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Liquid composite molding processes
No full textInternational audienceThe term liquid composite molding (LCM) encompasses a family of processes in which a dry fibrous reinforcement is impregnated by a liquid resin inside a sealed cavity. As the understanding and control of these processes improves, their field of application widens. LCM processes can be used as a replacement to decrease the environmental impact and improve the quality of composite parts made via traditional open mold processes. LCM processes can also provide a cost-cutting alternative to prepreg consolidation techniques while maintaining high part quality.In this chapter, after describing the variety of processes blanketed under the class liquid composite molding, the research advances in the monitoring and simulation of these processes are described. The subsequent section will then present the current usage of LCM techniques in the field of civil engineering, including some case studies, before outlining some future trends on the subject
Determination of mass transfer coefficients in high-pressure CO2-H2O flows in microcapillaries using a colorimetric method
No full textInternational audienceThis study presents a method for the experimental determination of the local volumetric mass transfercoefficientkLaLin a high-pressure two-phase flow of water (H2O) and carbon dioxide (CO2) in a micro-capillary using a colorimetric method. H2O and CO2 are fed continuously and co-axially injected athigh-pressure (10 MPa) and moderate temperature (303 K) into a microcapillary. Under the flow condi-tions studied, a segmented flow of CO2 in H2O is formed. The CO2 dissolves into the H2O-rich phase,thereby reducing the pH to about 3.3, depending on the pressure and temperature. The pH of the H2O-rich phase is determined over the entire length of the capillary using a pH sensitive indicator coupledwith high-speed imaging and analysis. The concentration of CO2 in the water-rich phase is deduced fromthis pH value using literature experimental data. The CO2 concentration data and the unit-cell model,which has been modified to account for high pressure conditions, have then been used to determinethe volumetric mass transfer coefficient, kLaL, of CO2 into the liquid phase along the entire length ofthe microreactor. The experimentally derived kLaL ranges between 1 and 13 s-1
The crucial role of the binder in biochar briquetting for coal replacement in an industrial process
No full textInternational audienceA drastic reduction in greenhouse gas emissions in the short term is necessary to meet the objectives set by the European Union under the Green Deal (2021), which aims to increase the share of renewable energy in the European energy mix from 18% in 2018 to at least 32% in 2030. In this context, carbon-intensive industrial processes, typically using fossil fuels, should move towards the use of alternative renewable fuels. Biomass can play a role in this scenario, as a renewable carbon-based bioresource, high available at a low cost, generating biogenic CO2 emissions. Biochar, obtained from thermochemical processes, such as pyrolysis, has thermal and processing properties closer to those of coal, which makes it a suitable biosourced alternative to fossil fuels at industrial scale.Densification leading to pellets or briquettes can contribute to cope with the specifications of industrial processes, as it increases the physical and energetic density of biochar and facilitates its handling. Previous studies pointed out the addition of a binder as crucial in the formulation of biochar briquettes, compared to biomass densification. Indeed, the high temperature and pressure applied in densification activate the natural binders inherent in biomass such as lignin, proteins, fats, and oils, which facilitates biomass particles adhesion during compression. As biomass components are partially decomposed in pyrolysis, their role as natural binding agents is less effective in biochar compaction [1]. Moreover, the binder improves the durability of the briquette and influences the combustion performance and emissions. Consequently, binder availability, efficiency, sustainability, and environmental impact need to be considered when selecting a binder for biochar densification. In this context, the present work aims to synthesize and compare binders used in biochar densification in the literature. This review is a first step in identifying the best densification conditions to produce biochar briquettes for their use as fuels for coal replacement in industrial processes.The main characteristics of the biochar briquettes impacting their