HIGH-PRESSURE BEHAVIOR OF MICROPOROUS MATERIALS: CRYSTAL-FLUID INTERACTIONS AND DEFORMATION MECHANISMS AT THE ATOMIC SCALE

Zeolite are crystalline, hydrated aluminosilicates characterized by a tetrahedral framework of TO4 units connected in such a way that sub-nanometric channels and cages occur. These structural cavities host the so-called extra-framework population, which mainly consists of alkali and alkaline-earth cations and small molecules, such as H2O. In the last decades, the scientific community showed a rising interest on the behavior of microporous and mesoporous compounds (e.g., zeolites) at high-pressure conditions, and in particular on the crystal-fluid interaction phenomena occurring at extreme conditions. As zeolites could act as an ideal carrier of H2O and others small molecules or monoatomic species (e.g., CO2, CH4, H2S, He, Ar, Kr, Xe,\u2026), experiments on zeolites compressed (and ambient to low/high T) in aqueous mixtures have important implications in the Earth Sciences. Furthermore, high-pressure experiments on synthetic zeolites may pave the way for new routes of tailoring new functional materials (made by hybrid host-guest architecture), bearing a potentially relevant technological impact. In this experimental thesis, after an overall introduction and a section on the high-pressure experimental techniques (Chapter 1 and 2 , respectively), the high-pressure behavior and the crystal-fluid interaction at the atomic scale of a selected series of natural and synthetic zeolites (i.e., AlPO4-5, leonhardite, laumontite, phillipsite) and a zeolites-like mineral (i.e., armstrongite) have been investigated by means of in-situ single-crystal X-ray diffraction, using \u201cpenetrating\u201d and \u201cnon-penetrating\u201d pressure-transmitting fluids. Into details: 1. AlPO4-5 (Chapter 3): the high-pressure behavior of AlPO4-5 has been studied by single crystal XRD using synchrotron radiation and a diamond anvil cell (DAC), with crystals compressed in silicone oil and methanol:ethanol:water =16:3:1 (m.e.w.) mixture. The high-pressure evolution of the crystalline structure and the deformation mechanism at atomic scale have been described on the basis of high-quality structure refinements, revealing adsorption phenomena of H2O (and likely methanol) already at 2 Kbar. Moreover, evidence of an incommensurately modulated structure of AlPO4-5 have been found. 2. Leonhardite and laumontite (Chapter 4): the H2O adsorption kinetics, at ambient pressure and temperature, of leonhardite to give laumontite has been investigated using single crystal XRD techniques. In-situ high-pressure XRD experiments, using synchrotron radiation and a DAC, have been performed in order to obtain the bulk moduli of the two minerals (previously unknown). A detailed description of the atomic deformation mechanisms has been addressed. 3. Phillipsite (Chapter 5): the pressure-induced deformation mechanisms, at the atomic scale, have been studied via single crystals XRD-experiments, using synchrotron radiation and a DAC. Despite no pressure-induced adsorption was observed, the experimental findings suggest a change in the deformation mechanisms induced by a re-arrangement of the extra-framework population. 4. Armstrongite (Chapter 6): the high-pressure evolution of this zeolite-like mineral has been studied in the m.e.w. as nominally penetrating fluid. A first-order phase transition has been detected between 4 and 5 GPa. In the Chapter 7 a detailed discussion of the aforementioned experimental findings has been addressed, along with their technological and geological implications. The results of the present studies have been published in peer-reviewed journals

High-pressure behavior of intermediate scapolite : compressibility, structure deformation and phase transition

Scapolites are common volatile-bearing minerals in metamorphic rocks. In this study, the high-pressure behavior of an intermediate member of the scapolite solid solution series (Me47), chemical formula (Na1.86Ca1.86K0.23Fe0.01)(Al4.36Si7.64)O24[Cl0.48(CO3)0.48(SO4)0.01], has been investigated up to 17.79 GPa, by means of in situ single-crystal synchrotron X-ray diffraction. The isothermal elastic behavior of the studied scapolite has been described by a III-order Birch\u2013Murnaghan equation of state, which provided the following refined parameters: V0 = 1110.6(7) \uc53, KV0 = 70(2) GPa (\u3b2V0 = 0.0143(4) GPa 121) and KV\u2032 = 4.8(7). The refined bulk modulus is intermediate between those previously reported for Me17 and Me68 scapolite samples, confirming that the bulk compressibility among the solid solution increases with the Na content. A discussion on the P-induced structure deformation mechanisms of tetragonal scapolite at the atomic scale is provided, along with the implications of the reported results for the modeling of scapolite stability. In addition, a single-crystal to single-crystal phase transition, which is displacive in character, has been observed toward a triclinic polymorph at 9.87 GPa. The high-pressure triclinic polymorph was found to be stable up to the highest pressure investigated

