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The reaction of lithium hydride (LiH) powder with pure water vapor (H2O and D2O) was studied by thermogravimetry and in situ infrared spectroscopy at 298 K over a large pressure range. The mean particle size of LiH is around 27 μm. At very low pressure, the hydrolysis starts with the formation of lithium oxide (Li2O). Then, both Li2O and lithium hydroxide (LiOH) are formed on increasing pressure, thus, creating a Li2O/LiOH bilayer. The reaction takes place through the consumption of LiH and the formation of Li2O at the LiH/Li2O interface and through the consumption of Li2O and the formation of LiOH at the Li2O/LiOH interface. Above 10 hPa, only the monohydrate LiOH·H2O is formed. This hydration reaction of LiOH into LiOH·H2O occurs at a lower pressure (8 hPa) after the first hydration-dehydration cycle. The hydrolysis mechanism proposed in this paper suggests that the diffusion of ionic species across the intermediate Li2O layer is the rate limiting step of the reaction.

Performance assessment of geological nuclear waste repositories entails modeling of the long-term evolution of the aqueous alterations of the fractured nuclear glass block, because the time scales under consideration are of several thousands of years and hence beyond the range of any direct experimental perspectives. In this study, our objective is to bridge the gap between the reservoir-scale flow and transport simulations and the micron-scale modeling of the glass-water interfacial processes by providing quantitative evaluation of the aqueous alteration of glass at the block scale. In particular, calculations of the equivalent diffusive, hydraulic, and alteration kinetics properties and reactive transport simulations are discussed. Prior to performing reactive transport modeling at the scale of the glass canister, the preferred upscaling techniques were first applied to a synthetic fracture network system with ends to compare the results of the borosilicate glass alteration with the discrete fracture modeling and the equivalent porous medium approach. The evolution of the altered glass obtained from reactive transport modeling applied to several realizations of the equivalent fracture network tessellation was compared to the experimental data of the aqueous alteration test of a nonradioactive full-scale SON68 glass canister. The proposed model agrees with the experimental data and offers, for the first time, an opportunity to better understand the impact of fracturing as the convection due to the radioactivity acting as a heating source on the corrosion of nuclear glass.

Understanding nuclear glass alteration in a fracture network of a block of nuclear glass is critical in predicting the release of the radionuclides in the subsurface and is relevant for the security of nuclear waste disposal. Here, we present an image processing-based fracture network characterization workflow that enables us to characterize a glass block fracture network, establish a link between a physical parameter representing an internal state of glass structural relaxation and an internal structure of the block fracture network, and generate multiple realizations of equivalent fracture networks by considering the variability of the fracture network parameters such as fracture distribution and apertures. The proposed workflow includes the following stages: (i) fracture network extraction, (ii) measurement of apertures of all distinct ramifications of the fracture network, (iii) image segmentation, (iv) anisotropy characterization, (v) passage to segment representation with the intention of modeling block equivalent fracture networks by using an algorithm of mesh growth, (vi) geostatistical modeling of average apertures and variables responsible for fracture spatial distribution, and (vii) simulation of equiprobable realizations of fracture network equivalent tessellations. Given this processing, the workflow is able to provide data for further steps including upscaling of diffusivity and permeability, and it facilitates reactive transport modeling at the glass block scale. As an illustrative example, we apply the proposed sequence of actions to a two-dimensional (2D) high-resolution image of two blocks of nuclear glass. This application brings into service both hard data obtained by direct measurement of the fracture network and soft physics-based explanatory data and considers the variability in the fracture network. The results show that implementation of the devised procedure presents an opportunity for better understanding of the impact of fracturing on aqueous alteration of glass.

Cisplatin (cis-diaminedichloroplatinum(II), CDDP) plays a crucial role in the treatment of various malignant tumors. However, its clinical efficacy and applicability are restricted by issues of toxicity and resistance. Here, for drug delivery purposes, the outer surface of MCM-41 mesoporous silica nanoparticles (MSNs) was functionalized with poly(ethylene glycol) (Mw = 10 000 g/mol) or low-molecular-weight (Mw = 1800 g/mol) branched polyethyleneimine (PEI). Given the strong affinity of sulfur for platinum, thiol-functionalized MSNs were synthesized for comparison by co-condensation with (3-mercaptopropyl)triethoxysilane. CDDP loading was performed either by adsorption or impregnation in aqueous media without the use of dimethyl sulfoxide as a solubilizer. CDDP loading capacities obtained by impregnation were higher than those obtained by adsorption and varied from 3.9 to 16.1 wt %, depending on the functional group. Loaded nanomaterials were characterized by scanning electron microscopy, scanning transmission electron microscopy–high-angle annular dark-field, and Raman spectroscopy. Depending on the functional groups, platinum-based species were either dispersed in the nanomaterials as nanocrystals or uniformly distributed as molecular species. The spectral signature of CDDP was strongly modified when platinum species were homogeneously distributed within the nanomaterials. Preliminary drug release studies performed at 37 °C showed that the behavior of CDDP-loaded MSNs strongly depends on the nature of the present functional groups. Among the functionalization routes investigated in this paper, PEI-based functionalization showed the most promising results for further applications in controlled drug release with the absence of burst release and a sustained release over 72 h.

