The formation kinetics and electric properties of anodic barrier oxides on Al, Hf, Nb, Ta, Ti, and Zr depend on the migration of ions, controlled by an electric field strength of up to 107 V cm−1. The high field model, based on ideas of Guntherschulze, Betz, Verwey, Mott, and Cabrera, explains only parts of the experiments. Contradictory models and investigations of the last 60 years are compared with new results, which enable a more detailed understanding of many aspects of the high field model, e.g. the shape of experimental transients, the time and field dependent concentration of mobile ions, the nature of the mobile species and the interaction of anion and cation transport, and the location of the rate determining step.

Thin anodic oxide layers on aluminium and other valve metals: high field regime

Raman spectra of FeO, Fe3O4, α-Fe2O3, α-FeOOH, and γ-FeOOH, the common products of iron oxidation, have been measured. The spectra of FeO and Fe3O4 appear to be identical. Armco iron oxidized in air at 250°C was examined by Raman spectroscopy after varying periods of exposure and the surface film was found to contain Fe3O4 and α-Fe2O3.

Raman spectra of possible corrosion products of iron

Stability and degradation of conducting polymers in electrochemical systems

Nanoporous tungsten oxide (WO3), with pores of 50 to 100 nm in diameter, has been obtained by galvanostatic (constant-current) anodization of tungsten in a 0.25 M oxalic acid electrolyte. At room temperature, the optimum current density for nanoporous formation is approximately 6.5 to 8 mA/cm2. Monitoring of the anodization voltage during the fabrication process reveals a close match with the theoretical model of Parkhutik et al. [V.P. Parkhutik and V.I. Shershulsky, J. Phys. D 25, 1258 (1992)] for growth of nanoporous Al2O3. The as-anodized films are amorphous and crystallize upon annealing at 350 °C in an oxygen atmosphere.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400065420

Fabrication of nanoporous tungsten oxide by galvanostatic anodization

Effect of anions on the nucleation and growth mechanism of polyaniline

The Anodic Oxidation of Iron: Overpotential Analysis for a Two‐Phase Film

This paper reports on an optical study of hydrogen insertion in the anodic oxide of vanadium. Ellipsometry is used to study the electrochromic processes which occur when anodically grown films of vanadium oxide are electrochemically reduced and subsequently reoxidized. Films up to 200 nm in thickness are grown by anodizing vanadium in acetic acid and acetone electrolytes. When the current is made cathodic, the outer surface of the V{sub 2}O{sub 5} film is reduced to H{sub 4}V{sub 2}O{sub 5}, and as coloring proceeds a phase boundary sweeps inward across the film toward the vanadium substrate. An optical inflection is observed when the phase boundary reaches the substrate, and no additional hydrogen is electrochemically bonded into the structure past this point.

An Optical Study of Hydrogen Insertion in the Anodic Oxide of Vanadium

Ellipsometric and electrochemical techniques are used to study the anodic oxidation of titanium in aqueous and non-aqueous electrolytes. Transparent oxide films with a refractive index of 2.48 grown on electro polished surfaces exhibit ideal valve-metal behavior up to a thickness of approximately 30 nm. Beyond this thickness the refractive index and low-frequency dielectric constant of the film both decrease, but thicknesses of 100 nm can be achieved prior to complete breakdown under suitable experimental conditions. Open-circuit transients are used to determine the relation between the current density and the electric field in the oxide film.

Electrochemical and Optical Properties of Anodic Oxide Films on Titanium

Utilisation de la methode du simplex pour suivre la croissance cristalline de la polyaniline a une electrode en titane. Influence du poids statistique pour evaluer l'epaisseur de la couche deposee

Analysis of Ellipsometric Data in Electrochemical Systems Using the Simplex Algorithm

Ellipsometry is used to study the optical properties of the oxide film grown on tungsten by anodization in acetic acid electrolyte. The tungsten substrate was found to have refractive index N= 4.080 and extinction coefficient K = 3.205 at a wavelength of 632.8 nm. At an anodizing current density of 172 {mu}A/cm{sup 2} the field in the oxide is 5.38 MV/cm. With the anodizing field applied, the index of refraction of the film in the field direction is Nz = 2.062 and transverse to the field is Nx = 2.176. When the field is removed, the oxide film retains a high degree of anisotropy, with Nz = 2.115 and Nx = 2.196. The fractional decrease in thickness is 1.1% when the field is removed. The analysis of data makes extensive use of correlation between optical and electrochemical measurements. In this paper the results are compared with the predictions of the theory of electrostriction, and with the results of studies of other oxides.

J. L. Ord

Papers

The Anodic Oxidation of Iron: Overpotential Analysis for a Two‐Phase Film

An Optical Study of Hydrogen Insertion in the Anodic Oxide of Vanadium

Electrochemical and Optical Properties of Anodic Oxide Films on Titanium

Analysis of Ellipsometric Data in Electrochemical Systems Using the Simplex Algorithm

Anodic Oxidation of Tungsten in Non‐Aqueous Electrolyte I . Optical Anisotropy of the Oxide Film