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Parruzot B.,CEA Marcoule Nuclear Site | Jollivet P.,CEA Marcoule Nuclear Site | Rebiscoul D.,Marcoule Institute for Separative Chemistry | Gin S.,CEA Marcoule Nuclear Site
Geochimica et Cosmochimica Acta | Year: 2015

The long-term behavior study of archaeological artifacts and natural minerals and glasses revealed discrepancies between laboratory and field data. For a better understanding of the cause of these discrepancies and to reinforce the use of basaltic glass as an analog for nuclear waste glasses, this study focuses on the determination of alteration rates and processes of synthetic basaltic glass in residual rate regime. Laboratory batch experiments were performed at high surface-to-volume ratios at 90 and 30°C for more than 1000days. In all the experiments, the residual rate regime was reached after about 6months. The residual alteration rates at 30 and 90°C were 4.0±1.0×10-6 and 9.5±3.2×10-6g·m-2·d-1, respectively. At 90°C, this residual alteration rate is five orders of magnitude lower than the forward alteration rate (0.8g·m-2·d-1). Altered powders and monoliths were characterized by Transmission Electron Microscopy and Time-of-Flight Secondary Ion Mass Spectrometry. From glass core to solution, the altered materials are structured as follows: pristine glass, gel (corresponding to the palagonitic layer of natural glasses) and intergranular clays. To assess the passivating properties of this alteration film, we used solid characterization, an isotopically-tagged post-leaching experiment and the measurement of mobile species diffusion coefficients through the alteration film at different stages of reaction using various techniques (solution analysis and X-ray Reflectometry). These characterizations showed that the alteration film formed during residual rate alteration is passivating even without clogged porosity within the gel. Diffusion coefficients of water and alkali metals - respectively diffusing to and from the pristine glass - through the alteration film dropped from 10-20 to 10-19 m2·s-1 during the first alteration stages to 10-25 m2·s-1 in residual rate regime. © 2014 Elsevier Ltd.

Steins P.,CEA Marcoule Nuclear Site | Poulesquen A.,CEA Marcoule Nuclear Site | Diat O.,Marcoule Institute for Separative Chemistry | Frizon F.,CEA Marcoule Nuclear Site
Langmuir | Year: 2012

Time-resolved rheology, small angle X-ray scattering (SAXS), and electron paramagnetic resonance (EPR) techniques were used to study the polymerization of geopolymers. These polymers are inorganically synthesized by the alkaline activation of an aluminosilicate source (metakaolin) in aqueous solution. The influence of the alkali activator (Na +, K +, and Cs +) was investigated at room temperature. As observed through the variation of the viscoelastic moduli (G′, G″), curing proceeds in steps that are well pronounced when NaOH is used. These steps correspond to a specific dissolution/polycondensation mechanism and are smoothed when the size of the alkali cations increases. This size effect also has an impact on the gelation time (maximum of tan δ). Structural analysis through SAXS experiments allows us to characterize these mechanisms on the nanoscale and to show that the growth of the geopolymer is due to the aggregation of oligomers with a size that is even smaller than the cation is chaotropic. Finally, water behavior during geopolymerization was assessed by using a spin probe. The results show that the spin-probe signal progressively disappears during the first moment of the reaction and reappears when the solid polymeric gel is formed, highlighting the role of water molecules in the different chemical reactions during the process. The EPR signal is in fact increasingly masked as the ion size decreases (because of the strength of the hydration shell). At the end of the reaction, some water molecules were released within the pores, restoring the visibility of the isotropic spin-probe signal. © 2012 American Chemical Society.

