Document Type

Dissertation

Date of Award

8-31-2021

Degree Name

Doctor of Philosophy in Chemical Engineering - (Ph.D.)

Department

Chemical and Materials Engineering

First Advisor

Edward L. Dreyzin

Second Advisor

Mirko Schoenitz

Third Advisor

Lisa Axe

Fourth Advisor

Rajesh N. Dave

Fifth Advisor

Melissa Liberatore-Moretti

Abstract

Metals as fuels have higher energy density per unit mass or volume compared to any hydrocarbon. At the same time, metals are common structural materials. Exploring metals as reactive structural materials may combine their high energy density with attractive mechanical properties. Preparing such materials, however, is challenging. Requirements that need to be met for applications include density, strength, and stability enabling the component to sustain the structure during its desired operation; added requirements are the amount and rate of the energy release upon impact or shock. Powder technology and additive manufacturing are approaches considered for design of reactive structural materials. Respectively, feedstock powders are of critical importance. These feedstock powders must have the chemical composition ensuring, along with mechanical characteristics, a rapid initiation of the reactive material upon impact or shock, and high total energy release. They also must have the morphology suitable for processing.

In this work, several powders designed to serve as feedstock for manufacturing reactive structural materials are prepared, tuned, and characterized. High-energy mechanical milling is the common manufacturing approach for such powders in this study. The materials include elemental metals, such as aluminum, with the narrowly sized spherical porous powder and magnesium, with custom powder coating. Composite powders combining metals and metalloids, e.g., boron-titanium and boron-zirconium, with different structures and morphologies are also prepared and characterized. Milling conditions are varied and it is shown that the structures, sizes, porosities, and shapes of the produced powder particles can be adjusted through such variation.

The experimental work includes characterizing ignition and combustion of the prepared powders. Custom experiments employing an electrically heated wire are used with all prepared materials. Particle combustion experiments, quantifying the particle burn time and temperatures are performed with selected materials. Additionally, thermal analysis is used extensively in addition to electron microscopy and x-ray powder diffraction. Microcalorimetry in oxidizing gas serves to quantify stability of the selected materials. Nitrogen adsorption is used for many prepared powders to characterize their specific surface area and respective porosity.

Prepared powders combine unique morphological properties making them amenable to additive manufacturing, in particular, with high reactivity and stability. It is expected that using them as feedstock will lead to design of a new generation of reactive structural materials.

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