Nanoscale Oxide Film Research Articles

A novel diffusion bonding of 6063Al based on a mode of diffusion-migrating and suspension-broken of surface oxide film

The breaking of surface oxide film in a technology area of ultrasonic-assisted diffusion joining manufacturing of large-size structure components is a challenge. In this work, a novel method of breaking surface oxide film of Al alloys based on first diffusion-migrating and then suspension-broken was investigated. Diffusion bonding of 6063Al alloys was performed by Zn interlayer at temperature below 400 °C. The oxide film migrated away from the Al alloy base metal by solid phase diffusion at 360 °C, and remained in the joint as a nanoscale oxide film. When temperature increased to 390 °C, the oxide film suspended in the Zn–Al eutectic liquid phase were rapidly broken up into small fragments through an instantaneous ultrasonic action (only 0.3 s). The change of acoustic pressure in the liquid metal proved that the suspended continuous oxide film was broken by the micro-jet acted simultaneously on both sides of oxide film induced by the ultrasonic cavitation effect. Finally, the inter-diffusion between Zn and Al at 360 °C was promoted by a longer holding time to obtain the homogeneous joint composed by Zn–Al eutectoid phase containing oxide fragments, and had a higher strength than the base metal. The breaking of oxide film and joint homogenization were performed under pressure-less condition, which effectively avoided the squeezed-out of the liquid phase. This technology shows a great potential for manufacturing large-size joint of industrial products.

Influence of high-temperature oxidation of SiC powders on curing properties of SiC slurry for digital light processing

Fabrication of silicon carbide (SiC) ceramics by digital light processing (DLP) technology is difficult owing to high refractive index and high ultraviolet (UV) absorptivity of SiC powders. The surface of the SiC powders can be coated with silicon oxide (SiO₂) with low refractive index and low UV absorptivity via high-temperature oxidation, reducing the loss of UV energy in the DLP process and realizing the DLP preparation of the SiC ceramics. However, it is necessary to explore a high-temperature modification process to obtain a better modification effect of the SiC powders. Therefore, the high-temperature modification behavior of the SiC powders is thoroughly investigated in this paper. The results show that nano-scale oxide film is formed on the surface of the SiC powders by short-time high-temperature oxidation, effectively reducing the UV absorptivity and the surface refractive index (<i>n</i>ʹ) of the SiC powders. When the oxidation temperature is 1300 ℃, compared with that of unoxidized SiC powders, the UV absorptivity of oxidized SiC powders decreases from 0.5065 to 0.4654, and a curing depth of SiC slurry increases from 22±4 to 59±4 μm. Finally, SiC green bodies are successfully prepared by the DLP with the the oxidized powders, and flexural strength of SiC sintered parts reaches 47.9±2.3 MPa after 3 h of atmospheric sintering at 2000 ℃ without any sintering aid.

Ultrasonic Induced Refinement of Induction Heated Oxide Coating on Titanium

Induction heating treatment (IHT) has recently been used to improve the bioactivity and biocompatibility of titanium and its alloys, greatly related to the formation of the nanoscale oxide coating. In this work, the effect of ultrasonic on the IHT oxidation behavior of pure titanium has been investigated. Ultrasonic-assisted IHT of pure titanium was carried out for 13, 20 and 25 s. Submicro-/nano-scale morphological coatings with rutile and anatase TiO2 were prepared on the surface of titanium substrates subjected to ultrasonic-assisted IHT. In particular, the TiO2 crystals were significantly refined by ultrasonic impact. An improvement in hydrophilicity and hardness of the oxide film was achieved by ultrasonic-assisted IHT. The refinement of TiO2 crystals is suggested to be caused by ultrasonic induced changes of energy, defect density and their correlation with diffusion of oxygen. The present study provides a potential method to refine the nanoscale oxide films on titanium substrates, which is promising for improving the wear resistance and bioactivity of titanium and its alloys.

Hydrogen interaction characteristic of nanoscale oxide films grown on iron–nickel based stainless steel by selective thermal oxidation

Hydrogen isotopes, the reaction ingredients in the nuclear fusion plant, can easily permeate through the stainless steel (SS) substrate, leading to the so-called hydrogen degradation. Generally, a widely accepted way to reduce the hydrogen permeation is to prepare a barrier coating on the substrate. Nevertheless, the coated layer has the inherent problem of incompatibility with the heterogeneous base materials. In this work, in-situ selective oxidation was used to explore the optimal oxides with the improved hydrogen resistance. Two types of layers thermally formed at 450 °C and 750 °C, respectively, were selected to investigate their hydrogen interaction characteristics. Comprehensive analyses, including Raman spectra, XPS, EIS and AES, indicate that the oxide formed at 450 °C is a better candidate of hydrogen permeation barriers, probably due to the formation of protective layers of chromia and FeCr2O4, while the oxides obtained at 750 °C, though exhibiting a much more stable phase, can rarely reduce hydrogen diffusion through the shortcuts of defects. This finding provides a potential new way to prepare a hydrogen permeation barrier.

