Influence des instabilités convectives sur l'état de surface finale des films polymères fabriqués par procédé de séchage.

Thèse de Doctorat de l'Institut Polytechnique de Grenoble, 31 Mars 200

Role of Bénard-Marangoni instabilities during solvent evaporation in polymer surface corrugations.

International audienceFilm formation through the drying of polymer solutions is a widely used process in laboratories and in many industrial applications such as coatings. One of the main goals of these applications is to control the film surface morphology. In many cases, evaporation has been found to yield corrugated patterns on the free surface of films. This has been interpreted in terms of either mechanical or hydrodynamic instabilities. In this article, we present experimental results where mesoscale 2D well-ordered surface corrugation patterns are formed during solvent evaporation from polystyrene/toluene solutions. The transformation of Bénard−Marangoni instabilities into surface corrugation is studied during the entire drying process using particle tracking, 3D morphology analyses, etc. We show that the corrugation wavelength is controlled by the Bénard−Marangoni instability, whereas the corrugation amplitude is controlled by a mechanism that involves a high evaporation rate

Role of Bénard−Marangoni Instabilities during Solvent Evaporation in Polymer Surface Corrugations

International audienceFilm formation through the drying of polymer solutions is a widely used process in laboratories and in many industrial applications such as coatings. One of the main goals of these applications is to control the film surface morphology. In many cases, evaporation has been found to yield corrugated patterns on the free surface of films. This has been interpreted in terms of either mechanical or hydrodynamic instabilities. In this article, we present experimental results where mesoscale 2D well-ordered surface corrugation patterns are formed during solvent evaporation from polystyrene/toluene solutions. The transformation of Bénard−Marangoni instabilities into surface corrugation is studied during the entire drying process using particle tracking, 3D morphology analyses, etc. We show that the corrugation wavelength is controlled by the Bénard−Marangoni instability, whereas the corrugation amplitude is controlled by a mechanism that involves a high evaporation rate

Mechanistic study of Diesel soot combustion over an AgMnOx catalyst

International @ INGENIERIE+NOG:DBI:CMIInternational audienceNon

Mechanistic study of diesel soot combustion over an AgMnOx catalyst

AIR:INGENIERIE:SURFACES+NOG:BBA:DBI:CM

Mechanistic study of diesel soot combustion over an AgMnOx catalyst

AIR:INGENIERIE:SURFACES+NOG:BBA:DBI:CM

Experimental Microkinetic Approach of the Catalytic Oxidation of Diesel Soot by Ceria Using Temperature-Programmed Experiments. Part 2: Kinetic Modeling of the Impact of the Ceria/Soot Contacts on the Rate of Oxidation

Bassou, Badr Guilhaume, Nolven Lombaert, Karine Mirodatos, Claude Bianchi, DanielAn experimental microkinetic approach of the catalytic oxidation of diesel soots is developed considering mechanical mixtures of ceria and soot (ceria/soot weight ratio R) to mimic the situation of a catalyst-coated filter. Three ceria/soot mixtures denoted as TC-R = 10, TC-R = 1, and LC-R = 10 have been prepared according to the tight and loose contacts, respectively. Temperature-programmed experiments (without O-2) performed on stabilized ceria/soot mixtures provide the rate of the CO2 production, R-CO2(T), via the reaction between carbon defect sites C-f of the soot and oxygen species transferred by the ceria particles. The R-CO2(T) curves present two peaks at low and high temperatures. The study is dedicated to the kinetic modeling of the R-CO2(T) curves at low temperatures. According to the experimental microkinetic approach, two plausible kinetic models of the reaction have been selected on the basis of literature data; they differ from the implication or not of oxygen diffusion on the ceria surface. The mathematical kinetic formalisms, associated with the models, consider that the ceria/soot contacts constitute key kinetic parameters of the soot oxidation and their properties, such as the average number of contacts N-c between a ceria particle and the soot particles and the average surface s(c) of a contact, included in the kinetic equations. Different kinetic parameters have been obtained using experimental procedures, such as the activation energy of oxidation of the carbon defect sites (187 KJ/mol) and the N-c values for the different ceria/soot mixtures (i.e., N-c = 4.3 for TC-R = 10). It is shown that the microkinetic approach permits obtaining theoretical R-CO2(7) curves consistent with the experimental data for the three mixtures, considering similar values of the kinetic parameters, except the N-c and R values. Moreover, the kinetic models have been extended to catalytic soot oxidation in the presence of O-2 by including its adsorption on ceria. This study confirms the interest of the experimental microkinetic approach for the understanding of the key kinetic parameters controlling the catalytic soot oxidation. Moreover, it provides a mathematical formalism for the comparison of the performances of different solid catalysts, in particular for the development of new formulations

