Showing papers on "Oxide published in 1971"

Oxidation of Ni ‐ Cr ‐ Al Alloys Between 1000° and 1200°C

Abstract: The oxidation of alloys in 0.1 atm of oxygen has been studied at temperatures of 1000°, 1100°, and 1200°C. Twenty‐one alloys with varying chromium [2–30 weight per cent (w/o)] and aluminum (1–9 w/o) contents were examined. It was found that all of the alloys initially underwent a period of transient oxidation before steady‐state conditions were established. The transient period of oxidation usually did not exceed 1 hr and was characterized by rapid conversion of thin surface layers of the alloys to oxides with the subsequent formation of continuous layers of one of the following oxides: , , or . Steady‐state conditions were established with the formation of these continuous oxide layers, and oxidation occurred by three different mechanisms which were characterized by the growth of an external layer of over a subscale of and Al2O3, the growth of an external layer of over an subscale or the growth of a continuous, external layer of .

Acidic and basic properties of hydroxylated metal oxide surfaces

Abstract: Hydroxyl groups on the surface of metal oxides are amphoteric in character. From experiments with anatase, rutile, η-alumina, α-Fe2O3,CeO2, and SnO2, half the OH groups are acidic in character, the other half are mainly basic and may be exchanged for other anions. This behaviour is explained by the structure of the hydroxylated surface. Acidity and basicity depend on the nature of the oxide. Several reactions are described for the determination of total OH content as well as the quantities of acidic and basic OH groups.

Electrical Properties of High‐Quality Stannic Oxide Crystals

Abstract: Single crystals of the wide bandgap semiconductor stannic oxide, SnO2, have been grown and studied electrically. A chemical vapor deposition technique using chlorine transport, no inert carrier gases, and low pressure has been used to grow stannic oxide crystals of higher purity and with almost an order‐of‐magnitude higher low‐temperature Hall mobility, 8800 cm2/V sec at 80°K, than have previously been available. Measurements of Hall mobility, carrier concentration, and resistivity have been made between 20 and 625°K on crystals with room‐temperature carrier concentrations between 8×1015 and 2×1018 cm−3. The effects of the crystal anisotropy on these measurements have been investigated and found to be small (all results reported are for the a direction). A donor level ∼35‐meV deep due to antimony and another level ascribed to oxygen vacancies at ∼140 meV have been observed. Polar optical mode scattering with a dominant characteristic temperature of 1080°C is the main carrier scattering mechanism above 250°K. Below 250°K acoustic deformation potential scattering dominates. Ionized impurity scattering is eventually important in all samples as the temperature is lowered. A polaron effective mass of 0.39 me has been found consistently in the analyses of the data. A technique of fabricating good Schottky barriers on SnO2 has also been developed and used to measure the net donor concentration in samples. The agreement found between these measurements and Nd from Hall measurements indicates that shallow trapping is not a problem in these crystals.

New Routes to Multicomponent Oxide Glasses

Abstract: Multicomponent oxide glasses can be produced not only by melting methods but also by hydrolysis and condensation of alkoxide complexes with several metals. This requires temperatures only up to the transformation range of the glass in question, usually 500–600 °C. The process does not pass through the molten phase. It is possible to obtain glasses or polycrystalline substances, depending on the composition. The method is particularly suitable for the production of thin, transparent multicomponent oxide layers of almost any composition on substrates. Some of these layers provide protection against climatic attack or against oxidation.

Theory of the differential capacity of the oxide/aqueous electrolyte interface

Abstract: The conditions under which an oxide surface in aqueous solution will obey the Nernst equation with respect to H+/OH– as potential-determining ions are investigated and a modified form of the Nernst equation is derived. This is combined with a model of the inner part of the double layer involving adsorption of both anions and cations of a supporting uni-univalent electrolyte and a discreteness-of-charge correction in their adsorption isotherms. Theoretical total differential capacities at the interface are compared with experimental data for TiO2 and SiO2.