On the P-induced behavior of the zeolite phillipsite : an in situ single-crystal synchrotron X-ray diffraction study

The elastic behavior and the structural evolution at high pressure of a natural phillipsite have been investigated by in situ single-crystal X-ray diffraction up to 9.44 GPa, using a diamond anvil cell and the nominally penetrating P-transmitting fluid methanol:ethanol:water (16:3:1) mix. Although no phase transition was observed within the P-range investigated, two different compressional regimes occur. Between 0.0001 and 2.0 GPa, the refined elastic parameters, calculated by a second-order Birch\u2013Murnaghan equation of state (BM-EoS) fit, are V0 = 1005(1) \uc53, K0 = 89(8) GPa for the unit-cell volume; a0 = 9.914(7) \uc5, Ka = 81(12) GPa for the a-axis; b0 = 14.201(9) \uc5, Kb = 50(5) GPa for the b-axis; and c0 = 8.707(2) \uc5, Kc = 107(8) GPa for the c-axis (Ka:Kb:Kc ~1.62:1:2.14). Between 2.0 and 9.4 GPa, a P-induced change in the configuration of H2O molecules, coupled with a change in the tilting mechanisms of the framework tetrahedra, gives rise to a second compressional regime, in which the phillipsite structure is softer if compared to the first compressional range. In the second compressional regime, the refined elastic parameters, calculated by a second-order BM-EoS fit, are V0 = 1098 (7) \uc53, K0 = 18.8(7) GPa for the unit-cell volume; a0 = 10.07(3) \uc5, Ka = 30(2) GPa for the a-axis; b0 = 14.8(1) \uc5, Kb = 11(1) GPa for the b-axis; and c0 = 8.94(2) \uc5, Kc = 21(1) GPa for the c-axis (Ka:Kb:Kc ~2.72:1:1.90). The evolution of the monoclinic \u3b2 angle with pressure shows two distinct trends in the two compressional regimes: with a negative slope between 0.0001 and 2.0 GPa, and a positive slope between 2.0 and 9.4 GPa. The mechanisms, at the atomic scale, that govern the two compressional regimes of the phillipsite structure are described

Pargasite at high pressure and temperature

The P-T phase stability field, the thermoelastic behavior and the P-induced deformation mechanisms at the atomic scale of pargasite crystals, from the "phlogopite peridotite unit" of the Finero mafic-ultramafic complex (Ivrea-Verbano Formation, Italy), have been investigated by a series of in situ experiments: (a) at high pressure (up to 20.1 GPa), by single-crystal synchrotron X-ray diffraction with a diamond anvil cell, (b) at high temperature (up to 823 K), by powder synchrotron X-ray diffraction using a hot air blower device, and (c) at simultaneous HP-HT conditions, by single-crystal synchrotron X-ray diffraction with a resistive-heated diamond anvil cell (Pmax = 16.5 GPa, Tmax = 1200 K). No phase transition has been observed within the P-T range investigated. At ambient T, the refined compressional parameters, calculated by fitting a second-order Birch-Murnaghan Equation of State (BM-EoS), are: V0 = 915.2(8) \uc53 and KP0,T0 = 95(2) GPa (\u3b2P0,T0 = 0.0121(2) GPa-1) for the unit-cell volume; a0 = 9.909(4) \uc5 and K(a)P0,T0 = 76(2) GPa for the a-axis; b0 = 18.066(7) \uc5 and K(b)P0,T0 = 111(2) GPa for the b-axis; c0 = 5.299(5) \uc5 and K(c)P0,T0 = 122(12) GPa for the c-axis [K(c)P0,T0 ~ K(b)P0,T0 > K(a)P0,T0]. The high-pressure structure refinements (at ambient T) show a moderate contraction of the TO4 double chain and a decrease of its bending in response to the hydrostatic compression, along with a pronounced compressibility of the A- and M(4)-polyhedra [KP0,T0(A) = 38(2) GPa, KP0,T0(M4) = 79(5) GPa] if compared to the M(1)-, M(2)-, M(3)-octahedra [KP0,T0(M1,2,3) 64 120 GPa] and to the rigid tetrahedra [KP0,T0(T1,T2) ~ 300 GPa]. The thermal behavior, at ambient pressure up to 823 K, was modelled with Berman's formalism, which gives: V0 = 909.1(2) \uc53, \u3b10 = 2.7(2)*10-5 K-1 and \u3b11 = 1.4(6)*10-9 K-2 [with \u3b10(a) = 0.47(6)*10-5 K-1, \u3b10(b) = 1.07(4)*10-5 K-1, and \u3b10(c) = 0.97(7)*10-5 K-1]. The petrological implications for the experimental findings of this study are discussed