behavior in combustion processes at industrial scale are related to their physical stability, structural properties, hot and cold mechanical properties, moisture content, carbon content, and calorific value [1]. These properties can be drastically impacted by the characteristics of the selected binder. According to the literature review, the most interesting binders for biochar densification include organic compounds, such as starch, molasses, lignin, and bio tar, and inorganic compounds, such as cement, clay, lime, plastic waste, and asphalt [2]. Organic binders were shown to bring to biochar briquettes good combustion performances, good bonding ability, high hydrophobicity, and low ash content. However, they typically present poor thermal stability, high price, and may be a source of toxic emissions. Inorganic binder benefits include their low cost, excellent thermal stability, strong adhesion, and limited toxic emissions. On the other hand, they present poor hydrophobicity, high ash content, and low calorific value. To find a compromise between these solutions, co-densification with several types of binders was suggested. More precisely, combining organic and inorganic binders would benefit from their synergic interaction leading to improved combustion and mechanical properties [3].The use of bio-oil as binder in biochar briquetting constitutes a circular economy approach integrating pyrolysis solid and liquid products in a biosourced fuel suitable for coal replacement. Bio-oil, also named tar, is a viscose liquid composed of a complex mixture of organic and inorganic compounds. Bio-oil is rich in phenolic compounds, which may present adhesive properties in biochar briquetting with a thermal activation or chemical modification [4]. Furthermore, its carbon-rich composition contributes to the calorific value of biochar briquettes (LHV around 20 MJ/kg) [5]. However, its use in biochar briquetting is still limited due to its high moisture content, poor adhesive properties in the raw state, and the risk of generating toxic emissions. As a result, modifying bio-oil to reduce its moisture content and increase the proportion of potentially binding compounds would improve its properties to be used as biosourced binder in biochar briquetting. Finally, the operating conditions of the combustion process of the densified biosourced fuel need to be well controlled. This mainly concerns physical and thermal fuel behavior, gas emissions, and variations in fuel characteristics, which impact combustion performances and safety. Thus, the behavior of biochar briquettes needs to be equivalent to that of fossil fuels currently used, as the impact of this fuel replacement in terms of Quality, Health, Safety & Environment (QHSE) should allow for defining the strategy for implementing this solution in the on-site. Common emissions associated with the combustion of biomass briquettes are SO2, NOx, particulate matter, and volatile organic compounds (VOC). However, the severity of the emissions depends on the type of biomass, its chemical composition, and that of the binder used in the densification process. [1] Nzihou, A. Ed.: Handbook on Characterization of Biomass, Biowaste and Related By-products. Cham: Springer International Publishing. (2020).[2]Olugbade, T.; Ojo, O.; Mohammed, T.: Influence of Binders on Combustion Properties of Biomass Briquettes: A Recent Review. BioEnergy Res., vol. 12, no. 2, pp. 241–259 (2019).[3]Kong, L.; Tian, S.; Li, Z.; Luo, R.; Chen, D.; Tu, Y.; Xiong, Y. L.: Conversion of recycled sawdust into high HHV and low NOx emission bio-char pellets using lignin and calcium hydroxide blended binders. Renew. Energy, vol. 60, pp. 559–565. (2013).[4]Pimenta, A. S.; Trianoski, R.; Pizzi, A.; Santiago-Medina, F. J.; de Souza, E. C.; Monteiro, T. V. da C.; Fasciotti, M.; Castro, R. V. O.: Effect of polymeric diisocyanate addition on bonding performance of a demethylated-pyrolysis-oil-based adhesive. Wood Sci. Technol., vol. 53, no. 6, pp. 1311–1337. (2019).[5]Cong, H.; Yao, Z.; Mašek, O.; Meng, H.; Sheng, C.; Wu, Y.; Zhao, L.: Co-combustion, co-densification, and pollutant emission characteristics of charcoal-based briquettes prepared using bio-tar as a binder. Fuel, vol. 287, p. 119512. (2021)
Desenvolvimento de nanopartículas poliméricas funcionalizadas para liberação controlada de Rivastigmina usada no tratamento da doença de Alzheimer
