Spectral and temporal luminescent properties of Eu(III) in humic substances solutions from different origins

International audienceAlthough a high heterogeneity of composition is awaited for humic substances, their complexation properties do not seem to greatly depend on their origins. The information on the difference in the structure of these complexes is scarce. To participate in the filling of this lack, a study of the spectral and temporal evolution of the Eu(III) luminescence implied in humic substance (HS) complexes is presented. Seven different extracts, namely Suwannee River fulvic acid (SRFA) and humic acid (SRHA), and Leonardite HA (LHA) from the International Humic Substances Society (USA), humic acid from Gorleben (GohyHA), and from the Kleiner Kranichsee bog (KFA, KHA) from Germany, and purified commercial Aldrich HA (PAHA), were made to contact with Eu(III). Eu(III)-HS time-resolved luminescence properties were compared with aqueous Eu$^{3+}$ at pH 5. Using an excitation wavelength of 394 nm, the typical bi-exponential luminescence decay for Eu(III)-HS complexes is common to all the samples. The components $\tau$1 and $\tau$τ2 are in the same order of magnitude for all the samples, i.e., 40 $\leq$ $\tau$1 ($\mu$s) $\leq$ 60, and 145 $\leq$ $\tau$2 ($\mu$s) $\leq$ 190, but significantly different. It is shown that different spectra are obtained from the different groups of samples. Terrestrial extract on the one hand, i.e. LHA/GohyHA, plus PAHA, and purely aquatic extracts on the other hand, i.e., SRFA/SRHA/KFA/KHA, induce inner coherent luminescent properties of Eu(III) within each group. The $^5$D0 $\rightarrow$ $^7$F$_2$ transition exhibits the most striking differences. A slight blue shift is observed compared to aqueous Eu$^{3+}$ ($\lambda_{max}$ = 615.4 nm), and the humic samples share almost the same $\lambda_{max}$ $\approx$ 614.5 nm. The main differences between the samples reside in a shoulder around $\lambda$$\approx$ 612.5 nm, modelled by a mixed Gaussian–Lorentzian band around $\lambda$$\approx$ 612 nm. SRFA shows the most intense shoulder with an intensity ratio of $I_{612.5}$/$I_{614.7}$ = 1.1, KFA/KHA/SRHA share almost the same ratio $I_{612.5}$/$I_{614.7}$ = 1.2–1.3, whilst the LHA/GohyHA/PAHA group has a $I_{612.5}$/$I_{614.5}$ = 1.5–1.6. This shows that for the two groups of complexes, despite comparable complexing properties, slightly different symmetries are awaited

Absolute Properties of the Eclipsing Binary Star V335 Serpentis

V335 Ser is now known to be an eccentric double-lined A1+A3 binary star with fairly deep (0.5 mag) partial eclipses. Previous studies of the system are improved with 7456 differential photometric observations from the URSA WebScope and 5666 from the NFO WebScope, and 67 high-resolution spectroscopic observations from the Tennessee State University 2 m automatic spectroscopic telescope. From dates of minima, the apsidal period is about 880 years. Accurate (better than 2%) masses and radii are determined from analysis of the two new light curves and the radial velocity curve. Theoretical models match the absolute properties of the stars at an age of about 380 Myr, though the age agreement for the two components is poor. Tidal theory correctly confirms that the orbit should still be eccentric, but we find that standard tidal theory is unable to match the observed asynchronous rotation rates of the components\u27 surface layers

Fractionation of Suwannee River fulvic acid and Aldrich humic acid on α\alpha-Al2_2O3_3: spectroscopic evidence

International audienceSorptive fractionation of Suwannee River Fulvic Acid (SRFA) and Purified Aldrich Humic Acid (PAHA) on $\alpha$-Al$_2$O$_3$ at pH 6 was probed in the supernatant using different spectroscopic techniques. Comparison of dissolved organic carbon (DOC) analysis with UV/Vis spectrophotometric measurements at 254 nm, including Specific UV absorbance (SUVA) calculation, revealed a decrease in chromophoric compounds for the non sorbed extracts after a 24 h contact time. This fractionation, only observable below a certain ratio between initial number of sites of humic substances and of $\alpha$-Al$_2$O$_3$, seems to indicate a higher fractionation for PAHA. C(1s) near-edge X-ray absorption fine structure spectroscopy (NEXAFS) confirmed this trend and points to a decrease in phenolic moieties in the supernatant and to an eventual increase in phenolic moieties on the surface. Time-resolved luminescence spectroscopy (TRLS) of Eu(III) as luminescent probe showed a decrease in the ratio between the $^5$D0$\rightarrow$$^7$F$_2$ and $^5$D0$\rightarrow$$^7$F$_1$ transitions for the fractionated organic matter (OM) that is thought to be associated to a lower energy transfer from the OM to Eu(III) due to the loss of polar aromatics. These modifications in the supernatant are a hint for the modification of sorbed humic extracts on the surface

Diagenetic smectite-to-illite transition in clay-rich sediments: A reappraisal of X-ray diffraction results using the multi-specimen method

