Didier Klein

IN SITU TIME-RESOLVED DIFFRACTION COUPLED WITH A THERMAL I.R. CAMERA TO STUDY MECHANICALLY ACTIVATED SHS REACTION: CASE OF Fe-Al BINARY SYSTEM

Abstract Mechanically activated self-propagating high-temperature synthesis (MASHS) provides an attractive practical alternative to the conventional methods of producing intermetallic compounds, such as iron aluminides. This process involves mainly the combination of two steps; the first step, a mechanical activation, where pure elemental (Fe+Al) powders were co-milled inside a planetary mill, for a short time at given frequency and energy shocks and, the second step, a self-propagating high-temperature synthesis (SHS) reaction, which uses the exothermicity of the Fe+Al reaction. Once ignited with an external source, these reactions become self-sustained and propagate to completion within seconds. The combustion front directly leads to the formation of a nanometric Fe–Al intermetallic with a relative density of 70–80%. To understand this self-sustained reaction, an in situ study in real time was investigated on samples which differ by the shock power during milling and the compaction pressure (porosity). When the combustion front goes through the sample, the time-resolved X-ray diffraction experiment (TRXRD) using synchrotron radiation coupled with an infrared thermography allows the in situ study of the phase formation and the temperature evolution during the MASHS process.

Nanostructured photocatalytic titania coatings formed by suspension plasma spraying

This paper describes formation of titanium dioxide coatings designed for photocatalytic applications, obtained by suspension plasma spraying (SPS), an alternative of the atmospheric plasma spraying (APS) technique in which the material feedstock is a suspension of the material to be sprayed. Two different TiO2 powders were dispersed in distilled water and ethanol and injected in Ar-H2 or Ar-H2-He plasma under atmospheric conditions. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) analyses were performed to study the microstructure of the titania coatings. Photocatalytic efficiency of the elaborated samples was evaluated from the conversion ratio of different air pollutants: nitrogen oxides (NOx) and sulfur dioxide (SO2). The morphology and crystalline structure of the deposits depended mainly on the nature of the solvent (water or alcohol) used in the preparation of the slurries. Dense coatings were obtained starting from aqueous suspensions and porous deposits were elaborated by plasma spraying of a PC105 alcoholic suspension. A significant phase transformation from anatase to rutile occurred when ethanol was used as a solvent. Different photocatalytic performances were observed as a function of the nature of the liquid material feed-stock, the spraying parameters, and the nature of the pollutant.

Comparison of the photocatalytic behavior of TiO2 coatings elaborated by different thermal spraying processes

This paper proposes a comparative study on the microstructure and photocatalytic performances of titanium dioxide coatings elaborated by various thermal spraying methods (plasma spraying in atmospheric conditions, suspension plasma spraying, and high-velocity oxyfuel spraying). Agglomerated spray dried anatase TiO2 powder was used as feedstock material for spraying. Morphology and microstructural characteristics of the coatings were studied mainly by scanning electron microscopy and x-ray diffraction. The photocatalytic behavior of the TiO2-base surfaces was evaluated from the conversion rate of gaseous nitrogen oxides (NOx). It was found that the crystalline structure depended strongly on the technique of thermal spraying deposition. Moreover, a high amount of anatase was suitable for the photocatalytic degradation of the pollutants. Suspension plasma spraying has allowed retention of the original anatase phase and for very reactive TiO2 surfaces to be obtained for the removal of nitrogen oxides.

Mechanically Activated SHS Reaction in the Fe-Al System: In Situ Time Resolved Diffraction Using Synchrotron Radiation

The Mechanical Activation Self propagating High temperature Synthesis (M.A.S.H.S.) processing is a new way to produce nanocrystalline iron aluminide intermetallic compounds. This process is maily the combination of two steps ; in the one hand, a mechanical activation where the Fe - Al powder mixture was milled during a short time at given energy and frequency of shocks and in the other hand, a Self propagating High temperature Synthesis (S.H.S.) reaction, for which the exothermicity of the Fe + Al reaction is used. This fast propagated MASHS reaction has been in -situ investigated using the Time Resolved X - Ray Diffraction (TRXRD) using a X - ray synchrotron beam and an infrared thermography camera, allowing the coupling of the materials structure and the temperature field. The effects of the initial mean compositions, of the milling conditions as well as of the compaction parameters on the MASHS reaction are reported.

A fuzzy configuration multi-agent approach for product family modelling in conceptual design

Product modelling is an essential issue in the configurable product design. Many attempts have been made for modelling the configurable products. However, most of conducted research considers the configurable product modelling as an arrangement problem of a predefined set of components into a valid product structure. This paper considers configuration not only as a structural problem but also as a collaborative design problem. Product configuration must consider explicitly different actors and their perspectives influencing simultaneously the design of configurable products. Solving product configuration problems requires collaboration of actors from multiple distributed views. Therefore, from process and product point of views, engineering design of configurable products can be assisted by multi-agents systems. Following up this consideration, this paper proposes a Fuzzy Configuration Grammar based agents to assist collaborative and distributed design for configuration. Based on the distributed fuzzy models, fuzziness of interactions during the collaborative and distributed design for configuration, a computational approach for product configuration is developed. Modelling and implementation of an agent-based system, called G-APIC (Grammars based Agents for Product Integrated Configuration), is presented. In this agent-based system, there are four communities of agents: requirement community of agents, function community of agents, physical solution community of agents and process constraint community of agents. A fuzzy set of consensual physical solution agents, a sub community of alternative physical solution agents satisfying both customer’s requirements and different process views constraints, emerges from intra and inter-communities interactions of agents. Then, the proposed Fuzzy Configuration Grammar allows the interactions between these fuzzy consensual solution agents. The optimal product configuration, a fuzzy set of interacted consensual solution agents, emerges from these interactions. A case study illustrates the proposed approach.

