1,035 research outputs found
Phase stability of hydrated borates at high pressure
No full textHydrated borates are a class of minerals made by clusters or chains of Bφx groups (φ represents an oxygen, an H2O molecule or an OH-) organized either in tetrahedra or in planar trigonal groups. Hydrated borates are believed to be a cheaper alternative to B4C for radiation-shielding concretes (Okuno et al., 2005), due to the large cross section (~3840 barns) for thermal neutrons of the isotope 10B, which represents about 20% of
the boron in nature. A comprehensive characterization of the crystal-chemistry, elastic properties, stability and structural behavior of natural borates at varying T and P conditions is advisable for modelling and understanding their role when utilized as aggregates in radiation-shielding concretes (Torrenti et al., 2010), in which the components are subject to pressure (by static compression) and temperature (by irradiation). Interestingly, all hydrated borates studied so far at high-pressure display one (or more) phase transition, and the pressure at which the phase transitions occur seems to be correlated to the H2O content of the minerals (e.g., Comboni et al., 2020, 2021). During the phase transitions, the most dramatic structural change is the increase
of the coordination number of part of the IIIB to IVB, by the interaction between the IIIB and one H2O molecule or OH- group, underlying the importance of the hydrogen bond network in the stability of the crystalline structure.
Comboni D., Pagliaro F., Gatta G.D., Lotti P., Milani S., Merlini M., Battiston T., Glazyrin K. & Liermann H.P. (2020) - High-pressure behavior and phase stability of Na2B4O6(OH)2·3H2O (kernite). J. Am. Ceram. Soc., 103, 5291-5301.
Comboni D., Poreba T., Pagliaro F., Battiston T., Lotti P., Gatta G.D., Garbarino G. & Hanfland M. (2021) - Crystal structure of the high-P polymorph of Ca2B6O6(OH)10·2(H2O) (meyerhofferite). Acta Crystallogr., B77, 940-945.
Okuno K. (2005) - Neutron shielding material based on colemanite and epoxy resin. Radiat. Prot. Dosim., 115, 258-261.
Torrenti J. & Nahas G. (2010) - Durability and Safety of Concrete Structures in the Nuclear Context. Int. Conf. Concr. under Sev. Cond., Merida, Mexico, 3-18
The anomalous high-pressure phase transition of inderite
No full textInderite, ideally [MgB3O3(OH)5∙5H2O], is a hydrated borate discovered in the Inder deposit (Kazakhstan) in 1937 and structurally characterized for the first time by Boldyreva [1]. Inderite is a Na-free hydrated borate and, unlike others common Na-bearing minerals like ulexite (NaCaB5O6(OH)6·5H2O) or borax (Na2B4O5(OH)4·8H2O). Therefore, inderite would not promote any deleterious Alcali-Silica Reactions (ASR, triggered by Na-bearing phases), if used as an aggregate in Portland cements. In the last years, phase transitions occurring at different pressures were discovered in a plethora of hydrous borates, including kurnakovite and meyerhofferrite [2,3] which share the same polyion unit [B3O3(OH)5]2-. The high-pressure stability field of this kind of hydrated borates, having polyions in isolated units, appears to be directly correlated with the total H2O content of the mineral itself. In this light, the high-pressure behaviour of inderite was investigated by an in-situ single-crystal X-ray diffraction (up to 17.4 GPa) under hydrostatic conditions. Results show: 1) inderite undergoes a first order phase transition between ~6.15 and ~6.45 GPa marked by a sudden 7.0 % volume decrease; 2) the structure of the high-pressure polymorph, inderite-II, was solved (Fig. 1); 3) as response to the phase transition, the boron site in planar-triangular coordination bonds to a H2O molecule, forming a tetrahedron; 4) inderite was found to be a highly anisotropic mineral.