Experimental Microkinetic Approach of the Catalytic Oxidation of Diesel Soot by Ceria Using Temperature-Programmed Experiments. Part 1: Impact and Evolution of the Ceria/Soot Contacts during Soot Oxidation

Bassou, Badr Guilhaume, Nolven Lombaert, Karine Mirodatos, Claude Bianchi, DanielThe present study is dedicated to an experimental microkinetic approach of the catalyst oxidation of the diesel soot using a filter coated with ceria. To mimic the situation encountered in this process, mechanical ceria/soot mixtures have been prepared according to the tight and loose contact concepts described in the literature with ceria/soot ratio R > 1. Diesel soots prepared on an engine test bench and commercial soot have been used. The evolution of the ceria/soot contacts (via the amount of oxygen transferred from ceria to soot) with the progressive oxidation of the soot is followed using temperature-programmed experiments (denoted as TPEs) that provide the rate of CO2 and CO productions [denoted as R-CO2(T) and R-CO(T)] during the increase in the temperature in helium in the range of 300-1100 K. During the first TPE, different surface processes implying pure soot and ceria contribute to R-CO2(T) and R-CO(T), making the evaluation of the oxygen transfer difficult. It is shown that these difficulties are suppressed by performing, on the same ceria/soot sample, successive cycles constituted by a TPE followed by adsorption of O-2 at 300 K that leads to the progressive oxidation of the soot. After three cycles, it is shown that, whatever the ceria/soot mixtures, the amount of oxygen that can be transferred from ceria to soot remains constant. This indicates that the ceria/soot surface contacts do not change during the soot oxidation, which is a conclusion consistent with recent literature data on environmental transmission electron microscopy (TEM). However, the amount of oxygen provided by ceria and available for the soot oxidation is dependent upon the type of ceria/soot mixtures, and this controls the performances of the catalyst evaluated by the decrease of the light-off temperature of the soot in a flow rate of 30% O-2/He. These conclusions are used in part 2 (10.1021/ef100582w) to provide a detailed kinetic modeling of the TPE experiments for the different ceria/soot mixtures, focusing on the key role of the ceria/soot contacts on the rate of soot oxidation. This provides a consistent formalism to understand the impact of the types of catalyst/soot mixtures on the performances

High-throughput approach to the catalytic combustion of diesel soot II: Screening of oxide-based catalysts

AIR:INGENIERIE:SURFACES+BBA:NOG:EIO:DFA:DBI:CM

In situ investigation of Diesel soot combustion over an AgMnOx catalyst

AIR:BIOVERT:MATERIAUX:INGENIERIE:SURFACES+NOG:BBA:GBR:DBI:FBS:ADS:BJO:CMIAn AgMnOx catalyst (3.5 wt.% Ag) incorporating silver ions in a Mn2O3 phase exhibits high performances for soot oxidation below 300 degrees C. Its structural and redox properties have been investigated under reaction conditions using in situ XRD and DTA-TGA measurements. The catalyst appears unmodified during soot combustion experiments under oxygen, but in the absence of oxygen the soot is stoichiometrically oxidised by lattice oxygen leading to catalyst bulk reduction according to the steps Mn2O3 -> Mn3O4 -> MnO. The isotopic reaction product composition ((CO2)-O-16, (COO)-O-18-O-16, (CO2)-O-16, (CO)-O-16 and (CO)-O-18) obtained during soot combustion experiments under O-18(2) reveals that the reaction follows a redox mechanism, in which the transfer of lattice oxygen from the catalyst to the soot is responsible for the soot ignition at low temperature. (C) 2012 Elsevier B.V. All rights reserved