Tesi sul tema "Dégradation de la membrane"
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Coulon, Romain. "Modélisation de la dégradation chimique de membranes dans les piles à combustibles à membrane électrolyte polymère". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00767412.
Oliveira, Filho Marcos Antônio. "Etude de la dégradation des membranes de filtration polymères exploitées en bioréacteurs à membranes". Thesis, Toulouse 3, 2022. http://www.theses.fr/2022TOU30060.
While membrane bioreactors (MBR) have been broadly applied to wastewater treatment, a comprehensive study of the aging of membrane materials under operating conditions of MBR at full-scale is necessary in order to understand and to anticipate it. Thus, the present research aim (i) to analyse the chemical action of sodium hypochlorite to commercial polyvinylidene difluoride (PVDF)/Polyvinylpyrrolidone (PVP) hollow fibers used in MBR, (ii) to describe membrane ageing of such materials in urban wastewater full-scale MBR based on a coupled characterization of harvested membranes and full-scale process indicators. To that end, ZeeWeed® 500D membranes were aged at bench-scale by single soaking in hypochlorite solution at a concentration (1000 ppm) and pH (9.0) similar to MBR cleaning protocols. In addition, membranes were sampled between 2016 and 2021 from modules from two urban wastewater treatment plants (capacities of 50,000 m3/d and 300,000 m3/d, respectively). Simultaneously, process data were collected and analyzed. Both bench-scale and full-scale aged hollow-fibers were characterized using similar analytical methods and compared considering the chlorine exposure dose (C x t). Significant differences were found between ageing mechanisms at both scales. At bench-scale, membranes presented stable mechanical properties. Three distinctive phases were observed for the changes on intrinsic permeability with an initial increasing phase up to a C x t of 78,000 ppm.h (+ 90% with respect to the initial permeability), because of hydrophilic agent degradation and the formation of small pores (diameter < 20 nm). Then, a decreasing phase is observed (from 78,000 ppm.h to 150,000 ppm.h), caused by a decline in porosity, likely due to a restructuration of PVDF chains. After 150,000 ppm.h, intrinsic permeability seemed to fluctuate around its initial values. At full-scale, a decline in mechanical properties is highlighted, probably linked to the dynamic conditions in the MBR (i.e. filtration, aeration and backwashing). Moreover, an increase in permeability is observed during the studied period (< 98,000 ppm.h) because of a more pronounced oxidation/dislodgement of PVP molecules (25% vs 40% from the initial PVP content, for full- and bench-scale respectively) leading to a higher porosity and the appearance of bigger pores (diameter > 40 nm). These changes favored irreversible fouling in contrary to bench-scale ageing. At full-scale, permeability index (the ratio of permeate flux and transmembrane pressure during the process) after each cleaning-in-place protocol decreases to around 20% over the studied period for both facilities. This decline is well correlated to the PVP content and intrinsic permeability, allowing the determination of key indicators to monitor membrane ageing. This study showed that understanding the mechanisms behind the action of NaOCl on supported PVDF membranes may not represent what actually occurs at full-scale operation. A non-negligible contribution of filtration conditions, mechanical stress due to aeration and backwashes, and residual fouling, specific to onsite operating conditions, may significantly change ageing mechanisms. Continuous autopsies of harvested fibers over the years and monitoring consistent full-scale operating indicators are still needed
Pellegrin, Bastien. "Analyse multi-échelle de la dégradation de membranes d'ultrafiltration en polyethersulfone - poly(N-vinyl pyrrolidone) en conditions d'usage". Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2084/.
Motivated by drinking water production plants reporting membrane failure issues, this study investigates the ageing of a commercially available PES / PVP UF hollow fiber. Proof is given that membrane degradation is mainly induced by sodium hypochlorite exposure. The effects on the PES chemical structure are limited, very low extend of chain scission occurs and the formation of an ortho-substituted phenol is observed as the main modification. Experiments show that the presence of PVP and/or PVP degradation products is a required condition for the PES oxidation to occur. On the other hand, PVP appears to be very sensitive to hypochlorite exposure. PVP radical oxidation mechanisms are identified presenting a maximal reaction rate for neutral to slightly basic pH and leading to the partial removal of the PVP degradation products from the membrane structure. Correlation of macroscopic and molecular characterizations demonstrates that PVP degradation is responsible for the membrane integrity loss (impairing selectivity and mechanical performance), while hypochlorite exposure also induces enhanced membrane / solutes interactions, leading to an accentuated fouling. The representativeness of static continuous hypochlorite exposure regarding the actual on-site membrane ageing is confirmed by the analysis of membranes extracted from an industrially operated module. Nevertheless, the hypochlorite dose parameter, widely used in the literature, is demonstrated to be inappropriate to describe the degradation rate: the hypochlorite concentration impact is shown to be dominating the exposure time impact on the degradation rate
Péron, Jennifer. "Nouvelles membranes de polybenzimidazoles sulfonés pour application en pile à combustible : étude des mécanismes de dégradation des assemblages membrane-électrodes". Montpellier 2, 2007. http://www.theses.fr/2007MON20108.
His work is related to the development of PEM fuel cells. The first part of the manuscript describes the preparation of new sulfonated polybenzimidazoles, allowing to obtain proton conducting membranes, using two different ways: direct sulfonation of the polymer backbone under mild conditions, introduction of a sulfonated monomer during polymer synthesis. Direct sulfonation lead to highly proton conducting polymers that can be used as polyelectrolyte in electrochemical devices like fuel cells. The second part describes the study that has been done to determine membrane-electrodes (MEA) degradation mechanisms during fuel cell operation. MEA characterisation during, and after, running at high potential allow us to evidence catalysts dissolution, and further migration, in the perfluorosulfonated ionomer. Pt(II) species present in the ionomer lead to radical formation and causes electrolyte degradation
Gaudichet-Maurin, Emmanuelle. "Caractérisation et vieillissement d'une membrane d'ultrafiltration d'eau". Phd thesis, Paris, ENSAM, 2005. http://pastel.archives-ouvertes.fr/pastel-00001528.
LACOMBE, CHRISTIAN. "Métabolisme du cardiolipide chez B. Subtilis : synthèse, dégradation, régulation, topologie". Poitiers, 1987. http://www.theses.fr/1987POIT2002.
Perrot, Carine. "Mécanismes de dégradation des membranes polyaromatiques sulfonées en pile à combustible". Phd thesis, Université Joseph Fourier (Grenoble), 2006. http://tel.archives-ouvertes.fr/tel-00145619.
Cette étude porte sur la compréhension des mécanismes mis en jeu lors du vieillissement de membranes alternatives, non fluorées, de type PEEKs et PIs, étape indispensable au développement de structures plus stables. Dans ce cas, le processus est avant tout chimique. Une démarche originale, qui consiste à étudier le mécanisme de dégradation sur des structures modèles, a été adoptée afin de contourner les difficultés analytiques propres aux polymères. Les vieillissements sont réalisés dans l'eau, éventuellement additionnée de H2O2 (identifié comme une des causes du vieillissement chimique des membranes en pile), à différentes températures. La démarche consiste à isoler par chromatographie les différents produits formés, à les identifier (RMN, IR, SM) et à les quantifier. Ceci nous a permis d'établir le mécanisme de vieillissement. Nous avons en particulier montré que le vieillissement d'une structure PEEKs résulte principalement d'une attaque par les bouts de chaîne qui se propage à l'ensemble. Ce mécanisme a été validé sur une membrane vieillie en ex-situ et testée en pile. Ces deux types de vieillissement conduisent à une diminution importante du degré de polymérisation (déterminé par CES) et à la formation des mêmes produits primaires de dégradation. En pile, une dégradation hétérogène est mise en évidence essentiellement côté cathode.
