Evidence of a kinetic isotope effect in nanoaluminum and water combustion

The normally innocuous combination of aluminum and water becomes violently reactive on the nanoscale. Research in the field of the combustion of nanoparticulate aluminum has important implications in the design of molecular aluminum clusters, hydrogen storage systems, as well as energetic formulations which could use extraterrestrial water for space propulsion. However, the mechanism that controls the reaction speed is poorly understood. While current models for micron-sized aluminum water combustion reactions place heavy emphasis on diffusional limitations, as reaction scales become commensurate with diffusion lengths (approaching the nanoscale) reaction rates have long been suspected to depend on chemical kinetics, but have never been definitely measured. The combustion analysis of nanoparticulate aluminum with H ₂O or D₂O is presented. Different reaction rates resulting from the kinetic isotope effect are observed. The current study presents the first-ever observed kinetic isotope effect in a metal combustion reaction and verifies that chemical reaction kinetics play a major role in determining the global burning rate. Burning insights: Kinetic limitation of nanoparticulate aluminum (nAl) combustion has never been observed and therefore is often described as solely diffusion controlled. The combustion analysis of nAl with H₂O or D₂O is presented and a distinct kinetic isotope effect measured. This first-ever observed kinetic isotope effect in metal combustion verifies that reaction kinetics play a major role in determining the global burning rate as particle sizes reach the nanoscale.