Oxide Surface Films on Metal Crystals

Macroporous tungsten oxide thin films were prepared by using a polystyrene microsphere template and the peroxitungstic acid precursor. Gold nanoparticles were introduced into the tungsten oxide film by two different methods, either in the polystyrene template, through a self-assembly process, or they were cast on the surface of the annealed film. Raman imaging experiments showed an enhancement effect of the intensity of the major tungsten oxide bands by the gold nanoislands. The electrochromic properties of gold-doped macroporous tungsten oxide are described and compared to those of the standard porous sol-gel film. The films with gold nanoparticles on the surface of the tungsten oxide film were found to have better electrochromic properties than the standard sol-gel tungsten oxide films and the ones doped with gold in the polystyrene template. The diffusion coefficients of protons in the gold-doped tungsten oxide films were determined from both Cyclic Voltammetry (CV) and Electrical Impedance Spectroscopy (EIS) measurements. The results indicate a faster diffusion of the proton in the porous film, compared with a compact tungsten oxide film. The model that evolves from the EIS data, involves fast charge transfer rates at the electrolyte/tungsten oxide film interface. The results demonstrated an enhancement of the coloration efficiency of the macroporous tungsten oxide films with Au nanoparticles on the surface of the film. The possible involvement of plasmon resonance of Au nanoparticles in the electrochromic process is discussed.

Hydroxyapatite formation on oxide films containing Ca and P by hydrothermal treatment

Ti-Ta alloys, having low Young’s modulus and high corrosion resistance1, are expected to be candidates for dental and orthopaedic implants. However, for implant applications, the surface properties of Ti-Ta alloys are needed to be more bioacitve. Anodic oxidation is an efficient surface treatment to modify Ti surfaces because it changes the chemical and physical characteristics of Ti surfaces. According to the report by Sul et al.2, an anodically oxidized Ti implant shows a strong response to bone because it surface incorporates P. Therefore, in this study, we attempt to fabricate a P-rich oxide on Ti-Ta alloys by anodic oxidation and hydrothermal treatment. In this study, Ti-50Ta plates (ϕ10×1 mm) were abraded to grade 800 silicon carbon paper. Then, the abraded samples were washed with acetone for 5 min followed by ethanol for 3 min in an ultrasonic cleaner, and finally dried at room temperature. Anodic oxidation of Ti-50Ta samples were performed in 30% phosphate acid solution. A high-density graphite plate was used as the cathode. The Ti-50Ta samples were galvanostatically anodized at a constant current density of 50 mA/cm2 up to 300 V for 2 min using a direct current power supply. After anodic oxidation, the samples were washed with distilled water and the dries at room temperature. The anodically oxidized samples were hydrothermally treated in a 500 ml Teflon autoclave containing 50% distilled water as a reaction reagent. The samples were treated at 200 ℃ for 6 h.Results show that after anodic oxidation, an oxide film with rough surface formed on a Ti-50Ta plate. A typical morphology, craters on the surface of oxide film, was observed and it is attributed to sparking occur on the surface. After hydrothermal treatment, crystals with size of ~100 nm formed on the anodic oxide film were observed in Fig. 1. These nano-crystals were suggested as P-O compounds. Sul et al. demonstrated that P-incorporated anodically treated films on Ti implants imparted much stronger bonding with bones than mechanically turned Ti implants. Consequently, this P-rich surface on Ti-Ta alloy is expected to possess a good biological ability.

The ZM5-0.1%RE magnesium alloy was heated to 800°C, when the surface oxide film was formed, the ZM5-0.1% RE Magnesium alloy which had being oxidized obtained by removing the surface oxidation film on the ZM5-0.1%RE magnesium alloy at room temperature. TGA curve, oxidaxion kinetics curves at constant temperatuers of the alloy and XRD spectrum of the surface film were analyzed in order to investigate the sureface oxidation behavior.The results show that the alloy still has anti-oxidation performance, And the oxide inerease occurred mostly between 400°C and 700°C，a layer of tight oxide film with 4-5.5um and composed of RE2O3, MgO, Al2O3 and Mg17Al12 was formed on the surface of magnesiurn alloy. The tight surface oxide film prevented the further oxidation of the base magnesiurn alloy, It show that the regeneration ability of oxidation film on ZM5-0.1%RE Magnesium Alloy was good.

Analysis of regional brain activation during mastication by functional magnetic resonance imaging

Research on oxidation wear mechanism of the cast steels

\nThis paper studies the electric breakdown discharge process of micro-arc oxidation film on the surface of aluminum alloy. Based on the analysis of the AC parameters variation in the micro-arc oxidation process, the following conclusions can be drawn: The growth of oxide film can be divided into three stages, and Oxide film breakdown discharge occurs twice in the micro-arc oxidation process. The first stage is the formation and disruptive discharge of amorphous oxide film, producing the ceramic oxide granules, which belong to solid dielectric breakdown. In this stage the membrane voltage of the oxide film plays a key role; the second stage is the formation of ceramic oxide film, the ceramic oxide granules turns into porous structure oxide film in this stage; the third stage is the growth of ceramic oxide film, the gas film that forms in the oxide film’s porous structure is electric broken-down, which is the second breakdown discharge process, the current density on the oxide film surface could affect the breakdown process significantly.\n

The evolution of the surface oxide film along the depth direction of typical aluminum alloy under medium-temperature brazing was investigated by means of X-ray photoelectron spectroscopy (XPS). For the alloy with Mg content below 2.0wt%, whether under cold rolling condition or during medium-temperature brazing process, the enrichment of Mg element on the surface was not detected and the oxide film was pure Al2O3. However, the oxide film grew obviously during medium-temperature brazing process, and the thickness was about 80 nm. For the alloy with Mg content above 2.0wt%, under cold rolling condition, the original surface oxide film was pure Al2O3. However, the Mg element was significantly enriched on the outermost surface during medium-temperature brazing process, and MgO-based oxide film mixed with small amount of MgAl2O4 was formed with a thickness of about 130 nm. The alloying elements of Mn and Si were not enriched on the surface neither under cold rolling condition nor during mediumtemperature brazing process for all the selected aluminum alloy, and the surface oxide film was similar to that of pure aluminum, which was almost entire Al2O3.

