Catalytic coatings on steel for low-temperature propane prereforming to solid oxide fuel cell (SOFC) application

Catalyst layers (4–20 lm) of rhodium (1 wt%) supported on alumina, titania, and ceria–zirconia (Ce0.5Zr0.5O2) were coated on stainless-steel corrugated sheets by dip-coating in very stable colloidal dispersions of nanoparticles in water. Catalytic performances were studied for low-temperature (6500 C) steam reforming of propane at a steam to carbon ratio equal to 3 and low contact time (0.01 s). The best catalytic activity for propane steam reforming was observed for titania and ceria–zirconia supports for which propane conversion started at 250 C and was more than three times better at 350 C than conversion measured on alumina catalyst. For all catalysts a first-order kinetics was found with respect to propane at 500 C. Addition of PEG 2000 in titania and ceria–zirconia sols eliminated the film cracking observed without additive with these supports. Besides, the PEG addition strongly expanded the porosity of the layers, so that full catalytic efficiency was maintained when the thickness of the ceria–zirconia and titania films was increased

Catalytic coatings on stainless steel prepared by sol–gel route

Stainless steel (flat and microstructured) substrates have been coated with sol–gel catalysts made up of metal nanoparticles (Rh, Ni, Pt) dispersed on alumina and alumina–ceria supports. The aluminum monohydroxyde (boehmite) sols were synthesized by hot hydrolysis/peptization of an aluminum alkoxide (Yoldas method). It is shown that the rheological properties of the sol, especially the thixotropy, play a key role on the homogeneity and the quality of the film deposited on the metal substrate. The catalyst layers have a very good adhesion, a thickness which can be easily controlled (in the range 0.1 to 10 μm), a large specific surface area and a good mechanical and thermal stability

Effect of cerium concentration on corrosion resistance and polymerization of hybrid sol–gel coating on martensitic stainless steel

Stainless steels are increasingly used in the aeronautics field for the manufacture of structural parts. One of them, the X13VD martensitic stainless steel (X12CrNiMoV12-3), known for its good mechanical properties, has a poor corrosion resistance in confined or severe environments. In the past years, Cr(VI) based pre-treatments have been currently used for corrosion protection of different metals, however, they are toxic and due to environmental regulations, they will be definitely banned in a near future. Alternatives to replace Cr(VI) show advantages and drawbacks considering key properties such as: corrosion resistance, adhesion of coatings, fatigue resistance, durability and reliability. However, some of their possible alternatives show high potential. In this paper, a process was developed to improve the corrosion resistance of the martensitic stainless steel. Organic–inorganic hybrid coatings with different cerium concentrations were deposited onto stainless steel by sol–gel process. Corrosion resistance of the coatings was evaluated by electrochemical impedance measurements and it has been proved that cerium concentration of 0.01 M into hybrid coating was an optimal content. Adhesion tests were also carried out by "nanoscratchtest" to characterize the coatings mechanical properties as a function of cerium concentration but results do not clearly show the influence of cerium for the coating adhesion toward the substrate. To try to correlate with the electrochemical properties, liquid 29Si NMR spectroscopy was then performed to investigate hydrolysis and condensation reactions of sol–gel process, and by this method, it was demonstrated that for higher cerium concentration (>0.01 M) there is a modification of the chemical structure of the sol–gel network

Accreditation Of Prior Experiential Learning As A Catalyst For Lifelong Learning: Analysis And Proposals Based On French Experiments

In this paper, the researchers analyse how lifelong learning can be enriched and develop a different perspective based on the experiment involving the accreditation of prior experiential learning (APEL) conducted in France at the university level. The French system for the accreditation of prior experiential learning, called Validation des Acquis de l’Expérience (VAE), accredits prior learning from past experiences (professional and otherwise) and can lead to full university degrees or diplomas. A literature review on lifelong learning shows that worldwide, it is based on different conceptions and approaches, according to the realities of the education and labour systems and the relationship between them. The researchers note however that work experience is less valued than the acquisition of new and complementary knowledge.Studies on VAE in France in higher education show that a thorough analysis of prior experiential learning: first, improves the quality of the experience as a potential source of skills; second, may provide ways to improve the candidate's experiential learning, and third, may help define the direction for lifelong learning. Therefore, recognition of this experiential learning could be a key catalyst for lifelong learning. The findings support two main arguments advocating a central role for the recognition of prior experiential learning in the lifelong learning process particularly in France: potentially individualized learning paths, personal empowerment and shorter training times; and a focus on experience - and not just professional experience - that is in tune with today’s societal changes and the aspirations/constraints of each individual