[1] Boldyreva A.M. Mem Soc russe Min, 1937, 2, 651–671
[2] Comboni D., Poreba T., Pagliaro F., et al. Acta Crystallographica Section B, 2021, 6, 940-945.
[3] Pagliaro F., Lotti P., Battiston T., et al. Construction and Building Materials, 2021, 121094
The role of temperature on the pressure-mediated adsorption in natural zeolites: the case of leonhardite
No full textWhile the high-pressure and high-temperature behavior of natural zeolites has been intensively studied in the
last decades, to the best of our knowledge, no in-situ X-ray diffraction studies have been performed combining
the effects of both. Experiments at these conditions could have crucial geological implications and potential
applications at the industrial level (e.g., high-P/T adsorption of alcohols compounds in zeolites to promote
methanol to olefins reaction). In this study, we present the results from the first pilot experiments, obtained
with an easy and reproduceable experimental set-up, performed with one of the most common natural zeolite,
i.e., laumontite ([(Ca4-xNax)Kx][Al8Si16O48]⋅(H2O)n, with n 16). This zeolite occurs in a wide range of natural
environments, including sedimentary deposits or volcanoclastic sequences interested by burial
diagenesis/metamorphism, as well as in hydrothermal vugs of volcanic rocks. Partially hydrated laumontite
(i.e., with 15 H2O molecules per unit cell) is often referred to as “leonhardite”. The behavior and adsorption
mechanisms of these minerals have been (already) well characterized at high-pressure by several authors(Gatta
et al. 2018; Comboni et al. 2018), leaving unexplored the effect induced by temperature increase. In-situ highpressure+high-temperature single-crystal synchrotron X-ray diffraction experiments were performed at the
ID15-b beamline, at the ESRF, Grenoble (France). Saltwater (0.35 wt% NaCl) was used as hydrostatic
pressure-transmitting fluid. The DAC was placed in a resistive heater, which allowed to increase the T up to
100(2)°C. Temperature was defined using a thermocouple placed very close to the P-chamber; T value was
consistent with what obtained by the analysis of the Au-powder pattern. In leonhardite, the temperature seems
to enhance the H2O adsorption, giving rise to a volume expansion at P <5 kbar. Above this pressure, the
compressibility becomes similar to that of fully hydrated laumontite [2]. Previous experimental findings
proved that leonhardite experiences a full hydration, at ambient PT conditions, only after about 24 hours,
whereas each data-point at high-PT required not more than 20 minutes: this further highlights the role played
by temperature on the kinetics of the P-mediated adsorption process (i.e., speeding up the adsorption process)
Fast and reproducible in vivo T <sub>1</sub> mapping of the human cervical spinal cord
No full textPurposeTo develop a fast and robust method for measuring T-1 in the whole cervical spinal cord in vivo, and to assess its reproducibility.MethodsA spatially nonselective adiabatic inversion pulse is combined with zonally oblique-magnified multislice echo-planar imaging to produce a reduced field-of-view inversion-recovery echo-planar imaging protocol. Multi- inversion time data are obtained by cycling slice order throughout sequence repetitions. Measurement of T-1 is performed using 12 inversion times for a total protocol duration of 7min. Reproducibility of regional T-1 estimates is assessed in a scan-rescan experiment on five heathy subjects.ResultsRegional mean (standard deviation) T-1 was: 1108.5 (77.2) ms for left lateral column, 1110.1 (+/- 83.2) ms for right lateral column, 1150.4 (+/- 102.6) ms for dorsal column, and 1136.4 (+/- 90.8) ms for gray matter. Regional T-1 estimates showed good correlation between sessions (Pearson correlation coefficient=0.89 (P value<0.01); mean difference=2 ms, 95% confidence interval +/- 20 ms); and high reproducibility (intersession coefficient of variation approximately 1% in all the regions considered, intraclass correlation coefficient=0.88 (P value<0.01, confidence interval 0.71-0.95)).ConclusionsT(1) estimates in the cervical spinal cord are reproducible using inversion-recovery zonally oblique-magnified multislice echo-planar imaging. The short acquisition time and large coverage of this method paves the way for accurate T-1 mapping for various spinal cord pathologies. Magn Reson Med 79:2142-2148, 2018. (c) 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited
