In-situ time-resolved X-ray diffraction experiments applied to self-sustained reactions from mechanically activated mixtures

Mechanically activated self-propagating high-temperature synthesis (MASHS) provides an attractive practical method for producing advanced materials su ch as ceramics, composites and intermetallics. This kind of reaction has be en investigated in-situ using the Time resolved X-Ray Diffraction (TRXRD), with an X-ray synchrotron beam (D43 beam line, LURE Orsay) coupled to simul taneous infrared thermography to study structural transformations and therm al evolution. With short acquisition times (from 30ms to 100ms per pattern) ), it has been possible to observe several steps before obtaining compounds . Two different compound formations have been described (i) Owing to the te mporal resolution of 100 ms between two consecutive diffractograms, it was possible to observe several steps before obtaining the niobium aluminide co mpound NbAl3. Indeed, the phase transformations corresponding to the alumin um melting plateau, the subsequent temperature increase to the ignition tem perature and the fast reaction between niobium and molten aluminum at such a temperature were well-identified. (ii) Despite a temporal resolution of 3 3ms between 2 consecutive diffractograms, no intermediate phase was observe d during the combustion front passage. The only reaction responsible for th e self-sustaining reaction is Mo + 2Si --> MoSi2 in the primary zone inside the combustion wave.