Preparation and electrical properties of dense micro-cermets made of nickel ferrite and metallic copper

Dense micro-cermets made of nickel ferrites and copper micrometric particles were obtained from partial reduction under hydrogenated atmosphere at 350 C of mixed copper nickel ferrites, and sintering in nitrogen at 980 C. The small copper particles are homogeneous in size and well dispersed in the spinel oxide matrix. No exudation of copper metal was observed after sintering. The micro-cermets prepared are semi-conducting materials with electrical conductivity lying from 44 to 130 S/cm at 980 C. Their overall characteristics make them interesting for inert anodes dedicated to aluminium electrolysis in melted cryolite

Study on the effect of cuprite content on the electrical and CO2 sensing properties of cuprite-copper ferrite nanopowder composites

The paper reports the synthesis and characterization of cuprite/copper ferrite nanopowder composites. The composites were synthesized using co-precipitation with oxalates precursor route. The phase and microstructure of the powder samples were characterized using X-ray diffraction, BET surface area analyzer and scanning electron microscopy. The powders were fabricated to device using a simple and efficient shaping technique. These devices were used further to carry out electrical property measurements in various atmospheres. The type of charge carriers were found by noting the sense of change in resistance when the air atmosphere on the sample was replaced with argon. CO2 responses were reported for the whole series of composites. The effect of cuprite concentration on the CO2 sensing performance was found to be independent of cuprite concentration up to certain limits (70%at)

Amorphous determination in calcium sulfoaluminate materials by external and internal methods

Sitio Web de la revista: http://www.icevirtuallibrary.com/toc/jadcr/currentExternal standard methodology has been successfully applied to quantify the known amounts of amorphous component that are increasingly added to cement-related materials. The consistency and accuracy of the methodology were demonstrated by the R2 values of the least-square fits determined against weighed amorphous amounts, which were close to 1.0 in all the series. This method requires common laboratory X-ray powder diffractometers (knowing the equipment constant) and avoids the dilution/alteration of the sample. However, the obtained values may be biased due to poor particle statistics. On the other hand, internal standard analysis in transmission geometry is suitable to determine the absolute amorphous and crystalline non-quantified contents that are less biased owing to enhanced particle averaging statistics. This method is, however, experimentally tedious due to the addition of the internal standard and the sample loading in the X-ray diffraction sample holders which represent inherent drawbacks to follow amorphous evolutions

Effect of synthesis method and morphology on the enhanced CO2 sensing properties of magnesium ferrite MgFe2O4

The synthesis and characterization of magnesium ferrite MgFe2O4 prepared by co-precipitation and sol gel combustion is reported. Structural characterization showed that all the samples have single spinel phase. The co-precipitated sample exhibits smaller grains and twice higher BET surface than the sol gel combustion samples. The powder was shaped to dedicated chemo-resistive home-made sensors devices. The electrical properties and sensing properties towards carbon dioxide of both MgFe2O4 powders were studied. The type of charge carriers were analysed on the basis of the change in resistance in the presence of air and argon. The sensing response towards CO2 was found to be dependent on the morphology of the powder sample and the CO2 concentration. A high response of 36% towards 5000 ppm of CO2 was reached which is good for this gas. The key role of the Mg ions modulating the electrical properties is discussed

Proposition d’un référentiel de compétences pour la formation des maitres de stage, des maitres de pratique et des superviseurs en psychologie et orthopédagogie clinique

La formation des psychologues et orthopédagogues cliniciens bénéficie du soutien de différents professionnels. Cet encadrement et cet accompagnement peuvent avoir lieu à différents moments, notamment durant les stages de master, lors d’une année supervisée et tout au long de leur carrière. Malgré le fait que les professionnels qui encadrent et accompagnent les (futurs) psychologues et orthopédagogues cliniciens exercent des compétences complexes, peu d’écrits, en Belgique francophone, balisent les compétences de ces acteurs importants. Le présent référentiel propose 6 compétences pour la formation des formateurs de terrain en formation initiale (maitre de stage), lors de l’année de pratique supervisée (maitre de pratique) et les autres formateurs rencontrés tout au long de la carrière (superviseurs) pour les domaines précités. Il constitue une adaptation d’un référentiel validé pour la formation des maitres de stages en enseignement (Baco et al., 2021 ; 2023). Il s’appuie sur la littérature propre au domaine du soin, ainsi que d’autres domaines professionnels. Cela permet de montrer le caractère transprofessionnel des compétences des formateurs, tout en préservant le caractère contextuel propre à chaque domaine professionnel. Par ailleurs, ce texte propose une définition d’un continuum. Il pourra soutenir les réformes de la formation initiale des psychologues et orthopédagogues cliniciens, dans la visée d’une amélioration continue du soin offert aux patients

Laser powder bed fusion applied to the manufacture of bulk or structured magnetic cores

International audienceRings based on pure iron have been manufactured by laser powder bed fusion. Different experimental conditions have been implemented to manufacture simple rings called “bulk”. Selected conditions were used to fabricate “structured” rings, made up of stacking of lamellae separated by weakly densified metal zones or by spacers. The magnetic properties of these rings were measured in order to determine their maximum flux density, their permeability and their magnetic losses. These properties, as well as the organizations of the magnetic domains observed by Magnetic Force Microscopy, were compared with those obtained for rings machined from castings parts or spark plasma sintered parts.The “bulk” rings resulting from laser fusion exhibit relatively high magnetic losses of the order of 80 W.kg-1 at 50 Hz under 1 T. However, this value can be lowered to about 30 W.kg-1 after a SPS treatment at 750 °C. In addition to lowering the magnetic losses, SPS annealing increases the densification of the material and thus the magnetic flux. The spacing of dense metal rings by less sintered zones or by spacers (“structured rings”), makes it possible to also greatly reduce the magnetic losses. Dividing these losses by a factor of 2 is thus possible by implementing a simple geometric arrangement

Selective Laser Decomposition of Silver Oxalate: A New Way of Preparing and Shaping Metallic Silver Patterns

International audienceA new process using the selective decomposition of silver oxalate is presented and applied to the production of transparent electrodes on a polymer substrate. It is indeed shown that the silver oxalate Ag2C2O4 can be reduced to the metallic silver state by the focused laser beam of a photolithography machine (λ = 405 nm, spot size 5 µm, power between 3 and 100 mW). Thin lines of silver of width close to 15 µm, for optimized insolation conditions, can thus be directly and easily, formed in a layer of oxalate deposited by spin coating on polycarbonate substrate. Since the metal and the oxalate are of very different chemical natures, the residual oxalate is dissolved by an ammoniacal solution without affecting the metal. The silver conductive lines have a very porous vermicular type microstructure which, however, ensures electrical conductivity. The resistive effects, which result from this not very compact filament organization, can be reduced by simply applying a uniaxial mechanical pressure perpendicular to the plane of the substrate. This operation irreversibly reduces the porosity by crushing the silver strands. One by one-centimeters samples with an electrical resistance of 10 Ω and an optical transparency of 95% (after correcting the effects of the substrate) were thus prepared. Their factor of merit expressed by (Transparency550nm)10 / Rpattern, close to 0.059 Ω−1, is at the state of the art. The selective decomposition of silver oxalates by a laser beam is therefore a very interesting way to easily make transparent conductors made of thin metallic patterns