189,419 research outputs found
Microporous compounds at non-ambient (P,T) conditions: mechanisms of structure deformation, phase transitions and crystal-fluid interactions
No full textMicroporous compounds are a class of open-framework materials; their structures contain cavities (in the form of channels or cages) with free diameters < 2 nm [1]. Zeolites, with their peculiar physical-chemical properties and diverse technological applications, are the most important group of this class, followed by feldspathoids and crystalline compounds with “hybrid” heterosilicate frameworks. The knowledge of the structural evolution of this class of materials under extreme conditions (i.e., high/low temperature, high pressure) is of paramount importance, especially for the potential implications in materials science and Earth sciences. Zeolites, for example, are an important bulk commodity: the world production of natural zeolites in 2016 was about 2.8 million of tons (price: 100-230 dollars per ton) and the consumption of synthetic zeolites was approximately 1.6 million of tons.
Few decades of high-temperature and high-pressure studies of zeolites disclosed that a complex interplay between the framework topology and the extraframework constituents drives the structural response to (T,P)-variations. Isostructural compounds, which differs for the extraframework population only, are an ideal target for studying how strong may be the control exerted by ions and molecules (that fill the structural cavities) on the bulk behavior of the material. An X-ray diffraction study of four end-members of the cancrinite-group of minerals (feldspathoids), conducted by in situ high-T and high-P experiments, revealed that even slight changes in the extraframework population exert a control on the mechanisms of structure deformation, which are reflected on the bulk elastic behavior of the mineral [2-5].
Microporous compounds usually accommodate isostatic compression mainly by tilting of the framework tetrahedra, around the bridging oxygen atoms, which act as hinges. However, symmetry or chemical constraints may hinder this mechanism: displacive phase transitions can occur in zeolites and zeolite-like materials, in order to accommodate thermal, pressure and chemical stresses. In this respect, the high-P behavior of SiO2-ferrierite is an interesting case study, as it undergoes, in a relatively narrow P-range, two displacive phase transitions with complex group-subgroup relationships (PmnnP121/n1(P-1)P21/n11, [6]).
In the last few years, a growing interest was devoted to the behavior of open-framework materials when compressed in the so-called “penetrating fluids”, i.e. fluids in which molecules are small enough to be intruded at high pressure into the structural cavities. Once more, SiO2-ferrierite may be considered an interesting case study. This zeolite has been compressed using three different P-media (i.e., 16:3:1 methanol:ethanol:H2O mixture, ethylene glycol and 2-methyl-2-propanol). The intrusion of the fluid molecules into the zeolite channels and cages was able to modify the bulk compressibility of the material and to prevent the transition to the P21/n11 polymorph, showing the strong control played by the extraframework population on the compressional behavior. Similar findings were also reported for other zeolites (e.g., the zeolite AlPO4-5 [7]). Several parameters were found to control the intrusion processes, among them: the sample size (e.g., powder vs. single crystal) and the kinetics of compression. The first controls the magnitude of the intrusion process, whereas the second may prevent the intrusion, as confirmed by fast-compression experiments on zeolites [6].
[1] C. Baerlocher, L.B. McCusker, D.H. Olson, Atlas of zeolite framework types, Elsevier, Amsterdam, 2007.
[2] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara, Am. Mineral. 2012, 97, 872.
[3] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara, G.E. Harlow, Z. Kristallogr. 2014, 229, 63.
[4] P. Lotti, G.D. Gatta, M. Merlini, M. Hanfland, Micropor. Mesopor. Mater. 2014, 198, 203.
[5] G.D. Gatta, P. Lotti, Am. Mineral. 2016, 101, 253.
[6] P. Lotti, R. Arletti, G.D. Gatta, S. Quartieri, G. Vezzalini, M. Merlini, V. Dmitriev, M. Hanfland, Micropor. Mesopor. Mater. 2015, 218, 42.
