Showing papers on "Oxide published in 1974"

Site-binding model of the electrical double layer at the oxide/water interface

Abstract: A site-binding model of the oxide/aqueous electrolyte interface is introduced, in which it is proposed that the adsorbed counter ions form interfacial ion pairs with discrete charged surface groups. This model is used to calculate theoretical surface charge densities of the potential-determining (H+/OH–) ions and the potential at the Outer Helmholtz Plane, which are shown to be consistent with experimental data for oxides. An explanation is provided for the difference between silica and most other oxides in terms of the dissociation constants of the surface hydroxyl groups.

X-Ray photoelectron spectroscopy of iron–oxygen systems

Abstract: X-Ray photoelectron spectroscopy has been used to study a series of iron oxides. It has been shown that iron metal has a different ionisation energy from a number of iron(III) oxides. Small perturbations to the energy of the iron (III) 2p electrons can be attributed to changes in crystal structure. Multiplet splitting and shake-up in the iron oxides contributes to iron 2p peak widths. The chemisorption of water has a marked effect upon the observed peak profiles; the oxygen 1s peaks due to oxide, hydroxyl, and adsorbed water have been characterised.

Oxides and Oxide Films

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The oxidation of metals

Abstract: A detailed review of the principles governing the oxidation of metals is presented. It covers the initial stages of oxidation, oxide film formation, thick film and scale formation and oxide structure.

The oxidation mechanism of Ni3Al containing yttrium

Abstract: The high-temperature oxidation behavior of Ni3Al (Ni-13.2 wt.% Al) with and without additions of 0.5 wt.% yttrium has been studied over the range of 900–1200°C in air. None of the commonly accepted rate laws were followed by the kinetics. Although the weight gains of samples containing yttrium were consistently 10–20% greater than those without yttrium, the steady-state scaling rates were identical. A quantitative x-ray diffraction technique was used to determine the kinetics of growth of the protective alpha-alumina layer (one of several oxides formed). The alumina growth followed the parabolic rate law under all conditions studied. The rate-controlling transport process in alumina was the enhanced diffusion of oxygen down grain boundaries. The presence of yttrium as nickel-rich intermetallics promoted the formation of nickel aluminate (spinel). A marked increase in scale adherence was observed for short times. At longer times, however, the outer layer of spinel and unreacted nickel oxide spalled off along with some of the inner alumina layer. Loss of adherence was caused by a complex yttrium-aluminum oxide which formed by the solid-state reaction of yttria and alumina. The poor scale adherence on Ni3Al was due to the formation of voids at the alloy-oxide interface. These voids concentrated the athermal stresses above the oxide-to-metal adherence strength. The voids were produced as a result of the selective oxidation of aluminum resulting from a “Kirkendall” effect in the substrate. During the selective oxidation process, a vacancy flux directed from the matrix to the metaloxide interface resulted in a supersaturation of vacancies. Equilibrium was maintained by the condensation of excess vacancies. The presence of yttrium as either nickel-rich intermetallics or internal oxide prevented the voids from forming. The yttrium-rich particles relieved the matrix of vacancy supersaturation by providing vacancy sinks. The chemical nature of the particles does not seem important. A necessary and sufficient condition for an effective vacancy sink appears to be the presence of an incoherent boundary between particle and matrix.

Composition—property relationships in inorganic oxide glasses

Abstract: By regarding glasses as oxygen polymers with a cross-linked network structure that can have different packing densities and varying degrees of cross-linking according to which network-forming elements and cations are present, the way in which many of their properties change with composition can be explained, at least qualitatively, in terms of the corresponding changes in cross-link density and network packing. The packing of an oxide network is conveniently measured by the oxygen density of the glass, and this and the cross-link density are readily calculated from the composition and actual density.