In this study, Superparamagnetic iron oxide nanoparticles (SPION) were functionalized in one pot with two organic molecules. Firstly, polyethylene glycol (PEG) was mixed for 46 hours to improve steric stability and then, two hours before the end of the reaction, dimercaptosuccinic acid (DMSA) was added to provide negative charges and thiol groups for post-functionalization. Three different molecular weights of PEG were used (550, 2000 and 5000 g mol-1). The main goal of this study was to characterize and quantify accurately the surface of SPION functionalized with two organic molecules. We demonstrated the advantages of coupling thermogravimetric and X-ray photoelectron spectrometry analyses to distinguish accurately the covering of SPION's surface. Thanks to the combination of these two techniques we were able to distinguish the amount of DMSA and PEG on SPION regarding the length of the polymer. We also showed that the length of the PEG influenced the quantity of DMSA adsorbed. With the smallest PEG (550 g mol-1) the presence of DMSA is almost ten times higher than with the two other PEG used proving that long polymers prevent the adsorption of small molecules on the surface of SPION.

We report a method to model, simulate and predict high-level nuclear waste (HLW) thermal behavior over short and long time-scales. The approach relies on an inverse method using homogenized thermal fluxes at the HLW package surfaces during the vitrification process. The thermal simulation can then be used as input in subsequent structural analyses. This allows us to compare for two different vitrification processes the developed thermal stress build-up investigated inside the glass block. The first process is the original experimental vitrification process, without the presence of the radionuclides. The second one is a simulation made possible by the proposed inverse method, where the cooling and solidification for a HLW integrate the long-term heat source of the radionuclides.

International audience; Iron oxide nanoparticles have the capability to cross Blood Brain Barrier (BBB) and hence are widely investigated for biomedical operations in the central nervous system. Before being used in humans, it is necessary to investigate their biocompatibility, dosimetry and biological interaction. In the present study, in-house synthesized superparamagnetic iron oxide nanoparticles (SPIONs) were functionalized using the polymer, PolyEthylene Glycol and a fluorophore (Rhodamine) (fSPIONs). The interaction of fSPIONs with murine oligodendrocytes 158N revealed that the nanoparticles were taken up by the cells via endocytosis, and there was a dose-dependent increase in the intracellular iron content as revealed by flow cytometry, transmission electron microscopy and confocal microscopy. Nanoparticles remained stable inside the cells even after 24 h. In addition, interaction and/or accumulation of nanoparticles was supported by the possibility to isolate treated cells even after 24 h. Cell sorting capacity using a magnet depended on the amount of particles. Noteworthy, whereas these nanoparticles can interact per cell. fSPIONs exhibited good biocompatibility as no toxicological response, including morphological changes, loss of viability, oxidative stress or inflammatory response (IL-1β, IL-6 secretion) was observed. These data show that the in-house synthesized fSPIONs have no accumulate on 158N oligodendrocytes without the side effects on 158N cells, and constitute interesting tools for biomedical applications on nerve cells, including cellular imaging and targeting (oxidative stress, inflammation and cell death) that could be detrimental when a subsequent use of these nanoparticles in humans is considered.

Hydrolysis of LiH at room temperature and under low relative humidity (RH < 2%) is studied by manometry working with heavy water either in closed (variable water vapor pressure) or open (constant water vapor pressure) system. Products of the reaction are characterized by XRD and FTIR. It is shown for the first time that the hydrolysis reaction occurs in two steps: first water is adsorbed on the LiH surface and then the hydrolysis reaction starts. In open system, for relative humidity lower than 0.04% only the formation of Li2O is observed while for higher moisture the reaction continues with the production of LiOD. The reaction rate is however extremely low and only a very small amount of LiH is transformed. The kinetic can be well predicted by the model of core shrinking limited by the diffusion through the layer of Li2O and/or LiOD surrounded LiH particles. For practical application, it is concluded that if LiH is stored under controlled humidity lower than 0.04% (40 ppm) there is no major risk to form LiOH in significant amount.

An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle creep conditions. Brittle creep may be an important slow deformation process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle creep due to slow crack-propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. Creep tests were performed at constant confining pressure (15 MPa) for water saturated conditions. Data were obtained by maintaining the differential-stress constant in steps of 24 h duration. A set of sensors allowed us to record strains and acoustic emissions during creep. The effect of temperature on creep was investigated from ambient temperature to 70°C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary creep, a large dilatancy was observed that did not occur in constant strain rate tests. This is correlated to acoustic emission activity associated with crack growth. As a consequence, slow crack growth has been evidenced in glass. Beyond secondary creep, failure in tertiary creep was found to be a progressive process. The data are interpreted through a previously developed micromechanical damage model that describes crack propagation. This model allows one to predict the secondary brittle creep phase and also to give an analytical expression for the time to rupture. Comparison between glass and crystalline rock indicates that the brittle creep behavior is probably controlled by the same process even if stress sensitivity for glass is lower than for rocks.

Mesoporous silica nanoparticles were synthesized at high pH using CTAB as a template and TEOS as a silica precursor. It was shown that varying the NaOH concentration between 5 and 27.5 mM allows the size, pore and silica structure of mesoporous nanoparticles to be precisely tuned. In particular, monodisperse nanoparticles with the MCM-41 structure with size ranging from 90 nm to 450 nm were obtained by increasing the NaOH concentration from 12.5 to 22.5 mM. It thus demonstrates that NaOH concentration must range between 12.5 and 15 mM in order to prepare MCM-41 silica nanoparticles with optimal size for nanovectorization. We also found that under usual conditions the aggregation of the obtained MSNs was due to the presence of carbonates and ethanol in the reaction mixture. Careful elimination of these species by using carbonate-free NaOH and purging with a N2 flow allows a highly stable suspension of non-aggregated MSN–MCM-41 to be obtained. After a complete CTAB extraction which was confirmed by Raman spectroscopy, cytotoxicity assays carried out in SW480 cancer cells show that these nanoparticles are not toxic up to 100 μg/mL.