No full textNanoparticles can enhance the treatment of diseases, especially when the diseased tissue is hard to access, as in the case of brain. For this reason, the present work aimed at developing biocompatible nanoparticles loaded with rivastigmine, a drug approved for the treatment of the Alzheimer's Disease, for sustained release of the drug to the brain. Methyl methacrylate (MMA), acrylic acid (AA), 2-hydroxyethyl methacrylate (HEMA) and butyl acrylate (BA) were the comonomers selected for synthesis of nanoparticles through miniemulsion polymerization. The combination of the surfactants provided the better latex stability and allowed the particle size control. The in-situ encapsulation of0.5% w/w drug was very efficient (90%) in absence of AA and HEMA and did not alter particle size. The immobilization of amino acid and proteins confirmed the versatility and superiority of the copolymers when compared to the PMMA. Release studies displayed sustained, and diffusion driven profiles, with higher release rates obtained with thelyophilized copolymers. Additionally, assays performed in human endothelial cells derived from pulmonary artery showed high cell viability. Thus, it has been shown that the produced nanoparticles can be potentially used to incorporate ligands and carry rivastigmine through physiological barriers.Non disponibleO uso de nanopartículas pode aperfeiçoar o tratamento de doenças, em especial as de difícil alcance, como disfunções cerebrais. Por isso, o presente trabalho visou ao desenvolvimento de nanopartículas biocompatíveis carreadoras de rivastigmina, fármaco aprovado no tratamento da Doença de Alzheimer, para liberação controlada e sítio-específica ao cérebro. Metacrilato de metila (MMA) e comonômeros funcionais (ácido acrílico (AA), 2-hidroxietil metacrilato (HEMA) e acrilato de butila (BA) foram escolhidos para síntese das nanopartículas por polimerização em miniemulsão. A combinação de surfactantes resultou em melhor estabilidade do látex e controle de tamanho de partícula. O encapsulamento in situ de 0,5%m/m de fármaco não modificou o tamanho e foi mais eficiente (90%) em materiais sem AA e HEMA. A imobilização de aminoácido e proteínas mostrou a versatilidade e superioridade dos copolímeros em relação ao PMMA. Ensaios de liberação exibiram perfil sustentado com destaque doscopolímeros liofilizados e mecanismo preferencial de difusão clássica. Ensaios em células endoteliais humanas derivadas da artéria pulmonar mostraram elevada viabilidade celular. Assim, mostrou-se que as nanopartículas produzidas apresentam grande potencial para incorporar ligantes e carrear rivastigmina através de barreiras fisiológicas
Approche multi-échelle de l’oxydation sous contrainte appliquée aux superalliages à base de nickel : de la déformation localisée aux prémices d’endommagement mécano-chimique
No full textNickel-based superalloys are widely used for structural applications at high and intermediate temperatures in severe atmospheres. Environmentally assisted degradation, i.e. oxidation and corrosion, alters not only the surface of the materials, but also their core properties due to a selective and progressive consumption of the reactive elements involved in the surface degradation processes. The material in a shallow region beneath the reactive surface subsequently shows a gradient in chemical composition, microstructure and physical properties. Despite the negligible scale of those gradients (from micrometers to hundreds of micrometers beneath the surface) relative to the dimensions of the structural component, the variability in mechanical behavior within the gradient often drives premature damage and progressive failure of the component. In order to quantify these developments, micromechanical characterization of the mechanical properties of gradient materials is important. Due to the high variability of mechanical properties within graded materials, micromechanical characterization techniques are required. Materials are characterized in aged and pre-oxidized at the temperature of 700°C. These same characterizations are also carried out at 800°C, in order to exacerbate the consequences of oxidation and to increase this gradient of properties at iso-duration of heat treatment. The mechanical characterization of ultrathin specimens (a few tens of micrometers thick) in tension and fatigue is carried out with macroscopic monitoring by image correlation. In addition to the macroscopic values, a specific investigation of the surface for full-field kinematic measurements allows obtaining local information on the deformation and damage mechanisms at the microstructure scale. The present project proposes to tackle the intricate multi-physics dimension of the environment-assisted deformation/damage evaluation by simultaneously correlating the macroscopic/mesoscopic and sub-microstructure/sub-micrometer deformation and the changes in surface reactivity (oxide microcracking, oxide spallation, fast-growing