Showing papers on "Oxide published in 1980"

Improvements in High Temperature Oxidation Resistance by Additions of Reactive Elements or Oxide Dispersions

Abstract: The improvement in oxidation resistance of high temperature alloys as a result of additions of rare earth elements, other reactive metals, or dispersions of stable oxides, has been known for many years. Two effects seem the most important: first, the adhesion between scale and alloy is markedly improved and this increases the alloy’s resistance to thermal cycling exposure; secondly, in some but not all cases the actual growth rate of the oxide is also reduced. The various models proposed to explain these phenomena are discussed in the light of currently available experimental evidence. The most significant of these involve modification to the early, transient stages of oxidation, doping of the oxide which changes its transport properties, mechanical keying of the surface scale to the substrate by the formation of intrusions of oxide penetrating into the alloy and the elimination of void formation at the alloy-scale interface. The efficacies of the various beneficial additions are compared.

Nitrous Oxide from Soil Denitrification: Factors Controlling Its Biological Production

Abstract: Increasing concentrations of nitrate, nitrite, and molecular oxygen enhanced production of nitrous oxide relative to molecular nitrogen during denitrification in soils. Soil acidity interacted with nitrate to increase the ratio of nitrous oxide to molecular nitrogen. In response to anoxic conditions, nitrous oxide production initially increased but nitrous oxide was then consumed, a pattern which resulted from the sequential synthesis of nitrogenous oxide reductases.

Vanadium oxide monolayer catalysts. 3. A Raman spectroscopic and temperature-programmed reduction study of monolayer and crystal-type vanadia on various supports

Abstract: Vanadium(V) oxide supported on 7-A1203, GO2, Cr2O3, Si02, Ti02, and Zr02 was studied by X-ray fluorescence, by X-ray diffraction, and especially by the combination of Raman spectroscopy and temperature-programmed reduction (TPR) for qualitative and quantitative structural analysis, respectively. Catalysts were prepared via ion-exchange and wet-impregnation methods. The V contents ranged from - 1 to 40 wt % V. At low surface concentrations only surface vanadate phases of two-dimensional character are observed for all carriers. According to Raman and TPR data the structure of these surface vanadate species is independent of the preparation technique. At medium and high surface concentrations, the webimpregnated samples already contain crystalline V20b At equal surface concentrations the ion-exchanged catalysts contain no V205 crystallites. An exception is Si02 on which also crystalline V206 is formed in both preparation techniques. Monolayer stability toward thermal treatment decreases in the order AZO>3 Ti02> Ce02,w hereas on heating ion-exchanged V/Si02 the crystalline V206 spreads out over the silica surface. The reducibilities of the ion-exchanged catalyats, as measured by TPR, can be used as a measure for the contact interaction between vanadia and the carrier oxides. At temperatures of 500-800 K, this interaction ranges from strong with titania to weak with silica as a carrier.

Glasses from metal alcoholates

Abstract: Developments in the technique of preparing oxide glasses from metal alcoholates through hydrolysis, gelling and heating at low temperatures have been reviewed. This technique makes it possible to produce (1) glasses of very high purity and (2) glasses of compositions which the conventional melting technique could not give because of immiscibility, crystallization and high melting temperatures. This technique can provide glasses having various shapes such as fibers, thin coating films, isolated films and bulk glasses. Discussion was made on the microscopic processes leading to fibers and bulk glasses.

Investigations of porous oxides as an antireflective coating for glass surfaces.

Abstract: There is no inorganic material that would satisfy the low index requirement of a single-layer antireflective coating for commercial soda-lime glasses. Such an antireflective coating would increase transmission 4-8% and cause corresponding efficiency increase in devices where energy is transmitted by radiation, e.g., solar collectors, and cathode ray tubes. MgF(2) with an index of 1.38 (vs 1.23 needed) is the lowest index coating material available and widely used by the industry. In this work, possible applications of porous oxide films as an antireflective coating were investigated. A porous aluminum oxide film is deposited on glass surfaces from a clear organometallic derived sol. The index of the oxide coating is reduced by the presence of pores hose size is <100 A; this constitutes up to 64% porosity. These pores, being considerably smaller than the wavelength of light, do not interfere with the optical transparency of the material but reduce the index of refraction; thus they make it possible to obtain transparent oxide materials and coatings with very low index.

