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

Highlights: • ALD of Al₂O₃ and ZnO are successfully applied to a Zr powder. • Zr particles are encapsulated by oxide coatings with precisely controlled thicknesses. • ALD Al₂O₃ coatings exhibit a unique surface-sealing effect. • Energy release of Zr can be controlled by the thickness of ALD Al₂O₃ coating. • Oxide coatings on Zr reduce the hazard of ignition by ESD. -- Abstract: 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.