Search

International audience; This paper studies the behavior of four different calcined clay-based geopolymers under sulfuric acid attack and gives insights into their degradation mechanisms. Pastes were cast using metakaolin and meta-illite and were activated by two different alkaline solutions. Mineralogical and microscopic characterizations were performed on pastes before and after attack. Results indicated that all pastes were affected by low leaching of alkali cations, and thus by a linkage disequilibrium of the geopolymer network. Meta-illite based geopolymers, which had not been addressed in the literature until now, hold promise for improving the durability of materials in aggressive environments.

International audience; The solidification/stabilization method was demonstrated to be an effective remediation technology for hazardous waste treatment. Three types of binding agents were tested in the present study in view of their potential use in solidification of contaminated sediments and soilsordinary Portland cement (OPC), granulated ground blast furnace slag (GGBS) activated by OPC and a Supersulfated (SSC) binders. An investigation into the impact of trace metals Zn, Cu, Ni and Cd on the hydration of the binders was performed by adding them into pure binders' systems. Hydration heat evolution of the binders was assessed through isothermal calorimetry and hydration products were analysed through XRD, NMR and XAFS analysis. Copper and zinc present the most perturbing effect on the early hydration delaying the main hydration peak occurrence while nickel and cadmium ions do not perturb or accelerate it. For example, the GGBS/OPC formulation without any metal addition has its MHP at 13.5 h, with the addition of 0.5%Zn the MHP appears 37 h later, with 0.5%Cu 11.5 h later, but with Ni and Cd 5 h earlier. The SSC formulation was shown to be the most sensitive on the trace metals (TM) addition. The electrokinetic and conductivity measurements of the binders using Zeta Potential apparatus showed a decrease in obtained values in the presence of Cu and Zn and an increase in the presence of Ni and Cd confirming the different behaviours of TM in the considered systems.

International audience; Small TiO 2 contents in the slag-glass significantly reduce their cementitious reactivity. We investigated the role of Ti in the glass network and its influence on slag-glass dissolution. XANES and EPR analysis showed that 67% of Ti was present as Ti(IV) with about 70% in [5] Ti and 30% in [4] Ti coordination, and 33% as Ti(III). The presence of Ti had only a minor impact on initial dissolution rates at pH 11 (R ≈ 10 − 6 mol glass .s − 1 .m − 2). During dissolution, Ti accumulated in an amorphous layer at the glass-surface. Ti-coordination in this layer was 50% [5] Ti and 50% [6] Ti. At pH 11, the layer was mainly composed of TiO 2 (66 wt%), but intermixed with a hydrotalcite-like phase at pH 13. The loss of cementitious reactivity in the presence of Ti appears to be not only due to stabilization of the glass structure but also to the formation of a Ti-rich surface-layer, that may become passivating.

Calcium is an essential component of osteogenesis and is often required for imparting significant bioactivity to synthetic bone substitutes and, in particular, silicate-based materials. However, the mechanism of calcium incorporation inside sol-gel silicates is poorly understood. In this work, we shed light on the determinant parameters for incorporation of calcium into acid-base-catalyzed sol-gel silicates at ambient temperature: increasing the pH above the isoelectric point of silicic acid and the nature of the calcium counterion in the calcium precursor are found to be the key. Based on our proposed reaction sequence, we were able to compare calcium precursors and select an ideal candidate compound for the synthesis of bioactive glasses (BG) and organic-inorganic hybrids at ambient temperature. Reproducible syntheses and gel times of SiO

International audience; The glass formation, crystallization behavior and structure were investigated in the ZnO-Al2O3-SiO2 system. The boundaries of the glass forming region are defined, indicating the absence of glasses along the ZnO-SiO2 binary and the role of Al to improve glass formation. The crystallization behavior has been clarified for representative glass compositions showing first crystallization of willemite near the ZnO-SiO2 binary and a metastable zinc aluminosilicate solid solution for higher Al2O3/SiO2 content. Gahnite appears as a second phase and is mainly present near the center of the tectosilicate join. Glass structure was studied using 27 Al NMR spectroscopy, neutron and X-ray diffraction and molecular dynamics simulation. Both Al and Zn are shown to be distributed between four-fold and five-fold sites. The proportion of [4] Al is more important near the ZnAl2O4-SiO2 join. A remarkable similar behavior is revealed for the glass forming ability and structural properties between MgO and ZnO aluminosilicate systems.; La formation du verre, le comportement en cristallisation et la structure ont été étudiés dans le système ZnO-Al2O3-SiO2. Les limites de la région de formation du verre sont définies, indiquant l’absence de verres le long du binaire ZnO-SiO2 et le rôle d’Al pour améliorer la formation du verre. Le comportement en cristallisation a été clarifié pour des compositions de verre représentatives montrant la première cristallisation de willemite près du binaire ZnO-SiO2 et une solution solide d’aluminosilicate de zinc métastable pour une teneur plus élevée en Al2O3/SiO2. La gahnite apparaît comme une deuxième phase et est principalement présente près du centre du joint tectosilicate. La structure du verre a été étudiée en utilisant la spectroscopie 27Al RMN, la diffraction des neutrons et des rayons X et la simulation par dynamique moléculaire. Il est démontré que Al et Zn sont répartis entre des sites de coordinence quatre et cinq La proportion de [4]Al est plus importante près du joint ZnAl2O4-SiO2. Un comportement similaire est révélé pour la capacité de formation du verre et les propriétés structurelles entre les systèmes d'aluminosilicate de MgO et de ZnO.

