Kyle Watson- Fast Reaction of Nano-Aluminum: A Study on Fluorination Versus Oxidation
Transcript of Kyle Watson- Fast Reaction of Nano-Aluminum: A Study on Fluorination Versus Oxidation
FAST REACTION OF NANO-ALUMINUM: A STUDY ON FLUORINATION VERSUS OXIDATION
BY
KYLE WATSON, M.S.M.E.
A THESIS
IN
MECHANICAL ENGINEERING
Submitted to the Graduate Faculty
of Texas Tech University in Partial Fulfillment of the Requirements for
the Degree of
MASTER OF SCIENCE
IN
MECHANICAL ENGINEERING
Approved
Michelle Pantoya
Chairperson of the Committee
Valery Levitas
Jordan Berg John Borrelli
Dean of the Graduate School August 2007
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Acknowledgments
There are many people who deserve recognition and special thanks for their
support and encouragements throughout my academic career. I would like to thank my
family and friends for their love and support. To my wife, Heather, thank you for all of
your love, selflessness, and support through my struggles, as well as, for all the laughter
and joy you bring into my life. I would also like to extend my gratitude to Dr. Michelle
Pantoya for her guidance in my research and in my graduate career. She has been an
integral part of my intellectual growth as a student researcher and in my preparation for
life after academia. I would like to recognize the combustion lab researchers, specifically
Charles Crane and Shawn Stacy. Charles, your help with the procurement card and the
responsibilities of the lab allowed me to focus more closely on my research. Shawn, your
work with the REAL Code (Tim Tec, LLC.) program was an important addition to my
research studies. Both are greatly appreciated and helped in the pursuit of my graduate
degree. I also extend thanks to Dr. Mark Grimson and the Texas Tech Experimental
Sciences staff for their guidance and aide in the taking of the SEM micrographs included
in this work. To my Lord and Savior, you are the guiding light and the foundation for all
of my accomplishments in life.
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Table of Contents
Acknowledgements............................................................................................................. ii
Abstract ................................................................................................................................v
List of Tables ..................................................................................................................... vi
List of Figures ................................................................................................................... vii
Chapter
I. Introduction ....................................................................................................................1
1.1 Overview...................................................................................................................1
1.2 Aluminum as a Fuel ..................................................................................................3
1.3 Teflon vs. Metallic Oxide as an Oxidizer .................................................................8
1.4 Open vs. Confined Burns and the Corresponding Modes of Heat Transfer ...........14
1.5 Objectives................................................................................................................16
II. Experimental ...............................................................................................................18
2.1 Sample Preparation .................................................................................................18
2.2 Open Burn Setup.....................................................................................................24
2.3 Confined Burn Setup...............................................................................................25
2.4 Data Acquisition .....................................................................................................26
III. Results and Discussion ..............................................................................................33
3.1 Open Burn Tray Results..........................................................................................33
3.1.1 Results and Initial Observations ........................................................................33
3.1.2 The Effects of Particle Size and the Addition of Teflon ...................................35
3.1.3 Implications .......................................................................................................41
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3.2 Confined Burn Tube Results...................................................................................42
3.2.1 Results and Initial Observations (Flame Speed Measurements) .......................42
3.2.2 Results and Initial Observations (Pressure Measurements)...............................44
3.2.3 The Effects of Particle Size and the Addition of Teflon ...................................46
3.2.4 Implications .......................................................................................................54
3.3 The Effects of Confinement ....................................................................................55
IV. Conclusions ...............................................................................................................61
References..........................................................................................................................62
Appendices.........................................................................................................................66
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Abstract
The use of fluorine as an oxidizing agent in thermite reactions yields higher heats
of combustion and an increase in gas production. Thus fluorination reactions have the
potential to excel in situations that require high pressures, temperatures, and flame
speeds. This study compares the propagation behaviors of Al/Teflon, Al/MoO3/Teflon,
and Al/ MoO3 in an effort to determine the effects that the replacement of oxygen with
fluorine (Teflon is 75% by weight fluorine) has upon the reaction characteristics in both
open and confined configurations. Data was collected from pressure sensors and high
speed recording of the reactions. The mass percent of Al was varied from 10% – 90% for
each composite to study the effects of composition. The composites were then further
tested at the optimum stoichiometry using either 50 nanometer or 1-3 micrometer Al as
the fuel to examine the effect of Al particle size on the reactions.
It was found that the addition of Teflon in an open burn configuration hinders the
reaction due to a loss of liberated fluorine gas to the surroundings resulting in less energy
to propagate the reaction and a higher rate of incomplete combustion. Nanoscale Al
produced faster flame speeds as a result of the increased sensitivity and homogeneity
associated with the smaller particles. The most significant flame speeds were found in
the Al/MoO3 composites in which less energy is lost in the form of escaping gas.
Confining the reactions and the intermediate and product gases promotes
enhanced convection yielding increased flame speeds. The reactions containing Teflon
exhibit much higher pressures which have a dual effect. Initially the increasing pressures
result in increasing flame speeds. However, there exists a threshold beyond which an
increase in pressure suppresses the reaction and reduces the flame speed.
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List of Tables
1. Material properties of the powders used......................................................................18
2. Al/Teflon composite mass ratios and corresponding equivalence ratios.....................22
3. Al/MoO3/Teflon composite mass ratios and corresponding equivalence ratios..........23
4. Al/MoO3 composite mass ratios and corresponding equivalence ratios......................23
5. Pressure results from the 4th pressure transducer (farthest from ignition) ...................44
6. Properties of the reactions assuming ideal burns with complete combustion .............45
7. Difference between optical and acoustical wave propagation rates ............................53
8. Mach number calculations for the flame speed of the reactions..................................54
9. Approximate maximum diffusive distance for the reactions.......................................57
10. Factor of increase due to confinement of each 50 nm Al composite...........................58
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List of Figures
1. Heat of Combustion for various compositions (Fischer 1998). Al/Teflon reaction heat of combustion calculated using REAL Code (Tim Tec, LLC.), a chemical equilibrium program, under the same thermodynamic conditions assumed to generate the data from Fischer. ....................................................................................................9
2. SEM micrographs of the powders used prior to mixing.
(a) 1-3 μm Al provided by AAE at 10,000x magnification (b) 50 nm Al provided by Nanotechnologies at 50,000x magnification (c) 44 nm MoO3 provided by Nanotechnologies at 50,000x magnification (d) 200nm Zonyl MP-1150 (Teflon) provided by Dupont ..........................................19
3. SEM micrographs of the post-mixed composites.
(a) 50 nm Al/Teflon composite (b) 50 nm Al/MoO3 composite (c) 50 nm Al/MoO3/Teflon composite All images taken at 75,000x magnification .................................................................21
4. Photograph of the open burn apparatus. Each interval corresponds to 1 cm increments used for defining a length scale for flame speed calculations. ....................................24
5. Picture of a prepared burn tube....................................................................................26 6. Picture of the instrumented confined burn apparatus. .................................................26 7. Schematic illustrating the test setup.............................................................................27 8. Consecutive still images displaying a typical confined burn. Each image corresponds
to one frame at a sample rate of 40,000 fps. The front edge of luminous activity is used to calculate flame speed.......................................................................................28
9. Typical pressure trace for a 50nm Al/Teflon confined burn........................................29 10. Al/Teflon open tray burn results. .................................................................................33 11. Al/MoO3/Teflon open tray burn results. ......................................................................34 12. Al/MoO3 open tray burn results...................................................................................34 13. Gas generation in the Al/Teflon, Al/MoO3/Teflon, and Al/MoO3 reactions. Values
determined using the REAL Code (Tim Tec, LLC.) chemical equilibrium program..36
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14. Adiabatic flame temperature in the Al/Teflon, Al/MoO3/Teflon, and Al/MoO3 reactions. Values determined using the REAL Code (Tim Tec, LLC.) chemical equilibrium program. ...................................................................................................37
15. Al/Teflon confined apparatus burn results...................................................................42 16. Al/MoO3/Teflon confined apparatus burn results........................................................43 17. Al/MoO3 confined apparatus burn results....................................................................43 18. Burning velocities of propane/air mixtures. Figures against curves show percentage
C3H8. (Egerton & Levevbre, 1954)..............................................................................49 19. Effect of pressure on the combustion rate of thermite mixtures:
1) BaO2/Zr 2) MoO3/Mg 3) PbO2/Zn (Ivanov et al., 1979) .....................................................................................................50
20. 50 nm Al open and confined burn results for all composites. .....................................56
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Chapter I
Introduction
1.1 Overview
The introduction of nanoscale particles into energetic materials, specifically
thermite composites, has provided the means to greatly alter the combustion
characteristics such as sensitivity, stability, and energy release (Aumann, Skofronick, &
Martin, 1995; Miziolek, 2002). The traditional thermite reaction is defined as “an
exothermic reaction which involves a metal reacting with a metallic or a non-metallic
oxide to form a more stable oxide and the corresponding metal or non-metal of the
reactant oxide” (Wang, Munir, & Maximov, 1993). A new class of thermites referred to
as metastable intermolecular composites (MIC) has been defined as “mixtures of
nanoscale powders of reactants that exhibit thermite (high exothermicity) behavior”
(Miziolek, 2002). This new class of composites utilizes nanoscale powders that result in
much higher propagation rates and ignition sensitivity. For example, aluminum (Al) and
molybdenum tri-oxide (MoO3) composites, when using average particle sizes between 20
and 50 nanometers, have been shown to react more than 1000 times faster than traditional
thermites (Aumann et al., 1995). These nanoscale composites are also capable of energy
output 2 times that of high explosives (Miziolek, 2002) and producing temperatures
above 3000 K (Valliappan, Swaiakiewicz, & Puszynski, 2005). The enhancement of the
combustion characteristics is often credited to the decrease in diffusive distance,
increased surface area, and increased homogeneity of the composite when using
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nanoscale reactants that have smaller nominal sizes and larger surface area to volume
ratios (Kubota & Serizawa, 1987). Before the introduction of MIC, classical thermites
were limited in their applications due to their relatively slow energy release rate,
incomplete combustion, and inability to support rapid detonation (Yang, Wang, Sun, &
Dlott, 2004b). Wang et al. (1993) reported on the useful applications of thermite
compositions with emphasis on synthesis and processing of materials. With the increased
performance and sensitivity of MIC, the applications have become much broader. This is
also attributed to the fact that MIC is semi tunable in that the reactive power, reaction
propagation rate, and reactive zone temperature can be partially controlled by altering
parameters such as the particle size, oxide layer thickness, density, and equivalence ratio
(Miziolek, 2002; Aumann et al., 1995; Valliappan et al., 2005). The increased versatility
of MICs translates into more diverse applications particularly of interest to the
Department of Defense.
One particularly interesting MIC is the Aluminum (Al) and Teflon composite.
For the Al/Teflon reaction the fluorine from Teflon replaces oxygen from the metal oxide
as the oxidizer. The reaction of Al with Teflon generates 21 GJ/m3, and the best
molecular explosive generates less than 12 GJ/m3 (Yang, Wang, Sun, & Dlott, 2004a).
Many thermite reactions occur in the gasless regime because their reactants and products
are of condensed form (Wang, Munir, & Maximov, 1993). The Al/Teflon reaction differs
as it produces a significant amount of gas. This may have substantial effects on
combustion and propagation characteristics when the reaction is confined. This study
compares the reaction of Al/Teflon composites, ternary composites of Al/Teflon/MoO3,
and Al/MoO3 composites in both open and confined configurations while varying Al
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particles sizes and mass percent of Al in the composition. The objective is to compare the
effects of using fluorine in place of oxygen by examining flame speeds and pressure
histories. Tests were conducted using nano-sized Teflon particles and/or nano sized
MoO3 particles combined with nano or micron sized Al particles to compare the effects
of fuel particle size in fluorination versus oxidation reactions. The composites were
ignited and flame propagation behaviors were examined in both open and confined
configurations.
1.2 Aluminum as a Fuel
Aluminum particles have been used extensively in energetic materials
because Al is readily available and has desirable properties as a fuel in reduction-
oxidation reactions such as high heats of combustion and high flame temperatures
(Fischer & Grubelich, 1998). One example is the addition of nano Al particles to solid-
rocket propellants which has improved density and specific impulse, making it a major
component in many formulations (Dokhan, Price, Seitzman, & Sigman, 2002).
Traditionally the Al particles used have been on the micron scale (10-6 m). Technology
in materials processing has provided the means to produce nanoscale (10-9 m) aluminum
powders in bulk. Particles are typically considered nano-particles at or below 100 nm
diameter or at or below 100 nm in at least one dimension. The reduction of particle size
from the micron to nanoscale has significant effects on the physical and material
properties of Al.
As particle size decreases it has been shown that there is a decrease in melting
enthalpy and melting temperature, therefore a nanoscale particle will exhibit a lower
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melting temperature than its micrometer counterpart (Eckert, Holzer, Ahn, Fu, &
Johnson, 1993; Revesz, 2005; Zhang, Lu, & Jiang, 1999). This is thought to be an effect
of the increase in fraction of surface atoms with the decrease in particle size (Eckert et al.,
1993; Revesz, 2005; Zhang et al., 1999). The changes in thermal properties in Al are
thought to have some impact upon reactions that utilize nanoscale Al particles when
compared to reactions that utilize micron scale Al particles, but these effects are largely
unexplored.