Ettringite at high pressure: structure evolution and elastic behaviour

In order to predict the elastic properties of the complex multi-component Portland cement, database of the thermodynamic parameters of the main constituents is needed. Ettringite (ideally Ca6Al2(SO4)3(OH)12\ub727H2O, with a=b \uf07e 11.21 and c \uf07e 21.43 \uc5, Sp. Gr. P31c) is a common crystalline phases in Portland cements. It contains more than 45 wt% of H2O. In the early hydration stages, the crystallization of ettringite governs the set rate of the highly reactive Ca3Al2O6 phase (also known as \u201cC3A\u201d), whereas in aged cements its formation is associated to degradation processes1. The crystal structure of ettringite is rather complex and it consists of [Ca3[Al(OH)6]\ub712H2O]-columns (in which Al(OH)6-octahedra are alternated with triplets of Ca(OH)4(OH2)4-polyhedra) and sulphate groups connected by a complex H-bonding net2. Previous studies on the behavior of ettringite at high pressure reported only the isotropic compressional behavior of ettringite 3,4. Because of that, the linear bulk moduli (Ka and Kc) and a full description of the deformation mechanisms at the atomic scale are still missing. We compressed a single crystal of ettringite up to 4.2 GPa by means of in-situ synchrotron X-ray diffraction, using a diamond-anvil cell 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), which dramatically changes at P>3 GPa (Fig. 1). At P>3 GPa, the bulk modulus KV of ettringite drops from 26.6(5) to 10.4(8) GPa. Such a softening is governed by the structural changes which affect mainly the elastic behavior on the ab plane (Ka drops from 21(1) to 7.3(8) GPa whereas Kc decreases only moderately). The structure refinements reveal that the elastic softening reflects the collapse of the H-bonding net, due an average decrease of the Odonor\ub7\ub7\ub7Oacceptor distances (up to 0.20 \uc5 in some cases), which mainly affect the interaction between the sulphate groups and the Ca(OH)4(OH2)4-polyhedra lying in the ab plane

Intermediate scapolite: behavior at non-ambient conditions and unusual symmetry

The scapolite series of minerals represents a complex non-binary solid solution, which end members are: marialite [Na4Al3Si9O24Cl], meionite [Ca4Al6Si6O24CO3] and silvialite [Ca4Al6Si6O24SO4]. The members which composition falls on the marialite-meionite joint appears to be the most common in natural occurrences [1,2]. The members close to marialite on one side and to meionite on the other side, are usually reported to crystallize in the tetragonal I4/m space group, whereas intermediate scapolites are usually found in the primitive space group P42/n. In this study, we report a scapolite of intermediate composition (Na1.86Ca1.86K0.23Fe0.01)(Al4.36Si7.64)O24[Cl0.48(CO3)0.48(SO4)0.01], which, based on both X-ray and neutron single-crystal diffraction data, shows an anomalous I-centered lattice (Figure 1), possibly due to anti-phase domains too small to be detected by diffraction techniques. The behavior at non-ambient conditions of the same sample has been investigated at high-P (ambient-T) by single-crystal XRD at the former ID09 beamline of ESRF (Grenoble) and at high-T (ambient-P) by powder XRD at the MCX beamline of the Elettra synchrotron (Trieste), providing the following thermodynamic parameters: \uf020\uf062V0 = 0.0143(4) GPa-1 and \u3b1V0 = 1.87(4)\ub710-5 K-1, respectively, which confirm that compressibility and thermal expansivity increase, along the solid solution series, from meionite to marialite [3-6]. A P-induced phase transition towards a triclinic polymorph has been observed at 9.87 GPa at ambient-T. An in situ single-crystal XRD experiment at combined high P and T (using a resistive-heated DAC), performed at the P02.2 beamline of the Petra-III synchrotron (Hamburg), allowed to detect the occurrence of the same phase transition at 10.51 GPa at 650 \ub0C