Consolidation Features of Aluminum-Alumina Compositions by Powder Metallurgy Methods

In this paper was followed the processing flow of aluminum-alumina compositions (10÷20% alumina) in powder state, aiming to obtain aluminum matrix composites reinforced with alumina particles, starting from selecting and mixing the grading fraction of both components reaching up to sintering; it was analyzed the way in which reflects the variation of grading fraction ratio (expressed through average particle diameter in the analyzed fractions limits) on the level of technological interest features: apparent density, tapped density, flowability, presability and on densification after sintering (in various environments). By transmission electron microscopy was observed that aluminum particles showed on the surface a nanoscale oxide film, so the sintering occurs between congeneric areas – by solid phase sintering mechanisms [1, 2, 3]. The analysis of thermophysical properties revealed a decrease of thermal diffusivity at an increase of alumina, simultaneous with the decrease of the densification level.

Measurement of the Oxide Film on Cold Rolled Steel by XPS and TEM

X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (TEM) with high annular dark-field (HAADF) microscopy have been used to characterize the nanoscale oxide film formed naturally on the surface of cold-rolled sheet of mild steel. Main aim of this research was to confirm that XPS could be used in determining the thickness of thin oxide film as a substitute for the laborious TEM analysis. The preparation and analysis technique for the XPS depth profiling has been investigated to characterize the oxide film. The selection of appropriate sputter rate and sputter area according to sheet material components and the exact estimation of sputter depth from sputter rate during depth profiling were essential for the determination of the nanoscale oxide thickness.

Quantification of Epitaxial Strain and Crystal Structure in Nanoscale Oxide Films Using Position Averaged Convergent Beam Electron Diffraction

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Oxide Films at the Nanoscale: New Structures, New Functions, and New Materials

We all make use of oxide ultrathin films, even if we are unaware of doing so. They are essential components of many common devices, such as mobile phones and laptops. The films in these ubiquitous electronics are composed of silicon dioxide, an unsurpassed material in the design of transistors. But oxide films at the nanoscale (typically just 10 nm or less in thickness) are integral to many other applications. In some cases, they form under normal reactive conditions and confer new properties to a material: one example is the corrosion protection of stainless steel, which is the result of a passive film. A new generation of devices for energy production and communications technology, such as ferroelectric ultrathin film capacitors, tunneling magnetoresistance sensors, solar energy materials, solid oxide fuel cells, and many others, are being specifically designed to exploit the unusual properties afforded by reduced oxide thickness. Oxide ultrathin films also have tremendous potential in chemistry, representing a rich new source of catalytic materials. About 20 years ago, researchers began to prepare model systems of truly heterogeneous catalysts based on thin oxide layers grown on single crystals of metal. Only recently, however, was it realized that these systems may behave quite differently from their corresponding bulk oxides. One of the phenomena uncovered is the occurrence of a spontaneous charge transfer from the metal support to an adsorbed species through the thin insulating layer (or vice versa). The importance of this property is clear: conceptually, the activation and bond breaking of adsorbed molecules begin with precisely the same process, electron transfer into an antibonding orbital. But electron transfer can also be harnessed to make a supported metal particle more chemically active, increase its adhesion energy, or change its shape. Most importantly, the basic principles underlying electron transfer and other phenomena (such as structural flexibility, electronic modifications, and nanoporosity) are now largely understood, thus paving the way for the rational design of new catalytic systems based on oxide ultrathin films. Many of the mechanisms involved (electron tunneling, work function changes, defects engineering, and so forth) are typical of semiconductor physics and allow a direct link between the two fields. A related conceptual framework, the "electronic theory of catalysis", was proposed a long time ago but has been largely neglected by the catalytic community. A renewed appreciation of this catalytic framework, together with spectacular advances in modeling and electronic structure methods, now makes it possible to combine theory with advanced experimental setups and meet the challenge of designing new materials with tailored properties. In this Account, we discuss some of the recent advances with nanoscale oxide films, highlighting contributions from our laboratory. Once mastered, ultrathin oxide films on metals will provide vast and unforeseen opportunities in heterogeneous catalysis as well as in other fields of science and technology.

An Investigation of Structures of Thermal and Anodic Tantalum Oxide Films

Tantalum oxide films produced from anodic oxidation and thermal oxidation at 400 and 800°C have been investigated with respect to long- and short-range structure by X-ray diffraction and X-ray absorption spectroscopy, respectively. Films formed at 800°C show orthorhombic structure with greater disorder compared to the powder reference, where six O atoms were observed at an average radial distances of powder) and Å (800°C Ta oxide film). Lower temperature films consist primarily of metastable and appear to be relatively stable for extended times of treatment with a first shell not unlike that of based on a linear combination analysis. Furthermore, using a linear combination of and α-Ta metal, the amorphous anodic oxide films studied as a function of thickness were observed to exhibit a relatively ordered local structure consistent with the high-temperature (i.e., 800°C) phase. This work demonstrates that the nanoscale oxide films formed on tantalum exhibit an ordered local structure, reflecting the very compact nature that enhances its corrosion resistance. © 2005 The Electrochemical Society. All rights reserved.