International audience; Ground granulated blast furnace slags (GGBS) are glassy by-products from iron production that are commonly used as supplementary cementitious materials in blended cements. The glass structure of seven industrial GGBS was investigated by Raman and Nuclear Magnetic Resonance spectroscopies. The complex composition of the slags induced multiple analytical challenges. Under usual continuous excitation, the Raman signal was masked by strong luminescence, so that analysis was carried out on a time-resolved Raman (TRR) device. TRR allowed to eliminate luminescence and resulted in exploitable spectra that showed variations in line with theoretical NBO/T values. The analysis of 27 Al and 29 Si NMR spectra was complicated by the presence of paramagnetic nuclei and the wide variety of environments. Nevertheless, 27 Al NMR showed that Al was present as a network former, mainly in 4-fold coordination and careful analyses of 29 Si NMR spectra allowed the comparison of glass network polymerization of industrial GGBS in line with the theoretical NBO/T based on their composition.

International audience; Water in calcium silicate hydrate (C-S-H) is one of the key parameters driving the macroscopic behavior of cement materials for which water vapor partial pressure has an impact on Young's modulus and the volumic properties. Several samples of C-S-H with a bulk Ca/Si ratio ranging between 0.6 and 1.6 were characterized to study their dehydration/hydration behavior under water-controlled conditions using 29 Si NMR, water adsorption volumetry, X-ray diffraction, and Fourier-transform near-infrared diffuse reflectance under various water pressures. Coherent with several previous studies, it was observed that an increase in the Ca/Si ratio is due to the progressive omission of Si bridging tetrahedra, with the resulting charge being compensated for by interlayer Ca, and that water conditioning influences the layer-to-layer distance and the achieved NMR spectral resolution. Water desorption experiments exhibit one step toward low relative pressure, accompanied by a decrease in the layer-to-layer distance. When sufficient energy is provided to the system (T ≥ 40°C under vacuum) to remove the interlayer water, the shrinkage/swelling is partially reversible in our experimental conditions. A change in layer-to-layer distance of less than 3 Å is measured in the C-S-H between the wet and dried states. When the bridging SiO 2 tetrahedra are omitted, interlayer Ca interacts with layer O and water interacts with the cations and potentially with the surfaces. This structural organization is interpreted as a mid-plane monolayer of water in the interlayer space, this latter accounting for about 30% of the volume of C-S-H particles.

An injectable purely apatitic calcium phosphate cement (CPC) was successfully combined to a water-soluble radiopaque agent (i.e., Xenetix® ), to result in an optimized composition that was found to be as satisfactory as poly(methyl methacrylate) (PMMA) formulations used for vertebroplasty, in terms of radiopacity, texture and injectability. For that purpose, the Xenetix dosage in the cement paste was optimized by injection of the radiopaque CPC in human cadaveric vertebrae under classical PMMA vertebroplasty conditions, performed by interventional radiologists familiar with this surgical procedure. When present in the cement paste up to 70 mg I mL-1 , Xenetix did not influence the injectability, cohesion, and setting time of the resulting composite. After hardening of the material, the same observation was made regarding the microstructure, mechanical strength and alpha-tricalcium phosphate to calcium deficient apatite transformation rate. Upon implantation in bone in a small animal model (rat), the biocompatibility of the Xenetix-containing CPC was evidenced. Moreover, an almost quantitative release of the contrast agent was found to occur rapidly, on the basis of in vitro static and dynamic quantitative studies simulating in vivo implantation. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2786-2795, 2018.

International audience; The stability of illite-smectite interstratified with respect to discrete illite and smectite minerals was investigated by measuring their thermodynamic properties. The standard thermodynamic properties of the illite-smectite ISCz-1 mineral (G, H, S, Cp, and V) were determined between 298.15 K and 375 K by using calorimetric methods. Moreover, the enthalpies of mixing between the illite and smectite layers were measured at 298.15 K by acid solution calorimetry from a complete series of illite-smectite interstratified minerals (Shinzan area, Japan). The measured values were slightly negative, with a minimum value of −3.7 kJ.mol−1. This contributed to the stability of the mixed-layer with respect to a mechanical mixture of illite and smectite. In addition, the model from Blanc et al. (2015) was implemented to estimate the thermodynamic properties of the interstratified illite-smectite ISCz-1 mineral. The predicted values were consistent with the experimental results. However, the estimates were slightly improved by considering the thermodynamic properties of the mixture of the illite and smectite components and then adding the terms of energies of mixing. This could be confirmed by establishing the stability domains of ISCz-1 and those of the corresponding illite and smectite end-members according to Meunier and Velde’s determination of the smectite to illite reaction pathways (Meunier and Velde, 1989).

