Correlation of Structure, Morphology and Energetics for Gasless Reactive Composite Powders

Metal based composite powders capable of highly exothermic, gasless reactions were prepared by mechanical milling, adjusting parameters to intentionally vary particle characteristics. Two material systems were explored. In Ni/Al composite, intermetallic phases form exothermically leading to self-heating and accelerated oxidation. In a self-contained fuel/oxidizer system, Al/Fe2O3, a classic thermite reaction occurs forming molten iron and aluminum oxide. For each composite material, fully-dense irregularly shaped powders, as well as porous spherically shaped powders are prepared and compared to each other. Particle characteristics such as size, shape, and morphology are observed by electron microscopy and low-angle laser light scattering. Scale of mixing and inclusion size are observed through image analysis and correlated to results of thermal analysis and ignition experiments. Specifically for the case of spherical powders, which are of interest for additive manufacturing techniques, milling parameters are optimized and associated with target size, uniformity of size, and sphericity. Finally, correlations are sought between morphological and energetic characteristics of the prepared materials.