1,721,042 research outputs found
FTIR spectroscopy of hydrogen in minerals: detection, structural environment, quantitative analysis and thermal behaviour
No full textHydrogen can be a major, a minor or a trace constituent of a large variety of minerals. It is usually bonded to oxygen to give H2O, OH-, or more rarely H3O+, H3O2- H5O2+ units, but also NH4+ or organic compounds. It can be a structural component in stoichiometric hydrates, hydroxides, and in many silicate minerals, or can be non-stoichiometrically present as a major extraframework component in microporous minerals (e.g. zeolites). Hydrogen also occur as a minor constituent in structural defects of nominally anhydrous minerals (NAMs) [1]. H exerts a strong influence on the chemical and physical properties of minerals; hence it has a controlling effect on many high-temperature geological processes (e.g. magma genesis, kinetic of phase transformations, etc.), as well as low-temperature alteration processes. Unfortunately, H is a rather elusive element, specially when it occurs in very low amounts, as in NAMs. Conventional micro-analytical techniques (EMPA) and X-ray diffraction are generally unsuitable to characterize this element; secondary ion mass spectrometry (SIMS) and neutron diffraction are not easily accessible and requires complex, time-consuming, analytical procedures. A possible alternative is offered by spectroscopy: Raman, Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR). FTIR is particularly suitable for hydrogen, since the O-H (C-H and N-H) bond absorbs the infrared radiation very efficiently. The relatively low cost, ease of use and ease of sample preparation makes the FTIR technique an extremely powerful tool for the study of H-bearing minerals [2]. Using FTIR spectroscopy we can: a) quantify hydrogen, b) study its distribution [3], c) distinguish its speciation, d) define the structural orientation of the O-H dipole, e) study phase transitions associated with H loss, and f) study thermal processes [4]. We present here the recent developments of the FTIR activities at Roma Tre and describe the new facilities which are currently available in our laboratories (high temperature stages, Focal Plane Array detectors). We will use, as examples, the most recent results obtained by our group, including studies on beryl, cordierite, feldspathoids, phospates and hydrocarbons-bearing materials.
[1] H. Keppler, J.R. Smyth (Eds.) Reviews in Mineralogy and Geochemistry 62 (2006) pp. 478.
[2] E. Libowitky, A. Beran, Emu Notes in Mineralogy 6 (2004) 227-279.
[3] G. Della Ventura, F. Bellatreccia, A. Marcelli, M. Cestelli Guidi, M. Piccinini, A. Cavallo, M. Piochi, Anal. Bioanal. Chem. 397 (2004) 2039-2049.
[4] E. Bonaccorsi, G. Della Ventura, F. Bellatreccia, S. Merlino, Micropor. Mesopor. Mater. 99 (2006) 225-235
Optical performances of SINBAD, the Synchrotron INfrared Beamline At DANE. 22, J) CESTELLI GUIDI, M., PICCININI, M., MARCELLI, A., NUCARA, A., CALVANI, P., BURATTINI. E.,
No full textSINBAD (Synchrotron Infrared Beamline At DANE) is the first Italian synchrotron radiation beamline operating in the infrared range. It collects the radiation emitted by DANE, an electron-positron collider designed to work at 0.51 GeV with a beam current I > 1 A. Here, the actual performances of the beamline, in terms of brilliance gain with respect to black bodies and polarization properties, are presented and discussed. Finally, the stability of the SINBAD source, a critical issue for Fourier transform infrared spectroscopy, is discussed
Comparison of 55Mn NMR, muSR and neutron diffraction in LaMnO3
No full textWe report zero-field Mn-55 NMR investigations of a single crystal LaMnO3 carried out up to 90 K. The temperature dependence of the resonance frequency is compared with determinations of the staggered magnetization from muSR and neutron diffraction on the very same single crystal. Large deviations are found and discussed
HT-FTIR micro-spectroscopy of cordierite: the CO2 absorbance from in situ and quench experiments
