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Polymers, Propellants, and Explosives –A Tutorial
By Richard R. Zito
Richard R. Zito Research LLC
3255 E. Lincoln St., Tucson AZ 85714
PART 1: BASICS
Types of Energetic Reactions (WISE Series C – Course 3)
Detonation: A supersonic decomposition reaction propagates through the energetic material to produce an intense shock in the surrounding medium, air, or water. All energetic material will be consumed in about 1 microsecond. This is the most violent reaction!
Partial Detonation: The amount of damage, relative to full detonation, depends on the proportion of material that detonates.
Explosion: Ignition and rapid burning of confined energetic material builds up high local pressures leading to violent pressure rupturing of the confining case or structure.
Deflagration: Involves a chemical reaction proceeding at subsonic velocity along the surface of and/or through an energetic material producing hot gases at high pressure (propulsion). The energetic material may be consumed in hundreds of milliseconds.
Burning: The energetic material ignites and burns non-propulsively. This is the least violent reaction.
The Explosive Train (WISE Series C – Course 3)
Large amounts of energetic material capable of detonation are almost never used in energetic subsystems! Instead…
“A sequence of energetic materials are used in an explosive train, beginning with a small amount of relatively sensitive material (e.g. lead azide) and proceeding through a series of explosives of increasing insensitivity and increasing quantity (e.g. nitrocellulose, TNT, etc.).”
Main ChargeBooster
Lead
S&A
Detonator
Why do some compounds explode?
An explosion involves the rapid evolution of both gas and energy (WISE Series C – Course 3). Consider sodium azide…..
2NaN (s) → 2Na(l) + 3N (g)3 2
N (azide ion)3-
N bond energy = 946 kJ/mole2
2
For binary compounds the N≡N bond energy is exceeded only by the C≡O (carbon monoxide) bond energy (1073 kJ/mole). Carbon monoxide is another important combustion product as well as CO (O=C=O) with a total bond energy of 2(695) 1390 kJ/mole.
m
Many azides are very explosive! Lead azide, mercury azide, and barium azide explode on impact and are used in detonation caps.
Ammonia is a basic raw material used in the manufacture of energetics.
Haber Process: N (g) + 3 H (g) → 2NH (g) DH= -46 kJ/mole2 32
Ammonia will react with both oxygen and water to yield:
NH + H O → NH + OH 23 4
+ -
NH + 2 O → H NO + H O3 2 23-+
Next Slide
Many nitrogen compounds are explosive!!!!
Chemical Name Formula Combustion Products Comments
ammonium nitrate (s) NH NO N O (g) + 2 H O (g) Can detonate by another high explosive (TNT) or traces of acid and chlorineion as catalysts.
4 3 2 2
Trinitrotoluene (s) (TNT) 2( C N O H )7 3 6 5 3N + 5H O + 7CO + 7C or
3 N + 5H + 12CO + 2C
2 2
2 2
High Explosive
NO
NOO N
HH
CH
2
223 “nitro”
group
Nitrogen Explosives, Propellants, and Oxidizers Continued…
Chemical Name Formula Combustion Products Comments
RDX (Research Department Explosive)
C H N O2 6 6 6
N N
N
High Explosive
NOO N
NO2
22
Propane- 1,2,3 trinitrate“nitroglycerine”)
C H N O3 5 3 9
Unstable colorless, oily, liquid.Will be discussed in detail later.
Chemical Name Formula Combustion Products Comments
Nitrogen Explosives, Propellants and Oxidizers Continued…
pentaerythritaltetranitrate (PETN)
C H N O5 8 4 12
NO
NO
O N
O N3
33
3
High Explosive
High Explosive and Propellant
cellulose nitrate (“nitrocellulose”)(Will be discussed in detail in the next section.)
Variable: C H N O
C H N O
C H N O
6 9 7
6 8 2 9
6 7 3 11
Chemical Name Formula Combustion Products Comments
Nitrogen Explosives, Propellants and Oxidizers Continued…
mercury fulminateO-N≡C-Hg-C≡N-O
Hg (ONC)2
Various:N , CO , HgO, CO, Hg, Hg(CN) , Hg(OCN) , Hg(OCN)CN
2
2
2
2
Will Detonate!
Lead Styphnate(lead 2,4,6 trinitroresorcinate)
NOO N22
NO2
O
O
-
-
2 -
Pb2+
Pb C H N O6 3 8
H
-
Will Detonate!