Sol–gel processing and characterization of (RE-Y)-zirconia powders for thermal barrier coatings

The effect of doping on the structural, morphological and thermal properties of ZrO2–XO1.5 (X=Y, La, Sm, Er) solid solutions for thermal barrier (TBC) applications was investigated. Oxide powders of various compositions from 9.7 to 40 mol% XO1.5 (X=Y, La, Sm, Er) were synthesised by the sol–gel route. The structural analysis of the powders was performed using X-ray diffraction analysis coupled with Rietveld refinements and the measurement of their specific surface area with the BET method. For each rare earth dopant, the morphology of the powders varies from monoliths to agglomerates of thinner particles when the doping amount increases. In order to determine the specific heat, the thermal diffusivity at room temperature and the thermal expansion coefficient of some selected compositions, DSC, laser thermal diffusivity and hightemperature dilatometry measurements were performed on samples densified by Spark Plasma Sintering. Working thermal characterisation indicated that zirconia doped with 30 mol% SmO1.5 and ErO1.5 have better insulation properties and a lower thermal expansion coefficient than our reference YSZ ceramic. These various compositions are very promising for the elaboration of multilayer TBCs by the sol–gel process

Sur les finalités de l’utilisation pédagogique des musées

La pédagogie muséale vise, entre autres, à ouvrir le musée à tous les enfants afin de leur faire découvrir des univers différents sur le mode actif. Mais la finalité sur laquelle cet article s’attarde est celle qui consiste à former la sensibilité de l’enfant. Ainsi, l’auteur montre comment une visite au musée bien réalisée peut contribuer à développer chez l’enfant des sentiments positifs à l’égard des objets présentés et, plus largement, à l’égard du monde humain présenté. Le musée peut en outre favoriser le développement d’attitudes affectives par rapport au temps de même qu’il peut aider à façonner des identités individuelles et collectives. Finalement, la didactique muséale initie l’enfant à l’autodiscipline dans le plaisir en lui apprenant simultanément à être actif au musée et à respecter les objets qui s’y trouvent. Museum education seeks to open up the museum to children, inviting them to discover whole new worlds. Among the objectives of museum education, I wish particularly to consider the formation of children’s sensibilities. A well-planned museum visit encourages children to have positive feelings for objects seen, and more broadly speaking, to acquire a sense of what it is to be human. The museum may also promote certain attitudes to time, and to identity, whether collective or individual. In short, museum education initiates children into pleasurable self-discipline, helping them to be active while in the museum and to respect the objects found there.

Sur les finalités de l’utilisation pédagogique des musées

La pédagogie muséale vise, entre autres, à ouvrir le musée à tous les enfants afin de leur faire découvrir des univers différents sur le mode actif. Mais la finalité sur laquelle cet article s’attarde est celle qui consiste à former la sensibilité de l’enfant. Ainsi, l’auteur montre comment une visite au musée bien réalisée peut contribuer à développer chez l’enfant des sentiments positifs à l’égard des objets présentés et, plus largement, à l’égard du monde humain présenté. Le musée peut en outre favoriser le développement d’attitudes affectives par rapport au temps de même qu’il peut aider à façonner des identités individuelles et collectives. Finalement, la didactique muséale initie l’enfant à l’autodiscipline dans le plaisir en lui apprenant simultanément à être actif au musée et à respecter les objets qui s’y trouvent. Museum education seeks to open up the museum to children, inviting them to discover whole new worlds. Among the objectives of museum education, I wish particularly to consider the formation of children’s sensibilities. A well-planned museum visit encourages children to have positive feelings for objects seen, and more broadly speaking, to acquire a sense of what it is to be human. The museum may also promote certain attitudes to time, and to identity, whether collective or individual. In short, museum education initiates children into pleasurable self-discipline, helping them to be active while in the museum and to respect the objects found there.

