Finite element simulations of the deformation of fused-cast refractories based on X-ray computed tomography

International audienceThis work consists in building a 3D numerical model of the microstructure of a fused-cast refractory (two-phase material)..

Comportement et endommagement de réfractaires électrofondus sous sollicitation thermomécanique

Les réfractaires électrofondus sont principalement utilisés comme parois internes des fours verriers, du fait de leur bonne résistance à la corrosion. Leur mode de fabrication, par fusion, conduit à des microstructures à faible porosité et très spécifiques, constituées de plusieurs phases cristallisées et d\u27une phase vitreuse intergranulaire. A haute température, ce verre remplit pratiquement tout l\u27espace entre les microcristaux, favorisant ainsi le fluage et contrôlant la fissuration. Le comportement mécanique (essais mécaniques, module d\u27élasticité) et les évolutions microstructurales (ESEM, microtomographie X) d\u27électrofondus type AZS et THTZ ont été étudiés sous diverses sollicitations thermiques ou thermomécaniques. Les résultats appuyés par des mesures d\u27activité acoustique, révèlent la coexistence de phénomènes de microfissuration et de guérison, principalement gouvernés par la transformation de phase de la zircone, les écarts de dilatation entre les phases et la viscosité du verre

Comportement mécanique et endommagement de réfractaires électrofondus sous sollicitation thermomécanique

Les réfractaires électrofondus sont principalement utilisés comme parois internes des fours verriers, du fait de leur bonne résistance à la corrosion. Leur mode de fabrication, par fusion, conduit à des microstructures à faible porosité et très spécifiques, constituées de plusieurs phases cristallisées et d'une phase vitreuse intergranulaire. A haute température, ce verre remplit pratiquement tout l'espace entre les microcristaux, favorisant ainsi le fluage et contrôlant la fissuration. Le comportement mécanique (essais mécaniques, module d'élasticité) et les évolutions microstructurales (ESEM, microtomographie X) d'électrofondus type AZS et THTZ ont été étudiés sous diverses sollicitations thermiques ou thermomécaniques. Les résultats appuyés par des mesures d'activité acoustique, révèlent la coexistence de phénomènes de microfissuration et de guérison, principalement gouvernés par la transformation de phase de la zircone, les écarts de dilatation entre les phases et la viscosité du verre.Fused cast refractories are generally used in glass industry for furnace linings, due to their good erosion-corrosion resistance. Their manufacture process, by fusion, leads to low porosity and very specific microstructures, composed of several crystallized phases and an intergranular glassy phase. At high temperature this glass maintains the crystalline structures and fills in almost the whole space between the microcrystals, promoting creep and controlling damage. The mechanical behaviour (mechanical tests, elastic modulus by bar vibration) and the microstructural evolutions (ESEM, X microtomography) of AZS and THTZ fused cast refractories have been studied under several thermal or thermomechanical sollicitations. Results, linked to acoustic activity measurements, reveal both microcracking and healing phenomena, essentially controlled by zirconia phase transformation, thermal expansion mismatch and glassy phase viscosity.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocLIMOGES-ENSCI (870852305) / SudocSudocFranceF

Access to Highly Fluorinated Silica by Direct F2 Fluorination

Silica is one of the major components of the earth and has been extensively used in both heterogeneous catalysis and chemical separations [1–5]. Numerous applications of silica are related to the hydrophobic-hydrophilic balance and surface reactivity, which both obviously depend on the surface chemistry. Because of high surface area and porous structure, mesoporous silica properties are strongly dependent on the surface reactivity of silanol species (Si-OH) and their interactions via H-bonds with other molecules such as water [6–7]. The surface of silica exhibits low Brønsted acidity without any Lewis acidity.However, surface modification reactions can be performed by using the Brønsted acidic sites of silica gels and such processes have been carried out to prepare thin coatings with a wide variety of organic groups and to adjust hydrophobic character [8]..

Microstructural and mechanical consequences of thermal cycles on a high zirconia fuse-cast refractory

International audienc

Thermochromic behavior (400 < T °C < 1200 °C) of barium carbonate/binary metal oxide mixtures

Irreversible thermochromism over a wide temperature range has been observed from the decomposition of a mixture of a barium carbonate and a metal oxide. The control of the reaction temperature can be predicted from the calculation of the Madelung energy of the barium/transition metal mixed oxide formed consecutively with the decarbonatation. Moreover, the Madelung energy of this formed mixed oxide may be predicted from bond valence considerations. This study offers a simple predictive approach to propose temperature indicators with significant optical contrast and a thermochromic temperature varying between 400 and 1200 °C

Chemical and morphological study of the sensitisatioin, activation and Cu electroless plating Al2O3 polycrystalline substrate

A study of the different stages of the electroless deposition of copper on polycrystalline alumina activated by a two-step method (sensitisation + activation) has been performed from both a chemical and a morphological point of view..

