The rheological response of magma to nanolitisation

Viscosity exerts a fundamental control on magmatic kinetics and dynamics, controlling magma ascent, eruptive style, and the emplacement of lava. Nanolites – crystals smaller than a micron – are thought to affect magma viscosity, but the underlying mechanisms for this remain unclear. Here, we use a cylinder compression creep technique to measure the viscosity of supercooled silicate liquids with different amounts of iron (0–20 wt% FeOtot) as a function of temperature, applied shear stress, and time. Sample viscosity was independent on the applied shear stresses, and as expected, melt viscosity decreases as temperature is increased, but only until a critical temperature where a time-dependent increase in viscosity occurs for samples contaning 6.0 wt% FeOtot or more. The magnitude of this increase is controlled by the melt iron content. At constant temperature, these changes are substantial and can reach up to three orders of magnitude for the sample with the most iron. Using transmission electron microscopy, X-ray diffraction, and viscosity modelling, we conclude that this viscosity increase is caused by the formation of nanolites. By using scaling approaches to test suspension effects with and without crystal aggregation, we conclude that the nanolites have only a minimal direct physical effect on the observed viscosity change. Rather, our models show that it is the chemical shift in the groundmass silicate melt composition associated with non-stoichiometric crystallisation that dominates the observed viscosity increase. These findings suggest that iron-rich silicates may encounter chemical viscosity jumps once certain elements are removed from the melt phase to form nanolites. Our work demonstrates an underlying mechanism for the role played by nanolites in viscosity changes of magmas

THERMOCHIMIE DES VERRES BOROSILICATES. CONTRIBUTION A L'ETUDE DE L'ALTERATION DES VERRES DE CONFINEMENT DE DECHETS RADIOACTIFS

PARIS7-Bibliothèque centrale (751132105) / SudocPARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

High temperature calorimetric studies of heat of solution of NiO, CuO, La2O3, TiO2, HfO2 in sodium silicate liquids

The enthalpies of solution of La2O3, TiO2, HfO2, NiO and CuO were measured in sodium silicate melts at high temperature. When the heat of fusion was available, we derived the corresponding liquid–liquid enthalpies of mixing. These data, combined with previously published work, provide insight into the speciation reactions in sodium silicate melts. The heat of solution of La2O3 in these silicate solvents is strongly exothermic and varies little with La2O3 concentration. The variation of heat of solution with composition of the liquid reflects the ability of La(III) to perturb the transient silicate framework and compete with other cations for oxygen. The enthalpy of solution of TiO2 is temperature-dependent and indicates that the formation of Na–O–Si species is favored over Na–O–Ti at low temperature. The speciation reactions can be interpreted in terms of recent spectroscopic studies of titanium-bearing melts which identify a dual role of Ti4+ as both a network-former end network-modifier. The heats of solution of oxides of transition elements (Ni and Cu) are endothermic, concentration-dependent and reach a maximum with concentration. These indicate a charge balanced substitution which diminishes the network modifying role of Na+ by addition of Ni2+ or Cu2+. The transition metal is believed to be in tetrahedral coordination, charge balanced by the sodium cation in the melts

Structure and reactivity of nanocrystalline calcium silicate hydrates: the parallel with clay minerals

