Effects of Grain Size and Shape of alumina aggregates on the Sinterability and Thermal Shock Resistance of Refractory Materials

The Concerted European Action on Sustainable Application of REFractories ( is a consortium created to drive sustainable refractory materials and processes in steel production. This project which runs from 2022 2025 seeks to improve the microstructure for increased sustainability and thermo mechanical performances of refractory castables. In this work, different formulations of alumina spinel refractory castables are considered The main objective is to propose a new design for the microstructure of refractory materials with improved thermo mechanical properties by considering • The nature of aggregates ( crystallinity, physical properties • The arrangement of the calcium aluminate phases network (formation temperatures, unique formation mechanisms, location and morphology

Reuse and recyclability of refractories from steel industry

Part of the CESAREF consortium, the study presented here is dedicated to the characterization of refractory material properties after usage for potential reuse and recyclability determination. The aim of this doctoral study is to provide an insight on the variation of specific materials’ key properties (such as thermal conductivity, thermal expansion, Young’s module, modulus of rupture) after operations. Mesoscale aging studies may allow to define appropriate Finite Element Models ( to foreseen operative conditions of the refractory. Furthermore, application of an adapted FMECA (Failure Modes, Effects, and Criticality Analysis) fatigue integrated approach can be a further reliable tool to better predict refractories’ lifetime. Also, MCDA (Multi Criteria Decision Approach) implementation could help in detecting the necessary strategies to define the most convenient recycling routes

Insights on numerical models to predict potential recyclability of spent refractories from steel making industry

The present study is part of the CESAREF (Concerted European action on Sustainable Applications of REFractories) doctoral network, started in late 2022. The aim of the consortium is the contribution to scientific breakthroughs inherent to refractories for steel making sector thanks to transversal competences deriving from academic and industrial realities. European green deal and circular economy targets set by EU for 2025 are also related to the massive consumption of refractory materials in the steel industry. Operative lifetimes of refractories range from hours to several months depending on their role. As a result of increasingly tightened policies and disposal costs, and due to recent supply chain shortages, end-of-life refractories recovery and recycling practices are receiving great attention. Some of the core requirements for sustainability and circularity are the reduction of open-loop and down scaling strategies, to maintain refractory materials value as long as possible, of the end-of-life materials. Over the years application of numerical models has proved to be a useful strategy for researchers facing in-use issues related to refractory materials. In this study, different finite element models (FEM) applied to end-use refractories are discussed to understand their suitability for potential recyclability prediction. Thermomechanical characterization of prior- and post-use materials allow to identify the critical issues related to numerical models' development. The comparison between empirical results and the appropriate numerical model allow us to identify suitable pathways to improve refractories sustainability

Full reciprocal-space mapping up to 2000 K under controlled atmosphere: the multipurpose QMAX furnace

We acknowledge the ESRF and the French Collaborating Research Group (F-CRG) for provision of synchrotron radiation facility beamtime. H. Song is thanked for his work on the preliminary thermomechanical calculations and the general sizing of the furnace. The building of the furnace has been realized under the technical supervision of D. de Barros. The experiments on the sapphire vicinal surfaces and on the IUCr zirconia powder were realized with the valuable help of C. Matringe (IRCER) and J. B. Marijon (PIMM), respectively. The authors are thankful to I. Cabodi and O. Bories (Saint-Gobain CREE) for the supply of the bulk-zirconia-based materials. M. Huger and F. Gouraud from the IRCER laboratory and T. O¨ rs and V. Michel from the PIMM labora-tory are strongly thanked for their involvement during these experiments. The oxidation experiments were realized in the frame of a research program funded by the CEA Paris–Saclay Centre in collaboration with R. Guillou, M. Lesaux, D. Menut and J. L. Bechade, who are also gratefully acknowledged.A furnace that covers the temperature range from room temperature up to 2000 K has been designed, built and implemented on the D2AM beamline at the ESRF. The QMAX furnace is devoted to the full exploration of the reciprocal hemispace located above the sample surface. It is well suited for symmetric and asymmetric 3D reciprocal space mapping. Owing to the hemispherical design of the furnace, 3D grazing-incidence small- and wide-angle scattering and diffraction measurements are possible. Inert and reactive experiments can be performed at atmospheric pressure under controlled gas flux. It is demonstrated that the QMAX furnace allows monitoring of structural phase transitions as well as microstructural evolution at the nanoscale, such as self-organization processes, crystal growth and strain relaxation. A time-resolved in situ oxidation experiment illustrates the capability to probe the high-temperature reactivity of materials.The QMAX furnace has been designed and built as part of the QMAX Project No. ANR-09-NANO-031 funded by the French National Research Agency (ANR). Experiments on the bulk-zirconia-based samples were done in the frame of the ASZTECH research program funded by the ANR (ANR-12-RMNP-0007)

