(596b) Studies on Combustion of Single Ni-Coated Al Particles in Normal and Reduced Gravity

Combustion of metal particles coated by another metal (e.g. aluminum coated by nickel) has been proposed as a method for studying intermetallic combustion reactions and for synthesis of intermetallic compounds. In propulsion applications, the reduced agglomeration and decreased ignition temperature of Ni-coated Al particles promise significant improvement of aluminized solid rocket propellant efficiency. Also, Al particles with thin Ni coatings are a candidate fuel for metal/CO2 propulsion on Mars.

Recently, we studied combustion of single Ni-coated Al particles (size 30-100 µm) in different gas environments (air, O2, CO2, Ar) using electrodynamic levitation and laser ignition. While many interesting results were obtained, ignition and combustion mechanisms of Ni-coated Al particles remain unclear. The detailed characterization of the process requires spatial and temporal resolutions that can be achieved only for particle sizes >1 mm. In this work, we ignited ~2.5 mm Ni-coated Al particles by a CO2 laser and studied the ignition and combustion processes using digital video recording and thermocouple measurements. To eliminate natural convection and liquid flow effects on combustion, experiments are planned under microgravity conditions onboard NASA's research aircraft.

The experimental setup includes a stainless steel reaction chamber, a CO2 laser and a high-speed high-resolution video camera. Spherical aluminum particles (diameter 2.38 mm), coated by nickel (5, 25, and 50 wt.% Ni), are mechanically drilled and installed using butt-welded thermocouples on a quick-detachable turntable inside the chamber. A two axes linear translation stage provides precise alignment of particles to the laser beam, which is directed through a ZnSe window into the chamber. A remote controlled motorized translation stage rotates the turntable during the flight, allowing for several experiments to be performed without opening the chamber. Experiments in normal gravity have demonstrated the effectiveness of our approach and provided interesting preliminary results. Detailed studies are currently in progress.