Coupling between Diffusion, Stress Field and Chemical Reaction in a Metal-Gas Oxidation

International audience

Studies on Instabilities and Patterns in Evaporating Liquids at Reduced Pressure and/or Microwave Irradiation

This paper summarizes our recent experimental and theoretical work on the instabilities in liquids and at interfaces which form during evaporation at reduced pressure and/or microwave irradiation. We have observed a variety of patterns (Benard rolls, Marangoni waves, Hickman interface deformations) which depend on the value of the reduced pressure and the power of the incident beam.

Evaporation from liquids : characteristics features, Institut Européen des Transuraniens

Near-coincidence lattice method for the determination of epitaxy strains during oxidation of metals

Abstract A theoretical method is proposed to evaluate the strains due to epitaxy between a metal and its oxide. Based on Bollmann’s approach of two adjoining grains, it uses the quantitative texture analysis of the two materials separated by the phase boundary. Our study of the Zr/ZrO 2 and Mo/MoO 3 systems reveals strong correlations between the criterion of best fit proposed by Bollmann and the orientation distribution function obtained by a quantitative texture analysis. The results of this study are used in a thermo-mechano-chemical simulation of the oxidation process of zirconium, which leads to this observation: two different zirconia orientations induce two different oxidation kineti…

Pattern Formation During Dry Corrosion of Metals and Alloys

About corrosion of metals and alloys, many exciting problems are not entirely solved. One of them concerns some morphological features such as, for example, stratified periodic structures that may appear, for example during the oxidation or sulfidation of metals and alloys. In this context, a high temperature corrosion kinetics is interpreted in terms of a bistable chemical system which can oscillate spontaneously if a feedback effect could exist. Some models analyse these patterning from a theoretical point of view. Stability analyses of the uniform standard steady state point out that it can be unstable by bifurcation and give rise to multilayered scales. Some non linearities, peculiar to…

Non Linear Phenomena in Oxidation of Metals and Alloys

Analyse de quelques exemples du comportement non conventionnel des couches de corrosion obtenues par oxydation ou sulfuration de certains metaux et alliages

Texture Effects on Zircaloy Oxidation : Experiment and Simulation

Micromechanical Approach of the High Temperature Oxidation of Zirconium

Possibilities of surface reaction coupling with transport phenomena

International audience; The thermodynamic approach of nonequilibrium phenomena allows, through the construction of entropy production, appropriate fluxes generalized forces to be identified, and the possibility of coupling to be detected. For the interface phase the expression entropy production consists of two parts: one for irreversible phenomena in the surface (chemical reactions and transport); and the second for transport processes between volumic phases due to the discontinuity of intensive surface parameters. Accordingly in the linear range, the phenomenological relations establishing the thermodynamic coupling between fluxes and forces of the same tensorial order may cause couplings…

Fundamental and technological aspects of the surface properties and reactivity of some metal oxides

Abstract As is usually accepted for many inorganic compounds, the surface properties often play a fundamental role in the overall properties of metal oxides, in particular when the oxide materials are used in the form of fine grains. One difficulty in characterizing these surface properties is to apply the results of studies performed on ideal surfaces to the actual materials in use. A way to accept this challenge can be to successively consider initial powders, polycrystalline pellets formed after thermal or mechanical treatment of these powders and, finally, monocrystalline surfaces prepared from these powders or pellets. This principle can be applied to the study of the surface propertie…

Determination of the stress distribution at the interface metal-oxide: Numerical and theoretical considerations

In this paper we give a brief presentation of the approaches we have recently developed on the oxidation of metals. Firstly, we present an analytical model based on non-equilibrium thermodynamics to describe the reaction kinetics present during the oxidation of a metal. Secondly, we present the molecular dynamics results obtained with a code specially tailored to study the oxidation and growth of an oxide film of aluminium. Our simulations present an excellent agreement with experimental results.

