It has been reported that the formation of uniform anodic oxidation coatings on aluminum in baths of mono-carboxylic acids (formic, acetic, propionic, butyric, valeric and benzoic acids) was difficult, and local corrosion on the surface was always observed.
In the present paper, the anodization of aluminum in mono -carboxylic acids (formic, acetic, propionic, butyric and lactic acids) was investigated by the constant voltage method (50V, formic acid bath: 15V).
Uniform anodic oxidation coatings was prepared in the above baths, and SEM observation of film surfaces and cross-sections revealed that the films had larger size pores (600-700Å) and cells than films formed in a sulfuric acid bath. It was observed that cells of the films dissolved in mono -carboxylic acids and fluoride ion were annexed in the upper parts of film.
In terms of dyeing affinity, the films were superior to films of the same thickness prepared in a sulfuric acid bath.

抄録全体を表示

On the basis of results obtained in a previous investigation, the growth mechanism of composite oxide films formed when anodizing Al covered with hydroxide was discussed by checking the behavior of ion transport, void formation, and current efficiency for oxide formation.
The mechanism that can be supported is as follows: during anodizing hydroxides are dehydrated to form dense crystalline oxides at the hydroxide/oxide interface, and the voids produced at the interface by shrinkage are repaired with new oxide produced by the outward transport of Al³⁺ across the oxide layer. At the same time, an amorphous oxide is formed at the oxide/metal interface, by the inward transport of O^2-ions. The amorphous oxide is then transformed to the crystalline oxide with the formatin of voids at the amorphous oxide/crystalline oxide interface at a rate increasing with increasing temperature. The voids thus formed are not filled up with Al₂O₃. The transport number of Al³⁺ions was estimated to be 0.32 and the current efficiency for oxide formation was 1.21. The volume fraction of the voids produced by the transformation of amorphous oxide to crystalline oxide was calculated to be 0.02-0.08, the value of which increases with increasing anodizing temperature.
An alternative mechanism was also considered, in which the transformation of hydroxide to crystalline oxide does not cause any void formation because of rapid rearrangement of atoms, but it seems to be less probable than the first.

抄録全体を表示

The impedance response, and the capacitance at 1kHz were measured on electrodes of copper, aluminum and steel in various neutral solutions, using an FFT analyzer and a LCR meter respectively. The series capacity C_s was represented in an electrode-solution system consisting of charge transfer resistance R_ct, double layer capacitance C_dl and solution resistance R_sol as C_s=C_dl (1+1/D²) where D=ωC_dlR_ct. The measured value of C_s was equal to the C_dl at D→∞ in systems combining a metal and a solution. The capacitance C_s of copper was in proportion to the surface area in 0.5mol/L Na₂SO₄ with 0.3g/L benzotriazole and 0.3g/L nicotinic acid. It was found that the surface area could be estimated by the C_s value measured at 1kHz in solutions where the distribution of C_dl was uniform on the metal surface.

抄録全体を表示

Hopeite and Phosphophyllite as zinc phosphate crystals were formed on galvannealed steel (GA) with alloy phase of FeZn₇ and cold rolled steel (CR). The distribution of crystal components were analysed by Auger electron spectroscopy for the surface region and depth profile.
No Mn or Ni was detected on the Hopeite crystal surface and it was therefore concluded that the crystal surface was made up of Zn₃(PO₄₎₂⋅4H₂O. Mn was, however detected on the Phosphophyllite crystal surface. These results correlated with those from X-ray photoelectron spectroscopy described in a previous paper.
In the depth profile analysis, Ar⁺sputtering was applied between 0-64.5min, and the intensity ratios were calculated for O/P, Zn/P, Fe/P, Mn/P and Ni/P from the Auger spectra and were plotted. For both Hopeite and Phosphophyllite crystal, the O/P ratio was constant in the bulk of the crystal layer, indicating that the structure of-PO₄ was maintained uniformely. The ratios of Mn/P and Ni/P were also constant in the bulk of crystal layer.
The ratios for Zn/P and Fe/P of the crystal on GA steel and for Fe/P of the crystal on CR steel, however, showed a radical increase in accordance with the sputtering time. It was thought that this phenomenon was in response to the steel itself through the porosity of zinc phosphate crystal.

抄録全体を表示

Studies were conducted on predicting by computer simulation the morphology of etch pits formed under various conditions.
A local dissolution model was applied to pit growth in the direction of pit diameter, in which it was assumed that Al dissolution occurs across the passive film, and that the rate is a function of a potential difference in the pit. The computer simulation showed that pit radius decreases with increases in temperature and current density.
The distribution of pit diameter obtained by the computer simulation was compared with statistical treatment of experimental results. It was found that the distribution of pit diameter can be calculated from the average of pit diameter.
An aluminum specimen was electrolytically etched in 0.85M HCl solution, and the results showed good agreement with the values obtained by simulation.

抄録全体を表示