Growth Of Anodic Oxide Films Research Articles

Growth of anodic oxide films on iron-triad metal monosilicides in sulfuric acid electrolyte

The mechanism and kinetics of electrochemical formation of anodic oxide films on iron-triad metal monosilicides in the 0.5 M H2SO4 solution in the potential range of 0.5 to 1.5 V (NHE) were studied by the methods of polarization and impedance measurements. It was concluded that the oxide films on the surface of studied silicides consisted predominantly of SiO2 and exhibited high barrier properties. The oxide film thickness and specific resistance in relation to the electrode potential were calculated from the impedance data. The constants of oxide film growth were determined.

Anodic oxide film growth on thin magnetron sputter-deposited titanium layer

A ~100nm thick sputter-deposited titanium layer on electropolished aluminium is used for the investigation of anodic film growth in 1M H3PO4. It is found that the thin titanium layer could not provide sufficient current efficiency for titanium anodic film growth when anodized to the voltage over 80V due to the occurrence of oxygen evolution. The ruptures of titanium anodic film and the sputtering layer are induced by the development of oxygen bubbles. The penetrated phosphoric acid electrolyte in the ruptured regions of sputtering titanium layer contacts with the aluminium substrate, which is leading to the anodic oxide growth of aluminium. The thickness of the titanium anodic film increases from 10 to 100V, however, it is reduced from 100 to 150V due to the thinning of titanium layer. Over 80V, the sputtering layer at some regions where it is completely ruptured, the anodic film growth of titanium could not be created. A thicker aluminium anodic film is formed on such regions due to the direct connection with the electrolyte.

Measurement of Stress Changes during Growth and Dissolution of Anodic Oxide Films on Aluminum

While stress is thought to play an important role in the development of self-organized porous films, mechanisms of stress generation during anodizing are not yet understood. In order to reveal depth distributions of stress in anodic films, phase-shifting curvature interferometry was used to monitor force transients (in-plane stress integrated through the sample thickness) during formation of anodic oxides on aluminum in phosphoric acid, as well as subsequent open-circuit dissolution. The measurements were not influenced significantly by electrostatic stress, internal stress in the metal samples, thermal stress, or stress induced by open-circuit dissolution. At typical current densities, the force became more compressive during anodizing, while a net tensile force change was measured after anodizing followed by complete oxide dissolution. Thus, it was revealed that anodizing generates both compressive stress in the oxide and tensile stress near the metal-oxide interface. Analysis of the open-circuit stress change revealed separate contributions from diffusional stress relaxations, and removal of residual oxide stress by dissolution. Residual stress distributions in the oxide, at nanometer depth resolution, were determined from measurements of dissolution rate and stress at open circuit, and validated through variations of the open-circuit dissolution rate.

Diagnosis of the Mechanism of Anodic Oxide Film Growth on Platinum in H2SO4

Diagnostic criteria for the growth of the anodic oxide film on platinum in H2SO4 are reported. The criteria apply to the generalized High Field Model (HFM), which postulates that the electric field within the film is dependent on the applied voltage and film thickness, and the Point Defect Model (PDM), which describes the electric field as being constant (independent of voltage and film thickness) during film growth. The constancy of the electric field in the passive film on platinum, as demonstrated in this work, is attributed to band-to-band Esaki tunneling, which buffers the electric field against changes in the applied voltage and film thickness. The Place Exchange Model (PEM), which is often invoked to describe the growth of the anodic film on Pt is rejected, because it does not predict a steady state in barrier layer thickness, which is observed experimentally. In this paper, we apply an analytical analysis of the oxide film growth transient on platinum in H2SO4 and demonstrate, unequivocally, that the PDM provides a superior theoretical framework than does the HFM or the PEM for interpreting oxide film growth on platinum. Importantly, we argue that the diagnostic criteria also apply to metal interstitial conductors, which is the mechanism of conduction proposed in the HFM for formation of the PtO oxide film on platinum, but with a thickness-dependent electric field, rather than being restricted to oxygen vacancy conductors alone, as originally derived for the PDM. Thus, the ability of the diagnostic criteria to differentiate between the HFM and the PDM, in this case, is a direct assessment of the dependence of the electric field strength on the applied voltage and barrier layer thickness, with the experimental results coming down on the side of the PDM.

