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WOS:000346545800018International audienceThe presence of plants induces strong accelerations in soil organic matter (SOM) mineralization by stimulating soil microbial activity a phenomenon known as the rhizosphere priming effect (RPE). The RPE could be induced by several mechanisms including root exudates, arbuscular mycorrhizal fungi (AMF) and root litter. However the contribution of each of these to rhizosphere priming is unknown due to the complexity involved in studying rhizospheric processes. In order to determine the role of each of these mechanisms, we incubated soils enclosed in nylon meshes that were permeable to exudates, or exudates & AMF or exudates, AMP and roots under three grassland plant species grown on sand. Plants were continuously labeled with C-13 depleted CO2 that allowed distinguishing plant-derived CO2 from soil-derived CO2. We show that root exudation was the main way by which plants induced RPE (58-96% of total RPE) followed by root litter. AMP did not contribute to rhizosphere priming under the two species that were significantly colonized by them i.e. Poa trivialis and Trifolium repens. Root exudates and root litter differed with respect to their mechanism of inducing RPE. Exudates induced RPE without increasing microbial biomass whereas root litter increased microbial biomass and raised the RPE mediating saprophytic fungi. The RPE efficiency (RPE/unit plant-C assimilated into microbes) was 3-7 times higher for exudates than for root litter. This efficiency of exudates is explained by a microbial allocation of fresh carbon to mineralization activity rather than to growth. These results suggest that root exudation is the main way by which plants stimulated mineralization of soil organic matter. Moreover, the plants through their exudates not only provide energy to soil microorganisms but also seem to control the way the energy is used in order to maximize soil organic matter mineralization and drive their own nutrient supply. (C) 2014 Elsevier Ltd. All rights reserved

White light and multicolor emission tuning in triply doped Yb3+/Tm3+/Er3+ novel fluoro-phosphate transparent glass-ceramics

New Yb3+, Er3+ and Tm3+ doped fluoro-phosphate glasses belonging to the system NaPO3-YF3-BaF2-CaF2 and containing up to 10 wt% of rare-earth ion fluorides were prepared and characterized by differential scanning calorimetry, absorption spectroscopy and up-conversion emission spectroscopy under excitation with a 975 nm laser diode. Transparent and homogeneous glass-ceramics have been reproducibly obtained with a view to manage the red, green and blue emission bands and generate white light. X-ray diffraction as well as electron microscopy techniques have confirmed the formation of fluorite-type cubic nanocrystals at the beginning of the crystallization process while complex nanocrystalline phases are formed after a longer heat-treatment. The prepared glass-ceramics exhibit high optical transparency even after 170 h of thermal treatment. An improvement of up-conversion emission intensity - from 10 to 160 times larger - was measured in the glass-ceramics when compared to the parent glass, suggesting an important incorporation of the rare-earth ions into the crystalline phase(s). The involved mechanisms and lifetime were described in detail as a function of heat-treatment time. Finally, a large range of designable color rendering (from orange to turquoise through white) can be observed in these materials by controlling the laser excitation power and the crystallization rate.Canadian Excellence Research Chair program (CERC) on Enabling Photonic Innovations for Information and CommunicationFAPESPCNPqINCT - INOF/CePOFANR (CrystOG ANR-12-JS08-0002-01

Synthèse par chauffage micro-ondes de verres de phosphates (élaboration de vitrocéramiques de type NZP par frittage réactif)

