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Showing papers on "Oxide published in 1972"


Journal ArticleDOI
TL;DR: In this paper, a detailed quantitative model for the adsorption of hydrolyzable metal ions at the oxide-water interface is presented in terms of the competition between the free energy changes faavorble to adaption, and the unfavorable change in solvation energy.

631 citations


Journal ArticleDOI
01 Jun 1972
TL;DR: In this article, the role of vacancy sinks is further confirmed by showing that oxide adherence is promoted in Fe-25Cr-4Al, in the absence of yttrium of scandium, by a distribution of Al2O3 particles.
Abstract: Oxidized alloys of Fe-25Cr-4Al, some containing small additions of elements (Yttrium or Scandium) which strongly promote oxide adherence, have been subjected to extensive structural studies by scanning, replication, and transmission electron microscopy as well as other techniques. The morphological details of the Al2O3 scales, which develop on these alloys during high temperature oxidation, and the structural changes at the oxide-substrate interfaces are discussed with respect to oxidation kinetics and oxide adherence. The oxide scales grow into the alloys at rates consistent with the diffusion of oxygen down grain boundaries of the fine-grained scales. Yttrium and expecially scandium additions tend to increase oxidation rates by providing rapid diffusion paths in the form of yttria and scandia stringers. More importantly, the morphological data led to the conclusion that the spallation of nonadherent scale is caused by distributions of small voids at the oxide-substrate interface. Consistent with this conclusion, it is found that the oxide scale is tenaciously adherent when voids are absent, as is the case when yttrium or scandium is added to the alloy. It is maintained that these alloy additions promote oxide adherence by forming vacancy complexes with excess vacancies or by providing internal oxide boundaries for the condensation of excess vacancies, which would have otherwise condensed at the oxide-substrate interface and formed the voids responsible for oxide spallation. The role of vacancy sinks is further confirmed by showing that oxide adherence is promoted in Fe-25Cr-4Al, in the absence of yttrium of scandium, by a distribution of Al2O3 particles. This result indicates that particles, which have been used in engineering alloys for strengthening purposes, can also promote oxide adherence. The morphological data are also discussed with respect to other mechanisms that had been proposed for oxide adherence.

369 citations


01 Jan 1972
TL;DR: In this article, the detailed electrophoretic mobility behavior for Si02 in aqueous solutions of Co(II), La(III), and Th(IV) has been determined as a function of metal ion concentration, pH, ionic strength, and percentage solids.
Abstract: Abstract The detailed electrophoretic mobility behavior, supplemented by streaming potential data, for Si02 in aqueous solutions of Co(II), La(III), and Th(IV) has been determined as a function of metal ion concentration, pH, ionic strength, and percentage solids. The several charge reversals (CR) observed are, in order of increasing pH, shown to represent the point-of-zero charge (PZC) on the Si02 substrate (CR 1), the pH of surface nucleation of metal hydroxide (CR 2), and at high pH, the PZC of the metal hydroxide coating (CR 3).

336 citations


Journal ArticleDOI
TL;DR: A series of alcohols and amines have been oxidised at oxide-covered nickel, silver, copper, and cobalt anodes in aqueous alkaline solutions as mentioned in this paper, and it was shown that the mechanism of these oxidations involves hydrogen abstraction from the substrate by an oxide species rather than direct electron transfer to the anode.
Abstract: A series of alcohols and amines have been oxidised at oxide-covered nickel, silver, copper, and cobalt anodes in aqueous alkaline solutions. The kinetics of these electrode processes have been studied and it is shown that the mechanism of these oxidations involves hydrogen abstraction from the substrate by an oxide species rather than direct electron transfer to the anode. The mechanism put forward is compared with those commonly suggested for the chemical reactions of transition-metal oxides and for heterogeneous catalysis.

