Simultaneous IR and time-resolved X-ray diffraction measurements for studying self-sustained reactions

Self-propagating high-temperature synthesis provides an attractive practica l method for producing advanced materials such as ceramics, composites and intermetallics. This kind of reaction has been investigated in situ using t ime-resolved X-ray diffraction, with an X-ray synchrotron beam (D43 beamlin e, LURE, Orsay) coupled to simultaneous IR thermography to study structural transformations and thermal evolution. With short acquisition times (30 ms per pattern) it has been possible to observe several steps before obtainin g compounds. Two different compound formations have been described: (i) the different steps of reaction, aluminium melting, subsequent temperature inc rease and fast reaction between Al and Ni at such temperatures that only Ni and AlNi are solid and all other compositions are liquid and well identifi ed; (ii) the formation of FeA1. Here, a portion of the iron seems to transf orm into its allotropic phase and this transition stabilizes the reaction t emperature at similar to 1173 K. In addition, the aluminium melting during the reaction explains why the nanostructure induced by the mechanical activ ation is maintained in the end product.