International audienceSmectite illitization is a common mineralogical reaction occurring during the burial diagenesis of clay-rich sediments and shales, and has thus attracted sustained interest over the last fifty years. Prior studies have concluded that smectite illitization proceeds through a steady set of homogeneous reactions involving intermediate mixed layers of varying compositions. In these intermediate structures, illite and smectite, or, more generally, expandable layers (I and Exp layers, respectively) coexist among the same crystallites giving rise to non-periodic structures (I-Exp) characterized by specific diffraction effects. Consistent with this model, reaction progress was characterized by the simultaneous increase in the illite content in I-Exp and in their stacking order leading to the following mineralogical sequence: smectite → randomly interstratified I-Exp with high smectite contents (> 50% Exp layers) → ordered I-Exp with high illite contents (> 50% I layers) → illite. Although reaction mechanisms have been extensively debated, this structural characterization has not been challenged, possibly due to a methodological bias. In the present study, X-ray diffraction patterns typical of the diagenetic illitization of smectite are interpreted using modern approaches involving profile fitting (multi-specimen method). Novel insights into the structure of intermediate reaction products are thus obtained. In particular, original clay parageneses are described including the systematic presence of illite, kaolinite, chlorite and a mixed layer containing kaolinite and expandable layers (K-Exp). In contrast to previous descriptions, the early stages of smectite illitization are characterized by the coexistence of discrete smectite and of a randomly interstratified I-Exp with a high content of illite layers (>50% I layers). Both the smectite and the I-Exp are authigenic and form under shallow burial, that is at low temperature conditions. With increasing burial depth, the relative proportion of I-Exp increases, essentially at the expense of discrete smectite, and the composition of I-Exp becomes slightly more illitic. In the second stage of smectite illitization, two illite-containing mixed layers are observed. They result from two parallel reaction mechanisms affecting the randomly interstratified I-Exp present in the shallow section of the series. The first reaction implies the dissolution of this randomly interstratified I-Exp and leads to the crystallization of an ordered I-Exp without significant illitization, possibly because of the low K-availability. The second reaction affecting the randomly interstratified I-Exp implies the growth of trioctahedral (Mg, Al) hydroxide sheets in Exp interlayers, thus developing di-trioctahedral chlorite layers (Ch layers) in the initial I-Exp to form an I-Exp-Ch. A layer-by-layer mechanism is hypothesized for this reaction. In this scheme, Mg cations released by the dissolution-recrystallization reaction of I-Exp likely represent the source of Mg for the formation of brucite-like sheets in expandable interlayers, and thus of the I-Exp-Ch. The reported structural characterization of smectite illitization intermediate products contradicts the conventional wisdom of a homogeneous reaction through a series of pure mixed layers of variable composition. In contrast, the coexistence of different phases implies a heterogeneous reaction via a sequence of intermediate phases and requires reassessing the reaction mechanisms proposed in the literature. The compositional range (relative proportion of the different layer types) of these phases is limited and smectite illitization proceeds essentially as relative proportions of the different phases vary. In addition, reaction kinetics and stability of the different intermediate products also need to be reconsidered

Particle Effects on the ISGRI Instrument On-Board the INTEGRAL Satellite

The INTEGRAL satellite was launched on October 17, 2002. All on-board instruments are operating successfully. In this paper, we focus on radiation effects on the Cadmium Telluride camera ISGRI. The spectral response of the camera is affected by cosmic particles depositing huge amount of energy, greater than the high threshold of the electronics. Our study raises the contribution of cosmic ray protons. Solutions are proposed to limit the degradation of spectral response of large pixel gamma cameras operating in space

A selection of thermodynamic properties for zeolites: application to the cement/clay interactions

Deep disposal concepts are usually based on a multibarrier concept that may involve a physical contact between clayey and cementitious materials. In such context, zeolites are a group of important phases, which group most of the transition phases between cement and the clayey barrier since zeolites have been shown to form readily after the weathering of clays in a hyperalkaline environment [1]. Thermodynamic properties can be found in the literature for some of the zeolites of interest in deep disposal contexts. However, there is still a lack of consistency among the available thermodynamics datasets. A first task realized in the present work consists in a critical selection of the thermodynamic datasets published so far. The selection could be achieved with some confidence for a rather large list of minerals. Some questions and uncertainties still remain for phases like phillipsite, chabazite or gismondine. Cases from the previous critical selection indicate the role of kinetics in the precipitation of zeolites, which can help in moderating the phase relations indicated by thermodynamics and can be related to field observations or experimental results. In addition, the concept of rock acidity can applied with success in order to investigate the phase relations between cements, zeolites and clayey materials

