Heat Treatment In Oxygen Research Articles

Formation of small particles of gold on alumina support films and their behaviour in oxygen and hydrogen atmospheres

Attempt has been successfully made to disperse ultrafine gold particles on alumina support films by keeping the substrate at elevated temperatures during metal deposition under vacuum of ≈ 10 -5 Torr. It is found that reasonable dispersion of particles occurs for a mean thickness of 0.5 nm at a substrate temperature of 125 °C. The resulting samples turn out to be quite suitable for model studies of the behaviour of gold/alumina catalyst. Electron microscope observations coupled with diffraction have provided evidence for emergence of gold particles without any compound formation with the residual gases present during deposition at 10 -5 Torr. The nature of dispersion and average particle size are shown to depend on substrate temperature and the amount of metal evaporated. Heat treatments in hydrogen and oxygen at 200–500 °C for various lengths of time led to an increase in particle size with a simultaneous decrease in number density (i.e. coarsening of particles) following, in all probability, the Ostwald ripening mechanism. The oxidizing atmosphere has been shown to be more favourable to coarsening or deactivation of the catalyst. Finally, it is indicated that gold particles prefer to facet giving well-defined shapes (e.g. hexagonal, pentagonal or rhombohedral) with faces corresponding to planes of relatively smaller interfacial energies.

XRD evidence of preferential orientation of platinum crystallites on graphite

It was found using X-ray diffraction that graphite-supported platinum particles (catalysts) preferentially oriented with their (111) planes parallel to the basal graphite planes after heat treatments in vacuum or oxygen. The degree of alignment was a function of time, temperature and gas atmosphere. It was found that preferential orientation first increased with time but then declined after lengthy treatment. Particle size analysis also indicated that the (average) particle size at which maximum {111} alignment occurred, increased with temperature, and is larger following vacuum treatments than oxygen treatments. The results can best be explained by assuming (i) weak Pt/graphite interaction, (ii) the platinum particles assume their normal equilibrium shape, and (iii) the particles lie on the basal graphite planes with their major surface planes.

Experimental Study on Crack Growth Behavior for Austenitic Stainless Steel in High Temperature Pure Water

Crack growth behavior of Type 304 stainless steel in a simulated BWR water environment was investigated for the quantitative characterization of subcritical flaw growth in BWR piping systems. Crack propagation rates under corrosion fatigue and stress corrosion cracking were generated using compact specimens. The effects of several parameters on the rates were discussed. Furthermore, surface crack growth behavior was examined under different modes of cyclic loading, and results were discussed in comparison with compact specimen data. The corrosion fatigue crack propagation rates strongly depended on the frequency and the stress ratio. The rates became higher as the frequency lowered and the stress ratio increased. No effect from dissolved oxygen concentration and heat treatment of the steel was observed in tests, where transgranular cracking mainly took place. Stress corrosion cracking rate data indicated KISCC was above 15 MPa•m1/2. On the other hand, surface crack growth behavior included scattered crack propagation rates. However, the relationship between da/dN and ΔK was basically similar to that obtained in the compact specimens, except under given test conditions, where the acceleration for the crack growth rate at a crack tip on the panel surface was different from that at the deepest point.

Electrical and optical properties of conducting N-type Cd 2SnO 4 thin films

Polycrystalline Cd 2SnO 4 thin films were prepared by d.c. reactive sputtering from CdSn alloy targets. X-ray spectroscopy revealed that the tin cations occupy the octahedral sites in a spinel structure. Mössbauer measurements confirmed this result. Measurements of the electron concentration, the mobility and the thermoelectric power as functions of the temperature revealed that the films were degenerate semiconductors. The electrical properties of the films after post-deposition heat treatment in oxygen indicated the origin of the free carriers and the nature of the scattering process. The fundamental absorption edge showed a Burstein shift. The electron effective mass was calculated from the IR plasma reflection.

The correlation of hydrogen diffusion with the relative concentrations of cubic and axial Fe3+ sites in KTaO3

Hydrogen in the form of OH− ions has been incorporated into Fe-doped KTaO3 single crystals by heat treatments in H2O vapor, air, and hydrogen gas. Heat treatments in argon and oxygen resulted in a removal of OH− from the crystal. The conditions resulting in the incorporation of OH− also produced a decrease in the intensity of an axial Fe3+ EPR signal relative to the cubic site iron spectrum while the removal of OH− was accompanied by a relative increase in the axial EPR signal. The removal of oxygen from Fe-doped KTaO3 by heat treatments in potassium metal vapor was also found to elminate the axial Fe3+ EPR spectrum. These results do not support the previously accepted oxygen vacancy model for the Fe3+ axial site configuration and are contrary to the results of similar investigations of Fe3+ in SrTiO3.

