Characterization and science of an aluminum fuel treatment process

Thesis: Sc. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, February 2018.Cataloged from PDF version of thesis.Includes bibliographical references.Presented is an inexpensive and highly effective method of activating bulk aluminum allowing it to react with water producing hydrogen gas and steam. The extreme energy density of the aluminum-water reaction, twice that of diesel fuel and forty-five times that of lithium-ion batteries, makes this new fuel a promising safe alternative to high-pressure hydrogen storage. Aluminum is the most abundant metal in the earth's crust and has long been recognized as a potential fuel source. The challenge however is disrupting the protective oxide layer in a cost effective and safe manner. In this work, I show that by exposing aluminum to a heated liquid gallium-indium eutectic bath, the protective oxide coating is disrupted allowing the eutectic to penetrate the grain boundaries. The result is an activated aluminum fuel that is highly reactive with water. Unlike other methods, which involve explosive aluminum powders, this treatment process can successfully treat large pieces of aluminum that are safe to handle while using less than 4% gallium-indium eutectic. The aluminum treatment process was characterized to maximize hydrogen yield and minimize gallium-indium content since these metals are expensive. Tests show that temperature of the liquid metal bath, immersion time, and treated metal composition affect hydrogen yield. A heated gallium-indium bath yielded activated aluminum that reacted to greater than 85% completion while using only 3-4 wt.% gallium-indium. The treatment process proved to be critically enhanced by cold working the aluminum allowing more favorable conditions for liquid metal to diffuse into the grain boundaries. Activating bulk aluminum was previously thought to be impractical and current approaches to using aluminum as a fuel shifted towards the use of powdered aluminum even though it is extremely dangerous to process and handle. This work presented herein shows indium is the key activating metal in the heated treatment bath and samples that treated in baths with higher indium content exhibited higher reactivity yet contain less overall gallium-indium content. This thesis provides the basic science and engineering know-how to guide the deterministic design of a large-scale aluminum treatment process for macro sized (e.g., 6 mm diameter spheres or wire), which was previously thought impractical.by Jonathan Thurston Slocum.Sc. D