Ce travail de recherche est orienté autour de deux axes de travail. Tout d abord, l élaboration par chauffage micro-ondes de nouveaux verres de phosphates d étain à bas point de fusion a été étudiée. En effet, ces verres présentent des températures caractéristiques basses mais possèdent cependant des durabilités chimiques souvent faibles. L idée envisagée pour palier à ce déficit est l introduction d oxydes de métaux de transition (comme WO , MoO , Nb O ...) pour engendrer in situ des réactions d oxydoréduction dans le bain fondu afin d améliorer la résistance à la lixiviation de ces verres tout en gardant des températures d élaborations acceptables. Différents systèmes vitreux ont été explorés et caractérisés. Dans un second temps, de nouvelles vitrocéramiques de type NZP ont été élaborées par frittage réactif de ces verres. Ces matériaux peuvent présenter des propriétés de superconduction ionique intéressantes pour des applications en tant qu électrolytes solides.n this work, two major areas of research were developed. First, the exploration of new tin phosphate glasses with low melting point, synthesized in a domestic microwave oven was carried out. Indeed, these glasses present low melting temperatures but are often characterized by poor chemical durability. In order to increase it, we studied the introduction of oxides (like WO , MoO , Nb O ...) in tin phosphate glasses to produce Sn thanks to in-situ redox reactions in glass melt. Different phosphate glass systems have been explored. In the other hand, new glass-ceramics with NZP type have been elaborated by glass sintering. These materials should present superionic conduction and are potential candidates for solid electrolyte applications.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Microwave synthesis and properties of NaPO3-SnO-Nb2O5 glasses

International audienceTin niobiophosphate glasses were produced using a domestic microwave oven under a nitrogen flow. The fast microwave melting method and the protective atmosphere prevent the oxidation of SnO. After 10 min of heating, the NaPO3, SnO, and Nb2O5 mixtures are homogeneous and permit to obtain transparent glasses. Three series of glasses with different Sn/Nb ratio were studied to determine the influence of each oxide. The glass transition temperature increases linearly with the amount of Nb2O5 and SnO. These variations are more important for compositions with high metallic cation proportions and with a low Sn/Nb ratio. The same evolutions were observed for the density, Vickers hardness, and elastic modulus while the thermal expansion coefficient decreases monotonously. The simultaneous insertion of SnO and Nb2O5 in phosphate glass matrix leads to a progressive strengthening of the glass network. The chemical durability of the glasses also increases as a function of the amount of metal oxides. We prepared a bulk glass sample with a dissolution rate of about 3.3 × 10−8 g cm−2 min−1 in renewed water conditions at 95 °C. This durability is equivalent to those of the window glass whereas the glass transition temperature remains lower than 485 °C

Parcours de soin TDL à travers l’Europe.

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Characterization of NaPO3-SnO-WO3 glasses prepared by microwave heating

International audiencePhosphate glasses containing tin and tungsten oxides were produced by microwave heating under a nitrogen protective atmosphere. Microwaves permit to heat the raw materials at temperatures close to 1000 °C in short time and to obtain homogeneous glasses in less than 10 min. All samples were characterized from thermal and mechanical point of view as function of metal oxide proportions. The equimolar addition of SnO and WO3 in sodium phosphate matrix involves a linear evolution of the different properties (T g, CTE, density, mechanical properties, and durability). Thus, we have shown a progressive strengthening of the network. The glass transition temperature does not exceed 405 °C, and the chemical durability is improved to four orders of magnitude. The dissolution rate is equal to 3.4 × 10−7 g cm−2 min−1 for 40NaPO3-30SnO-30WO3 glass composition and is comparable with those of the window glass

Macroscopic and micro-structural aspects of the lithium metaphosphate glass crystallization

International audienceThe LiPO3 glass crytallization have been investigated according to isothermal and non-isothermal approaches by using various techniques such as thermal analysis, helium pycnometry, scanning electronic microcospy and X-ray powder diffraction. Different experimental procedures have been developed to determine the crystallized volume fraction. The different results are a good agreement and leadto a better comprehension at a "macroscopic" scale of this first order transition. In addition, from "ex-situ" X-ray powder diffraction experiments, the understanding of the diffraction line intensities as a function of the annealing time, at a fixed temperature, has revealed a new metastable crystalline form of LiPO3 (named alpha) stable over a short time range. Attempts for indexing led to a possible monoclinic system close to that reported in literature for the thermodynamical stable variety (named beta). The micro-structure of annealed samples has been discussed in terms of crystallite sizes and lattice micro-distorsions at a nanometer scale. This study based on diffraction line broadening analysis was carried out with the integral breadth method. Finally, from "in-situ" X-ray powder diffraction experiments, evidence was shown that the LiPO3 glass matrix crystallizes first in a metastable LiPO3-alpha form which, in turn, transforms into the beta form

Characterisation of a new NZP material prepared from reactive sintering of a phosphate based glass

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