International audience; a b s t r a c t An experimental study of thermally or water-induced crack healing in an inactive borosil-icate glass, chemically analogous to that used in France for the vitrification of nuclear waste was carried out. Partial welding of glass plates was observed after annealing in air at 425 °C (77 °C below T g) when at least 20 MPa compressive stress was applied, while annealing at 450 °C under 20 MPa led to a complete disappearance of the interface. Closure of indenta-tion-induced cracks was observed during annealing at 400 °C in an ESEM as a result of viscous relaxation of residual stresses but it did not constitute a sufficient proof of crack healing. DCDC specimens were thus pre-cracked in an ESEM and then either annealed at various temperatures (350–490 °C) in secondary vacuum or in air, or left in water at 70–90 °C, sometimes under a compressive stress normal to the crack face. The specimens were then reloaded in the ESEM and the crack opening displacements under a given load were compared to those measured during pre-cracking. The cracks were bridged by an alteration layer over a distance from the crack tip which decreased as loading increased. The restraining effect of these bridges on crack opening was assessed via finite element simulations, using interface elements. The tensile strength of the bridging layer was estimated as 27–39 MPa after vacuum annealing at 400 °C, 11–20 MPa after 15 days in water at 90 °C and 44–78 MPa after 11 days in water at 70 °C under 5 MPa normal compression. Partially healed cracks did not resume propagation from their former crack tip, but due to branch cracks re-initiated a few hundred microns behind it which grow avoiding the healed area. This behaviour was explained using finite element simulations.

International audience; The aim of this study was to investigate the influence of the surface charge and coating of Superparamagnetic Iron Oxide Nanoparticles (SPIONs) on their in vitro and in vivo behaviors. Neutral and negatively-charged PEG-based SPIONs were synthesized and compared to Resovist (R), a carboxydextran-based SPION currently used in clinics. Their cytotoxicity, cell internalization, and potential as contrast agents for magnetic resonance imaging were assessed. Neutral pegylated SPIONs were internalized less readily by the reticuloendothelial system and showed a lower uptake by the liver, compared to negatively-charged SPIONs (with carboxydextran and PEG). These results suggested that the charge of functionalized SPIONs was more relevant for their biological interactions than the nature of their coating.

A crack network is introduced in glass by quenching heated samples. The sharp variation of temperature at the sample boundaries leads to tensile stresses that nucleate cracks. Then, they propagate in the entire sample. Quenching has been performed at 100, 200 and $$300\,^\circ \hbox {C}$$ . Cracks have been imaged with a scanning electron microscope. A transverse isotropic crack network is observed. Crack length and orientation have been measured. Obtained crack density has been compared to that inferred from elastic wave velocity measurements using effective medium theory. Cracked samples have been then submitted to creep tests. Two samples have been recovered, one before its failure and another after. Our observations show that vertical crack propagation takes place during brittle creep and that tertiary creep leads to a localized failure in a shear plane. The damaged and post-mortem microstructural networks have been documented.

Non Interaction Approximation (NIA) is currently used to relate effective elastic moduli to crack density. It also allows one to identify the anisotropy of the crack network.

The aim of this work is to develop novel organic-inorganic hybrid beads for colonic drug delivery. For this purpose, calcium pectinate beads with theophylline are prepared by a cross-linking reaction between amidated low-methoxyl pectin and calcium ions. The beads are then covered with silica, starting from tetraethyoxysilane (TEOS), by a sol-gel process. The influence of TEOS concentration (0.25, 0.50, 0.75 and 1.00 M) during the process is studied in order to modulate the thickness of the silica layer around the pectinate beads and thus to control the drug release. The interactions between the silica coating and the organic beads are weak according to the physicochemical characterizations. A good correlation between physicochemical and in-vitro dissolution tests is observed. At concentrations of TEOS beyond 0.25 M, the silica layer is thick enough to act as a barrier to water uptake and to reduce the swelling ratio of the beads. The drug release is also delayed. Silica-coated pectinate beads are promising candidates for sustained drug delivery systems.

The kinetics of glass alteration is studied in a reactor cell containing parallel glass plates with a small gap, representing an ideal crack geometry. The calibrated aperture of the crack is varied from a few tens to a few hundred micrometers. The glass coupons are immersed in a highly alkaline solution to obtain fast alteration. Although the cell is closed and isothermal, it is observed that vertical or horizontal configurations lead to very different alteration gel thickness profiles. This effect results from gravity-driven flow taking place in the vertical geometry due to glass leaching as opposed to essentially diffusive transport in the horizontal case. The advection velocity is estimated from a one-dimensional model of the coupled reaction/transport mechanism, based on a zero or first order reaction. The coupling between reaction and transport has a clear influence on the apparent alteration kinetics, a phenomenon generally ignored.

Cobalt sulfide prepared by aqueous precipitation using Na2S and a Co(II) salt is known to trap hydrogen at room temperature and low pressure. The importance of oxidation of the primary CoS precipitate with atmospheric oxygen with respect to its efficiency as a hydrogen absorber is demonstrated. This stage of oxidation produces a mixture of two solid phases: a partially crystallized cobalt hydroxide Co(OH)2 and an amorphous cobalt sulfide CoS2 with a Co(OH)2/CoS2 molar ratio of 1 as predicted by thermodynamics. This biphasic product is probably the basic cobalt sulfide CoSOH considered in older and even more recent work. This product traps molecular hydrogen with a H2/Co molar ratio of 0.5 whereas unoxidized CoS precipitate traps almost no hydrogen (H2/Co ¼ 0.025). Moderate acidic treatment of the absorber at room temperature leads to the selective dissolution of Co(OH)2. The remaining cobalt sulfide has CoS2 stoichiometry and reacts with hydrogen to form H2S gas and CoS. We showed that H2S released is reactive toward bases: CoS or Na2S were formed when H2S reacted with Co(OH)2 or NaOH, respectively. This proves that the hydrogen trapping reaction mechanism implies H2S as an intermediate species.