Spectroscopic Analysis of the Interface Between Si and Its Thermally Grown Oxide

Abstract: Spectroscopic ellipsometric data from 1.5–5.8 eV has been analyzed to determine the in situ optical response of the interface between Si and its thermally grown oxide. Results for , , and sample orientations show an interface of width consisting of atomically mixed Si and O of average stoichiometry . The optical data are not consistent with either microroughness at the interface or an abrupt transition between crystalline Si and or a significant accumulation of amorphous Si at the interface, but rather support a gradual transition region. The thickness and the average λ5461 refractive index of this region are in agreement with the fixed‐wavelength results, and , of Taft and Cordes. The oxide on the surface is shown to have a density about 1.2% less than that of corresponding oxides on and surfaces.

Solid Electrolytes and Their Applications

Abstract: 1. Defect Structure and Transport Properties.- 1. Introduction.- 2. Defect Structure.- 2.1. Types of Point Defects.- 2.2. Lattice Disorder and Association of Defects.- 2.3. Defect Equilibria.- 2.4. Energy of Formation and Motion of Defects.- 3. Experimental Methods.- 3.1. Density.- 3.2. X-Ray and Neutron Diffraction.- 3.3. Electrical Conductivity and Diffusion.- 3.4. Polarization Measurements.- 3.5. Impedance Measurement.- 3.6. Thermoelectric Power.- 3.7. Relaxation Methods.- 3.8. Miscellaneous Techniques.- 4. Materials.- 4.1. Fluorite-Type Oxides.- 4.2. ?-Alumina-Type Oxides.- 4.3. Silver-Iodide-Type Materials.- 4.4. Fluorides.- 4.5. Miscellaneous.- 5. Concluding Remarks.- References.- 2. Limiting Factors in Measurements Using Solid Electrolytes.- 1. Introduction.- 2. Electronic Conduction in the Electrolyte.- 2.1. Examples from Thermodynamic Measurements.- 2.2. Examples from Kinetic Measurements.- 3. Maintaining a Desired Chemical Potential at the Electrode-Electrolyte Interface.- 3.1. Influence of Electronic Conductivity.- 3.2. Influence of Chemical Reactions.- 3.3. Influence of the Gaseous Atmosphere.- 3.4. Equilibration of the Electrode Constituents.- 3.5. Polarization Effects at the Electrode-Electrolyte Interface.- 4. Effects of Porosity, Inhomogeneity, and Inadequate Mechanical Properties.- 5. Experimental Uncertainties.- 5.1. Limited Temperature Range of Study.- 5.2. Instrumentation Problems.- 6. Concluding Remarks.- References.- 3. Thermodynamic Studies of Alloys and Intermetallic Compounds.- 1. Introduction.- 1.1. General.- 1.2. Solid Electrolyte Galvanic Cell Method.- 1.3. Limitations of Data Derived from emf Measurements.- 2. Metallic Alloy Systems.- 2.1. Introduction.- 2.2. Binary Solid Metallic Alloys.- 2.3. Binary Liquid Alloys.- 2.4. Conclusion.- 3. Oxygen Dissolved in Metals and Alloys.- 3.1. Introduction.- 3.2. Dilute Alloys of Oxygen in Metals.- 3.3. Effect of Third Alloying Element on the Oxygen Activity.- 4. Fluoride Cells to Study Carbides, Borides, Phosphides, and Sulfides.- 5. Conclusion.- References.- 4. Thermodynamic Properties of Oxide Systems.- 1. Introduction.- 2. Comparison of the Solid Electrolyte Method with Other Methods for Thermodynamic Measurements.- 3. Types of Solid Electrolytes Used in the Study of Oxide Systems.- 4. Thermodynamic Measurements of Oxide Systems with Cells Involving Oxide Solid Electrolytes.- 4.1. Apparatus.- 4.2. Determination of the Free Energy of Formation of Oxides, Spinels, Silicates, and Other Compounds.- 4.3. Activity Measurements in Oxide Systems.- 4.4. Study of the Nonstoichiometry of Metallic Oxides.- 4.5. Some Special Studies of Oxides and Related Systems.- 5. Thermodynamic Measurements of Oxide Systems with Cells Involving Fluoride Solid Electrolytes.- 5.1. Introduction.- 5.2. Free Energy of Formation of Oxide Compounds.- 5.3. Measurement of Activities in Oxide Solid Solutions.- 6. Concluding Remarks.- References.- 5. Kinetic Studies.- 1. Introduction.- 2. Polarization Studies.- 2.1. Polarization Studies Involving Gaseous Electrodes.- 2.2. Polarization Studies Involving Liquid Electrodes.- 2.3. Polarization Studies Involving Solid Electrodes.- 2.4. Choice of Electrodes.- 3. Diffusion Measurements.- 3.1. Potentiostatic Techniques.- 3.2. Galvanostatic Techniques.- 3.3. Potentiometric Techniques.- 3.4. Combined Potentiostatic and Potentiometric Techniques.- 3.5. Evaluation of Experimental Techniques.- 4. Kinetics of Phase-Boundary and Diffusion-Controlled Reactions.- 4.1. Phase-Boundary Reactions.- 4.2. Diffusion-Controlled Reactions.- 5. Concluding Remarks.- References.- 6. Technological Applications of Solid Electrolytes.- 1. General.- 1.1. Introduction.- 1.2. Classification of Technological Applications.- 2. Oxygen Meters.- 2.1. Introduction.- 2.2. Determination of Oxygen in Gases.- 2.3. Measuring and Recording.- 2.4. Estimation of Gas Composition from po2 Measurement.- 2.5. Industrial Applications.- 2.6. Oxygen Determination in Liquid Metals.- 2.7. Determination of Oxygen in Liquid Steel.- 3. Oxygen Transfer to and from Materials.- 3.1. Introduction.- 3.2. Oxygen Pump and Probe.- 3.3. Coulometric Control of Oxygen in Liquid Metals.- 3.4. Other Applications.- 4. Energy Conversion.- 4.1. Introduction.- 4.2. Fuel Cells.- 5. Batteries with ?-Alumina Electrolytes.- 5.1. Sodium-Sulfur Battery.- 5.2. Other Systems Using ?-Alumina.- 6. Solid State Ionics.- 6.1. General.- 6.2. Energy Conversion Devices.- 6.3. Other Devices.- 6.4. Advantages and Limitations.- References.- 7. Fabrication.- 1. Introduction.- 2. Single Crystals.- 2.1. Stabilized Zirconia.- 2.2. Thoria.- 2.3. Calcium Fluoride.- 2.4. ?-Alumina.- 2.5. AgI-Type Compounds.- 3. Polycrystalline Materials.- 3.1. Zirconia-Base Materials.- 3.2. Thoria-Base Materials.- 3.3. ?-Alumina.- 3.4. AgI-Type Electrolytes.- 4. Electrodes.- 4.1. Oxygen Ion Conductors.- 4.2. ?-Alumina.- 4.3. Fluorides.- 4.4. Silver Ion Conductors.- 5. Joining of Materials.- 6. Conclusions.- References.