Nucléation et croissance d'oignons de carbone synthétisés par implantation ionique de carbone dans l'argent à haute température

thèse rédigée en mai 2001This work deals with the challenge of synthesizing new nanostructured materials. Our aim is to understand the nucleation and growth mechanisms of the different carbon phases synthesized by carbon ion-implantation into silver substrates held at high temperature (> 400 °C). Carbon onions, nanocapsules and an amorphous carbon layer are produced during the implantation experiments. These different carbon structures were characterized by using two complementary techniques : transmission electron microscopy (TEM and HRTEM) and resonant nuclear reactions analysis (RNRA). The size and microstructure of the carbon onions, but also the amount of the two other components, strongly depend on the implantation parameters. It is shown that the formation of the amorphous carbon component results from the preferential sputtering of silver, that allows the formation of a surface layer, and from a carbon precipitation at silver grains boundaries. To explain the nanocapsules formation, it is proposed that the carbon atoms precipitate on nanometric silver grains boundaries, leading to the formation of graphene layers around these grains. Surprisingly, the encapsulated metal grains are thrown out the graphitic matrix to leave the core of the nanocapsules empty. It is suggested that carbon onions nucleation occurs in two steps. Firstly, carbon atoms precipitate into the volume and form stable germs above a local critical concentration. Then, the progressive transformation of these precipitates into onion-like structures is attributed to the catalytic effect of the silver matrix on graphitisation and to the atomic displacements induced by the irradiation. It is proposed that the carbon onions growth is essentially due to the precipitation of the new implanted carbon atoms on the already formed carbon onions.Ce travail s'inscrit dans le cadre des études menées pour synthétiser de nouveaux matériaux nanostructurés. Notre but est de comprendre les mécanismes de nucléation et croissance des différentes phases de carbone synthétisées par implantation ionique dans des substrats d'argent portés à haute température (> 400 °C). Des oignons de carbone, des nanocapsules et une couche de carbone amorphe se forment au cours des implantations. L'étude de la formation de ces différentes structures est réalisée à l'aide de deux techniques complémentaires : la microscopie électronique en transmission (MET et METHR) et l'analyse par réaction nucléaire résonante (RNRA). La taille et la microstructure des oignons de carbone, ainsi que la proportion des deux autres composantes, dépendent fortement des paramètres d'implantation. Nous montrons que la formation de la couche de carbone amorphe résulte d'une précipitation préférentielle des atomes de carbone à la surface et aux joints de grains. Pour expliquer la formation des nanocapsules, nous supposons que les atomes de carbone précipitent aux joints de grains nanométriques formant des couches graphitiques autour de ces grains. De manière surprenante, il s'ensuit une éjection du grain de métal encapsulé en dehors de la cage graphitique pour laisser le cœur de la nanocapsule vide. Nous suggérons que la nucléation des oignons de carbone s'effectue en deux étapes. Tout d'abord, le carbone, très peu soluble dans l'argent, précipite majoritairement dans le volume et forme des germes critiques stables à partir d'une concentration critique locale. Ensuite, ces précipités se transforment progressivement en oignons de carbone sous les effets conjugués de l'effet catalytique de la matrice d'argent sur la graphitisation et des déplacements atomiques induits par l'irradiation. Nous proposons que la croissance des oignons de carbone est essentiellement due à la précipitation des nouveaux atomes de carbone sur les oignons déjà formés

Nucléation et croissance d'oignons de carbone synthétisés par implantation ionique de carbone dans l'argent à haute température

POITIERS-BU Sciences (861942102) / SudocSudocFranceF

Étude de l'évolution thermique de surfaces vicinales de monocristaux d alumine a (réalisation de substrats gabarits pour l élaboration de nanostructures auto-organisées)

Les systèmes nanostructurés comportant des îlots hétéroépitaxiés synthétisés sur des surfaces d oxyde présentent un grand intérêt fondamental et technologique. Dans de tels systèmes, le contrôle de l organisation, de la forme et de la taille des îlots est d une importance primordiale puisque ces caractéristiques déterminent les propriétés physiques finales. L utilisation des surfaces vicinales, présentant des marches périodiques semble être une méthode intéressante pour pouvoir auto-organiser des nanoparticules à la surface d un substrat. Ce travail est consacré à l étude approfondie du comportement des marches de surfaces vicinales de saphir sous traitement thermique. L un des objectifs de ce travail est d identifier des situations où les surfaces structurées sont suffisamment stables pour être utiliser comme substrats gabarits. Les substrats ont été traités à des températures allant de 1000 à 1500C pendant des durées de 0,5 à 64 h et sous différentes atmosphères (air, neutre et saturée en oxygène). La morphologie des surfaces a été suivie par microscopie à force atomique (AFM) et diffusion centrale sous incidence rasante (GISAXS). L observation de ces surfaces a permis de distinguer deux morphologies de surface : la première correspond à une mise en ordre monodimensionnelle des marches et la seconde morphologie à une mise en ordre bidimensionnelle. Au cours de ce travail, nous avons d une part montré que l on peut contrôler la structuration des marches en fonction des conditions du traitement thermique et de l'angle de taille et d autre part discuté les mécanismes de diffusion et de mise en ordre des marches.Nanostructured systems based on heteroepitaxial islands grown onto oxide surfaces are attracting intensive interest due to both the fundamental significance and potential application. In such nanosystems, the control of the shape, and the size of the islands is of prime importance in determining the overall physical properties. In addition, many of the applications so far envisaged also require precise arrangement of these structures into ordered arrays. The use of vicinal surfaces, which show atomic step separated by terraces or facet, appears as an attractive mean to produce self-organized arrays of nanostructures. This work is devoted to the detailed study of the step behaviour on vicinal surfaces of sapphire under annealing treatment. One of the objectives of this work is to identify situations, where the structured surfaces are enough stable to be used as templates. The substrates were annealed from 1000 to 1500 C during different times ranging from 0.5 to 64 h and under various environments (air, neutral and oxygen-saturated). The surface morphology was characterized by Atomic Force Microscopy (AFM) and Grazing Incidence Small-Angle X-ray Scattering (GISAXS). The observation of these surfaces allowed us to identify two surface morphologies: the first one corresponds to a one-dimensional ordering of steps and the second one to a two-dimensional ordering. During this work, we have demonstrated that we can control the step-ordering as a function of annealing conditions and miscut angle. Furthermore diffusion mechanisms and step-ordering processes are discussed.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Verres nanostructurés par séparation de phases dans le système silice oxyde d étain (Elaboration par voie sol-gel et caractérisation microstructurale)