We report a new development of the so-called MSU route, the first route to use nonionic surfactants and block-copolymers, for the synthesis of silica with bimodal porosity in the micromesoporous range. Among the different synthesis strategies that have been explored until now, the "two-step" process led to the formation of stable hybrid micelles before silica condensation. This mechanism provided a large freedom in the adjustment of the reaction parameters and consequently of the final material structure. We report here that these hybrid micelles are stable enough to allow them to be concentrated through a new three-step method that involves (i) hybrid micelle assembly, (ii) hybrid micelle concentration (HMC), and (iii) silica condensation that leads to monolithic bodies instead of the usual powder. The silica: surfactant ratio is critical to achieving a well-ordered structure that exhibits a final pore size in between zeolites and mesoporous materials with a bimodal distribution centered at 0.6 and 2.0 nm. This method allowed us to homogeneously insert metal salts that remain trapped between the hybrid micelles after the second step without any disturbance of the silica framework. This is illustrated in this report by the addition of aluminum with different rates. Aluminum was inserted homogeneously up to a Si:Al (respectively, Al:Si %) atomic ratio of 2.6 (respectively, 38%). The Al-MSU obtained by this method exhibits strong acidity with a homogeneous broad range of acidity strength that varies linearly with the aluminum content, as demonstrated by NH 3 TPD ranging from 100 to more than 600 °C and preliminary catalytic tests.

The colloidal and structural stabilities of MCM-41 mesoporous silica nanoparticles (MSNs) are of great importance in order to prepare optimal nanovectors. In this paper, MSNs (approximatively 160 nm in diameter) were synthesized using n-cetyltrimethylammonium bromide as a template and tetraethyl orthosilicate as a silica source under high N2 flow (MSN/N2) to obtain stable dispersions in water. The degradation of the porous nanoparticles was investigated by immersion in water. The morphology and the porous structure were studied by TEM, XRD, N2 sorption, and 29Si MAS NMR and were compared to that of MSNs prepared in ambient air (MSN/air). The volumetric properties of the MSN/N2 after 1 day in water were drastically more decreased than MSN/air (a pore volume decrease of 85 % for MSN/N2 and 59 % for MSN/air) and the 2D-hexagonal porous structure was totally lost. Furthermore, synthesizing MSNs under a high N2 flow leads to a decrease in the synthesis yield (45 % MSN/N2 and 75 % for MSN/air). The lower structural stability of the MSN/N2 is explained by the lower polycondensation degree of the MSN/N2 observed by 29Si MAS NMR (Q4/Q3 = 0.86 for MSN/N2 and 1.61 for MSN/air) and the lower silica molar ratio in the nanomaterials (SiO2/CTA = 3.9 for MSN/N2 7.1 for MSN/air). This allows for enhanced solubilization of silica in water. Four strategies were hence evaluated in order to reinforce the porous structure of the MSNs. Among them, the most efficient route was based on a pH adjustment of the colloidal suspension (pH 7.5) after 2 h of synthesis without any purification and while keeping a N2 static atmosphere (called MSN/N2/7.5). After 1 day in water, the volumetric and structural properties of MSN/N2/7.5 were similar to that obtained for MSN/air. The improvement of the stability arose as a result of the increase in the silica condensation (Q4/Q3 = 1.58) and silica molar ratio in the nanomaterials (SiO2/CTA = 6.8). After the post-treatment, the silica framework condensation is improved while keeping the colloidal stability, thus allowing further functionalization and/or drug loading. Cytotoxicity assays using SW480 cancer cells show a greater improvement in the cell viability.

High-level radioactive waste (HLW) vitrification is a manufacturing process designed to dispose of nuclear energy fission products over long-term timescales. We studied and modeled the thermomechanical phenomena occurring during the processing of the glass blocks, e.g. during their solidification and their cooling down. The thermomechanical modeling takes place in 3D FEM simulations. The relaxations of the borosilicate glass are to be taken into account through scripted algorithms. They allow us to describe accurately the evolution of the glass properties over its phase transition (the glass transition temperatures are non-uniform in the HLW package). A damage behavior within the frame of Continuum Damage Mechanics is also used to predict the glass cracking surface area.

Density functional calculations are performed to investigate the effect of hydronium–sodium interdiffusion in a sodium borosilicate glass. It is found that the substitution of the Na+ network modifiers does not alter the glass covalent network, whereas a bridging bond is systematically broken when the substitution involves Na+ ions bonded to BO4 tetrahedra. The systematic dissociation of hydronium into water and proton suggests that this chemical species probably has a short lifetime in the glass, due to the capability of anionic sites to trap the protons very strongly. The relative basicities of the sites involved are compared, and a nice correlation is found between hydroxyl bond lengths and hydrogen bond strengths present in the hydrated glass.

The neodymium trisborohydride Nd(BH 4 ) 3 - (THF) 3 (THF = tetrahydrofuran) has been used as a catalyst precursor for isoprene polymerization for the first time. Associated to an excess of Al(Et) 3 , the resulting catalyst is moderately active, giving a mixture of cis- and trans- polymer. Addition of a stoichiometric amount of MgBu 2 to Nd(BH 4 ) 3 (THF) 3 affords a stereospecific catalyst providing trans-1,4-polyisoprene, more than 96% regular. That dual component Nd/Mg system also shows a better efficiency and good control of the molecular weights. A molecular structure is tentatively attributed to a bimetallic active species, based on 1 H NMR experiments.