Surface aggregates produced on activated FeTi AS determined by X-ray diffraction

We identified the ternary oxide on activated TiFe as TiFeO x . It has an f.c.c. lattice with a 0 = 11.15 A ̊ . The oxide is unstable at 1000°C and decomposes into Ti 1.18FeO x and Fe 2Ti in accord with the Rostoker Ti-Fe-O phase diagram. The boundary limits regarding the homogeneous region for the non-stoichiometric Ti-FeO x phase, as proposed by Rostoker, were essentially confirmed. The possible role of TiFeO x in the activation of FeTi is discussed. The surface phases on activated FeTi can be modified by simple oxygen exposure and heat treatment techniques.

Reduction of nickel in mordenite and silica catalysts. Influence of support and pretreatment

The reduction of nickel loaded mordenite and silica catalysts has been studied by magnetic, volumetric and spectroscopic methods. Data related to changes in the nickel phase occurring during oxygen and hydrogen heat treatments are presented and discussed. The results indicate that the reduction of ionic nickel to metal is inhibited when the nickel coordination to surrounding oxygen atoms increases. The observed final distributions of nickel particles (metal and/or oxide) are strongly support-dependent. They are tentatively explained on the basis of the mobility of Ni(II) species during activation.

多層溶接金属のじん性とその支配因子 大電流ＭＩＧ溶接金属のじん性に関する研究

In previous papers, the authors demonstrated that the addition of Ti and B are extremely effective to improve the notch toughness of weld metal and verified the inherent and complex effects of Ti, B and oxygen on the refinement of microstructure.This paper deals with the notch toughness of weld metal produced by the multipass large current MIG arc welding. Attention was focused on the effects of alloying elements such as Ti, B, oxygen, nitrogen and post weld heat treatments on the notch toughness of weld metal. The results obtained were as follows:(1) Ti-B weld metal consisting predominantly of acicular ferrite structures gives the optimum toughness at Ti content of 0.02%. The oxygen content ranging from 300 to 500 ppm has little influence on its toughness.(2) Nitrogen deteriorates the notch toughness of Si-Mn-Mo weld metal significantly, whereas Ti-B weld metal shows highly tolerance to it.(3) The deleterious effect of stress relieved heat treatment on the notch toughness of Ti-B weld metal is due to temper embrittlement phenomenon which occurs during the cooling stage after heat treatment.(4) The toughness of quenched and tempered weld metal made by Si-Mn-Ni-Cr containing consumable wires gives good correlation with tensile strength and oxygen content, and the transition temperatures of Charpy impact test are lowered by decreasing oxygen content within the tensile strength range of 60-65 kg/mm2.

Solid-phase formation and decomposition of NiAl 2O 4 Spinel inclusions in corundum

On oxygen heat treatment of corundum doped with nickel spinel phase NiAl 2O 4 precipitates forming macroinhomogeneities. Subsequent vacuum heat treatment causes decomposition of the spinel with formation of metallic Ni. The reactions are shown to be due to oxygen diffusion.

Redispersion of platinum on alumina support

The increase in metal dispersion of several Pt Al 2O 3 catalysts, following a heat treatment in air or oxygen at 500 °C, has been studied as a function of sintering conditions, support pretreatment, and chlorine content. The changes in metal dispersion were followed by hydrogen chemisorption measurements. Heating the catalysts in H 2 at 600 °C resulted in a slow decrease in metal dispersion and simultaneous loss of chlorine was observed, which depended on the water content of the gas stream. A limiting value of dispersion was obtained after prolonged sintering (≥100 hr) and this behavior is consistent with a crystallite migration mechanism. Hydrogen sintered samples were easily redispersed by air treatment at 500 °C, the increase being dependent on the sintering time and the residual level of chlorine. Successive sintering (H 2)-redispersion (air) cycles performed on a given sample indicated a slow decrease in the final dispersion, particularly for heavily sintered samples. This trend was reversed by restoring the original level of chlorine. A metal-support interaction involving the platinum atoms and oxidizing sites on the alumina is postulated to explain these results. Heating the catalysts in air at >580 °C caused a very rapid decrease in metal dispersion, compared to hydrogen, and the presintered catalysts were redispersed by oxygen treatment at 500 °C. In this case the redispersion process was found to depend on time and the final dispersion actually exceeded the original value. These observations suggest that the redispersion of Pt Al 2O 3 catalysts occurs by different mechanisms depending on the sintering atmosphere. The origin of the alumina or the support pretreatment did not influence the redispersion process.

