1,721,082 research outputs found
Phase transitions and crystal structure evolution of hydrated borates at non-ambient conditions
Full text linkHydrated borates are a class of minerals composed of clusters or chains of Bφx groups (where φ represents an oxygen atom, a H2O molecule, or an OH- group) organized either in tetrahedra or planar triangular groups. Hydrated borates are considered a more cost-effective alternative to B4C in radiation-shielding concretes [1], primarily due to the significant cross-section (~3840 barns) for thermal neutrons of the 10B isotope, which represents approximately 20% of natural boron. It is advisable to comprehensively characterize the crystal chemistry, elastic properties, P-T phase stability fields, and structural behaviour of natural borates under varying temperature and pressure conditions to model and understand their role as aggregates in radiation-shielding concretes [2], where the components experience pressure (via static compression) and temperature (via irradiation). Since 2018, my research group has conducted an extensive study of economically valuable hydrated borates, as well as common complementary phases occurring in borates deposits. High-pressure investigations of all studied hydrated borates have revealed one or more phase transitions occurring at pressures below 11 GPa, and the occurrence of these transitions appears to be highly correlated with the H2O content of the minerals (e.g., [3-4]). In response to the phase transitions, the most significant structural change observed in our experiments is the increase in the coordination number of alkali/alkaline-earth cations as well as of part of the boron population, from IIIB to IVB, due to the interaction between IIIB and H2O molecules. This, on the other hand, emphasizes the importance of the hydrogen bond network, usually with complex and pervasive configuration, in preserving the stability of the crystalline edifice of this class of materials.
References
1. Okuno K. (2005). Radiat. Prot. Dosimetry. 115, 258–261.
2. Torrenti J. and Nahas G. (2010) Int. Conf. Concr. under Sev. Cond., Merida, Yucatan. 3–18
3. Comboni D., Pagliaro F., Gatta G. D., et al. (2020) J. Am. Ceram. Soc. 103:5291–5301
4. Comboni D., Poreba T., Pagliaro F., et al. (2021) Acta Crystallogr. B 77:940–945
Crystal-fluids interaction in zeolites at high pressure
No full textZeolites (natural or synthetic) are a class of open-framework silicates with cavities, in the form of channels or cages, with diameters shorter than 2 nm. These porous materials respond to the applied pressure differently, in response to the nature of the pressure-transmitting fluids, used to compress hydrostatically the materials under investigation. For instance, cavities can be accessed or filled by suitable guest chemicals, intruded in the zeolitic pores upon compression. Moreover, pressure can play an important role also in increasing the efficiency of zeolites as "nano-reactors", favoring the access of reactants and products to/from the catalytically active sites and the aggregation of molecules in the cavities. Over the last years [1,2,3], we have performed a series of experiments - by in-situ single-crystal and powder synchrotron diffraction using a number of penetrating and non-penetrating pressure transmitting fluids with a diamond anvil cell – in order to describe the crystal-fluid interaction upon pressure of a series of natural or synthetic zeolites with different topologies and compositions, expected to favor or not the penetration of liophilic/hydrophobic guest species. The following aspects were investigated: 1) the structural deformations of the tetrahedral framework in response to the isotropic compression regime; 2) the unit-cell variations with pressure and the elastic anisotropy; 3) the penetration of molecules of the P-fluid (e.g., H2O, methanol, ethanol, ethylene glycol), along with the host-guest and guest-guest interactions; 4) the reversibility extents of the observed phenomena.
The authors acknowledge the Italian Ministry of Education, MIUR-Project: “Futuro in Ricerca 2012 - ImPACT- RBFR12CLQD”
Crystal-fluid interactions in erionite-group zeolites under compression
No full textIn the last two decades many studies showed that hydrostatic compression is able to enhance or induce the intrusion of molecules (or solvated ions) into the structural nano-cavities of microporous materials, pointing out that this is a viable way to promote a mass transfer from fluids to structurally-incorporated molecules. A full understanding of this phenomenon in natural or synthetic zeolites might expand the number of their utilizations, e.g. tailoring of new materials, as catalysts in industrial processes [1,2]. In addition, this phenomenon bears an intrinsic relevance also in Earth Sciences, as zeolites may act as fluid carriers in the upper Earth crust, e.g. during the early subduction of oceanic sediments or altered basalts.
