Solid-state combustion of metallic nanoparticles: New possibilities for an alternative energy carrier

As an alternative to conventional methods of conveying and delivering energy in mobile applications or to remote locations, we have examined the combustion of nanostructured metal particles assembled into metal clusters. Clusters containing iron nanoparticles (∼50 nm in diameter) were found to combust entirely in the solid state due to the high surface-to-volume ratio typical of nanoparticles. Optical temperature measurements indicated that combustion was rapid (∼500 ms), and occurred at relatively low peak combustion temperatures (1000-1200 K). Combustion produces a mixture of Fe(III) oxides. X-ray diffraction and gravimetric analysis indicated that combustion was nearly complete (93-95% oxidation). Oxide nanoparticles could be readily reduced at temperatures between 673 K and 773 K using hydrogen at 1 atm pressure, and then passivated by the growth of a thin oxide layer. The nanostructuring of the particles is retained throughout the combustion- regeneration cycle. Modeling of the combustion process is in good agreement with observed combustion characteristics.