Composition Of Anodic Oxide Films Research Articles

Thermodynamic Functions of the Anodic Oxidation Reactions of Niobium and Tantalum

In this paper, we develop the thermodynamic models of electrochemical oxidation of niobium and tantalum that allow predicting the composition of their anodic oxides depending on the electrolyte composition. The reactivity of metals with respect to electrolyte anions was evaluated. It was revealed that doping additives can be included in the composition of anodic oxide films of Nb and Ta depending on the nature of the anions supplied by the electrolyte components. The thermodynamic modeling results will allow predicting the component compositions of anodizing solutions to obtain anodic oxide films of these elements with a specified composition.

Toward a quantitative description of the anodic oxide films on aluminum

A method to quantify the composition of anodic oxide films on aluminum using Infrared Spectroscopic Ellipsometry (IRSE) is proposed. It consists of obtaining the absorption coefficient of the film as a function of wavelength. Using values of the absorption coefficients for the pure components of the film, the percentages (mole or wt%) of each component in the sample can be calculated.The method is demonstrated in a study of the structure of the oxide film on electropolished aluminum and the anodically formed barrier layer film. Both surface oxides were found to be initially a form of amorphous Al 2O 3. While the barrier film is essentially free of water as prepared, the film on electropolished aluminum contained about 25 wt% water. Hydration of both types of films by immersion in boiling water results in the formation of pseudoboehmite (AlOOH). The technique may have more general applicability to the quantitative determination of the composition of corrosion films and other surface layers on metals.

Luminescence of Europium–Doped Anodic Oxide Films on Multilayer Titanium–Tantalum Composites

Luminescence of europium in anodic oxide films on thin–film Ti–Ta composites and the process of anodic oxidation of these by the method of chronovoltammetry are investigated for different orders of arrangement of metallic layers and temperatures of heat treatment. A correlation between the luminescence spectra and chronovoltammetric diagrams is noted. The luminescence is shown to be an efficient method for studying the complex phase composition of anodic oxide films. The luminescence spectra of samples are characterized by the presence of several types of luminescence centers inherent in the Eu3+ ion and the base. Conditions for the formation of Eu–doped anodic oxide films on a diffusion alloy, which are of interest for microelectronics as a new dielectric material, are determined.

Phase composition of anodic oxide films on transition metals: a thermodynamic approach

The phase composition of anodic oxide films on transition metals is analysed using thermodynamic calculations. The model of an oxide film represents a two-layer system M k O l /M m O n , where the outer layer M k O l is the highest oxide, and the inner layer M m O n is the lower oxide of the metal. The changes of the Gibbs energy Δ G r are considered for the reactions of oxidation and reduction at the M k O l /M m O n interface and it is shown that for Ti, Nb, Mo, and W the former reaction predominates, resulting in the formation of the highest oxides: TiO 2, Nb 2O 5, MoO 3, and WO 3. In the case of vanadium, the reaction of reduction proceeds preferentially, indicating the possibility of the lower oxide formation, namely VO 2. It is concluded that anodic films on Nb, Ti, Mo and W mainly consist of the corresponding highest oxides of these metals, and NbO 2, Ti 2O 3, MoO 2 or WO 2 layers are relatively thin, while in the films on vanadium the vanadium dioxide layer may be rather thick and only a very thin film near the outer boundary is close to the V 2O 5 stoichiometry. These results are in agreement with the experimental data on anodic oxidation of transition metals.

ChemInform Abstract: Effect of Film Formation Conditions on Structure and Composition of Anodic Oxide Films on Titanium.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

The effect of film formation conditions on the structure and composition of anodic oxide films on titanium

Anodic oxide films on titanium which were potentiostatically formed in 0.5 M H 2SO 4 solution at various temperatures from 303 to 353 K and different potentials have been examined by transmission electron microscopy, ex situ Raman spectroscopy, together with X-ray photo-electron spectroscopy. The structure and composition of the anodic oxide films were found to be strongly dependent on film formation temperature and potential. At temperatures higher than 333 K or at potentials more noble than 6 V, film crystallization occurs. After film crystallization, the film growth rate increases greatly. During anodic film growth, the electric field within the film was found to be of the order of 10 6 V cm −2. This electric field exerts significant electrostriction on the film and yields high internal compressive stresses in the film. The internal compressive stresses increase with temperature, particularly, at 323 K. The film crystallization at high temperatures or at high potentials is considered to be attributed to the high compressive stresses. The amount of bound water was found to increase markedly above 343 K, and the presence of bound water in the film plays an important role in stabilizing the passive film.