The physical changes that occur when Al particles are reduced in size from the
micron to the nanoscale play a significant role in the increased reactivity and
performance of the powder mixture. As the particle size decreases the surface to volume
ratio increases dramatically (i.e., on the order of 1/radius). When mixed as a composite
this increase allows for an increase in the number of contact points with the oxidizer and
improved mixture homogeneity (Valliappan, Swaiakiewicz, & Puszynski, 2005). The
smaller size of nano particles also allows for better distribution throughout the reactant
matrix leading to a more homogeneous mixture.
Inherent with Al particles is an aluminum oxide (Al2O3) coating, typically a few
nanometers in thickness, which acts as a passivation layer for the pure Al core (Pesiri,
Aumann, Bigler, Booth, Carpenter, Dye et al., 2004). Aluminum is pyrophoric, therefore
having no Al2O3 shell would result in the pure metallic particles spontaneously reacting
with oxygen in the ambient air. Lips (1977) conducted experiments firing hybrid-
propellant rocket motors using highly aluminized fuels. High-speed photography and
chemical analysis revealed that many of the Al particles only partially combusted. They
believed this was largely due to the oxide layer inhibiting the reaction (Lips, 1977). One
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side effect of using nanoscale Al particles as fuel is the increased percentage of Al2O3
which decreases the overall purity of the Al powder. Aumann, Skofronick, and Martin
(1995) studied the effects of oxide layer and the use of ultra-fine grain Al on ignition
sensitivities in an effort to decrease reaction sensitivity to electrical spark and friction
making the composites more stable and safer to handle in bulk. They found that ignition
threshold energies did not significantly decrease with increases in oxide layer thickness
of up to two times. However they did note significant decreases in ignition threshold
energies for ultra-fine grain Al when compared to bulk flat Al.
Typically, oxidizers must diffuse through the Al2O3 shell before interaction with
the pure Al core. Sometimes the oxide shell will reach its melting point (~ 2050°C),
which is higher than that of the pure Al core (~ 660°C), allowing the already molten Al to
escape and the oxidizer to react directly with the Al bypassing the diffusion stage
(Friedman & Macek, 1962; Revesz, 2005). It has been shown in recent studies by
Levitas, Asay, Son, and Pantoya (2005) that direct contact with the pure Al can occur
under rapid heating conditions through an alternate mechanism, referred to as a
dispersion mechanism, which promotes enhanced burn rates. Levitas et al. (2005)
concluded that the different thermal expansion rates of Al and Al2O3 and the volumetric
strain from the melting of Al lead to a tremendous build up of pressure on the interior Al
core. This pressure increase causes a large mechanical stress on the oxide shell
eventually leading to its failure and potential spallation. In micron scale particles,
pressure within the particle does not have the opportunity to build up because the shell is
weaker. In these larger particles failure most often appears as a crack occurring at a
material defect in the Al2O3 shell that allows the pure molten Al to escape and interact
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with the surrounding oxidizer. Rai, Lee, Park, and Zachariah (2004) showed the cracking
of an oxide shell and subsequent outflow of molten Al with a hot-stage TEM. Levitas et
al. (2005) also states that in nanoscale particles the oxide shell is virtually free of defects
and its strength approaches the theoretical strength. This allows the stress to build to a
point of ultimate failure, resulting in the rupturing of the Al2O3 shell. The rupture and
subsequent release of pressure disperses molten pure Al on the atomic scale throughout
the surrounding oxidizer. These dispersed Al clusters lack and oxide shell and are not
dependent on diffusion. The dispersion mechanism is valid only when the Al particles are
subjected to rapid heating. The expansion of the pure Al core during melting causes the
core to be under compression while the oxide shell is under tension (Rai et al., 2004).
This leads to the oxide shell being dynamically unstable. Rai et al. (2004) show through
molecular dynamics that there is a higher pressure rise in small particles and that the
increased curvature of oxide shell in small particles leads to higher tension. The higher
pressure and increase tension on the oxide shell lead to an increased likelihood for
smaller particles to spallate, consistent with the theory by Levitas et al. (2005).
Several studies have shown the effects of using nano particle Al in thermite
reactions. Moore, Pantoya, and Son (2007) conducted ignition and flame speed
experiments on Al/MoO3 composites for bimodal nano and micron Al particle size
distributions. Their results showed that ignition delay was reduced by up to 2 times when
using 80% nano particle and 20% micro particle Al when compared to tests using 100%
micro particle Al. They also reported significant increases in combustion flame speed as
the percent of nano particle Al was increased. Mench, Yeh, and Kuo (1998) studied the
effect of particle size in aluminized propellants by replacing 30 micrometer conventional
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Al particles with 180 nanometer Alex ( Alex is a trade name for nanometer scale Al
particle manufactured by Argonide, Inc. using the exploding wire technique) particles
and igniting in an optical strand burner. The addition of the Alex particles substantially
enhanced the propagation rates and increased the temperature sensitivity of the solid
propellants. They also found that the ignition delay time is several orders of magnitude
shorter for propellants using Alex particles. Valliappan, Swaiakiewicz, and Puszynski
(2005) studied the effect of nanoscale Al particles with various metallic oxides including
tungsten tri-oxide (WO3), molybdenum tri-oxide (MoO3), copper oxide (CuO), and Iron
Oxide (Fe2O3). Their results show flame speeds on the order of several hundreds meters-
per-second (up to 412 m/s) in unconfined burning configurations compared to flame
speeds in the range of centimeters-per-second for micron-scale thermites in an
unconfined burning configuration. Pantoya and Granier (2005) examined Al/MoO3
composites in the form of pellets as functions of Al particle size, equivalence ratio, and
density. They ignited the samples with a CO2 laser and recorded ignition and flame
propagation characteristics. They also conducted DSC tests to study reaction kinematics.
Their results showed that the composites using nano particle Al had reduced ignition
delay times of up to two orders of magnitude and that the combustion propagation rate
decreased as density increased. Bockman, Pantoya, Son, Asay, and Mang (2005) studied
the effects of varying the Al particle size in Al/MoO3 composite reactions. Their
experiments were conducted under a confined state using an instrumented burn tube
apparatus. They found that as the Al particle size was decreased the flame speed
increased. They reported increases from 750 m/s to 950 m/s when decreasing the Al
particle size from 121 nanometers to 80 nanometers. Further reduction of Al particle size
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did not yield any more significant increases in flame speed suggesting the possibility of a
critical diameter at which flame speed may no longer increase (Bockman et al., 2005).
Malchi, Foley, Son, and Yetter (in press 2007) examined the effects of increasing the
Al2O3 content in nano aluminum and copper oxide composites. The increase of Al2O3
effectively decreases the reaction flame temperature and reaction pressures due to the less
efficient and complete combustion associated with adding a diluting agent into the
composition. They conducted experiments in a constant volume pressure cell, open burn
tray, and instrumented burn tubes. They noted substantial drops in peak pressure and
pressurization rate with the increase in Al2O3. Their experiments also show a drop in
flame speed with the increase of Al2O3. Malchi et al. (in press 2007) conclude that the
gaseous products are of great importance to the propagation in Al/CuO composites and
that adding Al2O3 effectively reduces the gas in the system inhibiting the role of
convection. The decreased convective heat transfer results in slower propagation rates
and combustion instabilities (Malchi et al., in press 2007)).
1.3 Teflon vs. Metallic Oxide as an Oxidizer
Teflon, C2F4, as an oxidizer is atypical because it utilizes fluorine as the oxidizing
agent rather than oxygen. Fluorine is the most electronegative element making it an
excellent candidate as an oxidizer in a reduction-oxidation reaction. It has the potential to
exceed oxygen’s reactive power as illustrated in Figure 1.
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0 5000 10000 15000 20000 25000 30000 35000 40000
6Al+MoO3+3C2F4
4Al+3C2F4
Al+MoO3
C7 H5 N3 O6 (TNT)
C3 H6 N6 O6 (RDX)
C4 H8 N8 O8(HMX)
Heat of Combustion
KJ/m^3KJ/kg
Figure 1: Heat of Combustion for various compositions (Fischer 1998). Al/Teflon reaction heat of combustion calculated using REAL Code (Tim Tec, LLC.), a chemical
equilibrium program, under the same thermodynamic conditions assumed to generate the data from Fischer.
Similarly, Kubota and Serizawa (1987) found magnesium (Mg) with fluorine
produces a heat of combustion of 16.8 MJ/kg of Mg which is higher than the heat of
combustion produced by magnesium with oxygen. Lips (1977) showed that using highly
fluorinated oxidizers, in the form of liquid fluorine-oxygen mixtures, in combination with
highly aluminized rocket fuels resulted in more efficient combustion of aluminum
particles than reactions that contained no fluorine. The highly fluorinated reactions also
exhibited an increase in regression rate and maintained the performance of non-
fluorinated reactions (Lips,1977). Reactions containing fluorine may have many
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favorable characteristics for specific applications, such as higher gas production, that are
not attainable with the traditional reactions containing oxygen.
Teflon, or polytetrafluoroethylene, is a prime candidate as a fluorine source for
use in fast fluorination reactions. Manufactured by Dupont under the name Teflon®,
polytetrafluoroethylene is composed of a C2F4 molecular structure and has a 75% weight
percent of fluorine (Kubota & Serizawa, 1987). When added to metal/metal reactions,
Teflon results in a fluorine gas that improves reactivity and energy release (Parker,
Ladouceur, & Russell, 2000). Mass production of polytetrafluoroethlyene began in 1946
(Koch, 2002a). Most likely Teflon was discovered to be a viable oxidizer shortly after it
became commercially available (Koch, 2002a). One of the first extensively researched
fluorocarbon based pyrolant was a composite of magnesium, Teflon, and the binder Viton
(hexafluoropropene-vinylidenfluoride-copolymer), also known as MTV. MTV is
assumed to have first been developed in the mid 1950’s and was held in governmental
secrecy for around 10 years due to its potential use as an infrared decoy material (Koch,
2002a). Since being released to the public, MTV has been subjected too much research
and has been found to be useful in many military applications such as flares, tracers, and
countermeasures as well as other applications including incendiaries, propellants, and
more (Koch, 2002a). The discovery that decreasing the reactants particle sizes leads to
enhanced combustion behavior has led to the desire to decrease the size of the Mg
particles in MTV to achieve even better performance. Kubota and Serizawa (1987)
determined that burning rate in MTV does increase as Mg particle size is decreased. The
limitation of MTV is the physical particle size of Mg, which is not yet available
commercially on the nanoscale. With research confirming the benefits to using nano
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particles in energetic materials, a substitute nanoscale material with properties similar to
Mg is desired.
Aluminum has been studied as a viable substitute for Mg, as it can exhibit similar
combustible behavior and is readily available in the nanoscale market. The Al/Teflon
composite was found to have a similar stoichiometric composition when compared to
Mg/Teflon composites, with Al/Teflon being 26.5% Al and Mg/Teflon being 32.7% Mg
(Cudzillo & Trzcinski, 2002). Poehlein, Shortridge, and Wilharm (2001) conducted a
study of the effect of adding nanoscale Al particles in the form of Alex to MTV
composites. They found that mixtures containing Alex exhibited increased burn rates and
similar sensitivities when compared to control MTV composites. Mg/Teflon has
advantages over Al/Teflon such as a higher heat of combustion (Cudzillo & Trzcinski,
2002), but the ability to use Al particles on the nanoscale and the benefits associated with
using the nanoscale particles has led to an increased interest in the Al/Teflon composite.
Several studies have been conducted in an attempt to further understand the
Al/Teflon reaction under various conditions. Cudzillo and Trzcinski (2002) performed
calorimetric studies and differential thermal analysis (DTA) to determine heat of reaction
and explore the decomposition characteristics of Al/Teflon. Their studies were
conducted using 50 micrometer Al and heating the composite at 10 Kelvin per minute in
nitrogen for the DTA. They found the heat of combustion to be around 7800 kJ/kg. Their
DTA studies revealed 2 endothermic peaks, one occurring between 600 and 650 K and
the other around 933K, and 2 exothermic peaks, both between 800 and 900 K. The
endothermic peaks correspond to the melting points of both Teflon and then Al. The
exothermic peaks represent the Al/C2F4 Reaction. A third endothermic reaction, proposed
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to be corresponding to the degrading of Teflon causes the dip between the two
exothermic peaks. Dolgoborodov, Makhov, Kolbanev, Streletskii, and Fortnov (2005)
studied detonation in Al/Teflon mixtures. The experiments utilized the action of a shock
wave on the samples to initiate the steady detonation regime. Flame speeds varied
between 700 and 1300 m/s dependent upon percentage composition and density. They
found that porosity had a large effect upon detonation and that burn rates would increase
as stoichiometric conditions were approached. McGregor and Sutherland (2003)
conducted plate impact experiments on highly porous Al/Teflon mixtures at 40%
theoretical mass density (TMD) to determine conditions required for the onset of the
reaction. They found that the onset of the reaction did not occur at the shock front. It
occurred after the passage of the initial shock wave, possibly after the material was
shocked to a higher pressure by a second larger shock wave. Parker, Ladouceur, and
Russell (2000) studied Al/Teflon mixtures to examine its combustion behavior under
extreme conditions. They used spectroscopy to investigate reaction mechanisms and
rates. They conducted their experiments under high pressures initiating the reaction with
a laser pulse. Their results showed a two stage combustion reaction. First the initial Al
combustion occurred followed by the resulting carbon condensing to form graphite.
Tachibana and Kimura (1988) examined the ignition and combustion control of solid
propellants including Al/Teflon and HTPB-AP-Al, a conventional solid propellant, by
using arc discharge. Tachibana and Kimura calculated that certain compositions of
Al/Teflon composites will have a higher heat of combustion than HTPB/AP/Al. They
showed that dc arc discharge coupled with a high-frequency-discharge arc initiator is
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efficient in igniting and extinguishing reactions in Al/Teflon mixtures in certain fuel-
oxidizer ratio ranges. Burn rates could also be varied by altering the arc intensity.