Mesoporous bioactive glasses (MBGs) in the system SiO2-CaO-P2O5-Ga2O3 have been synthesized by the evaporation induced self-assembly method and subsequent impregnation with Ga cations. Two different compositions have been prepared and the local environment of Ga(III) has been characterized using 29Si, 71Ga and 31P NMR analysis, demonstrating that Ga(III) is efficiently incorporated as both, network former (GaO4 units) and network modifier (GaO6 units). In vitro bioactivity tests evidenced that Ga-containing MBGs retain their capability for nucleation and growth of an apatite-like layer in contact with a simulated body fluid with ion concentrations nearly equal to those of human blood plasma. Finally, in vitro cell culture tests evidenced that Ga incorporation results in a selective effect on osteoblasts and osteoclasts. Indeed, the presence of this element enhances the early differentiation towards osteoblast phenotype while disturbing osteoclastogenesis. Considering these results, Ga-doped MBGs might be proposed as bone substitutes, especially in osteoporosis scenarios., 35 pages, 8 figures

International audience; How cement-based materials behave in storage operating conditions is important in the context of a radwaste deep geological repository. In particular, we need missing thermodynamic data for ternary and low-pH cementitious materials that have high aluminum oxide content. This work reports calorimetric measurements performed on calcium silicate hydrate (C-S-H), calcium aluminate silicate hydrate (C-A-S-H) and magnesium silicate hydrate (M-S-H) gel phases. Coupled with solubility experiments and vapor adsorption isotherms, a complete set of thermodynamic parameters for C-S-H, C-A-S-H, and M-S-H is provided. The measurements are complemented by a model predicting thermodynamic properties, which is parameterized using results from this work. Predominance diagrams allow us to confirm the relation between M-S-H and low C/S phases. The diagrams support a discussion on kinetics that may play a role in relations with other Al-and Mg-bearing phases.

International audience; Two magnesium silicate hydrates (M-S-H) with structural magnesium/silicon ratios of 0.57 ± 0.08 and 1.07 ± 0.13 were synthesized at room temperature, with one year of synthesis duration. Their structure was clarified by considering results from X-ray diffraction, TEM, 29Si MAS NMR spectroscopy, TGA, and EPMA. A modeling approach appropriate to defective minerals was used because usual XRD refinement techniques cannot be used in the case of turbostratic samples, where coherency between successive layers is lost. M-S-H with Mg/Si ratio of ~ 0.6 appears to be structurally close to nanocrystalline turbostratic 2:1 Mg–Si phyllosilicates. The increase of the Mg/Si ratio from 0.6 to 1.2 occurs by increasing the occurrence of defects in the silicate plan. The layer-to-layer distance evolves from 9.46 Å to 14 Å under air-dried and ethylene glycol conditions, respectively. Crystallites have a mean size of 1.5 nm in the ab plane, and 2.4 nm along c*.

International audience; The 11B/10B ratio in calcite and aragonite is an important proxy of oceanic water pH. However, the physico-chemical mechanisms underpinning this approach are still poorly known. In the present study, we theoretically determine the equilibrium isotopic fractionation properties of structural boron species in calcium carbonates, BO33-, BO2(OH)2- and B(OH)4- anions substituted for carbonate groups, as well as those of B(OH)4- and B(OH)3 species in vacuum. Significant variability of equilibrium isotopic fractionation properties is observed among these structural species which is related to their contrasted coordination state, B-O bond lengths and atomic-scale environment. The isotopic composition of structural boron does not only depend on its coordination number but also on its medium range environment, i.e. farther than its first coordination shell. The isotopic fractionation between aqueous species and their counterparts in vacuum are assessed using previous investigations based on similar quantum-mechanical modeling approaches. At 300K, the equilibrium isotope composition of structural trigonal species is 7 to 15 ‰ lighter than that of aqueous boric acid molecules, whereas substituted tetrahedral borate ions are heavier than their aqueous counterparts by 10 to 13 ‰. Although significant uncertainties are known to affect the theoretical prediction of fractionation factors between solids and solutions, the usually assumed lack of isotopic fractionation during borate incorporation in carbonates is challenged by these theoretical results. The present theoretical equilibrium fractionation factors between structural boron and aqueous species differ from those inferred from experiments which may indicate that isotopic equilibrium, unlike chemical equilibrium, was not reached in most experiments. Further research into the isotopic fractionation processes at the interface between calcium carbonates and aqueous solution as well as long duration experiments aimed at investigating the kinetics of equilibration of boron environment and isotopic composition are therefore required to refine our understanding of boron coprecipitation in carbonates and thus the theory behind the use of boron isotopes as an ocean pH proxy.

In the present work the modifications induced by the geomimetic processing on the environment of silicon and aluminum atoms are finely characterized by solid state MAS NMR. The raw clay (Lat), a lateritic clay from Yaounde (Cameroon), contains kaolinite, quartz, hematite and goethite as major mineral phases. This material is treated under acidic conditions during 24 h (LatAF) and then under alkaline conditions during 18 days, leading to the final consolidated “geomimetic” product (LatAFCH). The samples have been characterized by 29Si and 27Al solid state NMR at each step of the process.The NMR spectra obtained for the starting clay indicate the presence of AlIV and AlVI populations together with silicon Q2 (0 or 1Al) and Q3 (0 or 1Al) environments located at δiso=-83 ppm and δiso=-91 ppm respectively.The acidic reaction during 24 h, does not significantly affect the silicon-rich layers. It induces a conversion of part of AlIV population into AlVI environment mainly related to the occurrence of six-fold organo-aluminum complexes when using fulvic acid. With inorganic acid, Al dissolution prevails.The neutralization (using lime) of the medium, followed by ageing for 18 days, promotes clay interactions with available calcium ions. The newly formed phases are cementitious CSH, CASH and CAH phases.

