Numerical approach for the description of different fracture modes for Zr/ZrO2 system — Deterministic and probabilistic aspects

International audienc

A General Approach for Kinetic Modeling of Solid-Gas Reactions at Reactor Scale: Application to Kaolinite Dehydroxylation

Understanding the industrial reactors behavior is a difficult task in the case of solid state reactions such as solid-gas reactions. Indeed the solid phase is a granular medium through which circulate gaseous reactants and products. The properties of such a medium are modified in space and time due to reactions occurring at a microscopic scale. The thermodynamic conditions are driven not only by the operating conditions but also by the heat and mass transfers in the reactor. We propose to numerically resolve the thermohydraulic equations combined with kinetic laws which describe the heterogeneous reactions. The major advantage of this approach is due to the large variety of kinetic models of grains transformation (~40) compared to the usual approach, especially in the case of surface nucleation and growth processes which need to quantitatively describe the grain conversion kinetics at a microscopic scale due to nucleation frequency and growth rate laws obtained in separate isothermal and isobaric experiments. The heat and mass transfers terms entering in the balance equations at a macroscopic scale depend on the kinetics evaluated at the microscopic scale. These equations give the temperature and partial pressure in the reactor, which in turn influence the microscopic kinetic behavior

Uranium cerium mixed oxalate decomposition reaction scheme studied by thermogravimetric analysis

International audienceThe aim of this work is the study of thermal decomposition, under inert atmosphere, of uranium, cerium mixed oxalate hydrate into mixed oxide and the confirmation of literature reaction scheme. The mixed oxalate is synthesized by a co-precipitation method and characterized through X-ray diffraction, infrared spectroscopy and thermogravimetric analysis. The experimental results indicate that the thermal decomposition takes place between 70DC and 900DC in three steps, including dehydration, decomposition into oxy-carbonate and conversion of oxy-carbonate into mixed oxide as last step

Experimental and thermodynamic modeling of Al2O3 corundum and TiO2 rutile structures forming on Ti-6Al-4V powder during oxidation

International audienceThe high affinity of Ti-6Al-4 V (Ti64) powder to oxygen impacts the quality of the powder during additive manufacturing. The oxide scale consists of a double layer with α-Al2O3 in the outer part and TiO2 in the inner one. Experimental and thermodynamic results are used to further understand the formation of these two oxide layers. Inert marker revealed the anionic growth of the duplex oxide scale. The thermodynamic results highlighted that interstitial aluminum enters and diffuses fast within TiO2 (rutile) to form Al2O3 as the surface layer. Moreover, α-Al2O3 is considered as a non-stoichiometric oxide with a very small excess of oxygen as dumbbells at high partial pressures of oxygen. A remarkable effect of the impurities on the concentration of native point defects is observed in this phase. Finally, a reactional mechanism with elementary steps for the oxidation of Ti64 powder is proposed

Experimental rate and Monte Carlo simulation of the nucleation and growth processes during the dehydration of Li2SO4 H2O single crystals

International audienc

Modèle de prédiction de la rupture dans les couches d'oxyde

Dans le cadre de la protection des phénomènes de corrosion, la description des phénomènes d’endommagement des couches en proche surface constitue un enjeu important. L’approche proposée, prenant en compte les phénomènes physiques complexes mis en jeu lors de la croissance des couches, a pour but de décrire tous les scénarii de rupture en s’appuyant sur les méthodes à discontinuité forte pour gérer la fissuration des couches et un modèle d’interface pour reproduire la décohésion métal/oxyde

Assesment of a Mechanical Model Associated With Oxide Scale Growth on T91 Steel at 550C Under Wet Atmosphere

International audienc

Physico-geometric kinetics of complex solid-state reactions

National audienceKinetic analysis of the solid-state reaction using thermal analysis (TA) is the established scientific tool and widely applied to many technological processes. However, many solid-state reactions proceed with complex behavior regulated by heterogeneous characteristics. Rather simple solid-state reactions should be described by considering consecutive physico-geometrical processes such as surface reaction–reaction interface shrinkage and nucleation–growth. Further, the surface product layer produced by the reaction regulates diffusion of gases that contribute to the reaction as reactant and product. The mass transfer phenomena influence on the rate behavior and sometimes impede the reaction. Formation of diffusion path in the surface product layer is necessary for the reactivation. As the result, the overall reaction proceeds as the multistep reaction caused by the physico-geometrical constraints. The concurrent or consecutive chemical reactions occurring in the solid-state exhibit more complex kinetic behavior. For these reactions, the comparing reaction steps can indicate differently signed TA signals, i.e., mass loss versus mass gain and exothermic versus endothermic effects. For extending basic kinetic theory and the kinetic calculation methods using TA data to be applicable to the complex solid-state reactions, detailed case studies for the selected reaction processes that exhibit different physico-chemical and physico-geometrical complexities are necessary. In this presentation, the cutting-edge of the kinetic analysis for the complex solid-state reactions is briefly reviewed with special attentions to (i) kinetic deconvolution analysis, (ii) induction period–surface reaction–phase boundary controlled reaction model, and (iii) impact of the evolved gas on the overall kinetics