REAL-TIME PROBE OF REACTION CENTERS IN SOLID COMBUSTIONS ON THE SUBSECOND TIME SCALE

A quick-scanning extended x-ray-absorption fine-structure (QEXAFS) technique has been devised to follow the local atomic coordination changes about selected reactants in a class of highly exothermic solid-combustion reactions. Real-time EXAFS measurements during the combustion were made in the time frame of a few seconds. By tuning the monochromator to a specific energy, at which maximum changes occur in an EXAFS feature of an element transforming from the reactant to the product phase, a time resolution of 20 ms was achieved. The Ni + Al --> NiAl reaction has been investigated in some detail in light of a possible intermediate phase in the so-called "after-burn" region. The present QEXAFS findings together with the recent time-resolved diffraction data on the same system lends experimental insights into the structural macrokinetics of this class of combustion systems.