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International audience; In this paper, the efficiency of gas nitriding on pure iron is observed regarding two types of pre-treatments prior to nitriding: chemical reduction by H2 and nanocrystallization by NanoPeening®. Thermogravimetric analysis reveals that both pre-treatments result in an increase in the transformation rate of nitrogen during the first 200 min of nitriding. Moreover, glow discharge optical spectrometry reveals that nanocrystallization by NanoPeening® leads to a deeper penetration of nitrogen in the material.

International audience; Comprehension of oxidation processes under the influence of an external polarization is still a challenge, despite numerous past studies. In this study, thermogravimetric analysis technique coupled with in situ application of an electric voltage was used to investigate oxidation of zirconium. The first technical challenge was to modify the thermobalance to integrate it with polarization equipment without perturbation of measurement and of oxidation behavior. Surprisingly, the oxidation rate was found to remain independent on the applied voltage, despite a large range of applied potentials, ± 200 V. Modeling of oxidation rates according to diffusion mechanism combined with investigation of polarization curves of the metal/oxide/electrode system has shown that a high electrical resistance appears at the oxide/electrode interface, even with addition of an intermediate gold layer. This resistance prevents from generating sufficient voltage drop through the oxide layer (> 10 V), necessary to modify the kinetics. Nevertheless, meaningful electrochemical properties using analogy with solid-oxide fuel cells have been observed, allowing to propose a comprehensive approach of oxidation phenomena under polarization.

International audience; The thermal decomposition of actinides oxalates greatly depends on the oxidation state of the cation, the gas involved and the physical characteristics of the precursor. In the actinides series, uranium(IV) oxalate U(C 2 O 4) 2 .6H 2 O can be viewed as a peculiar case, as its sensibility towards oxidation leads to a specific series of reactions when heating under oxygen atmosphere. In order to clarify the disagreements existing in the literature, particularly concerning potential carbonate intermediates and the possible transitory existence of UO 3 , we show here an extended characterization of the different intermediates through a combination of X-Ray diffraction, vibrational spectroscopies and X-Ray absorption near edge spectroscopy. In this frame, uranium oxidation was found to occur at low temperature (200°C) concomitantly to the onset of oxalate groups decomposition, leading to an amorphous oxo-oxalato compound. Pursuing the thermal conversion up to 350°C led to complete oxidation of U(IV) into U(VI), then to the formation of amorphous UO 3 still bearing adsorbed carbonates. The first pure oxide formed during the thermal conversion was further identified to sub-stoichiometric UO 3- after heating at 550°C. Finally, U 3 O 8 was obtained as the final stable phase after heating above 660°C. The mechanism of thermal conversion of uranium(IV) oxalate into oxide under oxygen is then driven by a complex interplay between redox reactions and decomposition of the organic fractions. Such chemical reactions were also found to significantly modify the morphology of the powder through HT-ESEM observations : decomposition led the size of the aggregates to reduce by 20% while uranium oxidation clearly promoted growth within the agglomerates. 2

Demandeurs: INSTITUT MINES TELECOM [FR]; The invention relates to a method for preparing a composite material comprising core-shell nanoparticles the core of which is made from a material which can absorb light and the shell of which is made from graphene, the method comprising the following steps: a) providing a substrate and an ink comprising nanoparticles which can absorb light, the nanoparticles being encapsulated in a polymer matrix; b) depositing the ink on a surface of the substrate, the surface or the ink comprising a carbon source selected from: • a polymer comprising an amide function and an aromatic function, • a hexose, • carbon nanoparticles, • self-assembled monolayers comprising aromatic rings, c) illuminating the surface of the ink-covered substrate with a pulsed light in order to bring the nanoparticles in the ink to a heating temperature greater than a dissociation temperature of the carbon in the carbon source, the carbon dissociated in this manner then being capable of diffusing or solubilising in the nanoparticles in the ink in order to form the composite material.; L’invention concerne un procédé d’élaboration d’un matériau composite comportant des nanoparticules de type cœur-coquille dont le cœur est fait d’un matériau apte à absorber la lumière et la coquille est faite en graphène, le procédé comprenant les étapes suivantes : a) fournir un substrat ainsi qu’une encre comportant des nanoparticules aptes à absorber de la lumière, lesdites nanoparticules étant encapsulées dans une matrice polymérique ; b) déposer l’encre sur une surface du substrat, ladite surface ou ladite encre comprenant une source de carbone choisie parmi : un polymère comportant une fonction amide et une fonction aromatique, un hexose, des nanoparticules de carbone, des monocouches auto-assemblées comprenant des cycles aromatiques, c) illuminer la surface du substrat recouverte d’encre avec une lumière pulsée pour porter les nanoparticules comprises dans l’encre à une température d’échauffement supérieure à une température de dissociation du carbone compris dans la source de carbone, le carbone ainsi dissocié étant alors apte à diffuser ou à se solubiliser dans les nanoparticules comprises dans l’encre pour former ledit matériau composite.

International audience; During a fire in an industrial facility, the main consequences concerning aerosol are the production of large amount of soot and potential resuspension of hazardous material in particulate form. Soot deposition quantification on walls in a room during a fire is essential for the prediction of aerosol quantities that can be transported in the ventilation ducts and clog high efficiency particulate air filters.For this purpose, accumulative resistive sensors, initially developed for monitoring Diesel Particulate Filters (DPF), have been used to quantify soot particles that are deposited on its sensing side. After validation of the fabrication process via electrical measurements, the sensor response has been studied under different polarization voltages and an experimental protocol for soot quantification has been qualified.Thanks to those protocols, it was first demonstrated that the polarization voltage has no influence on the deposition velocity. Then, the resistive sensor was calibrated at polarization voltages of 10 V and 0.1 V. For 0.1 V, results are less repeatable and do not allow to propose a correlation between conductance and deposited mass. Better repeatability was found for a polarization voltage of 10 V allowing to propose and develop a calibration procedure aiming to correlate sensor conductance and deposited mass of aerosol. Indeed, it was proved that the sensor has a blind zone, in terms of conductance, for mass deposit ranging from 0 to 230 mg/m2. A linear calibration curve with a good sensitivity of 2.49 µS.mg-1.m2 was obtained for deposited mass between 230 and 1630 mg/m2.

International audience; In the context of CO2 storage, we used ab initio-based atomic-scale modelings and simulations to study oxygen and carbon diffusion in CaCO3 calcite. In overall agreement with earlier experimental findings, oxygen diffusion is found to take place possibly by either interstitial or vacancy mechanisms depending on the thermodynamic conditions. Contrary to almost isotropic interstitial diffusion, the vacancy mechanism strongly favors oxygen jumps within (111) planes characteristic of the CaCO3 layered structure, with significant less-than-unity correlation factors. Our simulations show that such mechanisms cannot be applied to carbon, and complex point defects may be required to explain the diffusion of this element. While stability arguments indicate that vacancy complexes formed with CO or CO3 missing groups may be efficient candidates to convey C diffusion, no low-energy migration path could be identified for these complexes. Focusing on the mostly stable CO vacancy complex and using generic values for unknown migration energies, kinetic Monte Carlo simulations show that this complex mechanism may be responsible for C diffusion roughly 2 orders of magnitude above its oxygen counterpart.