Absolute Properties of the Eclipsing Binary Star BF Draconis

BF Dra is now known to be an eccentric double-lined F6+F6 binary star with relatively deep (0.7 mag) partial eclipses. Previous studies of the system are improved with 7494 differential photometric observations from the URSA WebScope and 9700 from the NFO WebScope, 106 high-resolution spectroscopic observations from the Tennessee State University 2 m automatic spectroscopic telescope and the 1 m coudé-feed spectrometer at Kitt Peak National Observatory, and 31 accurate radial velocities from the CfA. Very accurate (better than 0.6%) masses and radii are determined from analysis of the two new light curves and four radial velocity curves. Theoretical models match the absolute properties of the stars at an age of about 2.72 Gyr and [Fe/H] = −0.17, and tidal theory correctly confirms that the orbit should still be eccentric. Our observations of BF Dra constrain the convective core overshooting parameter to be larger than about 0.13 Hp. We find, however, that standard tidal theory is unable to match the observed slow rotation rates of the components\u27 surface layers

Role of carbonate minerals in the distribution of trace elements in marine clay formations

International audienceAnthropogenic radionuclides (RN) are generated by a wide range of industrial and medical activities. In the contexts of waste storage, the quantification of RN migration is of paramount importance. RN migration is partly ruled by the interaction of RN with the solid surfaces. Usually experiments are conducted at various scales from laboratory to the field in order to measure retention and retardation parameters of radiotracers. Whereas this experimental approach is mandatory to tackle the issue of RN migration, the understanding of the natural speciation of stable isotopes that are analog to RN brings additional useful information. In particular, the RN natural speciation sheds light on RN isotopic exchange and " irreversible " trapping mechanisms. This study aims at overviewing the association of natural trace elements (U, Th, Ni, I, Sr and Zn) with carbonate minerals in the Callovian-Oxfordian sedimentary formation that is under consideration for deep nuclear waste disposal in France. The combined use of sequential extraction techniques, microscopic and spectrometric techniques, as well as laser-ablation coupled to chemical analysis techniques made it possible to establish the distribution of I, Sr, U, Th and Ni in the various mineral and organic phases present in the clay rock. I and Sr and in a less extent U and Th are mainly carried by carbonates while Ni is distributed in a variety of phases including pyrite, sphalerite, chlorite, organic matter and muscovite

Structure of nanocrystalline calcium silicate hydrates

Nanocrystalline calcium silicate hydrates (C-S-H) are the main hydration products and the main binging phases in many types of cement, including ordinary Portland cement. As a result of its ubiquity is these engineered systems, C-S-H controls main cement physical and chemical properties. These properties depend on C-S-H calcium to silicon atomic ratio (Ca/Si), which is commonly described as ranging between 0.6 and 2.3. This means that C-S-H structure dictates cement macroscopic properties. As a consequence, its crystal-chemistry must be understood to be able to understand (and thus predict) cement properties. However, despites decades of study, its crystal structure is still a matter of debate. Depending on the authors and on the calcium to silicon ratio, the structure is described similar to one or more of the following minerals: tobermorite, jennite and possibly portlandite. Such inaccuracy largely results from its X-ray diffraction patterns, which exhibits only a few weak and mostly asymmetrical diffraction maxima and thus cannot be refined using classical methods. By using a specific formalism for the analysis of X-ray diffraction patterns, previously applied to phyllosilicates and phyllomanganates, it is here proposed that C-S-H can be described as a lamellar structure similar to nanocrystalline and turbostratic tobermorite, turbostratism meaning that there is the systematic presence, between adjacent layers, of a random rotation about the normal to the layers and/or a random translation in the layer plane. This model was validated using complementary methods (including transmission electron microscopy, synchrotron X-ray absorption spectroscopy and synchrotron high-energy X-ray scattering). From analysis of literature data, it is proposed that the evolution of C-S-H structure as a function of Ca/Si can be described as interstratification of two different types of layers having calcium to silicon ratios of 0.6 and 1.25, plus discrete Ca(OH)2 at higher ratios

Thermodynamic evidence of giant salt deposit formation by serpentinization: an alternative mechanism to solar evaporation

International audienceThe evaporation of seawater in arid climates is currently the main accepted driving mechanism for the formation of ancient and recent salt deposits in shallow basins. However, the deposition of huge amounts of marine salts, including the formation of tens of metres of highly soluble types (tachyhydrite and bischofite) during the Aptian in the South Atlantic and during the Messinian Salinity Crisis, are inconsistent with the wet and warm palaeoclimate conditions reconstructed for these periods. Recently, a debate has been developed that opposes the classic model of evaporite deposition and argues for the generation of salt by serpentinization. The products of the latter process can be called "dehydratites". The associated geochemical processes involve the consumption of massive amounts of pure water, leading to the production of concentrated brines. Here, we investigate thermodynamic calculations that account for high salinities and the production of soluble salts and MgCl2-rich brines through sub-seafloor serpentinization processes. Our results indicate that salt and brine formation occurs during serpentinization and that the brine composition and salt assemblages are dependent on the temperature and CO2 partial pressure. Our findings help explain the presence and sustainability of highly soluble salts that appear inconsistent with reconstructed climatic conditions and demonstrate that the presence of highly soluble salts probably has implications for global tectonics and palaeoclimate reconstructions