Citations are forever: Modeling constrained network formation
No full textDetermining the extent to which citation flows, and hence bibliometric indicators based on them, reflect some intrinsic value of scientific works is an important task made very difficult by endogeneity issues. This paper presents an approach which allows to go beyond the abundant anecdotal evidence by testing whether the citation behavior is free from environmental factors. The hypothesis of independence is strongly rejected, providing causal evidence of a Matthew effect at work: namely, the publication of a new work on behalf of an author increases the flow of citations to previous works. Such result is a step towards the estimation of biases affecting bibliometric indicators, at least when interpreted as measures of scientific productivity. The study is based on a novel framework for the study of endogenous network growth subject to constraints. Constraints can be both positive and negative, and change in time depending on the actions of the agents. The framework is not limited to citation networks, and can be applied to any context in which the formation of a link inhibits or implies the formation of another one
The role of temperature on P-induced crystal-fluid interaction : a study on LAU and HEU topologies
No full textNatural zeolites can be found in soil, oceanic basalts as well as sediments and diagenetic environments. Their peculiar reversible hydration property (i.e., the ability to adsorb and release H2O molecules) and the ability to overhydrate under pressure, make them suitable carriers of fluids in the upper Earth crust during the early stage of subduction. Despite the extensive study of high-pressure and high-temperature behavior of natural and synthetic zeolites over the last decades, few studies have yet combined the effects of both conditions. Experiments at combined high pressure and high temperature might provide valuable insights on the crystal-fluid interaction preocesses occurring in nature at the geological conditions of stability of zeolites, especially when these microporous compounds can act as carriers and moderators of the circulating fluids.
In this study, the in situ combined high-pressure and high-temperature behavior of two commonly occurring natural zeolites, heulandite and laumontite, was investigated. The P-induced crystal-fluid interaction of these two zeolites was studied at ambient-T by Comboni et al. [1] for laumontite and Seryotkin [2] for heulandite. These results have been used as benchmarks to evaluate the role of temperature on the crystal-fluid interaction. In-situ, HTHP single-crystal synchrotron X-ray diffraction experiments were conducted using a diamond anvil cell (DAC) surrounded by a resistive heater at the ID15b beamline at the European Synchrotron Radiation Facility in Grenoble (France). The setup allowed to reach temperatures of about 150(2)°C. Pressure was measured using the ruby fluorescence technique while temperature was monitored using a thermocouple located very close to the P-chamber, allowing a precise determination of both these variables. The results obtained were consistent with those calculated using the Au-powder pattern.
The results showed that temperature significantly increased the kinetics of H2O adsorption in laumontite, with respect to the compressional behavior at room conditions, leading to a volume expansion observable already at pressures < 5 kbar. It was previously found that laumontite hydrated at ambient conditions after 24 hours, while the presence of a temperature gradient reduced the time at about 15 minutes. Even for heulandite, the comparison with literature data suggests that a higher H2O adsorption rate was observed when the thermal gradient was applied.
References
[1] Comboni D., Gatta G.D., Lotti P., Merlini M. & Hanfland M. 2018. Crystal-fluid interactions in laumontite. Microporous Mesoporous Mater., 263, 86-95.
