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Overview of Energetic Materials Design for Army Systems

Kenneth K. KuoKenneth K. KuoThe Pennsylvania State UniversityThe Pennsylvania State University

University Park, PA 16802University Park, PA 16802

Presented at Presented at

NanoNano--Engineered Energetic Materials (NEEM) Engineered Energetic Materials (NEEM) MURI Kickoff MeetingMURI Kickoff Meeting

University Park, PAUniversity Park, PASeptember 14, 2004September 14, 2004

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General Usage of Solid Propellants as Energetic Materials

Military Applications:For producing high-temperature combustion products to generate thrust for missile propulsionFor generating high-pressure and high-temperature gases to hurl projectiles containing warheads or other objects

Commercial Applications:For rapid filling of automobile air bagsRockets for launching earth satellites Connection of electrical cablesEmergency airplane crew escape systemsMining, construction, etc.

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List of Ingredients used for Homogeneous(Double-Base) & CMDB Propellants

Plasticizer (oxidizer & fuel)NG: nitroglycerinTMETN: trimethylolethane trinitrateTEGDN: triethylene glycol dinitrateDEGDN: diethylene glycol dinitrate

Plasticizer (fuel)DEP: diethylphtalateTA: triacetinePU: polyurethane

Binder (fuel & oxidizer)NC: nitrocellulose

StabilizerEC: ethyl centralite2NDPA: 2-nitrodiphenilamine

Burning rate catalystPbSa: lead salicylatePbSt: lead stearatePb2EH: lead 2-ethylhexoateCuSa: copper salicylateCuSt: copper stearateLiF: lithium fluoride

High energy additiveRDX: cyclotrimethlyene trinitramineHMX: cyclotetramethylene

tetranitramineNGD: nitroguanidineADN: ammonium dinitramide

CoolantOXM: oxamide

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List of Ingredients used for Homogeneous Double-Base & CMDB Propellants (Continued)

OpeciferC: carbon black

Flame suppressantKNO3: potassium nitrateK2SO4: potassium sulfate

Metal fuelAl: aluminum

Combustion instability suppressantAl: aluminumZr: zirconiumZrC: zirconium carbide

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Flames of a Double-base Propellant at Different Pressures

p=10 atm

rb=2.2 mm/s

p=20 atm

rb=3.1 mm/s

p=30 atm

rb=4.0 mm/s

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Photograph of Two JA2 Propellant Strands Burning in an Opposing Configuration

This picture shows flow turning & carbonaceous residue ejection from the burning surfaces of the two opposing propellant strands.

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Temperature Profile of a Double-Based Propellant Flame

FOAM OR MELT LAYER

RONO2NO2

R’CHO

NO, H2

CO, CO2

N2, CO

CO2, H2O

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List of Ingredients Used for Heterogeneous (Composite) Propellants

OxidizerADN:ammonium dinitramideAP: ammonium perchlorateAN:ammonium nitrateNP:nitronium perchlorateKP:potassium perchlorateRDX:cyclotrimethylene trinitramineHMX: cyclotetramethylene

tetranitramineHNF: hydrazinium nitroformateDADNE (FOX-7):1,1-Diamino-2,2-

dinitroethylene

BinderPS: polysulfidePVC: polyvinyl chloridePU: polyurethaneCTPB: carboxyl terminatedpolybutadieneHTPB: hydroxyl terminated polybutadieneGAP: glycidyl azide polymer

Curing or crosslinking agentsPQD: paraquinone dioximeTDI: toluene-2, 4-diisocyanateMAPO: tris{1-(2-methl) aziridinyl} phosphine oxideERLA-0510: N,N,O-tri (1,2-epoxy propyl)-4-aminophenoIPDI: isophorone diisocyanate

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List of Ingredients Used for Heterogeneous(Composite) Propellants (Continued)

Bonding agentMAPO: tris{1-(2-methl)

aziridinyl} phosphine oxideTEA: triethanolamineMT-4: adduct of 2.0 moles

MAPO, 0.7 mole azipic acid, and 0.3 mole tararic acid

PlasticizerDOA: dioctyl adipateIDP: isodecyl pelargoneteDOP: dioctyl phthalate

Burning Rate CatalystFe2O3: ferric oxideFeO (OH): hydrated ferric oxidenBF: n-butyl ferroceneDnBF: di-n-butyl ferroceneLif: lithium fluoride

Metal FuelAl: aluminumMg: magnesiumBe: berylliumB: boron

Combustion Instability SuppressantAl: aluminumZr: zirconiumZrC: zirconium carbide

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Several Commonly Used Explosives

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Physicochemical Processes in the

