Caractérisation de l'endommagement d'origine thermique de réfractaires de type électrofondu par techniques acoustiques à haute température

International audienceL'étude des corrélations entre les évolutions du module d'Young mesuré par ultrasons en fonction de la température et les transformations physico-chimiques dans des réfractaires électrofondus à moyenne (40% massique) ou haute (94% massique) teneur en zircone a permis de mettre en évidence l'importance de l'endommagement. Le module d'Young de ces matériaux présente une évolution en boucle d'hystérésis. Au cours du chauffage, on observe une croissance de module sous l'effet de la guérison des défauts (différentiels de dilatation, phase vitreuse), et lors du refroidissement, une décroissance de module liée à l'endommagement. Cet endommagement, dont l'origine se trouve, soit dans les désaccords dilatométriques entre phases (contraintes internes), soit dans la transformation de phase de la zircone (changements volumiques) a également été mis en évidence par une mesure d'émission acoustique à haute température. L'évolution de la viscosité de la phase vitreuse joue un rôle majeur dans l'évolution de cet endommagement

Discrete Element Method (DEM) to support microstructure design of refractories

Discrete Element Method (DEM) to support microstructure design of refractorie

Caractérisation du comportement mécanique endommageable de réfractaires à haute température par couplage de techniques ultrasonores

Les réfractaires à base de cordiérite (2MgO.2Al2O3.5SiO2) et de mullite (3Al2O3.2SiO2) sont utilisés comme support de cuisson dans les fours, du fait de leur faible coefficient de dilatation (3-4.10-6°C-1) qui leur confère une très bonne résistance aux chocs thermiques. Constitués de deux phases présentant des coefficients de dilation très différents (1,5 à 3.10-6 pour la cordiérite et 6 à 7.10-6 °C-1pour la mullite), ces matériaux peuvent s'endommager au cours des cyclages thermiques du fait des contraintes internes induites. L'étude présentée porte sur la caractérisation de l'endommagement généré par ce différentiel de dilatation, grâce à l'application de méthodes ultrasonores comme l'échographie et l'émission acoustique (EA). La mise en œuvre couplées de ces deux techniques permet lors des cycles thermiques effectués (20°C à 1200°C) de suivre en continu, d'une part, l'évolution des propriétés élastiques (module d'Young) et, d'autre part, l'activité d'émission acoustique générée dans le matériau. Les réponses obtenues permettent de proposer une chronologie différenciée des mécanismes intervenant lors de la montée en température et du refroidissement

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

Performance prediction and assessment of reusability and recycling of refractory materials using the NDT sensoring approach and Machine Learning

Refractory materials are necessary for the Iron and Steel (I&S) sector to endure the demanding conditions of its manufacturing processes. These materials' brief service lives, which can range from a few minutes to several months, create substantial problems for consumption, disposal, and environmental effect. There is a rising need for sustainable solutions that are compliant with the European Green Deal's standards for reduced greenhouse gas emissions, increased energy efficiency, and life cycle assessments. The Concerted European Activity on Sustainable Applications of REFractories (Doctoral Network CESAREF), which aims to enhance research and practices linked to refractory material in the Iron & Steel industry, was founded in 2022 to address these concerns

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

Neutron diffraction measurements of residual stress distribution in large zirconia based refractory bricks produced by electro-fusion and casting

Electro-fusion and casting is used to produce large refractory bricks (∼250 kg) containing a high amount of ZrO2. These bricks are used in glass-making furnaces where good mechanical performance is required at very high temperatures (>1500 °C). During the manufacturing procedure, they develop large residual stresses as a result of the cooling conditions and structural phase transformations they underwent. This leads to stress concentration and crack formation at different length scales. In order to characterize these phenomena, a ‘multi-scale’ analysis approach is under development, where different internal strain measurement methods are combined. In this approach we benefit from different gauge volumes provided by various diffraction methods, ranging from a few hundred nanometres to a few tens of millimetres. In the present paper, the results of neutron diffraction measurements on large ZrO2 blocks are given. These results show the level of internal strains at the millimetre scale, based on (3¯11) reflection of the monoclinic ZrO2. Overall, a range of 0.025% tensile to 0.1% compressive strain was observed. Clear strain gradients were also visible, as larger values in the interior of the block were encountered

Huge local elastic strains in bulk nanostructured pure zirconia materials

From the liquid state to room temperature, two successive solid-state phase transitions occur in pure zirconia. It is well-known that the last one (tetragonal to monoclinic) is martensitic and induces large volume variations and shear strains. Elastic and inelastic behaviors of zirconia-based materials are strongly influenced by this transition and the associated strain fields that it induces. Knowledge of strain and stress at the crystal scale is thus a crucial point. Using fully dense pure zirconia polycrystals obtained by a fuse casting process, we have determined at a sub-micrometric scale, by X-ray Laue microdiffraction, the strains map at room temperature in as-cast specimens and after a post elaboration high temperature thermal treatment. We observed that the fluctuation of deviatoric elastic strain is huge, the standard deviation of normal component being in the range of 1–2%. The heat treatment tends to even further increase this range of fluctuation, despite the development of a multiscale crack network formed during the cooling. Correspondingly, the associated stress level is also huge. It lies in the 5 GPa range with stress gradient amounting 1 GPa μm−1.This work was done in the frame of the ASZTECH research program funded by the ANR (ANR-12-RMNP-0007). We acknowledge the ESRF and the French Collaborating Research Group (F-CRG) for provision of synchrotron radiation facilities beamtimes and beamline staff for their assistance. The authors are thankful to I. Cabodi and O. Bories (Saint- Gobain CREE) for the supply of the bulk zirconia-based materials