1,360,614 research outputs found
Codice penale e norme complementari
No full textTerza edizione del "Codice penale e norme complementari" (I blu Giuffrè) curata da E. Dolcini e G.L. Gatta, con la collaborazione di A. Galluccio, M. C. Ubiali e S. Bernardi
The behavior at non-ambient conditions of colemanite: a hydrous Ca-borate
No full textColemanite, CaB3O4(OH)3·H2O, is a common hydrous borate of large economic relevance, as it is one of the major commodities of boron with applications in the fields of glass and ceramic industries. Colemanite-rich layers are usually found in stratigraphic successions related to lacustrine basins in semi-arid to arid environments, associated to a local volcanic activity, which provides the source for boron. Despite the large economic relevance, the behavior of this mineral at non-ambient conditions of temperature and pressure was almost unexplored, which can provide a basis for understanding its stability during diagenetic and metamorphic processes. In this contribution, we report the highpressure behavior of colemanite (Lotti et al., 2017), based on in situ single-crystal synchrotron X-ray diffraction data up to 24 GPa, and its low-T behavior by in situ X-ray and neutron single-crystal diffraction. Colemanite was found to be stable up ~ 14.5 GPa, where a reconstructive phase transition towards a high-pressure polymorph (colemanite-II) with same symmetry (space group P21/a), but a six times larger unit cell volume, occurs. The elastic behavior of colemanite was described by fitting the experimental data with a III-order Birchurnaghan equation of state, yielding the following refined elastic parameters: KV0 = 64(4) GPa and KV' 5.5(7). The colemanite-tocolemanite-II phase transition induces an increase in the average coordination number of both the Ca and B cations. In particular, a fraction of the boron sites increases its coordination from triangular to tetrahedral by making a further bond with a H2O-oxygen atom. Although the phase transition occurs (at ambient temperature) at pressures far from those associated with the usual geologic environments of colemanite, the reported results disclosed flexible deformation mechanisms that borate compounds may adopt to accommodate pressure, thus providing new insights on the behavior of borate minerals at non-ambient conditions. The complex hydrogen-bonding network of olemanite has also been characterized, at ambient and low temperature conditions, by means of in situ single-crystal synchrotron X-ray and neutron diffraction experiments. A positional disorder, related to the presence of two mutually exclusive configurations of the H2O-molecule hydrogen atoms, was found both above and below ~ 0°C, where a displacive phase transition from the P21/a to the P21 space group occurs.
Lotti, P., Gatta, G.D., Comboni, D., Guastella, G, Merlini, M., Guastoni, A., Liermann, H.-P. (2017): High-pressure behavior and Pinduced phase transition of CaB3O4(OH)3*H2O (colemanite), J. Am. Ceram. Soc., in press, DOI: 10.1111/jace.14730
A low temperature X-ray single-crystal diffraction and polarised infra-red study of epidote
No full textThe effects of low-temperature on the crystal structure of a natural epidote [Ca1.925Fe0.745Al2.265Ti0.004 Si3.037O12(OH), a = 8.8924(7), b = 5.6214(3), c = 10.1547(6) angstrom and beta = 115.396(8)degrees at room conditions, Sp. Gr. P2(1)/m] have been investigated with a series of structure refinements down to 100 K on the basis of X-ray single-crystal diffraction data. The reflection conditions confirm that the space group is maintained within the T-range investigated. Structural refinements at all temperatures show the presence of Fe3+ at the octahedral M(3) site only [%Fe(M3) = 70.6(4)% at 295 K]. Only one independent proton site was located and two possible H-bonds occur, with O(10) as donor and O(4) and O(2) as acceptors. The H-bonding scheme is maintained down to 100 K and is supported by single crystal room-T polarised FTIR data. FTIR Spectra over the region 4,000-2,500 cm(-1) are dominated by the presence of a strongly pleochroic absorption feature which can be assigned to protonation of O(10)-O(4). Previously unobserved splitting of this absorption features is consistent with a NNN influence due to the presence of Al and Fe3+ on the nearby M(3) site. An additional relatively minor absorption feature in FTIR spectra can be tentatively assigned to protonation of O(10)-O(2). Low-T does not affect significantly the tetrahedral and octahedral bond distances and angles, even when distances are corrected for "rigid body motions". A more significant effect is observed for the bond distances of the distorted Ca(1)- and Ca(2)-polyhedra, especially when corrected for "non-correlated motion". The main low-T effect is observed on the vibrational regime of the atomic sites, and in particular for the two Ca-sites. A significant reduction of the magnitude of the thermal displacement ellipsoids, with a variation of U-eq (defined as one-third of the trace of the orthogonalised U-ij tensor) by similar to 40% is observed for the Ca-sites between 295 and 100 K. Within the same T-range, the U-eq of the octahedral and oxygen sites decrease similarly by similar to 35%, whereas those of the tetrahedral cations by similar to 22%.</p
Violazione di domicilio : aumento del minimo edittale e arresto facoltativo in flagranza
No full textSi dà conto delle modifiche alla disciplina del delitto di violazione di domicilio (art. 614 c.p.) apportate dalla l. 15 luglio 2009, n. 94
Crystal-fluid interactions in open-framework silicates
No full textThe structural evolution of microporous materials compressed hydrostatically in a fluid is drastically affected by the potential crystal-fluid interaction, with a penetration of new molecular species through the zeolitic voids in response to applied pressure.