Growth and crystallization behaviors of anodic oxide films on sputter-deposited titanium at very low potentials

Growth and crystallization of titanium anodized films were studied by performing the anodization of the sputter-deposited titanium samples under cyclic voltammetry (CV) mode at very low potentials. The surface features, crystalline behaviors and chemical compositions of the formed anodic oxide layers were detected by AFM, SE and XPS. It was found that the structure of the titanium anodized films is crystalline, even though the maximum oxidation potential (ϕmax) is very low (as low as 1000 mV). Both enlarging the applied voltage and reducing the potential scanning rate are beneficial for the growth and crystallization of titanium oxide films. It was thought that the internal compressive stress, other than the local joule heating accepted for many researchers, is the main force of stimulating the crystallization of anodic titanium oxide films at very low potentials.

Time dependence of growth and crystallization of anodic titanium oxide films in potentiostatic mode

The influence of anodizing time on formation and crystallization of potentiostatically formed titanium oxide films is studied both at “low” (10V) and “high” (30V) applied potentials. It is revealed that prolonging the anodizing time is beneficial for the growth and crystallization of titania anodic films, especially at low applied voltages. The titanium anodization process follows two distinct stages. In the film formation stage, the film thickness and crystallinity increase fast. While in the film aging stage, the thickness and crystallinity of titanium oxide films only slightly change with anodizing time due to the enhancement of film dissolution rate.

Electrochemical Investigation into the Dissolution Mechanism of Anodic Oxide Films on Silicon

ABSTRACTElectropolishing of p-type silicon has been investigated over a wide range of HF concentrations (0.01-11 wt. %) by potentiodynamic polarization. Oxide dissolution rates were determined from the plateau current densities observed in the electropolishing region during the reverse sweeps; i.e. where the growth and dissolution rates of the anodic oxide film are believed to be equal. Based on the shape of the CV curves the oxide dissolution process was treated as a corrosion process controlled by the dissolution of a salt film, that is its rate controlled by removal of dissolved products away from the surface rather than reactants to the surface as previously proposed. Although a contribution from HF from bulk to surface cannot be completely ruled out, because the removal of the initial dissolution product can be by either mass transport or further chemical reaction with HF species in solution this mechanism is capable of explaining the dependence of the dissolution rate on HF concentration for the whole range investigated.

A.c. Impedance Measurement of CP-Ti in 0.1 M NaOH Solution

A.c. impedances of mechanically polished CP-Ti specimens were measured at open-circuit potential (OCP) with immersion time and under applied anodic potentials between −0.2 and 1 VAg/AgCl in 0.1 M NaOH solution. Capacitances of native oxide films (Cox,na) grown naturally and capacitances of anodic oxide films (Cox,an) formed under applied anodic potentials were obtained to examine the growth of native and anodic oxide films in 0.1 M NaOH solution and how to use Cox,na for the surface area measurement of Ti specimen. 1/Cox,na and 1/Cox,an appeared to be linearly proportional to OCP and applied potential (Eapp), with proportional constants of 0.086 and 0.051 uF �1 V �1 , respectively. The Cox,na also appeared to be linearly proportional to geometric surface area of the mechanically polished CP-Ti fixture specimen, with proportional constants of 11.3 and 8.5 µF cm �2 at −0.45 VAg/AgCl and −0.25 VAg/AgCl of OCPs, respectively, in 0.1 M NaOH solution. This linear relationship between Cox,na and surface area is suggested to be applicable for the measurement of real surface area of Ti specimen.

Effect of Accumulation of Ti4+ in 0.1 M H2SO4 Electrolyte on Growth and Crystallization of Anodic Titanium Oxide Films

Effect of Accumulation of Ti4+ in 0.1 M H2SO4 Electrolyte on Growth and Crystallization of Anodic Titanium Oxide Films

Porous alumina thin films on conductive substrates for templated 1-dimensional nanostructuring

The growth of thin porous anodic aluminum oxide (AAO) films on silicon by anodizing Al on Ti/Au/Si and Ti/Pt/Si substrates in oxalic acid was demonstrated. Removal of the Al2O3 barrier layer was effected by selective chemical etching in H3PO4 and a reversed bias method in the anodizing solution. Ion transport and the influence of the Ti adhesion layer at the oxide–metal interface during the critical stages of anodization and pore opening were investigated. The AAO films may be exploited as templates in the creation of silicon-integrated nanostructured wire arrays. Electrodeposition of Pt into the AAO template yielded a nanowire array with superior methanol oxidation activity that can be integrated in a micro direct methanol fuel cell.

