Improvement of ignition and combustion performance of micro-aluminum particles by double-shell nickel-phosphorus alloy coating

A novel 'one-step' in-situ electroless plating method capable of controlling phosphorus content was proposed for the fabrication of spherical core-shell energetic Al@Ni-P composites, aiming to prompt particle ignition by adding easy-to-ignite P element. In this experimental study, the preparation and characterization of Al@Ni-P composites, as well as the effect of coating an alloy shell on the Al particle surface were mainly addressed. The morphology and chemical composition heterogeneity demonstrated that the Al@Ni-P composites possessed comparatively dense double-shell structure. Thermal analysis showed that these composites could accelerate the rate of energy release by decreasing the apparent activation energy (E-a) for particles oxidation. Laser ignition experiments were then conducted to examine the influence of Ni-P alloy on breaking through the barrier of ceramic phase Al2O3 shell to improve the ignition and combustion performances. Moreover, the composites with surface P of 12.68 at.% exhibited extremely shorter laser ignition delay time of 86 ms under 1 atm O-2 atmosphere, reducing by 65.46% compared with that of raw Al particle (249 ms); and the pressurization rate reached 88.08 kPa/s under 10 atm O-2 atmosphere, which is approximately 11 times that of raw Al particle (8.09 kPa/s). These drastic improvements were attributed to the synergistic effects of double-shell structure and intermetallic compound exothermic reaction, which enhanced mass and heat transfer. These results demonstrate that Al@Ni-P composites have a promising future in solid composite propellants, which exhibit shorter ignition delay time and more vigorous combustion than raw Al. This strategy is expected to provide a new method for the construction of complex core-shell structural materials in other research fields.