Cobalt and nickel aluminate spinels: Blue and cyan pigments

M2+-doped aluminate spinels (M=Co or Ni) were prepared by a polymeric route leading to pure phases for synthesis temperatures equal to 800 or 1200 °C and characterized by UV-vis-NIR spectroscopy, 27Al NMR and XRD refinements. Coloration of the synthesized pigments is clearly sensitive to the distribution of doping ions in the aluminate spinel lattice. As the synthesis temperature increased, a color shift from green to blue has been observed for Zn1−xCoxAl2O4 compound while coloration of Zn1−xNixAl2O4 compound remains greenish-gray. Hence, to improve pigment coloration and/or synthesis cost, two different strategies have been proposed: (i) the synthesis of aluminum over-stoichiometric spinel with Zn0.9Co0.1Al2.2O4+δ formal composition in order to force Co2+ to be located in tetrahedral sites and (ii) changing from ZnAl2O4 to MgAl2O4 as host lattices for Ni2+ doping ions in order to force Ni2+ to be located in octahedral sites

Optical properties versus temperature of Cr-doped γ- and α-Al2O3: Irreversible thermal sensors application

A thorough investigation by X-ray diffraction, UV–vis and luminescence spectroscopy is carried out to demonstrate how the chromium content of alumina matrices impacts the temperature of the γ→α irreversible phase transition. The Cr3+ contents influence slightly the phase transition temperature but control the brightness of the powders. Nice colorimetric contrasts from green to pink are observed between the two allotropic forms. Furthermore, drastic changes of the spectral distribution and of the intensity of luminescence are observed, thus allowing to use this pigment as a both thermochromic and luminescent thermal sensor. Additional measurements at low temperature revealed that the Cr3+ emission of the γ-Al2O3 matrix is constituted by a large band. A configurational diagram schematic approach suggested for the first time that this emission is due to spin-allowed 4T2→4A2 transition on this largely investigated γ-Al2O3 compound

Acute Clinical Events Identified as Relapses With Stable Magnetic Resonance Imaging in Multiple Sclerosis

International audienceImportance: Understanding the association between clinically defined relapses and radiological activity in multiple sclerosis (MS) is essential for patient treatment and therapeutic development.Objective: To investigate clinical events identified as relapses but not associated with new T2 lesions or gadolinium-enhanced T1 lesions on brain and spinal cord magnetic resonance imaging (MRI).Design, setting, and participants: This multicenter observational cohort study was conducted between January 2015 and June 2023. Data were extracted on June 8, 2023, from the French MS registry. All clinical events reported as relapses in patients with relapsing-remitting MS were included if brain and spinal cord MRI was performed within 12 and 24 months before the event, respectively, and 50 days thereafter with gadolinium injection.Exposures: Events were classified as relapses with active MRI (RAM) if a new T2 lesion or gadolinium-enhanced T1 lesion appeared on brain or spinal cord MRI or as acute clinical events with stable MRI (ACES) otherwise.Main outcomes and measures: Factors associated with ACES were investigated; patients with ACES and RAM were compared regarding Expanded Disability Status Scale (EDSS) course, relapse rate, confirmed disability accrual (CDA), relapse-associated worsening (RAW), progression independent of relapse activity (PIRA), and transition to secondary progressive (SP) MS, and ACES and RAM rates under each disease-modifying therapy (DMT) were estimated.Results: Among 31 885 clinical events, 637 in 608 patients (493 [77.4%] female; mean [SD] age, 35.8 [10.7] years) were included. ACES accounted for 166 (26.1%) events and were more likely in patients receiving highly effective DMTs, those with longer disease duration (odds ratio [OR], 1.04; 95% CI, 1.01-1.07), or those presenting with fatigue (OR, 2.14; 95% CI, 1.15-3.96). ACES were associated with significant EDSS score increases, lower than those found for RAM. Before the index event, patients with ACES experienced significantly higher rates of relapse (relative rate [RR], 1.21; 95% CI, 1.01-1.46), CDA (hazard ratio [HR], 1.54; 95% CI, 1.13-2.11), and RAW (HR, 1.72; 95% CI, 1.20-2.45). Patients with ACES were at significantly greater risk of SP transition (HR, 2.58; 95% CI, 1.02-6.51). Although RAM rate decreased with DMTs according to their expected efficacy, ACES rate was stable across DMTs.Conclusions and relevance: The findings in this study introduce the concept of ACES in MS, which accounted for one-fourth of clinical events identified as relapses