3,386 research outputs found
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
Recovery time profiling after short-, middle-and long-distance swimming performance
No full textPiras, A, Cortesi, M, Campa, F, Perazzolo, M, and Gatta, G. Recovery time profiling after short-, middle- and long-distance swimming performance. J Strength Cond Res 33(5): 1408-1415, 2019-We investigated cardiac autonomic responses and hemodynamic parameters on recovery time after short-, middle- and long-swimming performance. Ten male regional-level swimmers were tested to estimate time and frequency domains of arterial baroreflex sensitivity (BRS) and heart rate variability after 100, 200, and 400 m of front crawl. We found a BRS reduction for 90 minutes after a maximal 100- and 200-m front crawl event, meanwhile the reflex was restored back to the baseline value approximately 70 minutes after 400 m. The vagally mediated high-frequency power of R-R intervals was significantly reduced for 30 minutes after 400 m, and more than 90 minutes after 100 and 200 m, with a concomitant increase of sympathetic modulation. After 400 m, athletes have reduced their stroke volume for 50 minutes, which remained at the baseline level after 100 and 200 m. Heart rate was restored back after 90 minutes in all conditions, whereas total peripheral vascular resistance was significantly reduced for 50 minutes after 200 and 400 m, with a persistent reduction after 100 m. Time course of autonomic recovery after 3 different swimming performances is influenced by exercise intensity and duration, showing a rapid recovery after 400 m, an intermediate recovery after 200 m, and a significantly delayed recovery after a more strictly anaerobic performance like 100 m of front crawl. These results could encourage coaches to consider that athlete might be affected by the specific recovery time of the previous exercise performed, suggesting that the management of the exercise intensity, and appropriate monitoring of cardiac autonomic parameters might be helpful to know the physical condition of each athlete
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
Cs-zeolites under extreme conditions: comparative thermoelastic behaviour of Cs-ABW,Cs-CAS and Cs-ANA
No full text1. Introduction
Cs-bearing zeolites are extremely rare in nature. Pollucite, the Cs-counterpart of analcime, is the only natural Cs-rich zeolite. In the last decades, synthetic Cs-aluminosilicates have been prepared in search for suitable crystalline phases potentially usable as solid hosts for 137Cs γ-radiation source to be used in sterilization applications, or for fixation and deposition of radioactive isotopes of Cs. The thermo-elastic behaviour, the phase-stability and the main P-induced deformation mechanisms of two synthetic Cs-bearing zeolites, Cs-ABW (CsAlSiO4) and Cs-CAS (CsAlSi5O12), and one natural zeolite, pollucite Cs-ANA [(Cs,Na)AlSi2O6 x nH2O] have been recently investigated. Here we provide a comparative analysis of the response at high-pressure and high-temperature of the three mentioned Cs-rich zeolites.
2. Experimental Methods and Results
2.1. Cs-ABW
The elastic behavior of the synthetic zeolite CsAlSiO4 (a~9.446, b~5.439, and c~ 8.927 Å, space group Pc21n)[1] is under investigation by in-situ powder synchrotron X-ray diffraction with a diamond anvil cell under hydrostatic conditions. Data are currently available up to ~7 GPa. The material preserves its crystallinity and no phase transition appears to occur within the P-range investigated. Fitting the P-V data with a third-order Birch-Murnaghan equation-of-state (BM-EoS), we obtained: V0 = 457.9(4) Å3, KT0 = 42(1) GPa and K’ = 3.9(3). The “axial moduli” were calculated with a third-order “linearized” BM-EoS, substituting the cube of the individual lattice parameter (a3, b3, c3) for the volume. The refined axial-EoS parameters are: KT0a = 271(9) GPa (b_a = 0.00123(4) GPa-1), K’a = 4 (fixed) for the a-axis; KT0b = 181(3) GPa (b_b = 0.00184(3) GPa-1), K’b = 4 (fixed) for the b-axis; KT0c =14.5(5) GPa (b_c = 0.0230(8) GPa-1), K’c = 2.6(1) for the c-axis (KT0a : KT0b : KT0c = 19 : 12 : 1).
Previous high-temperature experiments showed that Cs-ABW transforms irreversibly to Cs-ANA framework-type zeolite at 1423 K [2].