Evaporation d'un liquide sous pression contrôlée de sa vapeur, présentation d'un modèle d'échange thermique à l'interface (Actes)

International audience

Caractéristiques des réactions endothermiques d'interface

The knowledge of the different thermodynamic states of an evaporative interface leads us to propose a formulation of the evolution laws (evaporation rate vs pressure) adapted to each regime (interfacial equilibrium or non equilibrium). Starting from fluid dynamics and irreversible thermodynamics, the model is able to determine the interface flux-forces relations which express the transport coefficients and the thermodynamic coupling effects. The theoretical results are compared to experimental data relative to water evaporation al T =313 K. Taking into account the different regimes arising for the deviation from equilibrium, the model reproduces quantitatively the experimental kinetic curve…

Rôle du flux thermique à l'interface dans l'interprétation de l'effet Smith Topley

International audience

Mechanical, Kinetic and Morphological Correlations during the Scale Growth of Niobium and Zirconium Oxides

Oxidation of niobium at 700°C and zirconium at 850°C, in air or oxygen pressures from 20 to I 000 hPa, lead to the formation in one case of a stratified Nb 2 O 5 oxide scale and in the other case a more compact ZrO 2 oxide scale. Analyses of the evolutions of phases, crystalline textures and mechanical stresses during oxidation are determined by X-ray diffraction techniques. Interactions between chemical processes, crystalline building and mechanical processes constitute together the driving force of the reaction and can explain the differences in morphologies of oxide scales.

Microchemical Model for High Temperature Oxidation of Zirconium

Instability and bistability during the growth of a corrosion scale on metals and alloys

This paper summarizes the main results for the interpretation of the self organized corrosion scales observed in oxidation or sulfidation of some metals or alloys. It consists also of a reconsideration of the classical theoretical concepts used in Reactivity of Solids. It proposes new theoretical tools that have been fruitfully utilized in other topics : non linear and coupled processes, stability analysis and bifurcation theory. Some examples are developed, where the corrosion kinetics at high temperature are interpreted in term of chemical bistable system able to oscillate spontaneously and mechanochemical couplings are also taken into account. In according with experimental results, all …

Self-Induced Stress and Matter Transport Interactions during Metal Oxidation

Mechanical Stresses: Inhibitor of Catalyst of High Temperature Oxidation?

Oxidation of metals is a complex reaction in which mechanical and chemical phenomena occur. A dynamic and macroscopic model is developed in order to simulate oxidation kinetics of a metal. It includes the stress/diffusion coupling in the bulk and the interfacial phenomena at metal/oxide interface. Its application to the Zr/ZrO 2 system shows the important role of stress field distribution in oxide on kinetic behavior. According to the sign of stress gradient in the oxide scale, the oxidation rate can speed up or slow down. The calculated kinetic curves could he fitted using a k p .t 1/n law where n and kp vary all over the process, like for the experimental kinetic curves.

Caractéristiques des réactions endothermiques d'interface. Recherche des états thermodynamiques d'interface en relation avec les écarts à l'équilibre t. 292, pp. 49 52.

International audience; L'endothermicité de la vaporisation peut donner des propriétés particulières à l'interface. L'exploration de la carte thermique du système associée à un modèle permet d'accéder aux profils thermiques dans chaque phase et d'établir les températures à l'interface; ses différents états thermodynamiques sont en relation avec l'écart à l'équilibre du système : équilibre interfacial près de l'équilibre, puis apparition d'une discontinuité de température, enfin déséquilibre de température et de potentiel chimique.

Micromechanical approach of the high temperature oxidation of zirconium: study of the Zr/ZrO2 interfacial epitaxy with Bollmann's method

The method of Bollmann has been used to determine the role of epitaxy in the formation of the mechanical stress field near the metal/oxide interface during the high temperature oxidation of zirconium. The strains due to epitaxy combine with those due to both oxygen diffusion in metal and thermal expansion of the metal/oxide composite in a model based on a micromechanical formalism. The calculated values are compared to experimental results and the applicability of Bollmann's method to this problem is discussed.

Low-pressure-MOCVD LaMnO3±δ very thin films on YSZ (100) optimized for studies of the triple phase boundary

Abstract This paper deals with the preparation of LaMnO 3± δ (LM) layers by low pressure-metal organic chemical vapor deposition (LP-MOCVD) using La(tmhd) 3 and Mn(acac) 3 as organometallic precursors. By thermogravimetric analysis, these precursors were found to be suitable for LP-MOCVD in a well-defined range of total pressure and temperature of sublimation. The activation energies of the sublimation process were found to be independent of the pressure within the appropriate range (0.06–3 kPa) and their values were 177 and 100.5 kJ mol −1 for La(tmhd) 3 and Mn(acac) 3 , respectively. LM layers of various thickness ranging between a few and a few hundred nanometers with a controlled La/Mn …