Correlation of electrolyte-derived inclusions to crystallization in the early stage of anodic oxide film growth on titanium

Pure titanium has been subjected to anodization in sulfuric and phosphoric acid. For a better understanding of the oxide growth and properties of the final film, with a particular interest focused on the solution anions in the early stage of crystallization, microstructural analyses (Raman, Transmission Electron Microscopy [TEM]) of the oxide films were correlated to chemical depth profiling by glow discharge optical emission spectroscopy (GDOES). Raman spectroscopy shows that crystallization of the oxide films starts at potentials as low as 10–20 V. The onset of crystallization and the ongoing increase in crystallinity with increasing anodization potentials had already earlier been correlated to ac-impedance measurements [Jaeggi et al., Surf. Interface Anal. 38 (2006) 182]. TEM observations show a clear difference in the early phase of crystallization between oxides grown in 1 M sulfuric acid compared to 1 M phosphoric acid. Moreover, independent of electrolyte type, nano-sized pores from oxygen bubbles formation were revealed in the central part of the films. Until now, oxygen bubbles inside an anodically grown oxide have not been observed before without the presence of crystalline regions nearby. A growth model is proposed, in which the different starting locations of crystallization inside the films are correlated to the presence of the acid anions as residues in the film, as found by GDOES chemical depth-profiling.

Stress-affected and stress-affecting instabilities during the growth of anodic oxide films

The objective of the current paper is to (re-)address the question whether internal stress is a fundamental parameter driving some generic cases of growth instabilities commonly encountered during the growth of anodic oxide films, namely breakdown and pore initiation. This has been done by unraveling possible correlations between a key electrochemical characteristic of the instability event and the internal stress evolution, the latter being measured in situ during the very same anodising experiment. As such, we have been able to make more conclusive statements as compared to the merely speculative arguments in the literature whether these instabilities have a mechanical origin or not. In the case of breakdown, the two well-documented types of breakdown events encountered during galvanostatic Zr anodising were both found to be stress-affected: instantaneous compressive internal stresses were identified as the driving force for both the densifying phase transformation responsible for type-I breakdown, as well as for the buckling-induced delamination events observed during type-II breakdown. Pore initiation in anodic Al 2O 3 on the other hand was found not be stress-affected. Instead, pore formation is rather believed to induce itself a modification in the mechanical behaviour, and was therefore classified as stress-affecting.

Morphology and growth of porous anodic oxide films on Ti-10V-2Fe-3Al in neutral tartrate solution

Porous anodic oxide films were fabricated galvanostatically on titanium alloy Ti-10V-2Fe-3Al in ammonium tartrate solution with different anodizing time. Scanning electron microscopy (SEM) and field emission scanning electron microscopy (FE-SEM) were used to investigate the morphology evolution of the anodic oxide film. It is shown that above the breakdown voltage, oxygen is generated with the occurrence of drums morphology. These drums grow and extrude, which yields the compression stress. Subsequently, microcracks are generated. With continuous anodizing, porous oxides form at the microcracks. Those oxides grow and connect to each other, finally replace the microcrack morphology. The depth profile of the anodic oxide film formed at 1 800 s was examined by Auger electron spectroscopy (AES). It is found that the film is divided into three layers according to the molar fractions of elements. The outer layer is incorporated by carbon, which may come from electrolyte solution. The thickness of the outer layer is approximately 0.2–0.3 μm. The molar fractions of elements in the intermediate layer are extraordinarily stable, while those in the inner layer vary significantly with sputtering depth. The thicknesses of the intermediate layer and the inner layer are 2 μm and 1.0–1.5 μm, respectively. Moreover, the growth mechanism of porous anodic oxide films in neutral tartrate solution was proposed.

Growth of anodic oxide films on AC2A alloy in sulphuric acid solution

Growth behaviour of anodic oxide films on AC2A Al cast alloy was investigated in sulphuric acid solution using SEM, optical microscope (OM) and confocal scanning laser microscope (CSLM) and energy dispersive spectroscopy (EDS). The AC2A alloy contains three different types of second-phase particles: Al–Cu, Al–Cu–Fe–Si and Al–Si particles. The growth of anodic oxide films was critically retarded by the presence of non-reactive particles of Al–Si, while little effect was observed by the presence of active particles of Al–Cu and Al–Cu–Fe–Si. The most severe retardation effect on the growth of anodic films on AC2A alloy resulted from agglomerated Al–Si particles.