Changes induced on the surfaces of small Pd clusters by the thermal desorption of CO

The stability and adsorption/desorption properties of supported Pd crystallites less than 5 nm in size were studied by Auger electron spectroscopy and repeated flash thermal desorption of CO. The Pd particles were grown epitaxially on heat-treated, UHV-cleaved mica at a substrate temperature of 300°C and a Pd impingement flux of 4×1013 atoms/cm2 s. Auger analysis allowed in situ measurement of relative particle disperion and contamination, while FTD monitored the CO desorption properties. The results show that significant changes in the adsorption properties can easily be detected. Changes in the Pd Auger signal and the desorption spectrum during the first few thermal cycles are believed to be due to particle coalescence and facetting. The rate of this change is dependent on the temperature and duration of the desorption. Significant reductions in the amplitude of the desorptions peak occur during successive CO desorptions are attributed to increases of surface carbon, induced by the desorption of CO (an effect not observed on large single crystals). The contamination process could be reversed by heat treatment in oxygen or hydrogen.

A LEED-AES study of the reconstructed Pt(110) surface and the effect of oxygen treatment

The Pt(110) crystal face has been studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The stable reconstructed (1 × 2) surface structure transforms, reversibly, to the (1 × 1) structure upon heating in vacuum to 830 ± 30°C. Ion bombardment at 25°C also stabilizes the metastable (1 × 1) surface structure which converts, irreversibly and rapidly to the stable (1 × 2) structure upon heating in vacuum at <500°C. The diffraction beam intensities exhibit complex behavior when monitored as a function of temperature. Heat treatments in oxygen at high crystal temperatures (>800°C) result in the appearance of new (1 × 3), (1 × 5) and (“1 × 7”) surface structures while oxygen remains undetectable by AES. Adsorbed CO causes the (1 × 2) → (1 × 1) transformation while it does not affect the (1 × 3) surface structure.

Photoelectric properties of pure and aluminium doped CdS films

Photoelectric properties of pure and Al doped vacuum deposited CdS films have been studied to explore the possibility of their application in photoactivated liquid crystal light valves. The effect of heat treatment in oxygen atmosphere, rate of deposition and the extent of Al doping, etc. on the resistivity, photo-response spectral characteristics, rise and decay time of photo-current, etc. have been investigated. It has been found that in contrast to pure CdS films, the properties of Al-doped films significantly depend on both the rate of deposition and the extent of Al doping. The dark resistivity in all cases was found to increase with heat treatment in oxygen. Unlike pure CdS films, Al doped films show photo-conductivity which is enhanced by heat treatment. Al doped films deposited at higher rates show better photo response even at lower light levels. At various light levels the rise and decay time of Al-doped films were found to be fairly constant and lower than that for pure CdS films. All these properties have been explained in terms of the presence of trapping levels due to doping. These trapping levels are also indicated by TSC, optical absorption and EPR studies.

低速電子回折法（LEED）によって得られた銅-酸素系表面構造の「酸素圧-熱処理図」

The structure of oxygen-adsorbed copper {100} and {110} surfaces has been studied by low energy electron diffraction (LEED) technique. The surface structure data obtained by the present author and other researchers are summarized in a diagram as a function of surface temperature and oxygen pressure. Attention has been given to unify the notations of the surface structures in order to facilitate comparison of the data. The diagram, called “oxygen pressure-temperature diagram”, is a kind of the phase diagram for the surface, indicating the dependence of surface structure on oxygen pressure and heat treatment.

ChemInform Abstract: OPTICAL PROPERTIES OF TANTALUM OXIDE FILMS ON SILICON

AbstractDie Ta‐oxid‐Filme werden durch thermische Oxidation von im Vakuum auf Si‐Substraten aufgedampften Ta‐ Filmen hergestellt.

Thermal Behavior of Porous Silicon

Thermal behavior of porous silicon formed by anodic reaction in 50 wt% hydrofluoric acid has been investigated. It was found that the porous silicon films (PSF) step height before and after heat treatment was a strong function of the apparent PSF density, atmosphere, temperature, and time. Particularly, the heat treatment in wet oxygen resulted in a change from PSF virtual volume increase to decrease with increasing oxidation time when the apparent PSF density is very small. In dry oxygen, PSF always caused a virtual volume increase. Three exothermic peaks, which were apparently caused by the oxidation reaction, were observed at approximately 300°C, 630°C, and 800°C. Si-Si bond in as-grown PSF was very unstable and the bond changed easily into Si-O bond as the oxidation temperature increased. Diffraction peaks, apparently caused by the formation of β-cristoballite, were observed at 1100°C in dry oxygen.