International audienc

Modelling of the COx/glass interactions: case of the long term MVE experiment

International audienceHigh-level nuclear waste (HLW) is confined in a glass matrix packaged into stainless steel canister and carbon steel overpack. The Callovian–Oxfordian (COx) claystone layer located in the north-eastern Parisian basin is currently investigated as a potential host-rock. As the COx contains minerals that can feed the near-field with soluble elements (e.g. Mg) that can enhance the glass alteration, the study of the COx/glass interactions is of primary importance to evaluate the containment capacity of the glass over the time period required to the decrease of the radioactive elements. Several studies focused on clay behavior in temperature (Gailhanou et al., 2017), on the glass behavior (Gin et al., 2012) and on integrated system: glass/iron/clay (Schlegel et al., 2016) but no modelling study of the COx/glass interactions in situ at the temperature of the COx formation had already been made.This work aims at studying the glass alteration in presence of the COx in purely diffusive conditions. The studied glass is called SON68 and is the inactive analogous of the of the French R7T7 HLW glass. The vertical descending borehole is twelve meters deep and contains a two meters high test chamber with a series of three stacked clay blocks. Those blocks were drill in order to be filled with glass powder separated from the COx by sintered stainless steel filters (Linard et al., 2015). The test interval was then closed and saturated with synthetic porewater representative of the host-rock (Gaucher et al., 2009). To reach diffusive conditions, the pressure in the test interval was rose to 40 bars close to the expected pressure of the COx formation. A flow rate equal to 15 mL/minute between the interval and a module located in the drift is maintained. The pH, Eh, electrical conductivity, temperature and mass are measured online and samples can be collected at chosen time.A diffusive transport model based on the model developed by Appelo et al. (2008) was built. The hydrological parameters were implemented according to this work and to the particularity of the test (Linard, 2010). The model considers the COx whose parameters (minerals, exchangers) are based on the model published by Gaucher et al. (2009) and the glass (SON68). A glass alteration model based on the work of Frugier et al. (2008) has been implemented in Phreeqc. First the deuterium tracer was modeled with a porewater diffusion coefficient of 8 10-10 m2.s-1. The porosity of the formation was set to 0.18. Because of the complexity of the perturbation that occurred during the whole test, every external change influences the test is not yet considered in the modelling. Thus, the current model does not enable to reproduce the higher deuterium and iodine concentrations measured at 546 days (Figure 1.a) but match all the bromide data. Despite the difficulties on the hydrological parameters, the pH reaches a steady state in the modelling once the COx buffered the pH (Figure 1.b). The initial high pH is close to 9 that is the value imposed by the glass dissolution. This gap occurs because the system is closed in the model the first 427 days of reaction. However, it appears that several water entrance from the formation lower the pH in the system toward values usually encountered in the clay (pH 7.2). The modeled chlorine agrees with the measured one (Figure 1.b). This element is only influenced by the porewater chemistry and is not modified during the test. A difference appears for the sodium that is underestimated and remains at the value of the porewater injected at the beginning of the test. This discrepancy can be attributed to an underestimation of the water coming from the formation that is richer in sodium than the injected water and/or from the glass dissolution that is currently underestimated (Figure 1.b). The first explanation is assumed because the porewater measured in the field varies in function of the samples (Vinsot et al., 2008), so a difference with the injected water can occur. The second hypothesis is linked to the first one as a higher solution renewal will lead to higher glass dissolution and then to higher boron, lithium and sodium release in solution. Furthermore, desaturation process occurring during the drilling and leading to salt precipitation cannot be discarded. Those salt will dissolve during the entrance of the water coming from the formation (Vinsot et al., 2013). It is worth noting that the Si concentration is in equilibrium with cristobalite. Furthermore, modelling tests proved that secondary phases usually considered like hydroxyapatite or sepiolite highly influence the results and cannot be considered at thermodynamic equilibrium otherwise glass dissolution is overestimated.This model is a first step to investigate the interaction between the COx and the glass SON68. The several perturbations occurring during the test (water entrance, leakages, and thermal variations) have to be considered more accurately because they highly influence the system and then the glass dissolution. Improvements concerning these matters are already under progress

Structural defects in layered structures: Their determination and their impact on reactivity

International audienceClay minerals are layered structures that suffer from various and frequent crystallization faults, including point defects (e.g. layer vacancies and/or isomorphic cationic and anionic substitutions) and stacking defects (e.g. interstratification, well-defined or random stacking faults) that complicate the study of their structure, compared to most of other minerals. Determination of their crystal-structure is even further complicated by the small size of these minerals that possibly result from a "poisoning effect" induced by the presence of foreign cations in their layers. The determination of the actual crystal structure of clay minerals, in particular the nature and density of structural defects, is however of paramount importance to understand and model clay minerals reactivity. X-ray diffraction patterns of clay minerals often only exhibit 00l reflections and a few asymmetrical hk bands, while the hkl reflections are absent owing to the systematic occurrence of random stacking faults (i.e. turbostratism; random translations in the layer plane and/or random rotation about the normal). To overcome this problem, a mathematical formalism was developed that allows the calculation of X-ray diffraction patterns from structures affected by various density and nature of structural defects, including turbostratism. This development led to a better understanding of the structure from many clay minerals, including layer structure (e.g. nontronite) and, using a complementary analysis of 00l reflections, of interlayer water and cations organization . It is however obvious that not only clays suffers from the here above mentioned crystallization defects. Rather, nanocrystalline (i.e. particles smaller than 100 nm) and defective lamellar structures affected by turbostratism are ubiquitous in natural and man-made environments. One can for example cite manganese and iron oxides or nanocrystalline calcium silicate hydrates9 (C-S-H). The former two are reported to control the fate of many trace elements in the environment, including metals and actinides (in the case of vernadite, a manganese oxide) or oxyanions (in the case of fougèrite, an iron hydroxide). These minerals also often exhibit redox properties (e.g. Mn3+/Mn4+ or Fe2+/Fe3+) that enables for the degradation of organic compounds. Contrastingly, C-S-H is not found in natural environments, but is the main hydration product from various types of cement, including ordinary Portland cement, controls main cement chemical and physical properties, and exerts a strong control on trace elements mobility. All these minerals and phases have close structural similarities with clays, as already noticed decades ago, and thus methods used for the analysis of clay mineral structure are transposable to these phases. As for clays, a sound understanding of the crystal structure from these minerals and phases is a fundamental basis for many applications. First, the nature of point defects determines the type of elements that can be sorbed (typically, in the case of oxides, isomorphic substitutions create a limited layer charge deficit and favour the sorption of alkali and alkali-Earth elements as hydrated outer-sphere complexes, whereas layer vacancies favour the sorption of multivalent elements as inner-sphere complexes) and, second, the density of these defects dictate the overall reactivity.The present work will review recent applications of the specific method used to model X-ray diffraction patterns from nanocrystalline and defective lamellar structures, and will demonstrate that modelling can be used to retrieve accurate structural information, such as crystallite sizes and interlayer and layer structure, including nature and density of structural defects (Figure 1). The consistency between this method and other spectroscopic (e.g. synchrotron X-ray absorption spectrometry) or microscopic (e.g. transmission electron microscopy) techniques will be illustrated on nanocrystalline manganese (vernadite) and iron (fougèrite) oxides and nanocrystalline calcium silicate hydrates (C-S-H)

