1,791 research outputs found
The behavior at non-ambient conditions of colemanite: a hydrous Ca-borate
No full textColemanite, CaB3O4(OH)3·H2O, is a common hydrous borate of large economic relevance, as it is one of the major commodities of boron with applications in the fields of glass and ceramic industries. Colemanite-rich layers are usually found in stratigraphic successions related to lacustrine basins in semi-arid to arid environments, associated to a local volcanic activity, which provides the source for boron. Despite the large economic relevance, the behavior of this mineral at non-ambient conditions of temperature and pressure was almost unexplored, which can provide a basis for understanding its stability during diagenetic and metamorphic processes. In this contribution, we report the highpressure behavior of colemanite (Lotti et al., 2017), based on in situ single-crystal synchrotron X-ray diffraction data up to 24 GPa, and its low-T behavior by in situ X-ray and neutron single-crystal diffraction. Colemanite was found to be stable up ~ 14.5 GPa, where a reconstructive phase transition towards a high-pressure polymorph (colemanite-II) with same symmetry (space group P21/a), but a six times larger unit cell volume, occurs. The elastic behavior of colemanite was described by fitting the experimental data with a III-order Birchurnaghan equation of state, yielding the following refined elastic parameters: KV0 = 64(4) GPa and KV' 5.5(7). The colemanite-tocolemanite-II phase transition induces an increase in the average coordination number of both the Ca and B cations. In particular, a fraction of the boron sites increases its coordination from triangular to tetrahedral by making a further bond with a H2O-oxygen atom. Although the phase transition occurs (at ambient temperature) at pressures far from those associated with the usual geologic environments of colemanite, the reported results disclosed flexible deformation mechanisms that borate compounds may adopt to accommodate pressure, thus providing new insights on the behavior of borate minerals at non-ambient conditions. The complex hydrogen-bonding network of olemanite has also been characterized, at ambient and low temperature conditions, by means of in situ single-crystal synchrotron X-ray and neutron diffraction experiments. A positional disorder, related to the presence of two mutually exclusive configurations of the H2O-molecule hydrogen atoms, was found both above and below ~ 0°C, where a displacive phase transition from the P21/a to the P21 space group occurs.
Lotti, P., Gatta, G.D., Comboni, D., Guastella, G, Merlini, M., Guastoni, A., Liermann, H.-P. (2017): High-pressure behavior and Pinduced phase transition of CaB3O4(OH)3*H2O (colemanite), J. Am. Ceram. Soc., in press, DOI: 10.1111/jace.14730
T- and P-stability and thermo-elastic behavior of the ABW-compounds TlAlSiO4 and CsAlSiO4
No full textT- and P-stability and thermo-elastic behavior
of the ABW-compounds TlAlSiO4 and CsAlSiO4
Paolo Lotti,a G. Diego Gattaa,b, Domenico Caputoc, Marco Merlinia,
Paolo Apreac, Andrea Lausid, Carmine Colellac
aDipartimento di Scienze della Terra, Università degli Studi di Milano, Milano, Italy
bCNR - Istituto di Cristallografia, Sede di Bari, Bari, Italy
cDipartimento di Ingegneria Chimica, dei Materiali e della Produzione Industriale, Università degli Studi di Napoli “Federico II”, Napoli, Italy
dSincrotrone Trieste S.C.p.A. di Interesse Nazionale, Basovizza, Trieste, Italy
[email protected]
A large number of microporous compounds sharing the ABW framework topology have so far been reported in the literature. These compounds show a significant chemical variability, leading to interesting magnetic, optical or structural properties (see e.g. [1] and references therein). The ABW framework can be described as made by sheets of six-membered rings of tetrahedra, in which three tetrahedra have apical oxygen atoms pointing upward (U) and three downward (D), according to a “UUUDDD” scheme. The sheets are interconnected through the apical oxygen atoms, giving rise to elliptical 8-membered ring channels, where the extraframework population is hosted. The latter is generally represented by monovalent cations, with (as Li-ABW) or without (as Rb-, Cs- or Tl-ABW) H2O molecules. Only a few studies have so far been devoted to the phase-stability fields and thermo-elastic behavior of ABW compounds, in response to T and P.