A sample of MgO was successfully synthesized using thermal decomposition of hydromagnesite and compared to commercial material. The characterization of materials using XRD, SEM, BET and BJH methods showed that the thermal decomposition way led to rectangular mesoporous microsheets with high specific surface area of 100 m2 g−1. This porous magnesium oxide has been shown to be a potential candidate for CO2 capture at low temperatures range (30 and 50 °C), low pressures of CO2 ( $$ P_{{{\text{CO}}_{2} }} = 600\;{\text{mbar}} $$ ) and in the presence of water vapor ( $$ P_{{{\text{H}}_{2} {\text{O}}}} = 15\;{\text{mbar}} $$ ). In these conditions, our results show that 11% of MgO was converted to hydrated magnesium carbonate MgCO3·3H2O after 8 h of carbonation in a thermobalance and reached 54% after 24 h of carbonation using tube furnace. After carbonation, hydration reaction pore size and surface area have noticeably changed.

International audience; Since the Fukushima Daiichi accident, increased attention is paid to the vulnerability of Spent Fuel Pools (SFPs). In case of an accidental dewatering of the fuel assemblies, the fuel cladding would be exposed to an air-steam atmosphere and its oxidation is a key phenomenon since it drives the fuel assembly heat-up and degradation. In this study, we have investigated the corrosion kinetics of pre-oxidized and as-received Zircaloy-4 (Zy-4) plate samples at 850∘C. The low temperature pre-oxidation aims at simulating the corrosion scale that grows during the in-reactor use of the fuel. High temperature oxidation tests were carried out under mixed oxygen-steam-nitrogen atmospheres. In the different atmospheres investigated, a rather protective effect of the pre-oxide scale regarding subsequent high temperature oxidation has been observed, for limited time periods however. Post-test examinations of the samples demonstrated that the loss of the protection was associated to the spalling of the pre-oxide scale that initiated at sample edges, where the pre-oxide scale was cracked. For the steam partial pressure range investigated in this study (0–8 vol%), there was no noticeable effect of the steam partial pressure on the oxidation rate. Nevertheless, samples hydrogen pick-up were strongly correlated to steam partial pressures. Moreover, 18O isotopic labelling experiments suggested that the contribution of O2 and H2O to the oxidation process corresponds to their respective concentration in the gas phase.

International audience; In the present study, Au-V2O5 sensing material was tested as a sensing electrode for developing mixed-potential ammonia gas sensors. The results of gas sensing measurements indicated selective responses to NH3 while this selectivity was highly dependent on the temperature. Different V2O5 contents were tested in the sensing electrode. The results showed that by increasing V2O5 content from 15 wt.% to 50 wt.%, selective ammonia sensors could be achieved at 550 °C. The selectivity of Au-50%V2O5 sensor was also confirmed in gas mixtures of CO, NH3, NO, and NO2 gases. Modeling of the sensor responses in the ammonia concentration range 2-40 ppm at four oxygen concentrations was performed based on mixed-potential theory. Nernst and Butler-Volmer equations with an electron transfer assumption were used for data modeling.

International audience; Whilst Bayesian epistemology is widely regarded nowadays as our best theory of knowledge, there are still a relatively large number of incompatible and competing approaches falling under that umbrella. Very recently, Wallmann and Williamson wrote an interesting article that aims at showing that a subjective Bayesian who accepts the principal principle and uses a known physical chance as her degree of belief for an event A could end up having incoherent or very implausible beliefs if she subjectively chooses the probability of an event F for which she has much poorer evidence. They also argued that their own version of objective Bayesianism is completely immune to that challenge. In this article, after having presented the strongest version of Wallmann’s and Williamson’s argument, I will show that if successful, it has far-reaching consequences and would not only invalidate moderate subjective Bayesianism and imprecise probalism but also a form of objective Bayesianism that relies on conditionalisation, the principal principle, reference classes, and the principle of indifference applied to the most basic partitions. I then argue that their argument can be defeated by adding the rule that it is always irrational to choose a probability that can be computed from the known probabilities associated to one’s other beliefs. I finally argue that the authors’ main intuition that probabilities have different degrees of reliability favours imprecise Bayesianism over precise Bayesianism.

International audience; In this contribution brownmillerite-based nanocomposite cathode for Single-Chamber Solid Oxide Fuel Cells is developed. These cells can be very attractive especially for small and cheap devices because of the absence of seals. The efficiency of SC-SOFCs is strictly connected to the selectivity of anode and cathode, the bottleneck for this technology. The development of a cathode inert in fuel oxidation is particularly challenging. Our strategy is to start from a catalytically un-active support (CFA = Ca2FeAl0.95Mg0.05O5) and induce the formation of iron oxide based nanoparticles, expected to activate oxygen. Symmetric (CFA + FeOx/CGO/CFA + FeOx) and complete cells (CFA + FeOx/CGO/Ni-CGO) are studied in air and methane/oxygen 2:1 mixture. The Area Specific Resistance of CFA + FeOx is less than 1/3 that of CFA. The high selectivity allows to reach an efficiency of 25%; power still needs to be increased but we demonstrated the possibility to develop selective low cost electrodes. The effect of air, methane/oxygen exposure and the heat treatments were carefully investigated.

Thème de la communication: Métrologie des aérosols - Conférence 100% digital; International audience; During a fire in a basic nuclear facility, the main consequences concerning aerosols release are the production of suspended radioactive particles and of a large amount of soot. This work is part of a PhD dealing with the study of soot deposition in rooms during a fire, which is essential for the prediction of aerosol quantities that can clog high efficiency particulate air filters. For this purpose, a multi-sensor device will be developed for real time measurement of aerosol deposition in a room during a fire. The aim of this paper is to present the qualification of the resistive sensor that will be used for the collection and detection of soot particles produced by a mixture of Tributylphosphate (TBP) / Hydrogenated Tetrapropylene (TPH).; Au cours d’un incendie dans une Installation Nucléaire de Base (INB), les principales conséquences en termes d’émission d’aérosols sont la mise en suspension de particules radioactives et la production de suies. Ce travail s’inscrit dans le cadre d’une thèse portant sur l’étude du dépôt des suies dans les locaux, afin de prédire les quantités d’aérosols participant au colmatage des filtres à Très Haute Efficacité (THE). L’objectif final est de développer un dispositif multi-capteurs pour la quantification, en continu, des suies déposées sur les parois d’un local en situation d’incendie. Cette communication présente la qualification du capteur résistif qui sera utilisé pour la collecte et la détection des suies issues de la dégradation d’un mélange de Tributylphosphate (TBP) / Tetrapropylène Hydrogéné (TPH).