In this scenario, we focused on three natural zeolites, structurally characterized by six-membered rings of tetrahedra and belonging to the large group of ABC-6 open-framework materials: erionite, offretite and bellbergite. Erionite is a quite common zeolite in nature, where it forms in basaltic vugs, crystallizing from hydrothermal fluids. It shows an ERI-type framework, made by the repetition of AABAAC sequences of 6-membered rings of tetrahedra layers. Offretite (OFF framework type) shows an AAB sequence and is commonly intergrown with erionite, due the easy occurrence of stacking faults at B and C positions of the 6-membered rings layers. Bellbergite is a rather uncommon zeolite in nature, more famous for its synthetic counterparts [3], and shows an EAB framework with ABBACC sequence.
The crystal-fluid interactions during compression were investigated by means of in situ single-crystal X-ray diffraction, which allows to focus the study on the effects that interaction has on the crystal structure of zeolites. The experiments were performed at the ID15B beamline of the European Synchrotron Radiation Facility, using diamond anvil cells to apply hydrostatic pressures on the investigated samples and using different pressure-transmitting fluids: namely, the non-penetrating silicone oil and daphne oil 7575 and potentially penetrating methanol:ethanol:water 16:3:1 mixture, ethanol:water 1:1 mixture, methanol, distilled H2O and liquid Ne. As non-penetrating are intended those fluids which molecules have a kinetic diameter larger than the free diameter of the open-framework of the zeolite and, therefore, cannot be pressure-intruded into the crystal structure. The compressional experiments in non-penetrating fluids provide, therefore, a benchmark to which compare the behavior of the same microporous compound in a potentially penetrating fluid.
Among the investigated natural samples, erionite resulted to be the one with the highest magnitude of adsorption, as shown by Figure 1. The new adsorbed molecules act as “pillars” within the framework nanocavities, decreasing the compressibility of the structure, as it is clear comparing the unit-cell vs. pressure evolution of erionite compressed in silicone oil and methanol:ethanol:water (16:3:1) mixture, respectively (Figure 1). The obtained results also allow to conclude that the magnitude of the intrusion for a given zeolite is strictly related to the H2O content of the hydrous P-transmitting fluids, where the largest is the water fraction, the highest the magnitude of the intrusion and (sometimes) the lower the pressure at which it occurs. A comparison of the crystal-fluid interactions under pressure in natural erionite and in other synthetic zeolites (e.g. SiO2-ferrierite [4]), points out that the observed magnitude of intrusion in this study is surprisingly high for a natural zeolite, characterized by channels and cages already filled by extraframework cations and molecules. These results suggest that natural zeolites, despite being intrinsically less inclined to show pressure-induced crystal-fluid interaction with respect to synthetic ones, should not be a priori excluded as targets for the tailoring of new materials by exploiting hydrostatic compression, especially when a modest temperature is also applied. Moreover, the obtained results also suggest that the role of zeolites as fluid carriers or fluid moderators in the geological processes occurring in the upper Earth crust deserves a more comprehensive characterization for a full understanding.
Acknowledgements: ESRF is acknowledged for the provision of beamtime. The Italian Ministry of Education (MUR) is acknowledged for the support through the projects “PRIN2017—Mineral reactivity, a key to understand large-scale processes” (2017L83S77) and “Dipartimenti di Eccellenza 2023-2027”.
References (up to five):
[1] G.D. Gatta, P. Lotti, G. Tabacchi, Physics and Chemistry of Minerals 45, 2018, 115–138
[2] D. Comboni, F. Pagliaro, P. Lotti, G.D. Gatta, M. Merlini, S. Milani, M. Migliori, G. Giordano, E. Catizzone, I.E. Collings, M. Hanfland, Catalysis Today 345, 2020, 88–96.
[3] R. Aiello, R.M. Barrer, Journal of the Chemical Society A, 1970, 1470-1475.
[4] P. Lotti, R. Arletti, G.D. Gatta, S. Quartieri, G. Vezzalini, M. Merlini, V. Dmitriev, M. Hanfland, Microporous and Mesoporous Materials 218, 2015, 42-54
Unusual symmetry of intermediate scapolite
No full textThe 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 sample from Madagascar, which composition falls between those of the end-members marialite an meionite: (Na1.86Ca1.86K0.23Fe0.01)(Al4.36Si7.64)O24[Cl0.48(CO3)0.48(SO4)0.01]. Based on both X-ray and neutron single-crystal diffraction data, an anomalous I-centered lattice (I4/m space group) is observed. This unusual symmetry for an intermediate scapolite, may be assigned to the presence of anti-phase domains too small to be detected by diffraction techniques. In situ high-T X-ray diffraction investigations show that the I4/m space group is observed to be stable at least up to 1000 °C.