313 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the scale-forming reaction of Ni-20 wt. % Cr2O3 scales on dispersion-free systems must involve shortcircuit diffusion of chromium through the scale, and that it seems probable that an effect of the dispersion must be to retard or eliminate this short-circuit process.
Abstract: Alloys of Ni-20 wt. % Cr containing 3 vol. % of a dispersed oxide phase have been prepared by a mechanical alloying method and oxidized in oxygen at 100 Torr in the temperature range of 900 to 1200°C. It appears that the dispersed oxide has four distinct effects on the oxidation: (1) the selective oxidation of chromium to form a continuous protective Cr2O3scale is promoted; (2) the rate of growth of Cr2O3is reduced compared with particle-free alloys; (3) the adhesion of the Cr2O3is greatly improved; and (4)the scale-forming reaction appears to be at the scale-metal interface in alloys containing a dispersion, but at the scale-oxygen interface in alloys without a dispersion. It appears that the nature of the dispersed oxide is not important, since very similar effects can be obtained with ThO2,Y2O3,and CeO2dispersions. It is demonstrated that a logical deduction from this evidence is that the growth of Cr2O3scales on dispersion-free systems must involve short-circuit diffusion of chromium through the scale, and that it seems probable that an effect of the dispersion must be to retard or eliminate this short-circuit process. It is suggested that the oxide particles act as nucleation centers for the oxide, thus reducing the oxide grain size; and it is shown that this simple hypothesis is sufficient to explain a number of the experimental observations.

266 citations


Journal ArticleDOI
TL;DR: In this article, the electron conductivity mobility on weakly inverted Si surfaces covered with thermally grown oxide is reported at temperatures from 30 to 300 °K as a function of the surface oxide charge density.

245 citations


Journal ArticleDOI
TL;DR: In this paper, X-ray photoelectron spectroscopy measurements of solid cuprous oxide have shown the presence of three kinds of oxygen species: O2, H2O, and O2-H2O.

218 citations


Journal ArticleDOI
TL;DR: Ionic conduction in sintered oxides of the system Bi2O3-SrO was investigated by measuring the conductivity and ion transference number under various conditions as discussed by the authors.
Abstract: Ionic conduction in sintered oxides of the system Bi2O3-SrO was investigated by measuring the conductivity and ion transference number under various conditions. The ion transference numbers were measured by an oxygen concentration cell employing the specimen as the electrolyte.

216 citations


Journal ArticleDOI
S. Kar1, W.E. Dahlke1
TL;DR: In this article, the authors measured measured capacitance and conductance curves of MOS structures with different metal contacts on 20−40 cm−2 V−1 SiO2 films and non-degenerate Si have been investigated.
Abstract: MOS structures having different metal contacts on 20–40 A thick SiO2 films and non-degenerate Si have been investigated. These structures show large frequency dispersion of the measured admittance curves caused by carrier recombination in interface states. However, build-up of a Si inversion layer is not observed because the minority carriers are drained away by tunneling through the oxide into the metal. Interface state density distributions across the whole Si band gap are obtained by evaluating measured capacitance and conductance curves. Characteristic peaks of 0.12–0.30 eV half width are found for the metal contacts, Mg at 0.54 eV, Cu at 0.23 eV, Cr at 0.18 eV and 0.52 eV, and Au at 0.15 eV and 0.97 eV above the valence band edge. The position of a peak seems to be related to the valence of the metal. Interface states caused by Cr, Cu and Mg contacts are of acceptor type. Their capture cross-section obtained from conductance measurements varies between 10−7 and 10−18 cm−2. A rapid increase of the state density with decreasing oxide thickness or sample annealing indicates that the states are caused by metal diffusion through the oxide into the interface. An observed saturation of the state density at about 2 × 1013 cm−2 V−1 is possibly due to a limited solubility of metal impurities in the oxide.

216 citations


Journal ArticleDOI
TL;DR: In this paper, the photoelectron spectrum of tungsten metal using Al Kα X-rays has been studied as a function of a Tungsten oxide layer on the surface.

206 citations


Journal ArticleDOI
TL;DR: In this article, a single-crystal substrate of silicon is covered with evaporated gold and heated at relatively low temperatures (100-300°C) in an oxidizing atmosphere, a silicon dioxide layer is readily formed over the gold layer.
Abstract: When a single‐crystal substrate of silicon is covered with evaporated gold and heated at relatively low temperatures (100–300°C) in an oxidizing atmosphere, a silicon‐dioxide layer is readily formed over the gold layer. The mechanism and factors controlling this low‐temperature oxide formation have been investigated using backscattering of 2‐MeV He+ ions. The oxide layer is nonuniform in thickness and the initial growth of this layer is proportional to (time)1/2. Both oxidizing ambient and orientation of the substrate influence the growth rate, and the amount of gold determines the final thickness of oxide. A model is proposed to explain the oxide‐growth mechanism.