Au cours d'un incendie dans une Installation Nucléaire de Base (INB), les principales conséquences en termes d'émission d'aérosols sont la mise en suspension de particules radioactives et la production de suies. Ce travail s'inscrit dans le cadre d'une thèse portant sur l'étude du dépôt des suies dans les locaux, afin de prédire les quantités d'aérosols participant au colmatage des filtres à Très Haute Efficacité (THE). L'objectif final est de développer un dispositif multi-capteurs pour la quantification, en continu, des suies déposées sur les parois d'un local en situation d'incendie. Cette communication présente la qualification du capteur résistif qui sera utilisé pour la collecte et la détection des suies issues de la dégradation d'un mélange de Tributylphosphate (TBP) / Tetrapropylène Hydrogéné (TPH)., During a fire in a basic nuclear facility, the main consequences concerning aerosols release are the production of suspended radioactive particles and of a large amount of soot. This work is part of a PhD dealing with the study of soot deposition in rooms during a fire, which is essential for the prediction of aerosol quantities that can clog high efficiency particulate air filters. For this purpose, a multi-sensor device will be developed for real time measurement of aerosol deposition in a room during a fire. The aim of this paper is to present the qualification of the resistive sensor that will be used for the collection and detection of soot particles produced by a mixture of Tributylphosphate (TBP) / Hydrogenated Tetrapropylene (TPH).

Ce congrès est un événement digital: 4th international nanoFIS 2020 conference – 100% Digital at highest scientific level!; International audience; Ammonia detection at ambient with low-cost sensors is a challenge for various applications like breath analysis and agriculture. Such a challenge can be reached with functionalized SnO2 based gas sensors using silanization by 3-aminopropyltriethoxysilane (APTES) as an intermediate step before grafting with functional end group providing selectivity for the target gas. Moreover, operation at room temperature gives the opportunity to develop a sensor on a plastic substrate entirely manufactured by inkjet technology, by developing suitable inks, in particular to obtain SnO2 sensing element.

International audience; We studied the kinetics and mechanism of the dehydration reaction of calcium sulfate dihydrate to hemihydrate under controlled temperature and water vapor partial pressure. From kinetic and reaction rate curves obtained using thermogravimetric analysis (TGA) under isothermal and isobaric conditions, we determined the overall behavior of this dehydration reaction and the effects of the system’s intensive variables on its kinetics. We observed that the reactions take place with an initial induction period that decreases with increasing temperature, followed by a sigmoidal mass loss controlled by both nucleation and growth processes. Characterization of our samples at different points of the reaction allowed us to observe and confirm a surface nucleation process followed by isotropic growth of the nuclei with inward development of the solid product. We then employed the Mampel kinetic model based on the observed experimental results considering the physical nature of the investigated transformation and the real geometry of the particles. From this model, we obtained sets of kinetic parameters for the nucleation and growth processes and their evolution with temperature. We then proposed physicochemical mechanisms for both processes, and they were considered to interpret the kinetic parameters obtained previously. The mechanistic analysis of the system allowed determination of the effects of both temperature and water vapor pressure on the kinetic behavior of the reaction, which corresponds to a novel approach for the dehydration reaction of calcium sulfate dihydrate. The universal kinetic approach used to treat this chemical system in this work can be applied for studying the dehydration of other ionic hydrates.

International audience; HT-XRD analyses were performed on Zircaloy-4 sheet samples in steam and oxygen mixtures at high temperatures in order to investigate any possible relation between zirconia phase transformation and the breakaway oxidation. The tetragonal phase fraction decreases for temperatures less than 1000°C. At 1000°C and 1030°C, breakaway oxidation occurred, however, the tetragonal phase fraction remained constant during the isothermal oxidation showing no sudden decrease that could be attributed to the onset of breakaway oxidation. These results demonstrate that the tetragonal-to-monoclinic phase transformation in the external surface of the oxide could not be correlated to the occurrence of the breakaway oxidation.

International audience; While there are plenty of experimental studies pertaining to the dust generation from and dustiness of powders, few of them aim at reaching a theoretical understanding of the phenomena. In the present article, the literature on dustiness has been systematically reviewed with respect to its contribution to a better comprehension of the processes involved. The majority of industrial raw materials exist in the form of dry powders. Due to the complex interplay of multiple parameters, a theoretical understanding of dust generation processes is not trivial and presently relies on experimental studies using bench top testers called dustiness testers. Given the existence of several reviews about dustiness testers, the present review is limited to the presentation of the drop test and the rotating drum and a relatively new tester, the vortex shaker. The vortex shaker uses mechanical agitation (‘shaking’) of a small bulk solid sample to generate dust particles. Parametric studies related to sample mass, particle size and particle size distribution, moisture content, bulk density, particle shape, temporal evolution, angle of repose, and cohesion were reviewed. Approaches to modelling dustiness have been systematically reviewed. The simplest and most straightforward one consists of defining the dust emission as a result of empirical terms describing the ratio between the cohesion and separation forces. Good results could be reached through that approach but its simplistic assumptions may limit its validity to narrow ranges of conditions the parameters must be adapted to. To reach a more systematic understanding, numerical modelling methods such as computational fluid dynamics and discrete element method must be considered. Their combined use along with population balance modelling is currently the most complete approach but it is computationally very demanding. In order to make progress in theoretical dustiness studies, both the simplified and the numerical modelling approaches should be followed.

International audience; The present recommendations have been developed by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC). The recommendations provide guidance on kinetic analysis of multi-step processes as measured by thermal analysis methods such as thermogravimetry (TGA) and differential scanning calorimetry (DSC). Ways of detecting the multi-step kinetics are discussed first. Then, four different approaches to evaluation of kinetic parameters (the activation energy, the pre-exponential factor, and the reaction model) for individual steps are considered. The approaches considered include multi-step model-fitting as well as distributed reactivity, isoconversional, and deconvolution analyses. For each approach practical advice is offered on its effective usage. Due attention is also paid to the typical problems encountered and to the ways of resolving them. The objective of these recommendations is to help a non-expert with efficiently performing multi-step kinetic analysis and interpreting its results.