Multi-technique surface charaterization of oxide films on electropolished and anodically oxidized titanium

The widespread use of pure Ti in biomedical applications and in basic biomaterials research has led to an increasing interest in the properties of its surface oxides, and how they can be modified. In this work, which was part of a broad surface characterization of oxide films on pure Ti and Ti-6A1-4V, the chemical composition of anodic oxide films formed on pure Ti during electropolishing and anodic oxidation was investigated using multi-technique surface analysis (XPS, AES/SAM, SIMS, RBS and NRA). XPS and AES Ti line shapes show that the oxide formed is mainly TiO 2, but the chemical composition can be modified by anion adsorption and/or incorporation when H 2SO 4 or H 3PO 4 electrolytes are used. Modification of the anodic oxide film composition also occurs during sterilization; increased Ca and H levels are observed by SIMS and NRA after autoclaving. AES and XPS depth profiles, together with RBS measurements, show that the oxide thickness depends linearly on the anodizing potential in the range 5–80 V, with a growth constant α m≈ 1.1 × 10 16 oxygen atoms/V⋯ cm 2. The present results are compared with parallel studies of the composition and microstructure of thermal and anodic oxides on pure Ti and Ti-6A1-4V. The demonstrated systematic variation of oxide properties opens up the possibility to study the influence of specific surface properties on the biological response to Ti materials.

Effect of pH on the Distribution of Anions in Anodic Oxide Films Formed on Aluminum in Phosphate Solutions

The composition of anodic oxide films anodically formed on aluminum in phosphate solutions with different pH's was examined by chemical sectioning in a sulfuric acid solution combined with impedance measurements, solution analysis, and electron microscopy. The oxide films were found to consist of two layers: an outer layer containing phosphate and an inner layer consisting of pure . With increasing pH of the anodizing solution, the thickness of the outer layer increases and the phosphate concentration in the outer layer decreases. In the chemical sectioning, the dissolution rate of the outer layer increases with anodizing solution pH, while the dissolution rate of the inner layer is slower and unaffected by the anodizing solution pH. For the outer layer, there is a linear relationship between the phosphate concentration and the sectioning rate in the sulfuric acid solution. The mechanism of film formation during anodizing is discussed in terms of Al3+ transport through the oxide.

Anodic Oxide Thin Films on Iron in Neutral Borate-Boric-Acid Solution with and without Chloride Ion

The composition of anodic oxide films formed on iron in neutral borate-boric-acid solutions with and without chloride ions was examined by sensitive ESCA, IMMA, electron diffraction and FT-IR spectroscopy. In general, the oxide thin film consisted of a two layer structure of “Fe3O4 or γ-Fe2O3” next to the metal and “γ-FeOOH or ferric boron hydroxo complexes such as Fe(OH)(BO2)2 or FeOHB4O7” at the oxide solution interface, with iron in its trivalent state. The outermost part of the film contained minor impurities or contaminations such as boron, calcium and silicon, all of which were in the oxide state. The thickness of the passive film was about 20–50 Å. The addition of the chloride ion to borate solutions increases the amount of γ-FeOOH present. Corrosion pits are preferentially nucleated at inclusions such as Si and Mn.

The composition of anodic oxide films on Hg 0.8Cd 0.2Te

X-ray photoelectron spectroscopy (XPS) measurements have been made on a range of cadmium and tellurium compounds, including single-crystal wafers of CdTeO 3 and CdTe 2O 5, in order to identify the nature of anodically formed oxide films on Hg 0.8Cd 0.2Te. We find that the oxygen Auger parameter is significantly different for CdTeO 3 and CdTe 2O 5. Measurements of this parameter suggest that the most likely major constituents of the film are TeO 2 and CdTeO 3. Significant differential sputtering and chemical reduction effects resulting from Ar + ion bombardment were observed for TeO 2, CdTeO 3 and CdTe 2O 5. These effects cast doubt on the validity of quantitative XPS depth profiles of the anodic oxide.

In-depth profiles of anodic oxide films on FeNi alloy in boric acid-sodium borate solutions

The in-depth profiling of anodic oxide films formed for 1 h on a 55Fe-45Ni alloy in boric acid-sodium borate solutions was made by the simultaneous use of AES (Auger Electron Spectroscopy) and sputter-etching with Ar + ion to determine the thickness and composition of anodic oxide films and to elucidate the experimental variables which affect them. The anodic oxide film was thicker and richer in the Fe component in pH 6.48 solution than in pH 8.45 solution. It was estimated from the in-depth profile of the anodic oxide film that a significant part of the Fe component in the anodic oxide film was in the di-valent state. Enrichment of the Ni component at the oxide/substrate interface and depletion of Ni component in the film were measured as a function of pH and anodic potential. These results are explained in terms of the combination of the following factors: (i) preferential dissolution of the Fe component, (ii) preferential oxidation of the Fe component, and (iii) preferential anodic deposition of the Fe or Ni component.

A radiotracer study of the composition and properties of anodic oxide films on tantalum and niobium

The composition of anodic oxide films formed on tantalum in phosphoric and sulphuric acids and on niobium in phosphoric acid has been determined by the use of 32P- and 35S-labelled electrolytes. The films consist in all cases of a layer of stoichiometric pentoxide next to the metal and an outer layer characteristic of the anodizing electrolyte. This layered structure can only arise through the movement of both cations and anions during the growth of the film. The amount of a particular species that is incorporated into the film from the electrolyte increases with increasing solution concentration and current density and decreases with increasing temperature; variations in the amount of included material with temperature are entirely accounted for by changes in the relative contributions of cation and anion movement during film growth.It is shown that differences between films formed in phosphoric and sulphuric acids are due to the much larger degree of incorporation that occurs with the former. The incorporation of phosphorus into the oxide results in a decrease of dielectric constant and an increase of dielectric strength.