Ce travail est consacré à l élaboration par voie sol-gel de verres de silice et d oxyde d étain nanostructurés par séparation de phases. L étude de l évolution microstructurale de ce matériau a été effectuée durant la gélification des sols et lors de traitements thermiques de séparation de phases et de cristallisation de l oxyde d étain dans les xérogels. L essentiel des résultats expérimentaux a été obtenu au travers de campagnes de mesures de diffusion centrale des rayons X ou de diffraction des rayons X réalisées sur des sources de rayonnement synchrotron (SOLEIL et l ESRF). Des gels mixtes homogènes contenant jusqu à 50% d étain ont été obtenus. Le processus d agrégation régissant la gélification a été identifié comme étant un mécanisme RLCCA (Reaction Limited Cluster Cluster Aggregation). La modification des différents paramètres chimiques a essentiellement un effet cinétique sur la gélification. Après séchage, les xérogels obtenus ont été soumis à des traitements thermiques. Un prétraitement de séparation de phases à 250 C favorise la création de nanocristaux de petite taille. A cette température la séparation de phases est lente et semble être de la décomposition spinodale pour des xérogels contenant entre 10 et 30 % d étain. Des cristaux assez petits pour pouvoir observer des phénomènes de luminescence ont été obtenus avec un xérogel contenant 10% d étain après un prétraitement thermique de séparation de phases et un traitement de cristallisation à 350 C. Il est possible de rendre les xérogels transparents par un traitement thermique supplémentaire à 550 C, ceci sans modifier la taille des nanocristaux obtenue à 350 C.This work deals with the feasibility of the electrochemical hydrogen insertion into the substoichiometric titanium carbides TiCx (0.5 <= x <= 1) obtained by conventional reactive sintering (natural and hot pressing), and under the form of thin films, as obtained by magnetron reactive sputtering. The electrochemical hydrogen insertion in this material strongly depends on several parameters : (i) the elaboration process ; (ii) the crystalline structure ; and (iii) the stoichiometry of the carbide. The carbides TiCx obtained by hot pressing with x lower or equal to 0.70 present an ordered crystalline structure where the (111) carbon plans are partially empty, allowing the hydrogen insertion into the material. On the contrary, the carbides prepared by reactive sintering at high temperature (2100C) do not allow the hydrogen insertion whatever the carbide stoichiometry, because of the disorder of the carbon vacancies inside the crystalline structure. Nevertheless, it is possible to order these carbon vacancies by annealing at low temperature (730C), this treatment rendering again the carbon plans (111) partially empty, and so, allowing the hydrogen to penetrate inside the titanium carbide with a diffusion coeffcient estimated at 1.2 X 10-13 cm2.s-1 in TiC0.60. The electrochemical reaction of oxidation of the titanium carbide was also studied, and it is demonstrated that TiC oxidizes into TiO2 accompanied by a CO2 release.LIMOGES-BU Sciences (870852109) / SudocSudocFranceF

Nucleation and crystallization of tin oxide nanodots into silica based xerogels. A wide angle x-ray scattering quantitative study

International audienc

A new way to prepare tin oxide precursor polymeric gels

International audienceTransparent tin oxide gels are elaborated in the isopropoxide/toluene/isopropanol system. The gelation occurs at room temperature without any acid or base additions. The formation of the SnO2 precursor gels polymeric network is evidenced by Fourier transform infrared spectroscopy. The gelation time is studied as a function of the complexing ratio R = [acac]/[Sn(OR)4], the hydrolysis ratio W = [H2O]/[Sn(OR)4], the concentration of tin oxide precursor C = [Sn(OR)4], and the volume fraction of toluene P = (toluene volume) / (total solvent volume)