We recently reported on the controlled formation of highly stable metal hydroxide nanoparticles. Growth control and stabilization of particles were achieved by performing hydrolysis and polycondensation reactions of polymer-complexed metal cations, the polymers being double hydrophilic block copolymers (DHBCs). The present paper focuses on the characterization of the intermediate species in the formation process, namely the mixture of multivalent metal cations plus the oppositely charged polyelectrolyte–neutral block copolymers. Complexation of metal cations by the anionic block of the DHBCs leads to the spontaneous formation of colloidal objects. Small angle neutron scattering experiments show that the aggregates exhibit a well defined core–corona architecture: the core is compact and homogeneous while the diffuse corona is constituted of polymer segments in a good solvent. The core formation is due to the water insoluble metal cation–polyacrylate complex while the corona is constituted of the water soluble neutral polymer blocks. Cryo-TEM images allowed the revelation of well-dispersed inorganic-rich domains. The presence of the longer neutral blocks prevents macroscopic phase separation of the complex and leads to the formation of hybrid micellar aggregates.

International audience; Spinel iron oxide nanoparticles were obtained under supercritical water conditions in a continuous and fast (less than 10s) way by modifying the initial stoichiometric Fe II /Fe III molar ratio from (1/2) to (3/0), without base solution, and using citrates directly with iron precursors. This result opens the way of an economical and environmentally benign approach to synthesize superparamagnetic iron oxide nanoparticles (SPIONs) in important yields.

International audience; The modeling of the viscoelastic stress evolution and specific volume relaxation of a bulky glass cast is presented in this article and is applied to the experimental cooling process of an inactive nuclear waste vitrification process. The concerned borosilicate glass is solidified and cooled down to ambient temperature in a stainless steel canister, and the thermomechanical response of the package is simulated. There exists a deviant compression of the liquid core due to the large glass package compared to standard tempered glass plates. The stress load development of the glass cast is finally studied for different thermal load scenarios, where the cooling process parameters or the final cooldown rates were changed, and we found a great influence of the studied cooldown rates on the maximum stress buildup at ambient temperature.

The presented work takes place in the context of the storage of vitrified radioactive wastes. The mechanical behavior of crack in glass under pressure at low strain rate is of great interest. The present work is focused on the time dependency of crack propagation in glass. Experiments are performed in triaxial conditions on thermally cracked boro-silicate glass samples. The initial crack network is introduced through a thermal shock (the sample is slowly heated up to 300°C and then it is quenched into water at ambient temperature). The creep tests are performed by increasing the axial stress step by step (at constant confining pressure, temperature and pore fluid pressure). Results show that during creep tests, dilatancy is observed. This is not the case for regular triaxial test. The dilatancy is correlated to a non-zero acoustic emission rate that is evidenced by the sub-critical crack propagation. This crack growth induced localized failures. In addition, increasing temperature increases the strain rate and reduces the time to rupture. The different experiments performed at different temperatures allow to determine the activation energy (32 KJ/mol). The effect of confining pressure and differential stress is also investigated in order to extrapolate to long time scales, as in storage conditions.

Absolute aggregation rate constants of anionic polystyrene sulfate latex particles were measured in the presence of cationic poly(vinylamine) by time-resolved simultaneous static and dynamic light scattering. The colloidal stability depends sensitively on the polymer dose, pH, and ionic strength. While the stability ratio is strongly dependent on the ionic strength, the electrophoretic mobility depends much more weakly on it, and therefore the latter measurements cannot be used as a reliable measure of the suspension stability. In the fast aggregation regime, the presence of the oppositely charged polyelectrolytes leads to an enhancement of the aggregation rate with respect to the one in the presence of an indifferent electrolyte. This acceleration probably originates from attractive electrostatic interactions between surface charge heterogeneities.

We study the early stages of flocculation in suspensions of charged colloidal particles in the presence of oppositely charged polyelectrolytes. Absolute aggregation rate constants are determined by...

International audience; The functionalization of superparamagnetic iron oxide nanoparticles (SPIOs) by meso-2,3-dimercaptosuccinic acid (DMSA) was investigated. Under ambient conditions, the thiol groups from DMSA are not stable and do not allow a direct functionalization without storage in stringent conditions or a chemical regeneration of free thiols. In this study, we have developed a protocol based on poly(ethylene glycol) (PEG) grafting of SPIO prior to DMSA anchoring. We have observed that PEG helps to increase the stability of thiol groups under ambient conditions. The thiol functionalized SPIOs were stable under physiological pH and ionic strength as determined by Ellman's essay and allowed us to graft a thiol reactive fluorescent dye: tetramethylrhodamine-5-maleimide (TMRM).

Electrophoresis is the movement of particles suspended in a liquid under influence of an electric field. Electrophoretic forming of silicon carbide (SiC) requires the simultaneous deposition of SiC and sintering aids such as carbon and boron. The incorporation of the sintering additives was studied in two ways: co-deposition of a boron-containing SiC powder and carbon black, as well as the co-deposition of SiC, boron carbide and carbon black. A high final density after sintering (95%) was obtained with the two approaches.