Wetting of thin layers of SiO2 by water

Abstract: We have measured the contact angle θ of water on silicon and on very thin layers of silicon dioxide grown on silicon. The silicon is hydrophobic and θ is near 90°. Oxides thicker than 30 A are hydrophilic and θ is near 0°. For intermediate thicknesses, θ varies smoothly between these limits. Our results show that the interaction energy between water and the solid surface depends strongly on the oxide thickness. Consideration of different possible interactions leads us to conclude that this is due to corresponding changes in the structure or composition of the oxide surface.

The effect of yttrium and thorium on the oxidation behavior of Ni-Cr-Al alloys

Abstract: The effect of quaternary additions of 0.5% Y, 0.5 and 1.0% Th to a base alloy of Ni-10CR-5Al on the oxidation behavior and mechanism was studied during oxidation in air over the range of 1000 to 1200 C. The presence of yttrium decreased the oxidation kinetics slightly, whereas, the addition of thorium caused a slight increase. Oxide scale adherence was markedly improved by the addition of the quaternary elements. Although a number of oxides formed on yttrium containing alloys, quantitative X-ray diffraction clearly showed that the rate-controlling step was the diffusion of aluminum through short circuit paths in a thin layer of alumina that formed parabolically with time. Although the scale adherence of the yttrium containing alloy was considerably better than the base alloys, spalling did occur that was attributed to the formation of the voluminous YAG particles which grew in a mushroom-like manner, lifting the protective scale off the subrate locally. The YAG particles formed primarily at grain boundaries in the substrate in which the yttrium originally existed as YNi9.

Adsorption of aqueous mercury (II) complexes at the oxide/water interface

Abstract: The interfacial behavior of Hg(II) is similar to other hydrolyzable metal ions at the oxide/water interface in that the hydrolysis products adsorb strongly and can reverse the charge of the silica/water interface. However, the halide complexes of Hg(II), e.g., HgCl2°, are not strongly adsorbed at the oxide/water interface. Consequently, the adsorption of inorganic mercury(II) on the inorganic oxide components of marine sediments is likely to be very small.

The wetting of carbon by aluminium and aluminium alloys

Abstract: The contact angle made by molten aluminium with vitreous carbon was measured by the sessile drop method in vacuum at temperatures up to 1100° C. The effect on wetting behaviour of the oxide layer on the molten metal was highlighted by using two samples of aluminium in different states of oxidation. The investigation involved the variation of certain parameters affecting the stability of the oxide film, e.g. the temperature, additions of Ti, Si, Cr, Be, Ca and Li to aluminium and the time held at a certain temperature. The state of the molten aluminium surface under various experimental conditions was determined indirectly by surface tension measurements.

X-Ray photoelectron spectroscopy of some uranium oxide phases

Abstract: X-Ray photoelectron spectra of a variety of uranium oxides have been studied and compared with the spectrum obtained from the pure metal. The oxide phases studied were UO2·0, UO2·1, UO2·2, U4O9, U3O7, U3O8, and γ-UO3 where the formal oxidation number of uranium alters from IV to VI. Significant chemical shifts observed for U 4f and O 1s peaks are explained by consideration of chemical structure and changes in uranium and oxygen oxidation states. The surface oxidation of uranium dioxide powder in air has been studied by comparing the spectra with those of UO2 pellets and higher uranium oxides.

The binding equilibrium of sodium dodecyl sulfate to poly(ethylene oxide) in 0.1 M sodium chloride solution at 30°C

Abstract: The binding equilibrium of sodium dodecyl sulfate (SDS) to poly(ethylene oxide) in 01 M sodium chloride solution at 30°C was determined by using a dialysis technique The binding isotherm was characterized by a sudden uprise near 1 mM SDS and a saturation tendency towards the cinc (15 mM) The completion of binding in such a narrow concentration range is attributable to a strong cohesion between bound surfactant molecules, and to a smallness of the surfactanr cluster which is considered as distributed along the polymer chain

Use of the Langmuir method for kinetic studies of decomposition reactions: calcite (CaCO3)