Les PIs sont connus pour leur forte sensibilité à l'hydrolyse. Toutefois, nous avons pu montrer que la dégradation est relativement limitée à 80°C en raison d'une recombinaison des espèces hydrolysées.
Zhao, Zuzhen. "Détermination des mécanismes de dégradation d'électrodes modèles de pile à combustible à membrane échangeuse de protons". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00764891.
Sellin, Rémy. "Dégradation de catalyseurs Pt-C sous des conditions mimant celles d'une PEMFC en fonctionnement". Poitiers, 2009. http://theses.edel.univ-poitiers.fr/theses/2009/Sellin-Remy/2009-Sellin-Remy-These.pdf.
Fuel cell Pt/C catalysts were prepared via different colloidal methods. TGA, TGAMS, TEM and XRD studies from 323 to 573 K were carried out under oxidative and reductive atmospheres to mimic fuel cell anode and cathode working conditions and to accelerate ageing process. Under air flow, little aggregation of platinum is observed, but no fusion and increase of Lv. This is explained by the presence of oxygen species on the platinum surface. Under reductive atmosphere (H2 3%/He), aggregation and increase of the mean crystallite size are observed. Two kinetics of grain growth process seem to exist. Moreover, the carbon support undergoes degradation by combustion under air and reforming under reductive atmosphere. The effect of thermal treatment under controlled atmospheres on the electrochemical active surface area and on the electrocatalytic activity towards oxygen reduction reaction and CO oxidation of the Pt/C catalyst were evaluated
Terrisse, Anne-Dominique. "Modulation de l'activité des cellules tueuses naturelles par les fragments de dégradation de la chromatine". Toulouse 3, 1993. http://www.theses.fr/1993TOU30169.
Galan, Jean-Marc. "Mécanismes de dégradation de l'uracile permease, une protéine de la membrane plasmique de la levure saccharomyces cerevisiae". Paris 7, 1998. http://www.theses.fr/1998PA077059.
Parra, Restrepo Julian. "Caractérisation des hétérogénéités de fonctionnement et de dégradation au sein d’un électrolyseur à membrane échangeuse de protons (PEM)". Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0044.
Proton Exchange Membrane (PEM) electrolysis is among the best solutions to store energy from intermittent power sources such as solar and wind. The green hydrogen produced by this technology can meet the needs of industries that already consume hydrogen or can be used for new applications such as fuel cell cars. To continue the deployment of PEM electrolyzers, it is necessary to increase their lifetime and the active surface area of cells. By doing this, operating heterogeneities related to the distribution of gas/water, current and temperature may appear. This work aims to characterize the aging mechanisms and the heterogeneities that have a negative impact on the performance of the electrolyzer. A segmented cell for measuring local current densities and local potentials was developed. Different titanium porous transport layers (PTLs) were characterized and their influence on the transport of electrical charges and gas/water has been analyzed, which allowed identifying problems related to the variation of PTL microstructure along the electrolyzer. Also, a model describing the contact resistance between the catalyst layer and the PTL was proposed. The membrane temperature between the inlet and the outlet of the cell was estimated with an innovative method based on the electrochemical impedance spectroscopy. This method allowed characterizing the temperature differences with the water circulating in the channels as a function of current density. An accelerated stress protocol was developed and the influence of intermittent operation was studied. A critical potential threshold that accelerates aging was identified and performance recoveries linked to periodic drop of the cell potential were observed
De, Cazes Matthias. "Conception et étude d'un bioréacteur enzymatique à membrane pour le traitement d’effluents contenant des micropolluants réfractaires d'origine pharmaceutique". Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20052.
Pharmaceutical micropollutants such as antibiotics, hormones, anti-inflammatory or anti-cancer drugs are usually reluctant to conventional wastewater treatment processes and their disposal in the environment, even at low concentrations (< µg/L) may have an impact on human health. The enzymatic treatment of these effluents seems a promising alternative if the biocatalyst is immobilized on a membrane to enhance its stability and to enable its reuse. This thesis work aims at designing and optimizing bioreactors for micropollutants degradation. It is a collaboration (ENDETECH project) with other European research teams in charge of selecting the biocatalysts and developing analytical methods for the detection and characterization of transformation products
Azrague, Kamal. "Couplage entre photochimie et membrane pour la dépollution d'eaux turbides : mise au point d'un photoréacteur à membrane et étude cinétique et mécanistisque de la dégradation de polluants organiques". Toulouse 3, 2005. http://www.theses.fr/2005TOU30230.
This work was carried out in the field of the depollution of turbid water by an original method combining membranes and photochemistry processes. Two types of photoreactor with membrane were developed, one using the photocatalysis (irradiation of a semiconductor: TiO2), the other using V-UV photolysis process (V-UV: irradiation at 172 nm wavelenght). The advantage of these hybrid water and processes is that they can be applied to the depollution of limpid water, but also of turbid water and even of muds in aqueous suspension. For this study, the polluant models selected is the 2,4-dihydroxybenzoic acid (DHBA), contaminant agent resulting from the oxidation of the salisylic acid. The mineralisation of this compound was obtained for all photochemical processes used. The evolution of the various intermidiates formed during degradation was followed by various complementary analytical methods (UV-visible spectroscopy, GC, HPLC, HPLC/MS, TOC measurements). This study allows highlighting a different mechanism for the photocatalysis and V-UV photolysis. Indeed, in photocatalysis this compound reacts exclusively with the positive holes (h+) formed on the photocatalysor wheareas in V-UV photolysis an original mechanism of degradation of the DHBA implying only the hydroxyl radicals has been proved. Moreover, starting from the kinetics of mass transfer and degradation of the DHBA, it was possible to estabilish very good mathematical models describing the evolution of the pollutant in all compartments of the process. These models will allow, in an immediate future, to the dimensioning of pilot units
Zaton, Marta. "Study of the degradation of perfluorosulfonic acid fuel cell membranes and development of mitigation strategy". Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20197.