For the fluorine in Teflon to be available for interaction, the Teflon must first be
degraded. The thermal decomposition of Teflon is the reverse reaction of its
polymerization. It requires an energy input equal to the heat released during its formation,
which is approximately 172 kJ/kg (Koch, 2002b). Teflon decomposes starting around
803 K and completing around 893 K (Kubota & Serizawa 1987). During this
decomposition an exothermic gasification reaction occurs (Koch, 2002a) and fluorine is
abundantly produced (Tachibana & Kimura, 1988). Once degraded, fluorine ions are
available for interaction with the surrounding fuel.
Osborne and Pantoya (in press 2007) showed via differential scanning calorimetry
(DSC) and thermo-gravimetric analysis (TGA) that much of fluorine in Al/Teflon
composites utilizing micron scale Al particles escaped the reaction zone before
interaction with Al when subjected to slow heating conditions. This is evident by the
Teflon decomposition not overlapping with the phase change in Al2O3. This means that
the fluorine is available before there is a pathway for contact with the Al enabling
fluorine to leave the reaction zone before interacting with the fuel. They found that the
mixture lost ~25% of its mass before the reaction with Al occurred meaning that only
~17% of the Teflon reacted with the Al. Osborne and Pantoya (in press 2007) found that
this did not occur when the same experiments were conducted using nanoscale Al in the
Al/Teflon composites. The decomposition of Teflon and oxide layer phase change
corresponds for the composites using nanoscale Al. This mixture only lost ~6% of its
mass before the reaction with Al implying that 75% of the Teflon reacted with the Al. It
Texas Tech University, Kyle Watson, August 2007
14
is believed that this is because of the increased sensitivity of the nano Al particles which
are able to react with the fluorine oxidizer before it escapes the reaction zone. Based
upon the Osborne and Pantoya (in press 2007) results the Al/Teflon composites utilizing
micrometer Al particles may lose much of its fluorine oxidizer to the atmosphere before it
can react with the Al fuel.
1.4 Open vs. Confined Burns and the Corresponding Modes of Heat Transfer
Conduction, convection, radiation, and acoustic/compaction are four possible
modes of heat transfer in a thermite reaction. The primary mode responsible for the heat
transfer will have a large effect on the combustion characteristics of any reaction.
Conduction and convection are the predominant modes in most energetic materials with
radiation and acoustic/compaction becoming more important upon detonation (Asay,
Son, & Busse, 2004).
Classical thermites are typically considered to be conduction controlled due to the
slow reaction rates and the lack of gas to promote convective burning. These conduction
controlled reactions typically propagate at low speeds on scales of mm/s to cm/s (Brown,
Taylor, & Tribelhorn, 1998). Brown et al. (1998) found a qualitative connection between
the propagation rate and the number of contact points of the fuel and oxidizer. Due to the
different thermal and chemical properties of different systems, there is no direct
correlation between propagation rate and the number of contact points over the different
systems. However, altering the number of contact points within a single system revealed
that an increase in contact points yielded an increase in flame speeds (Brown et al.,
1998). Therefore, particle size will play an important role in the combustion
Texas Tech University, Kyle Watson, August 2007
15
characteristics of conduction controlled reactions due to the increased in number of
contact points improving the thermal transport properties of the mixture. Density effects
can also inhibit the role of convective burning and promote conduction dominant
reactions. When thermite powders are pressed into high density pellets, the interstitial
voids are decreased. The decrease in voids inhibits gaseous fluid movement resulting in a
shift towards a conductive dominant heat transfer mechanism (Prentice, Pantoya, & Gash,
2006).
Convective dominant burning has been described as the deep penetration of hot
product gases preheating the unreacted composites (Asay, Son, & Bdzil, 1996). The
transition from conduction to convective dominant reactions leads to a substantial
increase in flame speeds and energy release rates. Asay, Son, and Busse (2004) have
shown flame speeds on the order of m/s to km/s for convective controlled reactions
compared to the conduction controlled reactions reported by Brown, Taylor, and
Tribelhorn (1998) that proceed on the order of mm/s to cm/s. Highly porous materials are
more prone to convective burning due to increased gas penetration. Loose powders tend
to have increased convective heat transfer because of increased bulk fluid movement
(Prentice, Pantoya, & Gash, 2006). Asay et al. (2004) studied the heat transfer
mechanism in MIC. They conducted confined burns in barrier, pressure, and vacuum
experiments. Their experiments led to the conclusion that convection is the primary
mode of heat transfer in MIC materials.
Radiation and acoustic/compaction heat transfer are often not considered to be
significant in classical thermite reactions. In MIC, radiation has been shown to have a
negligible impact on the overall energy transfer (Begley and Brewster, in press 2007) but
Texas Tech University, Kyle Watson, August 2007
16
acoustic/compaction heat transfer may play a more important role as the speeds of over
Mach 1 may result in acoustical shockwaves. Further study is needed to determine the
extent of acoustical/compaction roles in heat transfer through MIC.
Confining reactions may change the dominant mode of energy transfer. When the
reaction is confined the product gases are not able to escape the reaction zone and are
propelled forward through the composite, possibly causing enhancement of the
convective heat transfer (Malchi, Foley, Son, and Yetter, in press 2007). The inability for
the gases to escape will also greatly increase the pressure within the tube conceivably
increasing the heat transfer from acoustical/compaction. Therefore under confinement
both classical thermites and MIC combustion behaviors will be greatly affected by the
change in mode of heat transfer and often will exhibit much higher flame speeds.
1.5 Objectives
The Al/Teflon reactions have the potential to show increased flame speeds based
on the increased amount of product gases produced from the reaction when compared to
oxidation reactions as well as the higher heat of reaction as seen in Figure 1. Also by
confining micron Al/Teflon reactions the fluorine is no longer able to escape the reaction
zone, as seen in the experiments by Osborne and Pantoya (2007), and may exhibit a more
complete and faster reaction. The objective of this study is to examine the influence of
Teflon in the Al/Teflon and Al/MoO3/Teflon reactions for loose powder mixtures burning
in a confined apparatus compared to burning in an open state. These reactions were also
compared to the Al/ MoO3 reactions in order to better resolve the role of Teflon as an
oxidizer in the reaction. This study will also examine the role of fuel particle size on the
Texas Tech University, Kyle Watson, August 2007
17
reaction behaviors by examining both nano and micron scale Al fuel particles while the
Teflon and MoO3 particles are constant nanoscale particles. Experiments were performed
using photographic data to resolve flame speeds and piezoelectric pressure transducers to
measure transient pressure behaviors. These results will impact the safe handling and
usage of thermites containing Teflon as a reactant.
Texas Tech University, Kyle Watson, August 2007
18
Chapter II
Experimental
2.1 Sample Preparation
Sample powders of Teflon (Dupont Zonyl MP1150) and/or MoO3 were combined
with either 50 nanometer or 1 -3 micrometer Al powder. The material properties and
manufactures are provided in Table 1.
Table 1: Material properties of the powders used.
Material Manufacturer Particle
Size
Surface
Area Morphology
Purity
(%)
Aluminum
Atlantic
Equipment
Engineers (AEE)
1 -3 μm <1 m2/g * Spherical 99
Aluminum Nanotechnologies 50 nm 39.8 m2/g Spherical 75
Zonyl
MP1150 Dupont 200 nm 5–10 m2/g Spherical 99 – 100
MoO3 Nanotechnologies 44 nm >50 m2/g * Rectangular 99
* Estimated values
Nanotechnologies uses x-ray diffraction, TEM imaging, and BET surface area
analysis to verify particle size ranges and purities. Dupont and AEE use laser microtrac
systems to determine particle size ranges. Scanning electron microscopy (SEM) images
Texas Tech University, Kyle Watson, August 2007
of the materials are provided, in Figure 2, to illustrate the extent in particle size range and
amount of agglomeration in the pre-mixed state.
Figure 2: SEM micrographs of the powders used prior to mixing. (a) 1-3 μm Al provided by AAE at 10,000x magnification
(b) 50 nm Al provided by Nanotechnologies at 50,000x magnification (c) 44 nm MoO3 provided by Nanotechnologies at 50,000x magnification
(d) 200nm Zonyl MP-1150 (Teflon) provided by Dupont
19
Texas Tech University, Kyle Watson, August 2007
The powders were mixed by mass percent of pure Al ranging from 10% - 90%.
The oxidizer consisted of 100% Teflon, 100% MoO3, or a mass ratio of 60% MoO3 and
40% Teflon. The Equations 2.1 - 2.3 represent the stoichiometric reactions for these
mixtures.
CAlFFCAl 64)(34 342 +→+ (2.1)
MoCOAlAlFMoOFCAl +++→++ 6)()(4)(36 323342 (2.2)
MoOAlMoOAl +→+ )(2 323 (2.3)
The mixtures are prepared by measuring the appropriate amount of powder for the
desired composition and suspending the mixture in hexanes. The solution was subjected
to ultrasonic waves using a Misonix Sonicator 3000 which promoted improved mixture
homogeneity and breaks up agglomerates. This process consisted of applying ultrasonic
waves in ten second intervals for a total of seventy seconds via a probe vibrating at
ultrasonic speeds. There was a ten second span between each interval to prevent
temperature buildup and possible thermal damage to the sample. The solution was
transferred to a glass pan and placed on a hotplate at 90°C for 10 minutes. This
evaporated the hexanes leaving only the powder mixture. The powder mixture was
reclaimed using a brush to collect the powder. Figure 3 displays the SEM images of the
mixed powders that help visualize the homogeneity obtained in this mixing procedure.
20
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21
Figure 3: SEM micrographs of the post-mixed composites.
(a) 50 nm Al/Teflon composite (b) 50 nm Al/MoO3 composite
(c) 50 nm Al/MoO3/Teflon composite All images taken at 75,000x magnification
The equivalence ratio of the powder mixtures is determined by Equation 2.4.
Only pure Al, excluding the oxide layer, was considered when calculating equivalence
Texas Tech University, Kyle Watson, August 2007
ratio. The mixing ratios and corresponding equivalence ratios are shown in Tables 2
through 4.
STO
ACT
AFAF
⎟⎠⎞
⎜⎝⎛
⎟⎠⎞
⎜⎝⎛
=φ (2.4)
Where: F= Mass of the fuel
A = Mass of the oxidizer
Table 2: Al/Teflon composite mass ratios and corresponding equivalence ratios.
Al size Mass % Pure Al Mass Al Powder Mass C2F4
Powder Equiv. Ratio 10 10 90 0.231676 20 20 80 0.521271 30 30 70 0.893607 40 40 60 1.390056 50 50 50 2.085084 60 60 40 3.127626 70 70 30 4.865196 80 80 20 8.340337
1 - 3
μm
Al
90 90 10 18.76576 10 13.33 90 0.231676 20 26.67 80 0.521271 30 40 70 0.893607 40 53.33 60 1.390056 50 66.67 50 2.085084 60 80 40 3.127626 70 93.33 30 4.865196 80 106.67 20 8.340337
50 n
m A
l
90 120 10 18.76576
22
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23
Table 3: Al/MoO3/Teflon composite mass ratios and corresponding equivalence ratios.
Al size Mass % Pure
Al Mass Al Powder Mass MoO3
Mass C2F4 Powder Equiv. Ratio
10 10 54 36 0.22854362 20 20 48 32 0.514223146 30 30 42 28 0.881525393 40 40 36 24 1.371261722 50 50 30 20 2.056892583 60 60 24 16 3.085338874 70 70 18 12 4.799416027 80 80 12 8 8.227570331
1 - 3
μm
Al
90 90 6 4 18.51203325 10 13.33 54 36 0.22854362 20 26.67 48 32 0.514223146 30 40 42 28 0.881525393 40 53.33 36 24 1.371261722 50 66.67 30 20 2.056892583 60 80 24 16 3.085338874 70 93.33 18 12 4.799416027 80 106.67 12 8 8.227570331
50 n
m A
l
90 120 6 4 18.51203325
Table 4: Al/MoO3 composite mass ratios and corresponding equivalence ratios.
Al size Mass % Pure Al Mass Al Powder Mass MoO3 Equiv. Ratio 10 10 90 0.296372 20 20 80 0.666836 30 30 70 1.143148 40 40 60 1.778231 50 50 50 2.667346 60 60 40 4.001019 70 70 30 6.223807 80 80 20 10.66938
1 - 3
μm
Al
90 90 10 24.00611 10 13.33 90 0.296372 20 26.67 80 0.666836 30 40 70 1.143148 40 53.33 60 1.778231 50 66.67 50 2.667346 60 80 40 4.001019 70 93.33 30 6.223807 80 106.67 20 10.66938
50 n
m A
l
90 120 10 24.00611
Texas Tech University, Kyle Watson, August 2007
2.2 Open Burn Setup
The open burn experiments consisted of the combustion of evenly distributed
lines of loose powder composites. The loose powder was loaded evenly into a channel
milled into an acrylic block. The block is of dimensions 152 x 30 x 12 mm, and the
channel is of dimensions 107.95 x 3.175 x 2.54 mm. A small piece of nicrome wire was
secured at one end of the channel to provide an ignition source. An illustration of the
open burn block is shown in Figure 4.
Figure 4: Photograph of open burn apparatus. Each interval corresponds to 1 cm increments used for defining a length scale for flame speed calculations.
