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Refractory masonry with dry joints is widely used in the steel-making industry for the linings of several high-temperature components (>1500 ∘ C) including steel ladles and furnaces. To properly optimize the design and performance of these linings, thorough numerical models that consider the presence of joints, joints closure and reopening and the nonlinear elastic-viscoplastic behaviour (creep and stress relaxation) of refractories at high temperature are required. The present study reports on the formulation, numerical implementation, and application of a homogenized multi-scale elastic-viscoplastic model for the simulation of refractory masonry linings with dry joints. Refractory bricks are considered to exhibit linear elasticity as well as rate-dependent plasticity. Four joint patterns are predefined based on the state of bed and head joints. The homogenized elastic-viscoplastic behaviour of each joint pattern is determined using finite element based nonlinear homogenization approach. The transition criteria between the four patterns are defined in terms of macroscopic stresses and strains. Verification of the developed homogenized constitutive laws is carried out by comparing the numerical results of the detailed micro models (brick and joints are considered) with the homogeneous equivalent material models. Furthermore, comparisons with experimental results of refractory masonry walls subjected to biaxial compression load at room and high temperature are carried out. Good agreements between the experimental and numerical results are obtained. Then, the validated models are employed to predict the mechanical behavior of refractory masonry structures subjected to different loading conditions. The present numerical model is able to simulate the orthotropic, compressible, rate-dependent homogenized behaviour of mortarless refractory masonry structures, and accounts for joints closure and reopening due to loading and unloading.

Reactive impregnation concerns many science and engineering areas, such as corrosion in the steel-making industry and chemical engineering. Furthermore, reactive impregnation can become dangerous in some applications. Simulating non-reactive impregnation with classical methods is the first step before computing reactive impreg++nation. However, existing numerical methods present problems such as high computational cost and spurious oscillation. To avoid these computational difficulties, we propose the Self-organized Gradient Percolation model. It is a numerical model based on probabilistic approaches and, in particular, on percolation methods. This work aims to present a 2D model based on the 1D developed model. The first results are free from spurious oscillation and drastically reduced the computational cost compared with the classical methods.

The interface between bricks and mortar is often the weakest part of masonry structures. For refractory linings, the interface strength must be measured at high temperature. Adapted slant shear tests and a new dedicated tensile test set up are proposed here for this purpose. To test the ability of the proposed method, it was applied on two representative brick/mortar couples from room temperature up to 1450 °C. Slant shear tests were conducted to measure ultimate compression and shear stresses and to identify temperature dependent parameters of the Mohr-Coulomb failure criterion. Tensile tests were performed to identify the tensile cut-off. Depending on the brick/mortar couples, the failure can appear at the interface or in the mortar. Cohesion and tensile strength decrease sharply over 900 °C.

International audience; Mortarless refractory masonry structures are widely used in the steel industry for the linings of many high-temperature industrial applications including steel ladles. The design and optimization of these components require accurate numerical models that consider the presence of joints, as well as joint closure and opening due to cyclic heating and cooling. The present work reports on the formulation, numerical implementation, validation, and application of homogenized numerical models for the simulation of refractory masonry structures with dry joints. The validated constitutive model has been used to simulate a steel ladle and analyze its transient thermomechanical behavior during a typical thermal cycle of a steel ladle. A 3D solution domain and enhanced thermal and mechanical boundary conditions have been used. Parametric studies to investigate the impact of joint thickness on the thermomechanical response of the ladle have been carried out. The results clearly demonstrate that the thermomechanical behavior of mortarless masonry is orthotropic and nonlinear due to the gradual closure and reopening of the joints with the increase and decrease in temperature. In addition, resulting thermal stresses increase with the increase in temperature and decrease with the increase in joint thickness.

International audience; The lifespan of refractory results from a complex interaction between chemistry, thermal conditions, and mechanics. The development of numerical models able to predict the results of such complex multi-physics couplings requires an intensive use of the thermodynamics of irreversible processes framework. Today, the main barriers to reach fully predictive simulations are: the access to relevant data at high temperature (chemical kinetics, chemical expansion coefficient, etc), the numerical complexity and the computational time. The theoretical framework is briefly illustrated on refractory lining applications with a focus on the impact of the swelling induced by corrosion. Then, the numerical difficulties to ensure the numerical convergence and the accuracy of the results when solving classical partial differential equations are examined. Finally, a new approach to model the capillary impregnation by slag, based on percolation theory, is proposed. The basics of this method and the first numerical results are presented.

