1,721,224 research outputs found
Crystal structure of lizardite 1T from Elba Island, Italy
No full textEuhedral lizardite-1T occurs in the Monte Fico quarries, Elba Island, Italy. Unit-cell parameters, for two crystals, each with space group P31m, are a = 5.338(4) and c = 7.257(6) and a = 5.330(4) and c = 7.269(6) Å. The crystal structures were refined to Rtot = 0.034 and 0.046, using 251 and 849 independent reflections, respectively. The topology determined from previous refinements is confirmed. -from Author
Grain size, chemistry, and structure of fine and ultrafine particles in stainless steel welding fumes
No full textA combined SEM-TEM study was performed on samples of metal inert gas (MIG) stainless steel (SS) arc welding fumes to characterize fine and ultrafine particle fractions in terms of size distributions, crystal structures, and chemistry. Overall observations indicate that welding fumes consist of a complex mixture of magnetite-like nanocrystals and non-spinel particles in different phases, with distinguishing grain size distributions and chemical features. Results confirm the great health hazard posed by MIG-SS ultrafine particles and illustrate the complex array of morphological and chemical features characterizing airborne dusts in working environments. The possible implications of these features in interaction and toxicity mechanisms are discussed. © 2009 Elsevier Ltd. All rights reserved
Mesh textures and bastites in the Elba retrograde serpentinites
No full textRetrograde serpentinized peridotites, belonging to the Internal Ligurid terrains, occur in eastern Elba island, Italy The mesh texture (with pyroxene bastites) is the typical textural arrangement. The mesh rims are apparently fibrous, with negative optical elongation; cores range from isotropic to microgranular. Optical and chemical determinations indicate harzburgite (75 % olivine and 25 % pyroxene) as the protolith for Elba serpentinites, with characteristics similar to mantle peridotites from ocean basins.
Microstructural analysis, led by transmission electron microscopy, indicates that the mesh rims, rather than being actually fibrous, consist of elongated lizardite crystals, having sharp triangular sections with apices pointing toward the mesh center; poorly crystallized material occurs in between adjacent lizardite sectors. The mesh cores consist of lizardite, chrysotile and polygonal serpentine, intermixed in variable amount and random mutual orientation. Bastites are generally poorly crystalline, formed by tiny lizardite lamellae with minor chrysotile.
Mesh rims and cores have chemical compositions variable from specimen to specimen, but almost constant within each specimen; cores are always aluminium-enriched with respect to the rims; when present, nickel (after olivine) occurs in the meshes. Bastites are chemically simpler than meshes, and, independently from their optical appearance, always have an aluminium-rich composition; chromium (after pyroxene) always characterizes bastites. Chemical data indicate absence of long range chemical fluxes during serpentinization.
The formation of the mesh texture (with bastites) is explained as a two-stage process. In stage I, the peridotite undergoes thermal fracturing and lizardite flakes start to decorate the pseudocubic fracture pattern (thus producing the mesh rim). Massive water arrival into the weakened peridotite induces stage III where serpentinization is completed forming the mesh cores and bastites. In stage I the reaction is thermodynamically controlled, in stage II the reaction is kinetically controlled
Arsenic adsorption on nanocrystalline goethite: the natural example of bolar earths from Mt.Amiata (Central Italy)
No full textBolar earths deposits from Mt Amiata
(Central Italy) consist of nanosized pseudo-spherical
goethite, with average crystal size of 10–15 nm (as
determined by X-ray powder diffraction and transmission
electron microscopy observations), possibly
associated to amorphous silica and minor sheet silicates,
quartz and feldspars. Chemical analyses revealed
high As contents (up to 7.4 wt% As2O5), thus indicating
the occurrence of a potentially dangerous contaminant.
Arsenic doesn’t occur as a specific As phase,
but it is strictly associated with goethite nanocrystals.
Eh and pH measurements suggest that As occurs as
arsenate anions (H2AsO4 – and HAsO4
2–), which are
easily and strongly adsorbed to goethite surfaces. The
high specific surface area, resulting from goethite
nanosize, and the absence of competitive anions explain
the extremely efficient adsorption of arsenate and
the anomalously high As content in bolar earths.
Overall physical/chemical data suggest stable arsenate
adsorption, with very limited risk for As release to the
environment
Growth and deformation mechanisms of talc along the Zuccale low-angle normal fault (Central Italy): a micro/nanostructural investigation
No full textRICERCA SPERIMENTALE SUL MODELLAMENTO DEGLI ALVEI A FONDO MOBILE IN SEGUITO AD UN ALLARGAMENTO DI SEZIONE
No full textDeterminazione delle curve isoparametriche per le piogge orarie: applicazione alla Toscana
No full textGrowth and deformation mechanisms of talc along a natural fault: a micro/nanostructural investigation
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