National corridors for climate change mitigation: managing industrial CO2 emissions in France

International audiencePlanning for the deployment of carbon dioxide capture and storage (CCS), infrastructure must consider numerous uncertainties regarding where and how much CO2 is produced and where captured CO2 can be geologically stored. We used the SimCCS engineering-economic geospatial optimization models to determine the characteristics of CCS deployment in France and corridors for pipelines that are robust to a priori uncertainty in CO2 production from industrial sources and CO2 storage locations. We found a number of stable routes that are robust to these uncertainties, and thus can provide early options for pipeline planning and rights-of-way acquisition

Crystal structure of synthetic Mg3Cr2Si3O12, the high-pressure Cr end-member of the knorringite-pyrope garnet series

Knorringite, the Cr-end-member of the pyrope garnet series (Nixon et al. 1968), often occur in high proportions in kimberlite garnets and is thus used for tracing high-pressure deep-earth conditions favorable to the formation of diamonds, in which knorringite-rich garnet can occur as inclusions. However, although the synthesis of knorringite is reported in the literature (Ringwood 1977; Irifune et al. 1982; Taran et al. 2004), the structure of the pure end-member has not been yet determined from experimental data. In this study, the crystal structure of knorringite, Mg3Cr2(SiO4)3, has been refined from high resolution synchrotron X-ray powder diffraction data recorded under ambient conditions on a polycrystalline sample synthesized at 12 GPa in a multi-anvil apparatus. The structure is cubic, space group Ia-3d, a = 11.5935(1), V = 1558.27(4) {\AA}3, dcalc = 3.97 g.cm-3. The Cr-O distance of 1.957(2) {\AA} is consistent with EXAFS results on the same sample. This short distance indicates a substantial compression of the CrO6 octahedron, compared to ambient pressure Cr3+-minerals such as uvarovite ( = 1.99 {\AA}, Andrut and Wildner 2002). Our experimental results thus confirm early empirical predictions based on series of high-pressure Cr-garnet end-members (Fursenko 1981), showing that the values of the Cr-O distance and the Cr-O-Si angle decrease with the augmentation of pressure and with the diminution of the size of the divalent cation

Electron sources for plasma electronics and different technological application

There are the following advantages of applying electron guns with plasma cathodes in devices exciting microwave radiation: stability of their parameters, high density of current, relative insensitivity to ion bombardment and the possibility of operating over a wide range of pressure values of a plasma-generating gas [1-5]. The given work aims at constructing the guns with the parameters necessary for the excitation of microwaves of high amplitudes in the slow-wave structures: the beam energy is 20-30 kV, the current is up to 5 A, and the pulse duration is 0,11÷1 ms. The principal problem arising during construction of heavy-current electron sources with plasma emitters consists in the following: it is necessary to provide such conditions of the gas volume, under which the discharge firing would be stable and the emissive plasma generation be effective, whereas a gas breakdown in the accelerating gap must be eliminated

EXAFS Signatures of Structural Zn at Trace Levels in Layered Minerals

Many in situ XAFS studies have shown that zinc incorporated in layered minerals is a major form of zinc in Zn-contaminated soils. Quantitative information on the local structural environment(s) and ordering of Zn in these minerals is required to better understand its behavior in soils. In this study, EXAFS spectroscopy was used to assess the structural environment of zinc incorporated at trace levels (40 ppm to 4,000 ppm) within the octahedral sheets of various natural and synthetic layered minerals. Results indicate that EXAFS data analyzed using ab initio FEFF calculations (FEFF 8.10) can unambiguously distinguish between zinc incorporation within the octahedral sheet of dioctahedral versus trioctahedral layered minerals and can determine the distribution (random or ordered) of zinc cations within the octahedral sheets of these minerals

Luminescence of uranium-bearing opals: Origin and use as a pH record

International audienceFluorescence of minerals has been long used for U exploration. It is proposed here that opal fluorescence can be used as a probe of the pH of the formation solution, bringing constraints for modeling U speciation and sequestration at the Earth's surface. We present a study of fluorescence spectroscopy of U in opals resulting from low-temperature (29 degre) alteration of mineralized rhyolitic lavas (Nopal I U deposit, Sierra Peña Blanca, Mexico). These opals show green fluorescence with a concentric distribution at microscopic scale, which is unambiguously assigned to uranyl groups (oxidized form of U). Spectra appear typical of uranyl in opal as reported in literature for other localities according to peak positions. When considering also the lifetime of fluorescence spectra (with time resolved laser fluorescence spectroscopy), fingerprinting indicates that uranyl occurs either as phosphate or hydroxo-polynuclear complexes trapped onto the opal internal surface. Data are indicative of a pH of opal formation around 8, as derived from both conditions of laboratory experiments and reference to calculated diagrams of speciation. This pH value is consistent with the Nopal geological formations that were potentially in contact with the aquifer involved in the hydrothermal process. In addition, the microscopic zoning of U suggests that the speciation has been stable since opal formation more than 50 ka ago, which allows the record of pH that prevailed at that time

The Structural Properties of Cations in Nuclear Glasses

International audienceThe structure of nuclear glasses and of simplified surrogates has been investigated using complementary diffraction and spectroscopic methods, together with numerical modeling. The diversity of structural surroundings of cations in glasses is reviewed at various scales. Cations usually occur in smaller sites in glasses than in crystals, with unusual site geometries such as 5-coordination. These sites may correspond to different structural positions. Network forming and networking situations illustrate the existence of a well-defined relationship with the glassy network, with cations improving glass stability. The complementary charge-compensation may sometimes give rise to a competition between cations. In that case, the cation may lose its stabilizing character and become a nucleating agent, as observed for “chameleon” elements, the coordination of which and hence the structural properties may change as a function of glass composition. Eventually, at the mesoscale, the heterogeneous distribution of cations has been recently visualized, providing keys to understand the nucleation processes in glasses

Greening effect in slag cement materials

International audienceThis article presents the first spectroscopic data describing the processes responsible for the temporary blue-green coloration that forms during the hydration of various materials containing Ground Granulated Blast-furnace Slag (GGBS) under anoxic conditions. UV-visible-near infrared Diffuse Reflectance (DR) spectra demonstrate a striking similarity of the coloring center forming during the curing of a broad range of GGBS-bearing materials (pure GGBS with different compositions, mix Portland cement/GGBS (30/70), concrete and mortar). All spectra are similar to those of polysulfide complexes contained in the interlayer spacing of a synthetic green-colored hydrated calcium aluminate phase (AFm). This “greening effect” demonstrates a progressive oxidation of sulfide-based compounds initially contained in these materials during curing of GGBS bearing materials