Portail des publications scientifiques IMT Mines Alès
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Fire behaviour of EPDM/NBR panels with paraffin for thermal energy storage applications. Part 2: Analysis of the combustion residues
No full textInternational audienceIn the first part of this work, novel elastomeric panels with paraffin for thermal energy storage applications were developed. Ethylene-Propylene Diene Monomer (EPDM) rubber filled with a shape-stabilized paraffin, as phase change material with a melting temperature of 28 °C, was covered with a nitrile-butadiene rubber (NBR) envelope. In order to improve the fire resistance, two selected flame retardants (FRs) were dispersed both in the EPDM core and in the NBR envelope. In this work, the combustion residues from cone calorimeter tests were analysed by various techniques to explain the combustion mechanisms and the interaction of FRs. Nuclear magnetic resonance (NMR) evidenced the complexity of the system, characterized by the formation of char, by the reactivity of organomodified montmorillonite (oMMT) in presence of phosphates and structural rearrangements of the inorganic components. The use of a flame retardant based on ammonium polyphosphate and synergistic agents (based on phosphorus) led to formation of different Al-O-P and Si-O-P compounds. The X-ray diffraction (XRD) analysis highlighted that the formation of silicon phosphate, from the reaction of ammonium polyphosphate and oMMT, was possible only at high phosphorus contents. From the phosphorus content detected through energy dispersive X-ray spectroscopy (EDX) it was possible to indicate that the phosphorus remained in the condensed phase during the combustion
Flammability of Thick but Thermally Thin Materials including Bio-Based Materials
No full textInternational audienceThe fire reaction of various types of flammable lightweight materials is investigated using a cone calorimeter. The influences of parameters such as sample density, sample mass, effective heat of combustion and heat flux on the mass loss after exposition are discussed. Interpretations of the hemp fibers’ tests results lead us to propose a phenomenological model able to calculate the peak of heat release rate (pHRR) of such thermally thin materials, with or without flame retardant. A database gathering the whole results of tests performed on a large set of materials including fibers, bio-resources panels, bio-based concretes and fabrics is used to validate the proposed model. Interestingly, the model is found to be relevant also for denser wood specimens. The model is based on the distinction of the contributions of the exposed top layer and the deeper layer to the combustion. Indeed, in such materials, the heat conduction is limited (either by the intrinsic properties of the material or by the formation of an insulating char) and therefore the pHRR only depends on a limited volume of materials directly absorbing the heat flux from the radiant cone. Accuracy and limitations of the model are discussed
Aminophosphonate CuO nanocomposites for uranium(VI) removal: Sorption performance and mechanistic study
No full textInternational audienceTwo aminophosphonate matrices (mono-aminophopshonate, MAP, and bi-aminophosphonate, BAP) are synthesized, varying the molar proportions of three precursors (thiocarbazide, p-phthalaldehyde, and triphenylphosphite). Nano-composites (CuO-MAP and CuO-BAP) are successfully elaborated by impregnation of the matrices with copper sulfate solution before processing to in situ precipitation of copper in alkaline solution (simultaneous partial Cu reduction). The sorbents are characterized using: TEM, XRD, elemental analysis, SEM-EDX, BET, titration (pHPZC), XPS and FTIR analyses. Uranium sorption properties are compared for the different sorbents through the study of pH effect (optimum close to 4.5), the uptake kinetics (equilibrium reached in 60 min) and sorption isotherms. Uptake kinetics are finely fitted by the pseudo-second order rate equation (and the resistance to intraparticle diffusion). The sorption isotherms are modeled by the Langmuir equation with maximum sorption capacity (mmol U g−1) decreasing according to CuO-BAP(1.15) ≫ CuO-MAP(0.80) > BAP(0.74) ≫ MAP(0.50). The enhanced textural properties and the increase in the density of sorption sites (probably completed by a better steric arrangement for improved reactivity) may explain this ranking. The sorption is endothermic: sorption capacity and affinity coefficient increase with temperature. Uranium is readily desorbed from loaded-sorbents (efficiency > 98 %) using either HCl (0.2 M) solution or acidified urea (0.25 M) solution (pH 2.5) for aminophosphonate matrices and nano-composites, respectively. The type of sorbent does not affect the stability at recycling: at the sixth cycle, the loss in sorption and desorption performances varies by 6.2–7 % and 4.2–4.9 %, respectively. CuO-BAP sorbent shows high potential for uranium recovery from complex acid ore leachate. The broad spectrum of bound metals does not allow producing a pure yellow cake after ammonia precipitation of eluate (containing up to 15–22 % impurities)
La science ensemble : pratique de l’interdisciplinarité au sein d’un projet d’observatoire de l’habitat du futur