Journal ArticleDOI
TL;DR: In this paper, a lattice diffusion of cations is proposed to account for segregation of transition elements in scales on oxidized ferrous alloys, based on considerations of diffusion paths through close-packed oxide lattices, the mobility of a cation is related to the difference in stabilization energies for octahedral and for tetrahedral sites.
Abstract: A mechanism based on lattice diffusion of cations is proposed to account for segregation of transition elements in scales on oxidized ferrous alloys. From considerations of diffusion paths through close-packed oxide lattices, the mobility of a cation is related to the difference in stabilization energies for octahedral and for tetrahedral sites, as estimated from crystal field theory. The proposed correlation between crystal field preference energy and cation mobility is substantiated by reference to experimental oxidation rates for certain transition elements. The ranking order established for ease of diffusion of cations through close-packed oxide lattices is then shown to agree with the measured distribution of elements in scales formed on iron-chromium alloys by oxidation at 600°C in CO2-based gas. The model also accords with previously published data on partitioning in oxides.

Journal ArticleDOI
01 Jun 1972
TL;DR: In this article, the rate of dissociation or formation of water vapor or carbon dioxide on the iron surface is about an order of magnitude greater than that on the surface of wustite.
Abstract: The internal reduction of high-grade granular hematite ore in hydrogen and carbon monoxide, and also the internal oxidation of porous iron granules in CO2-CO mixtures have been investigated. To assist the interpretation of the rate data for porous iron and iron oxides, rate measurements have been made also with dense wustite, previously grown on iron by oxidation. The iron formed by reduction of dense wustite is porous, similar to that observed when porous hematite is reduced. It is found that the rate of dissociation or formation of water vapor or carbon dioxide on the iron surface is about an order of magnitude greater than that on the surface of wustite. The results of the previous investigations using dense iron and wustite are in general accord with the present findings. The rate of reduction of hematite increases with increasing pore surface area of the reduced oxide. The results indicate that the rate of reduction of granules is controlled primarily by the formation of H2O or CO2 on the pore walls of wustite. The specific rate constants evaluated from internal reduction, using the total pore surface area, are about 1/50 to 1/100 of those for dense wustite. These findings indicate that with porous wustite or iron, the effective pore surface area utilized is about 1 to 2 pct of the total pore surface area. The rate of reduction in H2-CO mixtures is in accord with that derived from the rate constants for reduction in H2 and CO.

Journal ArticleDOI
TL;DR: In this article, a number of solid solutions based on ferroelectric Bi4Ti3O12 have been determined, and the structural stability of the perovskite layer and the bismuth oxide layer is investigated.

Journal ArticleDOI
TL;DR: In this article, the oxidation of Si and GaAs single-crystals, both cleaved and etched, has been studied at room temperature in air and it has been shown that the oxidation rate of GaAs follows the direct exponential law at least within a 2 years time interval.