Reaction constants and composition profiles in molten cryolite have been theoretically investigated. Hartree-Fock and density functional calculations were applied to determine the exact nature (structure and energetic) of complexes existing in molten cryolite. The aim of this work was thus the understanding of chemical processes occurring in the electrowinning of aluminum and was a demonstration of how computational chemistry (based on density functional theory) can help us to determine structures and reaction energies in particularly complex medium such as cryolite. An analytical study, based on mass balance and equilibrium constants has been undertaken. This was performed on molecular liquid entities taking into account the four-, five- and sixfold coordinated aluminum complexes of the AlF3-3NaF melt system. Moreover, the effect of calcium has been studied by substituting two sodium atoms with one calcium atom, thus leading to the CaNaA1F6 system. Two conformers (instead of three for Na) were obtained for this system. They can be described as representing the four- and fivefold coordinated aluminum complexes in molten cryolite. The structurizing effect of calcium was clearly illustrated by the resulting optimized structures, showing that calcium stabilizes the IV and V coordinations of aluminum. By computing reaction constants, we have obtained composition profiles that are presented with those based on experimental data. Comparisons point out that computational chemistry techniques match with experimental results, especially in the case of pure cryolitic melts. For the presence of the fivefold coordinated aluminum complex in cryolite, and the predominance of the fourfold coordinated complex with calcium, it is clear that these computational techniques show us correct trends in predicting the main species in molten media. © 1997 John Wiley & Sons, Inc.

Aluminum is produced throughout the world using the Heroult-Hall process, which consists in the electrolysis of alumina dissolved in cryolite melts. This dissolution of alumina gives rise to the formation of oxyfluoroaluminates, the structures of which vary with the composition of the electrolyte mixture. Up to now there has been no real consensus as to the structural entities of these fluoroaluminate ions. The lack of knowledge of the ionic species arising from the dissolution of alumina in molten cryolite has led us to undertake structural, energetic and vibrational studies of these species using the methods of computational chemistry. Conformational and vibrational analyses of the ionic complexes were performed with the DGauss software on Cray C98 and C916 machines located at Cray Research, Eagan, MN, USA. A systematic study was carried out on the complexes [ AlOF x ] 1− x (1 ≤ x ≤ 5), [ Al 2 OF x ] 4− x (4 ≤ x ≤ 9), [Al 2 O 2 F x ] 2−x (2 ≤ x ≤ 7), which are those most commonly suggested for interpreted experimental measurements. The Al 4 OF 10 and Al 4 OF 8 2+ complexes were also investigated because of their possible occurrence in the electrorefining process of aluminum. Some of the studied complexes are much more stable than the others and so are the complexes most probably involved in the electrowinning process of aluminum. These complexes are AlOF 2 − , Al 2 OF 6 2− and Al 2 O 2 F 4 2− . Their infrared spectra have also been calculated. Concerning the two complexes Al 4 OF 10 and Al 4 OF 8 2+ , we find that oxygen is three-coordinated and not fourcoordinated. The last atom of aluminum is stabilized by two fluoride bridges. This computational approach has enabled us to eliminate the majority of the structures suggested in the literature for oxyfluoroaluminate ions. Currently we are examining in our laboratory the effects of cations on the anionic complexes.

Quantum chemical calculations are used to study AlCly−xFx3−y (y = 5 or 6, x = 0,…,y) species that can occur in aluminum electrorefining melts. These theoretical studies are included in a wider research program concerning the chemical instabilities in the bulk of molten salts during the refinement process. Stabilization energies, equilibrium geometries and vibrational frequencies of the complexes are calculated using the Delley functional methodology described in Ref. [1] (B. Delley, J. Chem. Phys., 92 (1990) 508). These computational simulations, discussed and compared with the experimental results demonstrate that density functional calculations can be reliably used in the study of complexes existing in molten salts. Quantum chemical calculations are accurate tools for theoretically predicting structures, physical and chemical properties and vibrational frequencies of known entities as well as unknown compounds.

10 pages; International audience; For a better understanding of the thermomechanical behavior of glasses used for nuclear waste vitrification, the cooling process of a bulk borosilicate glass is modeled using the finite element code Abaqus. During this process, the thermal gradients may have an impact on the solidification process. To evaluate this impact, the simulation was based on thermal experimental data from an inactive nuclear waste package. The thermal calculations were made within a parametric window using different boundary conditions to evaluate the variations of temperature distributions for each case. The temperature differences throughout the thickness of solidified glass were found to be significantly non-uniform throughout the package. The temperature evolution in the bulk glass was highly responsive to the external cooling rates applied; thus emphasizing the role of the thermal inertia for this bulky glass cast.

International audience; Hybrid polyion complex (HPIC) micelles are nanoaggregates obtained by complexation of multivalent metal ions by double hydrophilic block copolymers (DHBC). Solutions of DHBC such as the poly(acrylic acid)-block-poly(acrylamide) (PAA-b-PAM) or poly(acrylic acid)-block-poly(2-hydroxyethylacrylate) (PAA-b-PHEA), constituted of an ionizable complexing block and a neutral stabilizing block, were mixed with solutions of metal ions, which are either monoatomic ions or metal polycations, such as Al3+, La3+, or Al-13(7+). The physicochemical properties of the HPIC micelles were investigated by small angle neutron scattering (SANS) and dynamic light scattering (DLS) as a function of the polymer block lengths and the nature of the cation. Mixtures of metal cations and asymmetric block copolymers with a complexing block smaller than the stabilizing block lead to the formation of stable colloidal HPIC micelles. The hydrodynamic radius of the HPIC micelles varies with the polymer molecular weight as M-0.6. In addition, the variation of R-h of the HPIC micelle is stronger when the complexing block length is increased than when the neutral block length is increased. R-h is highly sensitive to the polymer asymmetry degree (block weight ratio), and this is even more true when the polymer asymmetry degree goes down to values close to 3. SANS experiments reveal that HPIC micelles exhibit a well-defined core-corona nanostructure; the core is formed by the insoluble dense poly(acrylate)/metal cation complex, and the diffuse corona is constituted of swollen neutral polymer chains. The scattering curves were modeled by an analytical function of the form factor; the fitting parameters of the Pedersen's model provide information on the core size, the corona thickness, and the aggregation number of the micelles. For a given metal ion, the micelle core radius increases as the PAA block length. The radius of gyration of the micelle is very close to the value of the core radius, while it varies very weakly with the neutral block length. Nevertheless, the radius of gyration of the micelle is highly dependent on the asymmetry degree of the polymer: if the neutral block length increases in a large extent, the micelle radius of gyration decreases due to a decrease of the micelle aggregation number. The variation of the R-g/R-h ratio as a function of the polymer block lengths confirms the nanostructure associating a dense spherical core and a diffuse corona. Finally, the high stability of HPIC micelles with increasing concentration is the result of the nature of the coordination complex bonds in the micelle core.