This study reports the catalytic properties of Ag nanoparticles dispersed on mixed ionic and electronic conducting layers of LSCF (La0.6Sr0.4Co0.2Fe0.8O3) for propene combustion. A commercial and a synthesized LSCF powder were deposited by screen-printing or spin-coating on dense yttria-stabilized zirconia (YSZ) substrates, an oxygen ion conductor. Equal loadings (50 &micro, g) of Ag nanoparticles were dispersed via drop-casting on the LSCF layers. Electrochemical and catalytic properties have been investigated up to 300 &deg, C with and without Ag in a propene/oxygen feed. The Ag nanoparticles do not influence the electrochemical reduction of oxygen, suggesting that the rate-determining step is the charge transfer at the triple phase boundaries YSZ/LSCF/gas. The anodic electrochemical performances correlate well with the catalytic activity for propene oxidation. This suggests that the diffusion of promoting oxygen ions from YSZ via LSCF grains can take place toward Ag nanoparticles and promote their catalytic activity. The best specific catalytic activity, achieved for a LSCF catalytic layer prepared by screen-printing from the commercial powder, is 800 times higher than that of a pure Ag screen-printed film.

International audience; This study aims to universally describe the kinetic features of the thermal dehydration of lithium sulfate monohydrate across different temperatures (T) and atmospheric water vapor pressures (p(H2O)) as a model reaction of the thermal dehydration of crystalline hydrates. The features of the physicogeometrical consecutive process, comprising the induction period (IP)–surface reaction (SR)–phase boundary-controlled reaction (PBR), and the effect of p(H2O) on kinetic behavior were revealed experimentally under various heating conditions. Then, the accommodation function (AF), accounting for the effect of p(H2O) on the kinetic behavior, was derived by considering the consecutive/concurrent elementary steps of SR and PBR at the atomic and molecular levels. The universal kinetic descriptions for the IP and subsequent mass-loss process were realized by introducing the AF into formal kinetic equations and using the isoconversional kinetic relationship. Furthermore, by combining the physicogeometrical consecutive IP–SR–PBR(n) model and the formulated AF, the universal kinetic descriptions for each physicogeometrical reaction step across different T and p(H2O) conditions were obtained, which reveal novel kinetic features of each reaction step and these variations as the reaction step advances. The significance of the revealed kinetic features is discussed through demonstrating the development of the novel kinetic approach.

One of the most effective technologies in decreasing large-scale NOx emission produced by diesel engine vehicles is Urea-SCR (selective catalytic reduction) system. In order to prevent inducing excessive ammonia to the environment, an NH3 sensor is required at the exit of this system [1, 2]. In this study, highly selective ammonia sensors were developed to detect ammonia emissions from automotive exhaust. The sensors were fabricated with 8-YSZ electrolyte, a platinum reference electrode and a working electrode of Au-V2O5 (mass ratio 85/15), screen-printed on an alumina substrate. A platinum resistor was printed at the backside of the support to control the sensor temperature. The measured sensor’ response (ΔV) is the potential difference between reference and working electrodes. Figure 1 shows the responses of two identical sensors to 100 ppm CO, NO2, NO and 20 ppm of NH3 at four different temperatures. It can be seen that the sensors respond to all gases at lower temperatures while by increasing temperature to 600°C, the selectivity to NH3 is greatly improved. The selectivity of sensors was also confirmed by testing other possible interfering gases: no responses were observed for 20ppm of hydrogen and 100ppm of a hydrocarbon mixture. The stability of such sensors was studied at 550°C and 600°C. Since the sensors show no long-term stability at 600°C (electrode degradation), but remain stable at 550 °C, investigations were made to decrease the working temperature while maintaining selectivity. After testing different mass percentages of V2O5 in working electrode, we observed that by increasing this value to 50%, the working temperature of selective ammonia sensors could be decreased to 550°C with stable responses. Further investigations will be performed in order to gain deeper insight in sensing mechanism of V2O5 based working electrodes, which governs the sensor’s performance. References [1] K. Shimizu, I. Chinzei, et al. "Doped-vanadium oxides as sensing materials for high temperature operative selective ammonia gas sensors," Sensors and Actuators B, 141, 2009, pp. 410-416. [2] M. Van Nieuwstadt, I. Dpadhyay, et al. "Control of Urea SCR Systems for US Diesel Applications" in IFP Energies Nouvelles International Conference, Dearborn, USA, 2011, pp. 655-665. Figure 1

International audience; Magnesium sulfate-water vapor is an interesting working pair of thermochemical materials for compact inter-seasonal heat storage at low temperature. Total dehydration of magnesium sulfate heptahydrate shows a theoretical storage energy density of 2.8 GJ·m−3. However, kinetic data are poorly studied up to now making use of this material difficult for a practical storage application. In the present work, a kinetic study of the dehydration of MgSO4·6H2O powder at low temperature (35 to 60°C) and at low water vapor pressure (2 to 21 hPa) is carried out using thermogravimetric analysis in isobaric-isothermal conditions. A mathematical model is developed for this bivariant system and validated representing the mechanism of dehydration: water molecules diffusion in the solid solution followed by transfer of these molecules from the surface to the atmosphere. The transfer of water molecules at the surface during dehydration is identified as rate-determining step. The fractional conversion and reaction rate of the dehydration reaction are calculated and comparedto the experimental data.

International audience; In recent years, printed and flexible gas sensors have quickly emerged as an innovative area of great interest because of their lightness and low cost. These flexible sensors can be easily integrated into autonomous systems for many applications such as smart food packaging and premature disease detection. In this paper, a novel approach was applied to manufacture a fully inkjet-printed gas sensor on a flexible polymeric foil. Platinum heater and gold electrodes were printed on the top side of the substrate, separated by a thin insulating layer of printed polyimide. An aqueous sol-gel process was adopted to synthesize nanosized SnO2-based sol that guaranty a crystallization at 350 °C, which is entirely consistent with the polyimide foil. Then, the sol was transformed into a stable ink and inkjet printed over the gold electrodes. The printability of different inks was optimized to ensure flawless ejection of droplets, and the complex physico-chemical interactions between the inks and different interfaces were controlled to get well-defined patterns with high resolution. Finally, electrical measurements of the printed sensor were performed to characterize the response and the sensitivity to different concentrations of ethanol, ammonia and carbon monoxide gases, at working temperature of 300 °C, in dry and wet air.

International audience; The European standards “Euro” limit the emission of several pollutants from thermal engine vehicles. The particle number (PN) and particulate mass (PM) emissions are specifically limited since 2011, hence modern Diesel engines are equipped with a Diesel particulate filter (DPF). On-board diagnostic (OBD) regulations impose to perform the self-diagnostic of the DPF. Nowadays, this diagnostic is done through a very simple backpressure monitoring, but the forthcoming steps will probably require a more sophisticated system, such as a resistive soot sensor. The aim of this study is to investigate the mechanisms leading to the formation of bridge-like soot deposits brought to light by scanning electron microscopy. A 2D model taking into account the aerodynamic transport and the electrostatic effects was used to improve our understanding of the soot deposition process. The model presented in this paper includes a force that has been neglected so far in previous works about resistive soot sensors: the dielectrophoresis. In this theoretical frame, this force affects particles motion in such a way that they tend to numerically build the bridge-like structures that are observed experimentally. Simulation shown that the dielectrophoresis mainly impact large particles – over 150 nm diameter.