oxides, breakaway oxidation, etc.) at high temperature in various atmosphere conditions. The main aspiration of this in-situ experimental characterization is to bring a novel understanding and a more physical prediction of the local and time-evolving mechanical behavior of graded materials at the microstructure scale related to environmental interactions.Les superalliages à base de nickel sont largement utilisés pour des applications structurelles à haute température et à température intermédiaire dans des atmosphères sévères. La dégradation assistée par l'environnement, c'est-à-dire l'oxydation et la corrosion, modifie la surface des matériaux, mais également leurs propriétés à cœur en raison d'une consommation sélective et progressive des éléments réactifs impliqués dans les processus de dégradation de la surface. Le matériau situé à proximité de la surface réactive présente un gradient de composition chimique, de microstructure et de propriétés physiques. Malgré l'échelle négligeable de ces gradients (de quelques micromètres à quelques centaines de micromètres sous la surface) par rapport aux dimensions du composant structurel, la variabilité du comportement mécanique au sein du gradient entraîne souvent des dommages prématurés et la rupture progressive du composant. Afin de quantifier ces évolutions, la caractérisation micromécanique des propriétés mécaniques des matériaux du gradient est importante. En raison de la forte variabilité des propriétés mécaniques au sein des matériaux gradués, des techniques de caractérisation micromécanique sont nécessaires. La caractérisation de matériaux vieillis et pré-oxydés est réalisée à la température de 700°C, de même qu'à 800°C, afin d'exacerber les conséquences de l'oxydation et d'augmenter ce gradient de propriétés à iso-durée de traitement thermique. La caractérisation mécanique des éprouvettes ultraminces (quelques dizaines de micromètres d'épaisseur) en traction et fatigue est réalisée avec suivi macroscopique par corrélation d'image. En plus des valeurs macroscopiques, une investigation spécifique de la surface pour des mesures cinématiques plein champ permet d'obtenir des informations locales sur les mécanismes de déformation et d'endommagement à l'échelle de la microstructure. Le présent projet propose de s'attaquer à la dimension multi-physique complexe de l'évaluation de la déformation/de l'endommagement assisté par l'environnement en corrélant simultanément la déformation macroscopique/mésoscopique et sous-microstructure/sous-micromètre et les changements de réactivité de surface (microfissuration des oxydes, oxydes à croissance rapide, oxydation par rupture, etc. ) à haute température dans diverses conditions atmosphériques. L'objectif principal de cette caractérisation expérimentale in-situ est d'apporter une nouvelle compréhension et une prédiction plus physique du comportement mécanique local et temporel des matériaux gradués à l'échelle de la microstructure en relation avec les interactions environnementales
Matériaux à taux de graphène élevé à partir de la biomasse par traitement thermique
No full textGraphene is a bidimensional carbon material composed of sp2 hybridized carbon atoms forming a periodic net of aromatic cores. Graphenic materials possess outstanding physicochemical and thermal properties, namely a high electric and thermal conductivities, a high mechanical resistance and high specific area. Graphenic materials are mostly synthesized by complex and polluting thermochemical treatments of fossil-based resources. Replacing fossil precursors by lignocellulosic biomass, renewable and abundant, would green the synthesis of graphenic materials. In this study, “biochars” were produced by pyrolysis of commercial cellulose and lignin under different operating conditions. The carbon produced was investigated using a multi-scale approach to evaluate the development of the graphene fringes. An image analysis numeric tool was developed to quantify the graphene fringes using images from high resolution transmission electron microscopy. Cellulose and lignin chars prepared between 1000 and 1800 °C present graphenic structures with short and poorly stacked graphene fringes. The catalytic role of calcium, an alkaline earth metal non-toxic and abundant, was studied. The calcium impregnation of cellulose and lignin lead to the formation of graphenic structures with a well-developed anisotropy from 1400 °C, which implies a faster and/or greater diminution of the in-plane defects compared to the standard structural evolution for this kind of material. A two steps reaction mechanism was proposed. The first step is the formation of calcium carbide crystals