Pseudoboehmite

About: Pseudoboehmite is a research topic. Over the lifetime, 603 publications have been published within this topic receiving 9391 citations.

XPS study of the major minerals in bauxite: gibbsite, bayerite and (pseudo-)boehmite.

Abstract: Synthetic corundum (Al2O3), gibbsite (Al(OH)3), bayerite (Al(OH)3), boehmite (AlO(OH)) and pseudoboehmite (AlO(OH)) have been studied by high resolution XPS. The chemical compositions based on the XPS survey scans were in good agreement with the expected composition. High resolution Al2p scans showed no significant changes in binding energy, with all values between 73.9 and 74.4 eV. Only bayerite showed two transitions, associated with the presence of amorphous material in the sample. More information about the chemical and crystallographic environment was obtained from the O1s high resolution spectra. Here a clear distinction could be made between oxygen in the crystal structure, hydroxyl groups and adsorbed water. Oxygen in the crystal structure was characterised by a binding energy of about 530.6 eV in all minerals. Hydroxyl groups, present either in the crystal structure or on the surface, exhibited binding energies around 531.9 eV, while water on the surface showed binding energies around 533.0 eV. A distinction could be made between boehmite and pseudoboehmite based on the slightly lower ratio of oxygen to hydroxyl groups and water in pseudoboehmite.

Synthesis of High-Surface-Area Alumina Aerogels without the Use of Alkoxide Precursors

Abstract: Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl3·6H2O or Al(NO3)3·9H2O, followed by drying with supercritical CO2. This technique affords low-density (60−130 kg/m3), high-surface-area (600−700 m2/g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, high-resolution transmission electron microscopy, powder X-ray diffraction, solid-state NMR, acoustic measurements, and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl3 in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2−5 nm in diameter and of varying lengths, whereas the aerogels prepared from hydrated Al(NO3)3 in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5−15 nm ra...

Aluminum + water reaction

Abstract: During the aluminum + water reaction, aluminum ions and electrons are removed in separate steps at different sites on the surface. Ions are removed nearly uniform over the entire surface, which is covered at all times with a thin amorphous oxide film. The outer surface of this oxide is first hydrolyzed and then dissolves to yield soluble species which either remain in solution or, at intermediate values of pH, precipitate as a porous hydroxide of extremely small particle size. The hydroxide appears to be identical to pseudoboehmite. The overall rate of the corrosion reaction is controlled by this dissolution of the film and by the disposition of the soluble products. The corrosion rate is nearly independent of specimen potential, solution pH below 10, and of the presence in solution of many salts at concentrations as high as 1 mole/1. The rate is strongly dependent on temperature, on the presence of specific inhibitive salts, and increases rapidly at high pH. In environments which preclude oxide dissolution, e.g., water + dioxane mixtures or water vapour, the corrosion rate is drastically reduced. The corrosion rate is constant when no solid hydroxide is formed, and is otherwise a strong function of the amount of reaction. At high temperatures the rate decreases with time as the precipitated hydroxide hinders transport. At lower temperatures the rate may first increase with time as nucleation of hydroxide provides sinks for soluble species close to the interface, and then at long times the rate decreases as the hydroxide layer thickens. Electrons are removed more readily at special sites, and in our specimens these sites were primarily at the grain boundaries. Electron removal results in increased hydroxyl ion concentration, and this in turn results in more rapid attack on the protective oxide. At such cathodes the oxide film is maintained at a small constant thickness at which there is a balance between the rates of its dissolution by the basic solution and growth because of the great affinity of aluminum for oxygen. At cathodic sites there is thus anodic activity as well, but electron removal predominates. The metal is corroded more rapidly at cathodes, producing pronounced grain boundary attack in our specimens. Application of anodic potentials eliminates grain boundary attack.

The mechanism of phosphate adsorption by kaolinite, gibbsite, and pseudoboehmite

Abstract: Summary The adsorption isotherms (20°C) of phosphate on two potassium kaolinites and two aluminium oxides have been determined at pH values from 3 to 10 and at concentrations ranging from 10−4 to 10−2M. The reversibility of the adsorption with respect to pH and concentration has also been examined. The isotherms result from at least three types of adsorption site (regions I, II, and III) of widely different reactivities. The number of adsorption sites increases to a limit with decrease in pH for regions I and II. The behaviour of region III is more complex. The different adsorbents behave in essentially the same manner and differ only in the number of adsorption sites. It is tentatively suggested that regions I and II are located on an edge –Al(OH)2 of the adsorbents, while region III results from penetration into some amorphous region of the crystal surface.

Characterization of the oxide/hydroxide surface of aluminium using x‐ray photoelectron spectroscopy: a procedure for curve fitting the O 1s core level

Abstract: The performance of coated and bonded aluminium relies heavily upon its surface chemistry and hence characterization of the aluminium surface is important. A method to quantify the hydroxide concentration at aluminium oxide/hydroxide surfaces by curve fitting the O 1s peak is developed and tested in this paper. Pseudoboehmite, AlO(OH), is formed at the surface of aluminium after immersion in boiling water. The surface of this material was used to determine the binding energy of the unresolved O 1s component peaks that were referenced to the binding energy of the Al 2p oxide component. In vacuo heating resulted in changes in the elemental and functional composition that were consistent with dehydration of the pseudoboehmite. It is proposed that the resultant film comprises γ-alumina with residual hydroxide groups. The O 1s curve-fitting method was applied to air-formed films with known atmospheric exposure histories before and after heating in vacuo. The change in both the elemental composition and functional stoichiometry of the films upon heating was consistent with significant but incomplete dehydration. The probable surface phases are determined from the functional and elemental composition. Copyright © 2000 John Wiley & Sons, Ltd.