The temperature dependence and heat treatment behaviour of epitaxial (YSmCa)3(FeGe)5O12

The magnetic bubble parameters of an epitaxial garnet film of composition Y1.92Sm0.10Ca0.98Fe4.02Ge0.98O12 have been measured (i) in the temperature range -10 to 180 degrees C, and (ii) at 30 degrees C following heat treatments in either high-purity oxygen or high-purity nitrogen atmospheres. The uniaxial anisotropy constant of material which had been heat treated at temperatures between 700 and 950 degrees C increased with the temperature of the heat treatment due to an increase in the film/substrate lattice mismatch. Heat treatments at higher temperatures led to a lowering of the uniaxial anisotropy constant.

Heat-treatment behavior of the magnetic properties of epitaxial Sm0.4Y2.6Fe.3.8Ga1.2O12

Magnetization, characteristic length, uniaxial anisotropy constant, and domain wall mobility of garnet films have been measured following heat treatments in the range 900–1300 °C. Changes in the properties of films heat treated in oxygen are caused mainly by the lowering of the uniaxial anisotropy constant. The activation energy for this process is 4.1±0.2 eV, which is substantially lower than a previously reported value. Heat treatment in nitrogen leads to a lowering both of the magnetization and of the uniaxial anisotropy constant. The lowering of the magnetization is caused by a redistribution of Fe3+ and Ga3+ ions among lattice sites during the cooling part of the heat-treatment cycle. Heat treatments in oxygen are slightly more effective in lowering the uniaxial anisotropy constant than heat treatments in nitrogen.

Untersuchungen zur Konservierung von Raney-Nickel-Misch-Katalysatoren

The preservation of Raney-nickel and of various blended Raney-nickel catalysts by slow oxidation of the samples in atmospheric oxygen and subsequent controlled heat treatment and reduction was investigated. BET analysis of these catalysts have shown that their structure after partial reduction of the oxides—the so called ‘reactivation’—differs but little from the original structure of the not oxidized samples. Only after immersion into the electrolyte the structure of the preserved catalysts is changed markedly by hydratization of the oxides. The electrochemical investigations show that the properties of said catalysts depend strongly on their residual oxide concentration; the best current voltage performance was measured in the case of undoped or 1 per cent Ti alloyed Raney-nickel at an oxygen content of 1·7 resp. 1·8 per cent per weight. Catalysts doped with more Mo or Fe deteriorate under preservation. These catalysts are exhibiting a priori a high exchange current density caused by catalytically active surface oxides. This exchange current is not diminished by the preservation, but possibly the supply of hydrogen to the catalyst grains is rendered more difficult because a too high oxide concentration will inhibit the necessary surface diffusion of hydrogen on the walls of the pores. Therefore, application of preservation is useful only if it causes a so strong increase of exchange current density, that the corresponding decrease of surface diffusion becomes relatively less significant.

Physical and Chemical Properties of Aluminum Oxide Film Deposited by AlCl3-CO2-H2 System

The changes of structure and physico-chemical properties of aluminum oxide film with deposition and heat treatment temperatures have been investigated by infra-red spectroscopy, X-ray diffraction analysis, electron probe analysis, ellipsometry, microscopy and etch rate measurement. The films have been deposited on a heated silicon substrate in the temperature range of 400∼1000°C by AlCl3–CO2–H2 system and heat-treated in H2, O2 and Ar atmospheres between 500°C and 1300°C after deposition. Results show that the composition of the film is affected by the imperfection of reactions. By the heat treatment at high temperature aluminum oxide film crystallizes, and changes of structure and properties of the film depend on the deposition temperature as well as heat treatment procedures, and the film proceeds through various stages to α-alumina. The damage of the surface of the film by heat treatment is explained by the large thermal expansion coefficient of the film, and is also caused by vapor etch by HCl formed by the reaction between H2 gas and chlorine contained in the film deposited at low temperature. The growth of silicon dioxide film underneath aluminum oxide by oxygen heat treatment is limited by the substitutional diffusion of oxydizing species into aluminum oxide and the new formed film, and also depends on the strength of Al–O bond of aluminum oxide.