24
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25
The testing was conducted in an inert argon chamber to eliminate any interaction
of Al with ambient air. The argon chamber is fitted with acrylic viewing windows to
allow the reaction to be recorded with a high-speed camera. The reaction was initiated by
applying a voltage to the nicrome wire. Propagation data was recorded via the high-
speed camera.
2.3 Confined Burn Setup
The confined burn experiments consisted of the burning of the loose
powder composites in an instrumented tube similar to that originally designed by
Bockman et al. (2005). Polycarbonate tubes of 3.175 mm inner diameter, 25.4 mm outer
diameter, and 107.95 mm length were used. The polycarbonate was chosen due to its
high strength and optical clarity for viewing of the reaction. A nicrome wire was secured
into one end of the tube for use as an ignition source. The powder was loaded into the
tube maintaining constant mass at each composition. The sample mass varied with
changes in composition due to the change in density associated with different
compositions. The tubes were lightly tapped to eliminate any large voids without
mechanically packing the powder. A prepared tube is shown in Figure 5. The tube was
inserted into a 25.4 mm diameter opening bored through the center of a 50.8 mm square
by 107.95 mm long steel testing block instrumented with 4 PCB model # 113A22
pressure transducers at 25.4 mm increments. The testing block also had an 82.55 x 25.4
mm viewing window to allow the reaction to be captured by high-speed camera. The
polycarbonate tube has small (<1mm) holes that align with the pressure sensors. These
Texas Tech University, Kyle Watson, August 2007
holes provide ports for the pressure to escape and contact the pressure sensors. The
instrumented testing block is shown in Figure 6.
26
Figure 5: Picture of prepared burn tube.
Figure 6: Picture of instrumented confined burn apparatus.
The experiments were also conducted in the argon chamber described in section
2.2 to eliminate any possible reaction with the ambient air. The reaction was initiated by
a voltage applied to the nicrome wire. Data collection was triggered manually and there
was no synchronization to the application of voltage to the nicrome. Thus ignition
sensitivity data was not collected and alterations in ignition sensitivity were not observed.
Data was recorded in the form of flame propagation rate information from the high-speed
camera and pressure histories from the pressure sensors.
2.4 Data Acquisition
A schematic illustrating the test setup is displayed in Figure 7. Data was collected
in the form of high-speed video and voltage signals from pressure transducers.
Texas Tech University, Kyle Watson, August 2007
Figure 7: Schematic illustrating the test setup.
Data is captured from a high-speed video camera and pressure transducers
illustrated in Figure 9. Images from the high-speed camera are used to determine flame
speed. This was accomplished by tracking the flame front, considered here as the front
edge of luminous activity. A series of consecutive frames shows the progression of the
flame front in the confined state in Figure 8.
27
Texas Tech University, Kyle Watson, August 2007
Figure 8: Consecutive still images displaying a typical confined burn. Each image corresponds to one frame at a sample rate of 40,000 fps. The front edge of luminous activity is used to calculate
flame speed.
The high-speed camera used was a Vision Research Phantom vs. 7.1. The open
burn experiments were recorded at 20000 frames-per-second (fps). Confined burn
experiments were recorded at 40,000 fps. The Phantom software was used to determine
reaction flame speeds. The software will deduct the flame speed given a user defined
length scale and a time scale dependent upon the sample rate of the recording. The scale
was defined for each test using the marked 1 cm increments seen in Figures 4 and 6.
The pressure transducers were used to measure pressures generated in the
confined burns. The pressure transducers were not used in the open burn set-up. The
28
Texas Tech University, Kyle Watson, August 2007
PCB model # 113A22 transducers are routed to a PCB model # 482A22 signal
conditioner and subsequently to a National Instruments BNC-2110 data acquisition
board, as shown in Figure 7. The National Instruments board was controlled using
Labview version 8.0. Sample rates for tests with micron scaled Al were 50,000 points-
per-second (pps), and sample rates for tests with nanoscale Al were 100,000 pps. A
typical pressure trace is displayed in Figure 9.
-2
0
2
4
6
8
10
12
0.3091 0.3093 0.3095 0.3097
Time (sec)
Pre
ssur
e (M
Pa)
Sensor 1Sensor 2Sensor 3Sensor 4
Initial Pressure Rise (used to determine propagation rates)
Rise Time (time from initial rise to peak )
Pressurization Rate (dp/dt)
Peak Pressure
Figure 9: Typical pressure trace for a 50nm Al/Teflon confined burn.
29
Peak pressure, pressure rise time, pressurization rate, and pressure wave
propagation rate were determined from the pressure history data for the fourth sensor.
This sensor location was chosen for detailed analysis because at this location the reaction
achieved steady-state and yielded the most consistent data. Figure 9 shows that peak
pressure was found as the maximum pressure recorded. This value is directly related to
the amount of gas produced during reaction which has a significant impact upon the
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reaction. The rise time is the time difference between the maximum pressure and the
initial rise in pressure. The rise time is a good indication of the order of magnitude for
the reaction time and is sometimes referred to as the characteristic reaction time.
Diffusive distances, the distance that oxidizing gases will diffuse into the fuel oxide shell,
can be approximated as a function of rise time using Equation 2.5. If the estimated
diffusive distance is less than the thickness of the oxide shell, then diffusion can be
eliminated as a dominant reaction mechanism.
τDd 2=l (2.5)
Where: ℓd = Diffusive Distance
D = Diffusivity for oxygen and aluminum in alpha-alumina at 800°C (D ≈10-19 cm2/s according to Bergsmark, Simensen, and Kofstad (1989)) τ = Order of magnitude of the reaction time
(τ ≈ the pressure rise time)
The reactive power of a reaction can be estimated using the pressure rise time as
well. The reactive power will approximate how much energy can potentially be extracted
in an ideal combustion reaction. It can be calculated using Equation 2.6.
τMH
RP Rx ⋅Δ= (2.6)
Where: ΔHRx/ = Heat of reaction (based on mass)
M = Mass of reactants
τ = Order of magnitude of the reaction time (τ ≈ the pressure rise time)
30
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31
The pressurization rate is the slope of the increasing pressure versus time curve
and is taken over the most constantly increasing segment of that curve (i.e., from 5 to 95
% peak pressure) as seen in Figure 9. The pressurization rate can give insight to the
amount of gas released over a specific time. A slower pressurization rate can mean a
slower release of gases in the reaction. This coupled with the pressure rise time can give
a good indication of the amount of gas released and the time scale of gas being released
for a reaction. The pressure wave propagation rate is found using the known distance
between the pressure sensors and the difference between arrival times (point of first rise
for each sensor as depicted in Figure 9) of a sensor and its preceding sensor. The
pressure wave propagation will tell how fast the pressure is moving through the confined
space. This can be used to determine if the reaction reaches the point of detonation or if
it is a deflagration. If the pressure wave proceeds equal or faster than that of the optical
propagation wave the reaction can be considered to have reached detonation. If the
pressure wave propagates slower than the optical wave the reaction will be a deflagration.
The optical propagation rate, or flame speed, is deduced from the high-speed
camera data. It is primarily used as quantification for the speed of the reaction, but can
also give indication of detonation when compared to the pressure wave propagation rate
as described above. Another interesting characteristics derived from the optical
propagation rate is the Mach number achieved by the reaction. In many MIC reactions,
flame speeds can approach and exceed 1000 m/s, which would be in excess of Ma 3 if the
surroundings where considered to be air at room temperature. The achieving of such
Mach numbers could mean that there are significant acoustic effects in the reaction.
However, the reaction proceeds within the flame zone assumed to be at the adiabatic
Texas Tech University, Kyle Watson, August 2007
flame temperature for the reaction. This extreme temperature environment reduces the
Ma number calculation significantly. The Mach number can be estimated by the use of
Equations 2.7 and 2.8.
CVMa = (2.7)
Where: V = Optical propagation rate
C = Speed of sound in surrounding media (Calculated by Equation 2.8)
And
RTC γ= (2.8)
Where: γ = Cp/Cv (Constant pressure specific heat/Constant volume specific heat)
R = Gas constant of surrounding media
T = Temperature of surrounding media
32
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Chapter III
Results and Discussion
3.1 Open Burn Tray Results
3.1.1 Results and Initial Observations
The open burn tray flame speeds collected via high-speed camera are displayed in
Figures 10 through 12 (Error bars are provided but may be smaller than the point marker.
For error values see detailed Tables in Appendices). A detailed account is provided in
Tables 11 and 12 located in Appendix A. Peak flame speeds of 4.249 m/s, 410.636 m/s,
and 456.559 m/s were obtained for the nano Al samples of Al/Teflon, Al/ MoO3/Teflon,
and Al/ MoO3 composites, respectively. Peak flame speeds of 1.382 m/s, 0.334 m/s, and
4.116 m/s were found for the micron Al samples of Al/Teflon, Al/ MoO3/Teflon, and Al/
MoO3 composites, respectively.
33
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
0% 20% 40% 60% 80% 100%
Mass Percent Aluminum
Flam
e Pr
opag
atio
n (m
/s)
50 nm Al
1-3 µm Al
Figure 10: Al/Teflon open tray burn results
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34
0
50
100
150
200
250
300
350
400
450
0% 20% 40% 60% 80% 100%
Mass Percent Aluminum
Flam
e Pr
opag
atio
n R
ate
(m/s
) 50 nm Al
1-3 um Al
Figure 11: Al/MoO3/Teflon open tray burn results
0
100
200
300
400
500
600
0% 20% 40% 60% 80% 100%
Mass Percent Aluminum
Flam
e Pr
opag
atio
n R
ate
(m/s
) 50 nm Al
1-3 um Al
Figure 12: Al/MoO3 open tray burn results.
Texas Tech University, Kyle Watson, August 2007
35
It is immediately noticeable that reducing the Al particle size has immense impact
upon flame speed independent of composition. In each case the flame speed increases
significantly with the decrease in particle size. The most significant impacts on flame
speed when decreasing particle sizes were seen in the composites that contained MoO3
which increased by factors of over 100 at the optimal ratio compared to a factor of only 3
for the Al/Teflon reaction at its optimal ratio.
In the micron Al experiments, the Al/Teflon composite reached a flame speed
faster than that of Al/MoO3/Teflon composite but slower that the Al/MoO3 composite. In
the nano Al experiments the Al/Teflon composite was outperformed by both the
Al/MoO3/Teflon and Al/MoO3 composites. For the nano-mixtures there is a similarity in
the flame speed trends for mixtures containing MoO3 but not for the Al/Teflon
composite. The Al/Teflon composite exhibits a peak flame speed 100x slower than the
reactions containing MoO3, and the Al/Teflon composite differs in its optimal
composition, from 40% for the composites containing MoO3 to 50% for the Al/Teflon
composite.
3.1.2 The Effects of Particle Size and the Addition of Teflon
The reduced flame speed associated with the Al/Teflon reaction may be attributed
to fluorine gas escaping the reaction zone as seen in experiments by Osborne and Pantoya
(in press 2007). These open tray experiments do not trap gaseous intermediates or
products, thus gas escaping the flame zone would not participate in propelling the flame
front forward. A large portion of energy in the reaction escapes with the liberated fluorine
gases instead of contributing to accelerating the flame front. Thermodynamic
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equilibrium calculations using REAL Code (Tim Tec, LLC.) assuming thermal
equilibrium exists during reaction indicate the quantity of gas production as a function of
aluminum content for the binary and ternary mixtures (Figure 13). Figure 14 shows the
adiabatic flame temperatures associated with the studied reactions also determined from
thermal equilibrium calculations using REAL Code (Tim Tec, LLC.).
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0% 20% 40% 60% 80% 100%
Mass Percent Aluminum
Gas
Pro
duct
ion
(kg/
kgre
acta
nt)
Al/C2F4Al/MoO3Al/MoO3/C2F4
Figure 13: Gas generation in the Al/Teflon, Al/MoO3/Teflon, and Al/MoO3 reactions. Values
determined using the REAL Code (Tim Tec, LLC.) chemical equilibrium program.
36
Texas Tech University, Kyle Watson, August 2007
0.00
500.00
1000.00
1500.00
2000.00
2500.00
3000.00
3500.00
4000.00
0% 20% 40% 60% 80% 100%Mass Percent Aluminum
Adi
abat
ic F
lam
e Te
mpe
ratu
re (K
) Al/C2F4
Al/MoO3/C2F4
Al/MoO3
Figure 14: Adiabatic flame temperature in the Al/Teflon, Al/MoO3/Teflon, and Al/MoO3 reactions. Values determined using the REAL code chemical equilibrium program.
