Saturnisme | EPFL Graph Search

vignette|Aux États-Unis, de 1976 à 1980, la diminution des taux de plomb dans l'air (plomb issu de l'essence plombée) a été nettement corrélée à celle de la plombémie (taux de plomb dans le sang). En France, selon l'INSERM, la plombémie (taux de plomb dans le sang) moyenne est ainsi passée de à en 1998, soit encore près de 3 fois plus qu'aux États-Unis en 1991-1994 (). Depuis, la moyenne est même aux États-Unis tombée à en 1999-2002 Le saturnisme est la maladie non transmissible (sauf de la mère au fœtus via le cordon ombilical, ou au bébé via l'allaitement) d'intoxication aiguë ou chronique par le plomb. Le plomb n'a aucun rôle utile connu dans l'organisme humain, animal, fongique ou végétal. Il est toxique au niveau cellulaire, quelle que soit sa concentration. Chez l'humain, le seuil légal de danger ou quantité maximale tolérée est en France de de plomb par litre de sang alors qu'il était de en 1976, mais le consensus scientifique est que ses effets négatifs sur le cerveau e

Quasi-elastic neutrino reactions on carbon and lead nuclei

Soheyl Massoudi

We examine neutral-current quasi-elastic neutrino-nucleus reactions on C-12 and Pb-208 targets. We use the relativistic mean field theory approach to describe the nuclear dynamics. We compute the cross sections for the scattering of 150, 500 and 1000 MeV neutrinos on a C-12 target and study the effect of the strange-quark content of the nucleon which appears in these reactions via the isoscalar weak current. We compare our results with the data of the MiniBooNE experiment for mineral oil (CH2). We also calculate the cross section for the quasi-elastic neutron knockout reaction of 20-60 MeV neutrinos on a Pb-208 target which is relevant to plans to use lead as a target material in future supernova neutrino detectors.

Iop Publishing Ltd2018

Mechanisms of degradation of concrete by external sulfate ions under laboratory and field conditions

Aude Chabrelie

The durability of concrete is a major challenge for the construction, which devotes one third to one half of its annual investment to building maintenance. The lack of field data regarding concrete durability, especially in the case of exposure to sulfate ions ("sulfate attack") makes it difficult to determine the appropriate test methods and performance criteria. Additionally, the increased use of blended concretes (cement with mineral admixtures) suffers from a lack of experience regarding their long-term performance. Most results for sulfate resistance are derived from accelerated laboratory tests where performance criteria are based only on macroscopic properties, especially expansion. To fill this gap and better understand the mechanisms of sulfate attack under real conditions, a parallel study of laboratory micro-concrete and field concrete samples under sulfate exposure was undertaken, focussing on microstructural changes in addition to the typical macroscopic characterisation. Four exposure regimes were designed in the laboratory: full immersion (traditional test in "ponding"), pH-control, semi-immersion and wet/dry cycles. Pure Portland blends and slag blends with high level of slag replacement (70 wt.-%) were investigated. The exposure regime has been found to play a main role in the damage process. In ponding conditions, the damage process takes place three stages characterised by a first period of induction, followed by surface damage that finally extends to the bulk of the material. Paradoxically, the w/c-ratio does not seem to have much impact on the ionic transport phenomena but might be more decisive in the microstructure mechanical strength against local stresses. The slag blends, considered as sulfate resistant in ponding exposure, revealed bad performance under wet/dry cycles. This behaviour was attributed to poor proper physical resistance of the slag hydrates to the applied drying. Field observations tend to confirm the laboratory results and validate the test settings. It has been underlined that a direct relationship between the damage (e.g.; cracking/expansion) and the phase assemblage was not evident. However, the study highlights that sulfate combination with the hydrates of cement (e.g.; C-S-H) and to those of slag was found to play a role in the initiation of expansion, which would be initiated either by a swelling of the hydrates or by the precipitation of fine ettringite when the saturation level in sulfate of the hydrates has been reached.

