0000000000371439
AUTHOR
Frederic Charlot
In-situ time-resolved X-ray diffraction experiments applied to self-sustained reactions from mechanically activated mixtures
Resume . Le procede MASHS (Mechanically activated self-propagating high-temperature synthesis) apparait etre un procede alternatif interessant pour elaborer des materiaux tels que des ceramiques, des composites ou des intermetalliques. La formation au cours d'une reaction de combustion autoentretenue d'intermetalliques, tels que NbAlj et M0S12, a ete suivie in-situ et en temps reel en couplant la diffraction des rayons X, produits par le rayonnement synchrotron (Ligne D43, LURE - Orsay) et, une thermographie infrarouge. A partir de temps d'acquisition tres courts (de 30 ms a 100ms par diffractogrammes), il a ete possible de determiner simultanement les evolutions structurales et thermiques.…
Simultaneous Synthesis and Consolidation of Nanostructured MoSi2
A new process combining electric field activation and the imposition of pressure from mechanically activated powder mixtures is demonstrated as a means to simultaneously synthesize and densify nano-MoSi2 in one step. Nanophase reactants (Mo + 2Si) produced by mechanical activation are reacted by field activation with the simultaneous application of a uniaxial pressure. Mo + 2Si powders were comilled in a specially designed planetary mill to obtain nanometric reactants but to avoid formation of any product phases. These were then subjected to high alternating currents (1600 A) and pressures of 106 MPa. Under these conditions, a reaction is initiated and completed within a short period of tim…
One-Step Synthesis and Consolidation of Nanophase Iron Aluminide
The simultaneous synthesis and densification of nanophase iron aluminide is investigated. Elemental nanophase reactants produced by mechanical activation were reacted by field activation with the simultaneous application of uniaxial pressure. The process was demonstrated in this work by the synthesis of dense nanometric FeAl. Iron and aluminum powders were co-milled in a specially designed planetary mill to obtain nanometric reactants and to avoid formation of any product phases. These powders were then subjected to high AC currents (1250–1500 A) and pressures in the range of 70–106 MPa. Under these conditions, a reaction was initiated and completed within a short period of time (2.5–3.5 mi…
Développements récents de l'étude en temps réel par diffraction des rayons X couplée à une thermographie infrarouge : application au suivi de la réaction MASHS dans les systèmes FeAl, et MoSi2
La formation au cours d'une reaction de combustion autoentretenue et mecaniquement activee (MASHS) d'intermetalliques nanometrique, tels que les composes FeAl et MoSi 2 , a pu etre observee in-situ et en temps reel en couplant la diffraction des rayons X, produit par rayonnement synchrotron, et une thermographie infrarouge. La mise en oeuvre d'une telle experience est indispensable en raison de la vitesse importante (10 mm/s) de propagation du front de combustion. Des developpements recents realises au niveau des systemes de detections permettent d'obtenir des temps d'acquisition tres courts (quelques dizaines de millisecondes) et de reveler des etapes intermediaires au cours de la transfor…
In situ synchrotron characterization of mechanically activated self-propagating high-temperature synthesis applied in Mo–Si system
Abstract An original experiment was designed to monitor structural and thermal evolutions during the MASHS (Mechanically Activated Self-propagating High-temperature Synthesis) process in the Mo–Si system. Time-Resolved X-Ray Diffraction (TRXRD) coupled with an infrared imaging technique was performed to study, in situ, the formation of the α-MoSi2 phase in the combustion front. Despite a temporal resolution of 50 ms between two consecutive diffractograms, no intermediate phase was observed during the passage of the combustion front. The only reaction responsible for the self-sustentation is Mo+2Si→MoSi2 in the primary zone inside the combustion wave. The mechanical activation was found to i…