No full textIn this work, we address the intensity evolution of the CO2 FTIR bands of cordierite as a function of increasing T, by comparing data obtained from in situ versus quenching measurements. A natural well-characterized cordierite from Kragero (Arendal region, Norway) was studied up to 1200 °C using a heating stage fitted on a FTIR microscope. Two different oriented sections (001) and (010), respectively, were examined in order to check for the effect of the channel orientation on the CO2 release from the matrix. Spectra collected in situ show that increasing temperatures induces an increase in peak width for all CO2-related bands. The effects on the integrated absorbance Ai are different for the different modes. Most notably, the integrated intensity Ai of the anti-symmetric stretching mode (ν3) increases significantly up to 800 °C and then progressively decreases to 1000/1200 °C, depending on the sample orientation. Data obtained on quenched samples reveal that there is no variation in the band intensity for T < 900 °C, and thus, the absorbance increase observed for in situ measurements may be related to an increase in the molar absorption coefficient ε. Combination of in situ with quenched data reveals that the CO2 loss from the cordierite matrix starts around 800 °C and is strongly dependent on the thickness and shape of the examined sample: It is favored for small and tabular-shaped grains, while being significantly reduced for large and prismatic grains. Fracturing along direction normal to [001] multiplies the diffusion interfaces, thus enhancing the CO2 loss from the matrix
FTIR Imaging of lapis lazuli from Sar-E-Sang (Badakhshan, Afghanistan)
No full textFTIR focal-plane-arrays (FPAs) of detectors enable different imaging modalities with a spatial resolution comparable to micro-Raman but without any damage of the sample. This technique has been applied with great success to the study of organic or biological materials (Petitbois et al., 2008), however very few applications have been so far reported in Earth Sciences. One example is provided by the study of the distribution of water in volcanic glasses (Wysoczanski and Tani, 2006). In this work we characterize a sample of lapis-lazuli from the type locality at Sar-e-Sang (Badachshan, Afghanistan) by combining SEM, EMP, X-ray fluorescence imaging, X-ray diffraction and FTIR spectroscopy. Lapis-lazuli is an ornamental stone that has been widely used in antiquity; art works consisting of this deep-blue material have been found in archeological excavations of the middle-east to north Africa since the neolithic age (Barthelemy de Saizieu, B., 1988). Of the (few) worldwide sources of lapis lazuli, the Sar-e-Sang deposit located in the Badakhshan province of Afghanistan is the most famous for the finest quality of its material, and is often cited as the source for most of the lapis lazuli used for decorative purposes up to Reinassance. Lapis lazuli is a complex rock rather than a pure mineral. At Sar-e-Sang, it origin is related to regional methamorphism on dolomitic limestones, and typically consist of a fine-grained assemblage of feldspathoid-type minerals, pyrite, calcite, wollastonite and dolomite (Wyart et al., 1981). Carbon dioxide has been recently reported in lapis lazuli from numerous geographic localities (Smith and Klinshaw II, 2008) and tested as a possible tool for geo-sourcing natural ultramarine pigments in archeological or art conservation studies. These works have been systematically done on powdered materials, therefore the carrier of CO2 has not been identified with certainty. Recently, Bellatreccia et al. (2009) have shown that carbon dioxide is a widespread constituent in sodalite-group minerals, which are among the main constituents of lapis lazuli. In the present work we use high-resolution FTIR imaging to examine in detail the distribution of CO2 across an apparently single crystal of lazurite from the Sar-e-Sang deposit. SEM and optical observations show that the sample is composed of a very fine-grained mixture of different minerals; combining XRD and EMP analyses these could be identified as albite + sodalite + lazurite + dolomite. FTIR imaging shows that extremely high CO2 contents are exclusively associated with lazurite.
References
Barthelemy de Saizieu, B. (1988) Les sépultures néolithiques de Mehrgarh. Réfexions sur les cultes funéraires anciens. PhD thesis, Université de Paris X, 2 vv.
Bellatreccia, F., Della Ventura, G., Piccinini, M., Brilli, M. (2009) Mineralogical Magazine, in press.
Petibois C., Piccinini M., Cestelli-Guidi M.A., Déléris G. and Marcelli A. (2009) Nature Phot. 3, 177
Smith, G.D., Klinshaw II, R.J. (2008)
Wyart, J., Bariand, P., Filippi, J. (1981) Gems and Gemmology, 184-190.
