1,720,974 research outputs found
Augite-pigeonite exsolution: kinetics of the homogenisation
No full text10 International symposium on Experimental mineralogy petrology and geochemistr
Augite-pigeonite exsolution: kinetics of the homogenisation
No full text10 International symposium on Experimental mineralogy petrology and geochemistr
Electron diffraction tomography for the characterization of sub-micrometric minerals: application to metamict phases
No full textSingle-crystal X-ray diffraction can be performed only on crystalline domains of some cubic microns, while most
of hitherto unsolved minerals and many new synthetic phases do not grow in crystals of such dimensions. On
the other hand, interpretation of X-ray powder diffraction data may be problematic for polyphasic samples and
structures characterized by large cell parameters or pseudo-symmetry. Electron diffraction is able to deliver 3D
structural data from single crystallites of few nanometers. This ability derives from the high cross section
between electrons and matter and the possibility to focus the electron beam into a nanometric probe. In the
last years, electron diffraction tomography (EDT) emerged as an efficient method for acquiring complete and
quasi-kinematic data sets for ab-initio structure determination of sub-micrometric phases (Kolb et al., 2011).
The mineral charoite was one of the first structures determined on the basis of EDT data, and still one of the
trickiest crystallographic cases faced by electron diffraction. Despite the fact that charoite is a well-known and
commercially exploited mineral, its symmetry and structure determination was hampered because two
commensurate and pseudo-symmetric polytypes grow together inside fibers less than 1 μm thick
(Rozhdestvenskaya et al., 2011). In recent years, tomographic electron diffraction has been used for the
characterization of several minerals and products of experimental geology occurring as minor, sub-micrometric
phases in poly-mineralogical associations. The porous (S2)1+x[Bi9-xTex(OH)6O8(SO4)2]2 was the first natural phase
initially recognized, and subsequently structurally determined, by EDT alone (Capitani et al., 2014).
Recently, EDT has been employed for the characterization of metamict phases. Metamict minerals undergo
structural changes and amorphization due to the radioactive decay of hosted elements. Phase identification is
commonly done on the basis of compositional data alone, or by powder diffraction performed after the sample
has been heated in order to produce re-crystallization. Still, different compositional and mineralogical domains
may merge in the process. We therefore exploited EDT for the characterization of sub-micrometric crystalline
relicts in metamict domains, allowing single-crystal ab-initio determination of natural samples without the
need of any physical treatment
Near-atomic images of interfaces between twin-related lamellae in a synthetic 6H-SiC sample
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
TEM investigations of Ag- and Cu-free lillianite and heyrovskyite from Vulcano (Aeolian Islands, Italy)
No full textThermal decomposition of cement–asbestos at 1100 °C: how much “safe” is “safe”?
No full textThe products of cement-asbestos treated in air at 1100 degrees C were characterized by a multi-methodological approach to determine: (i) the effective deactivation of harmful asbestos fibers; (ii) the mineralogy and microstructure of the inert product and its possible use as a secondary raw material (SRM); and (iii) any potential health hazard of the SRM. For this purpose, energy-dispersive X-ray fluorescence spectrometry (EDXRF), X-ray powder diffraction (XRPD), scanning, and transmission electron microscopy (SEM and TEM) analyses were performed. The powdered SRM was also analyzed by dynamic laser scattering and solution leaching experiments, to determine grain size distribution and possible elements release. Our results confirm the deactivation of crocidolite and chrysotile asbestos fibers, but at the same time evidence a significant fraction of nanoparticles in the SRM and some critical releases of SO42-, F- and Cr6+ in solution. Both the nanoparticle fraction and the critical elemental release may pose human health concern and adversely affect potential applications of the SRM. Strategies to control the grain size distribution through adjusted thermal treatment conditions and microwave-assisted grinding operations are discussed. Possible routes to safely reuse the SRM are indicated
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