International audience; Mortarless refractory masonry is widely used in the steel industry for the linings of high-temperature components such as steel ladles and furnaces. Successful design of these large-sized structures requires a proper understanding of the interaction between material discontinuity introduced by the presence of mortarless joints, joints closure and reopening due to loading/unloading, and their effect on the thermomechanical response of the structure. In the present study, 3D thermomechanical models have been developed to analyze the effects of joints reopening on the thermomechanical behavior of mortarless masonry walls. Four joint patterns, with their corresponding equivalent elastic properties, have been defined based on the state of head and bed joints (open or closed). The effective elastic properties of each joint pattern have been calculated with the help of the finite element method and the strain energy-based homogenization technique. The joints reopening and closure criteria have been defined as a function of macroscopic stresses and strains. The developed material model has been implemented in a commercial finite element software and then used to analyze the thermomechanical behavior of refractory masonry walls. The numerical model has been validated by comparing the numerical results with experimental data (biaxial compression test of a flat wall). Both results are in good agreement.

International audience; Aim. - Eating disorders (EDs), disordered eating (DE) and obesity are thought to have overlapping aetiological processes. DE in obesity can jeopardize weight-loss results, and acyl ghrelin (AG) is a hormone that stimulates food intake and reward processes. The main study objective was to determine whether higher-than-expected concentrations of AG in common obesity are associated with DE symptoms. Methods. - The study population included 84 women, aged 20-55 years, free of established EDs: 55 were severely obese (OB) and 29 were of normal weight (NW). OB participants were stratified into two groups according to their median concentration of fasting AG distribution. The OB women with a high fasting plasma ghrelin concentration (HGC) were compared with both OB women with a low fasting plasma ghrelin concentration (LGC) and NW women. Participants were assessed by the Eating Disorder Inventory (EDI-2), Three-Factor Eating Questionnaire (TFEQ) and Hospital Anxiety and Depression Scale (HADS). Fasting glucose, insulin, leptin and ghrelin plasma concentrations were also quantified. Results. - Between the two AG groups of OB women, there was no statistical difference in either anthropometric or metabolic parameters, HADS, TFEQ or fasting hunger scores. However, the HGC group scored significantly higher than the LGC group on the drive-for-thinness subscale of EDI-2 (9.30 +/- 0.99 vs. 6.46 +/- 0.83, respectively; P = 0.033). Conclusion. - Results support the hypothesis of a potential relationship between fasting plasma AG concentrations and ED risk, regardless of mood and anxiety. AG may be considered a potential biomarker of vulnerability for developing EDs. (C) 2018 Elsevier Masson SAS. All rights reserved.

International audience; Mixed Ionic and Electronic Conductors (MIECs) are promising membrane materials for oxygen separation fromair at high temperature. The transient stage is critical due to the stress induced by the chemical strain, combinedwith the oxygen activity field through the membrane. In the literature, permeation models are able to predict theoxygen flux in steady state or to identify the slowest mechanism. In this paper, the proposed model aims topredict the oxygen activity fields through the membrane both in transient stage and steady state. A macroscopicapproach is proposed, the balance of a temporary species is introduced to take into account separately thedissociative adsorption, associative desorption and interface reaction between surface and bulk. New densitiesof probability are proposed to model dissociative adsorption and associative desorption in order to take intoaccount the difference between “classical” catalysis and the MIECs case. This model is implementing in the finiteelement software COMSOL Multiphysics© thanks to the combination of the modules “coefficient form PDE”and “coefficient form boundary PDE”. The results of the model are in good agreement with steady state andtransient stage experimental data. The different kinetics of oxygen release and oxygen intake are wellreproduced.

International audience; This publication presents new advances in the field of refractories characterization. These laboratory methods that combine experiments and numerical analyses and concern both the thermomechanical and thermochemical behaviour are illustrated through different examples: identification of asymmetrical creep, determination of elastic and inelastic properties, measurements of macroscopic deformation, phase transformations or corrosion kinetics. These advanced techniques offer the refractory community new opportunities to improve the knowledge and the prediction of the phenomena of degradation of the refractories.