Wysoczanski, R., Tani, K. (2006) J. Volcan. Geoth. Res., 156, 302-314
HT-FTIR micro-spectroscopy of cordierite: the CO2 absorbance from in situ and quenched experiments
No full textInhomogeneous electronic state of low-doped insulating manganites: NMR and μSR evidence
No full textWe report on an Mn-55 NMR investigation of calcium-doped manganite samples carried out at 4.2K. In the insulating members of the family. the localization or hole-rich Ferromagnetic clusters is revealed by the peculiar two-peaked spectra, and by distinct shifts of the resonance lines in an external field. Results are discussed in view of inelastic neutron scattering findings and combined La-139 NMR and pSR data
Speciation and diffusion profiles of H2O in water-poor beryl: comparison with cordierite
No full textThis paper reports on water speciation and diffusion in synthetic beryl samples treated in CO2-rich atmosphere, at 700 MPa and 700 and 800 °C, respectively.
The study has been conducted by means of polarized FTIR (Fourier transform infrared) integrated with FPA (focal plane array) imaging. As expected, the infrared spectra
show the presence of CO2 but also of minor H2O interpreted as resulting from moisture present in the starting
materials used for the experiments. FPA-FTIR images show that H2O diffuses into the beryl matrix along the structural channels oriented parallel to [001]. Spectra collected along
profiles parallel to the c-axis show subtle changes as a function of the distance from the crystal edge; these changes can be correlated to a progressive change in the H2O coordination environment in the channel, as a response to the
varying H2O/alkali ratio. In particular, the data show that when 2H2O > Na+ apfu (atoms per formula unit), H2O can
assume both type I and type II orientation; in the latter case,
each Na cation coordinates two H2O[II] molecules (doubly coordinated H2O). If 2H2O < Na+ apfu, then H2O[II] molecules are singly coordinated to each Na cation. The same type of feature is observed and commented for the structurally related cordierite. Diffusion coefficients and activation
energies have been also determined for both types of water molecules
Speciation and diffusion profiles of H2O in water-poor beryl: comparison with cordierite
No full textThis paper reports on water speciation and diffusion in synthetic beryl samples treated in CO2-rich atmosphere, at 700 MPa and 700 and 800 °C, respectively. The study has been conducted by means of polarized FTIR (Fourier transform infrared) integrated with FPA (focal plane array) imaging. As expected, the infrared spectra show the presence of CO2 but also of minor H2O interpreted as resulting from moisture present in the starting materials used for the experiments. FPA-FTIR images show that H2O diffuses into the beryl matrix along the structural channels oriented parallel to [001]. Spectra collected along profiles parallel to the c-axis show subtle changes as a function of the distance from the crystal edge; these changes can be correlated to a progressive change in the H2O coordination environment in the channel, as a response to the varying H2O/alkali ratio. In particular, the data show that when 2H2O > Na+ apfu (atoms per formula unit), H2O can assume both type I and type II orientation; in the latter case, each Na cation coordinates two H2O[II] molecules (doubly coordinated H2O). If 2H2O < Na+ apfu, then H2O[II] molecules are singly coordinated to each Na cation. The same type of feature is observed and commented for the structurally related cordierite. Diffusion coefficients and activation energies have been also determined for both types of water molecules
FTIR transmission spectroscopy of sideronatrite, a sodium-iron hydrous sulfate
No full text""This paper relates an infrared (IR) (6000–2500; 1400–400 cm−1) spectroscopic study of sideronatrite, Na2Fe3+(SO4)2(OH)·3H2O. Spectra in the 600–1250 cm−1 range are dominated by fundamental S–O absorption bands. Factor-group analysis based on the space group P212121 (Formula ) is in accordance with the observed band multiplicity. A broad and convolute absorption centred around 3400 cm−1 and a sharp band at 3605 cm−1 are observed in the 2900–3900 cm−1 frequency region. The resolution of the broad band is significantly improved at liquid nitrogen temperature; seven components can be fitted to the pattern and these can be assigned to H2O\\\/OH molecules in the structure. All components in the broad band and the sharp absorption at 3605 cm−1 are strongly polarized for E\\\/\\\/a, in accordance with the structure analysis results. Infrared transmission spectroscopy is a useful tool to identify these sulfate minerals occurring in specific geological environments. "
- …