The micron Al reactions containing Teflon exhibited flame speeds two orders of
magnitude lower than the Al/MoO3 reaction. It was also observed that the micron
Al/Teflon reaction proceeded at higher flame speed than that of the micron
Al/MoO3/Teflon reaction. The higher flame speed in the micron Al/Teflon composite
when compared to the Al/MoO3/Teflon composite is interesting. The Al/MoO3/Teflon
reaction may be expected to exhibit a higher flame speed because the mixtures containing
MoO3 have lower gas production and a similar flame temperature as seen in Figures 13
and 14. However, this is not the case. It is possible that the reaction in the
Al/MoO3/Teflon proceeds with Al reacting primarily with MoO3 because Teflon, which
has decomposed at 322°C (Osborne & Pantoya, in press 2007), is not available at the
37
Texas Tech University, Kyle Watson, August 2007
38
Al/MoO3 reaction ignition temperature of ~960°C (Pantoya & Granier, 2005). This
would lead to incomplete combustion and lower heats of combustion because of the
relatively low content of MoO3 and the limited contribution from Teflon particles. In the
micron Al/Teflon reaction there is an abundance of fluorine gas produced as the oxidizer
is entirely Teflon. Much of the liberated fluorine gas will escape the reaction zone but
due to the high quantity produced some of the fluorine gas will remain long enough to
react with the Al. Even though only a portion of the available fluorine may be reacting,
the fluorine that does react contains more energy than the oxygen reacting in the micron
Al/MoO3/Teflon reaction. Therefore, it may be that in both the micron Al/Teflon and
micron Al/MoO3/Teflon only a portion of the supplied oxidizer reacts (the fluorine
unable to escape in the Al/Teflon reaction and the supplied MoO3 in the Al/MoO3/Teflon
reaction) and the Al/Teflon proceeds at a higher flame speed due to the higher energy
content of fluorine compared to oxygen (i.e. the heat of reaction in the Al/Teflon reaction
is greater than that of the Al/MoO3 reaction as seen in Figure 1). As stated above, only
reacting with a portion of the oxidizer would lead to incomplete combustion in these
reactions. It is noted that these experiments were performed in an inert argon
environment such that oxygen from the ambient air does not contribute to the reaction.
The incomplete combustion would lead to slower heating rates with lower combustion
temperatures. The Al/MoO3 reaction having little gas production will not lose as much
energy to the surroundings and will experience a more complete combustion. The slower
propagation rates, in comparison to the Al/MoO3 reaction, seen in the composites
containing Teflon may be a result of the incomplete and inefficient combustion in these
composites.
Texas Tech University, Kyle Watson, August 2007
39
For nanometer Al reactions, the peak flame speed of the Al/Teflon reaction is two
orders of magnitude less than for both of the reactions containing MoO3. As in the micron
Al reactions the gaseous intermediates and products are not contained and energy is
allowed to escape. Therefore the reactions containing Teflon are prone to lose more
energy to the surrounding because much of the energy is in the form of liberated fluorine
gas that can escape the reaction zone. The increased sensitivity of nanoscale Al allows
the Al to react with more of the fluorine before it escapes than in the reactions containing
micron Al. The increased amount of fluorine reacting before it is able to leave the
reaction zone due to the increased sensitivity of the nanometer Al as well as the increased
homogeneity associated with using nanoscale particles explains the increase in the flame
speed of the nano Al/Teflon composite in comparison to its micron counterpart.
However this increase is small in comparison to that seen in the reactions containing
MoO3. Much of the liberated fluorine gas may still escape the reaction zone explaining
some of this difference in the amount of increase in flame speed. The Al/MoO3/Teflon
reaction, which proceeded at a slower rate than the Al/Teflon reaction when using micron
Al, proceeds at a much higher flame speed than the Al/Teflon reaction when using the
nanoscale Al. On the micron scale it was surmised that the Al/MoO3/Teflon reaction
proceeds slowly as a result of the Teflon not reacting in the Al/MoO3/Teflon reaction.
With the increased sensitivity of Al some of the Teflon may now be reacting before it
leaves the reaction zone. This would account for some increase in flame speed as less
energy is lost and more energy is applied towards the acceleration of the reaction.
However, much of the fluorine would still escape and only a slight increase between the
micron and nano Al reaction, such as what was seen in the Al/Teflon reaction, would be
Texas Tech University, Kyle Watson, August 2007
40
expected. Therefore another mechanism must be responsible for the large increases of
flame speed in the reactions containing MoO3.
The large increases in flame speed seen when comparing the micron and nano Al
reactions containing MoO3 in an unconfined configuration may be a result of a change in
the reaction mechanism. The micron Al reactions propagate at rates slow enough to
suggest that the reaction mechanism is predominantly diffusion. The nanoscale Al
reactions containing MoO3 propagate quickly enough and create heating rates fast enough
to promote the melt dispersion mechanism, causing the Al particles to spallate. The melt
dispersion mechanism in the nano Al composites containing MoO3 would explain the two
orders of magnitude increase in flame speeds. In the Al/Teflon reaction, the flame speeds
were not fast enough to suggest melt dispersion may be occurring. Therefore, there is
most likely no change in the dominant combustion mechanism and the reaction will
remain predominantly diffusion controlled. Thus the reaction would remain diffusion
controlled for the nano Al/Teflon reaction when going from the micron to nano Al
particles; whereas, the nano Al/MoO3/Teflon and nano Al/MoO3 would experience a
change to the melt dispersion mechanism with the decrease in particle size. The lack of a
change in reaction mechanism between the micron and nano Al/Teflon reactions would
explain only having a slight increase in flame speed as the only contributing factor would
be the increased amount of fluorine reacting due to the higher sensitivity of nanoscale Al
particles and the increased homogeneity of the composite. The shift to melt dispersion in
the reactions containing MoO3 would explain the similarity of the flame speed curves and
the large increase in flame speeds seen when comparing these reactions to the micron
reactions containing MoO3.
Texas Tech University, Kyle Watson, August 2007
41
3.1.3 Implications
For unconfined burning environments, adding Teflon to the mixture produces
fluorine gas that escapes from the flame zone allowing the loss of energy to the
surroundings. This energy is no longer contributes to the enhancement of the flame
propagation. With gaseous intermediates escaping, it is likely that incomplete
combustion occurs as only a portion of the oxidizing agent is reacting. Therefore, the
addition of Teflon to unconfined reactions allows energy to escape the reaction zone and
results in incomplete combustion and overall hinders the transfer of energy to the
accelerating flame front resulting in slower flame speeds.
Composites that produce little gas contain more energy within the reactants
themselves. In the unconfined state this energy still attributes to accelerating the flame
front as it is not in gaseous form where it can readily escape the reaction zone. This
allows for faster heating rates and higher flame speeds. When using nanoscale Al as the
fuel, heating rates can be attained that promote the melt dispersion mechanism resulting
in substantial increases in flame speed. In high gas reactions this was not achievable as
there was not enough energy retained within the reaction zone to create heating rates fast
enough for the melt dispersion mechanism to occur.
These results imply that achieving high flame speeds in an open environment can
be accomplished using nano aluminum particles combined with a metallic oxide that does
not produce a significant amount of gas.
Texas Tech University, Kyle Watson, August 2007
3.2 Confined Burn Tube Results
3.2.1 Results and Initial Observations (Flame Speed Measurements)
The Figures 15 through 17 show the confined burn results which are listed in
detail in Tables 13 and 14 found in Appendix A (Error bars are provided but may be
smaller than the point marker. For error values see detailed Tables in Appendices).
Composites with the 50nm Al particles exhibited peak flame speeds of 837.498 m/s,
957.216 m/s, and 960.234 m/s for the Al/Teflon, Al/MoO3/Teflon, and Al/MoO3
composites, respectively. The 1-3 micron Al experiments yielded peak flame speed of
348.279 m/s, 163.902 m/s, and 244.019 m/s for the respective composites of Al/Teflon,
Al/MoO3/Teflon, and Al/MoO3.
0
100
200
300
400
500
600
700
800
900
0% 20% 40% 60% 80% 100%
Mass Percent Aluminum
Flam
e Pr
opag
atio
n (m
/s)
50 nm Al
1-3 µm Al
Figure 15: Al/Teflon confined apparatus burn results.
42
Texas Tech University, Kyle Watson, August 2007
0
200
400
600
800
1000
1200
0% 20% 40% 60% 80% 100%
Mass Percent of Aluminum
Flam
e Pr
opag
atio
n (m
/s)
50 nm Al
1-3 µm Al
Figure 16: Al/MoO3/Teflon confined apparatus burn results.
0
200
400
600
800
1000
1200
0% 20% 40% 60% 80% 100%
Mass Percent Aluminum
Flam
e Pr
opag
atio
n R
ate
(m/s
) 50 nm Al
1-3 um Al
Figure 17: Al/MoO3 confined apparatus burn results.
43
Texas Tech University, Kyle Watson, August 2007
As in the open burn configurations, it is evident that particle size plays a major
role in the flame speeds. Each composite exhibits a significant increase in flame speed
with the decrease in particle size. In the confined state the increase in flame speed due to
the change in particle size was more consistent than in the open burn configuration. Each
composition increased by a factor less than 10 at its optimal composition. The Al/Teflon
reaction exhibited the fastest flame speed in the micron Al reactions. However the
Al/Teflon reaction had the slowest flame speed in the nano Al reactions.
The nanoscale Al experiments all yielded curves with similar peak flame speeds
at an optimal ratio of 40% mass Al. Also noted is the shift in optimal composition when
decreasing particle size in both experiments containing Teflon in the composition.
3.2.2 Results and Initial Observations (Pressure Measurements)
Pressure data was obtained at the optimal ratio for each composite and the final
sensor data (the farthest sensor from the point of initiation) is displayed in Table 5. A
more detailed account is provided in Tables 15 and 16 of Appendix B.
Table 5: Pressure results from the 4th pressure transducer (farthest from ignition).
Al Size
Mass %
Pure Al
Compo-sition
Mass (mg)
Peak Pressure
(MPa)
Rise Time
(µ sec)
Pressuriz-ation Rate (MPa/sec)
Pressure Propaga-tion Rate
(m/s)
Optical Propag-
ation Rate (m/s)
40 Al/Teflon 201.2 10.75 84.0 181746.25 762.00 837.50
40 Al/MoO3/Teflon 211.8 5.45 78.0 95877.06 846.67 957.22
50 nm Al
40 Al/MoO3 196.6 1.46 63.3 44922.16 823.15 960.23 50 Al/Teflon 400.6 4.18 784.0 29968.49 186.27 348.28
60 Al/MoO3/Teflon 384.2 0.38 2105.0 241.75 58.56 163.90
1 - 3 µm Al
40 Al/MoO3 362.7 0.82 245.0 3336.10 240.10 244.02
44
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45
An increase in peak pressure is consistent with the increase in flame speed when
the Al particle size is decreased. Also noted are the faster rise times, pressurization rates
and wave speeds associated with the composites containing 50 nm Al particles. One
observation is the slower optical and pressure propagation rates in the nanoscale
Al/Teflon reaction despite yielding the highest pressure and fastest pressurization rate.
The reactive power was calculated for each reaction using Equations 2.6. This
value along with the adiabatic flame temperatures and estimated gas production found
using the Real Code (Tim Tec, LLC.) chemical equilibrium program are displayed in
Table 6.
Table 6: Properties of the reactions assuming ideal burns with complete combustion.
Al Size
Mass % Pure Al Composition
Adiabatic Flame
Temp (K)
Heat of Reaction (kJ/kg)
Gas Generation (kg/kgreactant)
Reactive Power (KW)
40 Al/Teflon 2769 14309 0.81 3.43E+04 40 Al/MoO3/Teflon 2738 10277 0.39 2.79E+04
50 nm Al 40 Al/MoO3 2956 4979 0.03 1.55E+04
50 Al/Teflon 2769 14309 0.81 7.31E+03
60 Al/MoO3/Teflon 2738 10277 0.39 1.88E+03 1 - 3 µm Al 40 Al/MoO3 2956 4979 0.03 7.37E+03
The reactive power (mass based) and gas generation are the largest for the
Al/Teflon reaction. This implies that the Al/Teflon will have the highest amount of
convective heat transfer due to the large amounts of gas produced as well as having the
highest energy content of the composites tested.
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46
3.2.3 The Effects of Particle Size and the Addition of Teflon
In confined configurations, the intermediate gases cannot escape and instead
enhance the convective mode of energy propagation. Under confinement the composites
containing Teflon produced higher peak pressures as expected with the increased gas
generation (see Figure 13). In the micron Al reactions, the Al/Teflon composite
exhibited the highest flame speed corresponding with the highest peak pressure. This
may be a result of the increased convective heat transfer associated with the higher gas
production. The gases are forced through the composite instead of escaping to the
atmosphere. This results in preheating the reactants and leads to faster flame speeds.
Also, unlike in the open burn configurations, a large portion of the fluorine is most likely
reacting as it is unable to escape the reaction zone. The reaction with gaseous fluorine
results in more complete combustion enhancing the flame speed. The preheating of the
composite due to convective heat transfer as well as the more complete combustion
associated with the confinement of the gaseous oxidizer results in the higher flame speeds
in comparison to the open configuration reactions.
The micron Al/MoO3 reaction exhibited a higher flame speed than that of the
micron Al/MoO3/Teflon reaction. This was unexpected because the Al/MoO3/Teflon
reaction would be expected to have more gaseous byproducts and should experience a
larger increase in convective heat transfer when confined. However, according to the
peak pressures displayed in Table 5, the 1-3 μm Al/MoO3 reaction produced a larger
amount of gas than the1-3 μm Al/MoO3/Teflon reaction. This would lead to higher
levels of convective heat transfer in the micron Al/MoO3 reaction than in the micron
Al/MoO3/Teflon reaction. The lower than expected gas production and the slower flame
Texas Tech University, Kyle Watson, August 2007
47
speed in the Al/MoO3/Teflon may still be attributed to escaping fluorine gas as seen in
the open configuration burns. As discussed in the open burns, fluorine is available before
the reaction of Al/MoO3, since Teflon degrades at ~322°C (Osborne & Pantoya, in press
2007) and the ignition temperature of micron Al with MoO3 is not until ~960°C (Pantoya
& Granier, 2005). The liberation of the fluorine prior to the ignition of the Al and MoO3
is evident by the much slower pressurization rate and much longer rise time associated
with the Al/MoO3/Teflon reaction. Given the time between its liberation and the reaction
initiation the fluorine may still escape the reaction zone despite being confined. As in the
open burn configuration, the loss of some fluorine gas would again result in incomplete
combustion and lower flame speeds than what would be achievable if no fluorine was
able to escape. This incomplete combustion would also explain the low gas production in
the micron Al/MoO3/Teflon reaction as the main contributing oxidizer is the MoO3 which
does not result in high amounts of gas. The micron Al/MoO3 reaction exhibits a higher
gas production because it experiences a more complete combustion and contains almost
2x as much MoO3. The 1-3 μm Al/Teflon reaction may also experience the same
phenomenon of escaping fluorine gas. However, the abundance of fluorine produced
when using 100% Teflon as the oxidizer would result in the higher pressurization rate and
rise time leading to the increased flame speed and the higher pressure.
