Aluminum specimens coated with niobium oxide by a sol-gel method were galvanostatically anodized in a neutral borate solution. The time-variations in anode potential during anodizing were monitored, and the structure and dielectric properties of the anodic oxide film were studied by TEM, EDX, RBS, and electrochemical impedance measurements. It was found that the anode potential increases linearly with time after a rapid increase in potential at the initial period of anodizing. During anodizing, an anodic oxide film, which consisted of an inner Al2O3 layer and an outer Al-Nb composite oxide layer, grew at the interface between the Nb2O5 layer and the aluminum substrate. The interface between the outer and inner layers became more vaguer as the potential rose, and the concentrations of aluminum and niobium ions in the composite oxide layer also changed. The capacitance of the specimen after the sol-gel coating and anodizing was 150% as large as that without the sol-gel coating. This is due to the high dielectric constant of the composite oxide layer. The mechanism of the anodic oxide film's growth on the specimen coated with Nb2O5 is discussed in terms of the pore distribution in the Nb2O5 layer and the transport of Nb-cations across the anodic oxide film during anodizing.
Triangular nanohole array structures with high aspect ratios were fabricated by anodization of pretextured Al in an oxalic acid solution. By using the obtained anodic porous alumina with triangular openings as templates, an ordered array of TiO2 nanocylinders with triangular cross sections was fabricated. The preparation of TiO2 nanocylinders was carried out through the electrodeposition of TiO2 into the alumina nanoholes. The shapes and sizes of the obtained TiO2 nanocylinders were in good agreement with those of the pores of the alumina template. The triangular shapes of the TiO2 nanocylinders were successfully maintained even after heat treatment for crystallization to anatase from amorphous. The obtained TiO2 nanocylinders were isolated, and yielded the shape- and size-controlled TiO2 nanoparticles.
Electrodeposited White bronze (speculum : Cu-Sn 40mass%) shows promise as an alternative to nickel coating. Copper-tin(40mass%) alloy film was deposited over a current density range from 0.5 to 4A/dm2 and at a temperature of 25ºC in the following bath composition : 0.1474mol/L CuSO4, 0.0526mol/L SnSO4, 1.0mol/L sulfosuccinic acid, 0.4mol/L L-methionine and 3g/L polyoxyethylene-α-naphthol. The coexistence of L-methionine and polyoxyethylene-α-naphthol markedly inhibited the deposition of copper over a noble potential range, and markedly reduced subreaction. The copper-tin(40mass%) alloy film obtained was silvery white. Copper and tin ions in the effluent were separated as hydroxide, and the residual concentration of tin and copper ions in the bath shown above decreased to less than 5mg/L.
The ac etching process on high purity aluminum foil used in electrodes for electrolytic capacitors was investigated in 3.6wt% hydrochloric acid solution at 303K and 323K by applying an asymmetrical triangular current of 0.3A/cm2 with 5Hz. The time at the top of the current form of the anodic half cycle, tp, was varied in the range of 0 to 0.1s. Etching products developed on the etching cell during the process were characterized by SEM, XPS and gravimetric analysis. The etched layer contained the products of a duplex structure, consisting of an inner anodic film of Al2O3 and an outer hydrous oxide layer of Al2O3·1.6H2O, which was formed at all tp at 303K and the tp range of 0.075~0.1s at 323K, while no etched layer was observed at tp ≤0.05s at 323K, except for only a thin film of Al2O3. It seems to be that the variation of tp affects the concentration gradient of chloride ions in the vicinity of the aluminum electrode and results in the change of the specific surface area of aluminum, and tp also affects the concentration of the aluminum hydroxide deposited on the electrode during the cathodic half cycle.
In order to enhance the electrocatalytic activities of a hydrogen electrode and lower the price of the electrode, the possibility of Pt-Ni alloy plating as the electrode material formation was studied. It is generally hard to codeposit Pt and Ni, because they have considerably different standard oxidation-reduction potentials. Complexing agents were surveyed to bring the oxidation-reduction potentials of both Pt and Ni closer by drawing immersion potential-pH diagrams. Glycine was found to be useful for Pt ion as a complexing agent. The best electroplating condition was determined by measuring the current-potential curves of Pt and Ni ions and analysing the composition of the deposits. The plating bath composition was investigated by changing the Ni concentration and pH. The optimum bath composition and conditions were 0.009mol/dm3 NiCl2·6H2O, 0.001mol/dm3 K2[PtCl4] and pH4. It was confirmed by XRD analysis that the plating film obtained at optimum conditions was a Pt-Ni alloy. By changing the current density of the electroplating from 0.15A/dm2 to 1.0A/dm2, thin Pt-Ni alloy films could be obtained with Ni content between 35mol% and 67mol%. The film thickness obtained in this study was between 0.42μm and 0.75μm, and each metal was distributed uniformly on the surface and also in the depth direction.