International audience; Two commercial formulations of apatitic calcium phosphate cements (CPCs), Graftys Ò Quickset (QS) and Graftys Ò HBS (HBS), similar in composition but with different initial setting time (7 and 15 min, respectively), were combined to ovine whole blood. Surprisingly, although a very cohesive paste was obtained after a few minutes, the setting time of the HBS/blood composite dramatically delayed when compared to its QS analogue and the two blood-free references. Using solid state NMR, scanning electron microscopy and high frequency impedance measurements, it was shown that, in the particular case of the HBS/blood composite, formation of a reticulated and porous organic network occurred in the intergranular space, prior to the precipitation of apatite crystals driven by the cement setting process. The resulting microstructure conferred unique biological properties to this material upon implantation in bone defects, since its degradation rate after 4 and 12 weeks was more than twice that for the three other CPCs, with a significant replacement by newly formed bone. Statement of Significance A major challenge in the design of bone graft substitutes is the development of injectable, cohesive, resorbable and self-setting calcium phosphate cement (CPC) that enables rapid cell invasion with initial mechanical properties as close as bone ones. Thus, we describe specific conditions in CPC-blood composites where the formation of a 3D clot-like network can interact with the precipitated apatite crystals formed during the cement setting process. The resulting microstructure appears more ductile at short-term and more sensitive to biological degradation which finally promotes new bone formation. This important and original paper reports the design and in-depth chemical and physical characterization of this groundbreaking technology.

Concrete materials are made of various minerals and phases, whose spatial heterogeneous distributions impact the overall physical and chemical properties of the materials. We have investigated the heterogeneous distribution of minerals and phases in two types of concrete using quantitative X-ray intensity maps coupled with an innovative data treatment method based on image segmentation. This method provided quantitative data on spatial distribution, modal content and associated calculated formulas for each identified mineral and phase in the binder with micrometer resolution. We also obtained quantitative information on the porosity associated with the phases, making it possible to differentiate poorly hydrated cement phases (initial clinker hydration reaction) from highly hydrated phases (final cement product) despite their similar chemical composition, when expressed in terms of cationic formulas. We quantified the mineralogical and phase contents, independent of crystal size or crystallinity considerations. We report spatial resolution in the pozzolan hydration process over different observation scales for the two investigated concretes.

An injectable purely apatitic calcium phosphate cement (CPC) was successfully combined to a water-soluble radiopaque agent (i.e., Xenetix

International audience; Understanding calcium silicate hydrates (CSHs) is of paramount importance for understanding the behavior of cement materials because they control most of the properties of these man-made materials. The atomic scale water content and structure have a major influence on their properties, as is analogous with clay minerals, and we should assess these. Here, we used a multiple analytical approach to quantify water distribution in CSH samples and to determine the relative proportions of water sorbed on external and internal (interlayer) surfaces. Water vapor isotherms were used to explain the water distribution in the CSH microstructure. As with many layered compounds, CSHs have external and internal (interlayer) surfaces displaying multilayer adsorption of water molecules on external surfaces owing to the hydrophilic surfaces. Interlayer water was also quantified from water vapor isotherm, X-ray diffraction (XRD), and thermal gravimetric analyses (TGA) data, displaying nonreversible swelling/shrinkage behavior in response to drying/rewetting cycles. From this quantification and balance of water distribution, we were able to explain most of the widely dispersed data already published according to the various relative humidity (RH) conditions and measurement techniques. Stoichiometric formulas were proposed for the different CSH samples analyzed (0.6 < Ca/Si < 1.6), considering the interlayer water contribution.

Aluminate glasses are important materials from a fundamental structural point of view because Al is the only network former. They present also a technological interest because of their good IR transmission and ultralow optical losses. Aluminum in glasses of the system MO–Al2O3 (M = Ca, Sr, Ba) can have different coordination numbers, essentially 4 and 6, as a function of the MO/Al2O3 ratio. Using Raman spectroscopy and high field 27Al NMR spectroscopy, we have determined the structure of aluminum network as a function of MO/Al2O3 ratio with M corresponds to different alkaline–earth cations. Al is essentially in four-fold coordination with different amounts for Al2O3 between 50 and 75% but varies between Q2 and Q4 species as a function of MO/Al2O3 ratio where Q is tetrahedral species and n the number of bridging oxygen.

From one- to two- and three-dimensional MAS NMR solid-state experiments involving (31)P and (27)Al, we show that the structure of microporous alumino-phosphate AlPO(4)-40 contains at least four times more sites than expected, and we attribute two types of Al(IV) sites. The newly described (27)Al-(31)P MQ-HMQC opens new possibilities of describing details of three-dimensional bounded networks.

A large number of compositions within the SiO 2 –NaO 2 –B 2 O 3 (SNB) ternary glass system were investigated by various complementary techniques. Impedance spectroscopy was used to determine the parameters related to sodium ion diffusion in the glass structure; high-field boron NMR measurements on a series of samples identified and quantified the boron coordination as a function of the composition; exhaustive DTA measurements gave the glass transition temperature for all the compositions studied. Based on these results we demonstrate that the activation energy of sodium ion diffusion is closely related to the boron coordination number and involves two types of structural motifs: one corresponding to the sodium associated to non-bridging oxygen atoms, and the other to sodium compensating B IV motif. We also show that simple DTA measurements of the glass transition temperature can be used to define structural domains within this ternary composition range.

