COMBUSTION OF LITHIUM–ALUMINUM ALLOYS

ABSTRACT

The combustion of lithium–aluminum alloys was investigated by experiment and with a computational flame model. Five Li–Al alloy compositions were studied experimentally, ranging from pure Li to 26 wt% Li/74 wt% Al. Alloy samples were heated inductively in a crucible to temperatures ranging from 1000 to 1400 K and burned with oxygen/argon mixtures or with water vapor in a counterflow diffusion flame. Flame temperature profiles were measured using a Li resonance line reversal method, and relative lithium atom populations in the flame were determined using an absorption method. The products of combustion, analyzed using x-ray diffraction and field-emission scanning electron microscopy/energy dispersive x-ray spectroscopy, are Li₂O, γ-LiAlO₂, and β-Li₅AlO₄, with some solid LiOH produced during combustion in water vapor. Although aluminum monoxide gas was detected at ignition in water vapor in a limited number of tests, evidence indicates that aluminum does not burn in the vapor phase during steady-state combustion of the alloy in either oxygen or water vapor. Experimental results show that the lithium burns in the vapor phase and aluminum reacts on the surface or in the bulk phase to form γ-LiAlO₂ and β-Li₅AlO₄. Models of Li–Al alloy-fueled flames in oxygen and in water vapor indicate that Li₂O is the primary gas-phase product in dry oxidizers and that H₂ and LiOH are the primary gas-phase products in water vapor. Parametric studies comparing model predictions to experimental data provide insight into combustion mechanisms and flame structure for an alloy fuel.

Keywords:

• alloy
• aluminum combustion
• flame structure
• hydrogen generator
• lithium
• lithium hydroxide
• lithium oxide
• metal fuel
• vapor phase

Acknowledgments

This material is based on work supported by Dr. Richard Carlin of the Office of Naval Research under Contract No. N00014-00-D-0058, DO #0011. The authors would also like to acknowledge M.S. Angelone and H. Gong of the Materials Characterization Laboratory at Penn State for materials testing.

Notes

^a From Klanchar et al., 1997.

^a E=experimental; T=theoretical; R=review.

^a E = experimental; T = theoretical; R = review.

¹Data for Figures 1-4 were calculated using the NASA Chemical Equilibrium with Applications (CEA) code (McBride and Gordon, 1996).

Note: Here n is the reaction order; (c) refers to condensed products from gas-phase reactions; (l) refers to liquid species on the surface or in bulk.

Note: Here n is the reaction order; (c) refers to condensed products from gas-phase reactions; (1) refers to liquid species on the surface or in bulk.

²ICCD=International Center for Diffraction Data.