Nanometer scale aluminum is more sensitive to ignition. The composites
containing nm Al and Teflon produced twice the peak pressure than mixtures with
micron Al and Teflon. These results suggest that the main influence of particle size is in
the reactivity of the mixture. The nm Al particles are easier to initiate and more
completely react with the fluorine gas from the decomposed Teflon. That energy assists
Texas Tech University, Kyle Watson, August 2007
in the flame propagation. In the nano particle Al confined tests the flame speeds are
similar for all composites. Each reaction resulted in significant increases, on the order of
2 to 6 times, when reducing the particle size from the micron to nanoscale. The nm Al
particles exhibit rise times on the order of 80 microseconds, which can be considered the
characteristic time for a reaction to occur. These time scales are too fast for a diffusive
mechanism. According to Equation 2.5, 80 microsecond rise times will yield diffusive
distances on the order of 5 x 10-5 nanometers which is smaller than the oxide shell
thickness of the Al particles. Therefore these time scales are more consistent with the
melt dispersion theory. Achieving heating rates fast enough to promote the melt
dispersion mechanism as well as the increased homogeneity and sensitivity associated
with using nano particles explains the increases in flame speed when compared to the
reactions using micron Al.
The increased pressure associated with the more complete combustion leads to
enhanced convective heat transfer promoting the increases in flame speed. The high
levels of gas produced in the Al/Teflon would lead to higher levels of convective heat
transfer than seen in the Al/MoO3/Teflon and Al/MoO3 reactions. However, the nano
Al/Teflon reaction exhibited the slowest flame rate as well as the highest peak pressure
when confined. In this case, pressure may play a dual role, promoting convection and
enhancing flame speeds until a limiting pressure threshold is achieved at which point the
pressure than acts to suppress the reaction and flame propagation. Kuo (2005) shows that
in gaseous systems flame speeds are reduced as pressure increases according to:
where SL, is flame speed and P is pressure. 2/1−∝ pSL
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Texas Tech University, Kyle Watson, August 2007
This effect was shown in experiments by Egerton and Levevbre (1954) in which they
determined burning velocities of methane, propane, ethylene, and propylene while
varying pressure from ½ to 9 atm. Their results for the burning of the propane/air
mixtures are displayed in Figure 18.
Figure 18: Burning velocities of propane/air mixtures. Figures against curves show percentage C3H8. (Egerton & Levevbre, 1954).
These results show in gaseous mixtures the increase of pressure does retard the flame
speed of the reaction. This same principle can be applied to thermites as shown by
Ivanov, Surkov, and Viktoranko (1979). Ivanov et al. (1979) studied the effects of
pressure on various thermite composites including BaO2/Zr, MoO3/Mg, and PbO2/Zn.
The studies were conducted in a constant-pressure bomb with pressures varying from 1 to
80 atm. Figure 19 shows their results for the above-mentioned thermites.
49
Texas Tech University, Kyle Watson, August 2007
Figure 19: Effect of pressure on the combustion rate of thermite mixtures: 1) BaO2/Zr
2) MoO3/Mg 3) PbO2/Zn
(Ivanov et al., 1979)
As seen in Figure 19, increasing pressure initially causes an increase in flame speed in
the thermite composites. However, there exists some point at which the increase of
pressure will begin to reduce the flame speed of the reaction. If this point, or threshold
pressure, is exceeded then the effect of the increasing pressure will be to retard instead of
enhance the reaction propagation rate.
In the confining of these reactions there is a substantial increase of pressure that
should retard the flame rates. However the confining of these gases also leads to the
higher levels of convective heat transfer and a shift in reaction mechanism that enhances
the flame rate. Thus by confining the reaction the flame speed experiences both the
50
Texas Tech University, Kyle Watson, August 2007
51
retarding effects of the increasing pressure and the enhancing effects of the increased
convection and the shift in combustion mechanism. The large increases in flame speed
when compared to the open configuration burns suggest that the influence of the
increased convective heat transfer and change in combustion mechanism have a larger
impact on the reaction than the retarding effects of the pressure. However, the retarding
effect of the pressure would explain the lower flame speed in the nanoscale Al/Teflon
confined reaction. The amounts of gas produced by the Al/Teflon reaction leads to a
pressure double that of the other reactions. Therefore the retarding effects of the pressure
will be significantly larger, ~2x. There may be a threshold pressure that if exceeded the
effects of the pressure begin to overcome the increases in flame speed from the
convection and combustion mechanism. This would lead to the flame speed increasing
with the increase of pressure until this threshold pressure is achieved. After the threshold
pressure is exceeded the flame speed would begin diminishing as the pressure is further
increased. The Al/Teflon reaction, having double the pressure of the other reactions, may
have exceeded this threshold pressure causing its flame speed to begin diminishing. This
would explain the slower flame speed in the Al/Teflon reaction despite it exhibiting the
highest pressure and potential reactive power.
The reactions do not seem to achieve a detonation as evident by comparing the
optical and pressure propagation waves. If detonation was achieved the pressure
propagation rate would be equal to or exceed that of the optical wave. In all cases the
pressure propagation was slightly slower than the optical wave as shown in Table 7. This
suggests that detonation is not achieved. However in the nanoscale Al reactions, the
addition of Teflon, resulting in additional gas and higher pressures, seems to narrow the
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52
gap between the optical and pressure propagation rates. This infers that adding oxidizers
that result in high gas generation to nanoscale thermites may draw the reaction closer to a
detonation. However, as discussed above, too much gas and resulting pressure may
actually begin to hinder the reaction and could possibly prevent the detonation from
occurring. The opposite effect was seen in the micron scaled Al reactions. The addition
of Teflon and resulting higher gas content broadened the gap between the optical and
pressure propagation rates. The lower homogeneity associated with the using the micron
particles results in a less complete combustion and subsequent lower gas production. The
gas produced does effectively increase convective heat transfer which subsequently
increases the flame speed. Due to the lower gas production in these micron Al reactions,
there is not enough build-up of gases to increase the pressure wave propagation the extent
that the flame speed is increased. Therefore, in the micron Al reactions, the effects of
confining the gases has a greater effect on increasing the optical propagation rate due to
convection than it does at increasing the pressure propagation rate, and the difference
between the optical and pressure propagation rates broadens. This implies that using
oxidizing agents that produce large quantities of gas can bring a reaction closer to
detonation if it is confined and utilizes nanoscale particulates. However, a balanced
medium in which enough gas is introduced to accelerate the reaction rate and draw the
pressure wave propagation rate closer to the optical wave propagation rate without
exceeding the pressure at which the reaction rates begin to diminish is needed and may
result in very fast reactions with the potential to achieve detonation.
Texas Tech University, Kyle Watson, August 2007
Table 7: Difference between optical and acoustical wave propagation rates
Al Size Mass % Pure Al Composition Optical Minus Acoustical
Propagation Rate (m/s)
40 Al/Teflon 75.498 40 Al/MoO3/Teflon 110.549 50 nm Al 40 Al/MoO3 137.086 50 Al/Teflon 162.012
60 Al/MoO3/Teflon 105.341 1 - 3 µm Al
40 Al/MoO3 3.916
Another interesting result is the Mach number achieved by these reactions. The
Mach number was calculated assuming a combination of proceeding through the gas that
comprised the largest percentage of the gaseous byproducts of the reactions or proceeding
through air along with proceeding at the adiabatic flame temperature or proceeding at
room temperature. The gas medium, when not assumed to be air, for use in this
calculation was found using the REAL Code (Tim Tec, LLC.) chemical equilibrium
software to be AlF in the Al/Teflon reaction and CO in the Al/MoO3/Teflon and
Al/MoO3 reactions. The adiabatic flame temperatures were also found using the REAL
Code (Tim Tec, LLC.) chemical equilibrium software and are displayed in Table 6. The
Mach number was calculated using Equation 2.7 and the results are displayed in Table 8.
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54
Table 8: Mach number calculations for the flame speed of the reactions.
Al Size
Mass % Pure
Al Composition
Ma in gas medium at reaction
temp
Ma in air at reaction
temp
Ma in gas medium at room temp
Ma in air at room temp
40 Al/Teflon 1.18 0.79 3.61 2.42 40 Al/MoO3/Teflon 0.90 0.91 2.74 2.76
50 nm Al 40 Al/MoO3 0.87 0.88 2.75 2.77
50 Al/Teflon 0.49 0.33 1.50 1.01
60 Al/MoO3/Teflon 0.15 0.16 0.47 0.47 1 - 3 µm Al 40 Al/MoO3 0.22 0.22 0.70 0.70
Initially looking at the flame speeds, the reactions appear to approach Mach 3 as shown
by the Mach number calculation at room temperature shown in Table 8. If this was the
case acoustical effects may play a huge role and detonation in the reaction would be
imminent. However, considering the reaction occurs in air at the reaction temperature
yields Mach numbers on the subsonic regime and would be more consistent with a
deflagration. The actual Mach number will most likely be somewhere in between and
may be best represented by the Mach number calculation in the gas byproduct medium at
the reaction temperature. This number is probably slightly high as the gas will not be at
the adiabatic flame temperature but it will be much higher than that of room temperature.
These Mach numbers are on the order of Mach 1 and would suggest a reaction that is still
a deflagration but may be nearing detonation. This is consistent with the comparison of
the optical and acoustical propagation rates from above.
3.2.4 Implications
For confined burning environments, the addition of Teflon and associated
increase in gas enhances the convective heat transfer in the reaction. The confining of
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55
these gases allows more of the fluorine to remain in the reaction zone increasing the
amount of energy applied to the reaction resulting in more complete combustion and
faster propagation rates. The addition of the Teflon to the nano Al reactions narrowed the
difference between the optical and pressure propagation rates bringing the reactions
closer to detonation. However, despite the significant enhancements in flame speed seen
by initially increasing the pressure due to the high convective heat transfer rates and
confining of the oxide gases, there appears to be a point at which the increasing pressure
begins to retard the flame speed.
This implies that using an oxidizer that produces a large amount of gas can
significantly increase flame rates as well as bringing the reaction closer to achieving or
possibly achieving detonation as long as the pressure generated is not sufficient enough
to pass the threshold at which it will begin hindering the reaction. Therefore, to achieve
the fastest possible flame speeds and to achieve detonations a medium must be found that
produces just enough gas to create high pressures that approach but don’t exceed the
pressure threshold.
3.3 Effects of Confinement
To better illustrate the effects of confining the reactions, Figure 20 shows the burn
rates for each composite containing 50nm Al under both open and confined states (Error
bars are provided but may be smaller than the point marker. For error values see detailed
Tables in Appendices).
Texas Tech University, Kyle Watson, August 2007
0
200
400
600
800
1000
1200
0% 20% 40% 60% 80% 100%Mass Percent Aluminum
Flam
e Pr
opag
atio
n R
ate
(m/s
)
Al/Teflon ConfinedAl/Teflon OpenAl/MoO3/Teflon ConfinedAl/MoO3/Teflon OpenAl/MoO3 ConfinedAl/MoO3 Open
Figure 20: 50 nm Al open and confined burn results for all composites.
It is obvious that confinement has a profound effect on combustion characteristics
in these composites, as expected. All three composites showed substantial increases in
flame speed when going from the open to confined configuration. These increases are
likely a result of increased convective heat transfer due to the retaining of hot gases. This
enhances the convective heat transfer and the rate of heating of the composite. To
evaluate the potential combustion mechanism in these reactions diffusive distances were
estimated using Equation 2.5. The approximate diffusive distances were calculated as a
function of the pressure rise time and displayed in Table 9.
56
Texas Tech University, Kyle Watson, August 2007
Table 9: Approximate maximum diffusive distance for the reactions.
Al Size
Mass % Pure Al Composition Ld (nm)
40 Al/Teflon 5.80E-05 40 Al/MoO3/Teflon 5.59E-05
50 nm Al 40 Al/MoO3 5.03E-05
50 Al/Teflon 1.77E-04
60 Al/MoO3/Teflon 2.90E-04 1 - 3 µm Al 40 Al/MoO3 9.90E-05
These results suggest that the maximum distance that the oxidizing gas is able to
diffuse through is < 1nm. The oxide layers of the Al powders used are ~ 2nm. This
implies that the reactions under confinement cannot be diffusion controlled as the
oxidizing gas will not diffuse far enough to penetrate the aluminum particle’s oxide shell.
The melt dispersion mechanism proposed by Levitas, Asay, Son, and Pantoya (2005)
may be the dominant mechanism in these reactions as the heating rates and flame speeds
are fast enough to promote spallation of the Al particles.
Another significant observation was the factor by which each composite
increased. Table 10 displays the amount of increase in each composite.
57
Texas Tech University, Kyle Watson, August 2007
Table 10: The factor of increase due to confinement in each 50 nm Al composite.