International audience; Layered calcium organosilicate hybrids contg. covalently linked org. functionalities were synthesized by a sol-gel process from the reaction of calcium salt and organotrialkoxysilane with alkyl (from Me to octadecyl) and Ph functionalities in an aq./EtOH basic soln. at room temp. These hybrid org.-inorg. materials were characterized by XRD, TEM, FTIR, and solid state 29Si, 1H, and 13C NMR spectroscopy. The comparison of the basal distance measured by XRD and the length of the alkyl groups is consistent with a bilayer arrangement of the org. group inside the interlayer. The degree of basal ordering does not depend on the alkyl group length. Broad in-plane diffraction peaks are best explained by a smectite-like layer than by the parent inorg. calcium silicate hydrate (C-S-H) structure. This suggests the existence of edge-sharing Ca(O,OH)6 layers sepd. by well-organized organosilicates. FTIR, 13C, and 29Si NMR spectra exhibit the typical features of Si-C bonds, showing that the org. groups were not cleaved. Also, the 29Si NMR spectrum shows that silanes are fully hydrolyzed but weakly condensated. To the authors' knowledge, this is the first report of the synthesis and characterization of layered calcium silicate with org. functionalities directly bonded to the inorg. framework via Si-C bonds.

High-surface-area amorphous gallia–silica samples (Si:Ga=3, 10, 20, 40) were prepared by a sol–gel route involving hydrolysis of an ethanolic solution of silicon tetramethoxide and gallium nitrate. Nitrogen adsorption (77 K) showed the materials obtained to be basically mesoporous. The most frequent pore radius resulted to be 0.8 nm in all cases, while surface area ranged from 476 to 586 m2 g−1. Both, NMR spectroscopy and IR spectroscopy of adsorbed probe molecules (CO and pyridine) showed the gallia–silica samples to have distinctive Bronsted and Lewis acidity. According to NMR spectra of both 29Si and 1H, Bronsted acidity should be assigned to Si(OH)Ga groups formed by partial substitution of gallium for silicon in the silica matrix. Lewis acidity is assigned to coordinatively unsaturated Ga3+ ions.

International audience; γ-Ga2O3 and α-Ga2O3 samples were prepared as single-phase materials having a high surface area. 71Ga NMR showed the simultaneous presence of tetracoordinated (GaIV) and hexacoordinated (GaVI) in γ-Ga2O3, whereas in α-Ga2O3 most of the gallium present was found to be as GaVI. However, the apparent rate of methanol conversion into dimethyl ether (at 473 K) was nearly the same for both samples, when due account was taken of their respective surface area. The unexpected high activity of α-Ga2O3 was explained from IR spectroscopic results obtained by using acidity probes like CO and pyridine. These spectroscopic probe molecules showed, for both samples, the presence of strong Lewis acid sites related to coordinatively unsaturated (cus) GaIV ions which, for the case of α-Ga2O3, strongly suggests surface reconstruction. By contrast, CO2 adsorption revealed a higher basicity for the α-polymorph, as compared to γ-Ga2O3. This basicity can be directly correlated to a larger amount of surface GaVI ions which results in a higher degree of ionicity.

International audience; Cumene conversion under an excess of benzene is studied over a series of mordenite (MOR) zeolites (Na-MOR, HNa-MOR, H-MOR and dealuminated H-MOR) by in situ 13C and 1H MAS NMR spectroscopy in the temperature range 298–473 K. By tracing the fate of 13C labeled atoms in the benzene molecule, intermolecular transalkylation, disproportionation and isomerization reactions are highlighted. The reactivity of MOR-based catalysts in these reactions is found to increase in the following order: Na-MOR473 K, strong acid sites). The reaction mechanisms are discussed.

A magic angle spinning (MAS) NMR probe has been developed to allow in situ measurements of NMR spectra. Two applications are targeted with this device: i) in situ and operando MAS NMR spectroscopy of working catalysts and ii) the hyperpolarized (HP) 129Xe spectroscopy of porous materials under MAS and continuous flow conditions. The construction of the MAS probe is described and the usefulness of this system is demonstrated by studying the adsorption of hyperpolarized xenon on AlPO-41 and ITQ-6 zeolites. The high stability of the HP xenon flow allowed us to perform two-dimensional exchange experiments under MAS conditions, in a short time and with very good resolution.

27 Al decoupling has been used to remove residual J-coupling interactions between 31 P and 27 Al in microporous aluminophosphates AlPO 4 -14 and AlPO 4 -40. In combination with 1 H high-power decoupling, 27 Al adapted decoupling yields 31 P spectra with optimal sensitivity and resolution. The importance of double-resonance decoupling is further demonstrated by incorporating this technique in the MQHETCOR sequence. Unambiguous assignment of all the AlPO 4 -14 nuclear magnetic resonances is achieved by combining multiple-quantum evolution in the 27 Al dimension and double-resonance decoupling in the 31 P acquisition domain.

Bioactive glass hybrids are among the most promising materials for bone regeneration, but the incorporation of calcium, a key element for mineralization properties of the implant, into the inorganic part of the hybrid network is challenging. We present here a synthesis route towards both class I and II gelatin-bioactive glass hybrids allowing the efficient incorporation of calcium ions at low temperature.

