Stripped porous anodic film formed on aluminum in chromic acid solution was thinned with an argon ion beam and examined in a high-resolution electron microscope. Diffraction patterns obtained from several different areas of the film showed different degree of crystallization. TEM images of areas where many diffraction spots were detected showed clear lattice images of almost the entire field except for the vicinity of the pore walls. Both from the lattice images, which showed distances and angles between crystal planes, and from the analysis of diffraction patterns, the film was identified as γ-alumina. Other diffraction spots and lattice distances were also found and were presumably caused by the slightly mixed other crystal forms of alumina in the film. Careful observation showed many disordered mosaic fractions in the lattice images of the crystalline film, and even taking into account the effect of crystallization by beam irradiation, this fact suggests that the original film was composed of a mixture of ordered and disordered structures.
A study was conducted on the relationship between the anodizing conditions on aluminum as determined by pulse current with a negative component and the microstructure of the anodic oxide films. Anodic oxidation was carried out in solutions of 15 wt% H2SO4, 5 wt% H2C2O4 and 10 wt% CrO3, with the reversing cycle set at 13.3Hz. The cells and pores of the films obtained in the sulfuric acid using pulse current with a negative component were uniform size, and size was not significantly influenced by the anodizing conditions. In films formed using pulse current with a negative component in the oxalic acid solutions, cell and pore size was uniform. The pores divided into branches, and the degree of branching became greater as the duty factor decreased. The microstructure of the films prepared in the chromic acid solutions was similar to that of films prepared in the oxalic acid baths.
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
There are two factors preventing ion permeation during electrodialysis using porous anodic alumina membranes-electrostenolysis in the pores, and sealing of the pores by a hydration reaction. The mechanism of occurrence of electrostenolysis was investigated using an electrodialysis cell of the construction Pt/NiSO4/sulfuric acid membrane/H2C2O4 or Na2SO4/Pt. With an oxalic acid catholyte at a pH value of 2∼6.5, ions were unable to permeate the membrane as an insoluble nickel compound (NiC2O4) precipitated into the pores, but with a sodium sulfate catholyte and a pH range 1∼65 they were able to permeate. Electrodialysis was carried out by using membranes treated to different sealing times in boiled water, and the amount of Ni ions permeated to the cathode compartment was measured. Ni ion permeation ceased for sulfulic acid membranes in 2 minutes, and for Kalcolor membrane in 10 minutes. SEM observations revealed that the pores of sulfulic acid films were completely sealed, however those of Kalcolor films had become smaller but were not completely sealed.
Anodic oxide films have been prepared for use as gas separation membranes on aluminum, having ultrafine pores of a diameter considerably smaller than those referred to in previous studies. Anodic films formed at the same voltage were found to have pore diameters that depended on the electrolyte, increasing in the order sulphuric acid, oxalic acid, chromic acid and phosphoric acid. Since the rate of dissolution of anodic films in sulfuric acid is rather high, oxalic acid was chosen as the most suitable electrolyte for the preparation of membranes with ultrafine pores. By using the method of a sudden voltage drop during anodizing or changing electrolyte from barrier type to porous type duplex anodizing, it was possible to form pores having a diameter only one-half to one-third of that of pores formed under steady state anodizing. Pores formed at 5V and directly measured with an electron microscope was 5nm in the case of the first of these methods and 3.5nm for the second. It is also found that the rate of chemical dissolution of the films formed at voltage around 5V was extremely low. It was also clarified that heterogeneously proceeded sealing during immersion in hot water, that is to say granular hydrates precipitated, and eventually filled up the pores.
