Tuning ignition and energy release properties of Zirconium powder by atomic layer deposited metal oxide coatings

Ultra-fine powders of reactive metals are promising fuels/additives for propellants. However, the metal surfaces make these materials very unstable in ambient atmosphere. This study explored the method of applying thin films of inorganic materials onto the surface of Zr powder and investigated the effects of different surface coatings on the energy release and ignition process of Zr. Thin films of Al2O3 and ZnO were deposited on a commercial micron-scale Zr powder by atomic layer deposition (ALD). Growth kinetics of ALD films on the Zr particles were studied using various tools. Chemical and structural characterizations revealed that the Zr particles were completely encapsulated by uniform Al2O3 or ZnO films. The thicknesses of the encapsulation layers could be precisely controlled. ALD Al2O3 coatings exhibited a unique surface-sealing effect, which inhibited the low temperature oxidation of Zr in ambient air. Laser and electrostatic discharge (ESD) ignition tests revealed that ALD Al2O3 coatings extended the ignition delay and reduced the ESD sensitivity of the Zr powder. In comparison, ALD ZnO coatings could not form effective gas diffusion barriers, therefore they could not change the oxidation process of Zr and only showed modest effects on ignition and ESD sensitivity of the Zr powder.