The recent availability of very high field (800 MHz) and very high magic angle spinning rates (35.5 kHz) can lead to important improvements in the field of solid state NMR of half integer quadrupolar nuclei showing important or severe second-order quadrupolar broadenings (7A1A1, 1GaGa…). We give experimental examples of these improvements in the case of both crystalline, defect-bearing and amorphous materials.

We describe a new pulse sequence that separates spinning sidebands by order for MAS NMR spectra of half integer quadrupolar nuclei broadened to second order. This two dimensional experiment is based on the modulation of each spinning sideband by its order with nine pulses (QPASS: quadrupolar phase adjusted spinning sidebands). The experimental spectra are compared with simulation for the case of 71Ga in β-Ga2O3.

International audience; The possibility to understand the phenomena of oxygen diffusion in the solids may be decisive to explain the role of framework oxygen atoms in a catalytic mechanism or in catalyst regeneration steps. In this work, two highly efficient characterization techniques have been associated: the O-17/O-16 isotopic exchange and the O-17 high field solid-state NMR spectroscopy. This combination leads to a powerful tool to investigate the interaction between gaseous dioxygen molecule and lattice oxygen atoms. Here, it permits to demonstrate the enhancement of the participation of zeolitic oxygen atoms in the exchange with the gas phase when ceria is simply mixed with NaX

Unlike the long-range order of ideal crystalline structures, local order is an intrinsic characteristic of real materials and often serves as the key to the tuning of their properties and their final applications. Although researchers can easily assess local ordering using two-dimensional imaging techniques with resolution that approaches the atomic level, the diagnosis, description, and qualification of local order in three dimensions is much more challenging. Solid-state nuclear magnetic resonance (NMR) and its panel of continually developing instruments and methods enable the local, atom-selective characterization of structures and assemblies ranging from the atomic to the nanometer length scales. By making use of the indirect J-coupling that distinguishes chemical bonds, researchers can use solid-state NMR to characterize a variety of materials, ranging from crystalline compounds to amorphous or glassy materials. In crystalline compounds showing some disorder, we describe and distinguish the contributions of topology, geometry, and local chemistry in ways that are consistent with X-ray diffraction and computational approaches. We give examples of materials featuring either chemical disorder in a topological order or topological disorder with local chemical order. For glasses, we show that we can separate geometric and chemical contributions to the local order by identifying structural motifs with a viewpoint that extends from the atomic scale up to the nanoscale. As identified by solid state NMR, the local structure of amorphous materials or glasses consists of well-identified structural entities up to at least the nanometer scale. Instead of speaking of disorder, we propose a new description for these structures as a continuous assembly of locally defined structures, an idea that draws on the concept of locally favored structures (LFS) introduced by Tanaka and coworkers. This idea provides a comprehensive picture of amorphous structures based on fluctuations of chemical composition and structure over different length scales. We hope that these local or molecular insights will allow researchers to consider key questions related to nucleation and crystallization, as well as chemically (spinodal decomposition) or density-driven (polyamorphism) phase separation, which could lead to future applications in a variety of materials.

International audience; This article reports on the identification, synthesis, and in-situ structure determination of a new crystalline calcium borosilicate compound of composition CaSi1/3B2/3O8/3. Synthesis was carried out by complete crystallization on annealing from a corresponding glassy composition in the widely studied CaO–SiO2–B2O3 ternary system. The crystallographic structure was determined ab initio using electron diffraction information and the charge flipping algorithm performed on synchrotron and neutron powder diffraction data collected in situ at high temperature. CaSi1/3B2/3O8/3 is found to crystallize in the Pna21 (no. 33) orthorhombic space group, with a = 12.1025(4) Å, b = 5.2676(1) Å, c = 3.7132(1) Å, and V = 236.71(1) Å3 at 650 °C. Solid-state 29Si and 11B NMR experiments have confirmed the existence of finite chains along the c axis, formed by corner-sharing SiO4 tetrahedra and BO3 units. Silicon and boron species share a crystallographic site, and the Si/B distribution induces different possible arrangements of the chains which are discussed in light of DFT calculations. At room temperature, the existence of a superstructure, resulting from the ordering within nanoscale domains, was explored by transmission electron microscopy.

International audience; In-situ sampling was performed in the Andra Meuse/Haute Marne (France) Underground Research Laboratory (URL) allowing the study of two cement based materials/claystone interfaces that have undergone 4 to 5 years of interaction. The first interface concerned a shotcrete that was sprayed on the wall of an access drift at the laboratory level and the second one, a class G cement paste that was injected in a borehole filled from the surface and was intercepted during the excavation of a new gallery. In the first case, the hydrodynamic conditions were controlled by the ventilation of the drift; while in the second, the cement paste and claystone materials were considered saturated and far from any mechanical perturbation. A multi scale investigation was carried out to identify any evidence of alkaline perturbation in the cement based materials and the claystone. Chemical, mineralogical, and textural measurements were thus performed on the different materials in contact at the nanometer to a centimeter scale. Results showed that all the perturbations resulting from the geochemical contrast between the cement materials and the claystone were limited to a mu m scale on each side of the interfaces. Carbonation was observed in the cement materials leading to an opening or a clogging of the porosity according to the hydrodynamic conditions and the formulation of the cement material. The distribution of the cation exchange population was also modified in the claystone in contact with the cement paste where a potassium saturation of the exchangeable fraction was identified. The originality of the present work is that realistic field controlled samples from the Andra URL were studied, hereby allowing the evaluation of the impact of natural heterogeneities of the in-situ experimental conditions (that is, hydrodynamic conditions, engineered damage zone, mineralogical variations) on the perturbations at the cement paste/claystone interfaces. An important result is that the clogging of porosity was not homogenous along the interfaces.