2.2. Cs-CAS
The elastic and structural behavior of the synthetic zeolite CsAlSi5O12 (a~16.753, b~13.797 and c~5.023 Å, space group Ama2) were investigated up to ~8.5 GPa by in-situ single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions [3]. No phase-transition occurs within the P-range investigated. Fitting the P-V data with a third-order BM-EoS gives: V0 = 1155(4) Å3, KT0 = 20(1) GPa and K’ = 6.5(7). The “axial moduli”, calculated with a third-order “linearized” BM-EoS, are: KT0a = 14(2) GPa (b_a = 0.024(3) GPa-1), K’a = 6.2(8) for the a-axis; KT0b = 21(3) GPa (b_b = 0.016(2) GPa-1), K’b = 10(2) for the b-axis; KT0c = 33(3) GPa (b_c = 0.010(1) GPa-1), K’c = 3.2(8) for the c-axis (KT0a : KT0b : KT0c = 1 : 1.50 : 2.36). The HP-crystal structure evolution was studied on the basis of several structural refinements at different pressures. The main deformation mechanisms at high-pressure are governed by tetrahedral tilting, the tetrahedra behaving as rigid-units. A change in the compressional mechanisms was observed at P ≤ 2 GPa. The P-induced structural rearrangement from 0.0001 up to 8.5 GPa is completely reversible.
Further experiments have been devoted to the high-temperature behavior of CsAlSi5O12. In-situ high-temperature single-crystal and powder X-ray diffraction experiments were performed to describe its anisotropic thermal expansion [4]. The evolution of the unit-cell constants show a significant decrease in expansion above 773 K. At 773 K, a displacive phase transition from the acentric low-T space group Ama2 to the high-T centrosymmetric Amam was found. Thermal expansion below the phase-transition is governed by rigid-body tetrahedra rotations, accompanied by stretching of T–O–T angles. Temperature-dependent unpolarized Raman spectra between room temperature and 1270 K confirm the nature of the phase-transition (i.e. disordered static–disordered dynamic type) and the crystallinity of CsAlSi5O12 at least up to 1270 K.
2.3. Cs-ANA
The elastic behavior and the phase-stability of a natural pollucite, (Cs,Na)AlSi2O6 x nH2O, were investigated at hydrostatic pressure by in-situ single-crystal X-ray diffraction with a diamond anvil cell [5]. Pollucite experiences a P-induced phase transition at P=0.66 +/- 0.12 GPa from cubic (Ia d) to triclinic symmetry (P ). The phase transition is completely reversible and without any appreciable hysteresis effect. No further phase transition has been observed up to ~9 GPa. Fitting the P-V data of the low-P cubic polymorph with a BM-EoS, we obtained: V0=2558.3(4)Å3, KT0= 41(2)GPa and K’T = 4 (fixed). For the high-P triclinic polymorph, a third-order BM-EoS fit gives: V0=2577.5(40)Å3, KT0=25.1(9)GPa and K’T = 6.5(4). The axial bulk moduli of the high-pressure triclinic polymorph were calculated with a third-order “linearized” BM-EoS. The EoS parameters are: KT0(a)= 25.5(17)GPa (b_a = 0.0131(11) GPa-1) and K’T(a)= 6.8(6) for the a-axis; KT0(b)= 23.2(15)GPa (b_b = 0.0145(10) GPa-1) and K’T(b)= 7.7(7) for the b-axis; KT0(c) = 25.2(10)GPa (b_c = 0.0132(6) GPa-1) and K’T(c) = 6.8(4) for the c-axis, resulting in a modest elastic anisotropy (KT0(a):KT0(b):KT0(c) = 1.10:1:1.09).
A previous experiment based on in-situ high-temperature powder X-ray diffraction up to 1470 K (at room P) showed that synthetic cubic pollucite (CsAlSi2O6) preserves its crystallinity within the T-range investigated, without any evidence of phase transition between 290 and 1470 K [6].
3. Discussion
The experiments aimed to describe the phase-stability fields, the thermo-elastic behavior and the P/T-induced structure evolutions of Cs-ABW, Cs-CAS and Cs-ANA show that these three compounds are crystalline at least up to 8-9 GPa. This results is surprising if we consider their microporous nature.
