Structure Of Oxide Films Research Articles

Influence of Dissolved Hydrogen on Structure of Oxide Film on Alloy 600 Formed in Primary Water of Pressurized Water Reactors

Influence of Dissolved Hydrogen on Structure of Oxide Film on Alloy 600 Formed in Primary Water of Pressurized Water Reactors

ゾル・ゲル法によりＳｉＯ２を被覆したアルミニウムのアノード酸化 新規な高耐電圧アノード酸化皮膜の作製

Aluminum specimens were covered with SiO2 film by a sol-gel coating and then anodized galvanostatically in a boric acid solution. Time variations in the anode potential during anodizing were monitored, and the structure and dielectric properties of anodic oxide films were examined by TEM-EDX, and electrochemical impedance measurements. It was found that anodizing of aluminum coated with SiO2 films leads to the formation of anodic oxide films that consist of an outer Al-Si composite oxide layer and an inner Al2O3 layer at the interface between the SiO2 film and the metal substrate. The breakdown potential of anodic oxide films formed on specimens with SiO2-coating was about 100 V higher than that without SiO2 coating. The capacitance of specimens after sol-gel coating and anodizing was slightly higher than that without sol-gel coating. In the film formation mechanism, the conversion of Al2O3 into Al-Si composite oxide at the interface between the inner and outer layers is discussed in terms of inward transport of Si-bearing anions across the outer layer.

Structure and properties of anodic aluminum oxide films produced in HNO3 solutions

Amorphous films produced by electrochemical oxidation of aluminum in an aqueous 10 M HNO3 solution were studied. The parameters of the nearest neighbor atomic configuration were evaluated from x-ray scattering intensities, and the surface morphology of the films was examined by scanning electron microscopy. The results demonstrate that the electrochemical dissolution of the Al substrate prevails over the oxide film growth, which results in a large specific surface area of the films.

Composition and Structure of Anodic Oxide Films on Titanium–Aluminum Alloys by Fast Electron Reflection Diffraction, Rutherford Backscattering, and Secondary Neutral Particle Mass Spectrometry

Anodic oxide films on some Ti–Al alloys are studied using fast-electron reflection diffraction, Rutherford backscattering, and secondary neutral-particle mass spectrometry. The films are amorphous, with a small amount of crystalline phases, and comprise a mixture of TiO2 and Al2O3. The Ti/Al ratio in an anodic film corresponds to that in the alloy matrix. Constants of anodic oxidation of the alloys are determined.

Structure and optical properties of CVD molybdenum oxide films for electrochromic application

Vibrational and optical properties of MoO3 thin films have been studied by Raman and infrared spectroscopy. The films were deposited onto Si substrates at a temperature of 150 °C by chemical vapor deposition of Mo(CO)6 at atmospheric pressure and different amounts of oxygen in the reactor. The Raman and IR spectral analyses show that the as-deposited films are in general amorphous. Post-deposition annealing at 300 and 400 °C leads to crystallization and the MoO3 film structure is a mixture of orthorhombic and monoclinic MoO3 modifications. Transformation of the monoclinic crystallographic modification to a thoroughly orthorhombic layered structure is observed for films heated at temperatures above 400 °C.

Effects of Hydrogen Peroxide on Intergranular Stress Corrosion Cracking of Stainless Steel in High Temperature Water, (V)

The difference in electrochemical corrosion potential of stainless steel exposed to high temperature pure water containing hydrogen peroxide (H2O2) and oxygen (O2)is caused by differences in chemical form of oxide films. In order to identify differences in oxide film structures on stainless steel after exposure to H2O2 and O2 environments, characteristics of the oxide films have been examined by multilateral surface analyses, e.g., X-ray diffraction (XRD), Rutherford back scattering spectroscopy (RBS), secondary ion mass spectroscopy (SIMS) and X-ray photoelectron spectroscopy (XPS). Preliminary characterization results of oxide films confirmed that the oxide film formed under the H2O2 environment consists mainly of hematite (α-Fe2O2), while that under the O2 environment consists of magnetite (Fe3O4). Furthermore oxidation at the very surface of the film is much more enhanced under the H2O2 environment than that under the O2 environment. It was speculated that metal hydroxide plays an important role in oxidation of stainless steel in the presence of H2O2. The difference in electric resistance of oxide film causes the difference in anodic polarization properties. It is recommended that several anodic polarization curves for specimens with differently oxidized films should be prepared to calculate ECP based on the Evans diagram.

