(178g) Ignition Mechanisms of Metal-Coated Aluminum Particles

Combustion of aluminum particles coated with high-melting metals (e.g. nickel, iron, etc.) is useful in both propulsion and materials synthesis applications. Metal-coated Al particles may potentially be used in place of Al in solid rocket propellants to lower particle ignition temperature and decrease agglomeration. They may also be utilized for the continuous combustion synthesis of aluminide powders.

Previous studies on small (10-100 micron) Ni-coated Al particle combustion did not provide sufficient information on ignition mechanisms. The current research reveals such details by using laser ignition of larger (~2.5 mm) particles. Experiments are performed using Ni-coated and Fe-coated Al particles in both CO₂ and argon environments. Ignition mechanisms are determined by using digital high speed video, particle thermocouple temperature measurements, and EDX analysis.

It was found that ignition of Ni-coated Al particles relies entirely on intermetallic reactions between Ni and Al and is independent of gas environment. By turning off the laser at different stages, a critical temperature, lower than the ignition temperature, was determined such that self-ignition subsequently occurs owing solely to the intermetallic reactions.

Experiments in microgravity on board NASA research aircraft are scheduled for summer, 2006. By eliminating the disturbing effects of gravity, these experiments will identify the intrinsic ignition and combustion mechanisms.