Date of Award

Spring 2016

Document Type

Dissertation

Degree Name

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

Department

Chemical, Biological and Pharmaceutical Engineering

First Advisor

Edward L. Dreyzin

Second Advisor

Rajesh N. Dave

Third Advisor

Mirko Schoenitz

Fourth Advisor

S. Basuray

Fifth Advisor

Christopher J. Morris

Abstract

Recent interest in reactive material has shifted to more custom formulations targeting specific applications. In this work, preparation and characterization of nanomaterials used for several energetics and energy applications are addressed.

The main challenge of this effort is to design and prepare nanomaterials which have significant improvements associated with combustion dynamics, reaction rates, sensitivity, biocidal effectiveness, moisture stability, and are environmentally safer over the existing energetics. Nanomaterials that are used to defeat stockpiles of chemical and biological weapons, modify ionosphere properties for transmission of optical and radio signals, and for energy storage are prepared under room or cryogenic temperatures via mechanical milling.

This offers a scalable and versatile method for modifying or creating nanostructured composite materials. Additionally, nano-composite films used for on-chip energetics are prepared using electrochemical etching via solutions containing hydrofluoric acid, ethanol and hydrogen peroxide. Lastly, a less sensitive bimetal nano-powder for replacement of commonly used nano-sized aluminum is prepared by electro-exploded wires of pure metals.

Morphology and phase compositions of nanomaterials are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Thermal analysis is performed using thermo-gravimetry (TG), differential scanning calorimetry (DSC), and bomb calorimetry. TG results indicate the stability of the biocidal content as well as the individual decomposition and oxidation reactions involving the nanomaterials. DSC results are used to quantify the thermal energy storage capabilities and material performance upon cycling for energy storage materials. Bomb calorimetry results establish the energy density of nano-composite films and furthermore, agrees with thermodynamic equilibrium calculations for on-chip energetics.

Ignition temperatures of several nanomaterials are determined at heating rates of 103 to 105 K/s using a heated filament experiment. In a separate ignition experiment, the electrostatic discharge (ESD) ignition stimulus is used to characterize minimum ignition energy and cloud combustion characteristics. Aerosol combustion inside a constant volume explosion vessel is used to determine the combustion performance. Additionally, single particle combustion times as a function of particle size are quantified using products of hydrocarbon flame as the oxidative environment. Propagation velocities of the combustion event are also measured under air, nitrogen and vacuum environments using a high-speed video camera for several nanomaterials.

Nanomaterials prepared for bioagent defeat application in comparison to pure Al or Mg metals have substantially reduced ignition temperatures and longer combustion times. Their stability and effectiveness to inactivate bioagents are also substantially improved.

For on-chip energetics, moisture-stable and perchlorate-free compositions of nano-composite films are prepared; however, slower propagation rates compared to previous composite systems are seen.

The efficiency and overall charge of the refractory metal, samarium (Sm), in the starting composition is substantially improved by increasing the reactive interface surface area, via mechanical milling, within the nano-energetic material used as the heat source for Sm evaporation. Altering the interface chemistry of nano-energetic materials helps to achieve high reaction rates and consequently, high combustion temperatures to ionize Sm metal while inhibiting undesired reaction between Sm and the components of the nano-energetic material.

Lastly, the Al-Ni bimetal nano-powders prepared with doped amount of nickel could be used as replacement for aluminum nano-powders. It is observed that the bimetal powder is oxidizing slower than n-Al, leading to its greater stability during handling and storage. Furthermore, the bimetal powder is less ESD-ignition sensitive than n-Al with similar combustion temperatures.

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