This thesis describes the study the chemical degradation of perfluorosulfonic acid (PFSA) membranes used in proton exchange membrane fuel cells, in order to gain a better understanding of the mechanisms leading to failure, and to propose strategies to mitigate this degradation. Studies of membrane chemical decomposition were performed on pristine Nafion and on cerium and manganese ion exchanged membranes. The effectiveness of Mn and Ce species as free radical scavengers was studied by using accelerated stress tests: in situ in a single fuel cell under open circuit voltage (OCV), and ex situ using Fenton's reagent. Membrane chemical degradation was assessed by the fluoride emission rate (FER). Significant reduction in FER was observed with Mn and Ce ion modified Nafion. These observations were related to the fuel cell performances losses and migration or elution of metal ions, as evaluated by SEM/EDX and HPLC, and to changes in the oxidation state of the metal species, determined by XPS. The results have been used to provide further guidance on materials strategies to mitigate membrane chemical degradation. A composite nanofibre CeOx/PFSA mat was prepared by electrospinning of a mixed dispersion of Nafion® ionomer with CeOx nanoparticles synthesised by flash combustion. The electrospinning technique allows fabrication of a homogenous material with well controlled thickness and highly dispersed CeOx. This mat was assembled with PFSA membranes by hot-pressing. These nanofibre mats are the means of siting the CeOx radical scavenger specifically in close proximity to one or other catalyst layer, rather than distributed throughout the membrane. The new membranes were further investigated by OCV hold testing in a fuel cell. The results show that MEAs integrating a non-modified PFSA membrane, or a PFSA membrane modified by an interlayer of nanofibre PFSA (no CeOx) only, demonstrate a marked drop in OCV with time, and high FER. In contrast an MEA comprising a CeOx nanofibre interlayer gives very stable open circuit voltage and low fluoride emission. Finally it was observed that the nanofibre – ceria interlayer is more effective when incorporated at the anode side. Post mortem analysis of the MEAs and analysis of exhaust water were combined to draw a picture of the overall degradation processes occurring in cerium oxide protected and non-modified MEAs. X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy analyses of aged MEAs indicated a lower degree of degradation for CeOx protected membranes than for a non-modified PFSA membrane. These results are in agreement with OCV profile and fluoride emission rate. In conclusion this new approach to the strategy of incorporating of radical scavengers to mitigate membrane chemical degradation efficiently increases membrane durability, and allows location of the radical scavenger within the MEA at the sites potentially most exposed to radical attack
Monin, Guillaume. "Stabilisation chimique des électrolytes polymères pour pile à combustible". Phd thesis, Université de Grenoble, 2012. http://tel.archives-ouvertes.fr/tel-00728176.
Gaumont, Thomas. "Résistance protonique d’électrodes de piles à combustible à membrane (PEMFC) : effets de l’humidité et des dégradations". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0002/document.
This work focuses on the development of electrochemical impedance spectroscopy (EIS) methods to measure the protonic resistance of PEMFC active layers. Experimental spectra of a cathode fed with nitrogen are fitted to a volumetric electrode impedance model to yield the protonic resistance of the electrode and that of the membrane in controlled humidity conditions. In addition, EIS measurements are performed on a cathode fed with oxygen, delivering current and producing water. The protonic resistances of the membrane and of the electrode are obtained in several conditions of gas stoichiometry and of current density. The effective humidity within the membrane and within the electrode is estimated using the calibration obtained in controlled humidity conditions. Thus, the monitoring of a MEA self humidification is achieved with spatial resolution using a segmented cell designed in our lab. The effective humidity is higher in the catalyst layer than in the membrane. A second part of this work is dedicated to the catalyst layer degradations. Accelerated stress tests consisting in a membrane chemical degradation protocol, a carbon degradation protocol, a start-up protocol and a dry operation regime are performed. A compaction of the electrode due to carbon corrosion is detected during start-up protocols. A strong chemical attack of the ionomer has been observed within the membrane, close to the cathode side. However, no degradation of the ionomer within the cathode has been measured
Cordier, Baptiste. "Compréhension des processus cellulaires associés à l' enveloppe de Bacillus subtilis : GluP, une protéase intramembranaire impliquée dans la dégradation des protéines membranaires & CmmB, un cofacteur de la synthèse de la paroi bactérienne". Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4006.
The bacterial cell envelope is an obligatory barrier. It is a fundamental component in essential cellular processes such as morphogenesis and cell division. It hosts about a quarter of the proteins encoded in the genome. My work was aimed at understanding the function of two membrane proteins in the building and the dynamics of the cell envelope in the model bacterium Bacillus subtilis.GluP is a rhomboid intramembrane protease. Usually, rhomboids cleave transmembrane segments within the membrane to modulate protein functions. In eukaryotes, they participate in many cellular processes and their dysfunction lead to several pathologies. However, prokaryotic rhomboid functions remain almost totally unknown. Our results suggest that GluP is involved in bacterial membrane protein quality control, in a process akin to pseudo-rhomboid dependent endoplasmic reticulum associated protein degradation in eukaryotes. GluP forms a complex with FtsH, a major protease in protein quality control. That complex is not involved in the cleavage of a membrane substrate but in its degradation. We propose that GluP is required for the dislocation of the transmembrane segment, thus facilitating full-length substrate degradation by FtsH in the cytoplasm. My thesis second objective was to understand the role of the CmmB protein in morphogenesis. The absence of CmmB leads to slightly enlarged cells. CmmB seems to belong to the peptidoglycan synthesis machinery for cell-wall elongation. Our data support the idea that it is required for the proper activity of one or several penicillin-binding proteins (PBPs). In particular, we propose that CmmB is a cofactor of the PBP2a transpeptidase
Touhami, Salah. "Apparition, détection et propagation des défauts à l'anode des piles à combustible à membrane échangeuse de protons". Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0151.
Defects known to shorten the lifetime of polymer electrolyte membrane fuel cells (PEMFC) can appear on different membrane electrode assembly (MEA) components and under different forms due to manufacturing processes or operational aging of the fuel cell. This work concerns the occurrence, detection, and propagation of defects in PEMFC MEA, and more specifically at the anode. To this end, an accelerated stress test (AST) combining potential and humidity cycles -induced by load variations-, and open-circuit hold is applied to standard MEA, and to MEA with initial defects. Those customized MEA were intentionally prepared with a lack of active layer at the anode, the defect being located either near the hydrogen inlet or near the hydrogen outlet. Periodic electrochemical characterizations were carried out using a segmented instrumented linear cell, allowing to monitor the cell performance through the currents, electrode potentials, and local impedance, as well as the evolution of the electrochemical active surface (ECSA) at the anode and cathode during the ageing test, with a spatial resolution along the channels. An electrochemical impedance spectroscopy study was conducted jointly, using equivalent electrical circuits, and focusing on the detection of the anodic contribution to the global impedance of the cell. Results showed an accelerated degradation of the MEA and the first evidence of defect propagation, in terms of loss of ECSA at the anode. This propagation occurred in the direction of the hydrogen flow. The ECSA at the cathode also appeared to be impacted, although apparently homogeneously. Significant membrane thinning was also observed in the defective segments, with probable propagation to adjacent segments, but over a longer time period
Hanafi, Yamina. "Étude de la dégradation de membranes en polyéthersulfone / polyvinylpyrrolidone au contact de l’hypochlorite de sodium". Thesis, Rennes 1, 2017. http://www.theses.fr/2017REN1S170.
During industrial operations, filtration polymer membranes are regularly chemically-stressed during cleaning and disinfection steps. Although these latter are still unavoidable to restore the membrane performance and to prevent the proliferation of microorganisms, they lead, however, to membrane premature ageing, which impairs the membrane separation properties. The aim of this thesis was to investigate the impact of sodium hypochlorite, a widely used cleaning and disinfection agent, on polyethersulfone (PES) / polyvinylpyrrolidone (PVP) membranes. Electrokinetic measurements highlighted the degradation of PES, although the chemical resistance of this latter is well-acknowledged. The degradation of PES occurred through two distinct mechanisms depending on the pH of the sodium hypochlorite solution: (i) the PES-chain scission, which was found to result mainly from the HClO species, and (ii) the hydroxylation of the PES aromatic rings by the °OH free radicals that are formed in the sodium hypochlorite solution. Moreover, the degradation of PVP by a ring opening mechanism and its partial release from the membrane were confirmed. Experiments carried out with pure PES membranes as well as with PES / PVP membranes with different PVP contents showed that the PES-chain scission mechanism occurred whatever the PVP concentration. On the other hand, the presence of PVP was found to promote the hydroxylation of the PES aromatic rings. Furthermore, the PES-chain scission mechanism appeared to play the major role in the worsening of the membrane filtration performance. Under the ageing conditions of this study it seems that neither the PES hydroxylation nor the PVP degradation play a significant role in the worsening of the membrane rejection properties. Finally, the membrane structure was found to be substantially altered by the action of sodium hypochlorite, especially for membranes containing PVP
Ros, Manon. "Implication du collagène de type I, de son organisation et de sa dégradation dans la progression tumorale". Thesis, Bordeaux, 2020. http://www.theses.fr/2020BORD0267.