[2] Seryotkin, Y.V. 2015. Influence of content of pressure-transmitting medium on structural evolution of heulandite: Single-crystal X-ray diffraction study. Microporous and Mesoporous Mater., 214, 127-135
Thermal and compressional behaviour of natural borates: a potentially aggregates in radiation-shielding concretes
No full textNatural borates represent the first worldwide source of boron. Boron is a key constituent in different industrial sectors, including glass, ceramics, agricultural, metallurgical, electronics, textile, cosmetics, and chemistry. Recent technological developments have further expanded the use of borates, as underlined by the doubling of global production in the last decade. The recent addition (on 2014) of borates to the European Union list of Critical Raw Materials is a further evidence of the large global demand for this commodity. Due to the ability of 10B (ca. 20% of the natural boron) to absorb thermal neutrons, related to its high cross-section for the 10B(n,α)7Li reaction (~3840 barns), several recent studies investigated the utilization of natural borates as light aggregates in radiation-shielding materials, such as concretes. In this light, the use of natural borates would provide also an economic advantage: synthetic B4C, for example, proved to be efficiently adopted in this field, but its use is hindered by the high costs of synthesis.
In order to characterize the phase stability field, the thermo-elastic properties, and the mechanisms of thermal-induced dehydration, we have investigated the behavior at non-ambient T and P of some of the most common hydrous borates, i.e. kernite, colemanite, kurnakovite, ulexite, and meyerhofferite, by means of in situ single-crystal synchrotron Xray diffraction. In situ non-ambient conditions were obtained using diamond anvil cells (for high-P), nitrogen cryostats (low-T), and gas blowers (high-T). High-pressure experiments show that all the analyzed borates remain stable at pressures exceeding those to which radiation-shielding materials may be subjected. Among them, colemanite shows the lowest bulk compressibility (KV0=67(4) GPa and KV0’=5.5(7), where = ∂KV0/∂P; βV0 = 1/KV0 = 0.0149(9) GPa-1). The refined isothermal bulk moduli for ulexite and kurnakovite are ~ 37 GPa (βV0 ~ 0.0270 GPa-1), which lie between those of other minerals commonly used as aggregates in concretes, while kernite and meyerhofferite are slightly softer (KV0 ~ 30 GPa; βV0 ~ 0.0333 GPa-1).
The high-temperature experiments on kurnakovite and colemanite show that the presence of structural H2O leads to dehydration processes that result in a structural collapse. In the light of a potential application as aggregates, this phenomenon is more critical in kurnakovite (~48% H2O), where the crystal structure is no longer stable above 120 °C, while in colemanite (~22% H2O) significant dehydration starts at T > 240°C. The structural collapse of kurnakovite at relatively low temperatures implies severe questions on its potential applicability in radiationshielding concretes, while the thermal-induced dehydration of colemanite should not represent an issue for several applications of radiation-shielding materials
The role of temperature in P-induced crystal fluid interaction: the case of LAU and HEU topology
No full textZeolites are a class of open-framework aluminosilicate minerals commonly present in soil, oceanic basalts and sediments and diagenetic environments. Zeolites may act as fluid carriers in the upper Earth crust during the early subduction stage thanks to their unique features: the reversible hydration (i.e., the ability of adsorb and release H2O molecules or other small molecules, e.g., CO2, CH4, SO2) and the ability to overhydrate. During the last decades, the high-pressure (HP) and high-temperature (HT) behavior of natural and synthetic zeolites have been intensively investigated but, at the best of our knowledge, no experiments have ever been conducted combining the effects of both thermodynamic variable. Experiments at these conditions (i.e., simulating the PT gradient), using a H2O-based solution as P-transmitting fluids (PTFs), provide a realistic description of crystal-fluid interaction phenomena. In this study, we have investigated the HPHT behavior of heulandite and laumontite, two of the most common natural zeolites, whose presence have been described in a wide range of natural environments. The characterization of the crystal-fluid interaction induced by P in these two species has already been performed by Comboni et al. (2018) and Seryotkin (2015) for laumontite and heulandite, respectively, and was adopted as reference in order to evaluate the T gradient effect. In-situ HPHT single-crystal synchrotron X-ray diffraction experiments were performed at the ID15b beamline, at the ESRF, Grenoble (France). The set-up, easily
reproducible, consist of a membrane-driven diamond anvil cell (DAC) placed in a resistive heater which allowed to increase the T up to 150(2)°C. Pressure was determined by the ruby florescence method, while temperature was measured using a thermocouple located very close to the P-chamber, allowing a precise determination of both (results were consistent with the values calculated by the Au-powder pattern).