[7] P. Lotti, G.D. Gatta, D. Comboni, M. Merlini, L. Pastero, M. Hanfland, Micropor. Mesopor. Mater. 2016, 228, 158
Eredità cartesiane nella cultura britannica
No full textIl volume indaga la presenza di Descartes e del cartesianesimo nella cultura filosofica e scientifica britannica, documentandola da differenti prospettive attraverso un ampio arco temporale che va dal Seicento all'Ottocento. Oltre alle riflessioni complessive di G.A.J. Rogers e di Carlo Borghero, il volume raccoglie contributi sui dibattiti intorno al metodo cartesiano e al progetto di riforma pansofico di Comenio (M. Savini), su Henry More e la dottrina dell'estensione spirituale (I. Agostini), su Henry More e le 'Passioni dell'Anima' (A. Taraborrelli), sulla polemica tra Le Grand e Sergeant (J.R. Armogathe), sulla critica di Sergeant al cogito (B. Lotti), su Locke e la critica a Malebranche (C. Giuntini), su Malebranche e Hume (A. Pyle), sui temi della mente e della coscienza da Descartes a Reid (E. Levi Mortera), su Newton lettore di Descartes (F. Giudice), sul ritorno della fisica cartesiana nella scienza dell'Ottocento (P. Dessì). Completa il volume una Bibliografia delle opere di Descartes pubblicate in Inghilterra nei secoli XVII e XVIII (L. Nicolì)
Behavior of B-containing ceramic materials at extreme conditions of temperature and pressure
No full textBoron is a fundamental resource for the modern society, as confirmed by the doubling in the world production of ore minerals during the last decade (US Geological Survey, 2007, 2017). The applications of boron in the ceramic industry mainly concerns the production of: i) super-hard light ceramics (e.g., B4C), ii) ultra-high temperature ceramics for extreme refractories applications, and iii) composite materials for the shielding of neutron radiation, due to the large absorption capacity of 10B (Carter et al., 1953). The understanding of the technical properties of materials at non-ambient conditions of T and P, requires the understanding of the (T, P)-induced deformation of the crystal structure at the atomic scale. In this contribution are reported three examples concerning B-containing compounds: I) synthetic mullite-type Al5BO9, II) natural londonite, and III) natural colemanite. I) The synthetic Al5BO9 compound is a commercially relevant ceramic material (Fischer & Schneider, 2008). It belongs to the group of mullite-type compounds, with crystal structures characterized by infinite chains of edge-sharing AlO6 octahedra. Al5BO9 shares with mullite (sensu stricto) several technical properties, among those: a low thermal expansion coefficient (αV0 = 1.36(2)⋅10-5 K-1, Fisch & Armbruster, 2012) and high thermal and pressure stability. In addition provides lower density (for aerospace ceramics applications) and neutron absorption capacity. Its high-P behavior was studied up to 26 GPa (Gatta et al., 2010, 2013), disclosing that the low compressibility (KV0 = 1/βV0 = 164(4) GPa, βV0 = 0.0061(1) GPa-1) and the anisotropic compression are strictly controlled by the mullite-type crystal structure. The chains of AlO6 octahedra act as pillars, which counteract the compression along the [100] direction. On the contrary, the higher compressibility on the plane perpendicular to the chains direction (100) is controlled by the occurrence of interpolyhedral tilting mechanisms. II). The high-P behavior of Al5BO9 suggests that inhibiting the tilting among the coordination polyhedra may be adopted for tuning lower compressibilities. In this respect, suitable structures can be searched among the materials provided by Nature (i.e. minerals). Londonite, for example, is a rare mineral with ideal chemical formula (Cs,K)Al4Be5B11O28, with Cs > K. Londonite is characterized by high symmetry (space group: P-43m) and a highly close-packed structure. Its high-T (Gatta et al., 2011) and high-P behaviors (Gatta et al., 2017) have been investigated by means of in situ diffraction techniques. High-P data showed that londonite is stable in its cubic symmetry at least up to 24 GPa and disclosed a significantly low compressibility (KV0 = 212(7) GPa), approaching that of carbide ceramic compounds (KV0 ~ 250 GPa). Such a stiffness is controlled by the high symmetry and close-packing of the structure, which prevent the inter-polyhedral tilting and allow the accommodation of the bulk compression only through the compression and distortion of the polyhedra. In this light, synthetic counterparts of londonite are promising materials for neutron shielding and Cs-disposal applications. III) Colemanite, CaB3O4(OH)3⋅H2O, is not a ceramic compound, but a relevant B-ore mineral. Its high-P behavior (Lotti et al., 2017) provides a window on the behavior of boron at extreme conditions. The experimental diffraction data collected up to ~ 24 GPa show the occurrence of a reconstructive phase transition at ~ 14.5 GPa. Remarkably, the phase transition induces a fraction of the boron atoms to increase their coordination from triangular to tetrahedral, by making new bonds with close H2O-oxygen atoms.