Metastasis is one of the leading causes of cancer death. During this process, tumor cells acquire invasive capacities in order to degrade the extracellular matrix (ECM) and invade surrounding tissues. Type I collagen is the main component of the ECM, and the enzymes mediating collagen peptidic cleavage (MMPs) are well characterized.Tumor invasion has been shown to be stimulated by activation of the GALA pathway, inducing a general increase in O-glycosylation. In the first project, we show that the ER resident protein calnexin is hyperglycosylated when GALA is activated, in vitro as well as in vivo in mouse and human liver tumor. In these conditions, calnexin and its ER binding partner ERp57 are relocated to the invadosomes, which are structures involved in ECM degradation. We could highlight that calnexin/ERp57 complex is an oxidoreductase essential for collagen degradation. Indeed, once in invadosomes, they reduce extracellular collagen disulfide bond before collagen cleavage by MMPs. In vivo, liver tumor growth and lung metastasis of breast and liver cancer cells are inhibited by anti-Cnx antibodies. We could highlight that collagen disulfide bond reduction is a key step in ECM degradation and tumor invasion.In a second project, we focused on cell migration, which is a key step during tumor progression and metastasis formation. Several structures and cell-cell communication processes (such as migrasomes, exosomes or extracellular vesicles) are already shown to promote tumor cell migration. Indeed, these mechanisms allow cells to release cellular content in order to induce or inhibit cellular processes, including cell migration.Here we described new structures made by cells during cell migration. These structures are membrane depositions found outside the cell, along type I collagen fibers. They composed of several protein families such as collagen binding receptors. These structures look to be involved in cell-cell communication to promote tumor migration and could provide a new process involved in tumor migration
Scohy, Marion. "Mécanismes de dégradation des catalyseurs modèles anodiques à base d'iridium dans les électrolyseurs de l'eau PEMWE". Thesis, Université Grenoble Alpes (ComUE), 2019. http://www.theses.fr/2019GREAI058/document.
With the need for a drastic reduction of greenhouse gases, the deployment of fuel cells is one of the considered solutions. Decarbonated hydrogen production is subsequently a major challenge to enable an efficient energetic transition. From this perspective, Proton Exchange Membrane Water Electrolyser (PEMWE) is a technology of interest, especially if coupled with renewable energy sources. Key challenges are still to be addressed before commercializing this technology, in particular at the anode. Iridium oxide, a costly and rare material, is implemented in anodic catalytic layers to catalyse the Oxygen Evolution Reaction (OER) while being resistant to harsh acidic and oxidative conditions. It nonetheless undergoes some degradations.In this work, different iridium model surfaces for the OER where studied to understand mechanisms involved during the first oxidations step and oxygen evolution. After characterisations by Dynamic Electrochemical Impedance Spectroscopy (DEIS), an innovative technique used to study dynamic systems, structure-activity-stability relationships towards the OER were studied by comparing iridium model surfaces ((111), (210) and nanostructured (210)). Results showed that after few hours at high potential (> 1.6 V vs. Reversible Hydrogen Electrode)), these surfaces, with different initial chemical compositions and structures, tend to the same state. Finally, iridium and nickel@iridium thin films were studied, to model core@shell particles. Results indicate that the nickel dissolution lead to the formation of a porous layer more active towards the OER. These findings could help to design active iridium catalysts for the OER
Meyer, Gilles. "Etude des modes de dégradation de membranes polyimides sulfonés en pile à combustible H2/O2". Clermont-Ferrand 2, 2004. http://www.theses.fr/2004CLF21533.
Combernoux, Nicolas. "Traitement d'effluents nucléaires aqueux : étude de la dégradation des membranes d'osmose inverse sous irradiation gamma". Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4374.
The treatment of nuclear liquid wastes by reverse osmosis (RO) involved issues of the water radiolysis and the membrane ageing due to ɣ irradiation effects. Membrane performances (permeability, strontium and cesium retention) were assessed after ɣ irradiation. Irradiation was carried out with an external 60Co source in different conditions that simulated real used of the process (dose from 0.1 to 1 MGy, dose rate of 0.5 and 5 kGy.h-1, with or without oxygen or water). Several analytical methods were performed to evaluate irradiation effects (ATR-FTIR, XPS, gas production, water soluble species released from the membrane). The methodology developed led to relevant information due to an innovative analytical protocol. Membrane performances started dropping between 0.2 and 0.5 MGy with oxygen and water (dose rate 0.5 kGy.h-1). This shift was linked to chains scissions inside the membrane active layer. The membrane degradation was weaker without oxygen or water or at high dose rate (5 kGy.h-1). Results showed that each analysis comforted each other. Membrane performances were also evaluated with three different types of liquid effluents, representing radioactive effluents from a post-disaster situation (groundwater type), disaster situation (seawater) or process water. Experiments were carried out at lab and pilote scales. Results indicated that the treatment of each effluent was possible by RO with an adequate choice of membrane and operating parameters. Finally, the time to reach an integrated dose threshold for the membrane in real conditions was estimated with the RABBI software : a dozen of days in the case of disaster situation to several years in the two other cases
Prulho, Romain. "Analyse multi-échelle de la dégradation de membranes polymères d'ultrafiltration au contact de l'hypochlorite de sodium". Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2013. http://tel.archives-ouvertes.fr/tel-00866935.
Kergomard, Jeanne. "Activité enzymatique sur lipides végétaux : couplage de mesures interfaciales à l'échelle moléculaire (nm) et de mesures cinétiques de dégradation à l'échelle de l'objet (µm)". Electronic Thesis or Diss., Rennes 1, 2022. http://www.theses.fr/2022REN1S075.