Infra-red studies of rutile surfaces. Part 2.—Hydroxylation, hydration and structure of rutile surfaces

Abstract: A model for the surface structure of rutile is proposed, based on infra-red studies of a crystalline rutile sample prepared by the combustion of Ti(iso-PrO)4. It is suggested that the exterior surfaces of the rutile crystals correspond to three low index crystal planes—namely the (100), (101) and (110). Of these the first two are capable of adsorbing molecular water as ligand coordinated to Ti4+ surface ions, whereas the (110) crystal face adsorbs water dissociatively leading to the presence of equal quantities of two types of OH– ions. One of these types is associated with a surface Ti4+ ion which is five coordinate with respect to lattice oxide ions whereas the other type is bound to a surface Ti4+ ion which is only four fold oxide ion coordinate. It is possible to rationalize the observed thermal dehydroxylation and dehydration properties of the oxide and also account for its pyridine adsorption properties.

Benzotriazole as Corrosion Inhibitor for Copper

Abstract: The effect of benzotriazole (BTA) on corrosion of copper in 5% NaCl has been studied by immersion tests, potentiostatic polarization, AC impedance measurements, and ellipsometric investigations. It was found that BTA when present in the corrosive environment is a good inhibitor. The good electronic conductivity of the film formed on copper, the decreased double capacity, small film thickness, and decreased current on anodic polarization curves indicate that BTA is chemisorbed on the surface. This prevents adsorption of oxygen and formation of a prenucleation layer which is the forerunner of oxide formation. Discrepancies with results obtained by other investigators using infrared reflectance techniques are discussed.

Josephson Tunneling Barriers by rf Sputter Etching in an Oxygen Plasma

Abstract: A new technique for fabricating Josephson tunneling barriers has been developed. Oxide tunnel barriers with estimated thicknesses from 20 to 50 A have been formed on lead films with indium underlayers and on niobium films. The technique includes an rf sputter etching step in argon for cleaning followed by an rf sputter etching step in oxygen. During the latter, an oxide film is grown having a steady‐state thickness which is attributed to a balance between sputtering and oxidation rates. Different oxide thickness may be obtained by varying process parameters such as oxygen pressure and rf power.

Photoinjection Studies of Charge Distributions in Oxides of MOS Structures

Abstract: Determination of the nature and distribution of oxide charge in MOS structures is important to an understanding of oxide charging phenomena. In addition to their relevance to device failure mechanisms, it appears that charging phenomena may be used to advantage in memory device applications. The physical mechanism dominating the voltage dependence of photoinjected currents in SiO2 is the scattering of electrons in the region of the oxide between the injecting electrode and the image force potential maximum. Since the spatial position of the potential maximum depends on the electric field resulting from space charge in the oxide as well as the field due to the applied voltage, analysis of the V‐I characteristics of photoinjected currents can provide information about the spatial location of oxide charge. Presented in this paper are the results of an analysis of the effects of oxide space charge on the voltage dependence of photoinjected currents. It is shown that effective charge distributions in SiO2 can ...

Surface chemistry of AlPO4—a mixed oxide of Al and P

Abstract: The surface chemistry of pure AlPO4 was studied by infra-red spectroscopy in an attempt to explain why this material shows low catalytic activity despite its high acidity. Two major bands (3680 and 3800 cm–1) in spectra of dry AlPO4 were shown to represent chemically distinct types of surface OH groups. The band at 3800 cm–1 is assigned to Al—OH and that at 3680 cm–1 to P—OH. Study of adsorbed NH3 and pyridine showed both Lewis and Bronsted acid sites on the surface. Chemisorption of NH3 also produced NH2 and OH groups, showing the presence of “strained” oxide links. Adsorption of CO2 and HCI revealed very few “α-sites” or reactive surface oxide ions. The evidence suggests that the surface largely resembles a prism face (10text-decoration:overline10) of tridymite-form AlPO4, holding vicinal pairs of OH groups, with one group attached to Al and the other to P. Condensation produces acidic Al—O—P links in which O is held primarily by the P atom. The inactivity of AlPO4 probably reflects the inadequacy of PO groups as base sites rather than a lack of suitable acid sites.

Interaction of oxygen with polycrystalline tungsten. i. sticking probabilities and desorption spectra.

Abstract: The interaction of oxygen with a polycrystalline W filament has been studied in the temperature range 300–1200°K and for exposures between 10−7 and 1 torr·sec. Both sticking probabilities and desorption spectra have been measured. After low exposures (〈2×10−6 torr·sec) the adsorbate is all desorbed as O atoms with first order kinetics. With higher exposures, oxygen is removed as oxides: WO, WO2, WO3, W2O6. The desorption spectra for each of these species are complex, and nine distinct and reproducible oxide states are identified. Saturation coverages in each of these states are independent of adsorption temperature in the range 300–1200°K. At a total coverage of 8.5×1014 O2 molecules cm−2, 2.2×1014 O2 molecules cm−2 are desorbed as oxides; after exposures 〉 10−2 torr·sec at 300°K, the total uptake rises to 15×1014 O2 molecules cm−2. At temperatures between 500 and 1000°K and exposure up to 1 torr·sec, a multilayer oxide film is formed of unlimited thickness. The desorption product from this oxide film is ...