REFERENCES
Carter, R.S., Palevsky, H., Myers, V.W., Hughes, D.J. (1953): Thermal neutron absorption cross sections of boron and gold.
Phys. Rev., 92, 716-721.
Fisch, M. & Armbruster, T. (2012): Thermal Expansion of Aluminoborates. In: “Minerals as Advanced Materials II”, S.V.
Krivovichev, ed., Springer-Verlag, 255-268.
Fischer, R.X. & Schneider, H. (2008): Crystal chemistry of borates and borosilicates with mullite-type structures: a review.
Eur. J. Mineral., 20, 917-933.
Gatta, G.D., Rotiroti, N., Fisch, M., Armbruster, T. (2010): Stability at High Pressure, Elastic Behavior and Pressure-Induced
Structural Evolution of “Al5BO9”, a Mullite-Type Ceramic Material. Phys. Chem. Miner., 37, 227-236.
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.
Gatta, G.D., Lotti, P., Merlini, M., Liermann, H-P., Fisch, M. (2013): High-Pressure Behavior and Phase Stability of Al5BO9,
a Mullite-Type Ceramic Material. J. Am. Ceram. Soc., 96, 2583-2592.
Gatta, G.D., Lotti, P., Comboni, D., Merlini, M., Vignola, P., Liermann, H-P. (2017): High-pressure behavior of
(Cs,K)Al4Be5B11O28 (londonite): A single-crystal synchrotron diffraction study up to 26 GPa. J. Am. Ceram. Soc.,
DOI: 10.1111/jace.14936.
Lotti, P., Gatta, G.D., Comboni, D., Guastella, G., Merlini, M., Guastoni, A., Liermann, H-P. (2017): High-pressure behavior
and P-induced phase transition of CaB3O4(OH)3⋅H2O (colemanite). J. Am. Ceram. Soc., 100, 2209-2220.
US Geological Survey (2007): Mineral Commodity Summaries. US Geological Survey, 195 p.
US Geological Survey (2017): Mineral Commodity Summaries. US Geological Survey, 202 p
Crystal Chemistry of Natural REE-Phosphates and Arsenates and their (T,P)-Behavior
No full textRare Earth Elements (REE, i.e. lanthanides, Y and Sc) are nowadays fundamental components in many technological applications. For their strategic importance and supply risk, REE have been included in the EU list of the so-called “critical raw materials” [1]. This has recently fostered the study of REE minerals, aiming at a deeper understanding of their crystal chemistry, formation and accumulation processes. This contribution focusses on the crystal-chemical features and (T,P)-behavior of REE phosphates and arsenates from Mt. Cervandone (Western Alps, Italy), where REE minerals are common constituents of Alpine quartz-bearing hydrothermal veins, cross-cutting pegmatitic dykes intruded in leucocratic gneisses of the metamorphic basement.
