High Pressure Ignition and Combustion of Aluminum Hydride

Abstract

An experimental study was conducted to determine the high pressure ignition characteristics of α-aluminum hydride. Aluminum hydride particles were heated on a platinum filament at heating rates of approximately 1 × 10⁵ K/s in a pressure vessel for pressures ranging up to about 7 MPa, in order to quantify the ignition temperature and to observe the ignition process. Experiments were conducted in air, argon, and nitrogen as the pressurizing environment. This study revealed that the dehydrogenation of aluminum hydride is not a function of pressure under the conditions tested. In addition, ignition temperatures were found to be approximately linearly related to pressure until pressures exceeded about 0.4 MPa, at which point they remained constant through the highest pressures tested. High speed imaging of the ignition process showed a dramatic change in the ignition behavior for pressures above 0.4 MPa, corresponding to what we believe is a threshold for H₂/air autoginition or perhaps even an explosion limit. We find that the combustion behavior of aluminum hydride particles shared many traits similar to what has been previously observed with aluminum particles including a diffusion flame surrounding the particle, spinning, jetting, and explosions/fragmentation. Quenched particles also showed clear evidence of gas phase combustion with parent particles containing nanofeatures, which were condensed from the gas phase. The results of this study provide additional understanding on the ignition and combustion process of aluminum hydride at extreme conditions, which may be useful in modeling efforts or in the development of solid propellants.

Keywords:

• Alane
• Aluminum hydride
• Combustion
• Ignition

Additional information

Funding

This research effort was supported through the ILIR program at the Naval Surface Warfare Center–Indian Head Division (NSWC-IHD) and the Army Research Office.