On the basis of recent experimental findings and computational modelling studies, it was observed that when no crystal-fluid interaction occurs, the effects of pressure are mainly accommodated by tilting of (quasi-rigid) tetrahedra around the bridging O atoms. Tilting of tetrahedra is the dominant mechanisms at low-mid P-regime, whereas distortion and compression of tetrahedra dominate the mid-high P regime. The deformation mechanisms are governed by the topological configuration of the tetrahedral framework, but the compressibility of the cavities is controlled by the ionic and molecular host content, resulting in different unit-cell volume compressibility in isotypic structures. One of the most common deformation mechanisms in zeolitic framework is the increase of channels ellipticity.
Not all the zeolites experience a P-induced intrusion of new monoatomic species or molecules from the P-transmitting fluids. For example, natural zeolites, with well-stuffed channels at room conditions, tend to hinder the penetration of new species through the zeolitic voids. Several variables govern the sorption phenomena at high pressure: the “free diameters” of the framework cavities, the configuration of the extraframework population, the partial pressure of the penetrating molecule in the fluid (if mixed with other nonpenetrating molecules), the rate of P-increase, the surface/volume ratio of the crystallites under investigations, the temperature at which the experiment is conducted. The most recent findings allow us to provide an overview of the intrusion phenomena of monoatomic species (e.g., He, Ar, Kr), small (e.g., H2O, CO2) and complex molecules, along with the P-induced polymerization phenomena, (e.g., C2H2, C2H4, C2H6O, C2H6O2, BNH6, electrolytic MgCl2·21H2O solution), with potential technological and geological implications.
Gatta, G.D. (2008): Does porous mean soft? On the elastic behaviour and structural evolution of zeolites under pressure.
Z. Kristallogr., 223, 160-170.
Gatta, G.D. & Lee, Y. (2014): Zeolites at high pressure: A review. Mineral. Mag., 78, 267-291.
Gatta, G.D., Lotti, P. & Tabacchi, G. (2017): The effect of pressure on open-framework silicates: elastic behaviour and
crystal-fluid interaction. Phys. Chem. Minerals, 45, 115-138
From Nature to materials science: (Cs,K)Al4Be5B11O28 (londonite) as a super-hard material
No full textLondonite is a rare Cs-bearing mineral with ideal chemical formula (Cs,K)Al4Be4(B,Be)12O28 (with Cs > K). The building block units of the structure of londonite are represented by clusters of four edge-sharing Al-octahedra linked to B- and Be-tetrahedra. Gatta et al. (2011) investigated the phase stability and the elastic behavior of londonite up to 4.85(5) GPa (at room-T) and up to 1000°C (at room-P) by in situ X-ray powder diffraction data, but no structure refinements were possible. Whether no phase transition was observed within the pressure-range investigated, londonite
proved to have an extremely high bulk modulus: KP0 = 280(12) GPa, similar to those of carbides (e.g., B4C with KP0 ~ 245-306 GPa; Lazzari et al., 1999; Fujii et al., 2010). Considering the thermo-elastic properties and the significantly high fraction of boron (B2O3 ~50 wt%), the synthetic counterparts of londonite could be considered a potential inorganic host for 10B in composite neutron-absorbing materials. Furthermore the high content of Cs makes londonite-type materials potential host for nuclear waste. However, to date, because of the absence of structural data at high pressure and to the modest P-range investigated by Gatta et al. (2011), a comprehensive description of the P-induced deformation mechanisms at the atomic scale is still missing. In this study, the isothermal compressional behaviour of londonite is studied by in situ single-crystal synchrotron X-ray diffraction experiment with a diamond anvil cell up to 25 GPa. The compressional behavior and the deformation mechanisms at the atomic scale are described. Londonite does not experience any phase transition or change of the compressional behavior within the P-range investigated.Fujii, T., Mori, Y., Hyodo, H., Kimura, K. (2010): X-ray diffraction study of B4C under high pressure. J. Phys. Conf. Ser., 215,
012011.