The mineral species under study are the isostructural monazite-(Ce) (ideally CePO4) and gasparite-(Ce) (CeAsO4), Sp. Gr. P21/n, hosting the larger Light REE, and the isostructural xenotime-(Y) (YPO4) and chernovite-(Y) (YAsO4), Sp. Gr. I41/amd, hosting the larger Heavy REE. They define two solid solutions characterized by the monoclinic monazite-type and the tetragonal zircon-type structures, respectively. Chemical data obatined by WDS electron microprobe analysis show that an almost complete solid solution occurs along the xenotime-chernovite tetragonal series, with Y being the dominant cation in the 8-coordinated A site followed by the HREE, whereas a strong depletion in LREE is observed. The latters populate the 9-coordinated A site in the monoclinic structure of monazite and gasparite, for which an apparent miscibility gap is observed among the end members, differently to what observed in samples from other localities [2]. Single-crystal XRD analyses on samples with different crystal chemistry pointed out the prevailing control exerted by the composition of the tetrahedra (P vs. As) on the size and disortion of the structural units and, in turn, of the unit cell volume, independently from the REE composion of the A site. In situ single-crystal and powder synchrotron XRD esperiments have been performed at high-T (Elettra, Trieste), high-P (ESRF, Grenoble; PETRA-III, Hamburg) and combined HPHT (PETRA). The interplay among the crystal chemical and structural features control the bulk response of the investigated REETO4 phases to external thermal and compressional stimuli. The results showed that the monazite-type structure is more compressibile and expandable than the tetragonal zircon-type, whereas, among the zircon-type minerals, chernovite is more compressibile than xenotime, but at high temperature xenotime shows the higher thermal expansion coefficient. In situ HPHT XRD experiments have been performed for the first time on monazite and chernovite: monazite was found to be stable within the investigated range (T < 500 °C and P < 20 GPa), whereas chernovite, which at ambient-T undergoes a phase transition to a scheelite-type polymorph at P > 8-12 GPa, at 250 ≤ T (°C) ≤ 500 preserves the zircon-type tetragonal structure at P < 20 GPa, even though with signs of structural destabilization above 12-15 GPa. A comparison with the thermo-elastic parameters reported in the literature for synthetic end members (see e.g. [2,3]) suggests that further studies on complex multi-component natural solid solutions are needed for a thorough comprehension of the structure-related properties in these minerals.
[1] G.A. Blengini, F. Mathieux, L. Mancini, M. Nyberg, H.M. Viegas Study on the EU’s list of Critical Raw Materials. Executive Summary. Publication Office of the European Commission, Luxembourg, 2020.
[2] F. Pagliaro, P. Lotti, A. Guastoni, N. Rotiroti, T. Battiston, G.D. Gatta, Mineral. Mag. 2022, 86, 150.
[3] D. Errandonea Phys. Status Solidi B. 2017, 254, 1700016
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
P-induced crystal fluid interaction: the case of ERI and OFF topologies
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., Catizzon
T- and P-stability and thermo-elastic behavior of the ABW-compounds TlAlSiO4 and CsAlSiO4
No full textT- and P-stability and thermo-elastic behavior
of the ABW-compounds TlAlSiO4 and CsAlSiO4
Paolo Lotti,a G. Diego Gattaa,b, Domenico Caputoc, Marco Merlinia,
Paolo Apreac, Andrea Lausid, Carmine Colellac
aDipartimento di Scienze della Terra, Università degli Studi di Milano, Milano, Italy
bCNR - Istituto di Cristallografia, Sede di Bari, Bari, Italy
cDipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università degli Studi di Napoli “Federico II”, Napoli, Italy
dSincrotrone Trieste S.C.p.A. di Interesse Nazionale, Basovizza, Trieste, Italy
[email protected]
A large number of microporous compounds sharing the ABW framework topology have so far been reported in the literature. These compounds show a significant chemical variability, leading to interesting magnetic, optical or structural properties (see e.g. [1] and references therein). The ABW framework can be described as made by sheets of six-membered rings of tetrahedra, in which three tetrahedra have apical oxygen atoms pointing upward (U) and three downward (D), according to a “UUUDDD” scheme. The sheets are interconnected through the apical oxygen atoms, giving rise to elliptical 8-membered ring channels, where the extraframework population is hosted. The latter is generally represented by monovalent cations, with (as Li-ABW) or without (as Rb-, Cs- or Tl-ABW) H2O molecules. Only a few studies have so far been devoted to the phase-stability fields and thermo-elastic behavior of ABW compounds, in response to T and P.