Mass % Pure Al Increases by a multiple of
10 N/A 20 0.1 30 180.3 40 260.7 50 177.0 60 214.6 70 167.3 80 57.7
Al/T
eflo
n
90 N/A 10 N/A 20 30.0 30 1.9 40 2.3 50 3.5 60 3.6 70 7.3 80 7.2 A
l/MoO
3/Tef
lon
90 0.0 10 32.3 20 23.330 2.140 2.150 3.760 12.770 40.280 0.0
Al/M
oO3
90 0.0
58
All of the composites showed an increase in flame speed when confining the
reaction. This is a direct effect of the enhanced convective heat transfer as a result of the
confinement of the intermediate and product gases as well as the more complete
combustion associated with the retaining of oxidizer gases. The Al/Teflon composite
would see the most effect from the confining of these gases due to the abundance of gas
produced in that reactive system. The increases in Al/ MoO3 and Al/ MoO3/Teflon were
small in comparison to those achieved by the Al/Teflon composite. The higher level of
Texas Tech University, Kyle Watson, August 2007
59
gaseous production in the Al/Teflon reaction would account for a part of the difference in
the amount of increase seen when confining the Al/Teflon reaction compared to the
reactions containing MoO3. However a significant part of this difference may be owed to
the mechanism controlling the reactions.
The combustion mechanism may be responsible for much of the large factor of
increase in flame speed exhibited when confining the Al/Teflon reaction. The
Al/MoO3/Teflon and Al/MoO3 composites, when using the nanometer Al particles,
achieved heating rates fast enough to promote the melt dispersion mechanism in both the
open and confined states. The Al/Teflon was most likely still diffusion controlled in the
open configuration burns; whereas, it had likely made a switch to the melt dispersion
mechanism in the confined state burns. Therefore the increases in flame speed when
confining the Al/MoO3/Teflon and Al/MoO3 reaction can be mainly contributed to the
increased convective heat transfer and more complete combustion when under
confinement as the reaction mechanism remained the same for both configurations. A
large portion of the increase seen when confining the Al/Teflon reaction may be a result
of a shift in reaction mechanism from diffusion to the melt dispersion.
Even though confining of the gaseous Al/Teflon reaction had much larger effects
than the confining of the less gaseous Al/MoO3/Teflon and Al/MoO3 reactions, there
was a negative side effect. As discussed in the earlier section, the large pressure
associated with confining such a gaseous reaction plays a dual role. On one hand it
serves to increase the convective heat transfer increasing the flame speed. On the other at
some point it becomes a hindrance and begins to retard the flame speed. The Al/Teflon
reaction could have experience an even larger factor of increase due to confinement had
Texas Tech University, Kyle Watson, August 2007
60
the pressure not started to negatively effect its flame speed. Therefore, for confining a
reaction to have the most impact the reacting species must produce enough gas to create
pressures large enough to promote high levels of convective heat transfer without
exceeding the pressure threshold at which the flame speeds begin to reduce.
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61
Chapter IV
Conclusions
The use of fluorine as an oxidizing agent in thermite reactions yields higher heats
of combustion as well as increased gas content. In open burn configurations the
increased gas content reduces flame propagation speeds because gas liberated during the
reaction escapes the reaction zone. In the confined state these gases are contained
promoting enhanced convection as well as more complete burning. Confining the
reaction also leads to increases in pressure. The increased pressure promotes convection
and accelerates flame speeds. It also causes the pressure wave propagation rate to draw
closer to the optical propagation rate; however, both reaction configurations result in
deflagrations with Ma numbers less than 1. At a critical threshold, beyond 5 MPa but less
than 10 MPa, further increases in pressure beyond 5 MPa but less than 10 MPa begin to
suppress flame propagation. This is evident in the Al/Teflon reaction as it has more
reactive power and more gas production than the other composites yet it exhibits lower
optical and acoustic propagation rates. The pressures achieved by the nano Al/Teflon
reaction in confined burning configuration crossed the pressure threshold such that
propagation rates are reduced. These results imply that in open configurations faster
flame speeds will be achieved by using oxidizers that result in low gas output reactions as
less energy is lost to the surrounding in the form of escaping gases. In the confined
configuration the fastest flames speeds will be achieved by using oxidizers that produce
enough gas to increase the peak pressure just below its critical threshold. Too high a peak
pressure begins to suppress the reaction and reduce the flame speed.
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62
References
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Asay, B.W., Son, S.F., & Busse, J.R. (2004). Ignition characteristics of metastable
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Texas Tech University, Kyle Watson, August 2007
66
Appendix A Detailed high-speed camera data
Texas Tech University, Kyle Watson, August 2007
67
Mas
s (m
g)Re
sult
Velo
city
1 (m
/s)V
elocit
y 2
(m/s)
Velo
city
3 (m
/s)A
vg. V
el. (m
/s)St
. Dev
.St
. Err
or10
%20
3.30
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
20%
206.
200
ign.
0.15
20.
128
0.14
30.
141
0.01
20.
007
30%
200.
200
ign.
1.48
01.
625
1.88
01.
662
0.20
30.
117
40%
201.
200
ign.
3.04
23.
210
3.38
63.
213
0.17
20.
099
50%
203.
900
ign.
3.54
04.
309
4.89
84.
249
0.68
10.
393
60%
200.
800
ign.
2.73
12.
500
2.63
02.
620
0.11
60.
067
70%
203.
000
ign.
2.03
72.
459
2.43
72.
311
0.23
80.
137
80%
200.
300
ign.
1.33
71.
402
1.25
71.
332
0.07
30.
042
90%
202.
300
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
0
10%
249.
000
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
020
%24
9.60
0ig
n.12
.714
11.3
3311
.049
11.6
990.
891
0.51
430
%25
0.40
0ig
n.38
0.00
132
0.00
137
0.13
635
6.71
332
.174
18.5
7540
%25
0.80
0ig
n.41
8.18
340
0.09
741
3.62
941
0.63
69.
407
5.43
150
%25
0.10
0ig
n.22
1.30
323
1.63
923
7.90
423
0.28
28.
383
4.84
060
%24
9.80
0ig
n.73
.691
74.4
9880
.702
76.2
973.
836
2.21
570
%25
0.50
0ig
n.9.
323
9.76
610
.529
9.87
30.
610
0.35
280
%24
9.70
0ig
n.1.
131
1.19
71.
225
1.18
40.
048
0.02
890
%25
0.70
0ig
n.0.
310
0.28
90.
297
0.29
90.
011
0.00
6
10%
249.
800
ign.
2.55
12.
711
2.98
22.
748
0.21
80.
126
20%
249.
600
ign.
26.1
7722
.446
22.9
9523
.873
2.01
41.
163
30%
250.
400
ign.
419.
841
453.
463
431.
812
435.
039
17.0
429.
839
40%
251.
200
ign.
432.
317
440.
398
496.
962
456.
559
35.2
2320
.336
50%
249.
600
ign.
208.
335
192.
305
205.
131
201.
924
8.48
34.
897
60%
250.
300
ign.
31.0
4832
.486
29.4
6130
.998
1.51
30.
874
70%
250.
500
ign.
3.85
23.
837
4.29
03.
993
0.25
70.
149
80%
249.
900
ign.
0.84
50.
821
0.86
30.
843
0.02
10.
012
90%
250.
800
ign.
0.06
10.
012
0.09
50.
056
0.04
20.
024
Ope
n Bu
rns
% A
l
Al/MoO3Al/Teflon Al/MoO3/TeflonTa
ble 1
1: 5
0 nm
Al c
ompo
site o
pen
burn
flam
e spe
ed re
sults
.
Texas Tech University, Kyle Watson, August 2007
68
Mas
s (m
g)Re
sult
Velo
city
1 (m
/s)V
elocit
y 2
(m/s)
Velo
city
3 (m
/s)A
vg. V
el. (m
/s)St
. Dev
.St
. Err
or10
%40
1.6
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
020
%40
4.1
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
030
%40
2.3
ign.
0.54
80.
488
0.48
60.
507
0.03
50.
020
40%
403.
4ig
n.0.
802
0.82
90.
793
0.80
80.
019
0.01
150
%40
3.0
ign.
1.35
21.
327
1.46
61.
382
0.07
40.
043
60%
400.
8ig
n.0.
646
0.62
80.
563
0.61
20.
044
0.02
570
%40
8.0
ign.
0.11
30.
109
0.09
40.
105
0.01
00.
006
80%
403.
8no
ign.
00
00.
000
0.00
00.
000
90%
401.
9no
ign.
00
00.
000
0.00
00.
000
10%
450.
700
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
020
%45
0.20
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
30%
449.
800
ign.
0.07
20.
079
0.06
80.
073
0.00
60.
003
40%
450.
100
ign.
0.12
70.
129
0.12
60.
127
0.00
20.
001
50%
450.
300
ign.
0.33
40.
315
0.30
00.
316
0.01
70.
010
60%
449.
300
ign.
0.33
80.
321
0.34
20.
334
0.01
10.
006
70%
449.
600
ign.
0.20
40.
239
0.22
00.
221
0.01
80.
010
80%
450.
500
ign.
0.05
00.
052
0.05
00.
051
0.00
10.
001
90%
449.
500
ign.
0.00
10.
001
0.00
10.
001
0.00
00.
000
10%
450.
600
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
020
%45
0.20
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
30%
449.
500
ign.
2.22
81.
546
1.44
31.
739
0.42
70.
246
40%
450.
300
ign.
2.77
13.
183
2.90
52.
953
0.21
00.
121
50%
449.
800
ign.
3.76
94.
570
4.00
94.
116
0.41
10.
237
60%
448.
900
ign.
1.29
41.
310
1.46
51.
356
0.09
40.
055
70%
450.
400
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
080
%45
0.60
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
90%
449.
600
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
0
Al/Teflon Al/MoO3/Teflon
% A
l
Tabl
e 12:
1-3
µm
Al c
ompo
site o
pen
burn
flam
e spe
ed re
sults
.Al/MoO3
Ope
n Bu
rns
Texas Tech University, Kyle Watson, August 2007
69
% A
lM
ass (
mg)
Resu
ltVe
locit
y 1 (m
/s)Ve
locit
y 2 (m
/s)Ve
locit
y 3 (m
/s)Av
g. V
el. (m
/s)St
. Dev
.St
. Err
or10
%20
0.80
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
20%
202.
600
ign.
0.01
40.
013
0.01
60.
014
0.00
20.
001
30%
204.
100
ign.
304.
967
272.
959
320.
962
299.
629
24.4
4314
.112
40%
201.
200
ign.
821.
538
853.
594
837.
362
837.
498
16.0
289.
254
50%
203.
200
ign.
779.
282
730.
404
746.
458
752.
048
24.9
1414
.384
60%
201.
500
ign.
632.
121
574.
230
480.
496
562.
282
76.5
1544
.176
70%
202.
800
ign.
380.
716
363.
689
415.
583
386.
663
26.4
5315
.273
80%
201.
000
ign.
77.2
4182
.380
71.1
2576
.915
5.63
53.
253
90%
201.
600
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
0
10%
249.
600
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
020
%23
5.40
0ig
n.33
6.76
536
7.85
334
9.79
035
1.46
915
.612
9.01
430
%21
3.80
0ig
n.73
6.23
565
0.78
068
4.63
969
0.55
143
.033
24.8
4540
%21
1.80
0ig
n.99
4.03
090
9.06
596
8.55
395
7.21
643
.602
25.1
7450
%19
3.20
0ig
n.78
7.85
985
2.91
380
8.53
581
6.43
633
.239
19.1
9060
%16
6.80
0ig
n.27
2.05
629
6.81
224
8.47
227
2.44
724
.172
13.9
5670
%14
2.10
0ig
n.71
.628
78.5
7366
.040
72.0
806.
279
3.62
580
%13
7.20
0ig
n.8.
778
7.55
99.
239
8.52
50.
868
0.50
190
%12
7.80
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
10%
223.
600
ign.
84.2
5988
.039
94.2
7988
.859
5.06
02.
921
20%
218.
700
ign.
526.
895
593.
093
551.
758
557.
249
33.4
3919
.306
30%
209.
500
ign.
897.
302
876.
656
930.
695
901.
551
27.2
6915
.744
40%
196.
600
ign.
931.
044
979.
549
970.
109
960.
234
25.7
1614
.847
50%
189.
300
ign.
734.
958
760.
721
773.
521
756.
400
19.6
4111
.340
60%
181.
800
ign.
415.
838
386.
231
378.
099
393.
389
19.8
6211
.467
70%
174.
100
ign.
162.
991
185.
955
132.
935
160.
627
26.5
8915
.351
80%
166.
600
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
090
%16
0.30
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
Al/Teflon Al/MoO3/TeflonTa
ble 1
3: 5
0 nm
Al c
ompo
site c
onfin
ed b
urn
flam
e spe
ed re
sults
.Al/MoO3
Texas Tech University, Kyle Watson, August 2007
70
Mas
s (m
g)Re
sult
Velo
city
1 (m
/s)V
elocit
y 2
(m/s)
Velo
city
3 (m
/s)A
vg. V
el. (
m/s)
St. D
ev.
St. E
rror
10%
401.
5no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
20%
402.
9no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
30%
405.
2ig
n.13
9.33
2812
6.83
713
3.57
813
3.24
96.
254
3.61
140
%40
0.6
ign.
291.
817
301.
542
294.
184
295.
848
5.07
12.
928
50%
403.
1ig
n.33
8.99
335
1.00
735
4.83
834
8.27
98.
267
4.77
360
%40
2.3
ign.
316.
204
306.
216
310.
242
310.
887
5.02
52.
901
70%
404.