International audience; In this article, we test a horizontal detect and avoid algorithm for UASs flying in Terminal Control Areas. We have used recorded commercial traffic trajectories and randomly built thousands of conflict scenarios with UASs to check the ability of such an algorithm to ensure the separation with commercial aviation. We consider two different types of UASs, flying at 80kn or 160kn, with six different missions: flying straight or turning and leveled, climbing or descending. We only focus on horizontal maneuvers at constant speed in order to not interfere with the TCASs of aircraft, nor rely on most UASs poor ability to change speed. The article investigates the influence of the various parameters on the separation achieved and the amount of maneuvers required, especially the strategy used to select the best maneuver among the allowed headings. The analysis of our results shows that, amid two basic and “extreme” strategies that favor either minimal heading changes or the robustness of the maneuvers, the combination of both, switching from the first one to the second whenever the distance between the UAS and aircraft falls under a given threshold, gives the best results with very few remaining airproxes, while keeping low the amount and amplitude of maneuvers.

Finite element (FE) computations have been performed to analyze the thermo-chemo-mechanical behavior of SiC-based refractory parts in linings used in waste-to-energy plants. These parts are in contact on one side with smoke and ashes at high temperature, and on the other side with the pressurized vapor pipe. Three multi-layered lining designs have been studied: two with tiles and one with a concrete panel. A coupled model taking into account the transport of dioxygen in the gas through the porosity, the reaction of dioxygen in contact with silicon carbide particles and the formation of solid components gradually clogging the pores, has been implemented in the finite element code ABAQUS ? . These phenomena affect the mass diffusion rate of dioxygen through the refractory layer and induce a macroscopic swelling of the material. The analysis of the numerical results allows for a better understanding of the influence of the lining design and the nature of the ceramics on the lifespan of such refractory parts. HighlightsPaper proposes an analysis of behavior of SiC-based refractory linings which are subjected to a chemical environment.The model takes into account the transport of oxygen in the gas through the porosity.The model takes into account the chemical expansion induced by oxidation.Three designs of the lining are studied.The obtained results allow the highlighting of the design effect in relation with material properties.

Mixed ionic and electronic conductors (MIEC) are promising materials for ion transport membrane (ITM) based technologies. A reliable design of these membranes requires a better knowledge of their macroscopic mechanical properties. These properties are linked to the composition of membrane materials, but also in a large part to the manufacturing process. Then, the mechanical characterization set-up must allow using specimen very similar in term of manufacturing process as the final parts in. The use of the diametric compression test on thin plates is investigated here, combined with full-field measurements. Guideline for sample size, solution for classical artifact and a dedicated I-DIC algorithm are proposed. Then, Young modulus and tensile strength of seven MIEC compositions of the lanthanum-ferrite perovskite series (La (1− x ) Sr x Fe (1− y ) Ga y O 3−δ , La 0.5 Ba 0.5 Fe 0.7 Co 0.3 O 3−δ and La 0.5 Ca 0.5 Fe 0.7 Co 0.3 O 3−δ ) were determined at room temperature and at 900 °C.

International audience; Three-dimensional (3D) fabrics of commingled yarns offer the possibility of a low-cost and fast manufacturing of complex-shaped composite parts. Textile-reinforcement behavior during the forming process is very important since the appearance of defects (for example wrinkles, yarn misalignment or breakage) can significantly affect the mechanical properties of the final part. Experimental characterization of the mechanical behavior of textile-reinforcements is expensive, time consuming, and a large scattering of results is often observed. To overcome this, meso-scale modeling is an interesting method to study and understand the textile behavior at the unit cell level. To perform realistic simulations, an accurate modeling and, therefore, knowledge of the yarn mechanical behavior are needed. In this paper, a simple protocol is proposed and validated in order to investigate the tensile behavior of commingled polypropylene/glass yarns. Influence of specimen length and strain rate are highlighted. A comparison of tensile behavior of yarns before and after weaving is carried out in order to evaluate the weaving damage effect. Finally, a model describing the commingled yarn behavior is proposed. The parameters of the model are defined. Their dependency to strain rate, specimen length, and weaving damage are highlighted.