Pollucite only shows a P-induced phase-transition, at a modest pressure (~0.7 GPa). The high-pressure polymorph of Cs-ANA shows an almost isotropic elastic behaviour (i.e. KT0(a):KT0(b):KT0(c) = 1.10 : 1 : 1.09). More anisotropic is the elastic response of Cs-CAS (i.e. KT0(a):KT0(b):KT0(c) = 1 : 1.50 : 2.36). In contrast, Cs-ABW appears to be one of the most anisotropic crystalline materials, with KT0(a) : KT0(b) : KT0(c) = 19 : 12 : 1. The elastic anisotropy in Cs-CAS and Cs-ABW reflects the configuration of the channels, and follow a general principle concerning the HP-behavior of microporous materials [7]: the open framework structures tend to accommodate the effect of pressure, by cooperative rotation of the tetrahedra, usually increasing the ellipticity of the channel systems and maintaining the original elliptical configuration, without any “inversion” in ellipticity. An in-situ high-pressure single-crystal diffraction experiment on Cs-ABW is in progress, aimed to describe the main deformation mechanisms responsible for the so drastic anisotropic behavior of this zeolites.
The thermal stability of the three mentioned microporous materials is also surprising. Despite its microporous structure, pollucite is currently considered as a “ceramic” material [6], with potential technological applications due to its modest thermal expansion. Previous experiments suggest that, among the crystalline phases of the Cs2O-Al2O3-SiO2 system, Cs-ANA shows the highest T-stability [2].
Even the chemical stability of the Cs-bearing zeolites is someway surprising. Pollucite, for example, is able to retain Cs when immersed into a fluid phase, even under hydrothermal conditions, better than several other Cs-bearing materials [5]. This behavior is ascribable to the topological configuration of the Cs-polyhedron and its bonding environment, to the small dimension of the sub-nanopores where the Cs-sites lie and to the high flexibility of the ANA framework type. The Cs-retention of CsAlSi5O12 was recently examined by treating the powdered compound in boiling 1M NaCl solution [8]. After more than one month of exposure at extreme exchange conditions, only small amounts of Cs occupying the eight-membered ring channels are extracted. Results show that Cs is strongly bonded to the tetrahedral framework.
The key to explain the thermal and chemical stability of the mentioned zeolites is in: 1) the significantly modest, or absent, amount of H2O as extra-framework molecules, 2) the (long) ionic radius of Cs+, which allows high coordination-numbers with the framework anions, 3) the modest free-diameters of the channel systems, which hinder the cation migration. Only natural Cs-ANA contains a low amount of H2O (<2wt%), whereas Cs-ABW and Cs-CAS are anhydrous materials.
On the basis of their high thermo-elastic and chemical stability, the three aforementioned Cs-bearing zeolites, especially Cs-ANA, may be considered as functional materials usable for fixation and deposition of radioactive isotopes of Cs, or as solid hosts for 137Cs γ-radiation source to be used in sterilization applications. However, further experiments are needed to investigated potential self-radiation damage of the crystal structures due to 137Cs.
References
[1] GATTA G.D., ROTIROTI N., ZANAZZI P.F., RIEDER M., DRABEK M., WEISS Z., KLASKA R., Am. Mineral. 93 (2008), 988-995.
[2] DIMITRIJEVIC R., DONDUR V., PETRANOVIC N., J. Solid State Chem. 95 (1991), 335–345.
[3] GATTA G.D., ROTIROTI N., FISCH M., KADIYSKI M., ARMBRUSTER T., Phys. Chem. Miner. 35 (2008), 521-533.
[4] FISCH M., ARMBRUSTER T., KOLESOV B., J. Solid State Chem. 181 (2008), 423-431.
[5] GATTA G.D., ROTIROTI N., BOFFA BALLARAN T., SANCHEZ-VALLE C., PAVESE A., Am. Mineral., 94, (2009), 1137-1143.
[6] KOBAYASHI H., YANASE I., MITAMURA T., J. Am. Ceramic Soc. 80 (1997), 2161–2164.
[7] GATTA G.D., LEE Y., Phys. Chem. Minerals 32 (2006), 726 – 732.