Thermal stability and high-temperature behavior of the natural borate colemanite: An aggregate in radiation-shielding concretes

Colemanite is a natural borate that can be used as an aggregate in neutron-radiation shielding concretes. In this study, we report its thermal behavior, up to 500 degrees C, by describing: 1) its dehydration mechanisms and 2) its thermo-elastic parameters. The thermal expansion of colemanite is significantly anisotropic. The refined volume thermal expansion coefficient at ambient conditions is: alpha(V0) = 4.50(10).10(-5) K-1. The loss of structural H2O occurs at least from similar to 240 degrees C, and at T > 325 degrees C an irreversible amorphization occurs, followed by a complete dehydration. The potential implications on the use of colemanite as concrete-aggregate are discussed. (C) 2019 Elsevier Ltd. All rights reserved

High-pressure behavior of natural borate colemanite. An in situ synchrotron single-crystal X-ray diffraction study

Colemanite is an inoborate compound and a common constituent in natural borate deposits. In addition, it is an economically relevant mineraI commodity, not only as a primary source for B, but a1so for its applications in the production of 1ightweight concretes and ceramics. Despite its relevance in industriaI applications, its elastic behavior, phase stability and structure evolution with pressure have never been investigated. Here we report the high-P behavior of a natural colemanite based on an in-situ synchrotron single-crystal X-ray diffraction study performed at the P02.2 beamline at PETRAIII, Hamburg, Germany. Colemanite, which crystallizes in the monoclinic P2 la space group (a =8.712 A, b = 11.247 A, c = 6.091 A, beta= 110.12\ub0, V = 560.4 A3), undergoes a reconstructive phase transition between 13.95 and 14.91 GPa, toward a monoclinic polymorph (S.G.: P2/n, a = 11.726 A, b = 10.206 A, c = 23.45 A, beta =95.07\ub0, V= 2796 A3, at 14.91 GPa). A III-order Birch-Murnaghan EoS fit leads to a refined bu1k modulus at ambient conditions of 76(8) GPa [i(v' =4.4(10)], for colemanite in the phase stability field: 0.0001-13.95 GPa. The structure of colemanite is made by infinite chains of corner-sharing B-polyhedra alternated by chains of cornersharing Ca-polyhedra (coordination number 8). Of the three crystallographicaIly independent B sites, one shows a triangular coordination and the others a tetrahedral coordination. In the high-P polymorph, only three over eighteen independent B-sites (116) show a triangular coordination, the other fifteen being B(O,OH)4 tetrahedra. Two independent corner-sharing bora te chains are interconnected through corner and edge-sharing chains of Ca-polyhedra (C.N. 8 or 9). X-ray diffraction patterns collected during P-release show that the plme transition is completely reversible and colemanite fully recovers its starting structura1 features

High-pressure behavior and P-induced phase transition of CaB3O4(OH)3·H2O (colemanite)

Colemanite (ideally CaB3O4(OH)3\ub7H2O, space group P21/a, unit-cell parameters: a ~ 8.74, b ~ 11.26, c ~ 6.10 \uc5, \u3b2 ~ 110.1\ub0) is one of the principal mineralogical components of borate deposits and the most important mineral commodity of boron. Its high-pressure behavior is here described, for the first time, by means of in situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell up to 24 GPa (and 293 K). Colemanite is stable, in its ambient-conditions polymorph, up to 13.95 GPa. Between 13.95 and 14.91 GPa, an iso-symmetric first-order single-crystal to single-crystal phase transition (reconstructive in character) toward a denser polymorph (colemanite-II) occurs, with: aCOL-II=3\ub7aCOL, bCOL-II=bCOL, and cCOL-II=2\ub7cCOL. Up to 13.95 GPa, the bulk compression of colemanite is accommodated by the Ca-polyhedron compression and the tilting of the rigid three-membered rings of boron polyhedra. The phase transition leads to an increase in the average coordination number of both the B and Ca sites. A detailed description of the crystal structure of the high-P polymorph, compared to the ambient-conditions colemanite, is given. The elastic behaviors of colemanite and of its high-P polymorph are described by means of III- and II-order Birch-Murnaghan equations of state, respectively, yielding the following refined parameters: KV0=67(4) GPa and KV\u2032=5.5(7) [\u3b2V0=0.0149(9) GPa-1] for colemanite; KV0=50(8) GPa [\u3b2V0=0.020(3) GPa-1] for its high-P polymorph