International audience; The oil sands industry usually leads to the production of large quantities of mineral waste, such as fluid fine tailings (FFT), whose disposal is often challenging. Electrokinetic geocomposites (eGCP) installed into the FFT disposal area could improve in-situ dewatering: they allow draining the water expulsed during FFT consolidation as well as imposing a voltage across FFT to displace water by electro-osmosis. This paper presents a laboratory device specifically developed to evaluate eGCP performance for sludge dewatering. Based on the oedometer principle, the device aims at studying sludge consolidation as a function of boundary conditions (mechanical stress and/or voltage), with drainage and electrical conduction ensured by two eGCPs positioned on both sides of the sludge layer. Preliminary results obtained with one particular eGCP are presented: the solid content was increased from 42% to 66%, which led to a significant improvement of the shear strength from nearly 0 kPa to a mean value of 40 kPa. The energy required for this experiment was 71 Wh (3.5 kWh per m3 of sludge). The filtration performance remained satisfactory; the sludge particles were retained upstream of the filter, with a clean water flowing through.; L'industrie des sables bitumineux produit de grandes quantités de résidus minéraux liquides, sous forme de boues difficiles à stocker. Des géocomposites électrocinétiques (eGCP) installés directement dans les parcs à résidus pourraient en améliorer l’assèchement : les eGCP peuvent à la fois drainer l’eau expulsée durant la consolidation et imposer une ifférence de potentiel électrique aux bornes des couches de boues afin de provoquer la migration de l’eau par électro osmose. Cet article présente un dispositif expérimental développé spécialement pour évaluer les performances des eGCP avec des boues minières. Basé sur les principes d’un ½domètre, le dispositif permet d’étudier la consolidation en fonction des conditions aux limites, le drainage et la conduction électrique étant assurés par deux eGCP positionnés de chaque côté de la couche de boue. Des résultats préliminaires sont présentés : l’expérience a conduit à un assèchement important, la siccité de la boue passant de 42% à 66% et la résistance au cisaillement de 0 kPa à 40 kPa en moyenne. L’énergie consommée durant le traitement a atteint 71 Wh (3,5 kWh par m3 de boue). La filtration a été correctement assurée par l’eGCP : les particules de boue ont été retenues et de l’eau propre s’est écoulée à travers l’eGCP.

International audience; It is a common practice to design refractory linings with the help of thermal computations, thermochemistry analyses and strong workman know-how. Their mechanical design is often limited to simple thermo-elastic computations. Sometimes computations are refined considering non-linear mechanical behaviour, even if corrosion often induces additional chemical strain and strong change in service of the mechanical behaviour of the refractory. The aim of this presentation is to briefly recast the irreversible thermodynamic framework in order to underline the implications of some basic thermodynamic concepts in term of refractory behaviour modelling. Then, the use of these concepts to develop fully 3D finite element simulations accounting simultaneously for thermal, mechanical and chemistry phenomena will be illustrated on the particular case of SiC-based refractory. Comparison between long duration oxidation test at high temperature and model prediction allows the validation of the proposed approach. Then, an extension to the industrial case of refractory lining in Waste to Energy plant will be illustrated. The interest of taking into account the thermo-chemo-mechanical coupling effects is shown.

International audience; In refractory masonry lining of industrial furnaces the compressibility of mortars is critical for the thermo-mechanical integrity of the structure.Compressive stress-strain behaviour of refractory mortars has been measured during drying at room temperature and in the service temperaturerange of 300-1400◦C. The results have been explained using fractographic analysis and distinct element method computer modelling. The mortarfailure has been shown to occur due to formation of shear bands of micro-cracks. The propagation of cracks preferably follows the shortest pathbetween larger pores and is influenced by grain cohesion and interlocking. Tests with mortars featuring calcium aluminate cement, mono aluminiumphosphate, water glass and bentonite clay binders have indicated that besides increasing the cohesion between the grains the binder reduces theinternal friction that promotes higher compressibility. It has been found that the mortar with clay has the highest compressibility. The mortar withcement shows the most stable behaviour.