No full textInternational audienceCet article propose l'observation ethnographique et l’analyse interdisciplinaire d’un projet scientifique constitué d’une diversité de disciplines autour de la thématique de l’habitat du futur. Matérialiser par un appartement truffé de capteurs habité à l’année (universitaire) par deux étudiants volontaires et sélectionnés, la collaboration entre les chercheurs y prend une forme originale qui permet de réévaluer ce que représente l’Interdisciplinarité au sein de la recherche scientifique contemporaine. Fait social complexe, elle devient elle-même un objet sur lequel les acteurs projettent des stratégies et des attentes à la conjonction des multiples dimensions qu’elle sous-tend aussi comme organisation de la collaboration, méthodologie, perspective de résultats et incitation institutionnelle ambivalente
An Anisotropic and Asymmetric Causal Filtering Based Corner Detection Method
No full textInternational audienceAn asymmetric-anisotropic causal diffusion filtering-based curvature operator is proposed in this communication. The new corner operator produces optimal results on small structures, such as, corners at pixel level and also sub-pixel level precision. Meanwhile, this method is robust against noises due to its asymmetric diffusion scheme. Experiments have been performed on a set of both synthetic and real images. The obtained results are promising and better without any ambiguity as compared with the two referenced corner operators, namely Kitchen Rosenfeld and Harris corner detector
Flammability of thick but thermally thin materials including bio-based materials
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Purpose in life and accelerometer-measured physical activity among older adults
No full textInternational audienceObjective: Purpose in life is associated with engagement in physical activity and better cognitive health. This study examines the association between purpose in life and patterns of physical activity measured with an accelerometer and whether these patterns mediate the association between purpose and episodic memory among older adults.Methods and measures: This research is a secondary analysis of data from the accelerometry sub-study of the National Health and Aging Trends Study. Participants (N = 747; mean age = 79.20) reported on their purpose, wore an accelerometer for eight days, and completed an episodic memory task.Results: Purpose in life was associated with healthier patterns of physical activity, including higher total activity counts (β = .10, p = .002), more active bouts per day (β = .11, p = .003), less activity fragmentation (β = -.17, p < .001) and more sedentary fragmentation (β = .11, p = .002). These associations were generally similar across age, sex, race and education. Higher total activity counts and less activity fragmentation were associated with better episodic memory and accounted for part of the association between purpose and episodic memory.Conclusion: Purpose in life is associated with healthier patterns of physical activity measured through accelerometry among older adults and such patterns may be one factor in the pathway from purpose to healthier episodic memory
De la valorisation d’une plante invasive (Baccharis halimifolia) vers l’écoconception d’un panneaux bois local
No full textInternational audienceBaccharis halimifolia L. (Asteraceae) est un arbuste invasif au fort potentiel de développement sur le littoral camarguais. Les équipes des Ateliers Luma, en collaboration avec le centre de recherche C2MA de l’IMT Mines Alès sont à l’initiative de recherches qui permettraient de valoriser les broyats issus des campagnes d’arrachages de Baccharis halimifolia L. (Asteraceae) en panneaux biosourcés et biodégradables d’usage non-structurels. Dans le cadre d’un projet collaboratif, réalisé dans l’équipe Polymères, Composites et Hybrides (PCH), il a été possible de mettre au point un procédé expérimental permettant de fabriquer des panneaux de Baccharis en utilisant un liant biosourcé. Trois granulométries de broyats ont été thermo-compressées avec ce liant puis soumis à des essais de flexion 3 points pour évaluer leurs performances mécaniques. En complément, la qualité de l’interface fibre-liant a été évaluée par microscopie électronique à balayage. L’objectif est de mettre en lien les observations faites à l’échelle microstructurale et les résultats obtenus en essais mécaniques
Errors in surface energy estimation of fibres for Liquid Composite Moulding processes and potential origins
No full textInternational audienceFor a better understanding of the behaviour of new eco-reinforcements, such as recycled carbon fibres, during Liquid Composite Moulding processes (LCM), fibres surface analysis and wetting properties are studied. However, this type of analysis, using the Owens and Wendt relation requires special procedures, specifically for estimation of the contact angle. Based on two tensiometric methods, carbon and basalt fibres with different sizing are characterised in first approach. The main contribution of this study is to evaluate the error in surface energy and its components determination associated to the measurement of an alleged equilibrium contact angle deriving from static or quasi-static data