followed by their decomposition into graphene fringes.Le graphène est un matériau carboné bidimensionnel constitué d'atomes de carbone hybridés sp2 formant un réseau périodique de noyaux aromatiques jointifs. Les matériaux graphéniques présentent des propriétés physico-chimiques et thermiques remarquables, notamment une grande conductivité électrique et thermique, une grande résistance mécanique et une haute surface spécifique. Les matériaux graphéniques sont actuellement synthétisés par des procédés thermochimiques complexes et polluants. Il est envisagé de remplacer les précurseurs fossiles habituellement utilisés par de la biomasse lignocellulosique, ressource renouvelable et abondante, pour réduire l'impact environnemental de la synthèse de matériaux graphéniques. Dans cette étude, des « biochars » ont été produits par pyrolyse de cellulose et de lignine commerciales selon différentes conditions opératoires. Le carbone produit a été étudié selon une approche multi-échelle afin d'évaluer le développement des feuillets de graphène. Un outil numérique d'analyse d'images a notamment été développé pour quantifier les feuillets de graphène à partir d'images en microscopie électronique en transmission à haute résolution. Les biochars de cellulose et de lignine préparés entre 1000 et 1800 °C présentent des structures graphéniques courtes avec un empilement irrégulier des feuillets de graphène. Le pouvoir catalytique du calcium, un métal alcalino-terreux non toxique et abondant, a été étudié. L'imprégnation de la cellulose et de la lignine avec du calcium permet la formation de structures graphéniques à l'anisotropie très développée dès 1400 °C, ce qui implique une diminution plus rapide et/ou plus grande des défauts intra-plans par rapport à l'évolution structurale normale attendue pour ce type de précurseur. Un mécanisme réactionnel a été proposé. La formation de la structure graphénique a été décrite par un processus en deux étapes dont la première serait la formation de cristaux de carbure de calcium qui se décomposeraient ensuite pour former des feuillets de graphène
Influence du modèle utilisé pour le calcul de constantes d'équilibre à température modérée pour des électrolytes
No full textInternational audienceThe formation of a solid mineral deposit can cause major problems in the operation of industrial processes such as high pressure acid leaching. Knowledge of the chemical speciation and solubility product of the mineral can help control or inhibit its formation. This speciation is based on the knowledge of the thermodynamic equilibrium constants of the dissociation/ complexation reactions involved in the system and their temperature dependencies. It also depends on the concentration of the different species in the system, the pressure and the activity coefficients of the chemical species present in their molecular or electrolyte form. From these thermodynamic quantities and the state of the system, it is possible to predict the direction of the reaction, i.e. whether the reactants or the products of the chemical reactions are favoured. This work presents and compares different models for the calculation of activity coefficients for ionic strengths between 0.001 - 6 molal and the calculation of thermodynamic equilibrium constants at temperatures up to 300 °C (at zero ionic strength). It confirms the need for reliable thermodynamic data for modelling aqueous systems.La formation d’un dépôt solide minéral peut engendrer des problèmes majeurs dans la conduite de procédés industriels comme la lixiviation acide à haute pression. La connaissance de la spéciation chimique et du produit de solubilité du minéral peut permettre de contrôler ou d’inhiber sa formation. Cette spéciation repose sur la connaissance des constantes d'équilibre thermodynamique des réactions de dissociation/ complexation impliquées dans le système et de leurs dépendances en température. Elle dépend également de la concentration des différentes espèces dans le système, de la pression et des coefficients d'activité des espèces chimiques présentes sous leur forme moléculaire ou électrolytique. À partir de ces grandeurs thermodynamiques et de l'état du système, il est possible de prévoir le sens d'évolution de la réaction c’est-à-dire si les réactifs ou les produits des réactions chimiques sont favorisés. Ce travail présente et compare différents modèles pour le calcul des coefficients d'activité pour des forces ioniques comprises entre 0.001 – 6 molal et le calcul des constantes d'équilibre thermodynamique à des températures jusqu'à 300 °C (à force ionique nulle). Il confirme la nécessité d’avoir des données thermodynamiques fiables pour la modélisation de systèmes aqueux