Abstract: The Langmuir method for measurement of vapour pressures has been tested for use in studies of decomposition reactions. The isothermal weight loss in vacuum from cleavage (10text-decoration:overline11) planes of calcite (CaCO3) single crystals was measured continuously at temperatures from 934 to 1013 K. The rate was constant until approximately 80% of a 1 mm slice had decomposed. The apparent activation enthalpy was 205 kJ (49 kcal) mol–1. Micrographic examination showed an approximately 30 µm thick layer, probably a metastable form of calcium oxide, separating the calcite from the growing layer of oriented stable calcium oxide. The 30 µm layer yielded a single X-ray diffraction peak which was displaced slightly from the strongest (220) peak of the oriented normal calcium oxide. Lower apparent activation enthalpies measured in previous studies of calcite decomposition in inert atmospheres are suggested to result either from partial diffusion control of the process or from catalysis of the direct formation of normal calcium oxide by carbon dioxide or a component of the system atmosphere. The ratio of the measured decomposition rate in vacuum to the maximum rate, which can be calculated from the Hertz–Knudsen–Langmuir equation, is suggested to be a useful parameter in correlating and predicting decomposition reaction rates.

The thermal decomposition of calcium, sodium, silver and copper(II) acetates

Abstract: The thermal decomposition of the acetates of calcium, sodium, silver and copper(II) have been investigated using thermogravimetry and differential thermal analysis, together with analysis of the gaseous products formed during the decomposition process. The results indicate that the major organic product formed is either acetone or acetic acid, depending on whether the final solid product is the oxide or the metal.

Production of metal ion containing carbon fibers useful in electron shielding applications

Abstract: An improved process is provided for the formation of metal ion containing carbon fibers which particularly are suited for utilization in electron shielding applications. An acrylic fibrous material is formed having substantially uniformly dispersed therein a halide of a transition metal. The metal halide (e.g. a chloride) present within the fibrous material is (1) converted to an oxide, (2) the fibrous material containing the metal oxide is heated in an oxygen-containing atmosphere until thermally stabilized, and (3) the thermally stabilized fibrous material is carbonized or carbonized and graphitized at a more highly elevated temperature in an appropriate atmosphere. The resulting product comprises ions of a transition metal substantially uniformly dispersed in an amorphous carbon or graphitic carbon matrix. The halide of a transition metal may be incorporated into the acrylic precursor by co-spinning and/or padding prior to thermal stabilization. The conversion of the halide of a transition metal to an oxide prior to thermal stabilization may be conducted by contact with a base or with an oxidizing agent as described.

The Growth of Hydrous Oxide Films on Aluminum

Abstract: The weight gains of Al specimens immersed for short times in water at 50°–70°C were measured. An analysis of these data and published results at other temperatures indicated that the kinetics of pseudoboehmite film growth in the temperature range 50°–100°C is determined initially by the nucleation and growth of hydrolysis sites on the amorphous oxide surface, and subsequently by solid‐state diffusion through the pseudoboehmite layer. At 40° C, pseudoboehmite and bayerite were observed to grow simultaneously at first, with bayerite crystallization eventually becoming the dominant process. The two oxide phases occupied completely separate layers.

Iron-containing mica flake pigments

Abstract: Novel mica flake pigments optionally coated with TiO2, ZrO2 and/or the hydrates thereof, having a uniform iron-containing layer thereon consisting of an iron(III) oxide hydroxide, magnetite and/or the Fe2O3 modifications obtained therefrom by annealing at a temperature below 1,100* C., are produced by gradually adding an aqueous solution of an iron salt in the presence of an oxidizing agent, to an aqueous suspension of the mica flakes at a constant temperature and a constant pH, thereby forming on the mica flakes a continuous uniform layer consisting solely of a single iron(III) oxide hydroxide modification or of magnetite. The thus-coated flakes are then separated, washed, dried and optionally annealed in a conventional manner at a temperature of up to 1,100* C. to convert the layer to Alpha Fe2O3 or gamma -Fe2O3.