International audience; The thermodynamic properties of three aluminous 2:1 clay minerals were acquired at 1.013 bars and at temperatures between 5 and 500 K using various calorimetric methods. Calorimetric measurements were performed on hydrated and dehydrated

The synthesis and structure resolution of RbLaF 4 are described. RbLaF 4 is synthesized by solid-state reaction between RbF and LaF 3 at 425 °C under a nonoxidizing atmosphere. Its crystal structure has been resolved by combining neutron and synchrotron powder diffraction data refinements (Pnma, a = 6.46281(2) Å, b = 3.86498(1) Å, c = 16.17629(4) Å, Z = 4). One-dimensional 87Rb, 139La, and 19F MAS NMR spectra have been recorded and are in agreement with the proposed structural model. Assignment of the 19F resonances is performed on the basis of both 19F- 139La J-coupling multiplet patterns observed in a heteronuclear DQ-filtered J-resolved spectrum and 19F- 87Rb HMQC MAS experiments. DFT calculations of both the 19F isotropic chemical shieldings and the 87Rb, 139La electric field gradient tensors using the GIPAW and PAW methods implemented in the CASTEP code are in good agreement with the experimental values and support the proposed structural model. Finally, the conductivity of RbLaF 4 and luminescence properties of Eu-doped LaRbF 4 are investigated. © 2012 American Chemical Society.

International audience; Ordering of disordered materials occurs during the activated process of nucleation that requires the formation of critical clusters that have to surmount a thermodynamic barrier. The characterization of these clusters is experimentally challenging but mandatory to improve nucleation theory. In this paper, the nucleation of a magnesium alumino-silicate glass containing the nucleating oxide TiO 2 is investigated using neutron scattering with Ti isotopic substitution and 27 Al NMR. We identified the structural changes induced by the formation of crystals around Ti atoms and show important structural reorganization of the glassy matrix.

Silicate, calcium-silicate, and phosphosilicate glasses of the composition 80 SiO2–(20 − x) Na2O − x Me2O (where x = 0, 10 and Me = Li or K), 48.7 SiO2–26.9 CaO–(24.4 − x) Na2O − x Me2O (where x = 0, 12.2 and Me = Li or K), and 46.1 SiO2–2.6 P2O5–26.9 CaO–(24.4 − x) Na2O − x Me2O (where x = 0, 12.2 and Me = Li or K) have been studied with high resolution solid state NMR methods. The quantification of the different Qn species was obtained for each sample by 29Si MAS–NMR analysis. The 23Na MQ-MAS–NMR was used to distinguish the different 23Na sites present in the glasses. The presence of phosphorus in the Na2O phosphosilicate revealed the presence of three Na ionic sites, while the mixed alkali effect resulted in the absence of the third and most ionic site. Quantum mechanical calculations were performed for the identification of the structures observed in our glasses detected by MAS–NMR and MQ-MAS–NMR.

article i nfo Nucleation is the initiating event for the formation of any crystal from undercooled melt. Although the classical nucleation theory describes qualitatively many aspects of the crystallization process, the mechanisms favoring the first steps of nucleation are still unknown and required the full identification of the catalytic sites. In this work, we report a structural investigation of the system 2MgO-2Al2O3-5SiO2+ TiO2, a major glass-ceramic for scientific and industrial interest, in order to understand the structural influence of Ti as a nucleating agent. X-ray scattering and 27 Al Nuclear Magnetic Resonance studies were carried out on 2MgO-2Al2O3-5SiO2+xTiO2 glasses, with 0 mol% ≤x ≤15.5 mol%. No evidence of phase separation can be detected in the initial glasses by Transmission Electron Microscopy at nanoscale and Ti atoms appear to be homogeneously distributed within the glassy structure. We explain that the presence of TiO2 favors nucleation by the formation in the initial glass of high-coordinated Al species and the presence of structural fluctuations that mimic the initial crystalline phase precipitating in the glass. The understanding of the parent glass structure appears as a critical constraint to understand the pathways promoting nucleation.

From one- to two- and three-dimensional MAS NMR solid-state experiments involving (31)P and (27)Al, we show that the structure of microporous alumino-phosphate AlPO(4)-40 contains at least four times more sites than expected, and we attribute two types of Al(IV) sites. The newly described (27)Al-(31)P MQ-HMQC opens new possibilities of describing details of three-dimensional bounded networks.

International audience; The structure of the glass 2MgO–2Al2 O3 –5SiO2 –TiO2 was investigated using neutron diffraction with isotopic substitution. Reverse Monte Carlo (RMC) modeling was used to reproduce experimental structure factors derived from diffraction experiments. The local environment of titanium atoms was determined and it corresponds to an average of 5.4 ± 0.2 oxygen atoms at a mean distance of 1.86 ± 0.02 ̊A. This coordination number agrees with the predominance of fivefold coordination, with the coexistence of four- and sixfold coordination in similar amounts. 27 Al nuclear magnetic resonance (NMR) results revealed that the proportion of highly coordinated aluminum atoms in this titanium-bearing glass was higher than in the titanium-free sample. RMC modeling was used to interpret the structural role of these [5] Al species and we show a trend for preferential bonding between [5] Al and Ti atoms. This favored linkage is important to understand the role of titanium dioxide as a nucleating agent in inorganic glass-ceramics fabrication.