[1] D.K. Teerstra, B.L. Sheriff Chem. Geol. 1997, 136, 233 [2] E. Sokolova, F.C. Hawthorne Can. Mineral. 2008, 46, 1527
High pressure behaviour of AIP04-5 in penetrating/ non penetrating pressure medium
Full text linkAluminophosphate are objects of a growing research interest due to their potential technologieal and industriaI applications [e.g 1,2]. Their large channels serve as ideaI host for organie compounds and small polymers. Among those, AIP0-5 is a synthetic zeolite characterized by an open-framework of (P,AI)O4 tetrahedra. The tetrahedra are connected to form six-and twelve-membered rings, in such a way that a large channel (0~7.3À), parallel to the [001] direction, occurs. Klap et al. [3] underlines that every crystal of AIP0-5 is built up by three different microdomains, in which the positions of the framework oxygen atoms are slightly different; the main effect of the structural disorder is the very large anisotropie displacement parameters of the framework oxygens. We performed two in situ single-crystal synchrotron X-ray diffraction experiments using both penetrating (methanol:ethanol:H20 mix, m:e:w) and non-penetrating (silicon oil) pressure media [4]. The structure refinements showed that: 1) for compression in m:e:w mix, H20 molecules are absorbed at low-P regime, forming a H20-network by H-bonding interaction; 2) the elastic parameters of the super-hydrated AIP04 5 are different if compared to the one compressed in silicon oil; 3) the structural deformation mechanisms of super-hydrated and regular AIP04 -5 are different; 4) evidence of a incommensurately modulated structure occur (according to [3]), and there is an evolution of the non-Bragg reflections with pressure.
The author acknowledges the ltalian Ministry of Education, MIUR-Project: "Futuro in Ricerca 2012 -ImPACT-RBFR12CLQD".
[lJ Tang Z.K. et al. Applied Physies Letters 1998; 73, 2287-2289.
[2] Yang W.S. et al. Microporous and mesoporous materials 20i6; 219,87-92. [3J Klap G.J. et al. Mieroporous and mesoporous materials 2000; 38,403-412. [4J Gatta, G.D. Mieroporous and Mesoporous Material 2010; 128, 78-84
P-induced crystal-fluid interaction in 6-membered ring zeolites: the case of ERI, OFF and EAB topologies
No full textPressure (P)-induced intrusion of molecules (or solvated ions) into the structural nano-cavities of microporous materials opened a new route to promote a mass transfer from fluids to structurally-incorporated molecules. A full understanding of this phenomenon in natural or synthetic zeolites might expand the number of their utilizations, e.g. tailoring of new materials, as catalysts in industrial processes [1,2]. On the other hand, from the geological point of view, the study of this phenomenon is unveiling the role played by zeolites as fluid carriers in the upper Earth crust, e.g. during the early subduction of oceanic sediments or altered basalts.
We have investigated the high-P behaviour, promoting P-mediated crystal-fluid interaction, of three different zeolites with structural homologies: erionite (ERI framework type, 6-membered ring sequence: AABAAC), offretite (OFF, with AAB seq.), bellbergite (EAB, with AABCCB seq.) and its synthetic counterpart. These studies allowed to 1) a better understanding of the potential role played by erionite as fluid carrier during the early subduction, being this mineral a constituent of ocean floors basaltic alteration [3] and 2) compare the mechanisms adopted by structurally similar 6-mRs frameworks to accommodate the bulk compression and the crystal-fluid interactions.
Synchrotron X-ray diffraction experiments have been performed on natural single crystals of erionite, bellbergite and offretite. Additionally, experiments have been performed on powder samples with EAB framework (synthetized according to the Aiello-Barrer protocol [4] and treated in order to obtain Na- and K- forms). Both non penetrating (silicone oil and daphne oil 7575) and potentially penetrating P-transmitting fluids (methanol:ethanol:water 16:3:1 mixture, ethanol:water 1:1 mixture, methanol, H2O, liquid Ne) have been used.
Among the natural samples, erionite resulted to be the one with the highest magnitude of adsorption. The new adsorbed molecules act as “pillars” within the framework nanocavities, decreasing the compressibility of the structure. Moreover, the magnitude of the intrusion resulted to be strictly related to the H2O content of the hydrous P-transmitting fluids.
