Développer les compétences transversales pour engager les étudiants dans un APP de spécialité : retour d’expérience

À l’IUT 1 de Grenoble, les enseignantes de thermodynamique et d’expression-communication ont introduit une dimension interdisciplinaire à un enseignement organisé sous forme d’apprentissage par problèmes (APP) pour répondre aux difficultés d’engagement des étudiants. Le point central a été d’accompagner la montée en compétences des étudiants sur le travail de groupe. Parallèlement, une réflexion a été menée sur les ressources et leur mise à disposition ainsi que sur l’organisation de l’environnement de travail. Ces actions ont permis de tirer un premier bilan ouvrant des perspectives dans un contexte de développement de l’approche par compétences dans les Instituts Universitaires de Technologie (IUT) et à l’Université en général

Reduction and Oxidation Behavior of Ni<i>_x</i>Fe_3–<i>x</i>O_4−δ Spinels Probed by Reactive in Situ XRD

A semiempirical crystal model based on the hard sphere model is proposed to determine the oxygen deviation from stoichiometry (δ) of a mixed metal spinel of general formula A<i>_x</i>B_3–<i>x</i>O_4−δ from its lattice parameter. The model was calibrated with data for Ni- and Mn-ferrites taken from the literature. We demonstrate that the lattice parameter of a Ni<i>_x</i>Fe_3–<i>x</i>O_4−δ spinel can be predicted within a precision of 0.01 Å. This model was used to monitor the value of <i>x</i> and δ of Ni<i>_x</i>Fe_3–<i>x</i>O_4−δ nanopowders (with initial <i>x</i> = 0, 0.25, 0.5, and 1) during reactive in situ X-ray diffraction H₂ reduction and CO₂ oxidation at 400 °C. Results show that H₂ reduction occurs in two steps: (i) transition from a γ-type (δ < 0) to a regular (δ ≈ 0) spinel and (ii) preferential reduction of nickel from the spinel lattice to form a (Ni,Fe) solid solution. The face-centered cubic configuration for this alloy is favored in cases of high initial contents of nickel (<i>x</i> = 0.5, 1), and body-centered cubic for samples with low initial nickel content (<i>x</i> = 0, 0.25, 0.5). A subsequent CO₂ reoxidation of the samples shows that the process is partly reversible: iron will first be preferentially reintegrated into the lattice, and the initial excess of oxygen will be partially replenished. In addition to providing a thorough description of the phases and their evolution during reaction, these results describe the thermochemical behavior of nonstoichiometric nickel ferrites for the first time

Dielectric and magnetic properties of NiFe2O4 at 2.45GHz and heating capacity for potential uses under microwaves

International audienceThis paper presents the dielectric and magnetic properties, measured at 2.45 GHz, of a new nickel ferrite, NiFe2O4, synthetized by plasma technology. These properties were measured by the small perturbation method in a resonant cavity, from 293 to 513 K. Using these values, the adiabatic heating of nanoparticles of NiFe2O4 under microwave irradiation was also modeled. The wave propagation equation (Maxwell׳s equation) coupled to the heat transfer in the solid was numerically solved. The influence of parameters such as the bed volume, its porosity, the microwave incident power or the microwave system geometry is discussed. This study demonstrates that NiFe2O4 nanoparticles can be rapidly heated up to at least 513 K under microwaves and can probably achieve higher temperatures according to the thermal insulation. The magnetic contribution to heating overcomes the dielectric one in the explored temperature range. Very efficient energy yield (>90%) can then be achieved when the magnetic field position is centered over the bed

Development and cost analysis of solar micro-reactor arrays for hydrogen production

International audienc