添加剤の効果

Porous anodic oxide films formed on Al in an oxalic acid solution were hydrated in water at 99.5°C with and without additions of chromate, phosphate or nickel acetate. The hydrated films were then dissolved in a chromic acid-phosphoric acid solution. The changes in film structure during the hydration and dissolution experiments were followed by gravimetry and by impedance measurements in a neutral borate solution.(1) As in pure hot water, pores of the film were filled up (or sealed) with hydrous oxide in a short time in waters containing chromate and nickel acetate, although slight dissolution of the film was observed. The water with phosphate did not hydrate the film but dissolved it to some extent.(2) In the chromic acid-phosphoric acid solution, films hydrated in chromate-containing hot water dissolved faster and films hydrated in hot water containing nickel acetate dissolved slower than those hydrated in pure hot water. For all films, the dissolution rate was controlled by the dissolution of hydrous oxide which fills up the pores. The dissolution rate in general decreased with increasing electric resistance of the hydrous oxide.The significance of the three existing methods of verifying the degree of “sealing”, the coloring method, the impedance measuring method and the acid dissolution method, is discussed.

Piezo‐Electrocapillary Effect: A New Effect Observed in Porous Anodic Oxide Films

A new effect, the Piezo‐Electrocapillary (PEC) effect, has been observed in wet, porous anodic films subject to ultrasonic bulk compressional waves. When wetted with a high resistivity polar liquid, these films behave as if they were piezoelectric in that they act as transducers for ultrasonic waves. This is due to the motion (in response to an acoustic wave) of charged liquid located within a Debye length of the inner pore walls which creates an electrical current and externally measurable alternating voltage. As derived in this paper and confirmed by experiments, the voltage output depends on the resistivity, compressibility, and viscosity of the liquid. Transducer sensitivity equal to that of sputtered 10 μm thick has so far been obtained.

Properties of porous anodic aluminum oxide films as membranes.

The details of a method of preparing anodic aluminum oxide membranes are presented. The porous oxide layer consists of close-packed cells of oxide, hexagonal in shape, each of which contains a single pore formed perpendicularly to the surface of the aluminum substrate. This special structural feature is essentially important for ultrafiltration and gas separation. The rejection characteristics are examined, using aqueous and nonaqueous solutions of macromolecules. The permeability of gases is also examined at different temperatures. The flow of gases is explained by the Knudsen regime alone.

多孔質アルミニウム・アノード酸化皮膜と熱水との反応 ＩＩＩ インピーダンス測定による水和皮膜の酸溶解特性の解析

Porous anodic oxide films formed in an oxalic acid solution were hydrated to various extents by allowing them to react with hot water at 99.5°C. The films were then dissolved in a chromic acidphosphoric acid solution and the dissolution was followed by impedance measurements in a neutral borate solution. The results were analyzed by plotting the log of the absolute value of impedance against the log of the frequency. The equivalent circuit of the hydrated film was found to consist of the capacitance of the barrier oxide layer (Cb) combined in series with a parallel combination of the capacitance and resistance components of the hydrous oxide formed in the pores (Ch and Rh). The values of Cb-1, Rh and Ch-1 and the their variation with the dissolution time (td) were determined. It was found for the films filled up with the hydrous oxide that the film-dissolution proceeds uniformly from the outside at a rate controlled by the dissolution of hydrous oxide, the dissolution rate decreases with the time of the reaction with hot water (th). The outermost part of the hydrous oxide formed at th>30min was very resistant to acid-dissolution. It was recognized that the decrease in dissolution rate is always accompanied by an increase in the specific resistance of the hydrous oxide. The barrier oxide layer next to the metal begins to dissolve at the time when the outer part of the film containing the hydrous oxide in the pores is completely dissolved. The dissolution characteristics of the barrier layer itself is little affected by the hot water treatment. These findings agree quite well with the results of a previous investigation conducted by gravimetry.

多孔質アルミニウム・アノード酸化皮膜と熱水との反応 ＩＶ 重量法およびポアフィリング法による皮膜構造の解析

Porous anodic oxide films formed on Al in an oxalic acid solution were hydrated for various periods by reaction with hot water. As reported earlier, the hydrous oxide is formed on the entire surface of the pore-walls to fill up the pores in about 10min, and then the hydration slowly continues from the outer surface so that the outermost part of the film becomes completely hydrated. Using gravimetric data and assuming the composition and density of the hydrous oxide to be Al2O3⋅2H2O and 2.6, the thickness of the fully hydrated portion of the film, Hhy, the thickness of the film portion containing the unhydrated pore-wall, Hox, and the thickness of the unhydrated pore-wall, δ, were calculated. In another series of experiments, the hydrated films were re-anodized with constant currents, ir, of 0.01 and 0.5mA/cm2 in a neutral borate solution to examine potential-time characteristics. For the smaller anodizing current, the steady potentials are related to the thicknesses of the barrier layers remaining unhydrated; they agree well with those estimated from capacitance measurements. Re-anodizing with the larger current causes dehydration of the hydrous oxide in the pores at the barrier layer/hydrous oxide layer interface, and voids produced by the dehydration are filled up with new oxide formed by the transport of Al3+ ion through the barrier layer. The growth of the barrier layer is reflected in the voltage-time characteristics. The transport number of Al3+ ion, TAl3+, was found to be 0.24. Using this value, Hog was estimated from the voltage-time curve. The values of Hox obtained as a function of the hydration time, th, were in good agreement with those estimated by gravimetry.

