Search

Energetic materials research focuses on performance analysis of cost-effective solid materials which safely, precisely, and efficiently transitions stored chemical potential energy to kinetic energy at a rate throttled through chemical or architectural means. Heterogenous compositions of metal fuels and solid materials with a high storage capacity of condensed oxidizing elements, such as oxygen and/or fluorine, is a class of energetic material of interest given its relatively high reaction enthalpies and adiabatic flame temperatures. In the wake of the earliest instances of metal fuels being used as a high energy additive during World War II, characterizing the reaction mechanisms of micron and nanoparticle aluminum fuels with various oxidizer sources has been a primary subject of research within the solid energetics community. The advent of nanotechnologies within the past two decades brought with it the promise of a prospective revolution within the energetics community to expand the utility and characterization of metallized energetic materials in solid propellants and pyrotechnics. Significant prior research has mapped reactivity advantages, as well as the many short comings of aluminum-based nanoscale energetic formulations. Examples of short comings include difficulties of materials processing, relative increase in native oxide shell thickness, and particle aggregate sintering before primary reaction. The less than flaw-less promises of nanoscale aluminum fuels have thus become the impetus for the development of novel architectural solutions and material formulations to eliminate drawbacks of nanomaterial energetics while maintaining and improving the benefits. This dissertation focuses on further understanding reaction mechanisms and overall combustion behavior of nanoscale solid energetic composite materials and their potential future applications. My research branches out from the heavy research involved in binary, aluminum centric systems by developing gen

ZBLAN glass is a heavy metal fluoride glass that tends to undergo heavy devitrification, resulting in a crystalline material. It has many applications, including its use as an optical waveguide for fiber‐optic technology. However, when the glass is processed with traditional casting techniques, crystallites form readily that act as scattering centers, which results in large attenuation losses. In this study, it has been experimentally demonstrated that processing ZBLAN rapidly with a heating rate of 25 000 K/min and cooling rate of 4000 K/min yields test samples that are fully amorphous and retain a disordered molecular arrangement characteristic of its molten state. This novel method was developed using a specifically designed equipment named a Rapid Electro‐thermal Processing Device, or “REPD.” The REPD applies ohmic heating and thermal conduction to a heat sink to rapidly process the ZBLAN material. The absence of crystallites in the rapidly processed ZBLAN test samples were verified using transmission electron microscopy (TEM) analysis. Applying a theoretical algorithm, the critical cooling rate for yielding fully amorphous ZBLAN glass was determined to be 1081 K/min for a sample volume of 9.4 × 10−8m3.

Industrial gasifiers and combustors are assumed to reach particle heating rates of 10(5)-10(6) degrees C/s and understanding how particles behave in these extreme conditions can improve the utilization of solid fuels in these reactors and in downstream applications. By studying intermediate devolatilization processes during solid fuel pyrolysis, detailed models for solid fuel conversion can be formulated. Key objectives of this study included (1) investigate possible mechanisms that promote the formation of synthesis gas components and char, (2) compare the devolatilization behavior of pyrolysis by varying particle size, hold time, and temperature and (3) correlate char deactivation with hold time. The objectives of the study were accomplished using a wire-mesh reactor with a uniform heating rate of 500 degrees C/s in nitrogen under atmospheric pressure. A design of experiments approach was used to quantify the effects that hold time, temperature, and particle size had on char yield, evolved gas composition, and apparent activation energy of pine stem wood and wheat straw. Key results indicate that with increased temperature and hold time more volatiles evolve from the fuels and favor carbon monoxide and methane production at higher temperatures. Apparent activation energy of the volatile matter decreases with hold time. An abbreviated model for apparent activation energy correlates well with experimental data and assumes that along a devolatilization pathway, that not all volatiles are driven from the fuel.

We have investigated the origin of significantly high thermal stability of Zr50Cu40Al10 metallic glass and its crystallization behavior as compared to Zr70Cu20Al10 and Zr70Cu30 glassy alloys, by differential scanning calorimetry (DSC), x-ray diffraction (XRD) and resonant ultrasound spectroscopy (RUS) techniques. It was found from XRD and DSC analyses that (i) constituent atoms in Zr50Cu40Al10 are highly close-packed in a glassy state and (ii) Zr50Cu40Al10 glass shows a complicated crystallization process when it is heated at conventional heating rates, but when it is rapidly heated, the ordered B2-type ZrCu is dominantly formed. The high thermal stability and its crystallization behavior are discussed in terms of the long-range-diffusion of atoms and elastic strain energy.

We have investigated the origin of significantly high thermal stability of Zr50Cu40Al10 metallic glass and its crystallization behavior as compared to Zr70Cu20Al10 and Zr70Cu30 glassy alloys, by differential scanning calorimetry (DSC), x-ray diffraction (XRD) and resonant ultrasound spectroscopy (RUS) techniques. It was found from XRD and DSC analyses that (i) constituent atoms in Zr50Cu40Al10 are highly close-packed in a glassy state and (ii) Zr50Cu40Al10 glass shows a complicated crystallization process when it is heated at conventional heating rates, but when it is rapidly heated, the ordered B2-type ZrCu is dominantly formed. The high thermal stability and its crystallization behavior are discussed in terms of the long-range-diffusion of atoms and elastic strain energy.

Outline and Motivation 1) Out-of-band frequency response in communications circuits: a) Effect of parasitic elements on network performance; b) Degradation in filter rejection ratios; c) EMP propagation on signal path; d) Need for wideband circuit characterization and verification throughout the communications network (RF and IF path, mixer, A/D, power vias, etc.). 2) Experimental study of device upset using direct RF injection: a) Identify RF characteristics that produce bit errors, latch-up; b) What are the EMP effects at the device level? c) Modulation and nonlinear circuit response. 3) Directions to pursue: a) Experiment; b) Modeling., The original document contains color images.

Rapid heating and cooling (i.e. rates of temperature change greater than one million degrees K/sec) have become a major new approach to materials processing in the metallurgy and electronics communities; rates up to 10 to the 14th power degrees K/sec have been reported in the literature. This report assesses where the capability for rapid energy transfer into a condensed phase, developed as part of materials processing research, might also be utilized to give new insights into physical properties or to explore new concepts in physics. The unique aspect of the rapid heating/cooling technology is the short time frame, 10 to the minus 8th power - 10 to the minus 12th power sec used to transfer the energy. Electron and laser beams are the most likely heating sources since they can generate short, intense, controlled pulses; rapid cooling must depend on conductive heat flow and is thereby restricted to thin film configurations. The perceived physics research opportunities are organized about four categories: mass transport, energy transport, theoretical concepts and dynamic measurement capability. The section on mass transport examines issues in nucleation, solidification , segregation, melting and metastable structure. The section on energy transport examines issues in beam-matter interactions, thermalization processes, interfacial energy transfer, thermoelectric effects, and thermoacoustic coupling. (Author)