Portail HAL UHA (Université de Haute-Alsace)
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Comparaison d'approches de navigation en formation pour une flotte de robots mobiles
No full textInternational audienc
Fouilles archéologiques à Serra del Cedro et Civita di Tricarico (Programme Ignobilia Oppida Lucanorum) (2023)
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Strains, stresses and microcracks in pure zirconia polycrystals
No full textInternational audienceIn pure dense zirconia-based materials, cooling induces a martensitic phase transition associated with a large variation of the ZrO2 molecular volume and an anisotropic thermal expansion, both leading to very high level of internal stresses and the formation of large multiscale microcrack networks. We investigate in this work the relationships between the main crystal planes or directions and the orientation of the microcracks using specimens that have undergone a single thermal cooling from the liquid state to room temperature. Two distinct crack orientations have been identified. The first one is observed on the {001}m planes of monoclinic crystals, and the second one on the {110}c planes of the parent cubic phase. We propose to explain these observations through the calculation of stresses and strains at the crystal scale induced by phase transitions all along the cooling process. The experimental observations of crack orientations are in good agreement with the strain model based on a phenomenological approach of the martensitic transformation. Accordingly, the strain accommodation mechanisms that occur during this transition appear to be a critical factor in the formation of crack or twin boundary between individual monoclinic crystals
« C’est Hierome Giglio Italien qui parle, duquel j’ay traduit ce chapitre » : transmission des savoirs et énonciation dans les Diverses Leçons d’Antoine du Verdier
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Oxidation of magnesium particles in a fluidized bed reactor
No full textInternational audienceMagnesium is a promising fuel for the metal-enabled cycle of renewable energy and for space power systems. However, the existing methods for combustion of magnesium powders have difficulties with maintaining flame stability. Further, the kinetics and mechanisms of high-temperature oxidation of magnesium powders, needed for combustion modeling, are still not well understood. In the present work, a fluidized bed reactor was used to study the oxidation of spherical magnesium particles in an oxygen/helium environment at temperatures of 530, 550, and 570 °C. The extent of conversion was determined based on the measured oxygen concentration in the exhaust gas. The obtained curves of the extent of conversion and of the conversion rate were analyzed using the Avrami-Erofeev equation and the Mampel-Delmon model. The activation energy obtained with the Avrami-Erofeev equation was 191 or 198 kJ∙mol−1, depending on the dimension (3 or 2, respectively). The Mampel-Delmon approach has shown that the activation energies of nucleation and growth are equal to 189 and 120 kJ∙mol−1, respectively, i.e., the former is virtually the same as the apparent activation energy obtained with the Avrami-Erofeev model at a dimension of 3. With increasing temperature, the rate of nucleation rises faster than the rate of growth. The results obtained with the Mampel-Delmon approach help understand the oxidation mechanism, while the Avrami-Erofeev equation and the obtained apparent activation energy can be used in combustion modeling for simplicity
Investigation of the Morphology, Composition, and Structure of Dehydrated Sewage Sludge of a Pulp and Paper Enterprise
No full textInternational audienceThe composition, structure, and morphology of dehydrated sewage sludge, a by-product of pulp and paper production, were studied. The thermal characteristics of sewage sludge were investigated. An elemental analysis of the sewage sludge was carried out, the results of which revealed a large number of noncombustible elements (5.5%), including heavy metals (vanadium, chromium, nickel, zinc, and strontium), compared to other types of fuel. Thermogravimetric studies on the thermal decomposition of dehydrated sediment were carried out. The thermogravimetric and differential thermogravimetric curves were described, and the temperature ranges of drying, release of volatile substances, and combustion of coke residue were determined. Microscope photos showed that the particle size of the sediment varied from 0.5 and 350 nm, and amorphous flakes and crystalline inclusions were the main elements of its structure
Cocoa Pod Husk Carbon Family for Biogas Upgrading: Preliminary Assessment Using the Approximate Adsorption Performance Indicator