Chemical Name Formula Combustion Products Comments
Nitrogen Explosives, Propellants, and Oxidizers Continued…
Will Detonate!(less sensitive to friction)
diazo dinitro phenol (DDNP)
C H N O6 2 4 5
NO
NO
O N2 2
2
Ammonium Chlorate 2(NH ClO )4 3
(Heat)→
2NH Cl + 3 O (g)4 2Oxidizer for solid propellant
Ammonium Perchlorate 2(NH ClO )4 4 Oxidizer (more stable than chlorates)
(Heat)→ 2NH Cl + 4 O (g)4 2
Chemical Name Formula Combustion Products Comments
Nitrogen Explosives, Propellants, and Oxidizers Continued…
unsymmetrical dimethyl hydrazine (UDMH)
Rocket fuel (hypergolic with NO , LOX, or HNO )3
2C H N2 8 2
PEL = 0.5 PPMN-NH
HH C
H C3
3
hydrazoic Acid 2(HN ) 3N + H3 2 2 Colorless, dangerously explosive liquid.
sodium azide 2(NaN ) 2Na(l) + 3N (g)3 2
nitronium perchlorate NO ClO2 4Reacts violently with organic matter
Definition: Hypergolic fuel spontaneously ignites on contact with its oxidizer, or air.
Chemical Name Formula Combustion Products Comments
Nitrogen Explosives, Propellants, and Oxidizers Continued…
dinitrogen pentoxide 2(N O )2 5 4NO + O2 2 Colorless unstable crystals
N-O-NO
O
O
O
NO NO2+
3-
nitrogen fluorodichloride NFCl2 Explosive
tetraflurohydrazine N F2 4
Explosive reaction with hydrogen
Chemical Name Formula Combustion Products Comments
Nitrogen Explosives, Propellants, and Oxidizers Continued…
nitrogen trichloride NCl 3 A pale yellow explosive photosensitive oil
difluoroamine HNF2 A colorless explosive liquid
chlorine nitrate ClNO3 Reacts explosively with organic mater
fluorine nitrate FNO 3 Intrinsically explosive
Nitrogen dioxide + nitric acid
NO + HNO2 3
Powerful oxidizing agent with aniline
This list contains the more common and simpler nitrogen explosive, propellants, and oxidizers, and should not be considered complete!!!
NH2
Chemical Name Formula Combustion Products Comments
Non-Nitrogen Energetics
Lower aluminum alkyls AlR3 →+6H O
2
2Al(OH) + 3H3 2
A reactive liquid that is hypergolic in air, exploding with water.
Salts of aluminum hydride
AlH
H H
H
=AlH4-
M AlH+4- →
+4H O24H + Al(OH) + M OH
2 3+ -
Explosively hydrolyzed by water
Salts of gallium hydride M GaH4
+ -
Chemical Name Formula Combustion Products Comments
Non-Nitrogen Explosives Continued…
boron triiodide
B
I
I I
BI3 →
2H O2
3HI + B(OH)3
White solid below 43 C. Explosively hydrolyzed.
beryllium alkyls R-Be-R→
Be(OH) + H2 2 Hypergolic with air,
explosively hydrolyzed.methylpotassium KCH
3 Pyrophoric
hydrides NaH→H
+Na + H (g)+
2 The hydrides in general are very reactive with air and water (hypergolic).
(NaH, RbH, CsH, BaH)
This is only a partial list for the lighter elements.
3H O2
PART II: POLYMERS
What is a polymer?
Definition: A polymer is a large molecule (macromolecule) whose structure depends on the monomer(s) (small molecule(s)) used in its preparation. – M. Stevens
Note: Webster’s definition is wrong!!!
Let A and B be “monomer”, then several types of polymers are possible:
…..-A-A-A-A….. Homopolymer…..-A-B-A-B-A-B-……. Alternating Copolymer…..-A-A-B-A-B-B-A-B-…… Random Copolymer…..A-A-A-B-B-B-A-A-A-B-B-B-…… Block Copolymers
…….and there are many other variations on these basic schemes!
How are polymers formed?
Monomers must have reactive (“sticky”) ends.
Let R and R’ be monomers without their reactive end groups.Let g and g’ be reactive end groups.
Examples of monomer linkages:
1) g-R-g + g’-R’-g’ → …..-R-gg’- R’-g’g-R-…………… + NO WASTE PRODUCTS
A B ……-A-B-A-B-……… (alternating copolymer)Special Case:
g-R-g + g-R-g → ……-R-gg-R-gg-R-gg-……. + NO WASTE PRODUCTS
A A …..-A-A-A-A-A-…. (homopolymer)
Formation Continued….
The production of waste products complicates the simple picture.
Let R and R’ be monomers without their reactive end groups.Let g and g’ be reactive end groups.