In this study, we focused our attention to two synthetic ABW compounds: TlAlSiO4 and CsAlSiO4, which gain interest for the pollutant and/or toxic nature of the hosted extraframework cations (Tl+ or Cs+). TlAlSiO4 has been investigated up to 950 °C (at room-P) and up to 8 GPa (at room-T) by means of in-situ synchrotron powder diffraction with a diamond anvil cell and with a high-temperature furnace [2]. No phase transition has been observed within the T- and P-range investigated. A II-order Birch-Murnaghan equation of state (II-BM EoS) fit of the P-V data led to a refined bulk modulus KV0 = 48.8(2) GPa. A polynomial fit of the T-V data led to a refined volume thermal expansion coefficient αV,25°C = 4.44(3)*10-5 K-1. CsAlSiO4 has been investigated up to 1000 °C (at room-P) and up to 10 GPa (at room-T) by means of in-situ synchrotron powder diffraction [3]. As for the Tl-analogue, no phase transitions have been observed within the T- and P-range investigated. A II-BM EoS fit of the P-V data gave a refined KV0 = 41.3(3) GPa. A polynomial fit of the T-V data led to a refined αV,20°C = 3.63(1)*10-5 K-1. Both the studied ABW-compounds show a remarkably anisotropic thermo-elastic pattern, resembling that of “layered materials” (e.g. phyllosilicates), where the stacking direction of the 6mR-sheets is significantly more compressible and expandable than the sheets plane. Such a behavior appears to be governed by the nature of the ABW topology of the framework. The high stability and flexibility of TlAlSiO4 and CsAlSiO4 at high-T (at room-P) and high-P (at room-T) suggest these compounds as functional materials for the fixation and storage of the Tl+ and Cs+.
[1] V. Kahlenberg, R.X. Fischer, W.H. Baur, Z. Kristallogr. 2001, 216, 489-494.
[2] G.D. Gatta, P. Lotti, M. Merlini, D. Caputo, P. Aprea, A. Lausi, C. Colella, Micropor. Mesopor. Mater. 2014, submitted.
[3] G.D. Gatta, M. Merlini, P. Lotti, A. Lausi, M. Rieder, Micropor. Mesopor. Mater. 2013, 163, 147-152
P-induced crystal-fluid interactions in erionite-K : a natural nano-sponge
No full textThe study of the high-pressure behaviour of microporous compounds, e.g. zeolites, experienced, in last decades, a raising interest related to the P-mediated intrusion of solvated ions/molecules, from the so-called “penetrating” P-transmitting fluids into the zeolitic structural voids [1]. These phenomena may occur when the molecules have a kinetic diameter that allow their adsorption into the structural cavities and may be potentially exploited in the tailoring of functional materials. In this study, we have investigated the P¬-mediated intrusion of H2O and alcohols molecules, carried by the P¬-transmitting fluids, into the structural cavities of the natural zeolite erionite-K, by means of in situ high-pressure single-crystal synchrotron X-ray diffraction, using a diamond anvil cell, at the Xpress beamline of the Elettra synchrotron (Trieste, Italy). Erionites are a series of minerals belonging to the zeolite group, with a wide chemical variability expressed as solid solution among three end-members: erionite-Ca, erionite-K and erionite-Na. The samples we analysed are classified as erionite-K, with an average chemical formula: K2.31Na0.02Ca2.15Mg0.69Ba0.04Sr0.02(Al9.00Si27.19)O72·18.66H2O.