Health organizations now recommend diversifying and increasing our dietary intake of polyunsaturated fatty acids (PUFA) omega-3, which are essential for the proper functions of our cells. To meet these recommendations, plant membranes, and in particular photosynthetic membranes, represent a real potential, as they contain specific lipids, and in particular galactolipids, whose degradation by enzymatic reactions provides PUFA omega-3. Due to their particular composition, these systems present phase coexistences and thus lateral heterogeneity impacting their digestibility. In order to optimally exploit plant lipid sources, it is necessary to understand their fate in the human gastrointestinal tract. The results obtained in this research work provide an in-depth understanding of the mechanisms of interaction between digestive enzymes and plant membrane assemblies. In particular, this work is the first to investigate the digestion of heterogeneous monolayers of galactolipids and phospholipids by close analogues of the main enzymes responsible for the gastrointestinal degradation of plant lipids in humans. The originality of this study is based on a thorough characterization of the interfacial behavior of plant lipid systems, presenting a chemical heterogeneity inducing a physical heterogeneity. The digestibility of these heterogeneous plant lipid assemblies was studied at the molecular scale, but also at the micronic object scale. This work allowed to report the substrate specificity of the studied lipases and phospholipases (rDGL, sPLA2-IB, gPLRP2) on plant polar lipids. In particular, the galactolipase, but also phospholipase A1 activities of gPLRP2 were observed in heterogeneous galactolipid and phospholipid systems. The genericity of action of these enzymes with respect to the physical state of the membranes has also been demonstrated. We demonstrate here that at the lipid interfaces, a high content of polyunsaturated acyl groups can amplify the local compressibility and be an asset for the insertion of digestive lipases. This physical aspect remains to be confronted with the chemical specificity of the enzyme. Overall, plant lipid assemblies are rich in polar lipids and particularly galactolipids, which concentrate significant quantities of omega-3 PUFA, and are bioaccessible under model conditions under the action of gPLRP2. These assemblies also exhibit surface-active and oxidative stability properties characterized in this work. The galactolipase activity of PLRP2 at the level of modulable model membrane monolayers, but also at the level of natural membrane assemblies, opens the way to the development of plant-based dietary alternatives to vectorize omega-3 PUFA, and contribute to rebalancing human and animal diets
Akiki, Tilda. "Modélisation de la dégradation de la production de puissance d'une pile à combustible suite aux sollicitations mécaniques". Phd thesis, Université de Technologie de Belfort-Montbeliard, 2011. http://tel.archives-ouvertes.fr/tel-00607268.
De, Moor Gilles. "Approche multi-échelle des mécanismes de vieillissement des coeurs de pile à combustible". Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAI049/document.
In spite of strong improvements in fuel cell design this last ten years, Proton Exchange Membrane Fuel Cell are still suffering of premature end of life. Failure of the heart of fuel cell, composed of membrane and catalysts, is commonly responsible for fuel cell shutdown. This work brings an original contribution in understanding membrane degradation mechanisms. Different ageing tests were analyzed, in laboratory as well as in real life operating conditions (up to 13000 hours of solicitations). Within a multi-scale approach, from macroscopic to microscopic, and with a systematic usage (hundreds of samples fully characterized), some degradation mechanisms were established. Firstly, macroscopic tools were specifically developed to rapidly track state of health of all the cells from each stack. With the help of these tools, we were able to identify defects inter and intra-cell. It was also possible to discriminate between gas crossover or electronic short-circuit defects, both responsible for current leaks. This systematic approach on each samples put forward some specific areas within the membrane where degradation was promoted. Secondly, physico-chemical characterizations were performed on membrane targeted areas. It was shown that membrane degradation is strongly localized in some specific channels of the bipolar plates and favored by specific operating conditions in the gaz inlets areas
Martinez, Mathieu. "Nouvelles membranes conductrices protoniques à l’état anhydre". Grenoble INPG, 2009. http://www.theses.fr/2009INPG0173.
The purpose of this thesis was to study the effect of the starting acid (strength, structure, size, type…) and of the water concentration on the CLIP’s properties. We showed that thermal stability was controlled by the anion’s basicity and its nature (Td > 300°C). On the other hand, conductivity has been found dependent on the size and the type of the anion (best conductivities for small sized super acid anion). Membranes are based on the association of a CLIP with a polymer (Nafion®, sulfonate polysulfone, polyimide). Nafion® based membranes showed good conductivities but poor mechanical properties at high temperature. Sulfonated polysulfone based membranes have both low toughness and low conductivities. The last studied electrolyte, based on macroporous polyimide, exhibited the highest conductivities and the best thermomechanical properties; they seem to be the most adapted membranes for the PEMFC application
Lamibrac, Adrien. "Étude des dégradations dans les piles à combustible PEMFC pendant les phases de démarrage/arrêt". Thesis, Université de Lorraine, 2013. http://www.theses.fr/2013LORR0117/document.
This works contributes to the identification of the various degradation mechanisms in Polymer Electrolyte Membrane Fuel Cell during start-up and shut-down operations. Single start-ups and shut-downs are first analysed using a cell with segmented cathode current collectors. Thus, internal currents which occur during these operations can be measured. Carbon dioxide measured in the cathode exhaust gas reveals that they result partially from carbon oxidation. Another contribution is the reversible or non reversible redox reactions involving platinum. The heterogeneity of the non reversible platinum oxidation between the inlet and outlet of the cathode is evidenced by the in-situ monitoring of the Electrochemical Surface Area during long-term start-up and shut-down aging protocols. Post-mortem analysis reveals another level of heterogeneity, which concerns also carbon oxidation, between land and channel. From these experiments, it appears also that degradations are more important when gases are injected with a low velocity in the anode compartment and when air is used instead of nitrogen to flush the anode compartment during shut-down. The influence of the MEA characteristics on the extent of the degradation observed during these aging protocols is also analyzed. High platinum loading in the anode and high surface carbon electrodes accelerate the drop of the electrical performances, while increasing the cathode platinum loading limits their decay. Finally, numerical simulations of start-ups complete the experimental results. Reversible platinum oxidation was found to be one of the main contribution to the internal currents
Mezzi, Rania. "Contrôle tolérant au vieillissement dans des systèmes pile à combustible PEMFC". Thesis, Bourgogne Franche-Comté, 2019. http://www.theses.fr/2019UBFCD031.
The objective of this work is to realize an aging-tolerant control for a proton exchange membrane fuel cell system (PEMFC). In order to achieve this goal, supervision tools, including the monitoring of critical variables, the state of health evaluation and the prediction of the future state are studied and realized. The information collected are used to adapt the system control strategy. The priority of the monitoring system developed is to ensure the energy supply required by the user, while ensuring minimal degradation of the fuel cell. The work consists on determining optimal temperature values, cathode and anode stoichiometry coefficients, and fuel cell current to provide the power required by the load, while extending the lifetime of the PEMFC. The proposed strategy avoids reversible damage and slows the aging rate of the components, while maintaining the value of the voltage in an optimal and low degrading operating range. This voltage variation range was determined by studying the degradation mechanisms of PEMFC
Maheshwari, Neeraj. "Biofuntionalisation of PLGA based polymer nanoparticles for vectorization : interaction with biomimetic lipid membranes and bio-controlled release". Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2357.
This thesis aims at developing PLGA nanoparticles for controlled release and investigating its interaction with phospholipid bilayers mimicking cell membranes. For passive controlled release the physiochemical changes were monitored by incubating the PLGA (50:50) NPs in different buffered pH conditions at increased time intervals. PLGA exhibited dissimilar degradation behavior with pore formation for high pH (basic conditions) maintaining the volume of the particles but change in the density, while at low pH it showed surface erosion. There is decrease in the particle size upon incubating in low pH. This study was carried out using DLS, ESEM and spectrophotometry. For active release the walls of PLGA (75:25) capsules were modulated using phospholipids. The release of hydrophilic fluorescent probe Calcein was monitored with increasing the temperature. It was observed that with DOPC (0.31mM) the release can be triggered using detergents or an enzyme (PLA2). We propose the formation of a lipid-polymer complex within the polymer matrix forming plugs which are vulnerable to enzymes/detergents inducing release. The effect of PLGA NPs over the phospholipid bilayers mimicking cell membrane was carried out using molecular fluorescent probes (Prodan and Laurdan). The study was carried out by calculating the generalised polarisation (GP) under the influence of PLGA NPs (50:50 and 75:25). It is found that the interaction is a surface phenomenon and there is no influence of NPs over the permeability of model membranes LUVs and SUVs. The Tm value of the phospholipids is also maintained when studied with Laurdan. Prodan probe GP studies provide first original method to determine the Tg of PLGA in complete aqueous conditions. It is a rapid and easy method which determines the Tg value of PLGA in real time using very small quantity of the sample. This interaction is not affected by the composition of the bilayer mimicking cell membranes
Belhadj, Mariem. "Impact et optimisation des microporeux sur le vieillissement et la gestion en eau en pile à combustible". Thesis, Université de Lorraine, 2017. http://www.theses.fr/2017LORR0196/document.