アルミニウムアノード酸化皮膜の細孔電解機構について

A modified explanation of the mechanism of metal deposition on the porous anodic oxide film of aluminum separated from the substrate is proposed as a result of measuring anion effect of the catholyte, membrane potential and ionic permeability. A concentration cell, Cu/CuSO4 (0.1mol)/oxide film/CuSO4 (x mol)/Cu was constructed and its EMF was measured by a potentiometer. Oxalic acid film manifested very low asymmetrical potential which well responded against the ionic concentration, whereas sulfuric acid film showed very high asymmetrical potential with less reproducibility. By utilizing tracer technique, diffusion and migration velocity of sulfate ion was determined. From these results, Cu2+ ion is supposed to be permeable to the pores of the oxide film. When insoluble copper salts are precipitated in the pores, diffusion and migration of Cu2+ ion are surpressed and bath voltage rises introducing a high bipolar in the pores. This might be interpreted by the fact that the metallic deposit occurred at the anolyte side of the oxide film. Once the metallic deposit has begun in the pores, further metallic deposit is able to continue by the electronic conduction of the metal itself.

Distribution of Phosphate Ions in the Porous Anodic Oxide Film Formed on Aluminium in Phosphoric Acid Solution

A porous oxide film having parallel pores is produced when aluminium is anodized in such a solution as phosphoric acid and a thin compact oxide layer called the barrier layer exists at the bottoms of pores, The thickness of pore-wall, which is a half of the distance between the adjacent pores, is nearly the same as that of the barrier layer, b (Fig. 1). lt has been known that a small amount of phosphate ion is included in the film as the result of coordination of these iions towards aluminium ions in the oxide.In this investigation, the distribution of phosphate ion across pore-wall( =1000A) was measured for the film formed at 100 V (vs. SCE) in 4% HsPO kept at 250C, a technique of dissolving the film in 2 mol/l H2SOG solution being utilized. The dissolution of. the filrp proceedsYff the surface of pore-wall in such a manner that pore widens evenly. all thro.ugh ihe depth of the pore (Fig. 1), so that the distribution of, phosphate ion was determined-by measur the time-variations of the amounts of phosphate and aluminium ions in solutio4 during dissolution (Fig. 2). The concentration of phosphate izefo at 900 A (Fig. 4). The average concentration of phosphate be abeut O.14 mg-PO/rng-Al. The to that across the pore-waH, in view o eiectronmicroscepy. The mechani sm of film growth explaining described. nearly constant irrespective of, but increases gradually and decreases nearly equal to in the film was estimated to distribtition of phosphate across the barrier laYer was similar of the results of examination of the film by ESCA and the phosphate distribution is described.

アルミニウム陽極酸化皮膜中への金属の析出機構

Electrodeposition of metals on the anodized alumina film being completely free from the substrate metal, was studied with respect to the systems of CuSO4/oxalic acid and other solutions.Evolution of hydrogen at the Al anode was explained in terms of the mechanism of electrostenolysis.Al foil (20μ in thickness) was anodized in 3% oxalic acid, by which the substrate metal was completely converted into alumina foil.The results obtained were as follows:(1) The electrostenolysis of metals occurred on the porous part of oxide films.(2) The electrostenolysis did not occur when the ionic mobility of alumina film was large; whereas, when the ionic current reached a limiting value, the electronic current in the oxide film became predominant so that the electrostenolysis occurred.(3) The SO42-ion was permeable to the oxide film formed in 3% oxalic acid bath; whereas, oxalate ion was not permeable to the film.(4) The evolution of hydrogen at the anode was actually detected and the possibility of electrode-position of metals, which are nobler than H+ion, on the porous anodic oxide film was considered to be related with the mechanism of metal deposition in the “Anorok Verfahren (Asada's Process).”

Electron-microscopy of Porous Anodic Oxide Films on Aluminium by Ultra-thin Sectioning Technique: Part 1. The Structrual Change of the Film during the Current Recovery Period

Electron-microscopy of Porous Anodic Oxide Films on Aluminium by Ultra-thin Sectioning Technique: Part 1. The Structrual Change of the Film during the Current Recovery Period