International audience; The biphasic product CoS2 + Co(OH)(2) obtained by oxidation of cobalt sulfide is known to trap hydrogen at room temperature and low pressure according to a balanced reduction equation. Adding various inorganic compounds to this original absorber induces their reduction by hydrogen in the same conditions at a significant rate: (i) excess cobalt hydroxide is reduced to metallic cobalt; (ii) nitrate ions are reduced to ammonia; (iii) sulfur and sodium thiosulfate are reduced to H2S or NaHS and Na2S, respectively. Without a hydrogen absorber these inorganic compounds are not reduced by H-2, suggesting synergetic effects involving H-2 and the hydrogen absorber. Amorphous cobalt polysulfide, CoS5, is also reduced by hydrogen at room temperature and releases H2S gas. In the presence of a base to neutralize H2S gas, the reaction rate is initially slower than with the CoS2 + Co(OH)(2) mixture due to the higher stability of polysulfide chains but the H-2 trapping yield is improved, making CoS5 a good candidate for H-2 trapping.

The structure of cryolite is investigated with a theoretical approach based on LDF calculations. In fact, experimental techniques for structural studies are difficult to perform in cryolite melts because of hard experimental conditions (high temperature, corrosiveness, etc.). Use of the DMol software allows us to determine the stabilities and the vibrational frequencies of AlF, AlF, and AlF isolated complexes. The results obtained compared with published experimental works confirm that AlF should be considered in the dissociation scheme of cryolite as previously evidenced by other authors. © 1994 John Wiley & Sons, Inc.

International audience; Stable suspensions of citrated SPIO nanoparticles were synthesised in one step using a hydrothermal continuous process. Citrates control the crystallite size and the oxidation degree of metallic ions despite the very short reaction time (4 s). Magnetite particles, Fe2.94O4, with an average size of 4 nm and good monodispersity were obtained.

[1] Fluid flow in rocks is allowed through networks of cracks and fractures at all scales. In fact, cracks are of high importance in various applications ranging from rock elastic and transport properties to nuclear waste disposal. The present work aims at investigating thermomechanical cracking effects on elastic wave velocities, mechanical strength, and permeability of cracked glass under pressure. We performed the experiments on a triaxial cell at room temperature which allows for independent controls of the confining pressure, the axial stress, and pore pressure. We produced cracks in original borosilicate glass samples with a reproducible method (thermal treatment with a thermal shock of 300°C). The evolution of the elastic and transport properties have been monitored using elastic wave velocity sensors, strain gage, and flow measurements. The results obtained evidence for (1) a crack family with identified average aspect ratio and crack aperture, (2) a very small permeability which decreases as a power (exponential) function of pressure, and depends on (3) the crack aperture cube. We also show that permeability behavior of a cracked elastic brittle solid is reversible and independent of the fluid nature. Two independent methods (permeability and elastic wave velocity measurements) give these consistent results. This study provides data on the mechanical and transport properties of an almost ideal elastic brittle solid in which a crack population has been introduced. Comparisons with similar data on rocks allow for drawing interesting conclusions. Over the timescale of our experiments, our results do not provide any data on stress corrosion, which should be considered in further study.

Cet article a été présenté lors du 19. International Workshop on Computational Mechanics of Materials (IWCMM 19) ; Constanta (Roumanie) - (2009-09-01 - 2009-09-04) / Atelier; International audience; In a geological storage context, the durability of nuclear glass is first and foremost determined by its alteration rate and by the surface being leached. This surface is comprised of a network of three-dimensional cracks due to the stress relief generated by the cooling of glass packages. In order to improve the methods employed so far for quantifying the impact of a fissure network on the life time of glass packages in geological disposal, we have developed a software, referred to as FRAGMA, which can be used to generate a realistic 2D geometry of the fissure network inside the glass based on mechanistic analogies. This type of tool is required for providing a mesh adapted to the calculation codes simulating water flow and glass alteration in such a medium. The main principles of this tool have been developed and its parameters have been defined based on the analysis of theoretical fracture processes and observations of real fissure networks. The 2D networks developed using FRAGMA are compared with cross-sections of real networks. It is outlined that the general structure of the fracture maps is correctly reproduced, compared to the observations; consequently, it is relevant to apply the tool for further studies in order to generate more complex crack networks, and to study the channeling in such structures, as expected by the strong organized pattern of the experimental fracture maps

First-principles techniques have been employed to study the reactivity of water into a calcium aluminosilicate glass. In addition to the well known hydrolysis reactions Si – O – Si + H 2 O → Si – OH + Si – OH and Si – O – Al + H 2 O → Si – OH + Al – OH , a peculiar mechanism is found, leading to the formation of an AlO3–H2O entity and the breaking of Al–O–Si bond. In the glass bulk, most of the hydrolysis reactions are endothermic. Only a few regular sites are found reactive (i.e. in association with an exothermic reaction), and in that case, the hydrolysis reaction leads to a decrease of the local disorder in the amorphous vitreous network. Afterwards, we suggest that ionic charge compensators transform into network modifiers when hydrolysis occurs, according to a global process firstly suggested by Burnham in 1975. Our theoretical computations provide a more general model of the first hydrolysis steps that could help to understand experimental data and water speciation in glasses.