Thème de la communication: Métrologie des aérosols; International audience; During a fire in a basic nuclear facility, the main consequences concerning aerosols are the production of suspended radioactive particles and of a large amount of soot. This work is part of a PhD dealing with the study of soot deposition during a fire, which is essential for the prediction of aerosol quantities that can clog high efficiency particulate air filters. For this purpose, a multi-sensor device will be developed for real time measurement of aerosol deposition, in a room during a fire. The aim of this paper is to present the qualification, at different polarization voltages, of the resistive sensor that will be used for the collection and detection of soot particles.; Au cours d’un incendie dans une Installation Nucléaire de Base (INB), les principales conséquences concernant les aérosols sont la mise en suspension de particules radioactives et la production de suies. Ce travail s’inscrit dans le cadre d’une thèse portant sur l’étude du dépôt des suies afin de prédire les quantités d’aérosols participant au colmatage des filtres à Très Haute Efficacité (THE). L’objectif final est de développer un dispositif multi-capteurs pour la quantification, en continu, des suies déposées sur les parois d’une INB en situation d’incendie. Cette communication présente la qualification, à différentes tensions de polarisation, du capteur résistif qui sera utilisé pour la collecte et la détection des suies.

Conférence digital - Online – Live and on-demand - digital conference, Thème: Fuel materials, absorbers and fuel cladding interaction; International audience

Au cours d'un incendie dans une Installation Nucléaire de Base (INB), les principales conséquences en termes d'aérosols sont la mise en suspension de particules radioactives et la production de suies. Ce travail s'inscrit dans le cadre d'une thèse portant sur l'étude du dépôt des suies afin de prédire les quantités d'aérosols participant au colmatage des filtres à Très Haute Efficacité (THE). L'objectif final est de développer un dispositif multi-capteurs pour la quantification, en continu, des masses de suies déposées sur les parois d'une INB en situation d'incendie. Cette communication présente une qualification, à différentes tensions de polarisation, du capteur résistif qui sera utilisé pour la collecte et la détection des suies., During a fire in a basic nuclear facility, the main consequences in terms of aerosol are the production of suspended radioactive particles and of a large amount of soot. This work is part of a PhD dealing with the study of soot deposition on walls in a room during a fire, which is essential for the prediction of aerosol quantities that can clogg high efficiency particulate air filters. For this purpose, a multi-sensor device will be developed for real time measurement of aerosol deposition, in a room during a fire. The aim of this paper is to present a qualification, at different polarization voltages, of the resistive sensor that will be used for the collection and detection of soot particles.

Ce colloque est organisé sous le parrainage de l’Association Française de Cristallographie (AFC), la Société Française de Minéralogie et Cristallographie (SFMC), et la Société Française de Métallurgie et de Matériaux(SF2M).; National audience; La fragilisation par l’hydrogène est un phénomène complexe dont de nombreux aspects sont encore mal compris à l'heure actuelle. Il a été confirmé que ce phénomène peut provoquer des ruptures brutales de pièces. La tomographie a permis de visualiser la porosité dans un échantillon d’acier moulé et d’estimer le volume et la distribution des cavités.

International audience; In some of the currently developed Sodium Fast Reactor (SFR) designs the core configuration will berearranged to include internal spent fuel storage positions, with the benefit of avoiding an externalsodium pool. However, in-vessel storage of failed fuel pins can lead to a direct contact betweencoolant and fuel, i.e. in a scenario where the cladding was breached, leading to their potential inter-action in case of oxide based fuel forms (UO2 and MOX). The reaction product of sodium and oxidefuel is generally denoted as Na3MO4 (where M=U, Pu), and characterized by unfavorable physical properties, which might result in fuel swelling and/or pulverization, with the consequence of fissileisotopes or fission products dissemination into the primary system. The understanding of the corro-sion mechanism and kinetics between liquid sodium and oxide based nuclear fuel becomes then ofprior importance for establishing the feasibility of an internal storage of failed fuel pins.In this contribution, we will present the results of out-of-pile tests that we perform to provide a basicknowledge of defective fuel pin behavior in contact with liquid sodium. With the aim to determinethe physical mechanism involved in the sodium-fuel reaction, we firstly focused on the behavior of UO2 corrosion by sodium.In order to cover the internal storage scenario, isothermal experiments were performed inside cap-sules with stagnant liquid sodium and UO2 at 800°C. To establish the influence of the grain orienta-tion on the growth process of the reaction product, well-oriented ( and ) single crystalswere used and finally to extend the behavior to the fuel pellet, a polycrystalline UO2 sample wastested as well. The corrosion product was analyzed by XRD, SEM-EDX and RAMAN. It consists ina homogeneous layer, whose morphology depends on the crystallographic orientation of the UO2 corroded grain or single crystal. However, the thickness of the corrosion layer does not seem todepend on the crystallographic orientation of the UO2 corroded grain that was unexpected.A tentative interpretation of UO2 corrosion by sodium is proposed. This interpretation will be usedfor further study on the modelling of MOX-sodium interaction. There the influence of Pu on the corrosion process will be addressed and added to the UO2-Na model.

International audience; Resistive soot sensors capable of measuring the mass concentration of particles in an exhaust pipe have been developed in a previous work. In particular, it has been shown that these sensors have an optimal sensitivity for a certain polarization voltage depending on the nature of the particles.This work shows that this effect can be explained by an equilibrium between the creation of soot bridges between the two collecting electrodes and their destruction initiated by Joule effect due to the polarization voltage. Based on this assumption, a model is proposed to predict the load curve (response versus time) of the sensor. In addition, the high frequency sampling of the sensor response has revealed some jumps of the sensor response (electrical conductance), which are exploited through a statistical approach to obtain additional information on the nature of the collected particles.

International audience

Session: A5 Oxide Based Sensors and Actuators; International audience; One of the most effective technologies in decreasing large-scale NOx emission produced by diesel engine vehicles is Urea-SCR (selective catalytic reduction) system. In order to prevent inducing excessive ammonia to the environment, an NH3 sensor is required at the exit of this system. In this study, highly selective ammonia sensors were developed to detect ammonia emissions from automotive exhaust.The sensors were fabricated with 8-YSZ electrolyte, a platinum reference electrode and a working electrode of Au-V2O5 (mass ratio: 85:15), screen-printed on an alumina supports. A platinum resistor was printed at the backside of the support to control the sensor temperature. The measured sensor response (ΔV) is the potential difference between reference and working electrodes. Figure 1 shows the responses of two identical sensors to 100 ppm CO, NO2, NO and 20 ppm of NH3 at four different temperatures. It can be seen that the sensors respond to all gases at lower temperatures while by increasing temperature to 600 °C the selectivity to NH3 is greatly improved. The selectivity of sensors was also confirmed by testing other possible interfering gases and no responses were observed for 20ppm of H2 and 100ppm of a hydrocarbon mixture. The stability of such sensors was studied at 550 °C and 600 °C. Since sensors showed no long term stability at 600 °C (electrode degradation), but remain stable results at 550 °C, investigations were made to decrease the selective working temperature while maintaining selectivity. After testing different mass percentages of V2O5 in working electrode, we observed that by increasing this value to 50%, the working temperature of selective ammonia sensors could be decreased to 550 °C with stable responses. Further investigations will be performed in order to gain deeper insight in sensing mechanism of V2O5 based working electrodes, which governs the sensor’s performance.

