scholarly journals Gem-Quality Tourmaline from LCT Pegmatite in Adamello Massif, Central Southern Alps, Italy: An Investigation of Its Mineralogy, Crystallography and 3D Inclusions

Minerals ◽  
2018 ◽  
Vol 8 (12) ◽  
pp. 593 ◽  
Author(s):  
Valeria Diella ◽  
Federico Pezzotta ◽  
Rosangela Bocchio ◽  
Nicoletta Marinoni ◽  
Fernando Cámara ◽  
...  
Keyword(s):  
Rare Earth ◽  
Manganese Content ◽  
Diffraction Method ◽  
Structural Data ◽  
Massif Central ◽  
X Ray ◽  
Geological Processes ◽  
Chemical Studies ◽  
Micro Tomography ◽  
Cation Sites

In the early 2000s, an exceptional discovery of gem-quality multi-coloured tourmalines, hosted in Litium-Cesium-Tantalum (LCT) pegmatites, was made in the Adamello Massif, Italy. Gem-quality tourmalines had never been found before in the Alps, and this new pegmatitic deposit is of particular interest and worthy of a detailed characterization. We studied a suite of faceted samples by classical gemmological methods, and fragments were studied with Synchrotron X-ray computed micro-tomography, which evidenced the occurrence of inclusions, cracks and voids. Electron Microprobe combined with Laser Ablation analyses were performed to determine major, minor and trace element contents. Selected samples were analysed by single crystal X-ray diffraction method. The specimens range in colour from colourless to yellow, pink, orange, light blue, green, amber, brownish-pink, purple and black. Chemically, the tourmalines range from fluor-elbaite to fluor-liddicoatite and rossmanite: these chemical changes occur in the same sample and affect the colour. Rare Earth Elements (REE) vary from 30 to 130 ppm with steep Light Rare Earth Elemts (LREE)-enriched patterns and a negative Eu-anomaly. Structural data confirmed the elbaitic composition and showed that high manganese content may induce the local static disorder at the O(1) anion site, coordinating the Y cation sites occupied, on average, by Li, Al and Mn2+ in equal proportions, confirming previous findings. In addition to the gemmological value, the crystal-chemical studies of tourmalines are unanimously considered to be a sensitive recorder of the geological processes leading to their formation, and therefore, this study may contribute to understanding the evolution of the pegmatites related to the intrusion of the Adamello pluton.

High Resolution EM Study of Wüstite

1974 ◽  
Vol 32 ◽  
pp. 352-353 ◽  
Author(s):  
Sumio Iijima
Keyword(s):  
High Resolution ◽  
Diffraction Method ◽  
X Ray Diffraction ◽  
Repeat Distance ◽  
X Ray ◽  
Integral Number ◽  
Deviation From Stoichiometry ◽  
Wide Range ◽  
Cation Sites ◽  
Range Of Variation

Wüstite (Fe1-x0) has recieved considerable attention because of a wide range of variation in x. The deviation from stoichiometry is known to be due to vacancies on cation sites. Koch and Cohen, having studied this material in detail using an X-ray diffraction method, concluded that the defects present in Fe1-x0 are clusters of 13 octahedral vacancies and 4 tetrahedral ions. These clusters are arranged periodically but the repeat distance in the [100] direction is not an integral number of structures of the basic NaCl-type. The observed spacing of superstructure peaks may correspond to the average repeat distance.

scholarly journals Al-Si-Re Alloys Cast by the Rapid Solidification Process / Stopy Al-Si-Re Odlewane Metodą Rapid Solidification

2015 ◽  
Vol 60 (4) ◽  
pp. 3057-3062
Author(s):  
M. Szymanek ◽  
B. Augustyn ◽  
D. Kapinos ◽  
J. Żelechowski ◽  
M. Bigaj
Keyword(s):  
Rare Earth ◽  
Rare Earth Elements ◽  
Rapid Solidification ◽  
Structure Refinement ◽  
Diffraction Method ◽  
Solidification Process ◽  
Thin Strip ◽  
X Ray Diffraction ◽  
X Ray ◽  
Casting Technique

The aim of the studies described in this article was to present the effect of rare earth elements on aluminium alloys produced by an unconventional casting technique. The article gives characteristics of the thin strip of Al-Si-RE alloy produced by Rapid Solidification (RS). The effect of rare earth elements on structure refinement, i.e. on the size of near-eutectic crystallites in an aluminium-silicon alloy, was discussed. To determine the size of crystallites, the Scherrer X-ray diffraction method was used. The results presented capture relationships showing the effect of variable casting parameters and chemical composition on microstructure of the examined alloys. Rapid Solidification applied to Al-Si alloys with the addition of mischmetal (Ce, La, Ne, Pr) refines their structure.

scholarly journals Structural And Electrical Properties Of The Selected Rare-Earth Oxychlorides