The erionite-type framework is based on the repetition of six-membered rings with a sequence AABAAC. This stacking leads to a structure characterized by the presence of large cages (23-hedron, called “erionite-cage”), superposed along the c-axis, hosting most of the extra-framework population.
To constrain the crystal-fluid interaction, we performed two high-P ramps using different P-transmitting media: 1) with the non-penetrating silicone oil, up to 2.60(5) GPa, and 2) with the potentially penetrating methanol:ethanol:H2O = 16:3:1 (hereafter mew) mixture, up to 4.97(5) GPa.
Silicone oil data allowed the refinement of the isothermal bulk modulus of the pristine sample, expressed as KV0 = 44(1) GPa (βV0 = KV0-1 = 0.0227(5) GPa-1, where βV0 is the bulk volume compressibility), after a fit of a II-order Birch-Murnaghan equation of state to the experimental P-V data.
The P-V data from the mew ramp unambiguously show a marked decrease in compressibility, which is unequivocally related to the P-induced intrusion of H2O (and possibly alcohols) molecules from the P-transmitting fluid. This phenomenon, which appears to be irreversible in decompression, apparently occurs in three different steps, approximately at 0.2, 1.2 and 2 GPa. In addition, the magnitude of the intrusion appears to be comparable with that observed for synthetic zeolites as SiO2-ferrierite [2] or AlPO4-5 [3] and this is somehow unexpected if we consider that the studied erionite is a natural sample, with structural cavities largely filled by extra-framework cations and H2O molecules.
Further experiments, with different classes of potentially penetrating fluids, will allow to fully understand and constrain the P-induced adsorption phenomena in natural erionite.
[1] Gatta GD, Lotti P, Tabacchi G Phys. Chem. Miner. 2018 45, 115-138.
[2] Lotti P, Arletti R, Gatta GD, Quartieri S, Vezzalini G, Merlini M, Dmitriev V, Hanfland M Micropor. Mesopor. Mater. 2015 218, 42-54.
[3] Lotti P, Gatta GD, Comboni D, Merlini M, Pastero L, Hanfland M. Micropor. Mesopor. Mater. 2016 228, 158-167
Cancrinite-group minerals at non-ambient conditions: vishnevite and davyne
No full textIsotypic 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. In order to describe a model for the thermo-elastic behavior of these isotypic compounds, we have recently investigated the high-pressure (up to ca. 8 GPa) and low-temperature (100 ≤ T (K) ≤ 293) characteristics of the (CO3)-rich end-members cancrinite {[(Na,Ca)6(CO3)1.2-1.7][Na2(H2O)2][Al6Si6O24]} and balliranoite {[(Na,Ca)6(CO3)1.2-1.7][Ca2Cl2][Al6Si6O24]}, by means of in situ single crystal X-ray diffraction. The results [1-4] showed 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, governed by the different coordination environment of the extraframework population within the cages. We are extending our investigation on (SO4)-rich members of the group, and in particular on vishnevite {[(Na,Ca,K)6(SO4)][Na2(H2O)2][Al6Si6O24], analogue of cancrinite} and davyne {[(Na,Ca,K)6(SO4,Cl)][Ca2Cl2][Al6Si6O24], analogue of balliranoite}. High-pressure and low-temperature in situ single-crystal X-ray diffraction experiments are currently in progress. A preliminary analysis allowed an early description of their high-pressure behavior. Vishnevite, which is apparently stable up to 7.40(2) GPa, shows a change of the compressional behavior, with an increase of compressibility, between 2.47(2)-3.83(2) GPa. Experimental data within the range 0.0001-2.47(2) GPa have been fitted with a II-order Birch-Murnaghan equation of state (II-BM EoS, K' = 4), giving the following refined elastic parameters: V0 = 733.5(4) Å3, KV0 = 51(1) GPa; a0 = 12.762(2) Å, Ka0 = 59.8(9) GPa; c0 = 5.2013(9) Å, Kc0 = 38.0(6) GPa. A III-BM EoS fit of the experimental data within the range 3.83(2)-7.40(2) gave: V0 = 757(6) Å3, KV0 = 30(3) GPa KV' = 2.6(5); a0 = 12.84(2) Å, Ka0 = 40(3) GPa, Ka' = 1.8(4); c0 = 5.33(4) Å, Kc0 = 16(3) GPa, Kc' = 3.6(5). A re-arrangement of the extra-framework population within the channels appear to control the observed change of the compressional behavior. A significantly less pronounced increase of compressibility was observed for cancrinite at 4.62(2)-5.00(2) GPa [2]. Davyne does not show any loss of crystallinity nor a change of compressional behavior up to 7.18(2) GPa. Experimental data have been fitted with a III-BM Eos, leading to the following refined parameters: V0 = 761.6(4) Å3, KV0 = 46.8(9) GPa, KV' = 3.6(3); a0 = 12.815(2) Å, Ka0 = 50.3(9) GPa, Ka' = 4.0(3); c0 = 5.355(1) Å, Kc0 = 41.6(9) GPa, Kc' = 2.9(2), showing a strong similarity with the elastic behavior of balliranoite at high pressure[4].