Combustion of Nitramine Composite Propellants

Luminous final flame

Decomposed and reacted gaseous products

Preparation zone for the final flame

First stage reaction zone

Radiative heat feedback to

surface

Solid RDX or HMX crystal

Solid fuel binder

Decomposed fuel gases

Decomposed fuel gases

Vapor phase RDX or HMX

Liquid melt layer

Products of heterogeneous

reaction

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Desirable Features of Solid Propellants

•Deliver high specific impulse (Isp) and high impetus (Im)

• Generate high flame temperature and low molecular weight combustion products

• Has high propellant density for achieving high ρprIsp• Be environmentally friendly

-Reduced levels of NOx, SOx, CO, & other undesirable gases (e.g., HCl)-Reduced particulates

• Possess low vulnerability characteristics for insensitive munitions-Thermally stable (up to 180° C)-Reduced ESD hazards-Reduced impact, friction, and shock sensitivity

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Desirable Features of Solid Propellants (Continued)

•Good physical properties (mechanical and thermal)-Low glass transition temp (<-60°C) -High dewetting stress-Low thermal expansion coefficient -High fracture toughness-Low absorption of moisture -Strong bonding properties

•Have low-hazard manufacturing and easy-handling characteristics•Have long-term storage capability and suitable aging characteristics•Produce minimum smoke thus reducing chances of detection•Require low manufacturing cost•Possess desirable burning characteristics

-Low pressure exponent (n) for propellant burning rate-Low temperature sensitivity (σp, Πk)-Low sensitivity to cross-flow velocity (erosive burning)-Suitable ignition behavior-High reproducibility in ignition and burning characteristics

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Different Types of Propellant Grains for Various Gun Ballistic Applications

Fast Core Disc Propellant

Ball Propellants

Cylindrical Grain

Center Perforated Propellant Grain

Stick Propellant Grain

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Many Different Types of Propellant Grains for Various Rocket Applications

Thru

stTh

rust

Thru

st

Thru

stTh

rust

Thru

st

Time

Time

Time

Time

Time

TimeTubular

Rod and tube

Double anchor Dual composition

Multi-fin

Star

Progressive

Neutral

Dual thrust

Neutral

Two-stepthrust

Regressive

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Important Properties Associated withSolid Propellant & Its Burning Rate Law

SYMBOL DESCRIPTIONa (Ti) Pre-exponential factor of the Saint Robert’s burning rate law ( ) n

b ir a T P=for propellant at an initial temperature of Ti

n Pressure exponent in the above burning rate lawao Pre-exponential factor of the Saint Robert’s burning rate law for propellant

at an initial reference temperature, Ti,ref i.e., ,( ) exp ( )i o P i i refa T a T Tσ = −

σP Temperature sensitivity, 1 bP

b i P

rr T

σ ∂

≡ ∂ A Arrhenius pre-exponential factor [ ]exp /b a u sr A E R T= −Ea Activation energyQs Net heat release from the burning surface reactionλP Thermal conductivity of the propellantb Coefficient in the following surface temperature vs. pressure relationship:

,( ) ( )ms s ref refT T b P P− = −

m Exponent in the above surface temperature vs. pressure relationship

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Advantages of Energetic Nano-particles for Combustion and Propulsion

Faster ignitionHigher specific surface area enhances rate of heat transferHigher reactivity of nano-sized energetic materials

Burning time for nano-particles much shorter than large particlesD2-law for particle burning implies that a factor of 10 decrease in D results in a reduction of 100 in burn timeLeading to more complete combustion in volume-limited propulsion systems

Structural properties and gelling capabilitiesNano-particles can provide greater flexibility in designing new energetic fuels/propellants with desirable physical propertiesNano-particles can act as gelling agent for liquids (no inert or low-energy gellant necessary)

Higher density for increased propulsive performance Most energetic additives (e.g., Al, B, and Ti) have higher density than conventional fuel ingredients and oxidizer particles leading to increased density impulse when they are incorporated into propellants/fuels.

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Heats of Oxidation and Densities for Several Energetic Fuels in Comparison with HTPB

0

20

40

60

80

100

120

140

Alum

inum

(Al)

Boro

n (B

)

Bery

llium

(Be)

Car

bon

(C)

Iron

(Fe)

Lith

ium

(Li)

Mag

nesi

um (M

g)

Silic

on (S

i)

Tita

nium

(Ti)

Tung

sten

(W)

Zirc

oniu

m (Z

r)

HTP

B

Gravimetric Heat of Oxidation [kJ/gmfuel

]

Volumetric Heat of Oxidation [kJ/cm3fuel

]

Material Density [g/cc]Aluminum 2.700

Boron 2.340 Beryllium 1.850 Carbon 2.267

Iron 7.870 Lithium 0.534

Magnesium 1.740 Silicon 2.330

Titanium 4.510 Tungsten 19.300 Zirconium 6.520

HTPB 0.920

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Why Nano-Sized Energetics are Attractive for Combustion Enhancement

The higher volumetric heat of oxidation in combination with the higher densities make these fuels (i.e. B, Al, W, etc.) beneficial for use in volume limited propulsion systems.Nano-sized boron particles are highly attractive since the residence time is less of an issue due to the decreased ignition delay and combustion times.The relatively high volumetric heat of oxidation of aluminum and short ignition delay have made it a main focus of nano-particle combustion research.Many researchers have tested the effect of nano-sized Al particles on the propulsive performance of solid propellants and solid fuels and found positive effects.