Influence de la microstructure obtenue par procédé de fabrication additive SLM sur le comportement mécanique de revêtements base cobalt
No full textThe aim of this experimental work is to identify the levels of damage necessary to activate different plastic strain mechanisms under volume fatigue and surface fatigue stresses (obtained indirectly by friction tests) of CoCrMo type hardfacing obtained by the SLM additive manufacturing process. While the surfacing processes on aeronautical mechanical parts are preferably performed by powder projection, the Selective Laser Melting (SLM) process is based on "powder bed" technology within the ICA-Albi laboratory. The interactions between powders and laser beams by powder bed technology can be considered as exploratory compared to powder projection processes and thus lead to coatings with microstructural particularities. The study of the plastic deformation behaviour via specific material parameters is undertaken by defining a mass percentage of additive elements necessary to activate the plastic deformation mechanism by phase transformation. This thesis initiates a study on the damage behaviour under multi-stress loading. Four-point plane bending fatigue tests are performed for different levels of mechanical loading to stress the volume. Tribological tests are carried out to engage different physical mechanisms of strain accommodation and thus study the synergy between frictional loading and surface degradation. In combination with tribological and fatigue tests, microstructural investigations and physical-chemical analyses have allowed the identification of damage mechanisms.L'objectif de ce travail expérimental est d'identifier les niveaux d'endommagements nécessaires pour activer différents mécanismes de déformation plastique sous sollicitations en fatigue volumique et en fatigue de surface (obtenue indirectement par des essais de frottement) de rechargements de type CoCrMo obtenus par le procédé de fabrication additive SLM. Si le procédé de rechargement sur des pièces mécaniques aéronautiques se fait préférentiellement par projection de poudre, au sein du laboratoire ICA-Albi, le procédé de Selective Laser Melting (SLM) est basé sur la technologie "lit de poudres". Les interactions "poudres/faisceau laser" par technologie en lit de poudres peuvent être considérées comme exploratoires par rapport aux procédés par projection de poudre et ainsi conduire à des revêtements présentant des particularités microstructurales. L'étude du comportement sur la déformation plastique via des paramètres spécifiques matériaux est engagée en définissant un pourcentage en masse d'éléments d'addition nécessaire pour activer le mécanisme de déformation plastique par transformation de phase. Cette thèse initie une étude sur le comportement à l'endommagement sous sollicitations multi-contraintes. Des essais en fatigue flexion plane 4 points sont effectués pour différents niveaux de chargements mécaniques permettant de solliciter le volume. Des essais tribologiques sont réalisés pour engager des mécanismes physiques d'accommodation de la déformation différents et ainsi étudier la synergie entre la sollicitation de frottement et la dégradation de surface. Associées aux essais tribologiques et aux essais en fatigue, des investigations microstructurales et des analyses physico chimiques ont permis d'identifier les mécanismes d'endommagement
Simulations of a full sonoreactor accounting for cavitation
No full textInternational audienceIn spite of the increasing interest in ultrasound processing applications, industrial scale-up remains limited, in particular by the unavailability of predictive computer tools. In this study, using a previously published model of cavitating liquids implementable as a non-linear Helmholtz equation, it is shown that a full sonoreactor can be modelled and simulated. The model includes the full transducer and the vibrations of the vessel walls, using the physics of elastic solids and piezo-electricity. The control-loop used by the generator to set the optimal frequency is also accounted for. Apart from the geometry, the unique input of the model is the current feeding the transducer whereas the dissipated electrical power, transducer complex impedance and working frequency are available as outputs. The model is put to the test against experiments realized in different geometries, varying either the input current or the transducer immersion depth. Despite the overestimation of the power dissipated in the liquid, the evolution of the acoustic load in both cases is reasonably well reproduced by simulation, which partially validates the method used