Within the scope of the long term behaviour of the R7T7 glass, which is the French nuclear glass, leaching and its coupling with transport mechanisms is studied. Experiments carried out on a SON 68 glass (inactive R7T7 type glass) model cracks in static basic conditions show a strong coupling between solution transport and glass leaching, depending on crack aperture. Moreover, gravity driven convective transport was evidenced for vertical model cracks, whereas only molecular diffusion was detected for horizontal model cracks under the same alteration conditions. In addition, an original device was developed to study the influence of temperature gradients on alteration kinetics as a convective driving force. These experiments show conclusively that thermally- or gravity-induced convective flow must be taken into account, even if such convective effects have not been established experimentally in neutral condition, which is more realistic condition for geological storage. A modeling, based on a porous geochemical software (HYTEC) accounting for both chemistry and transport, has been successfully applied to describe alteration within simple silicate glass cracks. It will be extended to study SON 68 glass model cracks, and more complex fracture networks.

International audience; The aim of the study was to compare the potassium efflux measurements (flame photometry (FP), specific electrode (SE) and atomic absorption photometry (AAP)) using a model of erythrocytes exposed to an oxidative stress in various conditions of osmolarity. Human erythrocytes were incubated in 3 different values of osmolarity and in the presence of 50 mM AAPH, potassium efflux was measured by FP, SE and AAP at t = 0 and every 30 min for 2 h. These methods were similar for the measurement of global potassium efflux. However, SE detected important amounts of potassium at the beginning of the experiment or in absence of AAPH in comparison with AAP and FP. It is noteworthy that these different methods of measurements were not altered by the osmolarity. FP and AAP make it possible to study the potassium efflux during oxidative stress while SE should be used only for global measurements.

Stable hairy lanthanum hydroxide nanoparticles were synthesized in water by performing hydrolysis and condensation reactions of lanthanum cations in the presence of double hydrophilic polyacrylic acid-b-polyacrylamide block copolymers (PAA-b-PAM). In the first step, the addition of asymmetric PAA-b-PAM copolymers (M-w,M-PAA < M-w,M-PAM) to lanthanum salt solutions, both at pH = 5.5, induces the formation of monodispersed micellar aggregates, which are predominantly isotropic. The core of the hybrid aggregates is constituted of a lanthanum polyacrylate complex whose formation is due to bidentate coordination bonding between La3+ and acrylate groups, as shown by ATR-FTIR experiments and pH measurements. The size of the micellar aggregates depends on the molecular weight of the copolymer but is independent of the copolymer to metal ratio in solution. In the second step, the hydrolysis of lanthanum ions is induced by addition of a strong base such as sodium hydroxide. Either. occulated suspensions or stable anisotropic or spherical nanoparticles of lanthanum hydrolysis products were obtained depending on the metal complexation ratio [ acrylate]/[La]. The variation of that parameter also enables the control of the size of the core-corona nanoparticles obtained by lanthanum hydroxylation. The asymmetry degree of the copolymer was shown to influence both the size and the shape of the particles. Elongated particles with a high aspect ratio, up to 10, were obtained with very asymmetric copolymers (M-w,M-PAM/ M-w,M-PAA >= 10) while shorter rice grain- like particles were obtained with a less asymmetric copolymer. The asymmetry degree also influences the value of the critical metal complexation degree required to obtain stable colloidal suspensions of polymer-stabilized lanthanum hydroxide.

The aggression of erythrocytes by an oxidative stress induces hemolysis. This paper aims to valid a model of erythrocytes in terms of composition of the phosphate buffer solution and of concentration of a well-known oxidant, AAPH. Three compositions of phosphate buffer solution are mixed with three concentrations of oxidant. The influence of these two parameters on hemolysis is independently studied by a variance analysis and a Kruskal-Wallis test when ANOVA is not available. The hemolysis rate increases with time at fixed oxidant concentration, but is not influenced by the composition of the buffer solution. The highest hemolysis rate, 90%, was only measured within 2 h with the highest oxidant concentration. If we retain this concentration of oxidant, the lower concentration of the buffer can by eliminated by a significant less hemolysis and the highest concentration of the buffer can by chosen in regard of the better precision for a similar hemolysis compared to the mean buffer. We hope to study the effect of anti-oxidant agent with such a model of erythrocytes.

This study was carried out to investigate hemoglobin behavior and the role of cell membrane during oxidative stress of human red blood cells induced by a water-soluble radical initiator, 2,2'-azobis(amidino-propane) hydrochloride (AAPH) and compare the observed data to the one obtained with purified human haemoglobin solution. The different forms of hemoglobin were identified and quantified by multiwavelength visible spectrometry using multiple linear regression analysis. Hemolysis was quantified by the Drabkin method. Oxidative stress on purified hemoglobin solutions induced an early formation of Hb(+). In intact erythrocytes, no modified form of haemoglobin was found. Only the hemoglobin released by hemolysis in the extracellular medium was notified in the same way as purified haemoglobin. Thus, the cell membrane appears to protect intraerythrocytic hemoglobin toward an extracellular oxidative stress. Oxidative stress-induced by hemolysis does not seem to be due to changes in intraerythrocytic hemoglobin forms.