The properties of aluminum oxide and nitride films prepared by d.c. sputter-deposition from metallic targets

Thin films of aluminum nitride and aluminum oxide were prepared at 540 K substrate temperature by d.c. magnetron sputtering from a metallic Al-target in pure nitrogen and oxygen atmosphere, respectively. Characterization of the films was performed by X-ray diffraction, X-ray reflection and by optical transmission spectroscopy. The stoichiometric composition of the films was ascertained by X-ray photoelectron spectroscopy. As a function of reactive gas pressure, the deposition rate showed, in general, a logarithmic decrease with increasing pressure. Oxide films were deposited at about a fourth the rate of nitride films as consequence of the lower sputtering yield. For the oxide films, specific gravity and static refractive index showed weak changes with pressure and amounted to 2.7 g/cm3, which is only approximately 68% of the bulk value, and 1.65, respectively. In contrast, low-pressure sputter-deposition of nitride films resulted in high-density films of approximately 97% the bulk value and a refractive index close to 2.1. Nitride films show a strong (002) texture (c-axis orientation) with large nanograins up to 90-nm length. Oxide films are in general amorphous. The very different structure of nitride and oxide films is related to the more complicated crystal lattice of the oxide and to higher-atomic Al–O complexes ejected from the target. It is concluded that stronger thermalization of these species compared to those ejected by nitride sputtering is responsible for insufficient enhancement of the mobility of the ad-atoms.

Oxidation resistance of AlN–(TiB2–TiSi2) ceramics in air up to 1450 °C

Abstract With the aid of DTA, TG, XRD, SEM and EPMA methods the kinetics and mechanism of oxidation of both composite powders and monolithic ceramics of AlN–(TiB2–TiSi2) system with different content of components were studied in the air up to 1450 °C under isothermal and non-isothermal conditions. It was established that the oxidation isotherms of monolithic ceramics follow the parabolic and paralinear rate law. According to the kinetic data and results of investigation of composition, morphology and structure of oxide films that are formed at different temperatures, the AlN–based ceramics containing up to 30% (TiB2–TiSi2) solid solutions are the corrosion-resistant and have the high adhesion of oxide layer in relation to substrate material. The activation energies of oxidation calculated for ceramics with 10% (TiB2–TiSi2) are: E1 =180 kJ/mol for the temperature range up to 1300 °C and E2=630 kJ/mol at 1350–1450 °C. The change of activation energy value is associated with the change of oxide layer composition: at the oxidation till 1300 °C the oxides of individual elements are, mainly, formed on the samples while above 1350 °C the formation of very dense surface film containing β-tialite Al2TiO5 takes place.

Rôle de la précipitation sur l'oxydation d'un alliage Fe-Cr-Al dans l'air à 1100° C

A study by thermo-gravimetry of the kinetics of oxidation of the alloy Fe-22Cr-4Al was carried out at 1100°C in ambient air, for durations up to 25 hours. The morphology of oxide scales formed at high temperature and the structure of oxide films were then observed and analyzed by scanning electron microscopy. The kinetic study, performed by thermo-gravimetry, showed the existence of two stages, of which only the second corresponds to a parabolic law, with the formation of a protective coating of αalumina. The presence in the alloy of foreign elements, added or not, led to the formation of precipitates whose distribution and number were studied by the analysis of metallographic images of surfaces. The influence of a preliminary cold work before oxidation was examined. The results showed that this mechanical treatment has no influence on the nature of the precipitates, but modifies their size. It comes out from this study that the nucleation and growth of these precipitates enter in competition with the formation of the layer of alumina, by accelerating the total oxidation rate during the first stage, and modify the morphology and the adherence of the formed alumina layer. The precipitates obtained at the interface have morphologies such that the internal stresses could then be modified considerably in terms of intensities and of distribution ; their relaxation would cause the warped state of the samples observed after oxidation.

Preparation,Structure and Properties of Electrochromic Rhodium Oxide Films

Preparation,Structure and Properties of Electrochromic Rhodium Oxide Films

Resonance frequency and removal torque analysis of implants with turned and anodized surface oxides.