[8] FISCH M., ARMBRUSTER T., LIBOWITZKY E., Topics in Chemistry and Materials Science, vol 4 (2010) 61-70. Advanced Micro- and Mesoporous Materials – 08, Eds. K. Hadjiivanov, V. Valtchev, S. Mintova, G. Vayssilov, Sofia, Heron Press Ltd, ISSN 1314-0795
High-pressure adsorption on methanol in synthetic MFI-zeolites
No full textIn the recent years, a raising interest related to the P-induced intrusion of ions/molecules from the so-called “penetrating” P-transmitting fluids into the zeolitic structural cavities have been object of a number of experiments. The P-induced adsorption process is controlled by a number of factors, recently reviewed by Gatta et al. (2018), and is enhanced when the kinetic diameter of the P-transmitting fluid’s molecules is smaller than the free diameter of the framework cavities. This property can be exploited in potentially relevant technological applications. MFI-synthetic zeolites are presently employed as catalyst in the production of olefins (fundamental building blocks in the production of plastics, rubbers, or polymers) starting from methanol. This process is one of the most prominent alternative way for producing olefins avoiding the use of oil derivatives (Stöcker, 1999; Olsbye et al., 2012). The recent literature is focused on investigations of small- and medium pore-type microporous/zeolitic catalysts suitable for the methanol conversion to hydrocarbons. On this basis, in this study we investigated, by means of in situ powder and single-crystal synchrotron X-ray diffraction, the P-induced intrusion of methanol in different samples of synthetic MFI-zeolites, characterized by different framework and extraframework compositions, using a diamond-anvil cell. Thanks to these experiments we were able to : (i) draw conclusions about the use of pressure as preferential way to induce a “cold” adsorption of methanol into the zeolite cavities (and therefore potentially increasing the efficiency of the methanol-to-olefins process); (ii) analyze the role of the framework’s and extraframework’s crystal-chemistry in the adsorption process; (iii) compare the magnitude of the methanol intrusion in single crystal with respect to powders.
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
Olsbye U., Svelle S., Bjørgen M., Beato P., Janssens T.V.W., Joensen F., Bordiga S., Lillerud K.P. (2012). Angew. Chem. Int. Ed., 51, 5810-5831
Stöcker M. (1999) Methanol-to-hydrocarbons: catalytic materials and their behavior. Micropor. Mesopor. Mater., 29, 3-48
Cancrinite-group minerals ([CAN]-framework type) at non-ambient conditions
No full textAll the isotypic minerals of the cancrinite-group share the [CAN]-framework type, built up by layers of single six-membered rings of tetrahedra centered in an “A” or “B” position, according to the ABAB stacking sequence. The resulting framework has the following secondary building units: 12-membered ring channels parallel to the [0001] axis, bound by columns of base-sharing cages, and the so-called can units. A large chemical variability is shown by both natural and non-natural isotypic compounds. Among the natural species, the majority shows an alumino-silicate framework (Al6Si6O24), and two subgroups can be identified according to the extraframework content of the can units: the cancrinite- and the davyne-subgroups, showing Na-H2O and Ca-Cl chains, respectively. Several cations, anionic and/or molecular groups lie in the channels.
The description of the phase-stability fields and the of the thermo-elastic behavior of the cancrinite-group minerals play a key role in the study of the natural and industrial processes where these compounds are primary constituents (a short summary of which is in [1,2]).
We aim to model the thermo-elastic behavior and (P,T)-induced structure evolution of these isotypic compounds, with a focus on the influence played by the different extraframework constituents on the structure deformation mechanisms. The study is restricted to the chemical compositions commonly occurring in Nature, delimited by the (CO3)-rich and (SO4)-rich end-members within the two aforementioned subgroup: cancrinite {[(Na,Ca)6(CO3)1.2-1.7][Na2(H2O)2][Al6Si6O24]} and vishnevite {[(Na,Ca,K)6(SO4)][Na2(H2O)2][Al6Si6O24]}, balliranoite {[(Na,Ca)6(CO3)1.2-1.7][Ca2Cl2][Al6Si6O24]} and davyne {[(Na,Ca,K)6((SO4),Cl)][Ca2Cl2][Al6Si6O24]}, respectively. The high-pressure and low-temperature (T < 293 K) studies of the carbonate end-members (i.e. cancrinite and balliranoite) have been performed by means of in situ single-crystal X-ray diffraction. The results [1-4] show that, though sharing a similar volume compressibility and thermal expansivity, these minerals have a different thermo-elastic anisotropy, being more pronounced in cancrinite. This is due to different (P,T)-induced structure deformation mechanisms, likely governed by the different coordination environment of the cage population. An in situ high-temperature (293 ≤ T(K) ≤ 823(7)) single-crystal X-ray diffraction study of cancrinite, allowed the description of thermo-elastic behavior and anisotropy. An irreversible dehydration process takes place at 748(7) K. Preliminary results of the high-pressure studies of the sulfatic end-members (i.e. vishnevite and davyne) are available. A clear change of the elastic behavior of vishnevite, with an increase of compressibility, is shown between 2.47(2)-3.83(2) GPa. A similar increase of compressibility was also reported for cancrinite at 4.62-5.00(2) GPa.