Journal ArticleDOI
01 May 1972
TL;DR: In this article, single crystals of five low molecular weight and one high molecular weight fractions of Poly(ethylene-oxide) were grown isothermally from the supercooled melt using the self seeding procedure.
Abstract: SummarySingle crystals of five low molecular weight and one high m. w. fractions of Poly(ethylene-oxide) were grown isothermally from the supercooled melt using the self seeding procedure. Growth was arrested by rapid quenching of the specimens, which gives rise to highly contrasted outgrowths decorating all the nucleating sites of the crystals, whereas the homogeneously nucleated melt remains optically transparent. This self-decorating procedure delineates the crystal edges and outlines the surface roughness of the lamellae. The surface decoration contrast allows to distinguish between lamellae constituted by folded and fully extended chains.For the five low m. w. fractions the temperature coefficient of the growth rate,G, undergoes at least one sharp transition which can be interpreted by the stepwise variation of the thickness of growing lamellae with crystallization temperature,Tc. For each fraction the transition from extended chain to folded chain crystal growth is extremely sharp and it is accompanied by a radical change in the crystal habit and the surface texture of the lamellae.Chain folded lamellae thicken isothermally during their growth, provided they are surrounded by molten polymer. This isothermal extension of chains can be detected morphologically. It involves two different molecular mechanisms: a nucleation process characterized by incubation periodτ and a growth process characterized by a rateGΦ. Both of these parameters depend strongly onTc and molecular weight. All these features are discussed and tentatively interpreted in terms of kinetic theories of polymer crystal growth.ZusammenfassungEinkristalle von 5 niedermolekularen und einer hochmolekularen Fraktion von Polyäthylenoxyd wurden isotherm aus unterkühlter Schmelze unter Anwendung des self-seeding-Verfahrens kristallisiert. Das Wachstum der Kristallite wurde durch rasche Kühlung der Proben abgebrochen, was Anlaß zu hochkontrastierten Aufwachsungen führt, die die Kristallite umgeben, während die homogene Schmelze optisch transparent bleibt.Diese „Selbstdekorationsprozedur“ erfolgt an den Kanten und Außenlinien der Oberflächenrauhigkeiten der Lamelle. Das Verfahren erlaubt, zwischen Lamellen aus gefalteten Ketten und denen aus gestreckten zu unterscheiden.Für 5 niedermolekulare Fraktionen durchläuft der Temperaturkoeffizient der WachstumsgeschwindigkeitG mindestens einen scharfen Übergang, der durch die schrittweise Variation der Dicke der Lamellen mit der KristallisationstemperaturTc erklärt werden kann. Für jede Fraktion ist der Übergang von gestrecktkettigen zu gefaltetem Kristallwachstum extrem scharf und von einer radikalen Änderung im Habitus der Kristalle und der Oberflächentextur der Lamellen begleitet.Kettengefaltete Lamellen verdicken sich isotherm während ihres Wachsens, vorausgesetzt daß sie von geschmolzenen Polymeren umgeben sind. Diese isotherme Streckung der Ketten kann morphologisch beobachtet werden. Es spielen zwei verschiedene molekulare Mechanismen mit: Ein Keimbildungsprozess, charakterisiert durch eine Inkubationsperiodeτ und ein Wachstumsprozeß, charakterisiert durch seine GeschwindigkeitGΦ.Beide Parameter hängen stark vonTc und dem Molekulargewicht ab. Alle diese Wesenzüge werden diskutiert und interpretiert in Termen der kinetischen Theorien des Polymerwachstums.RésuméEn utilisant le procédé d'autoensemencement on a fait croître des monocristaux de divers Polyoxyéthylènes (cinq fractions de bas poids moléculaire et une de poids moléculaire élevé) à partir du polymère surfondu. Une trempe permet d'arrêter la croissance des cristaux et donne lieu à une décoration contrastée de tous les sites des cristaux susceptibles d'initier une croissance, alors que le liquide surfondue résiduel cristallise par germination homogène et reste transparent. Cette «autodécoration» délimite les bords du cristal et met en évidence la rugosité éventuelle de la surface des lamelles. La décoration superficielle permet de distinguer entre les lamelles formées de chaînes repliées et étendues.Pour les cinq fractions de bas poids moléculaire, la variation thermique de la vitesse de croissance,G, présente au moins une transition nette qui peut être interprétée par la variation discontinue de l'épaisseur des lamelles avec la température de cristallisationTc. Pour chaque fraction, la transition de la croissance en chaîne étirée à celle en chaîne repliée est très nette, et s'accompagne d'une modification importante de la forme des cristaux et de leur état de surface.Les lamelles formées de chaînes repliées s'épaississent d'une mainière isotherme pendant leur croissance si elles sont entourées par du polymère fondu. Cette extension isotherme des chaînes peut être observée morphologiquement. Elle implique deux mécanismes moléculaires différents: en processus de germination, caractérisé par un temps d'incubationτ, et un processus de croissance, caractérisé par une vitesse,GΦ. Ces deux paramètres dépendent fortement de la masse moléculaire et deTc. L'ensemble de ces phénomènes est analysé sur la base des théories cinétiques de la croissance des cristaux de polymères.

