Development of Passivated Pyrophoric Metal Powders (hafnium and Zirconium) with Reduced Electrostatic Discharge (esd) Sensitivity

High-density metals such as hafnium and zirconium are of interest to the propellant, explosive, and pyrotechnic industry due to their high oxidation enthalpies; however, these metal fuels suffer from electrostatic discharge (ESD) complications creating safety concerns. Previous attempts to passivate these powders have failed due to abrasion of the protective coatings. Two novel methods for desensitizing hafnium powder based on technology developed by MACH I, Inc. were successfully demonstrated in a Phase I SBIR project: both approaches negate abrasion complications. First, ReactiveMilling (RM) of hafnium powder with NH4OH to 800 °C in a N2 atmosphere produces a thin protective coating of HfN on hafnium. The olive-gold material exhibited elevated ESD thresholds. The second method, RM of hafnium and aluminum powders in an Ar atmosphere to 700° C followed by nitridation at 610°C, generated a protective intermetallic coating (Al2Hf) on hafnium, which also exhibited excellent passivation levels. These materials were fully characterized by optical, SEM, and XRD analyses.