Various anodizing conditions and follow-up processes have been investigated to obtain films that have fine pores and are transparent in the infrared region One of the most successful minimizations of pore diameter was achieved by a combination of reducing the voltage in the process of forming a film in oxalic acid, and sealing the film with humidity. This film has fine pores at the section near the barrier layer, pore diameter was estimated at 1nm by measuring the dependence of gas permeability on the molecular diameter of different gases The pores are so fine that the separation factor for He and Xe is twice as large as the value predicted by Knudsen's law We have also developed films that have fine pores at the center, as well as films with fine pores at the surfaces, both have pore shapes that are symmetrical along the axis. Some of these films are capable of incorporating molecules into the film Films formed in chromic acid electrolyte are transparent at wavelengths of 1∼9μm
In order to find out the mechanism of elelctrolytic coloring of anodic oxide film of aluminum, the electrolytically colored films in several electrolytes such as nickel, cobalt, copper, tin, selenium and aluminum-magnesium solution were used for the anodic stripping. In the nickel solution and the cobalt solution, nickel and cobalt in the film pores were dissolved at the peak potential of the anodic polarization curves, and the films were completely decolorized. This suggests that nickel and cobalt in the colored films would be deposited in the film pores under the metallic state. In the copper solution and the tin solution, the films were not completely decolorized. This implies that copper and tin would not only be deposited under the metallic state but deposited under the state of oxide and hydroxide. In the selenium solution, the film was not decolorized at all. This suggests that selenium would be deposited under the state of oxide. The aluminum-magnesium solution yielded a white film, which was slighty decolorized. This implies that aluminum was not dissolved because of being deposited in the film pores under the state of oxide and hydroxide, while magnesium was dissolved because of uncomplete oxidization and hydration. The result is that the anodic stripping method provided three kinds of deposit states in the film pores; only metal, only metal oxide (hydrate), and a mixture of them.
Anodic oxide films of aluminum, containing ferromagnetic particles electrodeposited in their pores (magnetic composite alumina films) have high perpendicular magnetic anisotropy, making these films suitable for use in hard disks and other magnetic recording media. This study was undertaken to obtain these films with magnetically harder characteristics. By controlling the anodizing conditions, pore widening process and electrodeposition of iron particles, it was possible to obtain films having a coersive force He of greater than 2000oe, a magnetic energy product (BH) max of greater than 0.2MG·Oe, and thickness of 20∼100μm. These films were formed on the sides of rotary drums and were given multipolar magnetization making them applicable for high-precision magnetic rotary encoders.
Porous anodic Al2O3 films 50μm in thickness formed in oxalic acid solution were detached cathodically from aluminum substrate. The films were then dipped in an aqueous solution of 2.92 wt. % Tb (NO3)3, and heat-teated at 550°C for 10 minutes in air. The light-emitting device was fabricated by sandwiching the Al2O3 film between sheets of 110 glass. At voltage of 280V AC 50Hz or above, a bright green light emission was obseorved, with peaks at 489, 542, 583, 620nm. This emission is not intrinsic electroluminescence but is due to the air-plasma collision excitation of the Al2O3: Tb3+ phosphor that is formed on the pore walls of the film by the heat-treatment.
The bath compositions and conditions suitable for anodizing of aluminum die casting were investigated in baths of amine alkalinity (etheylenediamine, diethylamine and triethylamine) with additions of ammonium fluoride and ammonium carbonate. In the amine baths (0.1mol/L) with added ammouium fluoride (0.3mol/L) and ammonium carbonate (0.3mol/L), thick, grayish-black coatings (about 13μm) were obtained by anodizing for 30min at a current density of 2A/dm2. The effects of the addition of polyhydric alcohols on the thickness and hardness of the anodized-coatings were also investigated in the above amine baths. The thickest (about 16μm) and hardest (about 50 by Marten's scratch hardness test, load of 50g) coating was formed in triethylamine (0.1mol/L) with ammonium fluoride (0.1mol/L), ammonium carbonate (0.3mol/L) and polyethylene glycol (20%), by anodizing for 30min at 2A/dm2. It was considered that the formation of the thick coating in the bath containing polyethylene glycol was caused by diffusion of the Joule heat produced by anodizing, and the prevention of the dissolution of the anodized coating. SEM showed that the anodized coatings formed in amine alkaline haths have larger pores (about 1000Å) than those in sulfuric acid bath.
