1,414 research outputs found
A low temperature X-ray single-crystal diffraction and polarised infra-red study of epidote
No full textThe effects of low-temperature on the crystal structure of a natural epidote [Ca1.925Fe0.745Al2.265Ti0.004 Si3.037O12(OH), a = 8.8924(7), b = 5.6214(3), c = 10.1547(6) angstrom and beta = 115.396(8)degrees at room conditions, Sp. Gr. P2(1)/m] have been investigated with a series of structure refinements down to 100 K on the basis of X-ray single-crystal diffraction data. The reflection conditions confirm that the space group is maintained within the T-range investigated. Structural refinements at all temperatures show the presence of Fe3+ at the octahedral M(3) site only [%Fe(M3) = 70.6(4)% at 295 K]. Only one independent proton site was located and two possible H-bonds occur, with O(10) as donor and O(4) and O(2) as acceptors. The H-bonding scheme is maintained down to 100 K and is supported by single crystal room-T polarised FTIR data. FTIR Spectra over the region 4,000-2,500 cm(-1) are dominated by the presence of a strongly pleochroic absorption feature which can be assigned to protonation of O(10)-O(4). Previously unobserved splitting of this absorption features is consistent with a NNN influence due to the presence of Al and Fe3+ on the nearby M(3) site. An additional relatively minor absorption feature in FTIR spectra can be tentatively assigned to protonation of O(10)-O(2). Low-T does not affect significantly the tetrahedral and octahedral bond distances and angles, even when distances are corrected for "rigid body motions". A more significant effect is observed for the bond distances of the distorted Ca(1)- and Ca(2)-polyhedra, especially when corrected for "non-correlated motion". The main low-T effect is observed on the vibrational regime of the atomic sites, and in particular for the two Ca-sites. A significant reduction of the magnitude of the thermal displacement ellipsoids, with a variation of U-eq (defined as one-third of the trace of the orthogonalised U-ij tensor) by similar to 40% is observed for the Ca-sites between 295 and 100 K. Within the same T-range, the U-eq of the octahedral and oxygen sites decrease similarly by similar to 35%, whereas those of the tetrahedral cations by similar to 22%.</p
Crystal-fluid interactions in open-framework silicates
No full textThe structural evolution of microporous materials compressed hydrostatically in a fluid is drastically affected by the potential crystal-fluid interaction, with a penetration of new molecular species through the zeolitic voids in response to applied pressure.
On the basis of recent experimental findings and computational modelling studies, it was observed that when no crystal-fluid interaction occurs, the effects of pressure are mainly accommodated by tilting of (quasi-rigid) tetrahedra around the bridging O atoms. Tilting of tetrahedra is the dominant mechanisms at low-mid P-regime, whereas distortion and compression of tetrahedra dominate the mid-high P regime. The deformation mechanisms are governed by the topological configuration of the tetrahedral framework, but the compressibility of the cavities is controlled by the ionic and molecular host content, resulting in different unit-cell volume compressibility in isotypic structures. One of the most common deformation mechanisms in zeolitic framework is the increase of channels ellipticity.
Not all the zeolites experience a P-induced intrusion of new monoatomic species or molecules from the P-transmitting fluids. For example, natural zeolites, with well-stuffed channels at room conditions, tend to hinder the penetration of new species through the zeolitic voids. Several variables govern the sorption phenomena at high pressure: the “free diameters” of the framework cavities, the configuration of the extraframework population, the partial pressure of the penetrating molecule in the fluid (if mixed with other nonpenetrating molecules), the rate of P-increase, the surface/volume ratio of the crystallites under investigations, the temperature at which the experiment is conducted. The most recent findings allow us to provide an overview of the intrusion phenomena of monoatomic species (e.g., He, Ar, Kr), small (e.g., H2O, CO2) and complex molecules, along with the P-induced polymerization phenomena, (e.g., C2H2, C2H4, C2H6O, C2H6O2, BNH6, electrolytic MgCl2·21H2O solution), with potential technological and geological implications.
Gatta, G.D. (2008): Does porous mean soft? On the elastic behaviour and structural evolution of zeolites under pressure.
Z. Kristallogr., 223, 160-170.
Gatta, G.D. & Lee, Y. (2014): Zeolites at high pressure: A review. Mineral. Mag., 78, 267-291.