References. [1] Lotti, P., Gatta, G.D., Rotiroti, N., Cámara, F. (2012): Am. Mineral., 97, 872-882; [2] Gatta, G.D., Lotti, P., Kahlenberg, V. (2013): Micropor. Mesopor. Mater., 174, 44-53; [3] Gatta, G.D., Lotti, P., Kahlenberg, V., Haefeker, U. (2012): Miner. Mag., 76, 933-948; [4] Lotti, P., Gatta, G.D., Rotiroti, N., Cámara, F., Harlow, G.E. (2013): Z. Kristallogr., in press
Anisotropic compressional behavior of ettringite
No full textA Portland cement is a complex multi-component system and, to predict its elastic properties, an exhaustive database of the thermodynamic parameters of the main constituents is needed. Ettringite (ideally Ca6Al2(SO4)3(OH)12·27H2O, with a=b =11.21 and c =21.43 Å, Sp. Gr. P31c) is one of the most important crystalline phases in Portland cements: its crystallization, in the early hydration stages, governs the set rate of the highly reactive “C3A” phase (Ca3Al2O6), whereas in aged cements the formation of ettringite is commonly associated with degradation processes (Taylor et al. 2001). The crystal structure of ettringite is significantly complex with a H-bonding net which connects [Ca3[Al(OH)6]·12H2O]-columns (in which Al(OH)6-octahedra are alternated with triplets of Ca(OH)4(OH2)4-polyhedra) to sulphate groups (Gatta et al. 2019). Despite the previous studies at high pressure on this material (e.g., Cuesta et al. 2017, Clark et al. 2008), the linear bulk moduli (Ka and Kc) and a description of the deformation mechanisms at the atomic scale are still missing. In this light, we have investigated the compressional behavior of ettringite up to 4.2 GPa by means of in-situ single-crystal synchrotron X-ray diffraction, using a diamond-anvil cell (DAC) and the mix methanol:ethanol (4:1) as P-transmitting fluid.
Ettringite shows a marked anisotropic compressional pattern (Ka 21(1) GPa, Kc 47(1) GPa). This anisotropic elastic scheme dramatically changes at P>3 GPa; KV0 drops from 26.6(5) to 10.4(8) GPa), which mainly affects the structure on the ab plane (Ka drops from 21(1) to 7.3(8) GPa whereas Kc decreases only moderately). Structure refinements reveal that the elastic softening reflects the collapse of the H-bonding network, due an average decrease of the Odonor···Oacceptor distances (up to 0.20 Å in some cases), which mainly affect the interaction between the sulphate groups and the Ca(OH)4(OH2)4-polyhedra.
References:
Clark S.M., Colas B., Kunz M., Speziale S., Monteiro P.J.M. 2008. Effect of pressure on the crystal structure of ettringite. Cem. Concr. Res., 38, 19-26.
Cuesta A., Rejmak P., Ayuela A., De la Torre A.G., Santacruz I., . Carrasco F.L., Popescu C., Aranda M.A.G. 2017. Experimental and theoretical high pressure study of calcium hydroxyaluminate phases, Cem. Concr. Res., 97, 1–10.
Gatta G.D., Hålenius U., Bosi F., Cañadillas-Delgado L., Fernandez-diaz M.T. 2019. Minerals in cement chemistry: a single-crystal neutron diffraction study of ettringite, Ca6Al2(SO4)3(OH)12·27H2O. Am. Mineral., 104, 73-78.
Taylor H.F.W., Famy C., Scrivener K.L. 2001. Delayed ettringite formation, Cem. Concr. Res., 31, 683–693
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
Introduzione
No full textL'Introduzione di Elide casali traccia le coordinate cronologiche (età moderna, l"'età dei maghi" secondo la definizione di Paolo Rossi), spaziali (Romagna) e culturali (scienza e letteratura) cui si riferiscono i saggi elaborati da una serie di collaboratori ( F. Bacchelli, G. Cerasoli, L. Michelacci, F. Gatta, A. Natale, M. Carreras, G. Ernst, E. Zinato, G. Olmi, M. Prandi) su una serie di testi e fonti presenti nelle Raccolte Piancastelli conservate presso la Biblioteca Comunale"A. Saffi" di Forlì"
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
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