2015 ◽  
Vol 60 (3) ◽  
pp. 1595-1602 ◽  
Author(s):  
M. Dziubaniuk ◽  
J. Wyrwa ◽  
M. Bućko ◽  
M. Rękas
Keyword(s):  
Rare Earth ◽  
Electrical Properties ◽  
Single Phase ◽  
Electrochemical Impedance ◽  
Diffraction Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Average Grain Size ◽  
Structural And Electrical Properties ◽  
Sintering Conditions

Abstract The preparation and sintering conditions of the selected rare-earth oxychlorides REOCl (Re=La, Nd, Sm, Gd) were determined. The purity of materials phase compositions was confirmed by X-ray diffraction method. Further analysis of the data enabled lattice parameters and average grain size determination. The electrical properties of the single phase REOCl materials were investigated by Electrochemical Impedance Spectroscopy in wide temperature range in atmospheric air. The spectra were analyzed by the equivalent circuit fitting. Basing on the values of equivalent circuits parameters the specific conductivities were calculated and presented in the Arrhenius coordinates. Energies of activation were calculated. The determined structural and electrical properties of four different rare-earth oxychlorides were directly compared.

Temperature dependence of structure parameters in natural magnetite: single crystal X-ray studies from 126 to 773 K

1996 ◽  
Vol 52 (3) ◽  
pp. 450-457 ◽  
Author(s):  
H. Okudera ◽  
K. Kihara ◽  
T. Matsumoto
Keyword(s):  
Single Crystal ◽  
Temperature Dependence ◽  
Temperature Rise ◽  
Structural Parameters ◽  
Diffraction Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Dimensions ◽  
Increasing Temperature ◽  
Cation Sites

Structural parameters and their thermal changes in natural magnetite, Fe3O4, have been studied using the single-crystal X-ray diffraction method in the temperature range 126–773 K. The cell dimensions, oxygen coordinate and atomic mean square displacements (m.s.d.'s) reversibly change as a function of temperature. The coordinate of oxygen remains almost constant at x = 0.2549 (1) below ~600 K, but increases with increasing temperature above this temperature. This characteristic behavior of the oxygen coordinate with temperature indicates that the cation disordering over the tetrahedral (A) and octahedral (B) cation sites occurs above 600 K. All atomic m.s.d.'s increase monotonously with temperature rise. The m.s.d.'s of the B atom show a unique temperature dependence. At lower temperatures the B atom prefers to vibrate along [111], but this preference is reduced with a temperature rise up to 630 K, above which the m.s.d. normal to [111] becomes dominant.

X-ray micro tomography in the scanning electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 106-107 ◽  
Author(s):  
W. Brünger
Keyword(s):  
Electron Beam ◽  
Electron Microscope ◽  
Scanning Electron Microscope ◽  
Target Surface ◽  
The Body ◽  
X Rays ◽  
Cross Sectional ◽  
X Ray ◽  
Micro Tomography ◽  
Scanning Electron

Reconstructive tomography is a new technique in diagnostic radiology for imaging cross-sectional planes of the human body /1/. A collimated beam of X-rays is scanned through a thin slice of the body and the transmitted intensity is recorded by a detector giving a linear shadow graph or projection (see fig. 1). Many of these projections at different angles are used to reconstruct the body-layer, usually with the aid of a computer. The picture element size of present tomographic scanners is approximately 1.1 mm2.Micro tomography can be realized using the very fine X-ray source generated by the focused electron beam of a scanning electron microscope (see fig. 2). The translation of the X-ray source is done by a line scan of the electron beam on a polished target surface /2/. Projections at different angles are produced by rotating the object.During the registration of a single scan the electron beam is deflected in one direction only, while both deflections are operating in the display tube.

Tubulin structure at intermediate resolution

1995 ◽  
Vol 53 ◽  
pp. 852-853
Author(s):  
K. H. Downing ◽  
S. G. Wolf ◽  
E. Nogales
Keyword(s):  
High Resolution ◽  
Structural Data ◽  
Therapeutic Drug ◽  
Zinc Ions ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Negative Stain ◽  
Functional Mechanisms ◽  
Tubulin Structure

Microtubules are involved in a host of critical cell activities, many of which involve transport of organelles through the cell. Different sets of microtubules appear to form during the cell cycle for different functions. Knowledge of the structure of tubulin will be necessary in order to understand the various functional mechanisms of microtubule assemble, disassembly, and interaction with other molecules, but tubulin has so far resisted crystallization for x-ray diffraction studies. Fortuitously, in the presence of zinc ions, tubulin also forms two-dimensional, crystalline sheets that are ideally suited for study by electron microscopy. We have refined procedures for forming the sheets and preparing them for EM, and have been able to obtain high-resolution structural data that sheds light on the formation and stabilization of microtubules, and even the interaction with a therapeutic drug.Tubulin sheets had been extensively studied in negative stain, demonstrating that the same protofilament structure was formed in the sheets and microtubules. For high resolution studies, we have found that the sheets embedded in either glucose or tannin diffract to around 3 Å.