[1] G.D. Gatta, P. Lotti, V. Kahlenberg, U. Haefeker Miner. Mag. 2012, 76, 933.
[2] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara Am. Mineral. 2012, 97, 872.
[3] G.D. Gatta, P. Lotti, V. Kahlenberg, Micropor. Mesopor. Mater. 2013, 174, 44.
[4] P. Lotti, G.D. Gatta, N. Rotiroti, F. Cámara, G.E. Harlow Z. Kristallogr. 2013 (in press)
In situ synchrotron studies of open-framework silicates at non-ambient temperature and pressure
No full textThe combined use of synchrotron X-ray diffraction (XRD) techniques and devices for in situ studies at non-ambient temperature and/or pressure allowed a deep investigation of the behavior of open-framework silicates at these conditions. Displacive phase transitions are common mechanisms adopted by framework compounds to accommodate the bulk expansion or contraction, whenever structural distortion is no more possible or energetically efficient. The zeolite mordenite, for example, crystallizes, at ambient condition, in the Cmc21 space group and undergoes a P-induced transition to a primitive polymorph. In situ single-crystal synchrotron XRD allowed to identify the space group symmetry (Pbn21) of the high-P phase and solve its framework structure, allowing to describe the deformation mechanisms triggered by the phase transition at the atomic scale. In the case of minerals, the fundamental thermo-elastic parameters and their relationship with the crystal structure can be accurately determined. Scapolites are common metamorphic minerals able to accommodate volatiles down to the lower crust, which members represent a complex non-binary solid solution. Modelling the role played by the crystal chemistry on the scapolites behavior is possible by investigating the response of the solid-solution members to T and P variations. Our group recently investigated the behavior of an intermediate scapolite (with anomalous I4/m symmetry) by in situ XRD studies at high-P (ambient-T), high-T (ambient-P) and combined high-T and P, at synchrotron facilities, providing a comprehensive characterization of the elastic and structural response, as well as of a pressure-controlled phase transition to a triclinic polymorph (at ~ 9-10 GPa) observed at 25 and 650 °C. In situ synchrotron studies on framework silicates at variable P/T also allows a better understanding of phenomena, which may be exploited in materials science and technological applications, in particular promoting crystal-fluid interactions at extreme conditions. MFI-zeolites, for example, can be adopted as catalysts in the methanol-to-olefin conversion and pressure may be adopted as a tool to improve the process efficiency, by promoting a larger loading of methanol molecules into the zeolites structural pores. In situ high-P powder XRD experiments on all-silica (silicalite) and slightly cation-exchanged MFI zeolites, using non-penetrating silicone oil and penetrating methanol as P-fluids, showed a higher efficiency in methanol adsorption by pure silicalite in the lower pressure regime and, conversely, a higher methanol intrusion in cation-exchanged zeolites at P > 0.5 GPa
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