Thème : Novel measurement principles and new instrumentation; International audience

In this study, we have investigated, for the very first time, the oxygen electrode reactions on Ag/YSZ electrochemical catalysts both in oxygen and under reaction conditions compatible with the ethylene epoxidation reaction. Electrochemical Impedance Spectroscopy (EIS) in combination with in-situ Raman spectroscopy and catalytic activity measurements were used to identify and understand the main oxygen reaction pathways. The results obtained suggested that the rate limiting step under an O2 reaction atmosphere (at 300 °C) is the O2 adsorption/dissociation process on the Ag catalyst-electrode. In addition, the polarization resistance increased with time under the presence of O2. This was attributed to the formation of Ag2O on the catalyst surface or near surface, which limits the oxygen electrode reactions. Finally, we observed that the addition of ethylene in the feed stream hinders the electrode reaction, due to its competitive chemisorption with oxygen on Ag. These results give new insights into the design of selective Ag/YSZ catalyst for ethylene epoxidation. Keywords: Electrochemical Impedance Spectroscopy (EIS), Oxygen electrode reaction, Ag/YSZ, Ethylene epoxidation

International audience; Bayesian methods are growing ever more popular in chemical kinetics. The reasons for this and general challenges related to kinetic parameter estimation are shortly reviewed. Most authors content themselves with using one single (mostly uniform) prior distribution. The goal of this paper is to go into some serious issues this raises. The problems of confusing knowledge and ignorance and of reparametrisation are examined. The legitimacy of a probabilistic Ockham’s razor is called into question. A synthetic example involving two reaction models was used to illustrate how merging the parameter space volume with the model accuracy into a single number might be unwise. Robust Bayesian analysis appears to be a simple andstraightforward way to avoid the problems mentioned throughout this article.

International audience; The atmospheric gas that contributes to the thermally induced reaction in the solid–gas sys-tem as the product or reactant is one of the most relevant factors to control the kinetics and mechanisms of the reaction Because of the heterogeneous feature of the reactions in the solid–gas system, change in the atmospheric conditions imposes the dramatical change in the physico-geometrical reaction mechanism and overall kinetics in a complex manner of the interactions of the component physico-chemical reaction steps.

International audience; Thermal decomposition of Ca(OH)2 under atmospheric water vapor exhibits special features, including an induction period (IP) and a subsequent sigmoidal mass-loss behavior under isothermal conditions. Atmospheric water vapor reduces the reaction rate at a specific temperature and causes a systematic shift of the mass-loss curve, which was recorded at a specific heating rate, to higher temperatures as the water vapor pressure, p(H2O), increases. The challenge in this study was to universally describe the kinetics of thermal decomposition under various p(H2O) conditions by introducing an accommodation function in the fundamental kinetic equation. The accommodation function in the multiplied form of two p(H2O) components with a variable exponent in each component was derived on the basis of the classical nucleation and interface reaction theories. The universal kinetic approach was realized by applying the accommodation function to formal kinetic analyses of the Arrhenius plot for the IP and the Friedman plot for the mass-loss process. Furthermore, the overall reaction process under isothermal conditions was analyzed kinetically on the basis of the physico-geometrical consecutive reaction model, which was composed of an IP, a surface reaction (SR), and a phase boundary-controlled reaction (PBR). Subsequently, the kinetic parameters for each physico-geometrical reaction step were determined by the modified Arrhenius plot with the accommodation function. The impact of the atmospheric water vapor on the kinetics of thermal decomposition was characterized in connection with physico-geometrical reaction mechanisms through the interpretation of the kinetic parameters and these variation behavior patterns as the overall reaction advanced.

International audience; Currently, one of the current issues related to the additive manufacturing is the change in the properties of Ti-6Al-4V powder during this process. This change has been attributed to the interaction of this powder with its gaseous environment that can contain a small quantity of oxygen, nitrogen, carbon dioxide and/or water vapour. Therefore, the aim of this work is to study the effect of oxygen and nitrogen partial pressure as well as the effect of the temperature on the corrosion of the Ti-6Al-4V powder. The results show that the temperature and the oxygen partial pressure have an effect on the kinetic corrosion, which is not the case of nitrogen partial pressure. This study is a first step towards a better understanding of the aging of Ti-6Al-4V powder during additive manufacturing processes.

International audience; We employ a rigorous thermodynamic modeling approach to investigate the water adsorption phenomena on two calcium sulfate compounds, AIII-CaSO4 and CaSO4·0.5H2O. In part 1 of this work ( Ind. Eng. Chem. Res., 2019, DOI: 10.1021/acs.iecr.9b00856), we prepared these two products by the dehydration of synthetic CaSO4·2H2O and obtained quantitative adsorption data as a function of the temperature and water vapor partial pressure. In this part, we develop macroscopic solution models (ideal and nonideal) to model monolayer adsorption on AIII-CaSO4. This allowed the calculation of the energies of adsorption for this phenomenon, evidencing a physisorption mechanism. For the CaSO4·0.5H2O, we interpreted the water adsorption using a multilayer adsorption model (BET model). For both materials, we showed that nitrogen adsorption data was not sufficient to represent their entire surface areas and porosity profiles compared to their water vapor sorption capacity.