Gatta, G.D., Vignola, P., Lee, Y. (2011): Stability of (Cs,K)Al4Be5B11O28 (londonite) at high pressure and high temperature: a
potential neutron absorber material. Phys. Chem. Miner., 38, 429-434.
Lazzari, R., Vast, N., Besson, J.M., Baroni, S., Dal Corso, A. (1999): Atomic structure and vibrational properties of icosahedral B4C
boron carbide. Phys. Rev. Letters, 83, 3230-3233
P-induced crystal fluid interaction: the case of ERI and OFF topology
No full textThe P-induced intrusion of molecules or solvated ions within the nanocavities of open-framework minerals, such as zeolites, has been extensively investigated during last decades (e.g., Gatta et al., 2018, and references within). This peculiar property might be exploited to tailor new multifunctional materials or to enhance industrial catalytic processes involving zeolites (Comboni et al., 2020). In addition, from a geological point
of view, a constraint of this phenomena might shed light on the role played by zeolites as fluid carriers in the upper Earth crust, e.g., during the early subduction of altered basalts or oceanic sediments. The aim of the present study is to characterize the high-pressure behavior, promoting the crystal-fluid interaction, on two different natural zeolites species belonging to the ABC-6 family: erionite (AABAAC) and offretite (AAB)
(ERI and OFF topology, respectively). Similarities of the framework between these two species resulted in quite common intergrowth, at least in natural samples (Passaglia et al., 1998). Samples were compressed in non-penetrating and penetrating P-transmitting fluids (PTFs). Investigations were conducted via in-situ high pressure single-crystal synchrotron X-ray diffraction, using a diamond anvil cell (DAC), at the ID15b beamline of ESRF (Grenoble, France) and P02.2 of PETRA-III (Hamburg, Germany). Different PTFs have been employed during the experiments: non-penetrating i) silicone oil and daphne oil (7575) and potentially penetrating, ii) alcohols: water mixtures, iii) pure H2O, iv) Ne. The obtained unit-cell P-V patterns revealed the adsorption of H2O molecules within the structural cavities; in addition, the structure refinements allowed to describe the deformation mechanisms as well as the location of the adsorbed molecules. Interestingly, the magnitude of the absorption phenomena in natural erionite appeared to be comparable with what observed in synthetic zeolites (i.e., AlPO4-5, Lotti et al., 2016), highlighting the great potential of erionite as a mineralogical carrier of fluids in the upper Earth crust.
Comboni D., Pagliaro F., Lotti P., Gatta G.D., Merlini M., Milani S., Migliori M., Giordano G., Catizzone E., Collings I.E. & Hanfland M. (2020) - The elastic behavior of zeolitic frameworks: The case of MFI type zeolite under high-pressure methanol intrusion. Catal. Today, 345, 88-96.
Gatta G.D., Lotti P. & Tabacchi G. (2018) - The effect of pressure on open-framework silicates: elastic behaviour and crystal-fluid interaction. Phys. Chem. Miner., 45, 115-138.
Lotti P., Gatta G.D., Comboni., Merlini M., Pastero L. & Hanfland M. (2016) - AlPO4-5 zeolite at high pressure: Crystalfluid interaction and elastic behavior. Microp. Mesop. Mater., 228, 158-167.
Passaglia E., Artioli G. & Gualtieri A. (1998) - Crystal chemistry of the zeolites erionite and offretite. Am. Mineral., 83, 577-589
Conversazione e narrazione nei racconti di Marina Mizzau (con note sul dialogo cinematografico e televisivo)
No full textIl saggio applica l'analisi della conversazione ai racconti di Marina Mizzau, racconti in cui il dialogo ha un ruolo centrale. L'analisi dei dialoghi dei racconti consente di mettere a fuoco, per contrasto, l'inverosimiglianza dei dialoghi cinematografici e televisivi, una inverosimiglianza tuttavia richiesta dai generi specifici in cui sono inseriti e che l'inserimento di tratti linguistici tipici dell'oralità non è sufficiente a scalfire
A MULTI-METHODOLOGICAL STUDY OF A GEM-QUALITY SYNTHETIC DARK BLUE BERYL
No full textBeryl is an accessory mineral commonly found in pegmatitic rocks, with ideal chemical formula Be3Al2Si6O18 and crystal structure consisting of six-membered rings of Si-tetrahedra, linked by Al-octahedra and Be-tetrahedra, forming a three-dimensional framework. The “extra-framework” content (alkali cations, water and carbon dioxide molecules) lies in the six-membered ring channels parallel to [0001].