The aim of this work is to understand the mechanism of gas diffusion layer degradation. Comparing to other PEMFC components, these layer has not been much discussed in the literature. First, in order to study ageing phenomena, ex-situ physico-chemical degradation of the GDL is carried out using acid and water immersion or electrochemical degradation at high potential. Several spectroscopic, microscopic and electrochemical techniques have been used to identify GDL degradation properties. The results of these experiments show that physicochemical properties of GDL depend strongly on the operating conditions of the ASTs produced. The structure of the GDL aged at 1.2 and 1.4 V vs. ECS has been severely changed. However, immersed GDL in acid or water did not actually show any change in morphology and structure compared to its initial state. On the other hand, the results obtained indicate that, independently of the operating conditions, and contrary to what has been mentioned in certain publications, the PTFE of the macro and microporous layers is relatively stable during AST compared to the carbon compounds. Moreover, the impact of aging of the GDL on the fuel cell response determined by chronopotentiometry, polarization curves and impedance spectroscopy show a degradation of the electrical performance of the cell, at high current density, in particular in the case aged GDL at 1.2 and 1.4 V vs. ECS. Finally, to compare ex-situ ASTs and in-situ aging impact, dynamic driving cycling, FCDLC, which consists of a variation of the current and the voltage of the fuel cell over a cycle of 1200 seconds, was conducted for 1000 hours. The result of the electrochemical characterization during cycling show that the active surface is degraded and the leakage current density is increased. However, this FCDLC does not affect the GDL properties compared to the results obtained with the ex-situ degradation experiments
Suárez, Santiago Hernán. "Gestion de l'énergie d'un système de piles à combustible alimenté par un réservoir d'hydrogène à hydrure métallique". Electronic Thesis or Diss., Bourgogne Franche-Comté, 2022. http://www.theses.fr/2022UBFCA019.
This thesis work is part of the contribution to the scientific and technological advancement of the use of renewable energies based on a PEMFC fuel cell system powered by hydrogen from a metal hydride tank. The first part of the work was devoted to the characterisation of two commercial tanks of this technology with emphasis on their performance degradation. Stochastic methods were used to study the impact of cycling (charge/discharge) on the variation of the tanks' intrinsic parameters. In a second part, the results of this study were implemented through an energy model of the tank developed under the MATLAB /Simulink environment. The model was validated experimentally on a specially designed test bench. The ageing phenomenon was highlighted, providing a significant advance, particularly with a view to the industrialisation of this type of solution. Finally, the thermo-fluidic coupling between the fuel cell and the hydride tank was experimented, modelled and numerically simulated
Abbou, Sofyane. "Phénomènes locaux instationnaires dans les piles à combustible à membrane (PEMFC) fonctionnant en mode bouché (dead-end)". Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0208/document.
This work investigates the local transient phenomena occurring in proton exchange membrane fuel cells (PEMFC) operated with a dead-ended anode. The dead-end mode consists in closing the anode outlet, which leads eventually to local hydrogen starvation due to the excessive accumulation of liquid water and nitrogen (because of membrane crossover) in the anode compartment. Such fuel-starvation events may remain undetected but can entail a significant rise of the anode (and thus cathode) potentials and accelerate carbon corrosion and catalyst degradation. To access local information, we developed an innovative segmented linear cell with reference electrodes along the gas channels. By simultaneously monitoring the local potentials and current densities during operation, we assessed the impact of fuel starvation and observed strong local cathode potential excursions close to the anode outlet. Aging protocols based on fuel cell operation with a dead-ended anode (longer than in real use condition) showed non-uniform cathode ElectroChemical Surface Area (ECSA) losses and performance degradation along the cell area: the damage was more severe in the regions suffering the longest from fuel starvation. Parametric studies completed by numerical simulations showed that the fuel starvation is mainly governed by liquid water accumulation in the anode channels, as well as nitrogen crossover through the membrane. As a consequence, water management impacts significantly the cathode potential variations and thus the resulting electrode degradation. Starting from this founding, we propose strategies to improve fuel cell lifetime
Saveleva, Viktoriia. "Investigation of the anodes of PEM water electrolyzers by operando synchrotron-based photoemission spectroscopy". Thesis, Strasbourg, 2018. http://www.theses.fr/2018STRAF002/document.
Development of oxygen evolution reaction (OER) catalysts for proton exchange membrane water electrolysis technology depends on the understanding of the OER mechanism. This thesis is devoted to the application of near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) and near edge X-ray absorption fine structure (NEXAFS) techniques for operando investigation of the Ir, Ru - based anodes. For Ru-based systems, we observe the potential-induced irreversible transition of Ru (IV) from an anhydrous to a hydrated form, while the former is stabilized in the presence of Ir. Regarding single Ir-based anodes, the analysis of O K edge spectra reveals formation of electrophilic oxygen OI- as an OER intermediate. Higher stability of Ir catalysts supported on antimony-doped tin oxide (ATO) is related to their lower oxidation. This work demonstrates different OER mechanisms on Ir, Ru-based anodes involving anion and cation red-ox chemistry, correspondingly, regardless the oxide nature
Robert, Mylène. "Impact of degradation and aging on properties of PFSA membranes for fuel cells". Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0004.
Although proton-exchange membrane fuel cells (PEMFC) are nowadays considered as a safe and clean energy technology, they still suffer from durability and reliability issues restricting their widespread commercialization. Innumerable studies have already led to a better understanding of aging phenomena and highlighted membrane degradation as one of the main factors limiting PEMFC lifetime. This study aims at bringing some clarifications on the chemical and mechanical degradation mechanisms of membranes through ex-situ aging protocols as well as understanding the impact of these degradations on the membrane structure and functional properties. First, it was necessary to clarify the influence of Fenton’s reaction, an ex-situ aging protocol widely recognized in the literature, on the chemical degradation of Nafion™ membranes. The results confirmed that Fenton’s reagents concentration significantly influenced polymer chemical decomposition, both from a chemical and morphological point of view. Subsequently, we chose to monitor the evolution of pure chemical degradation of Nafion™ membranes as a function of time and to study its impact on the membrane structure, water sorption and diffusion properties, as well as operability in fuel cells. In that respect, various characterization techniques such as 19F or 1H-NMR as well as FTIR spectroscopies allowed us to correlate physico-chemical properties of the membrane to its structural characteristics and to thus highlight several indicators of chemical degradation. Finally, a custom-made device has been developed to study the impact of conjoint mechanical and chemical stress on Nafion™ membranes. The objective of this device was to replicate aging conditions close to those encountered during fuel cell operation
Sangely, Matthieu. "Dégradation biologique des polychlorobiphényles". Thesis, Toulouse, INPT, 2010. http://www.theses.fr/2010INPT0094/document.