Gatta, G.D., Lotti, P. & Tabacchi, G. (2017): The effect of pressure on open-framework silicates: elastic behaviour and
crystal-fluid interaction. Phys. Chem. Minerals, 45, 115-138
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 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
Cancrinite-group minerals ([CAN]-framework type) at non-ambient conditions
No full textAll the isotypic minerals of the cancrinite-group share the [CAN]-framework type, built up by layers of single six-membered rings of tetrahedra centered in an “A” or “B” position, according to the ABAB stacking sequence. The resulting framework has the following secondary building units: 12-membered ring channels parallel to the [0001] axis, bound by columns of base-sharing cages, and the so-called can units. A large chemical variability is shown by both natural and non-natural isotypic compounds. Among the natural species, the majority shows an alumino-silicate framework (Al6Si6O24), and two subgroups can be identified according to the extraframework content of the can units: the cancrinite- and the davyne-subgroups, showing Na-H2O and Ca-Cl chains, respectively. Several cations, anionic and/or molecular groups lie in the channels.
The description of the phase-stability fields and the of the thermo-elastic behavior of the cancrinite-group minerals play a key role in the study of the natural and industrial processes where these compounds are primary constituents (a short summary of which is in [1,2]).
We aim to model the thermo-elastic behavior and (P,T)-induced structure evolution of these isotypic compounds, with a focus on the influence played by the different extraframework constituents on the structure deformation mechanisms. The study is restricted to the chemical compositions commonly occurring in Nature, delimited by the (CO3)-rich and (SO4)-rich end-members within the two aforementioned subgroup: cancrinite {[(Na,Ca)6(CO3)1.2-1.7][Na2(H2O)2][Al6Si6O24]} and vishnevite {[(Na,Ca,K)6(SO4)][Na2(H2O)2][Al6Si6O24]}, balliranoite {[(Na,Ca)6(CO3)1.2-1.7][Ca2Cl2][Al6Si6O24]} and davyne {[(Na,Ca,K)6((SO4),Cl)][Ca2Cl2][Al6Si6O24]}, respectively. The high-pressure and low-temperature (T < 293 K) studies of the carbonate end-members (i.e. cancrinite and balliranoite) have been performed by means of in situ single-crystal X-ray diffraction. The results [1-4] show that, though sharing a similar volume compressibility and thermal expansivity, these minerals have a different thermo-elastic anisotropy, being more pronounced in cancrinite. This is due to different (P,T)-induced structure deformation mechanisms, likely governed by the different coordination environment of the cage population. An in situ high-temperature (293 ≤ T(K) ≤ 823(7)) single-crystal X-ray diffraction study of cancrinite, allowed the description of thermo-elastic behavior and anisotropy. An irreversible dehydration process takes place at 748(7) K. Preliminary results of the high-pressure studies of the sulfatic end-members (i.e. vishnevite and davyne) are available. A clear change of the elastic behavior of vishnevite, with an increase of compressibility, is shown between 2.47(2)-3.83(2) GPa. A similar increase of compressibility was also reported for cancrinite at 4.62-5.00(2) GPa.
References. [1] Lotti, P., Gatta, G.D., Rotiroti, N., Cámara, F. (2012): Am. Mineral., 97, 872-882; [2] Gatta, G.D., Lotti, P., Kahlenberg, V. (2013): Micropor. Mesopor. Mater., 174, 44-53; [3] Gatta, G.D., Lotti, P., Kahlenberg, V., Haefeker, U. (2012): Miner. Mag., 76, 933-948; [4] Lotti, P., Gatta, G.D., Rotiroti, N., Cámara, F., Harlow, G.E. (2013): Z. Kristallogr., in press
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
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
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
Digestibility and nitrogen balance of diets based on faba bean, pea seeds and soybean meal in sheep
