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We report the size-selective photocatalytic decomposition of organic molecules using crystalline anodic TiO2 nanochannel films as the photocatalyst. The porous TiO2 films were formed by anodizing titanium at 20 V in glycerol electrolyte containing various amounts of K3PO4, K2HPO4, and KH2PO4 at 433K. Regardless of the electrolyte composition, the as-formed TiO2 films had a crystalline anatase structure. The basicity of the electrolyte markedly influenced the morphology of the TiO2 nanochannel films; more regular nanochannels developed with increasing basicity of the electrolyte. Because the diameter of the nanochannels in the films formed in a basic electrolyte was as small as similar to 10 nm, the anodic TiO2 nanochannel films with a thickness of 5 mu m revealed a selective photocatalytic decomposition of methylene blue (MB) in a mixture of MB and direct red 80 (DR) kept under UV irradiation. The importance of the diameter of the nanochannels and their uniformity for size-selective decomposition of organic molecules were investigated.

We report the size-selective photocatalytic decomposition of organic molecules using crystalline anodic TiO2 nanochannel films as the photocatalyst. The porous TiO2 films were formed by anodizing titanium at 20 V in glycerol electrolyte containing various amounts of K3PO4, K2HPO4, and KH2PO4 at 433K. Regardless of the electrolyte composition, the as-formed TiO2 films had a crystalline anatase structure. The basicity of the electrolyte markedly influenced the morphology of the TiO2 nanochannel films; more regular nanochannels developed with increasing basicity of the electrolyte. Because the diameter of the nanochannels in the films formed in a basic electrolyte was as small as similar to 10 nm, the anodic TiO2 nanochannel films with a thickness of 5 mu m revealed a selective photocatalytic decomposition of methylene blue (MB) in a mixture of MB and direct red 80 (DR) kept under UV irradiation. The importance of the diameter of the nanochannels and their uniformity for size-selective decomposition of organic molecules were investigated.

Barrier-type, nanocrystalline anodic films have been formed on a ZE41 magnesium alloy under a constant current density of 5 mA cm-2 in a glycerol/fluoride electrolyte, containing 5 vol.% of added water, at 293 K. The films contain magnesium, fluorine and oxygen as the major species, and lower amounts of alloying element species. The films grow at an efficiency of ∼0.8 to 0.9, with a formation ratio in the range of ∼1.2 to 1.4 nm V -1 at the matrix regions and with a ratio of ∼1.8 nm V -1 at Mg-Zn-RE second phase. At the former regions, rare earth species are enriched at the film surface and zinc is enriched in the alloy. A carbon- and oxygen-rich band within the film suggests that the films grow at the metal/film and film/electrolyte interfaces. © 2014 The Authors. Published by Elsevier Ltd.

X-ray photoelectron spectroscopy is used to investigate the oxidation states of molybdenum in thin films formed potentiostatically, over a range of potentials, in either 1 mol dm− 3 H2SO4 or 10 mol dm− 3 NaOH at 20 °C. Mo 3d spectra suggested that MoO2 and Mo(OH)2 were the main components of the films, with smaller amounts of MoO3 and possibly Mo2O5. O 1s spectra indicated the presence of oxygen as oxide and hydroxide species and as bound water. Ion beam analysis revealed the formation of thin films at all potentials, with significant losses of oxidized molybdenum to the electrolyte.

The contamination of the surface of 316L stainless steel in the electrospray ionization source of a mass spectrometer is investigated using an accelerated method of contamination from a mixture of human blood plasma, diluted in methanol, and a water/acetonitrile mobile phase. Solid contaminants containing organic and inorganic components are identified. The morphology and composition of the contamination are shown to depend upon the orientation and temperature of the stainless steel, with the morphology showing self-organizing features as the contamination builds. A model is proposed to explain the morphology, involving rapid evaporation of the droplets that impinge on the stainless steel surface.

Nanoporous films have been formed on 316L stainless steel in 5 mol dm−3 sulphuric acid at 60 °C by square wave pulse polarization between active or transpassive and passive potentials, and characterized using glow discharge optical emission spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, Rutherford backscattering spectroscopy and nuclear reaction analysis. The films are shown to be chromium- and molybdenum-rich relative to the substrate, and to consist mainly of sulphates, oxides and hydroxides. The morphology and composition of the films are discussed in relation to the polarization conditions and mechanism of film formation.