International audience; Silicon carbide-based refractory castables (SiC-RC) have high mechanical and chemical resistances at high temperature. Nevertheless when subjected to both high temperature and aggressive oxidizing environment, due to phase transformation, a chemical strain appears that leads to additional stresses in industrial parts and may cause degradation. In this paper, macroscopic constitutive equations are proposed to model the complex relationship between stress, strain, temperature and oxidizing atmosphere in porous SiC-RC. To model the kinetics of the chemical swelling, oxygen content in the porosity of the heterogeneous material is estimated. It depends on both the oxidation reaction of SiC-based grains and the diffusion of oxygen through the connected porosity in the castable. The macroscopic chemical strain associated to the local SiO2 formation takes only place when the local small voids cannot absorb the reaction product anymore. Besides, the reduction of porosity is accompanied by a reduction in the gas permeability and consequently a reduction in the diffusion of oxygen. The multi-physical model is implemented in the finite element code Abaqus . It accounts for heat transfer,reactive oxygen transport and chemically induced strain. A validation test was carried out on a cylindrical sample subjected to high temperature with a thermal gradient in ambient air. Comparison between experimental results, microscopic observations and numerical results showed that the model provides a good description of the main physical phenomena.

Mixed Ionic and Electronic Conductors are promising materials for oxygen transport membranes at high temperature. The mixed conduction leads to oxygen semi-permeation properties. This oxygen transport properties is linked to the ability of the membrane material to reversibly adsorb and desorb oxygen and to diffuse oxygen through the lattice [1]. However, the defect equilibrium with the surrounding atmosphere induces a “chemical” expansion in the same order than the thermal expansion. Mechanically, the transient stage is critical due to the stress induced by the chemical and thermal strain [2]. To predict this strain, the oxygen activity field through the membrane needs to be known. Usually, to model, the membrane is divided into three zones: the bulk, where oxygen bulk diffusion takes place and the two surfaces where oxygen exchanges between atmosphere and membrane take place. Oxygen bulk diffusion is well described by the Wagner theory [3]. The surface exchanges include the adsorption/desorption, dissociation/association and incorporation/exclusion of oxygen. A consensus has not yet emerged regarding the oxygen surface exchange models proposed in the literature. Two categories of models are reported: one corresponds to an extension of the Wagner theory to the surface [4] and the second corresponds to a chemical approach by kinetic laws [1, 5]. Different experiments have been performed to characterize the surface exchange and bulk diffusion parameters. The measures reported by Geffroy et al. on membrane surfaces during steady oxygen flow exhibits a large chemical potential gap between the membrane surfaces and the surrounding gases [6]. From our knowledge, this experimental data cannot be reproduced by a single model from literature. Moreover, although the combination of Wagner extension approach on the high oxygen side and kinetic approach on the low oxygen side makes it possible to reproduce results in steady state, it does not allowed to investigate transient stage. The proposed talk deals with a new macroscopic surface exchange model describing both oxidizing and reducing surface for transient stage. This model assumes that the oxygen flow is governed by the association/dissociation of adsorbed oxygen and by the high energetic cost of oxygen reduction/oxidation. Then, the balance of a transient species at the membrane surface is introduced to account for these two phenomena. The first results obtained are in accordance with oxygen semi-permeation measurements reported by Geffroy et al. [6]. The computation of isothermal expansion tests realized by Adler [7] in transient stage, using the proposed exchange model and the chemical expansion model proposed by Valentin et al. [8], present also a good correlation with experimental results. [1] S.B. Adler et al, Mechanisms and rate laws for oxygen exchange on mixed-conducting oxide surfaces, J Catal, (245), 91-109, 2007. [2] O. Valentin et al, Chemical expansion of La0.8Sr0.2Fe0.7Ga0.3O3-δ, Solid State Ionics, (193), 23-31, 2011. [3] C. Wagner, Equations for transport in solid oxides and sulfides of transition metals, Prog Solid State Ch, (10), 3-16, 1975. [4] H.J.M. Bouwmeester et al, Importance of the surface exchange kinetics as rate limiting step in oxygen permeation through mixed-conducting oxides, Solid States Ionics, (72), 185-194, 1994. [5] S. J. Xu et al, Oxygen permeation rates through ion-conducting perovskite membranes, Chem Eng Sci, (54), 3839-3850, 999. [6] P.M. Geffroy et al, Influence of oxygen surface exchanges on oxygen semi-permeation through La(1-x)SrxFe(1-y)GayO3-δ dense membrane, J Electrochem Soc, (158), 1-9, 2011. [7] S.B. Adler, Chemical expansivity of electrochemical Ceramics, J. Am. Ceram. Soc., (84), 2117-2119, 2004. [8] O. Valentin et al., Thermo-Chemo-Mechanical Modelling of Mixed Conductors in Transient Stages, Adv. Sci. Rech., (65), 232-237, 2010.