In this study, we focused our attention to two synthetic ABW compounds: TlAlSiO4 and CsAlSiO4, which gain interest for the pollutant and/or toxic nature of the hosted extraframework cations (Tl+ or Cs+). TlAlSiO4 has been investigated up to 950 °C (at room-P) and up to 8 GPa (at room-T) by means of in-situ synchrotron powder diffraction with a diamond anvil cell and with a high-temperature furnace [2]. No phase transition has been observed within the T- and P-range investigated. A II-order Birch-Murnaghan equation of state (II-BM EoS) fit of the P-V data led to a refined bulk modulus KV0 = 48.8(2) GPa. A polynomial fit of the T-V data led to a refined volume thermal expansion coefficient αV,25°C = 4.44(3)*10-5 K-1. CsAlSiO4 has been investigated up to 1000 °C (at room-P) and up to 10 GPa (at room-T) by means of in-situ synchrotron powder diffraction [3]. As for the Tl-analogue, no phase transitions have been observed within the T- and P-range investigated. A II-BM EoS fit of the P-V data gave a refined KV0 = 41.3(3) GPa. A polynomial fit of the T-V data led to a refined αV,20°C = 3.63(1)*10-5 K-1. Both the studied ABW-compounds show a remarkably anisotropic thermo-elastic pattern, resembling that of “layered materials” (e.g. phyllosilicates), where the stacking direction of the 6mR-sheets is significantly more compressible and expandable than the sheets plane. Such a behavior appears to be governed by the nature of the ABW topology of the framework. The high stability and flexibility of TlAlSiO4 and CsAlSiO4 at high-T (at room-P) and high-P (at room-T) suggest these compounds as functional materials for the fixation and storage of the Tl+ and Cs+.
[1] V. Kahlenberg, R.X. Fischer, W.H. Baur, Z. Kristallogr. 2001, 216, 489-494.
[2] G.D. Gatta, P. Lotti, M. Merlini, D. Caputo, P. Aprea, A. Lausi, C. Colella, Micropor. Mesopor. Mater. 2014, submitted.
[3] G.D. Gatta, M. Merlini, P. Lotti, A. Lausi, M. Rieder, Micropor. Mesopor. Mater. 2013, 163, 147-152
Cyclosporine a in Ullrich congenital muscular dystrophy: Long-term results
No full textSix individuals with Ullrich congenital muscular dystrophy (UCMD) and mutations in the genes-encoding collagen VI, aging 5-9, received 3-5mg/kg of cyclosporine A (CsA) daily for 1 to 3.2 years. The primary outcome measure was the muscle strength evaluated with a myometer and expressed as megalimbs. The megalimbs score showed significant improvement (P = 0.01) in 5 of the 6 patients. Motor function did not change. Respiratory function deteriorated in all. CsA treatment corrected mitochondrial dysfunction, increased muscle regeneration, and decreased the number of apoptotic nuclei. Results from this study demonstrate that long-term treatment with CsA ameliorates performance in the limbs, but not in the respiratory muscles of UCMD patients, and that it is well tolerated. These results suggest considering a trial of CsA or nonimmunosuppressive cyclosporins, that retains the PTP-desensitizing properties of CsA, as early as possible in UCMD patients when diaphragm is less compromised. Copyright © 2011 Luciano Merlini et al
On a Frequency-Stabilized Single Current Inverse Source Formulation
No full textSeveral strategies are available for solving the inverse source problem in electromagnetics. Among them, many have been focusing in retrieving Love currents by solving, after regularization, for Love’s electric and magnetic currents. In this work we present a dual-element discretization, analysis, and stabilization of an inverse source formulation providing Love data by solving for only one current. This results in substantial savings and allows for an effective quasi-Helmholtz projector stabilization of the resulting operator. Theoretical considerations are complemented by numerical tests showing effectiveness and efficiency of the newly proposed method
A Fast Quasi-Conformal Mapping Preconditioner for Electromagnetic Integral Equations
No full textBoundary Element Methods (BEMs) are efficient strategies to numerically solve electromagnetic radiation and scattering problems. Unfortunately, however, classical BEM formulations suffer from ill-conditioning when the frequency is low, or the discretization density is high. In the past, several remedies have been presented for these ill-conditioning problems including preconditioners based on Calderón identities, hierarchical bases, and current decompositions. While effective, these strategies however require ad-hoc procedures including mesh-refinements, new basis function definitions, and adapted fast methods that, if not implemented properly, can become computationally cumbersome
Pargasite at extreme conditions: a comprehensive P-T study
No full textPargasite is a Ca-amphibole associated to medium- or high-pressure/high-temperature conditions. The occurrence of hydroxyl groups into the amphibole’s structure has proved to be a significant agent in the water cycle within the upper mantle (e.g., Gill 1981). In order to better understand the water cycle in the upper and potentially lower mantle, it is of critical importance to determine the stability of all hydrous minerals subducted into the mantle. However, despite their geological importance, only a few in situ high-pressure (HP) and high-temperature (HT) studies have been performed in order to describe the P-T stability fields, the thermo-elastic behaviour and the P- or T-induced deformation mechanisms of amphiboles at the atomic scale. The compressibility of tremolite, pargasite and glaucophane were investigated by Comodi et al. (1991) on the basis of in situ single-crystal X-ray diffraction experiments with a diamond anvil cell (DAC) up about 4 GPa. However, as pointed out in Welch et al. (2007), there is a need to extend the compressibility measurement to P higher than 10 GPa, in order to improve the accuracy of the refined isothermal bulk modulus values and their P-derivatives. Furthermore, to the best of our knowledge, no simultaneous in situ P-T studies have been conducted on amphiboles so far. This lack of knowledge prevents a detailed description of the behaviour of amphiboles that are stable at HP-HT conditions and consequently it is still difficult to assess their petrological implications. In this light, we have selected crystals of pargasite from the peridotite of the “phlogopite peridotite unit” of the Finero maficultamafic complex (Ivrea-Verbano Formation, Italy) (Cowthorn, 1975), in order to describe: a) the HP elastic behaviour of this amphibole and its deformation mechanisms at the atomic scale up to 20 GPa, by single-crystal synchrotron X-ray diffraction with a diamond anvil cell, b) its HT behaviour, along with its potential de-hydroxilation, by in situ X-ray synchrotron powder diffraction using a hot air blower device (up to 823 K), and c) its phase stability field 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). The thermal and compressional behaviour of pargasite are now fully described within the P- and T-range investigated and the petrological implications of our experimental findings are discussed.