Examples of monomer linkages:
1) g-R-g + g’-R’-g’ → …..-R-Link- R’-Link’-R-…………… + WASTE PRODUCTS (LEAVING GROUP)
A B ……-A-B-A-B-……… (alternating copolymer)
Where Link = gg’ minus waste productsLink’= g’g minus waste products
Note that g-R-g ≠ R-Link (although R is shared)and g’-R’-g’ ≠ R’-Link’ (although R’ is shared)
Formation Continued
Special Case:
g-R-g + g-R-g → ……-R-Link-R-Link-R-Link-……. + WASTE PRODUCTS (LEAVING GROUP)
A A …..-A-A-A-A-A-…. (homopolymer)
Link = gg minus leaving group
Note g-R-g ≠ R-Link. However, the sub-molecule R is shared.
Waste Products
Waste products (called leaving groups) are typically very small stable molecules like water (e.g. during polyester or cellulose formation) or carbon dioxide (e.g. during homopolymerization of isocyanate). The thermodynamic stability of these small molecules drives the equilibrium of polymer formation reactions to the right (completion).
An Example of Polymer Formation (Cellulose – a “natural” polymer)
H O2 b(1,4) Glycoside Linkage
14 4
(b pyranose Form)
Properties of Polymers
The Testing of Polymers
PART III: SIMPLE (1 COMPONENT) EXPLOSIVES AND MONERGOLS
What is “nitrocellulose” (cellulose nitrate)?
H NO3
(nitric acid)
H O2
+ -
-
Cell-OH + HNO → Cell-NO + H O3 23
Cellulose + nitric acid → “nitrocellulose” + water
How much nitrogen (nitrate) is enough?
“Gun Cotton”
All natural OH groups replaced(~13.5% N by wt.)
Harmless(lacquers, textile fibers, plastics)
-
Rocket Fuel
~2 OH groups replaced per ring (4 per unit)(10% N by wt.)
-
M13 rocket for the Katyusha launcher (Musée de l’Armée)Note: Cellulose nitrate will burn in space.
Note: First man-made plastic (Parkesine) 1862. Eventually became “celluloid”
What other “alcohols” can be made to explode?(Sugar, cellulose, and glycerin are all on the alcohol (OH ) family)-
│C│C│C│
OH
OH + HNO
OH
3
H O2OH │
C│C│C│
NO 3
NO 3
NO 3
Glycerol (“glycerin”)(1,2,3 propanetriol)
Glycerin nitrate (“nitroglycerin”)(1,2,3-Propane trinitrate)
“Dynamite” is nitroglycerin stabilized by absorption onto diatomaceous earth.- invented by Alfred Nobel in 1866
How much cellulose is enough?
Cotton90% cellulose
Munitions
Wood30-40% cellulose
Magicians flash paper
Oatmeal 3.3% cellulose
(by wt.)
Exploding cookies?!?!
PART IV: COMPOSITE ENERGETICS
Solid Propellants and Rocket Motors
NOZZLE
FUEL
BINDER (polyurethane)
OXIDIZER
“GRAIN”
CASING
Solid Propellants and Rocket Motors- Cont.
Thrust
Time
SOLID FUEL ROCKET MOTOR
O + H O
O + H O2 2
22
(Binder-casing interface)
Grain
Casing
Progressive Profile
Neutral Profile
Regressive Profile
What is Polyurethane?
Binder Formation Problems
1) Volumes of diisocyanate and dihydroxy compounds must be equal to within ±1%.2) Excess dihydroxy compounds result in suspension of liquid droplets.3) Excess diisocyanate → additional crosslinking → change in binder properties → less elastic binder.
Binder Formation Problems - Continued
4) Reaction of diisocyanate with water vapor forms polyuria and CO gas.2
WaterVapor
DISCARD!!!
Binder Formation Problems - Continued
5) Contamination of dihydroxy compounds with water vapor can result in gas bubbles when mixed with the diisocyanate. Some of these bubbles will remain in the solidified in the binder.
100 m
Gas Bubble
Polyurethane will react with oxygen in air!(Crosslinking Reactions – Hardening, Embrittlement)
A)
B)
Polyurethane will react with water vapor in air!(Scission Reaction – Softening, Weakening)
The net effect of aging after 8,151 days (22.32 years)
What is Viton?
Hexafluoro-propylene
vinylidene fluoride
1) Viton is a common binder for explosives.2) HF acid is a byproduct of viton combustion.3) Any combustion residue must be handled using protective equipment.
Summary
1) Types of energetic reactions.2) The explosive train.3) Why do some molecules explode?4) The structure of explosive molecules.5) What are polymers, how are they formed, and what are their properties?6) What are composite energetics?7) How do rocket motors work?8) What are polyurethane binders?9) What kind of chemical reactions can polyurethane binders undergo?10) What is a Viton binder and how is it formed?