International audience; The structure and properties of glasses and melts in the MgO-Al2O3-SiO2 (MAS) and CaO-MgO-Al2O3-SiO2 (CMAS) systems play an important role in Earth and material sciences. Aluminum has a crucial influence in these systems, and its environment is still questioned. In this paper, we present new results using Raman spectroscopy and 27Al nuclear magnetic resonance on MAS and CMAS glasses. We propose an Al/Si tetrahedral distribution in the glass network in different Qn species for silicon and essentially in Q4 and VAl for aluminum. For the CMAS glasses, an increase of VAl and VIAl is clearly visible as a function of the increase of Mg/Ca ratio in the (Ca,Mg)3Al2Si3O12 (garnet) and (Ca,Mg)AlSi2O8 (anorthite) glass compositions. In the MAS system, the proportion of VAl and VIAl increases with decreasing SiO2 and, similarly with calcium aluminosilicate glasses, the maximum of VAl is located in the center of the ternary system.

Two series of mesoporous aluminosilicate materials of the Al-MCM-41 type have been prepared from pre-formed ZSM-5 crystals. The synthesis involved the alkaline attack of the zeolite alone (M(−)/ x samples) or in the presence of an external silicon source (e.g. fumed silica, M(S)/ x samples) followed by a conventional 48 h hydrothermal treatment (100 °C) with cetyltrimethylammonium chloride as the structure directing agent. The effect of sodium hydroxide concentration (0.8 M ≤ x ≤ 3 M) on the properties of the final materials was investigated by powder XRD, nitrogen sorption, pyridine sorption (IRFT), SEM, TEM, MAS and 2D MQ-MAS 27 Al NMR. It was shown that the addition of fumed silica to the synthesis gel results in the improvement of the mesopore network structure. The stability of M(−)/ x and M(S)/ x materials towards boiling water (5 days) as well as their activity in the acid-catalysed transformation of methylcyclohexane at 350 °C were compared to those of ZSM-5, Al-MCM-41 and of a Al-MCM-41//ZSM-5/H mechanical mixture. Because of the existence of a 2-fold pore system with zeolite domains, M(S)/0.8 and M(S)/1.9 composites are more efficient catalysts than amorphous Al-MCM-41 and a mechanical mixture of Al-MCM-41 and ZSM-5. The best combination in terms of hydrothermal stability and catalytic activity was found for the M(S)/1.9 sample.

International audience; MgAl2O4 and ZnAl2O4 spinels have been irradiated by swift heavy ions (86Kr and 36S) simulating the irradiation by fission products for applications in the transmutation targets. The structures of unirradiated and irradiated spinel samples have been studied by NMR spectroscopy, with 27Al magic angle spinning and multiple-quantum magic angle spinning experiments. The parameters of fluence and electronic stopping power have been compared. For 86Kr ions, the obtained spectra are modified by irradiation: we observe a rise of the amount of aluminum in tetrahedral sites and a widening of the lines associated with the different aluminum environments compared with those of the pristine samples. Site exchange in the cationic sublattice is then observed and can be quantified from NMR spectra, determining the inversion parameter. An inversion parameter of 0.77 is estimated for the MgAl2O4 spinel irradiated with 1013 Kr ions/cm2, for a value of 0.275 in the pristine samples. Moreover, a line attributed to aluminum in 5-fold coordination with oxygen is observed in irradiated spinel samples at the maximum fluence for krypton. These new aluminum environments can characterize a transition layer which could change toward an amorphous layer, increasing the electronic stopping power and/or the fluence.

International audience; A new gallium trimesate Ga12O(OH)12({OH}4,{H2O}5)[btc]6 24H2O, called MIL-96, (btc = 1,3,5- benzenetricarboxylate or trimesate species) was hydrothermally synthesized under mild conditions (210 C, 5 h) in the presence of trimethyl 1,3,5-benzenetricarboxylate in water and characterized by single-crystal X-ray diffraction technique. The MIL-96 (Ga) structure exhibits a three-dimensional metal– organic framework containing isolated trinuclear l3-oxo-bridged gallium clusters and infinite chains of GaO4(OH)2 and GaO2(OH)4 octahedra generating a hexagonal network based on 18-membered ring. The two types of gallium groups are connected to each other through the trimesate species which induce corrugated chains of gallium octahedra, linked via l2-hydroxo bonds with the specific -cis–cis–trans- sequence. The 3D framework of MIL-96 reveals three kinds of cavities (two of them have estimated pore volumes of 480 and 860 A˚ 3), in which are encapsulated free water molecules. The latter species are removed upon heating at 150 C. The MIL- 96 (Ga) compound was characterized by 71Ga solid state NMR at different magnetic fields (14.1 and 17.6 T). 71Ga spectra of MIL-96 (Ga) show the gallium exhibits relatively weak quadrupolar interactions compared to those observed in other MOF-type gallium carboxylates that have very strong quadrupolar interactions (MIL-61 and MIL-53).