2ig
n.29
8.95
527
7.70
325
3.61
927
6.75
922
.683
13.0
9680
%40
0.3
no ig
n.0
00
0.00
00.
000
0.00
090
%40
3.2
no ig
n.0
00
0.00
00.
000
0.00
0
10%
338.
300
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
020
%35
3.20
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
30%
363.
900
ign.
61.9
8259
.771
64.9
3462
.229
2.59
01.
496
40%
384.
200
ign.
115.
627
113.
377
129.
866
119.
623
8.94
15.
162
50%
400.
300
ign.
142.
854
136.
365
144.
831
141.
350
4.42
92.
557
60%
420.
000
ign.
172.
959
160.
164
158.
584
163.
902
7.88
34.
551
70%
455.
200
ign.
93.2
5583
.930
90.6
0389
.263
4.80
52.
774
80%
472.
500
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
090
%48
3.20
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
10%
303.
500
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
020
%32
1.70
0ig
n.79
.209
81.8
0487
.253
82.7
554.
106
2.37
030
%34
6.80
0ig
n.11
5.04
512
6.18
411
8.98
112
0.07
05.
649
3.26
140
%36
2.70
0ig
n.23
0.34
325
8.58
824
3.12
624
4.01
914
.144
8.16
650
%38
0.20
0ig
n.76
.607
71.4
6294
.684
80.9
1812
.196
7.04
260
%39
6.30
0ig
n.11
.831
10.5
9510
.883
11.1
030.
647
0.37
370
%41
4.60
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
80%
437.
300
no ig
n.0.
000
0.00
00.
000
0.00
00.
000
0.00
090
%45
3.50
0no
ign.
0.00
00.
000
0.00
00.
000
0.00
00.
000
Con
fined
Bur
ns%
Al
Tabl
e 14
: 1-3
µm
Al c
ompo
site
conf
ined
bur
n fla
me
spee
d re
sults
.Al/Teflon Al/MoO3/Teflon Al/MoO3
Texas Tech University, Kyle Watson, August 2007
71
Appendix B Detailed pressure transducer data
Texas Tech University, Kyle Watson, August 2007
Tes
t #Pe
ak P
ress
ure
(psi
)Pe
ak P
ress
ure
(MPa
)R
ise
Tim
e (s
ec)
Ris
e T
ime
(µ s
ec)
Ris
e R
ate
(psi
/sec
)R
ise
Rat
e (M
Pa/s
ec)
Prop
agat
ion
Rat
e (m
/s)
Sam
ple
Rat
e (p
ps)
Tes
t 111
87.7
298.
1891
0283
70.
0001
414
013
0738
8390
141.
2463
846.
667
Tes
t 214
96.6
910
.319
3138
50.
0000
770
2659
0926
.17
1833
37.9
7484
6.66
7T
est 3
1481
.496
10.2
1455
492
0.00
006
6032
8377
02.3
722
6407
.978
635
Tes
t 420
84.2
2314
.370
2111
20.
0000
770
3352
9913
.21
2311
80.6
0463
5T
est 5
1344
.742
9.27
1669
318
0.00
008
8025
7679
06.4
217
7663
.453
846.
667
Tes
t 614
40.9
769.
9351
7936
3N
/AN
/AN
/AN
/AN
/AT
est 7
1755
.003
12.1
0031
922
N/A
N/A
N/A
N/A
N/A
Tes
t 811
19.3
537.
7176
6693
2N
/AN
/AN
/AN
/AN
/AT
est 9
2124
.743
14.6
4958
667
N/A
N/A
N/A
N/A
N/A
AV
G15
59.4
3944
410
.751
9560
30.
0000
8484
2636
0066
.23
1817
46.2
5176
2.00
02St
. Dev
.35
9.72
1590
52.
4801
9295
43.
2094
E-0
532
.093
6131
8220
296.
376
5667
6.94
611
5.93
4790
6St
. Err
or11
9.90
7196
80.
8267
3098
51.
4353
E-0
514
.352
7001
3676
228.
298
2534
6.70
0851
.847
6145
4
Tes
t 171
6.68
94.
9413
965
0.00
007
7013
7386
49.5
9472
4.64
9884
6.66
7T
est 2
704.
027
4.85
4095
086
0.00
009
9011
5987
15.2
7997
0.32
2884
6.66
7T
est 3
600.
195
4.13
8198
678
0.00
008
8010
5097
42.1
7246
2.11
7984
6.66
7T
est 4
916.
754
6.32
0796
059
0.00
007
7018
9091
1513
0373
.753
846.
667
Tes
t 573
9.48
25.
0985
4869
60.
0000
880
1477
2742
.53
1018
54.4
784
6.66
7T
est 6
1061
.105
7.31
6061
126
N/A
N/A
N/A
N/A
N/A
Tes
t 772
4.28
64.
9937
7596
9N
/AN
/AN
/AN
/AN
/AT
est 8
1000
.325
6.89
6997
796
N/A
N/A
N/A
N/A
N/A
Tes
t 665
3.37
84.
5048
8253
9N
/AN
/AN
/AN
/AN
/AA
VG
790.
6934
444
5.45
1639
161
0.00
0078
7813
9057
92.8
795
877.
0627
846.
667
St. D
ev.
161.
2934
212
1.11
2078
945
8.36
66E
-06
8.36
6600
2732
6605
7.99
2251
8.67
620
St. E
rror
53.7
6447
374
0.37
0692
982
3.74
17E
-06
3.74
1657
3914
6062
5.53
710
070.
6581
0
Tes
t 115
4.48
11.
0651
0895
60.
0000
440
4558
415
3142
9.16
3763
5T
est 2
192.
468
1.32
7020
090.
0000
440
6711
020
4627
0.85
2184
6.66
7T
est 3
162.
078
1.11
7488
425
0.00
004
4063
3116
143
651.
8166
846.
667
Tes
t 421
5.26
1.48
4165
392
0.00
004
4094
9679
365
478.
0884
6.66
7T
est 5
164.
611.
1349
4595
0.00
022
220
7464
13.8
5146
.341
7742
3.33
Tes
t 623
8.05
21.
6413
1069
30.
0000
550
6331
195
4365
2.05
184
6.66
7T
est 7
230.
445
1.58
8862
277
0.00
007
7039
5066
127
238.
8476
846.
667
Tes
t 820
5.13
1.41
4321
503
0.00
004
4067
1107
246
271.
2106
846.
667
Tes
t 934
9.48
12.
4095
8657
10.
0000
330
1380
1951
9516
1.09
8312
70A
VG
212.
445
1.46
4756
651
6.33
33E
-05
63.3
3333
3365
1540
9.08
944
922.
1624
823.
148
St. D
ev.
59.5
8601
444
0.41
0831
095.
9791
E-0
559
.791
3037
3636
891.
497
2507
5.48
3122
3.11
7030
1St
. Err
or19
.862
0048
10.
1369
4369
71.
993E
-05
19.9
3043
4612
1229
7.16
683
58.4
9437
74.3
7234
338
Tab
le 1
5: 5
0nm
Al c
ompo
site
pre
ssur
e te
sts
resu
lts.
Al/MoO3/TeflonAl/Teflon Al/MoO3
100k
100
k
10k
100k
10k
72
Texas Tech University, Kyle Watson, August 2007
73
Tes
t #Pe
ak P
ress
ure
(psi
)Pe
ak P
ress
ure
(MPa
)R
ise
Tim
e (µ
sec)
Ris
e T
ime
(sec
)R
ise
Rat
e (p
si/s
ec)
Ris
e R
ate
(MPa
/sec
)Pr
opag
atio
n R
ate
(m/s
)Sa
mpl
e R
ate
(pps
)
Test
111
19.3
537.
7176
6693
20.
0002
222
013
8863
7095
743.
147
211.
667
50 k
Test
267
8.70
24.
6794
8536
50.
0005
500
1882
471.
2912
979.
182
127
Test
356
7.27
33.
9112
0948
80.
0004
400
2570
455.
3317
722.
665
254
Test
426
8.44
21.
8508
4235
90.
0019
1900
2532
474.
5917
460.
797
84.6
67Te
st 5
397.
598
2.74
1341
594
0.00
0990
086
1038
.526
5936
.651
425
4
AV
G60
6.27
364.
1801
0914
80.
0007
8478
443
4656
1.95
2996
8.48
818
6.26
68St
. Dev
.32
6.99
1240
92.
2545
2514
70.
0006
7177
671.
7737
7153
7759
2.9
3707
7.19
676
.902
2364
2St
. Err
or14
6.23
4928
61.
0082
5429
70.
0003
0043
300.
4263
6424
0493
2.66
1658
1.42
634
.391
7256
5
Test
127
.857
0.19
2067
246
0.00
132
1320
2261
1.29
155.
8993
535
.277
7850
k
Test
258
.246
0.40
1592
016
0.00
1818
0070
907.
7548
8.89
171
50.8
Test
358
.246
0.40
1592
016
0.00
2929
0032
921.
8322
6.98
802
84.6
67Te
st 4
73.4
420.
5063
6474
40.
0024
2400
1381
3.06
95.2
3769
263
.5
AV
G54
.447
750.
3754
0400
50.
0021
0521
0535
063.
4825
241.
7541
958
.561
195
St. D
ev.
19.1
1982
326
0.13
1826
535
0.00
069
690
2513
9.84
7117
3.33
314
20.8
8267
553
St. E
rror
9.55
9911
631
0.06
5913
268
0.00
0345
345
1256
9.92
3686
.666
569
10.4
4133
776
Test
116
4.61
1.13
4945
950.
0002
121
083
0087
.857
23.2
537
254
Test
298
.767
0.68
0974
465
0.00
031
310
2894
25.2
1995
.516
423
0.90
91Te
st 3
96.2
330.
6635
0315
0.00
024
240
4305
2129
68.3
377
282.
222
Test
455
.714
0.38
4134
491
0.00
016
160
3376
67.1
2328
.132
623
0.90
91Te
st 5
144.
351
0.99
5265
068
0.00
031
310
4689
74.9
3233
.468
211.
6667
Test
615
7.01
31.
0825
6648
10.
0002
424
054
6482
.437
67.8
634
230.
9091
AV
G11
9.44
80.
8235
6493
40.
0002
4524
548
3859
.733
3336
.095
324
0.10
2666
7St
. Dev
.42
.660
4210
50.
2941
3323
75.
8224
E-0
558
.223
7065
1928
93.3
1329
.952
424
.614
3995
2St
. Err
or17
.416
0439
60.
1200
7939
12.
377E
-05
23.7
6972
8678
748.
3598
542.
9508
10.0
4878
652
Tab
le 1
6: 1
-3 µ
m A
l com
posi
te p
ress
ure
test
res
ults
.Al/MoO3/TeflonAl/Teflon Al/MoO3
50k
10k
10k
Texas Tech University, Kyle Watson, August 2007
74
Appendix C Additional Figures
Texas Tech University, Kyle Watson, August 2007
0.00
0
200.
000
400.
000
600.
000
800.
000
1000
.000
1200
.000
0%20
%40
%60
%80
%10
0%
Mas
s P
erce
nt A
lum
inum
Flame Propagation Rate (m/s)
Al/T
eflo
nAl
/MoO
3/Te
flon
Al/M
oO3
Figu
re 2
1: C
onfin
ed b
urn
resu
lts o
f com
posit
es c
onta
inin
g 50
nm
Al
75
Texas Tech University, Kyle Watson, August 2007
0.00
0
50.0
00
100.
000
150.
000
200.
000
250.
000
300.
000
350.
000
400.
000 0%
20%
40%
60%
80%
100%
Mas
s Pe
rcen
t Alu
min
um
Flame Propagation Rate (m/s)Al
/Tef
lon
Al/M
oO3/
Teflo
nAl
/MoO
3
Figu
re 2
2: C
onfin
ed b
urn
resu
lts o
f com
posit
es c
onta
inin
g 1-
3 μ m
Al
76
Texas Tech University, Kyle Watson, August 2007
77
0.00
0
100.
000
200.
000
300.
000
400.
000
500.
000
600.
000 0%
20%
40%
60%
80%
100%
Mas
s P
erce
nt A
lum
inum
Flame Propagation Rate (m/s)
Al/T
eflo
nA
l/MoO
3/Te
flon
Al/M
oO3
Figu
re 2
3: O
pen
burn
res
ults
of c
ompo
site
s con
tain
ing
50 n
m A
l
Texas Tech University, Kyle Watson, August 2007
78
0.00
0
0.50
0
1.00
0
1.50
0
2.00
0
2.50
0
3.00
0
3.50
0
4.00
0
4.50
0
5.00
0 0%20
%40
%60
%80
%10
0%M
ass
Per
cent
Alu
min
um
Flame Propagation Rate (m/s)
Al/T
eflo
nA
l/MoO
3/Te
flon
Al/M
oO3
Figu
re 2
4: O
pen
burn
res
ults
of c
ompo
site
s con
tain
ing
1-3 μm
Al
PERMISSION TO COPY
In presenting this thesis in partial fulfillment of the requirements for a master’s
degree at Texas Tech University or Texas Tech University Health Sciences Center, I
agree that the Library and my major department shall make it freely available for research
purposes. Permission to copy this thesis for scholarly purposes may be granted by the
Director of the Library or my major professor. It is understood that any copying or
publication of this thesis for financial gain shall not be allowed without my further
written permission and that any user may be liable for copyright infringement.
Agree (Permission is granted.)
Kyle William Watson_______ _________________ June 12, 2007____ Student Signature Date Disagree (Permission is not granted.) _______________________________________________ _________________ Student Signature Date