Bimetal Al–Ni nano-powders for energetic formulations

Abstract

Four bimetal Al–Ni nano-powders with compositions varied from 5 to 45at% of nickel were synthesized by explosion of electrically heated twisted pure Al and Ni wires in argon. The nano-powders were characterized using electron microscopy, x-ray diffraction, and thermal analysis. Materials were ignited using an electrically heated filament coated with powder and electrostatic discharge (ESD). The results were compared to those for pure nano-aluminum powder (n-Al) prepared using the same wire explosion technique. The nano-powders with high nickel concentrations contain fully reacted intermetallic phases, which are difficult to oxidize making them unattractive for energetic formulations. Nano-powders with lower nickel concentrations do not contain significant amounts of the intermetallic phases. No intermetallics were detected in the powder with 5at% Ni, which oxidized qualitatively similar to n-Al. The overall mass gain during oxidation for the bimetal powder was nearly identical to that of n-Al, suggesting the same heat release anticipated from their combustion. Oxidation kinetics assessed for this material accounting directly for the measured particle size distribution was compared to that of n-Al. The bimetal powder oxidized slower than n-Al, indicating its greater stability during handling and storage. The bimetal powder was less ESD-ignition sensitive than n-Al, but generated a stronger emission signal when ignited. Therefore, the bimetal powder with 5at% Ni is an attractive replacement of n-Al for advanced energetics with lower ESD sensitivity, better stability, and improved combustion performance.