Soil is a complex interface between all compartments of the environment. Their pollution contributes to the spread of many pollutants. PCBs are persistent toxic compounds in the environment. Widely used especially in dielectric oils, they now contaminate many industrial floors. Heat treatment of these soils is very expensive and can cause the emission of dioxins. The objective of this work is to study a biological treatment process for the degradation of PCBs in soils. Biological degradation of PCBs has been observed in the presence of two cultured organisms, Burkholderia xenovorans and Phanerochaete chrysosporium, confirming their technological potential under aerobic conditions. Under anaerobic conditions, a microbial community with the ability to degrade PCBs was developed. A study of the diversity of 16S rDNA gene within this community has identified the species in this community. An analysis of life cycle assess the environmental performance of two methods for treating soils contaminated with PCBs, one thermal and one biological. This analysis quantifies the environmental benefit of the biological process compared with the heat treatment
Navarro, Nathalie. "Dégradation sonocatalytique de composés organiques". Thesis, Montpellier 2, 2012. http://www.theses.fr/2012MON20197.
Unlike aqueous effluents from the PUREX process, aqueous effluents from advanced separation processes developed to separate the minor actinides (Am, Cm) contain organic reagents in large amounts. To minimize the impact of these organic compounds on the next steps of the process, and to respect standard discharges, it is necessary to develop new techniques of degradation of organic compounds. Sonochemistry appears as a very promising solution to eliminate organic species in aqueous nuclear effluents. Indeed, the propagation of an ultrasonic wave in a liquid medium induces the appearance of cavitation bubbles which will quickly grow and implode, causing local conditions and extreme temperatures and pressures. Each cavitation bubble can then be considered as a microreactor at high temperature and high pressure able to destroy organic molecules without the addition of specific reagents. The first studies on the effect of ultrasonic frequency on sonoluminescence and sonolysis of formic acid have shown that the degradation of formic acid occurs at the bubble/liquid interface. The most striking difference between low-frequency and high-frequency ultrasound is that the sonolysis of HCOOH at high ultrasonic frequencies initiates secondary reactions not observed at 20 kHz. However, despite a much higher sonochemical activity at high frequency, highly concentrated carboxylic acids in the aqueous effluents from advanced separation processes cannot be destroyed by ultrasound alone. To increase the efficiency of sonochemical reactions, the addition of supported platinum catalysts has been studied. In these conditions, an increase of the kinetics of destruction of carboxylic acids such as oxalic acid is observed
Saadi, Zoubida. "Etude de la dégradation fongique des polymères : cinétique de dégradation des polymères et caractérisation des sous-produits de dégradation : étude de l'écotoxicité de ces polymères". Le Mans, 2008. http://cyberdoc.univ-lemans.fr/theses/2008/2008LEMA1004.pdf.
Subject of current events, the biodegradability of polymers is always studied in a global context, that is to say, with regards to fungi and bacteria together. The present research project focuses on the purely fungal degradation of polymers. Apart from the core research, the results of this study suggest certain applications to reduce environmental problems : - to deteriorate materials with a specific fungal strain. - to better control the kinetics of the biodegradation of plastics (mulching films, packaging materials). - Accelerate bio-degradation. After selecting non-toxic fungi present in natural states (compost, soil) and verifying the inertness of PLLA and PBAT on fungal cultures, cellular growth tests in a glucose-free environment revealed a selectivity among fungi for certain polymeric substrata. The tests also highlighted the major role temperature plays in the fungal degradation of polymers. When temperatures get closer, or go beyond the glass transition temperature, the physical structures are more accessible to fungal enzymes. After determining fungal consortium in the degradation of PLLA and PBAT, respiration measurements in soil and compost, both sterilized then sowed, have confirmed temperature as the essential parameter of biodegradation. Taking place in unmodified soil and compost, the kinetics of biodegradation of these polymers revealed a fungi-bacterial synergy during biodegradation tests. This study of biodegradation – refined with a follow-up of the physical and chemical properties of the polymers – led to a better understanding of the various stages of hydrolysis as well as the mineralization of polymers. These investigations had to take into account the characterization of metabolizing products of PLLA and PBAT and a regular toxicity check for the environment
Bartisetiani, Muntalif. "Dégradation du pentachloronitrobenzène par les micromycètes". Université Joseph Fourier (Grenoble), 1993. http://www.theses.fr/1993GRE18004.
Mesplont, Martine. "Dégradation du pentachlorophénol par les micromycètes". Université Joseph Fourier (Grenoble), 1989. http://www.theses.fr/1989GRE18004.
Tognan, Malik. "Etude de dégradations des performances de Piles à Combustible PEM BT alimentées en H2/O2 lors de campagnes d'endurance : du suivi de l'état de santé en opération à la modélisation du vieillissement". Thesis, Toulouse, INPT, 2018. http://www.theses.fr/2018INPT0047/document.
This thesis work deals with the thematic of the Low Temperature Proton Exchange Membrane (PEM LT) Fuel Cell (FC) aging. The use of a FC inside a H2 battery (association of a FC, an electrolyzer and H2 / O2 tanks) in a stationary context is considered in an island micro-grid based on renewable energies (wind and solar power). Two axes linked with the FC use and aging in this context are investigated in this work: one of the axes is centered in the study of the FC performance decrease dynamics over time and the other on the development of methods and tools dedicated to the state of health monitoring during the FC operation. The first thematic is introduced through the exploitation of several aging campaigns performed on PEM FC stack prototypes under constant current solicitations. The stacks considered are fed with pure O2 on the cathode side. A focus is made on the aging heterogeneity inside the stacks and a decoupling between the nominal voltage degradation dynamics and the development of the H2 internal leak with time is highlighted for the different stacks and campaigns. A generic methodology dissociating the reversible and the irreversible voltage losses dynamics is proposed and is further used as a basis to model the nominal voltage degradation with time. The model built in this way is showing encouraging results and its potential use for prognostic purpose is suggested. Whereas these investigations focus on the FC performance degradations under constant current solicitation, the impact of load current dynamic variations on the FC aging is also treated with an experimental study performed on single cells. An ageing campaign under a dynamic load profile is performed on several single cells directly hybridized or not by supercapacitors. The hybridized cells are cycling on an almost-constant current profile whereas the non-hybridized cells are cycling on a dynamic one. A comparison of the performances evolution with time in both cases (hybridized and nothybridized) is done and highlights the effect of the dynamic cycling on the FC performance degradation. The second thematic dealing with the FC state of health evaluation is introduced with one of the main causes of the FC end-of-life: the development of the H2 internal leak between the anode and cathode compartments. Open Circuit Voltage (OCV) measurements performed during start-up and shut-down routines phases are scanned a posteriori in one of the aging campaign of the database. The objective is to seek some potential correlations between those OCV measurements and the H2 internal leak increase over time in order to develop internal leak indicators. A gases introduction operating sequence highlighting a link between the internal leak level and the OCV drift for some stack’s cells is identified during some start-up phases and reproduced during a complementary campaign. A last part of the manuscript is finally dedicated to the integration of a parasitic mechanism (the Pt oxidation) into the FC theoretical quasi-static and dynamic performance modeling. The model integrating this phenomenon is showing some abilities to explain and analyze several experimental features observed on classical performance characterization measurements (EIS, OCV measurements, large amplitude sinus sweep at very low frequency…), opening some perspectives for the FC state of health monitoring
Mai, Si Hai. "Etude de dégradation des voies ferrées urbaines". Phd thesis, Université Paris-Est, 2011. http://pastel.archives-ouvertes.fr/pastel-00659068.