Evidence for loss of protons and octahedral iron from oxidized biotites and vermiculites

Abstract: Infra-red examination of a weathered biotite and of biotites that have been converted to vermiculites and subsequently oxidized, indicates that oxidation of octahedral ferrous ions to ferric ions is associated with a reversible conversion of hydroxyl ions to oxide ions. Subsequently, in high-iron biotites, there is an irreversible loss of ferric ions from the octahedral layer, resulting in an increased number of dioctahedral sites. Electron microscopy and X-ray diffraction indicate that ejected ferric ions form either amorphous interlayer oxides or, when bromine is used as an oxidant, a crystalline external phase of β-FeOOH. The high refractive index of some oxidized vermiculites is shown to be due largely to submicroscopic iron oxides.

Gas generator composition and method

Abstract: A deflagrating composition yielding a gas comprising principally carbon dioxide and water vapor comprises a substantially homogeneous mixture of powders preferably having an average particle size less than about 25 microns. The composition has an oxygen bearing oxidizing powder and an organic reducing powder having the formula CxHyOz, having a melting point greater than about 165 DEG F, and a sufficiently low vapor pressure to have no more than a minute amount of sublimation prior to oxidation by the oxidizing powder upon ignition. The oxidizing powder and reducing power or "fuel" are sufficiently near stoichiometry to produce a gas comprising principally carbon dioxide and water vapor upon combustion for inflation of an automobile restraint bag with a non-toxic, at least partly condensable gas. In one embodiment the mixture further comprises an endothermic decomposition coolant having a thermal decomposition product selected from the class consisting of carbon dioxide and water and decomposable below the combustion temperature of the mixture. A method of this invention comprises inflation of a gas bag by combustion of a mixture like that described above. In one embodiment, the mixture may include a reducible metal oxide having a decomposition temperature in the same range as ferric oxide. In another embodiment the mixture is burned adjacent a reservoir of water for producing vapor for inflating the bag, to be followed by rapid deflation as the vapor condenses.

Infra-red studies of rutile surfaces. Part 1

Abstract: Samples of rutile prepared by hydrolysis of TiCl4 and by combustion of Ti(isoPrO)4 have been investigated by infra-red spectroscopic techniques to provide information on their surface hydroxylation and hydration. After outgassing at ambient temperatures the rutile surface carries both hydroxyl ions and adsorbed molecular water. The depopulation of the surface caused by raising the outgassing temperature follows a pattern that suggests there are two types of surface site for the adsorbed molecular species. Complementary studies of pyridine adsorption indicate that the molecular water is held on the surface as a coordinating ligand and also show the presence of two types of hydroxyl species on the ambiently outgassed oxide. Further studies of the adsorption of thionyl chloride, sulphur dioxide and hydrogen chloride vapours support the contention that the surface hydroxyls are ionic in character. In the case of HCl adsorption, evidence for two types of coordinately bonded water was found after exposure of the oxide to the dry acid gas. It was also found that the sample prepared from TiCl4, which carried chlorine in its surface layers, was more readily dehydroxylated than the “chlorine free” material prepared from the metal alkoxide. The chlorine containing sample also aggregated on storage whereas the pure material did not.

Isotopic exchange of oxygen 18o between the gaseous phase and oxide catalysts

Abstract: This review is concerned with the isotopic exchange (IE) of oxygenl8O between gaseous oxygen and solids.

On the transient oxidation of a Ni-15Cr-6Al alloy

Abstract: Stages in the development of a protective α-Al2O3 scale on a Ni-15Cr-6Al (wt.%) alloy have been examined. It is shown that prior to the formation of a continuous α-Al2O3 layer, a transient stage of oxidation occurs that consists of a rapid uptake of oxygen with conversion of a thin surface layer of alloy to predominantly spinel and the subsequent development of a discrete layer of Cr2O3. It is also shown that during the transient period of oxidation metastable phases of aluminum oxide are formed which transform to α-Al2O3 upon incorporation into the external oxide scale.