No full textThree digestibility and nitrogen balance trials were carried out to estimate nutritive value of Faba bean (Vicia faba minor) and Pea (Pisum sativum) seeds in comparison to soybean meal in sheep. In each trial 3 diets fed 6 Sarda breed wethers using a two replicated 3x3 Latin Square design. The first trial consisted of 2 level of Faba bean: 20 (FB20) and 38 (FB38) as fed ingredient with 13.8 and 17 CP diet content on DM basis, respectively, vs a level of soybean meal (S1: 15.8 CP, DM basis). The second trial consisted in 2 level of Pea seeds: 23 (P23) and 48 (P48) as fed ingredient with 12.6 and 15.2 CP diet content on DM basis, respectively, vs a level of soybean meal (S2: 14.5 CP, DM basis). Medium quality natural meadow hay completed diets of the first and the second trial. In the third trial, animals were fed 3 isonitrogenous (CP content - FB: 16.2, P: 16.5 and S: 16.4) and isocaloric diets. The diets consisted of good quality alfalfa hay and 3 mixed feeds characterized by the presence of only one of the 3 protein sources to study. Mineral-vitamin premix and different proportions of maize and dehydrated beet pulp supplemented mixed feeds. These 3 diets were formulated to fed lactating ewes in a successive experimental trial to verify their effects on milk production. The high content of Faba bean and Pea seeds, in the first two trials, didn’t show animal palatability problems. In the first trial, the highest organic matter digestibility (OMD) resulted for FB38 diet (71.3A FB20, 75.8B FB38, 71.2A S1). Crude protein digestibility (CPD) data showed the highest values in diets with the highest CP content: FB38 and S1 (73.3A FB20, 78.0Bb FB38, 76.8Ba S1); the same two diets showed the highest g/d retained N (7.7a FB20, 9.0b FB38, 9.2b S1). In the second trial, P48 diet showed highest OMD (69.7A P23, 76.2B P48, 67.5A S2), while no significant differences resulted among diets for CPD (70.9 P23, 74.7 P48, 74.3 S2) and g/d retained N (2.8 P23, 3.8 P48, 3.8 S2, g/d). In the third trial, CPD of pea diet showed the highest value (FB: 78.0Aa, P: 80.4B and S: 78.7Ab) but in N balance the same diet showed the lowest retained N value (FB: 4.6, P: 3.4A and S: 5.4B, g/d). Also in OMD pea diet showed the highest value and FB diet the lowest (FB: 75.7A, P: 77.5Bb and S: 76.7a). In conclusion, in the present study, small differences, significant or not, in digestibility and N balance were observed among diets due to protein sources. Although further studies are necessary, Faba bean and Pea seeds appear to be valid substitutes of soybean meal in sheep considering some known limits to use this feed (OGM, solvent extr.), farm management (self sufficiency) or economic reason (debit balance)
From Nature to materials science: (Cs,K)Al4Be5B11O28 (londonite) as a super-hard material
No full textLondonite is a rare Cs-bearing mineral with ideal chemical formula (Cs,K)Al4Be4(B,Be)12O28 (with Cs > K). The building block units of the structure of londonite are represented by clusters of four edge-sharing Al-octahedra linked to B- and Be-tetrahedra. Gatta et al. (2011) investigated the phase stability and the elastic behavior of londonite up to 4.85(5) GPa (at room-T) and up to 1000°C (at room-P) by in situ X-ray powder diffraction data, but no structure refinements were possible. Whether no phase transition was observed within the pressure-range investigated, londonite
proved to have an extremely high bulk modulus: KP0 = 280(12) GPa, similar to those of carbides (e.g., B4C with KP0 ~ 245-306 GPa; Lazzari et al., 1999; Fujii et al., 2010). Considering the thermo-elastic properties and the significantly high fraction of boron (B2O3 ~50 wt%), the synthetic counterparts of londonite could be considered a potential inorganic host for 10B in composite neutron-absorbing materials. Furthermore the high content of Cs makes londonite-type materials potential host for nuclear waste. However, to date, because of the absence of structural data at high pressure and to the modest P-range investigated by Gatta et al. (2011), a comprehensive description of the P-induced deformation mechanisms at the atomic scale is still missing. In this study, the isothermal compressional behaviour of londonite is studied by in situ single-crystal synchrotron X-ray diffraction experiment with a diamond anvil cell up to 25 GPa. The compressional behavior and the deformation mechanisms at the atomic scale are described. Londonite does not experience any phase transition or change of the compressional behavior within the P-range investigated.Fujii, T., Mori, Y., Hyodo, H., Kimura, K. (2010): X-ray diffraction study of B4C under high pressure. J. Phys. Conf. Ser., 215,
012011.
Gatta, G.D., Vignola, P., Lee, Y. (2011): Stability of (Cs,K)Al4Be5B11O28 (londonite) at high pressure and high temperature: a
potential neutron absorber material. Phys. Chem. Miner., 38, 429-434.
Lazzari, R., Vast, N., Besson, J.M., Baroni, S., Dal Corso, A. (1999): Atomic structure and vibrational properties of icosahedral B4C
boron carbide. Phys. Rev. Letters, 83, 3230-3233
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