The present experimental study was designed to address two issues. The first was to investigate whether oxide properties of titanium implants influenced bone tissue responses after an in vivo implantation time of six weeks. If such a result was found, the second aim was to investigate which oxide properties are involved in such bone tissue responses. Screw-shaped implants with a wide range of oxide properties were prepared by electrochemical oxidation methods, where the oxide thickness varied in the range of 200 nm to 1000 nm. The surface morphology was prepared in two substantially different ways, i.e. barrier and porous oxide film structures. The micropore structure revealed pore sizes of 8 microm in diameter, with a range in opening area from 1.27 microm 2 to 2.1 microm 2. Porosity ranged from 12.7% to 24.4%. The crystal structures of the titanium oxide were amorphous, anatase and a mixture of anatase and rutile type. The chemical compositions consisted mainly of TiO2. Surface roughness ranged from 0.96 microm to 1.03 microm (Sa). Each group of test samples showed its own, defined status with respect to these various parameters. The oxide properties of turned commercially pure titanium implants were used in the control group, which was characterized by an oxide thickness of 17.4 +/- 6.2 nm, amorphous type in crystallinity, TiO2 in chemical composition, and a surface roughness of 0.83 microm (Sa). Bone tissue responses were evaluated by resonance frequency measurements and removal torque tests that were undertaken six weeks after implant insertion in rabbit tibia. Implants that had an oxide thickness of approximately 600, 800 and 1000 nm demonstrated significantly stronger bone responses in the evaluation of removal torque values than did implants that had an oxide thickness of approximately 17 and 200 nm (P < 0.05). However, there were no difference between implants with oxide thicknesses of 17 and 200 nm (P = 0.99). It was concluded that oxide properties of titanium implants, which include oxide thickness, micropore configurations and crystal structures, greatly influence the bone tissue response in the evaluation of removal torque values. However, it is not fully understood whether these oxide properties influence the bone tissue response separately or synergistically.

Chemical and electronic structure of ultrathin zirconium oxide films on silicon as determined by photoelectron spectroscopy

We have measured the energy bandgaps of thermally evaporated ZrO 2 on Si(1 0 0) and a very-thin interfacial silicate (SiO x :Zr) layer formed by 500 °C annealing in dry O 2 from the onset of the energy loss spectra of O 1s photoelectrons. The valence band lineups at the interfaces among ZrO 2, SiO x :Zr and Si(1 0 0) have also been evaluated by analyzing the valence band spectra of thin heterostructures. By combination of the measured energy bandgaps and valence band lineups, we have determined the energy band alignments of as-evaporated ZrO 2/Si(1 0 0) and annealed ZrO 2/SiO x :Zr/Si(1 0 0) systems. The influence of 300–500 °C O 2-annealing on the energy distribution of electronic defect states in the films and at the interfaces has been demonstrated by total photoelectron yield measurements.

Manufacture of specific structure of aluminum-doped zinc oxide films by patterning the substrate surface

(0001)-oriented aluminum-doped zinc oxide films were prepared using a magnetron sputtering technique. High-resolution transmission-electron-microscopic images show that the oriented grains nucleate directly on the substrate surface and grow with equal lateral dimensions through the film thickness. A surface-energy-driven self-texture mechanism was proposed on the basis of process modes. A method for manufacturing specific film structure by patterning the substrate surface is tested and discussed.

Nanoporous structure of sputter-deposited silicon oxide films characterized by positronium annihilation spectroscopy

Positronium annihilation was applied to characterize the nanoporous structure of thin silicon oxide films sputter-deposited at different argon pressures ranging from 0.1 to 2.0 Pa. At higher argon pressures, the 3γ decay probability of ortho-positronium (o-Ps) was substantially enhanced. A comparison of this result with that obtained for capped samples indicated that: (a) 3γ annihilation is due to the intrinsic decay of o-Ps diffusing out from the film into vacuum and (b) films deposited at high argon pressures contain highly connected, open pores. Positron lifetime spectroscopy measurements on the capped films showed that the characteristic size of the pores can be as large as 2.6 nm, depending on the argon pressure.

Surface characteristics and structure of anodic oxide films containing Ca and P on a titanium implant material.

An anodic oxide film that formed on titanium with a mixture of beta-glycerophosphate sodium (beta-GP) and calcium acetate was investigated. The anodic oxide had interconnected pores (ca. 1-2 microm in diameter) and intermediate roughness (0.60-1.50 microm). In addition, it contained a mixture of amorphous, anatase, and rutile oxides. With an increase in the anodizing voltage and/or concentration of calcium incorporated into the oxide, the degree of oxide crystallinity increased. However, with an increase in the concentration of beta-GP, the degree of oxide crystallinity decreased. It was concluded that the surface roughness, oxide crystallinity, and surface composition of the anodic oxide were dependent on the voltage, current density, and concentration of the electrolyte. It was also concluded that the anodized surface could be optimized for maximum osseointegration.