Because of the peculiar beryl’s commercial value, a remarkable number of synthetic samples, emeralds and other various specimens with “exotic” colourations, are permanently present on the market [1].
In the present work a multi-methodological investigation of a synthetic Cu/Fe-bearing dark blue beryl [IV(Be2.86Cu0.14)Σ=3.00 VI(Al1.83Fe3+0.14Mn2+0.03Mg0.03)Σ=2.03 IV(Si5.97Al0.03)6.00 O18 (Li0.12Na0.04 0.40H2O)] has been performed by means of gemmological standard testing, combined with electron microprobe analysis, laser ablation inductively coupled plasma mass spectroscopy, thermogravimetric analysis, infrared spectroscopy and single-crystal X-ray diffraction. The aim of this work is to provide a full characterization of this material, covering gemmological properties, crystal structure and crystal chemistry.
The investigated 2.70 ct gem is uniaxial negative with refractive indices =1.590 and =1.582 and birefringence 0.008; the measured density is 2.77 g/cm3. These properties are the same reported for the natural aquamarine beryl [2]. Only the characteristic internal growth pattern can be useful for the separation of this gem material from its natural counterparts [3]. The chemical analyses reveal significant contents of iron and copper, the latter never found in any natural aquamarine beryl. The X-ray single-crystal structural refinements confirm that the gem maintains the space group P6/mcc and the general structural arrangement of the natural beryls, with unit-cell parameters: a~9.25 and c~9.22 Å. The analysis of the difference Fourier maps of the electron density suggests that Cu is located at the tetrahedral site (Wyckoff 6f-position), along with Be, whereas Fe shares the octahedral site with Al (4c-position). The channel content is distributed in two extra-framework sites: the first one occupied by water molecules (2a-position) and the second one (2b-position) mainly by alkali cations, in agreement with previous studies of natural beryls [4]. Infrared spectra show that the H2O molecules in the channel are present with two different configurations: one with the H•••H vector oriented //[0001] (“type I”) and the other with H•••H vector oriented perpendicular to [0001] (“type II”) [5, 6].
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References.
[1] J.I. Koivula, M. Tannous, K. Schmetzer, Gems & Gemology, 36, 360-379, 2000; [2] R. Webster, Gems: Their sources, Description and Identification, 6th ed., Butterworth-Heinemann, Oxford, 2006; [3] I. Adamo, A. Pavese, L. Prosperi, V. Diella, D. Ajò, G.D. Gatta, Gems & Gemology, submitted; [4] G.D. Gatta, F. Nestola, G.D. Bromiley, S. Mattauch, American Mineralogist, 91, 29-34, 2006; [5] D.L. Wood, K. Nassau, Journal of Chemical Physics, 42, 2220-2228, 1967; [6] D.L. Wood, K. Nassau, American Mineralogist, 53, 777-800, 1968
On the low-temperature behavior of the zeolite gobbinsite: a single-crystal X-ray diffraction study
No full textThe crystal structure, crystal chemistry and low-temperature (LT) behavior of a natural gobbinsite [(Na4.97K0.07Ca 0.48)Σ5.52[Al5.62Si10.29] Σ15.91O32·11.9H2O, Z = 1, a = 10.1185(4), b = 9.8035 (4), c = 10.1692(4) and V = 1008.75(10) 3, space group Pmnb] have been studied by in situ LT single-crystal X-ray diffraction. Five structural refinements were conducted on the basis of intensity data collected at 293 (room conditions), 250, 200, 150 and 100 K. Reflection conditions confirmed that the space group Pmnb is maintained within the T-range investigated. At room temperature, the same extra-framework population described by Gatta et al. [7] was found, with one site partially occupied by Na, one site partially occupied by Ca, and five sites partially occupied by water. At low-T a partial dehydration, likely induced by the N 2-flow, was observed, with a significant rearrangement of the extra-framework configuration. Low-T induced deformations of the 8- and 4-membered rings were observed, and the relationships between the main deformation mechanisms of the tetrahedral framework and the contraction along the unit-cell edges are discussed
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