Origin of Interface Instability during the Initial Growth of Porous Anodic Oxide Films

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Characterization of growth of anodic antimony oxide films by ellipsometry and XPS

The processes occurring consecutively during anodic oxidation of antimony in buffered phosphate solutions are followed by in situ ellipsometry. In the first stages of anodization, soluble species formation followed by formation of a highly hydrated film takes place. At higher potentials, the growth of a single layer of Sb 2O 3 anodic film occurs. Oxygen evolution occurring simultaneously with oxide growth is also detected. Surface chemical analysis by XPS allowed obtaining the chemical state and composition of the anodic antimony oxide films. The procedure followed in order to carry out the spectra deconvolution due to overlapping of O1s and Sb3d photoemission lines is discussed. The binding energy values obtained for O1s and Sb3d signals as well as the O/Sb atomic ratio indicates that the anodic film formed at low or high potentials is composed by Sb(III) species only. Hydration as well as phosphate ions incorporation into the film is also demonstrated.

Surface finish effect on the anodizing behaviour of Al-Si components obtained by sub-liquidus casting process

The aim of this study was to investigate the hard decorative anodizing components of A357 aluminium alloy, obtained in semisolid state by Sub Liquidus Casting® process, to improve its tribological properties and corrosion resistance. Components were heat treated in order to modify the shape and distribution of the eutectic silicon phase. The influence of shot peening pre-treatment on anodizing process was evaluated. Surface modifications were investigated as they might have beneficial effects on the wear and corrosion behaviour. Furthermore, the influence of surface condition on the anodization colouring behaviour of aluminium was studied. The microstructure and the surface finish influence on the anodic oxide film growth were studied by optical and scanning electron microscopy. Experiments using a tribometer (ball on disc configuration) were performed in order to evaluate the tribological properties of the material. Salt spray corrosion tests were used to study the corrosion properties before and after the anodizing process.

Origin of Interface Instability during the Initial Growth of Porous Anodic Oxide Films

not Available.

주조용 Al-Si-Cu 알루미늄 합금의 기계가공 및 주조된 표면에서의 양극산화피막 형성

The anodic oxidation behaviour of a cast component of AC2A Al alloy with machined surface and ascast surface was investigated in sulfuric acid solution. The anodized specimen showed relatively uniform and thick anodic oxide films on the as-cast surface, while non-uniform and very thin oxide films were formed on the machined surface. Non-anodized as-cast surface was observed to be covered with thick oxide scales and showed a number of second-phase particles containing Si, while non-anodized machined surface showed no oxide scales and relatively very small number of Si particles. Thus, the very limited growth of anodic oxide films on the as-cast surface was attributed to the presence of thick oxide scales and Si-containing second-phase particles on its surface.

Growth of porous type anodic oxide films at micro-areas on aluminum exposed by laser irradiation

Aluminum covered with pore-sealed anodic oxide films was irradiated with a pulsed Nd–YAG laser to remove the oxide film at micro-areas. The specimen was re-anodized for long periods to examine the growth of porous anodic oxide films at the area where substrate had been exposed by measuring current variations and morphological changes in the oxide during the re-anodizing. The chemical dissolution resistance of the pore-sealed anodic oxide films in an oxalic acid solution was also examined by measuring time-variations in rest potentials during immersion. The resistance to chemical dissolution of the oxide film became higher with increasing pore-sealing time and showed higher values at lower solution temperatures. During potentiostatic re-anodizing at five 35-μm wide and 4-mm long lines for 72 h after the film was removed the measured current was found to increase linearly with time. Semicircular columnar-shaped porous type anodic oxide was found to form during the re-anodizing at the laser-irradiated area, and was found to grow radially, thus resulting in an increase in the diameter. After long re-anodizing, the central and top parts of the oxide protruded along the longitudinal direction of the laser-irradiated area. The volume expansion during re-anodizing resulted in the formation of cracks, parallel to the lines, in the oxide film formed during the first anodizing.