National audience; Les alliages de zirconium sont utilisés comme matériaux de structure des crayons de combustible nucléaire pour les centrales nucléaires à eau légère en raison de leurs propriétés neutroniques, mécaniques satisfaisantes et de leur résistance à la corrosion. En conditions nominales de fonctionnement (environ 150 bar et 350°C), les tubes en alliage de zirconium sont sujets à une oxydation maîtrisée en présence d’eau pressurisée, servant de caloporteur. La démonstration de la sûreté des réacteurs nucléaires intègre l’étude des scénarios accidentels hypothétiques, tels que l’Accident de Perte de Réfrigérant Primaire (APRP). Dans ce scénario, une brèche dans le circuit primaire du réacteur peut conduire les crayons de combustible à être oxydés en milieu de vapeur d’eau à haute température (jusqu’à 1200°C). Il a été démontré [1]–[3] que dans l’intervalle de température [900-1050°C] et après un certain temps d’oxydation sous vapeur d’eau, le phénomène de breakaway peut apparaître. Il se manifeste par une accélération de la cinétique d’oxydation, par la perte du caractère protecteur de la couche d’oxyde et par l’absorption d’hydrogène du matériau. Un tel phénomène implique donc une détérioration des propriétés mécaniques de la gaine et menace son intégrité pendant et après le transitoire accidentel. Les mécanismes fondamentaux à l’origine du breakaway sont encore mal connus.Dans ce cadre, ce travail de thèse a pour objectif de caractériser les conditions d’apparitions du breakaway et d’améliorer la compréhension des mécanismes physiques sous-jacents. Pour ce faire, des essais d’oxydation sur des échantillons de Zy-4 en thermobalance symétrique ont permis d’étudier l’influence de la température, de la pression partielle de vapeur d’eau et du temps sur l’occurrence du breakaway. La couche d’oxyde formée a été caractérisée par des observations en microscopie optique et des analyses en DRX in-situ pour suivre l’évolution des phases de la zircone durant l’oxydation.

International audience; We studied in-situ the interaction of sodium metal with UO2+x (0 ≤ x ≤ 1) using thin films prepared by sputter deposition on Au substrate. X-ray Photoelectron Spectroscopy (XPS) and Grazing Incidence XRay Diffraction (GIXRD) characterized films before and after interaction. The results show that sodium does not reduce stoichiometric UO2 at room temperature. Plasmon loss peaks, observed at the Na1s photoemission (PE) line, are characteristic of metallic sodium particles, and point to a weak interaction between sodium and UO2. The oxidation of the sodium at room temperature takes place only on hyperstoichiometric uranium dioxide films. Indeed, sodium deposition on UO2+x (0 < x ≤ 1), eventually results in the complete reduction of U(VI) down to U(IV). Molecular and atomic oxygen affect differently the oxidation of uranium and sodium. The wetting of the gold by the sodium is much more important when sodium is oxidised by atomic oxygen. This leads to a shift of the Na1s core level peak, while molecular oxygen gives a peak broadening without shift. Atomic oxygen seems to play the same role as the interstitial oxygen present in the UO2+x film. The oxygen dissociation may be the limiting step of sodium oxidation on gold and on UO2. Heat treatment of sodium on UO3 at about 773 K leads to the formation of the NaUO3 film as demonstrated by a quantitative analysis by XPS and GIXRD. The results show also that once U(V) is formed, it stays stable up to at least 973 K, the temperature at which shrinkage of the film is observed.

National audience; L’émergence au niveau industriel de la fabrication additive métallique comme procédé à part entière pour la production et le commerce de pièces à haute valeur ajoutée apporte d’un point de vue scientifique des questionnements nouveaux.Différentes technologies ont été développées sur la base de la fabrication additive métallique comme par exemple la fusion sélective au laser (SLM) et la fusion par faisceau d'électrons (EBM). Ces deux procédés sont basés sur la fusion locale des poudres préalablement chauffées à 200°C (SLM) et 600°C (EBM) dans une enceinte contrôlée sous atmosphère inerte. Néanmoins, des traces d’impuretés dans cette atmosphère peuvent être présentes durant la fabrication des pièces.En effet, il a été observé que dans un procédé typique de fabrication additive métallique seule une faible proportion de la poudre est effectivement nécessaire pour la fabrication finale de la pièce : entre 30 et 90 % de la poudre est ainsi mise de côté selon le procédé et la géométrie de la pièce fabriquée. Cependant, cette poudre non utilisée ne conserve pas ses propriétés chimiques et rhéologiques au fil du temps: après un nombre de passages évalué de manière phénoménologique, celle-ci doit être mise au rebut. La réutilisation ou bien le recyclage de cette poudre devient alors un enjeu à la fois économique et écologique pour l’industrie. L’un des verrous de cette problématique se situe sur la réactivité de telles poudres avec leur environnement gazeux.Le titane est utilisé sous forme alliée pour sa résistance et sa légèreté dans des nombreux domaines tels que l’aéronautique, l’aérospatiale, la chimie, le secteur médical. Parmi les alliages du titane, le Ti-6Al-4V représente 50% du marché mondial, et les poudres de Ti-6Al-4V sont couramment utilisées dans les procédés de fabrication additive. En conséquence, il est nécessaire de comprendre l’interaction entre ces poudres et leur environnement gazeux. Malgré les nombreuses études sur la corrosion du Ti-6Al-4V, la majorité de celles-ci portent sur le Ti-6Al-4V massif (Du, 1994). En revanche, peu d’études ont été consacrées à la corrosion de poudres de Ti-6Al-4V et l’effet de la géométrie et des dimensions des grains sur les cinétiques de corrosion (Pijolat, 2018).Dans le but de comprendre et de modéliser la cinétique de corrosion de ces poudres, l’effet des différents paramètres thermodynamiques,i.e. la température et les pressions partielles d’oxygène et d’azote, ainsi que l’effet du temps ont été étudiés. Des expériences en thermobalance en condition isotherme et isobare ont été réalisées dans une gamme de température allant de 600 à 750°C pour des pressions partielles d’oxygène entre 0 et 20 hPa et d’azote entre 0 et 80 hPa. Des caractérisations physico-chimiques des échantillons en cours de corrosion et des produits de corrosion obtenus ont aussi été réalisées. Les résultats ont notamment mis en évidence la formation d’une double couche d’oxyde constituée de TiO2 (couche interne) et de Al2O3 (couche externe) avec une croissance préférentielle du TiO2. De plus, un effet bénéfique de la présence d’azote dans l’atmosphère a été observé.

International audience; The thermal dehydration of lithium sulfate monohydrate (LSM) exbibits significant induction period (IP) prior to mass-loss process under isothermal conditions. The average rate of IP is well described by conventional Arrhenius-type temperature dependence. The kinetic behavior of IP dramatically changes by the influence of the atmospheric water vapor pressure, p(H2O). In this study, a universal kinetic description for the induction period under various temperature, T,and p(H2O) was trialed through formalizing an accommodation function, a(p(H2O),P eq(T)),on the basis of classical nucleation theory. Characteristic kinetic behavior of the IP process is discussed by reviewing the results of the universal kinetic approach.

International audience; Demonstrating the satisfying cladding oxidation behavior in LOCA conditions and predicting accurately breakaway occurrence is of importance for the cladding producer and its customers. FRAMATOME developed a dedicated facility at his PAIMBOEUF plant in order to perform one- and two-sided oxidation tests in steam, with a tight monitoring (temperature, steam flow). M5Framatome claddings were oxidized at temperatures from 800 to 1100°C for at least 5000 s. Parabolic kinetics, protective oxides and a lack of significant hydrogen pick-up were observed. These tests confirmed the M5Framatome excellent behavior and the absence of breakaway in these conditions. Metallography and SEM observations allowed us to quantify the layers’ thicknesses of the oxide the oxygen-stabilized alpha phases. The metal/oxide interface roughness as well as the oxide porosity were also estimated by image analysis, and are shown to depend on the oxidation temperature. In parallel, Finite Element Modeling of the oxidation and the addition elements’ diffusion was developed. Diffusion equations take into account the evolution of the chemical potentials of the elements, computed thanks to the THERMOCALC software and the FRAMATOME ARTABAZ thermodynamic database. Calculated diffusion profiles are compared to experimental data and discussed.

