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

Texas Tech University, Kyle Watson, August 2007

ii

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.


iii

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


v

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.


vi

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


vii

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


viii

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


1

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


2

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


3

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


4

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


5

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


6

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


7

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


8

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.


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

9


10

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


11

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


12

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


13

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


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


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


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


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.


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


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


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


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


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


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


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


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


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.


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


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


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


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


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


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


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


34

0

50

100

150

200

250

300

350

400

450

0% 20% 40% 60% 80% 100%


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%


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.


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


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%


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


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


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.


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


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.


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.


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%


Flam

e Pr

opag

atio

n (m

/s)

50 nm Al

1-3 µm Al

Figure 15: Al/Teflon confined apparatus burn results.

42


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%


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


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


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.


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


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


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

48


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


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


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


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.


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.

53


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


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).


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


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


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


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


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.


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.


62

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66

Appendix A Detailed high-speed camera data


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

.


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


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


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


71

Appendix B Detailed pressure transducer data


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


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


74

Appendix C Additional Figures


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


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


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


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


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


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

kyle watson- fast reaction of nano-aluminum: a study on fluorination versus oxidation

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200nm zonyl

texas tech

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chemical equilibrium

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open burn