Le, Bouteiller Caroline. "Dégradation des sédiments marneux et suspensions hyperconcentrées". Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00603000.
Torres, de Dominguez Angeles. "Dégradation et biodégradation de polymères d'acide lactique". Montpellier 1, 1995. http://www.theses.fr/1995MON13506.
Detoc, Sylvie. "Étude des produits de dégradation du pentachlorophénol". Université Joseph Fourier (Grenoble), 1988. http://www.theses.fr/1988GRE18001.
Messaadi, Maha. "Dégradation des aciers frittés sous impact-glissement". Thesis, Ecully, Ecole centrale de Lyon, 2014. http://www.theses.fr/2014ECDL0011/document.
Sintered steel is used as a material for valve seat insert in automotive engines. During operation, a dynamic contact occurs between the valve and its seat. To investigate the wear behavior of sintered steel for this application, we have developed an impact-sliding tester using a ball on flat configuration. Impact-sliding experiments have been conducted at different impact angles (30°, 45°, 60°) with and without lubrication to investigate the surface damage of the sintered steel under this contact loading and to understand the effect of lubrication. As a first step, we investigated numerically the evolution of the contact pressure, stress and strain as a function of time. In fact, owning the experimental bench test, a finite element model was developed. Numerical results show an evolution from of dynamic behavior from permanent reciprocating sliding at low angles to an intermittent motion called multi-impacts at higher angles. Experimental electric resistance measurements seem to confirm these evolutions. As a consequence, shearing stress is reduced when plastic deformation increased with multi-impacts. Wear track observations are in good agreement with these findings. Our results have shown an important variation of the wear rate in relation to impact-sliding angle. In dry condition, a low wear regime is observed for low angles; whereas maximum wear is observed at 60° angle for lubricated contacts. The wear scar in the dry contact is deeper than in the lubricated one. The damaged surface of sintered steel is examined by a Scanning Electron Microscopy (SEM). In dry conditions, the contact area wears out quickly due to an adhesive-abrasive process. Under lubricated conditions, a fatigue crack opening is associated to a lower wear rate. The lubricated impact-sliding condition modifies the main surface damage phenomena. In addition, a comparison of wear volumes produced using pure mineral base oil and the same base oil containing an anti-wear, anti-friction additive (ZDDP), shows that this additive has only a weak effect on wear reduction under squeeze–sliding lubrication. A discussion of basic wear mechanisms is presented to explain the observations. The present research was carried out to study the combined aspects of impact and sliding failure mechanism at different contact temperatures. The tribological behavior was investigated both under reciprocating motion and with a dynamic impact-sliding loading. The measured friction coefficient decreases as the contact temperature increases. The presence of oxides seems to be the key factor of this evolution. When the loading changes to a combined impact with slides, wear rate and mechanisms of the sintered steel vary with temperatures. Scanning electron microscopy observations coupled with EDX analysis were investigated inside and outside of the wear track in order to understand the surface accommodation with temperatures
Parra, Guardado Ana Luisa. "Dégradation enzymatique de micropolluants récalcitrants d'origine pharmaceutique". Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTG013/document.
This work is focused on the study of the enzymatic depletion of recalcitrant pharmaceutical micropollutants in water. The potential degradation of three antibiotics (amoxicillin, ciprofloxacin and sulfamethoxazole) and one anti-epileptic (carbamazepine) was studied with three laccases: Pycnoporus sanguineus CS43, Trametes versicolor (Tv) and Myceliophtora thermophila. Free laccase systems were evaluated for pharmaceuticals depletion on model solutions in the presence or absence of redox mediators and the impact of several parameters on the performance of laccases for degradation were studied. The enzymes were then immobilized on different solid supports: commercial silica, laboratory synthetized nano-silica and clay based composite nanomaterials and used for degradation tests. A novel methodology for the covalent binding of laccases onto carriers was developed by using glutaraldehyde in vapour phase and the best immobilization conditions were determined through a 23 full factorial design. The immobilized Tv shown the highest activity and was tested in presence of redox mediators. Moreover, the reusability was evaluated in several degradation cycles and the toxicity of the solutions after treatment was assessed with the Microtox® test. In comparison to laccase immobilized on commercial silica, the Tv supported on laboratory synthetized materials showed higher activity and a better performance for the removal of target compounds
Buch, Xavier. "Dégradation thermique et fluage d'un adhésif structural epoxyde". Phd thesis, École Nationale Supérieure des Mines de Paris, 2000. http://tel.archives-ouvertes.fr/tel-00005634.
L'étude du comportement en température nous a permis de proposer un schéma réactionnel de dégradation thermique impliquant différents mécanismes moléculaires. L'effet principal est une dépolymérisation thermolytique qui conduit à une plastification du réseau. Nous avons montré que les molécules plastifiantes avaient une structure très proche de celles des durcisseurs. Il y a ensuite migration de ces molécules plastifiantes du cœur vers la surface des échantillons. En surface, ces molécules ont un comportement différent selon les conditions de vieillissement. Parallèlement à ces phénomènes, il y aurait des recombinaisons moléculaires au sein du réseau qui conduisent à la formation d'une structure thermiquement plus stable. Cette espèce thermostable nécessite de l'oxygène pour être dégradée selon un mécanisme de thermo-oxydation. Notre étude a également porté sur l'évolution de la température de transition vitreuse au cours du vieillissement thermique. Nous avons ainsi mis en évidence une évolution complexe caractérisée par une diminution de la Tg au cours du vieillissement suivie d'une augmentation.
L'étude du comportement mécanique de l'EA 9689 et d'assemblages collés acier/colle/acier nous a permis de mieux comprendre les potentialités de cet adhésif structural, mais aussi de proposer différentes hypothèses sur les mécanismes moléculaires responsables du fluage. Nous avons ainsi montré que les propriétés mécaniques de cet adhésif étaient très bonnes jusqu'à des températures d'environ 150°C. Au delà de cette température, on note une chute importante des propriétés mécaniques que l'on peut expliquer par un accroissement du caractère viscoélastique du polymère, et ceci alors même que la Tg est à une température bien supérieure (environ 230°C). Nous notons que les propriétés des assemblages collés sont intimement liées à la nature, et donc à la résistance, de l'interphase adhésif/substrat et qu'il est donc impossible de préjuger de la résistance de joints sans connaître au préalable celle de l'interphase formée. Nous nous sommes intéressé aux trois stades du comportement en fluage en portant une attention particulière sur le fluage stationnaire au cours duquel la vitesse de déformation est constante. Nous avons ainsi développé un modèle simple pour représenter l'évolution de la vitesse de fluage stationnaire avec la contrainte et la température. Ce modèle nous a permis de faire différentes hypothèses sur la nature des mécanismes de déformation par fluage. Nous postulons ainsi que dans des conditions "douces" (température et contrainte faibles), la déformation au cours du fluage stationnaire serait provoquée par des mouvements locaux des segments de chaînes identiques à ceux décrits pour expliquer la transition . En conditions de fluage plus "sévères" (température et/ou contrainte élevée), la déformation stationnaire serait due à des mouvements des chaînes macromoléculaires sur de longues distances analogues à ceux proposés pour la transition vitreuse.