Hydrophobic Properties of CuO Thin Films Obtained by Sol-Gel Spin Coating Technique-Annealing Temperature Effect

A new type of hot working die steel was designed by using JMatPro, and high-temperature oxidation tests were carried out in the ambient atmosphere at 600 ℃ and 700 ℃. The heat treatment process and oxidation mechanism of the designed 4Cr4Mo2NiMnSiV steel were studied in detail. XRD, SEM and EDS were used to analyze the crystallographic phases, surface and cross-section morphologies of the oxide films. The results show that the main phases in the 4Cr4Mo2NiMnSiV steel were γ and α + δ. During the high-temperature oxidation, oxidation of the Fe outer layer and Cr inner layer occurred. After oxidation at 600℃, the surface oxidation layer comprised a monolayer with an uneven morphology. The surface oxide film had two layers after oxidation at 700℃. The outer oxide layer mainly contained Fe2O3 and Fe3O4, while the inner oxide layer mainly contained Cr2O3. The microstructure was relatively regular and had a significant effect on the protection of the metallic matrix. When oxidized, the 4Cr4Mo2NiMnSiV alloy steel easily formed protective layers, such as Cr2O3 and SiO2, so that the test steel had excellent oxidation resistance at high temperatures.

Hybrid catalytic membrane systems have been produced by modifying porous ceramic membranes with metal oxide films. A two-layer cermet membrane consisting of a flexible stainless steel layer and an overlying porous TiO2 ceramic layer and a ceramic titanium carbide membrane are examined. The membrane surfaces have been modified by the alkoxide method using colloidal organic solutions of metal complex precursors. Producing a tetragonal single-phase ZrO2/Y2O3 coating on the cermet surface increases the abrasion strength of the ceramic layer. CO oxidation and the oxidative conversion of methane into synthesis gas and light hydrocarbons can be markedly intensified by modifying the membrane channels with Cu0.03Ti0.97O2±δ and La + Ce/MgO catalysts, respectively. A method has been developed for depositing, onto the geometrical surface of a membrane, a film of the new single-phase oxide P0.03Ti0.97O2±δ with an anatase structure and uniform pores of mean diameter 〈d〉 ∼ 2 nm. Blocks of zeolite-like silicalite can be formed on the surface of the phosphorus-titanium oxide film. The resulting hybrid membrane is characterized by an anisotropic permeability depending on the flow direction. This property has an effect on conversion and selectivity in the nonoxidative dehydrogenation of methanol.

Characterization of air-formed surface oxide film on a Co–Ni–Cr–Mo alloy (MP35N) and its change in Hanks’ solution

Interaction of nanostructured metal overlayers with oxide surfaces

This work studied Mo-TiC-xCr (x = 0.0, 0.5, 1.0 wt.%) matrix composites with different component gradients prepared by Spark Plasma Sintering (SPS). The high-temperature oxidation test was conducted at 1200 ℃ in the atmosphere to study the influence of Cr on the high-temperature oxidation behavior of TiC-reinforced Mo matrix composites. The phase composition and morphology of the oxide film were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS), and the goal was to determine the effect of the Cr content on the high-temperature oxidation properties of the Mo-TiC-xCr (x = 0.0, 0.5, 1.0 wt.%) matrix composites. The results showed that with increasing oxidation time, the oxide film on the surface of Mo alloy will crack and fall off easily, and the porosity gradually increases. Oxygen underwent vigorous oxidation through the pores and the inside of the matrix, and a protective MoO2 internal oxide film disappeared. With increasing Cr content, the high-temperature oxidation performance of the Mo alloy improved, the thickness of the oxide film decreased, warping of the surface oxide film was inhibited, the porosity decreased, and volatilization of MoO3 was inhibited. After oxidation, the surface oxide film was mainly composed of TiO2, MoO3, Cr2O3 and Cr2(MoO4)3 phases. The TiC particles dispersed in the matrix were oxidized to TiO2 to inhibit the oxidation of the alloy. The Cr formed a protective oxidation film of Cr2O3, which effectively reduced the porosity and delayed the volatilization of the MoO3, thus improving its oxidation performance.

The formation of films of valve metal oxides of the aluminum, zirconium, titanium, tantalum, niobium series with a thickness of about 100 nm by electrochemical anodization in an electrolyte based on a 1 % aqueous solution of citric acid is considered. The effect of films of anodic oxides of valve metals with a built-in electret charge on the process of blood hemostasis when it contacts the surface of oxide films is studied. It is found that films of oxides with a negative electric charge (oxides of aluminum and zirconium) slow down the process of blood hemostasis, and films of anodic oxides with a positive electric charge (oxides of niobium and tantalum) accelerate it. Recommendations are given for the use of coatings with a negative electric charge as implant coatings to ensure a thromboresistant effect. Positively charged valve metal oxides can be used in wound treatment to stop bleeding.