On High Temperature Oxidation of Chromium I . Oxidation of Annealed, Thermally Etched Chromium at 800°–1100°C

Abstract: Oxidation of annealed, thermally‐etched chromium has been studied at different oxygen pressures ranging from in the temperature range 800°–1100°C. A varied oxidation behavior is observed: at and 800°C the oxidation is approximately logarithmic, while above 900°C it is parabolic followed by repeated breakdowns and protective stages. At reduced oxygen pressures the oxidation behavior changes and becomes linear at the lower oxygen pressures. The different kinetics are correlated with properties of the scales which may crack, wrinkle, or balloon depending upon the reaction conditions. Large compressive stresses are built up in the scales during oxidation and the ability of the scale to deform increases dramatically with decreasing partial pressure of oxygen. Under most conditions the oxide scales become detached from the metal substrate. It is concluded that volume diffusion and transport along cracks and grain boundaries contribute to the growth of scales.

XPS and AES studies on oxide growth and oxide coatings on niobium

Abstract: Niobium surfaces show features that have been blamed on the unavoidable oxidation that occurs during the preparation of the Nb. To quantitatively measure the oxidation, XPS and AES profile measurements have been carried out for the typical procedures used in the preparation of Nb surfaces, such as ultrahigh vacuum annealing (UHV), oxipolishing (OP), electropolishing (EP), or handling in air, H2O, and H2O2. For the different surface preparations the oxidation proceeds as follows: At the Nb surface an inhomogeneous Nb2O‐NbO layer 1 nm or less thick exists which does not seem to depend much on oxidation technique. Then a dielectric oxide Nb2O5 grows homogeneously in UHV (?2 nm) or in OP(?3 nm), whereas EP(?3 nm) yields rough oxide layers that pick up impurities and charges easily. With time, all oxides grow more or less rapidly to a stable thickness of 6 nm. These results explain the observed behavior of Nb surfaces, especially their responses to the most sensitive measurements, namely, in superconducting rf cavities and tunnel junctions.