No full textInternational audienceThe preliminary selection of adsorbents for the separation of a gas mixture based on pure gas adsorption remains a critical challenge; thus, an approximate adsorption performance indicator (AAPI) was proposed for the initial evaluation of the adsorbents to separate the biogas main constituents (carbon dioxide/methane (CO2/CH4)) by studying their pure gas adsorption. Three samples derived from cocoa pod husk (CPH), namely Cabosse-500 (pyrolyzed at 500 °C), Cabosse-700 (pyrolyzed at 700 °C), and Cabosse-A-700 (activated with CO2 at 700 °C), were synthesized, characterized, and evaluated for the pure gases adsorption. This study presents an AAPI evaluation, which takes into account adsorption capacity, approximate selectivity, and heat of adsorption. Adsorption isotherms indicate the ability of the CPH family to selectively capture CO2 over CH4, as they have a high approximate selectivity (>1) thanks to their physical properties. Changing the pyrolysis temperature, activation methods, and varying the pressure can significantly change the choice of the most effective adsorbent; Cabosse-A-700 showed better performance than the other two in the low and high pressure range owing to its presence of micropores and mesopores, which enhances the CO2 adsorption and therefore the AAPI
Effet des paramètres agronomiques sur le développement des tiges et des fibres textiles de chanvre dans le Sud-Alsace : aspects physiques et mécaniques
No full textEconomic and ecological issues are driving the textile industry to relocate close to production sites and minimize its environmental impact. At the same time, current agronomic challenges are encouraging farmers to diversify crop rotation and reduce inputs (fertilizers, irrigation, etc.). The development of hemp in the Haut-Rhin region (Grand Est) would help meet all these challenges. This work showed that cultivation and retting can be adapted to Alsace's agropedoclimatic conditions by optimizing the cultivation itinerary and controlling field retting to extract the best possible fiber quality. To achieve this, studies were carried out over three seasons (2018, 2020 and 2021), focusing on the cultivation and field retting of hemp and, more specifically, analyzing the impact of several factors such as weather, variety and duration. This project is divided into two parts: the agronomic study and the fiber study. The agronomic analysis focuses on different matrices: soil, plants and fiber bundles. The fiber analysis focuses on the morphological and mechanical properties of hemp fibers. The results demonstrated the multitude of agronomic factors influence stem and fiber development during cultivation, as well as hemp's textile fiber productivity. On the other hand, climatic factors impacting the proliferation of microorganisms and the degradation of plant tissues during retting in the field are identified in order to control the extraction of textile fibers.Les enjeux économiques et écologiques poussent l’industrie textile à se relocaliser près des lieux de production et à minimiser son impact environnemental. Parallèlement, les défis agronomiques actuels incitent les agriculteurs à diversifier les assolements et à réduire les intrants (engrais, irrigation, etc.). La valorisation du chanvre dans le Haut-Rhin (région Grand Est) permettrait de répondre à tous ces enjeux. Ce travail de thèse a montré que la culture et le rouissage peuvent être adaptés aux conditions agropédoclimatiques alsaciennes en optimisant l’itinéraire de culture et en maîtrisant le rouissage au champ afin d’extraire la meilleure qualité possible de fibres. Pour ce faire, des études furent menées pendant trois saisons (2018, 2020 et 2021) en se focalisant sur la culture et le rouissage au champ du chanvre et plus particulièrement en analysant l’impact de plusieurs facteurs tels que la météo, la variété et la durée. Ce projet est divisé en deux parties : l’étude agricole et celle des fibres. L’analyse agronomique porte sur différentes matrices : sol, végétaux et faisceaux de fibres. L’analyse des fibres se concentre sur les propriétés morphologiques et mécaniques des fibres de chanvre. Les résultats ont montré qu’une multitude de facteurs agronomiques influencent le développement des tiges et des fibres pendant la culture, ainsi que la productivité en fibres textiles du chanvre. D’autre part, les facteurs climatiques impactant la prolifération des microorganismes et la dégradation des tissus végétaux pendant le rouissage au champ sont identifiés afin de maîtriser l’extraction des fibres textiles
Quantum-confined bismuth iodide perovskite nanocrystals in mesoporous matrices.
No full textInternational audienceEncapsulation of bismuth iodide perovskites within the ordered silica pores of various diameters results is quantum-confined nanocrystals
