COMBUSTION OF LITHIUM–ALUMINUM ALLOYS

Abstract

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.