Development of photocatalytic active TiO 2 surfaces by thermal spraying of nanopowders

Titanium dioxide is a very useful photocatalyst for the decomposition and diminution of environmental water and air pollutants. In such applications, it can be used as slurry or as immobilized coating obtained by different deposition methods. The studies performed in the last years showed that thermal spraying could be employed to elaborate TiO2 coatings with high performance for the decomposition of organic compounds. This manuscript presents a comparative study on the microstructure and photocatalytic performance of titania coatings obtained by different thermal spray techniques: atmospheric plasma spraying (APS), suspension plasma spraying (SPS), and high-velocity oxygen fuel spray process (HVOF). Different titania powders and suspensions were used to study the influence of the feedstock materials on the coating characteristics. The deposits were mainly characterised by SEM and X-ray diffraction. The photocatalytic performance was evaluated from the removal of nitrogen oxides. The experimental results showed that a drastic reduction of the pollutant concentration was obtained in presence of coatings elaborated by suspension plasma spraying. TiO2 coatings resulting from the spraying of agglomerated powder presentd less efficiency. That was mainly explained by the significant phase transformation from anatase to rutile that occurred in the enthalpic source during the spray processes.

Nozzle developments for thermal spray at very low pressure

Very low pressure plasma spraying has been the object of numerous studies for the past years. However, numerical simulations and experiments revealed some difficulties such as the presence of successive expansions and constrictions of the plasma jet that have an influence on the deposition efficiency and on the coating structure. Optimization of the plasma gun is thus required and the use of bell-contoured De Laval nozzle extensions seems particularly promising. In this paper, new developments concerning the use of an in-house bell-contoured nozzle extension are presented, and both numerical calculations and experiments were performed.

Elaboration and characterization of environmental properties of TiO2 plasma sprayed coatings

Titanium dioxide (TiO2) is an attractive material for numerous technological applications such as photocatalytical applications. These materials can in some conditions have the ability to allow the envi- ronmental purification of air and water by the decomposition and removal of harmful substances, such as volatile organic compounds (VOC), benzene compounds, NOx, SO2, etc. Our work was focused on the elab- oration and the evaluation of the environmental properties of titanium dioxide coatings by plasma spray techniques. The principle of plasma spraying consists by the injection in an enthalpic source (plasma) of the powder of one material to be sprayed. The molten powder is transported and accelerated by the plasma- producing gas flow and crushed on the target substrate, where the particles of material solidify with high speeds, thus forming the coating. The advantages of thermal spraying consist in the fact that the coating has stability, durability, adherence and cohesion. For this study, the initial powder material was an anatase TiO2. The photocatalyst coating was realized by a few kinds of thermal spray method: gas flame, APS (atmospheric plasma), VPS (vacuum plasma) and HVOF (high velocity oxygen fuel). The microstructures of the deposits, as a function of the coating process, are analysed by optical microscopy, scanning electronic microscopy, and the X-rays diffraction. To carry out the step of validation of these surfaces for their environmental function- alities, we used a control test process for the photocatalytic effectiveness with respect to nitrogen oxides. For that an original test chamber has been developed. Ultraviolet rays irradiated the coating specimens and the efficiency of NOx elimination has been controlled using a gas analyser. We studied the photocatalyti- cal properties of different obtained coatings as a function of various parameters (porosity, thickness, ratio anatase/rutile).

Distributed Fuzzy Product Configuration Using a Multi-Agent Approach

Abstract This paper proposes an agent-based approach to assist the product configuration in conceptual design. Based on the distributed fuzzy models, fuzziness of interactions during the collaborative and distributed design for configuration, a computational approach for product configuration is developed. The modelling and the implementation of an agent-based system, called APIC (Agents for Product Integrated Configuration), is presented. In this agent-based system, there are four communities of agents: specification community of agents, function community of agents, physical solution community of agents and production constraint community of agents. Through intra and inter-communities interactions of agents emerge the consensual physical solutions agents, a sub community of physical solution agents. The optimal product configuration is searched based on the affinities of the consensual physical solutions agents. A case study is presented to demonstrate the potential of this approach.

Environmental Applications of the Reactive Titania Coatings Elaborated by Suspension Plasma Spraying

This paper deals with the elaboration of titanium dioxide coatings, designed for photocatalytic applications, obtained by a non-conventional method of deposition: suspension plasma spraying (SPS). SPS is an alternative of the atmospheric plasma spraying (APS) in which the feedstock material is a suspension of the powder to be sprayed. The method consists in injection and atomization of a slurry (suspension of fine particles in a solvent) in an enthalpic source (plasma). TiO2 P25 powder (Degussa AG) was mechanically dispersed in distilled water and ethanol and injected in Ar-H2 or Ar-H2-He plasma under atmospheric conditions. SEM and XRD were performed to study the microstructure and the crystalline phases of the titania coatings. Photocatalytic efficiency of the elaborated samples was evaluated from the conversion rate of nitrogen oxides. The present results showed that the suspension plasma spraying allows to produce reactive surfaces for the removal of air pollutants, that in the same working conditions, present a higher photocatalytic activity compared to that of the initial raw powders.