Formation of titania-silica glasses by low temperature chemical polymerization

Abstract: Clear titania glasses were formed by a low temperature chemical polymerization technique in the TiO2SiO2 binary. The chemical method developed requires initial formation of soluble intermediate species capable of polymerizing into an oxide network. The process provides formation of an essentially organic-free, often monolithic, oxide network at temperatures below 500°C. Since the glass formation takes place by low temperature chemical polymerization, the high-temperature reactions such as crystallization, phase separation, etc., which restrict glass formation, can be avoided in the entire SiO2TiO2 binary.

Preparation of conducting and transparent thin films of tin‐doped indium oxide by magnetron sputtering

Abstract: High‐quality 800‐A‐thick films of tin‐doped indium oxide have been prepared by magnetron sputtering. It is shown that films with low resistivity (∼4×10−4 Ω cm) and high optical transmission (≳85% between 4000 and 8000 A) can be prepared on low‐temperature (40–180 °C) substrates with O2 partial pressures of (2–7)×10−5 Torr.

XPS measurements and structural aspects of silicate and phosphate glasses

Abstract: Detailed measurements of the shape of the 01s photoelectron lines from a range of silicate, alumino silicate, and phosphate glasses have been made. In the case of the silicate glasses contributions from bridging and non bridging oxygen atoms were separated. For phosphate glasses an additional component due to double bonded oxygen atoms could be determined by curve fitting procedures and by comparison with selected crystalline phosphates. The intensities of the photoelectrons from these oxygen types bonded in different ways and the chemical shifts between them could be correlated with alkali and alkaline earth oxide contents and with the cation field strength. The ionic binding character introduced into the glass networks is a non-localized effect because not only the non bridging oxygen atoms are influenced by the alkali and alkaline earth ions but also the bridging and double bonded oxygen atoms. In the case of the sodium alumino silicate glasses a coordination change is indicated at Al2O3/Na2O ∼ 0.4.

Oxygen Evolution on La1 − x Sr x Fe1 − y Co y O 3 Series Oxides

Abstract: series oxides with perovskite‐type structure were synthesized and were examined as the electrode for the oxygen evolution reaction in alkaline solution. The oxides except for , , and their neighbors were suitable for the electrode with respect to high conductivity. The catalytic activity for the oxygen evolution reaction increases along the direction from to in composition. It is concluded that the following two conditions are desirable for the perovskite‐type oxide with high catalytic activity for the oxygen evolution reaction: (i) the oxide has a broad band and (ii) the transition metal cation in the oxide exists as the higher oxidation state. In addition, it was found that the catalytic activity of is the highest in the oxides prepared in this study.

Electrical properties of binary semiconducting oxide glasses containing 55 mole % V2O5

Abstract: Binary semiconducting oxide glasses containing 55 mole % V2O5 and 45 mole % GeO2, TeO2, PbO, BaO or As2O3 have been prepared. Their electrical properties are shown to be sensitive to microstructure, most notably in the 55V2O5-45GeO2 and 55V2O5-45TeO2 systems. Structural models for electron hopping in these glasses are proposed.

High‐quality transparent conductive indium oxide films prepared by thermal evaporation

Abstract: Highly transparent (over 90% transmission in the visible range) and highly conductive (resistivity ≃2×10−4 Ω cm) indium oxide (undoped) films have been produced by thermal evaporation from an In+In2O3 source in a vacuum chamber containing low pressures of O2 These properties are comparable or superior to the best tin‐doped indium oxide films ever reported, and excellent reproducibility has been achieved Hall effect measurements have revealed that the observed low resistivity is primarily a result of the excellent electron mobility (≃70 cm2/V sec), although the electron concentration is also rather high (⩾4×1020/cm3) X‐ray diffraction measurements show distinctly polycrystalline In2O3 structure with a lattice constant ranging from 1007 to 1011 A Electrolytic electroreflectance spectra exhibit at least four critical transitions, from which we have determined the direct and indirect optical band gaps (≃356 and 269 eV, respectively) Burstein shifts due to the population of electrons in the conduction