Introduction to the Combustion of Energetic Materials

Transcription

1 Introduction to the Combustion of Energetic Materials Steve Son There is not a law under which any part of this universe is governed which does not come into play, and is not touched upon, in [the phenomena of a candle]. - Michael Faraday, 1861 Note: This predated theory of relativity

2 What are energetic materials? In general, this term is for combustible materials that require no additional oxygen Some may after burn with air, that is they are fuel-rich Energetic materials include (by application) Propellants (guns, rockets, actuators, air bags, ) Explosives (rapidly release energy, and generally gas, in explosive systems) Pyrotechnics (fireworks, igniters, incendiaries, )

3 History of Energetic Materials Roger Bacon ( ) brought the knowledge of black powder to Europe Kept the secret to himself

4 Albertus Magnus St. Albert the Great (Ca ) Spread knowledge of black powder across Europe

5 Alfred Nobel Family business was production of nitroglycerine Factory destroyed in 1864 Developed fulminate detonator Developed dynamite and blasting gelatine

6 Energetic Materials Energetic Materials (No oxidizer needed, temperature sensitive reactions, highly exothermic) Explosives Propellants Pyrotechnics

7 Power Densities Acetylene/air flame 10 2 W/cm 3 Deflagration of an energetic material (e.g. a gun propellant 10 6 W/cm 3 Detonating High Explosive W/cm 3

8 Applications Continued Blasting explosives for mining, tunneling, demolition, and weaponry Explosive bolts and actuators Propellants for rockets Gas generators, for airbag inflators: rapidly produce large amount of gas to inflate a nylon or polyester bag in some 50 milliseconds (inflates at 100 m/s) Light generators (sparklers), for fireworks or for rescue signals, including underwater signals: produce bright light (yellow-white by hot emission at >1500 K) and colored shimmering sparks Fire generators/heat generators, for domestic use (matches, fuel pellets for field stoves) or military purpose (incendiary grenades; thermites) Smoke generators, for rescue signals or military purpose (smoke grenades) Noise generators (firecrackers), for fireworks, for rescue signals, stungrenades Combustion synthesis Microthrusters, microactuators, micropyrotechnics

9 EM-Explosives Explosives (generates gas and heat rapidly) High Explosives (Easily detonatable) (Some propellants) Low Explosives (Hard to detonate) (Includes many propellants)

10 Pressure Output = f(ρ, N, M, Q)

11 A Variety of Structures and Energies

12 Monomolecular EMs Have Oxygen and Fuel on same Molecule What is the fuel? What is the oxygen? HMX Deflagrating or detonating

13 What Are Plastic-Bonded Explosives? NO 2 O N 2 N N N NO 2 N O 2 N HMX (95%) + Estane (2.5%) + BDNPA/F (2.5%) Equals...

14 Photomicrograph Of A Pressed Plastic-Bonded Explosive HMX grains PBX 9501 Photo courtesy of Dave Phillips and Cary Skidmore

15 EM-Explosives-High Explosives High Explosives (HE) Primary Explosives (Tend to be sensitive) (DDT in small samples unconfined) Examples: Lead Azide Mercury Fulminate Lead Styphnate (all listed are monomolecular ) Secondary Explosives (Less sensitive) (Detonate in resonable quantities) Examples: RDX, HMX, TNT, TATB (an insensitive high explosive ( or IHE)), Dynamites (a composite HE), ANFO (another composite) Tertiary Explosives (Often oxidizers) (Detonate in LARGE quantities) Examples: Ammonium Nitrate (AN) Ammonium Perchlorate (AP) Mononitrotoluene

16 EM-Propellants Propellants Monopropellants Examples: Nitromethane Hydrazine HAN Liquid Composite propellants Examples: LH2/LOX LOX/FO Hybrids i.e. LOX/HTPB Homogeneous Examples: NC (nitrocellulose, a single base ) NC/NG (a double base ) NC/NG/RDX (a triple base ) Solid Composite Examples: AP/HTPB AP/HTPB/Al NC/NG/RDX/Al/AP RDX/HTPB/Al/AP

17 Propellants

18 Energy Thermodynamic energy densities of monomolecular and composite systems High energy ADN / Al max. 23.kJ/cc Compression moldable Strategic propellants CL-20 (neat) 12.6 Tritonal 12.1 HMX (neat) 11.1 LX TATB (neat) 8.5 Comp. C-4 as used 8.0 LX TNT (neat) 7.6 Low energy

19 EM-Pyrotenics (i.e., everything else!) Energetic Materials Pyrotechnics Note: The international community will use pyrotechnics the same as EMs Examples: Fireworks of various kinds, Thermite (Redox, e.g. Al+Fe 2 O 3 ), intermetalic (e.g. Al+Ni), Igniters, Incendiaries Black Powder is interesting: 1) r~p, produces both gas and solid products 2) Has been used as a propellant (guns) 3) Used as a fuse (safety fuse) 4) Used extensively before dynamite and NC/NG as an explosive (low explosive) 5) Has not been observed to detonate, but effects often not much different 6) Tends to be rather spark sensitive (must be careful!)

20 Why study energetic materials? Exciting area of combustion science Unique combustion regimes (especially multiphase) Room for improvement (rich problems) Insensitive materials (USS Forrestal, USS Enterprise, other accidents -- I have PBS videos of these accidents) Safety issues (safer materials and systems needed) New requirements, most do not meet desired standards Higher performance Combustion synthesis Improved actuators (air bags) Advanced propulsion (fast, cheap, etc.) Applications to global war on terrorism Microscale energetic materials, micropyrotechnics, microactuators, microthrusters

21 Why study energetic materials? Room for improvement (rich problems) - cont d Green energetics will remain an issue Inorganic perchlorate compounds react to form the highly objectionable hydrogen chloride, HCl, combustion product In the presence of ambient water vapor, HCl product reacts to form hydrochloric acid aerosol, which appears on the EPA List of Toxic Chemicals Other toxic chemicals, e.g., potassium perchlorate, polyvinyl chloride, hexachlorobenzene ingredients, are present in many of the formulations/combustion products

22 Why study energetic materials? Room for improvement (rich problems) - Cont d Green energetics will remain an issue Non-chlorine containing inorganic nitrates do not produce HCl, i.e., better suited for oxidizers for green energetics, however, they lag in performance Many strategies for the reduction or elimination of HCl are considered New oxidizers/energetics: high-nitrogen compounds, energetic polymers/binders, optimized crystal structures (e.g., see papers in MRS Proceedings Volume 418 Decomposition, Combustion, and Detonation Chemistry of Energetic Materials, 1996), refs. 2,3 Lead-containing energetics (e.g. those found in primers and detonators) are also a concern