Impact of Rutile Fraction on TiO2 Visible-Light Absorption and Visible-Light-Induced Photocatalytic Activity

2018 ◽  
Author(s):  
David Maria Tobaldi ◽  
Luc Lajaunie ◽  
ana caetano ◽  
nejc rozman ◽  
Maria Paula Seabra ◽  
...  
Keyword(s):  
Photocatalytic Activity ◽  
Visible Light ◽  
Light Absorption ◽  
Solid Phase ◽  
Diffraction Method ◽  
Band Alignment ◽  
Quantitative Phase Analysis ◽  
Transmission Microscopy ◽  
Visible Light Absorption ◽  
X Ray

<div>Titanium dioxide is by far the most utilised semiconductor material for photocatalytic applications. Still, it is transparent to visible-light. Recently, it has been proved that a type-II band alignment for the rutile−anatase mixture would improve its visible-light absorption.</div><div>In this research paper we thoroughly characterised the real crystalline and amorphous phases of synthesised titanias – thermally treated at different temperatures to get distinct ratios of anatase-rutile-amorphous fraction – as well as that of three commercially available photocatalytic nano-TiO2. </div><div>The structural characterisation was done via advanced X-ray diffraction method, namely the Rietveld-RIR method, to attain a full quantitative phase analysis of the specimens. The microstructure was also investigated via an advanced X-ray method, the whole powder pattern modelling. These methods were validated combining advanced aberration-corrected scanning transmission microscopy and high-resolution electron energy-loss spectroscopy. The photocatalytic activity was assessed in the liquid- and gas-solid phase (employing rhodamine B and 4-chlorophenol, and isopropanol, respectively, as the organic substances to degrade) using a light source irradiating exclusively in the visible-range.</div><div>Optical spectroscopy showed that even a small fraction of rutile (2 wt%) is able to shift to lower energies the apparent optical band gap of an anatase-rutile mixed phase. But is this enough to attain a real photocatalytic activity promoted by merely visible-light?</div><div>We tried to give a reply to that question.</div><div>Photocatalytic activity results in the liquid-solid phase showed that a high surface hydroxylation led to specimen with superior visible light-induced catalytic activity (i.e. dye and ligand-to-metal charge transfer complexes sensitisation effects). That is: not photocatalysis <i>sensu-strictu</i>.</div><div>On the other hand, the gas-solid phase results showed that a higher amount of the rutile fraction (around 10 wt%), together with less recombination of the charge carriers, were more effective for an actual photocatalytic oxidation of isopropanol.</div>

A synchrotron X-ray study of the electron density in C-type rare earth oxides

1996 ◽  
Vol 52 (3) ◽  
pp. 414-422 ◽  
Author(s):  
E. N. Maslen ◽  
V. A. Streltsov ◽  
N. Ishizawa
Keyword(s):  
Heavy Metal ◽  
Rare Earth ◽  
Electron Density ◽  
Approximate Symmetry ◽  
Data Set ◽  
X Ray ◽  
Metal Atoms ◽  
Structure Factors ◽  
Deformation Electron Density ◽  
Synthetic Crystals

Structure factors for small synthetic crystals of the C-type rare earth (RE) sesquioxides Y2O3, Dy2O3 and Ho2O3 were measured with focused λ = 0.7000 (2) Å, synchrotron X-radiation, and for Ho2O3 were re-measured with an MoKα (λ = 0.71073 Å) source. Approximate symmetry in the deformation electron density (Δρ) around a RE atom with pseudo-octahedral O coordination matches the cation geometry. Interactions between heavy metal atoms have a pronounced effect on the Δρ map. The electron-density symmetry around a second RE atom is also perturbed significantly by cation–anion interactions. The compounds magnetic properties reflect this complexity. Space group Ia{\bar 3}, cubic, Z = 16, T = 293 K: Y2O3, Mr = 225.82, a = 10.5981 (7) Å, V = 1190.4 (2) Å3, Dx = 5.040 Mg m−3, μ 0.7 = 37.01 mm−1, F(000) = 1632, R = 0.067, wR = 0.067, S = 9.0 (2) for 1098 unique reflections; Dy2O3, Mr = 373.00, a = 10.6706 (7) Å, V = 1215.0 (2) Å3, Dx = 8.156 Mg m−3, μ 0.7 = 44.84 mm−1, F(000) = 2496, R = 0.056, wR = 0.051, S = 7.5 (2) for 1113 unique reflections; Ho2O3, Mr = 377.86, a = 10.606 (2) Å, V = 1193.0 (7) Å3, Dx = 8.415 Mg m−3, μ 0.7 = 48.51 mm−1 F(000) = 2528, R = 0.072, wR = 0.045, S = 9.2 (2) for 1098 unique reflections of the synchrotron data set.

Sign in / Sign up

Export Citation Format

Share Document