polymers, propellants, and explosives a...

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?