Guilbaud P.,CEA Marcoule Nuclear Site | Zemb T.,Marcoule Institute for Separative Chemistry
Current Opinion in Colloid and Interface Science | Year: 2015

We assemble here all available descriptions of oil-soluble surfactant aggregates with or without solutes, assumed to be located in the polar cores of reverse micelles. The presence of solutes is crucial for the formation of a well-defined interface, thus inducing a transition from a loose reverse aggregate into a more structured micelle. This transition can be followed by the concomitant decrease of the "critical aggregation concentration" (c.a.c.). The less organized state as reverse aggregates is predominant when no "nucleating" species such as water, salts, or acids are present. One way to understand this weak aggregation is a depletion driving to aggregates as pseudo-phases introduced by Tanford. Analogues coexisting pseudo-phases seem to exist: weak oil-in-water (o/w) aggregation with the so-called surfactant-free microemulsions, containing loose aggregates, and re-entrant phase diagrams presenting a lowest aggregation concentration (l.a.c.), as described in the seventies. © 2014 Elsevier Ltd.

Guilbaud P.,CEA Marcoule Nuclear Site | Zemb T.,Marcoule Institute for Separative Chemistry
ChemPhysChem | Year: 2012

Reverse micelles? The transition from weak aggregation to water-poor reverse micelles triggered by the presence of extracted ion pairs is modeled using molecular dynamics simulations (see picture). The presence of the ion induces a polar/apolar segregation and the formation of a curved film microstructure consistent with the classical inverse micelle. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Nikitenko S.I.,Marcoule Institute for Separative Chemistry
Advances in Physical Chemistry | Year: 2014

The most recent spectroscopic studies of single bubble (SBSL) and multibubble (MBSL) sonoluminescence reveal that the origin of extreme intrabubble conditions is related to nonequilibrium plasma formed inside the collapsing bubbles. Analysis of the relative populations of OH(A 2Σ+) vibrational states observed during MBSL in water saturated with noble gases shows that in the presence of argon at low ultrasonic frequency weakly excited plasma is formed. At high-frequency ultrasound the plasma inside the collapsing bubbles exhibits Treanor behavior typical for strong vibrational excitation. Plasma formation during SBSL was observed in concentrated HOpreequilibrated with Ar. The light emission spectra exhibit the lines from excited Ar atoms and ionized oxygen O 2 +. Formation of O 2 + species is inconsistent with any thermal process. Furthermore, the SBSL spectra in HOshow emission lines from Xe+, Kr+, and Ar+ in full agreement with plasma hypothesis. The photons and the "hot" particles generated by cavitation bubbles enable the excitation of nonvolatile species in solutions increasing their chemical reactivity. Secondary sonochemical products may arise from chemically active species that are formed inside the bubble but then diffuse into the liquid phase and react with solution precursors to form a variety of products. © 2014 Sergey I. Nikitenko.

Cambedouzou J.,Marcoule Institute for Separative Chemistry | Diat O.,Marcoule Institute for Separative Chemistry
Journal of Applied Crystallography | Year: 2012

A comprehensive method allowing experimentalists to perform a quantitative analysis of small-angle scattering patterns of powdered mesoporous materials of hexagonal symmetry is presented in this paper. Thanks to the rigorous processing of experimental data, and to a straightforward model for the small-angle scattering data simulation, the direct comparison of experimental and calculated patterns is made without any artificial background correction or ad hoc function. This allows the specific surface of mesopores to be estimated without resorting to other methods such as adsorption methods. This approach and its precision are discussed on the basis of the analysis of two real samples. © 2012 International Union of Crystallography. Printed in Singapore-all rights reserved.

Clavier N.,Marcoule Institute for Separative Chemistry | Podor R.,Marcoule Institute for Separative Chemistry | Dacheux N.,Marcoule Institute for Separative Chemistry
Journal of the European Ceramic Society | Year: 2011

The AXO4 monazite-type compounds form an extended family that is described in this review in terms of field of stability versus composition. All the substitution possibilities on the cationic and anionic sites leading to the monazite structure are reported. The phosphate, vanadate, chromate, arseniate, sulphate and silicate families are described and the unit-cell parameters of pure compounds and solid solutions are gathered. The stability limits of the monazite-type structure are discussed versus several models generally correlated with geometric criteria. The effects of physico-chemical parameters such as pressure, temperature and irradiation on the monazite-type structure stability are also discussed. The structural relationships between the monazite structure and the related structures (zircon, anhydrite, barite, AgMnO4, scheelite and monoclinic BiPO4, CaSeO3, rhabdophane and SrNp(PO4)2) are described. © 2011 Elsevier Ltd.

