Nanocomposite and mechanically alloyed reactive materials as energetic additives in chemical oxygen generators

Chemical oxygen generators are widely used for aircraft, spacecraft, submarines, and mine rescue. Oxygen-generating compositions typically include alkali metal chlorate or perchlorate that decomposes at increased temperatures, a transition-metal oxide as a decomposition catalyst, and a metal fuel that reacts with part of the produced oxygen to provide heat for a self-sustained propagation of the decomposition/combustion wave. To increase the oxygen yield per unit mass, it is of interest to minimize the amount of metal fuel, but decreasing its content leads to pulsating combustion and undesired fluctuations of the oxygen flow rate. The present paper explores the feasibility of replacing iron and tin, currently used in oxygen generators, with reactive materials, produced by arrested reactive milling and by mechanical alloying. Because of their high energy density, easy ignition, and good storability, these materials have the potential to improve the performance characteristics of oxygen generators. Thermodynamic calculations for combustion of sodium chlorate mixed with various reactive materials identified the most attractive additives providing high temperatures and high oxygen yield. Experiments on combustion of sodium chlorate-based mixtures with nanoscale cobalt oxide catalyst and the most promising energetic additives were conducted in an argon environment, using laser ignition. Infrared video recording was used to investigate the thermal wave propagation over the mixture pellet. The experiments have shown that mechanically alloyed Al/Mg (1:1 mass ratio) material is a promising alternative to iron and tin, because significantly smaller amounts of this additive are needed for a steady propagation of the combustion wave.