Ne atoms were able to penetrate into the 12mRs channel of the offretite framework in response to the applied pressure, with weak Van der Waals interactions with the extra-framework population. Methanol resulted to behave as a non-penetrating fluid for natural bellbergite, while it acts as a penetrating fluid in the synthetic counterparts. This highlighted the role of “secondary factors” on the occurrence of crystal-fluid interaction, e.g. the extra-framework content of the sample and the size of crystallites (single crystal of natural bellbergite vs. synthetic EAB powder).
References
[1] G.D. Gatta, P. Lotti, G. Tabacchi, (2018), The effect of pressure on open‐framework silicates: elastic behaviour and crystal–fluid interaction, Phys. Chem. Miner., 45, 115–138
[2] D. Comboni, F. Pagliaro, P. Lotti, G.D. Gatta, M. Merlini, S. Milani, M. Migliori, G. Giordano, E. Catizzone, I.E. Collings, M. Hanfland, (2020), The elastic behavior of zeolitic frameworks: The case of MFI type zeolite under high-pressure methanol intrusion, Catal. Today, 345, 88–96.
[3] F. Vitali, G. Blanc, P. Larqué, (1995), Zeolite distribution in volcaniclastic deep-sea sediments from the Tonga Trench Margin (SW Pacific), Clays and Clay Miner., 43, 92–104.
[4] R.Aiello, R.M. Barrer, (1970), Hydrothermal Chemistry of Silicates
The natural borate colemanite at non-ambient conditions: behavior at low temperature and high pressure
No full textColemanite, CaB3O4(OH)3*H2O, is a common mineral in borate sedimentary deposits in saline lakes, related to hydrothermal volcanic activity, and it is one of the main mineral commodities for the extraction of boron. Due to its relative abundance, in particular at the mine dumps, several recent works were devoted to explore its potential technological and industrial applications (see e.g. [1] for a list of references). Despite this interest, very few was known on the behavior of the colemanite crystal structure at non-ambient conditions of temperature and pressure. This contribution reports the results obtained from in situ low-temperature (T < 293 K) and high-pressure experiments.
A displacive phase transition from the centrosymmetric P21/a colemanite to a ferroelectric polymorph with P21 symmetry was long time known to occur in the T-range between 273 and and 263 K (e.g. [2]). Thermal analysis and in situ single-crystal X-ray diffraction data confirmed the transition, which was found to occur between 265 and 260 K. A thorough chemical analysis, performed by a combination of techniques, revealed the relative pureness of the natural sample of colemanite investigated, supporting the hypothesis that the absence of impurities reduces the T of transition to the ferroelectric state (i.e. it reduces the stability field of the ferroelectric polymoprh) [3]. Single crystal X-ray and neutron diffraction data (down to 104 and 20 K, respectively) showed that the transition has limited effects on the crystal structure of colemanite.
On the other hand, in situ high-pressure single-crystal X-ray diffraction experiments disclosed a much more complex scenario, with a first-order reconstructive phase transition occurring between 13.95 and 14.91 GPa, toward a denser polymorph with a = 3*aCOL, b = bCOL and c = 2*cCOL. Despite reconstructive, the transition is single crystal-to-single crystal and involves an increase in the average coordination number of both the Ca and B sites. The tripling of the a-axis and the doubling of the c-axis imply the split of every independent atomic site of colemanite in six new independent positions in the high-P polymorph. In particular, three of the six new sites, generated from the parent triangularly coordinated B, increase their coordination number from three to four, gaining a bond with a H2O oxygen. The elastic behavior of colemanite and of the high-P polymorph have been described by means of III- and II-order Birch-Murnaghan equations of state, respectively, yielding the following bulk moduli: 67(4) GPa (colemanite, KV' = 5.5(7)) and 50(8) GPa (high-P colemanite).
[1] P. Lotti, G.D. Gatta, D. Comboni, G. Guastella, M. Merlini, A. Guastoni, H-P. Liermann J. Am. Cer. Soc. 2017, in press, DOI: 10.1111/jace.14730.
[2] F.N. Hainsworth, H.E. Petch Can. J. Phys. 1966, 44, 3083.