Journal ArticleDOI
TL;DR: In this article, the current density i+ of platinum oxide layer formation was measured in dependence on potential e, time t and coverage ϑ or the equivalent layer thickness under potentiostatic conditions in 0.5 M H2SO4.

Journal ArticleDOI
TL;DR: In this paper, a low-frequency noise model for the epitaxial-channel surface field effect structure is presented where random modulation of the channel conductance arises from fluctuation of charges trapped at the oxide trap states near the Si-SiO 2 interface.
Abstract: A theoretical low-frequency noise model for the epitaxial-channel surface field-effect structure is presented where random modulation of the channel conductance arises from fluctuation of charges trapped at the oxide trap states near the Si-SiO 2 interface. In this model, charge fluctuation in the oxide traps arises from carrier tunneling between the fast interface surface states and the oxide trap states. A second fluctuation, at higher frequencies, arises from the random thermal emission and capture of electrons and holes at the fast interface states through the thermal or Shockley-Read-Hall process. Different oxide trap densities were introduced into the interface region of the metal-oxide-silicon field-effect structures using a carefully controlled and reproducible oxygen heat treatment technique. Energy distributions of the oxide trap densities are obtained from capacitance measurements. Humps are observed between the flat band and the onset of strong surface inversion (lower half of the bandgap) in both the noise power and the oxide trap density versus gate voltage (or surface band bending) plots. Theoretical noise power calculations using the experimental oxide trap density profile from the capacitance-voltage data agree very well with the experimental noise humps in both magnitudes and fine structures. It is shown that the frequency spectra of noise depend strongly on the oxide trap density profile in the oxide. It is suggested that the oxide traps are due to the excess oxygen at the SiO 2 -Si interface.

Patent
R Salemme1
02 Feb 1972
TL;DR: Sulfonated polyxylylene oxide membranes are very effective for the separation of water vapor from other gases as discussed by the authors, and such a gas separation is very selective and may be readily accomplished at atmospheric pressure.
Abstract: Sulfonated polyxylylene oxide membranes are very effective for the separation of water vapor from other gases. Such a gas separation is very selective and may be readily accomplished at atmospheric pressure. Membrane devices for humidifying or drying an air stream are described.

Journal ArticleDOI
TL;DR: In this article, the diffraction results for the Fe-Cr foils and previous diffraction studies for Fe foils were compared and it was concluded that the films tend to become amorphous as the Cr content of the alloy is increased.

Journal ArticleDOI
TL;DR: In this article, the formation and reduction of platinum oxide layers in 0.5 M H2SO4 was investigated by galvanostatic pulse measurements, and the results led to the conclusion that the properties of the layer are dependent on the formation conditions of layer, i.e. the formation rate, the ageing of layer and the method of the setting of the coverage (anodic/increase or cathodic/decrease).

Journal ArticleDOI
TL;DR: By ESR technique, the formation of adsorbed O2− and O− on TiSiO2, VSiO2 and Vγ-Al2O3 has been studied as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the thin oxide films of TiO2, ZrO2 and HfO2 have been deposited on single crystals of (111) silicon, by chemical vapor deposition (CVD) of the respective organometallic compounds.

Journal ArticleDOI
TL;DR: In this paper, the addition of a few mole per cent of or to the oxidizing atmosphere has been found to significantly improve the electrical stability of dry-grown films and to decrease the mobile ion contamination originating from the furnace tube, but to a large extent also passivates the films against ionic instabilities caused by contaminated metallization.
Abstract: The addition of a few mole per cent of or to the oxidizing atmosphere has been found to significantly improve the electrical stability of dry‐grown films. The results reported here were obtained with 30 min oxidation at 1150°C. The process not only decreases the mobile ion contamination originating from the furnace tube, but to a large extent also passivates the films against ionic instabilities caused by contaminated metallization. The use of or apparently also reduces the number of surface states at the interface. No significant change between standard and or oxides was observed in oxide charge, dielectric strength, dielectric constant and index of refraction, but the oxidation rate of Si is considerably increased in the presence of or . The mixture of and dry was also found to be very effective for the "cleaning" of quartz furnace tubes.