Cawthorn, R.G. (1975): The amphibole peridotite-metagabbro complex, Finero, northern Italy. J. Geol., 83, 437- 454.
Comodi, P., Mellini, M., Ungaretti, L., Zanazzi, P.F. (1991): Compressibility and high pressure structure refinement of tremolite,
pargasite, and glaucophane. Eur. J. Mineral., 3, 485-500.
Gill, J. (1981): Orogenic Andesites and Plate Tectonics. Springer, New York, pp. 390.
Welch, M.D., Càmara, F., Della Ventura, G., Iezzi, G. (2007): Non-ambient in situ studies of amphiboles. Rev. Mineral. Geochem., 67, 223-260
Phase stability and thermo-elastic behavior of CsAlSiO4 (ABW) : a potential nuclear waste disposal material
No full textThe thermo-elastic behavior and the P/T-induced structure evolution of a synthetic CsAlSiO 4 [ABW framework type, with Pc2 1n space group and lattice parameters: a = 9.414(1), b = 5.435(1), c = 8.875(1) Å at room conditions] have been investigated up to 1000 °C (at 0.0001 GPa) and up to 10 GPa (at 20 °C) by means of in-situ synchrotron powder diffraction. No phase transition has been observed within the temperature- and pressure-range investigated. P-V data were fitted with a third-order Birch-Murnaghan Equation of State (BM-EoS), giving: V 0 = 457.9(4) Å 3, K T0 = 42(1) GPa and K′ = 3.9(3) (with a second-order Birch-Murnaghan Equation of State: V 0 = 458.1(2) Å 3, K T0 = 41.3(3) GPa). The evolution of the "Eulerian finite strain" vs. "normalized stress" yields Fe(0) = 41.9(5)(1) GPa as intercept values, with an almost horizontal slope of the regression line. The evolution of the lattice parameters with pressure shows a remarkably anisotropic compressional pattern, along with subtle change in the axial elastic behavior along [1 0 0] and [0 1 0] at P > 4 GPa. The elastic parameters calculated with a "linearized" BM-EoS are: K T0(a) = 244(11) GPa for the a-axis (K(a)′ = 4); K T0(b) = 181(3) GPa for the b-axis (K(b)′ = 4), and K T0(c) = 14.5(5) GPa and K(c)′ = 2.6(1) for the c-axis. The volume thermal expansion with T was described by the polynomial function: V(T)/V 0 = 1 + α 0·T + α 1·T 2 = 1 + 3.63(1) × 10 -5·T - 3.8(1) × 10 -9·T 2. The structure reacts, in response to the applied T, by a negative thermal expansion along [1 0 0] (i.e. α 0(a) = -9.97(1) × 10 -6 °C -1), almost no expansion along [0 1 0] (i.e. α 0(b) = 0.36(1) × 10 -6 °C -1) and a pronounced positive expansion along [0 0 1] (i.e. α 0(c) = 47.46(6) × 10 -6 °C -1). The main P/T-induced structure deformation mechanisms, at the atomic level, are discussed
On the pathogenesis of collagen VI muscular dystrophies - Comment on article of Hicks et al
No full textThis letter to the Editor addresses the bases for the apparent discrepancy between our published work and a report by Hicks et al (Brain 2009, 132: 147–155). While confirming our finding that myoblasts from patients affected by Ullrich congenital muscular dystrophy (UCMD) display a latent mitochondrial dysfunction that can be unmasked by the addition of the F1FO ATPase inhibitor oligomycin (Angelin et al., 2007 Proc Natl Acad Sci USA 104: 991–6), Hicks et al. conclude that ‘PTP dysregulation may be a particular characteristic of the state of these cells in culture and is not specific to the collagen VI defect’. We extensively argue on the basis for this discrepancy, which is mostly non substantial, and conclude that the results of Hicks et al. (2009) reinforce our original suggestion that mitochondria play a key pathogenic role in UCMD and possibly other forms of muscular dystrophy, and that the permeability transition pore is a viable target for therapeutic intervention as shown in our earlier publications (Irwin et al. Nat Genet 2003 35: 267–7; Angelin et al., 2007 Proc Natl Acad Sci USA 104: 991–6; Merlini et al., 2008 Proc Natl Acad Sci USA 105: 5225–29; Angelin et al., 2008 Biochim Biophys Acta Bioenergetics 1777: 893–6)
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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