Hydroxide films were formed on aluminum specimens by immersing them in water at temperature (Tb) of 100-180°C, and the specimens were then anodized galvanostatically in a neutral borate solution to form composite oxide films. The formation behavior of the hydroxide and composite oxide films were followed by gravimetry, X-ray photoelectron spectroscopy, electron microscopy, and electric capacitance measurements. It was found that the growth rate of the hydroxide films increased with increasing Tb, and that the hydroxide/metal interface roughened increasingly due to the non-uniform growth of the hydroxide. The water content of the hydroxide (value of X in Al2O3·XH2O) decreased from 2.7 to 1.8 when Tb increased from 100 to 180°C. The composite oxide films that formed after boiling at different values of TbS were all composed of an outer crystalline oxide layer (thickness δo) and an inner amorphous oxide layer (thickness δi), and while δi did not depend on Tb, δo decreased with increasing Tb. The composite oxide films formed by anodizing to Ea=300V showed thickness/voltage ratios ((δo+δi)/Ea) of only 1.10 to 0.87nm/V, decreasing with increasing Tb. The capacitance and dielectric loss of the composite oxide films increased with Tb. The effect of Tb on the formation behavior of composite oxide films is discussed by considering the volume changes caused by the field-assisted dehydration of hydroxide to form a barrier oxide layer.
Ultramicrotomed sectional specimens of composite aluminum oxide films, formed by the sequential process of the reaction with boiling water followed by anodic oxidation, were examined using transmission electron microscopy. It was found that hydrous oxide films, the structure of which is indicated to be pseudoboehmite from infrared spectra, consist of a dense inner layer of relatively uniform thickness and a fibrous outer layer of uneven thickness. TEM observation showed that the composite oxide films consist of two layers-namely an outer crystalline oxide layer containing numerous voids and cracks, which was identified by electron diffraction as γ′-Al2O3 and an inner amorphous oxide layer. During anodizing, the total thickness of the composite oxide film increased with time, while the thickness of the inner dense layer of hydrous oxide film decreased linearly with time and disappeared after a certain period td. The thickness of the outer fibrous layer of the film remained almost unchanged during td and then decreased gradually. The electric field supported by the composite oxide film obtained by immersion in boiling distilled water for 15min and subsequently anodizing at 1mA/cm2 to 200V in 0.27MH3BO3/0.0092M (NH4)2O· 5B2O3·8H2O solution was found to be 12×106V/cm, which was somewhat higher when contrasted with the values in the range 10∼11×106V/cm obtained by testing several aluminum electrolytic capacitors for commercial use.
Smooth, bright copper electrodeposits were obtained in the range of 2.0-10.0A/dm2 from Cu(CF3COO)2 (600g/dm3)-MeOH baths at 40°C with a cathodic current efficiency was about 100%. As bath temperature increased, however, H2 evolution from the cathode during the electrodeposition was observed cathodic current efficiency decreased. If, however, electrodeposition was carried out at lower bath temperature and current density, bath oxidation occurred at the anode and anodic current efficiency was about 20%.
This study was carried out to improve the properties and as-plated conditions of 44wt%W Ni-W alloy, since that composition is considered optimum for the electroplated alloy. The experiments were conducted using citric acid-ammonia baths of pH 6, 70°C, containing 40g/L of NiSO4·6H2O, 70g/L of Na2WO4·2H2O plus citric acid and NH4OH, taking the citric acid concentration in the bath as the parameter. When citric acid monohydrate concentration was varied from 80g/L to 140g/L and the current density was kept constant at 10A/dm2, the composition of the plated alloys retained the value of 43±0.6wt%W, which closely corresponds to Ni4W stoichiometry. The alloys assumed the highest ductility at a citric acid concentration of 100g/L, and at citric acid concentrations exceeding 120g/L, the whole surface of the plates was mirror bright. As-plated alloy from 100g/L citric acid bath had a hardness of Hv 620, but showed a room temperature hardness of Hv 1310 after heating at 700°C for 1h, and a hot hardness of Hv 950∼980 at temperatures of 550∼670°C. It was also found that the quantity of the codeposited trace elements, carbon, oxygen, nitrogen and sulfur, was less for alloy plated from 100g/L citric acid bath than for all other alloys. From the results of measurements of electrode surface pH, crystallite size, physical density and trace elements in the alloys, it was inferred that the main species adsorbing on the electrode surface will change from hydroxide to citric acid, when citric acid concentration in the bath exceeds 100g/L.
Thermal decomposition of aluminum triisopropoxide resulted in chemical vapor deposition of a thin layer of alumina on the microporous structure of aluminum anodic oxide films. Properties of the deposition were analyzed with a scanning electron microscope and the mechanism of the deposition of the alumina film on the porous structure was discussed.