International audience; Corrosion tests of oxide-bonded SiC-based refractory cylinders with molten salts (mainly CaSO4, K2SO4) were performed at high temperature to enable better understanding of the corrosion mechanisms operating in these materials. Salt pellets were placed on the upper surface of small refractory cylinders. After they had been melted, the corrosive product soaked into the pores of the refractory cylinders and partially corroded the SiC phase. SEMEDS analyses showed thatCaSiO3 was the mainnewphase formed, growing from SiC aggregates into the pores.Theshapes of the initial and corroded cylinders were measured at room temperature using a 3D coordinate measuring machine equipped with a laser-plane sensor. These measurements enabled monitoring of the evolution of the residual radial deformation versus the depth from the surface in contact with the salt pellets, and consequently the characterisation of the local volume expansion induced by the phase change. Coupling SEM-EDS analyses with 3D digitising revealed the link between the corrosion product and the volume expansion.

International audience; Many bottom linings of refractory structures used in steel making industry are made of masonries with or without mortar. Several designs are possible: parallel, fish bone or radial. To compare the influence of these designs on the level of stress and displacements in the steel shell, the different masonries were modelled by an equivalent homogeneous material. The thermo-mechanical properties of this equivalent material were determined using a periodic homogenization method. They are temperature depending and depend of the joint states (open or closed in the two directions) for masonries with mortarless joints. This masonry model is used to simulate by the finite element method the behaviour of a simplified steel ladle. It demonstrates the influence of different parameters: presence or not of joints, dry joints/mortar joints, thickness of mortar joints, masonry design. It brings a help for the design of refractory masonry linings.

International audience; Many recent studies have focused on the development of perovskite membranes with high oxygen semi-permeation performance. However, the usual experimental setups used to measure oxygen semi-permeation values may lead to significant errors in the actual performance of the membrane materials. In this paper, special attention is paid to the experimental conditions and the associated impacts on oxygen semi-permeation measurements collected from the membrane. Furthermore, the experimental setups described in the literature do not allow the direct identification of the limiting step for oxygen transport through the membrane, i.e., either through bulk oxygen diffusion or oxygen surface exchange on both membrane surfaces. In this work, a specific experimental setup is proposed for the discrimination of oxygen bulk diffusion and surface exchange phenomena

The decrease of the dense layer thickness can lead to increase the internal stresses in the membrane due to the chemical expansion of membrane material under a large gradient of oxygen partial pressure. This chemical expansion due to p O 2 gradient through the membrane leads to important mechanical stresses in the membrane and commonly to the membrane rupture under large range of p O 2 , i.e. air/methane atmosphere. The solution suggested in this paper is the elaboration by tape casting and co-firing process of multilayer membranes with a specific design in order to decrease stresses due to the chemical expansion in working conditions.

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This study presents a viscosity sensor that converts the vibration amplitude at the resonance frequency of a needle immersed in viscous fluid, into electric current. The goal of this work is to provide a dedicated numerical tool for the sensor design, that couples fluid, structure and magnetism.Copyright © 2012 by ASME

International audience; This paper suggests a macroscopic model describing the thermo-chemo-mechanical behaviour of ceramic dense membrane for oxygen separation application. This work takes in account to oxygen permeation and strain induced by stoichiometry variation with working conditions. This model, developed within the traditional framework of phenomenological approach, is based on the assumption of strain partitions and requires only three state variables: oxygen activity, temperature and total strain. Oxygen bulk diffusion and surface exchanges are described thanks to the thermodynamic approach developed by Onsager. While many works focused on semi-permeation induced strain, the proposed model also includes the temperature effect on chemical expansion. Strains predicted by the proposed model are validated thanks to experimental test on La0.8Sr0.2Fe0.7Ga0.3O3-δ. Implemented in F.E.A code Abaqus, this model permits studying the design and the process management effects such as chemical shocks on the membrane reliability.

