Pyrophoricity of nano-sized aluminum particles

The temperature histories are calculated for spherical nano-sized aluminum particles with no protective oxide shell inserted in air at 300 K. In calculations, initial particle temperatures varied and the minimum initial temperature leading to the particle ignition was determined. The particle, initially without any oxide coating, was assumed to react adiabatically forming a monomolecular oxide coverage; the following oxidation was assumed to be governed by the Cabrera-Mott reaction mechanism. Convection and radiation heat losses were considered. Convection was accounted for using a transition regime heat transfer model by Fuchs. Aluminum particles with diameters less than about 68 nm are predicted to be pyrophoric, e.g., ignite without appreciable initial pre-heating.