Reinforced sol–gel thermal barrier coatings and their cyclic oxidation life

Cyclic oxidation life enhancement of sol–gel thermal barrier coatings is obtained via the reinforcement of the controlled micro-crack network that forms during the initial sintering of the deposit. Two different sol–gel methods are used to fill in the process-induced cracks, namely dipcoating and spray-coating. Filling parameters, for instance the number of passes or the viscosity of the sol are adjusted, using various techniques such as profilometry and microstructural analysis, to optimise crack filling. Cyclic oxidation tests are implemented at both 1100C and 1150C to investigate the efficiency of the various reinforcement procedures developed and address the influence of the specific microstructure on the oxidation behaviour

Structural study of metastable tetragonal YSZ powders produced via a sol-gel route

Sol-gel yttria stabilized zirconia (YSZ) is investigated in this paper. The final aim is to process YSZ powders into stable slurries in order to prepare thick coatings for thermal barrier to be applied on hot turboengine components. In fact, this system is well-known for its excellent thermomechanical resistance at elevated temperatures but the relationship between these performances and the structural and microstructural characteristics of these materials is not fully understood. This paper reports a preliminary study concerning recent progress on the structural properties control of YSZ powders synthesized by solâ��gel process and the main advantages of this process compared to conventional methods. As a first step towards this understanding, structural investigations of ZrO2 doped with various xmol%YO1.5 coatings, have been performed using X-ray diffraction, structural Rietveld refinement, Raman spectra analysis and transmission electron microscopy. The evolution of the crystallographic structure of YSZ powders after air annealing at various temperatures 1100 °C, 1200 °C and 1400 °C was studied to well understand the conditions of the formation of desired metastable tetragonal phase (t). Then, this work should allow to correlate chemical and thermomechanical parameters as YSZ formulation and sol-gel elaboration conditions, temperature and t phase performances

Les revêtements sol-gel pour l’anticorrosion

La voie sol-gel est une méthode de synthèse mais également un procédé de dépôt en phase liquide. Depuis plusieurs années, la communauté scientifique travaillant sur la technique de dépôt par voie sol-gel est impliquée dans des problématiques de durabilité des matériaux. Des travaux montrent les potentialités intéressantes de cette technique pour des applications anticorrosion et font émerger des solutions prometteuses pour le remplacement des couches de conversion chromatées. Ce procédé de « chimie douce » permet d’élaborer des revêtements hybrides ou céramiques sous forme de couches minces. Dans les procédés développés pour l’anticorrosion, les sols sont le plus souvent constitués de précurseurs de type alcoxydes de silicium, zirconium, ... fonctionnalisés ou non. Ce sol peut être déposé par dip-coating ou spray-coating sur différents substrats pour former un film mince qui, au cours du processus d’hydrolyse et de condensation, se transforme en gel. Ce gel, défini comme une structure tridimensionnelle, résulte d’une agrégation homogène de sorte que macroscopiquement ce milieu renfermant du solvant semble monophasé. Lorsque dans une étape ultérieure le solvant est éliminé par un étuvage à basse température, l’architecture du gel est détruite et le composé hybride obtenu sous forme de couche mince dense est appelé xérogel. Parmi les revêtements issus de la voie sol-gel destinés à la protection contre la corrosion, les plus avancés en terme de développement industriel sont des revêtements protecteurs de type barrière renfermant un promoteur d’adhérence pour peinture. Les travaux sur les couches anticorrosion dites actives renfermant des inhibiteurs de corrosion sont nombreux et s’orientent plus récemment sur la recherche d’architectures de couches tendant à optimiser leur efficacité dans le temps. Afin de montrer dans cette présentation le grand intérêt de ce nouveau procédé pour l’obtention de couches anticorrosion, nous faisons état de récents travaux issus de la littérature