The available literature on the crystal structure of the metastable alumina polymorphs and their associated transitions is critically reviewed and summarized. All the metastable alumina structures have been identified as ordered or partially ordered cation arrays on the interstitial sites of an approximately close-packed oxygen sublattice (either face-centered cubic or hexagonal close packed). The analysis of the symmetry relations between reported alumina polymorphs having an approximately face-centered cubic packing of the oxygen anions allows for an exact interpretation of all the complex domain structures that have been observed experimentally. Possible mechanisms for the phase transitions between the different alumina polymorphs also are discussed.

Metastable alumina polymorphs : Crystal structures and transition sequences

Interpretation theory in applied geophysics: Grant, F S ... Interpretation theory in applied geophysics Unknown Binding – January 1, 1965 5.0 out of 5 stars 1 rating. See all formats and editions Hide other formats and editions. The Amazon Book Review Book recommendations, author interviews, editors' picks, and more. Read it now. Enter your mobile number or email address below and we'll send you a ...

Interpretation Theory in Applied Geophysics Grant (McGraw-Hill, 140s.)

A correlation of O-H stretching frequencies (from infrared spectroscopy) with O…O and H…O bond lengths (from structural data) of minerals was established. References on 65 minerals yielded 125 data pairs for the d(O…O)-v correlation; due to rare or inaccurate data on proton positions, only 47 data pairs were used for the d(H… O)-v correlation. The data cover a wide range of wavenumbers from 1000 to 3738 cm−1 and O…O distances from 2.44 to 3.5 A. They originate from silicates, (oxy)hydroxides, carbonates, sulfates, phosphates, and arsenates with OH−, H2O, or even H3O 2 − units forming very strong to very weak H bonds. The correlation function was established in the form v(cm−1) = 3592−304 · 109·exp(-d(O…O)/0.1321), R 2 = 0.96. Because of deviations from ideal straight H bonds, i.e. bent or bifurcated geometry, dynamic proton behavior, but also due to factor group splitting and cationic effects, data scatter considerably around the regression line. The trends of previous correlation curves and of theoretical considerations were confirmed.

Correlation of O-H Stretching Frequencies and O-H O Hydrogen Bond Lengths in Minerals

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.

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

Publisher Summary This chapter discusses those methodological and theoretical problems that are of greatest concern to shell midden archaeologists. Archaeologists dealing with problems posed by shell middens often seem oblivious of substantial contributions made in previous work—understandably so, because the published literature of this subdiscipline is voluminous and has never been adequately synthesized. As a consequence, many archaeologists have busied themselves with reinventing the wheel, rediscovering useful methods or cogent explanations originally developed years before. While shell middens offer exceptional opportunities to study certain aspects of food gathering, they are by no means exclusively the product of hunting and gathering societies. The chapter reviews ethnographic and ethnohistoric data on shellfish gathering by members of many types of societies, whether primarily dependent on food gathering or food production, to the extent possible given the often incomplete nature of such sources. The chapter presents a comparison of the salient characteristics of different molluscan exploitative strategies and presents some hypotheses relating to the origins, maintenance, and decline of intensive molluscan exploitation.

Shellfish Gathering and Shell Midden Archaeology

The crystal structure of a synthetic boehmite sample has been refined to an R of 0.047 in the space group Amam from X-ray powder diffraction data. Inclusion of hydrogen atoms and/or refinement in the space group A21am gave poorer results. Cell dimensions were determined as a = 3.6936 (± 0.0003), b = 12.214 (± 0.001), c = 2.8679 (± 0.0003) A. All Al-O(OH) distances lie between 1.88 and 1.91 A. Shared octahedral edges are 2.51–2.52 A, and unshared octahedral edges are 2.86–2.87 A, in excellent agreement with those for layered silicates. The O-H … O distance between contiguous octahedral sheets is 2.71 A. The computed X-ray pattern matches closely with the experimental pattern, indicating the degree to which the crystal structure has been determined.

The crystal structure of boehmite

Shell growth in Tivela stultorum (Mawe, 1823) and Callista chione (Linnaeus, 1758) (Bivalvia): annual periodicity, latitudinal differences, and diminution with age

The crystal structure of a deuterated synthetic boehmite powder, γ-AIOOD, has been determined by time-of-flight neutron diffraction and Rietveld profile refinement in space group Cmcm to a weighted profile R of 3.71%. Cell dimensions are a = 2.868(1), b = 12.2336(4), and C = 3.6923(1) A. Alternate space groups for the boehmite structure suggested in the recent literature were found to be unacceptable. Atom positions, bond distances, and angles, with the exception of those involving hydrogen, were nearly identical to those determined by R. J. Hill in 1981 who studied a single crystal of boehmite by X-ray diffraction. All atoms were refined with anisotropic thermal parameters. The b value is 0.013 A larger, and the thermal ellipsoids of oxygen are slightly more anisotropic than those reported by Hill and may reflect the different samples studied.

Structure refinement of deuterated boehmite

Comparison of experimental and calculated X-ray powder diffraction data for boehmite

Investigation of a naturally occurring mixture of dioctahedral micas prompted an examination of X-ray diffraction (XRD) techniques for obtaining quantitative estimates of 1M and 2M1 mica proportions. A method for determining quantitative estimates has been developed that includes the effect of preferred orientation of mica particles as described by the March function. A diagram is presented from which the percentage of 2M1 and the March parameter (r) can be obtained from two peak-area ratios: 2.80 A/5.0 A and 2.80 A/2.58 A, which are measured on observed XRD patterns of mica mixtures. The ability of this peak-area ratio diagram to predict reasonably accurate proportions of 1M and 2M1 micas was tested by comparing calculated and observed XRD patterns over a range of 20 values from 16° to 40° for size-fractionated mixtures. Lack of accurate crystal-structure data for dioctahedral 1M mica proved an impediment to obtaining improved quantitative estimates of mica proportions.

Charles E. Corbató

Papers

The crystal structure of boehmite

Shell growth in Tivela stultorum (Mawe, 1823) and Callista chione (Linnaeus, 1758) (Bivalvia): annual periodicity, latitudinal differences, and diminution with age

Structure refinement of deuterated boehmite

Comparison of experimental and calculated X-ray powder diffraction data for boehmite

Quantitative analysis of mixtures of 1m and 2m1 dioctahedral micas by x-ray diffraction