ポアーフィリング法によるアルミニウムアノード酸化皮膜のブレークダウン電位上昇の試み

Aluminum covered with porous anodic oxide films was re-anodized in 0.5 kmolm-3-H3BO3 and 5×10-5kmolm-3-KOH solutions to examine the formation and breakdown of the oxide film.In H3BO3-solution, the pores were filled with new oxide during re-anodizing, resulting in the uniform thickening of the barrier layer until film breakdown started. The breakdown potential of the film formed by the “pore-filling” method was 200V higher at maximum than that formed by anodizing after electropolishing.In KOH solution, the pore-filling with new oxide was accompanied by local dissolution of oxide film, leading to the formation of rough interphase between oxide film and the substrate. The film breakdown potential of the film formed by the “pore-filling” was as high as that the the oxide film formed after electropolishing.Effects of the structure of porous anodic oxide films on the film breakdown potential during re-anodizing in H3BO3 solution are discussed.

Further Development of Ideas of G.V. Akimov on the Surface Oxide Films and Their Effect on the Corrosion and Mechanical Behavior of Aluminum Alloys

The importance of oxide films and their perfection in extending the application of aluminum alloys are shown. The composition and structure of oxide films formed by microarc oxidation on aluminum alloys of different alloying systems and production methods are studied. The dependence of the oxide coating properties on the parameters of microarc oxidation are found. The results obtained are discussed in terms of the existing concepts of microarc oxidation.

Morphology, Structure and Photoluminescence Properties of Zinc Oxide Films Prepared by Excimer Laser Irradiation of Sol–Gel-Derived Precursors

Morphology, structure and photoluminescence (PL) properties of zinc oxide (ZnO) films prepared by KrF-excimer-laser irradiation of sol–gel-derived precursors were studied. The precursors with a film thickness of 100 or 180 nm were irradiated by the laser at various energy fluences (Ef). Atomic force microscopy and transmission electron microscopy observations revealed that the laser irradiation at an Ef≥100 mJ/cm2 produced crystal growth of close-packed ZnO crystals in an upper layer. Laser irradiation at a high Ef (150 mJ/cm2) of the thinner precursor produced a remarkable crystallization throughout the film, resulting in larger grain size and smooth film surface. Our observation results suggest that the crystallization proceeds by sintering or solidification via melting. The films obtained at Ef≥100 mJ/cm2 showed green PL. The PL spectra were not significantly influenced by the excitation wavelength except for the thinner film irradiated at a high Ef (150 mJ/cm2); it showed a striking increase in the green PL intensity when excited at 275 nm instead of 325 nm. The unique excitation-wavelength dependence may be related to its characteristic threshold of electron excitation.

Effects of post-annealing on the structure and properties of Al-doped zinc oxide films

The effect of post-annealing on the transparent and conductive Al-doped zinc oxide films prepared by RF magnetron sputtering technique was investigated. The structural characteristics of the as-deposited and annealed films were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) while the resistance of films during annealing was measured in situ. It is shown that the as-deposited films were flat and smooth, but with plasma etching morphology on the surface, nevertheless, a decrease in roughness was found after the films were air annealed. A significant grain agglomeration into cluster was observed after hydrogen annealing at 500°C. Optical transmissions reveal a good transmittance within the visible wavelength spectrum region for all of the films. The resistance of the air-annealed films was increased due to a large number of oxygen chemisorbed on surface and grain boundaries as measured by XPS. However, it decreased for the films annealed in hydrogen at a higher temperature. The minimum resistivity obtained was 8.76×10 −4 Ω cm as annealed at 500°C for 1 h in hydrogen atmosphere.

Structure of thin aluminium-oxide films determined from valence band spectra measured using XPS

Very thin (<10 nm) aluminium-oxide films were produced by dry, thermal oxidation of a bare Al(4 3 1) substrate in the temperature range from 373 to 773 K at a partial oxygen pressure of 1.33×10 −4 Pa. The development of the structure of the grown oxide films has been determined from the analysis of the measured valence band (VB) spectra recorded from the oxidised metal using X-ray photoelectron spectroscopy. Two principal components (PCs) were recognised in the `oxide-film' upper valence band (UVB) spectra, as resolved from the measured VB spectra of the oxidised metal. On the basis of high-resolution transmission electron microscopy (HREM), one PC can be associated with amorphous aluminium oxide and the other PC with crystalline γ-Al 2O 3. From the relative contribution of the amorphous and γ-Al 2O 3 basic spectra to the resolved oxide-film UVB spectra, the development of the structure of the aluminium-oxide films as a function of temperature and time, as well as of thickness, is established. With increasing oxidation temperature a gradual transition from amorphous aluminium oxide to crystalline γ-Al 2O 3 occurs, as confirmed by the HREM analysis in the present work. Up to 1 nm the aluminium-oxide films are to a high-degree amorphous, above this thickness the aluminium-oxide films are predominantly crystalline.