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Numerous Design Parameters for Solid Propellant Formulation Consideration

Future gun/rocket propellants can be tailored with properly formulated and designed nano energetic materials, having:

• Suitable chemical composition with planned spatial distribution of chemical ingredients in propellant grain;• Desirable physical structure (including nano-sized ingredients and detailed structural arrangement);• Special coating of nano-sized energetic materials to posses IM characteristics; and • Desirable and compatible propellant grain geometry for achieving high ballistic performance.

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Thank you very much for your attention!!

Any questions or comments?

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Parameters & Properties of Solid Propellants Important for Their Transient Burning Behavior

SYMBOL DESCRIPTION λg Average thermal conductivity of gaseous product

adjacent to the propellant surface Cg Average constant-pressure specific heat of gaseous

product adjacent to the propellant surface Qs Net rate of heat release at the surface reaction region φc,s Solid-phase temperature gradient at the propellant

surface as a function of chamber pressure and mass burning rate (Zel’dovich map)

Yox Oxidizer loading fraction in the composite propellant

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Important Material Properties Related to the Foam Layer of Solid Propellants

SYMBOL DESCRIPTION ρ1 Density of the liquid µ Viscosity of the liquid C1 Specific heat of the liquid λ1 Thermal Conductivity of the liquid σ1-g Surface tension of the liquid Tmelt Liquefaction or melting temperature Eak Activation energy of the kth gas-phase reaction Bk Frequency factor of the kth gas-phase reaction αk Temp. exponent of the frequency factor of the kth

gas-phase reaction CPi Constant-pressure specific heat of the ith gas-

phase species

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Solid-Propellant Properties Governing Mechanical Deformation & Crack Propagation Process

SYMBOL DESCRIPTION aT Time-temperature shift factor in Schapery’s crack propagation

velocity equation: 11 ( )qcp I

T

AV Ka

= , where KI is the opening mode

stress intensity factor Erel Relaxation modulus of solid propellant under normal stresses go Equilibrium shear modulus, i.e., the asymptotic value of the relaxation

modulus for long periods of time G Relaxation modulus of solid propellant in shear

Vcp Crack propagation speed defined in ( ) qcp

PV a b Jt

∂= +

∂, where J is the

local J-integral value at the crack tip K Bulk modulus of elasticity 3kk kkKσ ε=

KIC Fracture toughness of solid propellant JIC Cohesive fracture resistance of solid propellant

g1…gm Coefficients of the Prony Series defined 1

exp( )Mo m mm

G g g β τ=

= + −∑

β1…βm Inverse relaxation times of the Prony Series defined above ν Poisson’s ratio ( )( )

2(1 )relEG

vττ =+

and ( )( )3(1 2 )

relEKvττ =

−

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Material Properties Related to Gas-PhaseFlame Region of Solid Propellants

SYMBOL DESCRIPTION CPi (T) Specific heat of the ith species as a

function of temperature Ea,n Activation energy of the nth reaction Dim Mass diffusivity of species i with

respect to the mixture λg (T) Thermal conductivity as a function of

temperature νg (T) Viscosity of gaseous mixture as a

function of temperature

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Physical, Thermal, Optical, & Sensitivity Properties of Propellants & Their Ingredients

Physical Properties Molecular Weight Melting Point Boiling Point Vapor Pressure as a Function of

Temperature Solubility in Different Solvents Volatility as a Function of Temperature Hygroscopicity as a Function of

Temperature and Relative Humidity Infrared Spectra Hardness Crystal and Optical Properties Crystalline Form (Crystal Structure) Unit Cell Dimensions Space Group Lattice Energy Refractive Energy Molar Refraction Bi Refringence Hazards Classification Transportation Classes Toxicity

Thermal Properties Heat of Formation Heat of Combustion Heat of Fusion Heat of Phase Transition Heat of Explosion Heat of Vaporization Heat of Detonation Free Energy of Formation Entropy at a Reference State Thermal Stability Coefficient of Thermal Expansion Sensitivity Properties Impact Sensitivity Brisance (Sand Test) Ballistic Mortar Initiation Sensitivity Electrostatic Discharge Sensitivity Dielectric Constant as a Function of

Temperature Shock Sensitivity Friction Sensitivity (Pendulum Tests) Confined “Cook-off” Temperature Explosion Temperature