Journal ArticleDOI
TL;DR: In this article, the authors measured the oxygen uptake of clean nickel from 24° to 450°C at oxygen pressures of. Ultra high vacuum techniques made it possible to start oxidation on specimens free of oxide and surface impurities such as C, Si, and S. This was followed by slower oxidation obeying a logarithmic rate law over the thickness range 8-30Aa.
Abstract: The oxidation of "clean" nickel has been investigated from 24° to 450°C at oxygen pressures of . Ultra‐high vacuum techniques made it possible to start oxidation on specimens free of oxide and surface impurities such as C, Si, and S. Oxygen uptake was measured manometrically with a capacitance gauge of submonolayer sensitivity. Initial rapid oxygen adsorption (and place exchange) on nickel was followed by slower oxidation obeying a logarithmic rate law over the thickness range 8–30Aa. Growth of thicker films was in accord with a parabolic rate law, transport through the oxide occurring predominantly via easy diffusion paths. The value of 41 kcal·mole−1 calculated from an Arrhenius plot of the parabolic rate constants from 300° to 450°C is an approximate measure of the activation energy for growth via leakage paths. A p1/6 dependence of the parabolic growth rate on oxygen pressure was found at 450°C.

Journal ArticleDOI
TL;DR: In this article, the voltammograms of Pt, Pd, Rh, Ir and Au are compared in sulphuric acid for concentrations of 1.5 M. The difference between the anion adsorption (Cl− and SO42−) and strong sulphURic acid on the shapes of the voltamograms is demonstrated.

Journal ArticleDOI
TL;DR: The vibrational frequencies of alkali metal cations in their equilibrium positions in borate, phosphate, germanate, silicate and vanadate alkali oxide glasses have been observed as cation mass dependent bands in the far-i.r. spectra of these vitreous systems as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, an oxygen uptake model based on an incorporation-chemisorption transition is proposed to explain the "stable layer" associated with the aluminum oxygen reaction at room temperature.

Patent
20 Apr 1972
TL;DR: In this paper, a method for direct bonding of metallic members to non-metallic members at elevated temperatures in a controlled reactive atmosphere without resorting to the use of electroless plating, vacuum deposition or intermediate metals is described.
Abstract: A method is described for direct bonding of metallic members to non-metallic members at elevated temperatures in a controlled reactive atmosphere without resorting to the use of electroless plating, vacuum deposition or intermediate metals. The method comprises placing a metal member such as copper, for example, in contact with a non-metallic substrate, such as alumina, heating the metal member and the substrate to a temperature slightly below the melting of the metal, e.g., between approximately 1,065*C. and 1,080*C. for copper, the heating being performed in a reactive atmosphere, such as an oxidizing atmosphere, for a sufficient time to create a copper-copper oxide eutectic melt which, upon cooling, bonds the copper to the substrate. Various metals, non-metals and reactive gases are described for direct bonding.

Journal ArticleDOI
TL;DR: In this paper, the role of various impurities in the thermally grown silicon dioxide films of metal-oxide-semiconductor (MOS) structures has been investigated and it has been determined that aluminum and sodium within such films strongly influence the radiation-sensitivity of the corresponding MOS devices.
Abstract: The role of various impurities in the thermally grown silicon dioxide films of metal-oxide-semiconductor (MOS) structures has been investigated. It has been determined that aluminum and sodium within such films strongly influence the radiation-sensitivity of the corresponding MOS devices. The results of the present investigation indicate that much of the radiation-induced positive space charge accumulated within the silicon dioxide films is directly related to the drift and accumulation of ions such as those of sodium. Ionizing radiation, as fran cobalt-60 gamna rays, liberates sodium ions, which are bonded by coulombic forces to non-bridging oxygens, and consequently, the sodium ions drift in the applied gate fields. The space charge due to the accumulation of sodium near the silicon dioxide-silicon interface then causes a perturbation in the surface properties of the silicon. The insight afforded by the above model provides a basis for the fabrication of surface-controlled devices less sensitive to radiation, as well as for the fabrication of radiation dosimeters where the converse in radiation sensitivity is desired. Utilizing appropriate dopants in the silicon dioxide films the desired radiation hardening and dosimetry objectives can be realized.