(247a) Nanostructured Intermetallic Foams

A highly porous intermetallic alloy was 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 % of gasifying agent. The reactant mixture was cold-pressed into cylindrical pellets with a constant density equal to 70% of the theoretical maximum density. Once ignited, flame propagation was observed to transition from normal to convectively dominant burning as more gasifying agent became present in the reactants. A critical Andreev number of 6 was determined to represent this transition. 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). Total porosity of the pellets was also measured and found to increase with increasing wt % of the nano-Al and gasifying agent.