Thermal treatment of anodized niobium and oxygen-containing niobium has been carried out to elucidate the thermal degradation mechanism of niobium capacitors and to clarify the influence of oxygen dissolved in niobium on thermal degradation. The capacitance and leakage current of the anodized specimens increase with thermal treatment above 423 K in air, although the oxygen content in the substrate has no significant effect up to 523 K. At increased temperatures, the changes in capacitance and leakage current are suppressed with increasing oxygen content. The anodic film formed on the Nb-50 at% O substrate thickens significantly during thermal treatment at 623 K in air, while only a slight reduction of the thickness is evident for those on the niobium and Nb-20 at% O substrates. In contrast, vacuum thermal treatment at 623 K causes thinning of the anodic film on niobium, with evidently no change in the film thickness on the Nb-50 at% O substrate. These are interpreted in terms of oxygen diffusion from the anodic film to the substrate as well as thermal oxide growth.

The present work demonstrates effective inhibition of field crystallization of amorphous anodic niobium oxide by incorporation of silicon species from substrate. The field crystallization, detrimental for capacitor application of niobium, occurs during anodizing of magnetron sputtered niobium at 100 V in 0.1 mol dm-3 ammonium pentaborate electrolyte at 333 K, while amorphous structure of the anodic oxide is totally retained during anodizing of magnetron sputtered Nb-12 at% Si. Even after prior thermal treatment in air, which accelerates field crystallization of anodic oxide on niobium, no crystallization occurs on the Nb-12 at% Si. Through examination of the crystallization behaviours of anodic films formed on a thin Nb-12 at% Si layer superimposed on a niobium layer as well as on a thin niobium layer superimposed on an Nb-12 at% Si layer, it has been confirmed that air-formed oxide or thermal oxide becomes a nucleation site for crystallization. Modification of the air-formed or thermal oxide by incorporation of silicon species inhibits the nucleation of crystalline oxide. The modification, however, does not influence the growth of crystalline oxide. The growth is suppressed by continuous incorporation of silicon species into anodic film from the substrate during anodizing.

Thermal treatment of anodized niobium and oxygen-containing niobium has been carried out to elucidate the thermal degradation mechanism of niobium capacitors and to clarify the influence of oxygen dissolved in niobium on thermal degradation. The capacitance and leakage current of the anodized specimens increase with thermal treatment above 423 K in air, although the oxygen content in the substrate has no significant effect up to 523 K. At increased temperatures, the changes in capacitance and leakage current are suppressed with increasing oxygen content. The anodic film formed on the Nb-50 at% O substrate thickens significantly during thermal treatment at 623 K in air, while only a slight reduction of the thickness is evident for those on the niobium and Nb-20 at% O substrates. In contrast, vacuum thermal treatment at 623 K causes thinning of the anodic film on niobium, with evidently no change in the film thickness on the Nb-50 at% O substrate. These are interpreted in terms of oxygen diffusion from the anodic film to the substrate as well as thermal oxide growth.

The present work demonstrates effective inhibition of field crystallization of amorphous anodic niobium oxide by incorporation of silicon species from substrate. The field crystallization, detrimental for capacitor application of niobium, occurs during anodizing of magnetron sputtered niobium at 100 V in 0.1 mol dm-3 ammonium pentaborate electrolyte at 333 K, while amorphous structure of the anodic oxide is totally retained during anodizing of magnetron sputtered Nb-12 at% Si. Even after prior thermal treatment in air, which accelerates field crystallization of anodic oxide on niobium, no crystallization occurs on the Nb-12 at% Si. Through examination of the crystallization behaviours of anodic films formed on a thin Nb-12 at% Si layer superimposed on a niobium layer as well as on a thin niobium layer superimposed on an Nb-12 at% Si layer, it has been confirmed that air-formed oxide or thermal oxide becomes a nucleation site for crystallization. Modification of the air-formed or thermal oxide by incorporation of silicon species inhibits the nucleation of crystalline oxide. The modification, however, does not influence the growth of crystalline oxide. The growth is suppressed by continuous incorporation of silicon species into anodic film from the substrate during anodizing.

