Combustion synthesis of metallic foams from nanocomposite reactants

Highly porous intermetallic alloys were created through self-propagating high-temperature synthesis. The reactants are composed of nano-scale particles of nickel (Ni), micron-scale particles of aluminum (Al), and nano-scale Al particles passivated with a gasifying agent, C13F27COOH. The concentration of nano-Al particles present in the reactant matrix was controlled according to the wt% gasifying agent. Flame propagation was observed to transition from normal to convectively dominant burning as more gasifying agent became present in the reactants. Ignition delay times were reduced by two orders of magnitude when only 2.24 wt% nm Al particles were present. The product alloy expanded by a factor of 14 in the axial direction with 1.6 wt% nm Al (corresponding to 10 wt% gasifying agent). The total porosity of the pellets increased by a factor of 8 (i.e., from 10 to 80% porosity for 0–14 wt% gasifying agent).