In-operando high-speed microscopy and thermometry of reaction propagation and sintering in a nanocomposite

An important proposed mechanism in nanothermites reactions - reactive sintering - plays a significant role on the combustion performance of nanothermites by rapidly melting and coalescing aggregated metal nanoparticles, which increases the initial size of the reacting composite powders before burning. Here, we demonstrate a high-speed microscopy/thermometry capability that enables similar to mu s time and similar to mu m spatial resolution as applied to highly exothermic reaction propagation to directly observe reactive sintering and the reaction front at high spatial and temporal resolution. Experiments on the Al+CuO nanocomposite system reveal a reaction front thickness of similar to 30 mu m and temperatures in excess of 3000 K, resulting in a thermal gradient in excess of 10(7) K m(-1). The local microscopic reactive sintering velocity is found to be an order of magnitude higher than macroscale flame velocity. In this observed mechanism, propagation is very similar to the general concept of laminar gas reaction theory in which reaction front velocity similar to (thermal diffusivity x reaction rate)(1/2).