Enrichment of copper beneath amorphous anodic films on relatively dilute, solid-solution Al-Cu alloys is necessary before copper can be oxidized and incorporated into the oxide layer. A similar enrichment arises during electropolishing, which also develops an amorphous oxide. In these cases, external polarization is applied, usually generating a relatively high oxidation rate. In contrast, enrichment behaviour at the corrosion potential has received less attention. The present study examines the corrosion of Al-Cu alloys, containing up to 6.7 at.% Cu, in 0.1 M sodium hydroxide solution at 293 K. Copper is again found to enrich in the alloy, similarly to behaviour with anodic polarization. However, following enrichment, discrete copper-rich particles appear to be generated in the corrosion product. These are suggested to be nanoparticles of copper, since the corrosion potentials of the alloys are low relative to that required for oxidation of copper. The corrosion rate increases with increase of both time and copper content of the alloy, probably associated with a greater cathodic activity due to an increasing number of nanoparticles. The corrosion proceeds with loss of aluminium species to the sodium hydroxide solution, but with retention of copper in the layer of hydrated alumina corrosion product. © 2008 Elsevier Ltd. All rights reserved.

The role of pre-treatment in the formation of a cerium conversion coating is investigated for the protection of AA2024-T3 and 7075-T6 alloys. The alloys were alkaline-etched and de-smutted in nitric acid, prior to cerium treatment in Ce(NO3)3 at 85 °C with H2O2 accelerator. Potentiodynamic polarization studies in 3.5% NaCl solution revealed a large shift of ∼ 300 mV of the corrosion potential below the pitting potential for the 7075-T6 alloy, which correlated with the development of a finely-textured, uniform coating. However, the formation of a uniform coating and protection was dependent upon the time of de-smutting, with non-uniform coatings resulting from extended times of de-smutting. In contrast, non-uniform coatings developed on the 2024-T3 alloy, with pitting potential at the corrosion potential, irrespective of the time of de-smutting. Findings for the 2024-T3 alloy indicate that extended de-smutting affects the enrichment of alloying elements. © 2008 Elsevier B.V. All rights reserved.

The enrichment of copper alloying additions near the surface of sputtering-deposited Al-1.3 at.%Cu, Al-2.7 at.%Cu and Al-30 at.%Cu alloys is investigated following immersion in nitric acid, which is used commercially as a de-smutting pre-treatment. Corrosion of the alloys is revealed at rates in the range 4-13 nm min-1, leading to enrichment of copper in the alloy surface regions. Enrichments are also generated by nitric acid treatment of AA2024-T3 and AA7075-T6 alloys, with levels similar to those achieved by etching in sodium hydroxide solution. Conventional durations of de-smutting treatments in nitric acid have minor influences on the magnitude of enrichment. © 2008 Elsevier Ltd. All rights reserved.

The anodic behaviour of sputtering-deposited Al–20at.%Mg–20at.%Cu alloy is investigated during anodizing and potentiodynamic polarization treatments using transmission electron microscopy, X-ray photoelectron spectroscopy and medium energy ion scattering. The composition of the alloy is close to that of the S-phase in 2024 aluminium alloy. The anodizing behaviour in both 0.1 M ammonium pentaborate and 0.1 M sodium hydroxide electrolytes follows the behaviour of more dilute, solid-solution, aluminium alloys, with enrichment of copper developing in the alloy during the growth of an alumina-based initial oxide containing incorporated magnesium species. Oxygen gas is generated following sufficient enrichment of copper for its oxidation to proceed and hence, for copper species to enter the oxide film. The generation of oxygen gas causes extensive damage to the film, which limits the voltage to relatively low values. Potentiodynamic polarization in 0.1 M sodium hydroxide electrolyte revealed mainly passive behaviour following an initial period of corrosion during which the passive film is developed. In this initial period, copper enriches in the alloy, beneath an oxide film containing aluminium and magnesium species. The magnesium species migrate faster through the film than the aluminium species and form a surface layer of MgO/Mg(OH)2, which protects against losses of aluminium species to solution and permits the establishment of the passive film. The steady open-circuit potential of the passivated alloy in the hydroxide solution is about −550 mV (SCE), compared with about −1940 mV (SCE) for aluminium.

Conversion coatings have been formed in two stages on sputtering-deposited aluminium using a chromate/fluoride bath. The first stage, common to all specimens, was conversion treatment for 1 min to produce a coating of thickness of about 70 nm, with associated thinning of the aluminium substrate. Further treatment was then carried out for 13 min, either immediately or with intervening ageing in humid air, water or laboratory air. Notably, ageing in laboratory air for 1 h was sufficient to prevent significant growth of new coating material upon re-immersion in the coating bath. In contrast, ageing in humid air or water allowed additional thickening of the coating, although with a reduced growth rate. The behaviour appears to be related to loss of free or weakly bound water from the coatings in laboratory air, with the composition and structure of the coating being modified such that transport of reactant and product species of the coating process is impeded.