Results of the P-V pattern in laumontite clearly indicated that temperature enhances the H2O adsorption, giving rise to a volume expansion at P < 5 kbar. Previous experimental finding highlighted that hydration of laumontite occurs at ambient condition after ~ 24h, while with the presence of a T gradient required no more that 20 min. Concerning heulandite, preliminary data seems to suggest a higher H2O adsorption. if compared
to that governed by the effect of P only.
Comboni D., Gatta G.D., Lotti P., Merlini M. & Hanfland M. (2018) - Crystal-fluid interactions in laumontite. Microp.
Mesop. Mater., 263, 86-95.
Seryotkin Y.V. (2015) - Influence of content of pressure-transmitting medium on structural evolution of heulandite: Single-crystal X-ray diffraction study. Microp. Mesop. Mater., 214, 127-135
High-pressure behavior of REE-bearing phosphates and arsenates
No full textATO4 compounds (A= Sc, Y, Ln, U and Th; T stands for tetrahedrally-coordinated cations, e.g. P and As), represent a wide class of minerals, which includes the REE-bearing arsenates chernovite-(Y) (YAsO4) and gasparite-(Ce) (CeAsO4), and the more common REE-bearing phosphates, xenotime-(Y) (YPO4) and monazite-(Ce) (CePO4). Chernovite-(Y) and xenotime-(Y) share the same HREE-enriched, zircon-type structure (I41/amd), whereas the LREE-enriched gasparite-(Ce) and monazite-(Ce) crystallize in the so-called monazite-type structure (P21/n). The HP behavior of the REETO4 compounds has been object of many studies, mainly focused on their synthetic counterparts. In this work, we have studied the HP and combined HP–HT behavior of natural samples of the abovementioned minerals, using in situ single-crystal synchrotron X-ray diffraction. A special attention was devoted to the relationships between chemical and structural features at non-ambient conditions. In particular, the compressional behavior of the REE-polyhedron, T-site tetrahedron and the deformation mechanisms acting at the atomic scale, poorly studied in the current literature, have been described and discussed. For both the arsenates and phosphates, the monazite-type minerals are found to be more compressible than the zircon-type ones, and the arsenates more compressible than the phosphate analogues. The analysis of the refined structure models showed that the T-tetrahedron is almost uncompressible and the nature of its dominant cation (As or P) significantly affects the response to (T,P)-stimuli of the A-polyhedron
Georesources, finding the perfect mixture between science and dissemination in PCTO activities
No full textThe critical role of georesources and the environmental footprint of human activities in
shaping the current and future society are sometimes overlooked by the public, especially by the
youngest generations. Mining is often associated with environmental threats and dangers while the
importance of georesources is greatly underestimated or, worse, neglected. This despite the fact that
responsible exploitation of georesources is a pivotal requirement to reshape the current economic
model into a more environmentally friendly while still maintaining a sustainable economic growth.
In the framework of PTCO (Paths for Transversal Skills and Orientation) activities we have organized
a 15-hours project aimed to sensibilize students to the needs and risks of mining activities.
Laboratories, movies, frontal lectures, thought experiments and the interactive visits to the Earth
Sciences facilities have been organized attempting to keep an informal context to obtain high levels
of engagement and participation. The project has so far been presented to 19 high school classes and
over 360 students. Following each cycle, students were invited to fill a three-minute anonymous
questionnaire to evaluate the project offering valuable insights for further improvement and
development of the activities. Not surprisingly, the most appreciated activity was at the lab facilities
at the department, which was deemed by the majority “too short”, highlighting the need to produce
more active-oriented environments to engage the students
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