Deme B.,Laue Langevin Institute | Zemb T.,Marcoule Institute for Separative Chemistry
Current Opinion in Colloid and Interface Science | Year: 2011

We analyse the experimental evidence of the hydration force near phospholipid bilayers when the "solvent" is a solution of carbohydrates. Two cases must be clearly distinguished: when sugar is dissolved, depletion causes a supplementary attractive force, while in the case of sugar linked to the lipid the contact pressure increases by orders of magnitude. Attractive interaction inferred between bilayers is sometimes derived from indirect evidence, i.e. scattering, attraction between layers adsorbed, shape of phase boundary limits, and without the simultaneous determination of the osmotic compressibility. Generally, water molecules in the first hydration shell of sugar compete with water molecules bound (by more than one kT in free energy) to lipid head-groups. A general result is that the decay length of any repulsive effect remains close to 0.2. nm, even in concentrated sugar solutions. A tentative general explanation of this experimental fact is given together with consequences, such as the possibility of several types of critical points appearing in bilayer stacks. Decay length as well as effective contact pressure is considered with respect to carbohydrate activity. © 2011 Elsevier Ltd.

Zemb T.,Marcoule Institute for Separative Chemistry | Duvail M.,Marcoule Institute for Separative Chemistry | Dufreche J.-F.,Marcoule Institute for Separative Chemistry
Israel Journal of Chemistry | Year: 2013

Separation of metals in the cationic form is the basis of hydrometallurgy. Ion-specific separation is achieved via selective transfer between liquid phases that have been emulsified in order to be in "close" contact. We show here how the organization of water-in-oil (w/o) "reverse" aggregates in the solvent phase controls the free energy of transfer of cations in the form of neutral salts between phases. Indeed, all known efficient ion separation mechanisms rely on complex fluids in the Winsor II regime, i.e. when a concentrated mixed salt solution is in equilibrium with a solvent phase containing self-assembled aggregates. Here, we point out that, in the general case of water-poor complex fluids containing extractant molecules, long-range interactions linked to w/o interface curvature participate in the selectivity of any multivalent ion extraction process. The free energy related to ion transfer between phases, i.e. the extraction free energy, is different from the complexation free energy. This difference is the key to the selectivity of the separation process. We give here general expressions linking complexation free energy and transfer free energy as derived from known adsorption isotherms, taking into account interfacial curvature, considered as a generalized scalar related to the packing near the interface. © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Grandjean A.,Marcoule Institute for Separative Chemistry | Toquer G.,Marcoule Institute for Separative Chemistry | Zemb T.,Marcoule Institute for Separative Chemistry
Journal of Physical Chemistry C | Year: 2011

We describe a parameter-free analytical model based on molecular force balance to quantitatively explain the wall thickness of silica-based mesoporous materials obtained by a sol-gel route. Simple synthesis routes were proposed 20 years ago that led to a welldeveloped class of porous materials with mesoscale pores (i.e., between 2 and 50 nm). The general route is a micelle-templated precipitation of silicate-based polymers. To optimize thermal stability and efficient resistance to leaching, the wall thickness must be as large as possible, whereas the microporosity has to be as low as possible. Experimental attempts to control wall thickness have appeared in more than 100 publications, but a clear general predictive model is not yet available. Here, we propose a rational evaluation of wall thickness based on molecular force balance that minimizes the free energy between adjacent micelles. The force balance takes into account the following three main uncoupled driving forces: repulsive electrostatic, repulsive hydration, and attractive van der Waals. We argue that our predictive model is an efficient guide for mesoporous material formulations. © 2011 American Chemical Society.

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