[3] H.H. Wieder, A.R. Clawson, C.R. Perkerson J. Appl. Phys. 1962, 33, 1720
High-pressure behavior of natural borate colemanite. An in situ synchrotron single-crystal X-ray diffraction study
Full text linkColemanite 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°, 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°, 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
Inderborite : a comprehensive reinvestigation of its technological features
Full text linkInderborite is a hydrated borate (ideal formula:...) often found in lower fractions alongside with the
five most important boron commodities (i.e., colemanite, kernite, ulexite, borax, tincalconite).
Nowadays, Turkish mines produce more than 70% of the worldwide B-minerals (e.g., Sarikaya borate
deposits, Baysal, 1973). Hydrated borates have been listed as critical raw materials by the EU (EU
Commission, 2017), and, because of the high neutron cross-section of B-10, they could be used as
aggregates in neutron-shielding Sorel or Portland concretes, enhancing their adsorption towards
thermal neutrons. In the forthcoming decades, with the advent of fusion power plants, it is predicted
that substantial quantities of neutron-activated elements (e.g., beryllium or tungsten), will be
produced (Gonzalez de Vincente et al. 2022). The main goal of this projects was to: i) re-investigate,
by means of a multi-methodological approach, the crystal chemistry (with a focus on the B isotopic
composition and trace elements) and structure of inderborite (even based on a single-crystal neutron
diffraction experiment), ii) assess the stability range of inderborite with respect to pressure and
temperature even for potential industrial utilization of this borates, iii) describe the structural
evolution of inderborite, at the atomic scale, with increasing pressure and temperature
Compressibility of hibonite (CA6): a single crystal synchrotron radiation high-pressure study
No full textThe elasticity of hibonite (ideally CaAl12O19, space group P63/mmc) has been investigated by synchrotron radiation high-pressure single crystal X-ray diffraction, using a membrane-driven diamond anvil cell mounting Boehler-Almax design diamonds and methanol:ethanol:water (16:3:1) and helium as pressure-transmitting fluids, at the ID15B beamline of ESRF, Grenoble, (λ = 0.4111 Å) up to 19.5 GPa. We collected 26 pressure data points. On compressing, no displacive phase transition has been observed. We have fitted lattice volume data with a BM2 EoS, using EosFit7c [1], and obtain zero-pressure isothermal bulk modulus (K0T) of 204(1) GPa and a unit-cell volume of 590.44(14) Å3. Linearized EoS were fitted using cubed lattice parameters [1] and obtained zero-pressure isothermal bulk modulus (K0T) of 256(3) GPa for a lattice parameter and of 141(1) GPa for c lattice parameter. Therefore, the structure is significantly stiff, and strain develops predominantly on the c direction. Hibonite structure is based on the periodic repetition along [0001] of ten layers of approximately closest-packed oxygen atoms. The sequence can be expressed as (chhhcchhhc), where c and h symbolize cubic and hexagonal closest-packed layers, respectively. The cubic close-packed layers constitute blocks that have the spinel structure (S = [M6O8]2+) and are interlayered between blocks having the hexagonal close-packed character R (= [AM6O11]2-), resulting in a staking with a S′RSR′S′ sequence, where R' and S' are rotated 180° around c relative to R and S. Hibonite has the structural formula A[XII]M1[VI]M2[V]M32[IV]M42[VI]M56[VI]O19, where Ca is 12‐ fold coordinated at site A and Al3+ ions are distributed over three distinct octahedra [M1, M4 and M5], the M3 tetrahedron, and the unusual fivefold coordinated trigonal bipyramid M2. The hibonite sample comes from Sierra de Comechingones (Argentina) and has composition (Ca1.01Na0.01)1.02 (Al11.58V0.33Ti0.02Mg0.06Si0.01)1.00O19. Structure refinements yields V ordered in M2[V] M42[VI] sites with composition M2(Al0.94V0.06) and M4(Al1.73V0.27)2 whereas Mg orders in M32[IV] (with composition M3(Al1.94Mg0.06)2). Evolution of polyhedral volumes show that M2[V] M42[VI] and A show a decrease of ca. 10% whereas it is lesser for the rest of the sites. The M2[V] M42[VI] and A sites belong to the R-block, whereas M1[VI]M32[IV]M56[VI] constitute the S-block. Therefore, there is a heterogeneity of the strain along [0001], which alternates between the S-blocks and the more compliant R-block. Congruently, high-T studies [2] have observed that the R-block expands more than the S-block. It remains uncertain if this heterogeneity is due to compositional stain (V ordered at the R-block) or to intrinsic behavior of the hibonite structure
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