International audience; Oxide bonded silicon carbide refractories are used successfully in solid waste-to-energy facilities (WtE). They are submitted to severe thermochemical stresses that limit their performance. Even if the corrosion resistance of silicon carbide is high, wear and failure of refractory lining are currently observed. For a better understanding of corrosion mechanisms, oxide bonded silicon carbide refractories, collected in the combustion chamber of several WtE facilities, were examined. The main mechanisms of corrosion, according to the environment of refractories, were determined. The chemical composition and the nature of the corrosive agents were calculated from the thermo-chemical modeling. They are mainly condensed phases of sulfates and chlorides (CaSO4, K2SO4, Na2SO4, KCl, and NaCl). In service conditions, these molten salts react with the SiC aggregates and the matrix of the refractories to form low melting compounds. The post-mortem analyses showed the formation of para-wollastonite in the porosity and around the SiC grains, on the hot face of refractory tiles. Other phases such as cristobalite and microline (KAlSiO8) were also formed down to the core of refractories. The volume expansion created by the formation of new mineral phases (cristobalite, para-wollastonite) causes the formation of micro cracks in the refractory lining. In this paper, the degradation mechanisms of oxide bonded silicon carbide refractories are presented and the main research developments for the future are discussed.

International audience; This paper is devoted to the modelling of a specific ramming mix mainly used in the high-temperature industry due to its high-compacting behaviour. This material has the ability to absorb the deformation of parts submitted to high thermal loads. Triaxial and instrumented die compaction tests were carried out in order to identify the shear and hardening behaviours, respectively. Tests on the ramming mix were led for a temperature range between 20 C and 80 C. The temperature effect is particularly observed on the material response when it is compacted. The main features of the behaviour of the ramming mix can be represented by the theoretical framework of the Modified Cam-Clay model. A single variable allows to accurately reproduce the hardening behaviour depending on the temperature. Moreover, an extension of the model for the hardening behaviour at high pressures is proposed. A good agreement between the experimental data and numerical tests is reached with this model.

International audience; An extension of the Bingham–Norton's rheological model accounting for high asymmetric tensile-compressive creep behavior is proposed for ceramics subjected to high temperature loadings. Such behavior is observed in heterogeneous ceramics made of grains having a high creep resistance embedded in a softer glassy phase. Two mechanisms of deformation are introduced: namely, under compressive stresses, grain facets are in contact and transmit the load, whereas under tensile stresses the grains are separated and the glassy matrix transmits the load. It leads to a difference in elastic stiffness and strain rate under tensile and compressive stresses. A new three-dimensional constitutive model is developed considering an additive decomposition of the stress tensor into a positive and negative part. Each stress tensor is the driving force of one mechanism of deformation that is characterized in a classical manner. A simplified identification of the model is performed at high temperature on a bauxite-based refractory, which is used in steel ladle linings. It is shown that for this ceramic few material parameters are sufficient to account for major differences of behavior observed in compression tests and three-point bend tests.

The response of a semi-infinite saturated porous medium subjected to a harmonic thermal loading on its free face is studied herein. The pressure diffusion equation that governs the fluctuation of the interstitial pressure is established. It allows us to obtain prevalent parameters, i.e. the thermal and fluid mass diffusivities and the coefficient of relative bulk variation. Closed-form solutions of the maximum fluid pressure Pmax and its location xcr are derived. It is shown that the location xcr of Pmax is localized and depends on the diffusivity ratio and the frequency of the thermal loading while the magnitude of Pmax depends on the diffusivity ratio and the thermal amplitude. Master curves for xcr and Pmax versus diffusivity ratio are built. It follows that three regimes can be distinguished: namely, thin spalling, thick spalling or in-depth cracking and no cracking. Copyright © 2003 John Wiley & Sons, Ltd.

Refractory materials are subjected to thermomechanical loads during their working life, and consequent creep strain and stress relaxation are often observed. In this work, the asymmetric high temperature primary and secondary creep behavior of a material used in the working lining of steel ladles is characterized, using uniaxial tension and compression creep tests and an inverse identification procedure to calculate the parameters of a Norton-Bailey based law. The experimental creep curves are presented, as well as the curves resulting from the identified parameters, and a statistical analysis is made to evaluate the confidence of the results.