A ras-Mutated Peptide Targeted by CTL Infiltrating a Human Melanoma Lesion 1

International audienceAgs derived from commonly mutated oncogenic proteins seem ideally suited as targets for tumor immunotherapy. Nonetheless, only a few mutated epitopes efficiently presented by human tumors have thus far been identified. We describe here an approach to identify such epitopes. This approach involves: 1) identifying tumors expressing a ras mutation and isolating the tumor-infiltrating lymphocytes (TIL); 2) transfecting COS cells to induce expression of unknown mutated peptides in the context of a patient's HLA class I molecules; and 3) screening epitope recognition by using TIL from the tumors expressing a ras mutation. By using this approach, there appeared to be a N-ras mutation (a glutamine-to-arginine exchange at residue 61 (Q61R)), detected in a melanoma lesion, which was recognized specifically by the autologous TIL in the HLA-A*0101 context. The ras peptide 55-64 Q61R was the epitope of these TIL and was regularly presented by Q61R-mutated HLA-A*0101 ؉ melanoma cell lines. This peptide and its wild-type homolog (55-64 wt) bound to HLA-A*0101 with similar affinities. However, only the mutated peptide could induce specific CTL expansion from PBL. All the CTL clones specific to the mutated peptide, failed to recognize the wild-type sequence on both COS and melanoma cells. These data thus show that oncogenic protein mutations can create shared tumor-specific CTL epitopes, efficiently presented by tumor cells, and that screening for oncogene-transfected COS cell recognition by TIL (from tumors containing mutations) is a powerful approach for the identification of these epitopes

Crystal structure of nano-sized synthetic CSH

The main component of Portland cement is a nano-sized and poorly-ordered phase commonly referred as "Calcium Silicate Hydrate" (CSH). Although the nature of this phase was first discussed almost 100 years ago, its detailed crystal structure is still uncertain, mainly because its X-ray diffraction (XRD) pattern exhibits only a few and broad diffraction maxima. As a consequence, CSH is often assumed to be "X-ray amorphous" and classical XRD pattern refinements cannot be performed. This difficulty has been circumvented by numerous authors by using a wide variety of physical methods taking advantage of magnetic radiations, X-rays, or neutrons (FTIR, NMR, EXAFS, SANS, PDF...) to probe the short-range order around Ca, Si and O. These data contributed to the development of, or supported, the currently held view that CSH are structurally related to the rare minerals tobermorite and/or jennite. Discrimination between these two models using local probes is highly difficult because tobermorite and jennite are both layered minerals and they have similar local order, i.e. layers built up of ribbons of silicon tetrahedra, with wollastonite-like structure, running at the surface of calcium layer. To date, no structural model was unambiguously determined, because no modeling of methods probing the long-range order was performed. We combined electron probe micro-analyses (EMPA), transmission electron microscopy (TEM) and powder XRD to determine the structure of four different nano-crystalline CSH synthetized at laboratory temperatures ranging from room temperature to 110 °C. It is demonstrated that the modeling of XRD patterns using a specifically developed method is able to capture most of the structural details from CSH crystals, such as crystallite size, lattice parameters and interlayer occupancy. The genetic link between CSH and its hypothesized natural equivalents is discussed

Corrosion at the carbon steel-clay borehole water interface under anoxic alkaline and fluctuating temperature conditions

International audienceCoupons of carbon steel were corroded in situ in anoxic clay porewater under slightly alkaline conditions. Sample damage was less than 1 $\mu$m for 9 months at 85 °C only, and corrosion interfaces were covered by a thin, protective layer of Fe-silicate. The damage was more significant for samples exposed to room temperature transients (up to 38 μm for two years), and the long-term surface differentiated in cathodic (Fe-silicate covered) areas and anodic crevices filled with siderite, chukanovite, $\beta$-Fe$_2$(OH)$_3$Cl, and covered by tubercles. Sulfide compounds were detected, and were related to the metabolism of sulfate-reducing prokaryotes detected by microbiological techniques