EPFL2010

Self and induced stabilized nanoparticles for electrocatalysis

Mériadec Limat

Since few decades the search of new catalysts formulations for fuel cell applications has motivated numerous projects especially due to the future lack of fossil fuel, environmental and economical reasons. Consequently, Direct Alcohol Fuel Cell (DAFC) or Direct Formic Acid Fuel Cell domains have received great attention. In spite of the promising results reported recently, these types of fuel cell still exhibit some problems. In fact, platinum, bulk or nanoparticles, undergoes surface poisoning involved by intermediates (as acetaldehyde, acetic acid, carbon monoxide) which are strongly bonded to the surface. These poisoning species block the active sites at the surface electrode and drastically decrease the catalytic activity and also the life-time of the cell. Probable solutions are suggested essentially in Pt-based alloys catalysts or nanocatalysts in order to avoid this phenomenon. Therefore, multicomponent catalysts deposited at carbon electrodes (Boron-Doped Diamond and Highly Oriented Pyrolytic Graphite) has been investigated during this thesis. These two substrates have been chosen due to their outstanding properties. In the first part of this study, self stabilized nanoparticles at BDD substrate have been studied. Ex-situ ternary Pt-Ru-Sn microemulsion-synthesized nanoparticles deposited at BDD substrate were investigated towards both methanol and ethanol electrooxidation. Such type of composite electrode seemed to possess a greater efficiency towards methanol oxidation than observed for ethanol, leading essentially for the latter to C2 oxidation products. The inability of this catalyst to activate the C-C bond scission can explain this observation. However, the major enhancement was observed for the methanol electrooxidation. Recent studies have shown that gold nanoparticles exhibited surprising catalytic activity, very different from the bulk, making them a privileged candidate to replace or be added to platinum. Gold nanoparticles prepared with a twofold technique (sputtering followed by a heat treatment in air) have been characterized with both outer and inner-sphere redox reactions. It has been observed that the resulting electrochemical behavior of such type of composite electrode was similar to a gold microelectrodes array, due to the high difference between the two material electrochemical rate constants. In a morphological point of view, the processes of nucleation and growth engaged in the stabilized and well-dispersed gold nanoparticles formation have especially attracted a great attention. At BDD surface, the gold nanoparticles were located at specific sites (grain boundaries, defects, impurities,…). This phenomenon has motivated further investigations at HOPG substrate, known to possess a quite smooth and perfect surface. In the second part of this thesis, induced stabilized nanoparticles at HOPG surface were studied. In a first time, HOPG was morphologically and electrochemically characterized. The surface state has appeared to be a key parameter, essentially with the presence of the two surface species, the edge plane and the basal plane. High modifications in the electrochemical behavior of HOPG electrode were observed after an anodic pretreatment in acidic media, due to surface concentration increase of the edge plane species, which are highly reactive. Based on these results a tailoring of the HOPG has been performed in order to create nanocontainers for a further gold deposition. HOPG surface has been bombarded by gold clusters and then oxidized (etching step) under well-defined experimental conditions, leading in a tailored pattern of nanopits with high reliability and reproducibility. Gold deposition was performed by evaporation. The gold nanoparticles were located in the created nanocontainers and were found to be stable under cyclic voltammetric measurements in acidic media. A new synthesis method for a bimetallic or alloy system formed by Au and Pt nanoparticles stabilized at tailored HOPG surface was developed. Pt electrodeposited at Au/HOPG electrode surface have been observed to preferentially deposit on Au. In fact, gold nanoparticles were used as nucleation sites for the platinum particles. The resulting Pt-Au/HOPG electrodes were then heated at 400 °C in vacuum conditions to improve interactions between both metals. The appearance of an alloy was observed and characterized by a negative shift in the peak potential of Pt oxides reduction. Thanks to these results, Pt-Au/HOPG composite electrodes were applied for electrocatalytic oxidation. At a surface composition of P55-Au45 alloy, Pt-Au/HOPG after the heat treatment has demonstrated a higher electrocatalytic activity than before the heat treatment towards formic acid electrooxidation. It seemed that electronic and geometrical effect was responsible of such enhancement. Finally, bismuth adsorption at both P55-Au45/HOPG and polycrystalline platinum was investigated towards formic acid electrooxidation. The effect of Bi adatoms has been essentially ascribed to geometrical restrictions for CO to adsorb at platinum active sites. Drastic enhancement in current density at a fixed potential and dramatic decrease of the onset potential of formic acid oxidation were observed. Thus, it seemed that avoiding the CO poisoning can be the most judicious development for new electrocatalysts in fuel cell applications.

EPFL2009