Thème: Métrologie des aérosols; International audience; During a fire in a basic nuclear facility, the main consequences in terms of aerosol are the production of suspended radioactive particles and of a large amount of soot. This work is part of a PhD dealing with the study of soot deposition on walls in a room during a fire, which is essential for the prediction of aerosol quantities that can clogg high efficiency particulate air filters. For this purpose, a multi-sensor device will be developed for real time measurement of aerosol deposition, in a room during a fire. The aim of this paper is to determine the orders of magnitude of the soot deposited mass in a room during a real scale fire; Au cours d'un incendie dans une Installation Nucléaire de Base (INB), les principales conséquences en termes d'aérosols sont la mise en suspension de particules radioactives et la production de suies. Ce travail s'inscrit dans le cadre d'une thèse portant sur l'étude du dépôt des suies afin de prédire les quantités d'aérosols participant au colmatage des filtres à Très Haute Efficacité (THE). L'objectif final est de développer un dispositif multi-capteurs pour la quantification, en continu, des masses de suies déposées sur les parois d'une INB en situation d'incendie. Cette communication présente les résultats de quantification des suies déposées lors d'essais de feux menés à échelle réelle.

International audience; Depuis 2011 et la norme Euro 5b, en plus d’imposer un seuil massique d’émission, les normes Euro successives imposent une limite sur le nombre de particules émises par les moteurs à combustion interne des véhicules légers. En outre, les nouveaux véhicules équipés de moteurs thermiques doivent être capables d’auto-diagnostiquer leur propre filtre à particules grâce à des dispositifs de mesure embarqués. Les capteurs de suie résistifs semblent être de bons candidats pour répondre à un tel besoin [1–3] et c’est dans ce contexte que se situe cette étude. L’objectif de ce travail est de mieux comprendre les mécanismes de captation des particules de suie sur la surface du capteur, en particulier en considérant le paramètre qu’est la taille des particules.

Marc Aurousseau, président du Codegepra, a remis le prix du meilleur poster à Joao Dal-Bo-Preturlan, doctorant centre SPIN (encadré par Laetitia Vieille et Loïc Favergeon).; National audience; Gypsum is the mineralogical term used to describe materials that are mainly constituted of calcium sulfate dihydrate (CaSO4·2H2O). These materials can be obtained either from natural or synthetic sources and are of paramount importance for modern construction material industry because they represent the main raw materials to produce plaster. This product is widely employed to manufacture gypsum wallboards and serves as an additive for other construction materials (e.g. cements). The production process of plaster consists in partially dehydrate gypsum in calcination furnaces, large-scale heterogeneous industrial reactors, to obtain calcium sulfate hemihydrate (CaSO4·0.5H2O), which is the main constituent of plaster. (Kuntze, 2015) In order to better understand the functioning of these industrial reactors and to be able to propose improvements in this matter, it is mandatory to better understand the thermodynamics of the CaSO4-H2O system and the reaction mechanism for each chemical transformation taking place during the calcination process. In this context, one of the objectives of the present work is to increase the current understanding about the reactivity of calcium sulfate dihydrate, clarify remaining questions on reaction kinetics, and propose a kinetic-geometric model of the transformation of this material. In order to perform this, the dehydration of a highly pure calcium sulfate dihydrate powder was monitored using thermogravimetric analysis under isotherm and isobaric conditions. This was performed in order to obtain kinetic and reaction rate curves. Temperature ranging from 86°C to 110°C and water vapor partial pressure ranging from of 10 hPa to 60 hPa were investigated. Morphological and textural characterizations of the solids were also employed to understand the way of transformation. Based on this knowledge, a kinetic nucleation-growth model was then proposed and applied to the experimental data in order to obtain kinetic parameters for nucleation and growth. A growth mechanism was written and the change of kinetic parameters with temperature and water vapor partial pressure was explained. (Mampel, 1940; Helbert et al., 2004; Pijolat et al., 2011)

National audience; According to new European driving cycle, while the vehicular emissions of NOx and CO have decreased over the past years, ammonia emissions have considerably increased. Among all NOx reduction approaches that have been developed, selective catalyst reduction (SCR) system using ammonia as a reductant is one the most reliable ways to control the NOx emissions from diesel engine vehicles and trucks. In order to optimize the conversion rates of NOx and to prevent inducing excessive NH3 to the air, an NH3 and NOx sensor is required to control the SCR system. Ivan Romanytsia et al. in 2015 have developed three-electrode mixed-potential selective NO2 sensors. Based on this study, we aim to develop sensors for selective detection of both NOx and NH3 for the exhaust of automotive. In this work, mixed potential gas sensors are fabricated by using two sensing materials of Au and Au-V2O5 as working electrodes, YSZ as electrolyte and platinum as reference and counter electrode. In order to evaluate the performance of the fabricated planar sensors, the response to different pollutant gases such as CO, NH3, NO2 and NO in respective amounts of 100, 20, 100 and 100 ppm are studied in a base gas composed of 12% O2 and 1.5% H2O, balanced with N2. The sensor signal (&#916Vref) is the difference of potential between the reference (Pt) and the working electrode. In order to take into account irreproducibility of the sensors due to fabrication process, all tests are reproduced with two sensors (A and B). Since NO2 is an oxidizing gas, the galvanostatic mode can only produce the electro-chemical reduction of NO2 at working electrode. Figure 1a shows the variations of the potential at 450 °C for different gases by applying a polarization current of 25nA from working to counter electrode. In these conditions, the responses to other interfering gases such as CO and NH3 are removed while there is relatively a good selectivity towards NO2. Concerning ammonia gas sensors, Au-V2O5 working electrodes displayed a high sensitivity to NH3 as well as fast response and recovery times at 600 °C (figure 1b). In order to achieve an integrated NOx and ammonia sensor, which works simultaneously at the same temperature, further investigations are needed.

International audience

International audience; Spent fuel pools (SFPs) are large structures equipped with storage racks designed to temporarily store irradiated nuclear fuel removed from the reactor. In case of prolonged loss of cooling conditions or in case of a loss of coolant accident, the pool water may drop below the top of the spent fuel assemblies. The uncovered part of the fuel would be exposed to a steam/air mixture and the exothermal oxidation process of the cladding would result in a fast degradation of the fuel assembly and to the release of fission products.