Laser Ignition of Energetic Materials

Dr S Rafi Ahmad founded and led the Centre for Applied Laser Spectroscopy (CALS) within the Department of Applied Science, Security and Resilience, Cranfield University from 1988 to 2013. He has been active for the last 3 decades in managing/supervising many R&D projects and PhD research students in the field of directed laser and applied laser spectroscopy. Dr Ahmad has authored 52 peer-reviewed publications in scientific journals, and co-authored a book with Dr Cartwright.Dr Michael Cartwright works on novel explosive compounds and the design of safer formulations and disposal of time expired and unexploded ordnance. He graduated in Chemistry from London University in the 1960s. His first employment was with the UKAEA at Windscale and Calder Hall establishment examining analytical methods for novel nuclear fuels and processing technologies. He researched on sterilisation methods for the Milton Division of Vick International followed by research in nuclear damage processes in solids and organo-metallic chemistry at the University of Bath before moving to Cranfield University at the Royal Military College of Science in 1986. Dr Cartwright has authored over 80 papers in refereed journals and published conference proceedings, and a co-authored book.

• About the Authors xiii Preface xvAcknowledgements xvii1 Historical Background 11.1 Introduction 11.2 The Gunpowder Era 21.3 Cannons, Muskets and Rockets 21.3.1 Musketry 71.3.2 Rocketry 91.4 Explosive Warheads 91.5 Explosives Science 11Bibliography 142 Review of Laser Initiation 172.1 Introduction 172.2 Initiation Processes 192.3 Initiation by Direct Laser Irradiation 212.3.1 Laser Power 212.3.2 Laser Pulse Duration 222.3.3 Absorbing Centres 222.3.4 Pressed Density 232.3.5 Strength of Confining Container 242.3.6 Material Ageing 252.3.7 Laser-Induced Electrical Response 252.4 Laser-Driven Flyer Plate Initiations 252.5 Summary and Research Rationale 272.5.1 Rationale for Research 28Bibliography 29References 293 Lasers and Their Characteristics 353.1 Definition of Laser 353.2 Concept of Light 363.3 Parameters Characterizing Light Sources 393.4 Basic Principle of Lasers 453.5 Basic Technology of Lasers 473.6 Comparison between Laser and Thermal Sources 483.7 Suitable Laser Sources for Ignition Applications 493.7.1 Nd:YAG Laser 503.7.2 Light Emitting Diodes (LEDs) 503.7.3 Diode Lasers 523.8 Beam Delivery Methods for Laser Ignition 533.8.1 Free Space Delivery 533.8.2 Fibre Optics Beam Delivery 543.9 Laser Safety 573.9.1 Laser Interaction with Biological Tissues 573.9.2 Precaution against Ocular Hazards 57Bibliography 594 General Characteristics of Energetic Materials 614.1 Introduction 614.2 The Nature of Explosions 614.3 Physical and Chemical Characteristics of Explosives 634.4 Fuel and Oxidizer Concept 644.4.1 Explosive Mixtures 664.4.2 Pyrotechnics 694.4.3 Rocket Propellants 734.5 Explosive Compounds 744.5.1 Chemical Classification 744.6 Thermodynamics of Explosions 804.6.1 Oxygen Balance 82Appendix 4.A 83A.1 Data for Some Explosives 83A.1.1 TNT (Trinitrotoluene) 83A.1.2 HNS(Hexanitrostilbene) 83A.1.3 DATB (1,3,Diamino,2,4,6,trinitrobenzene) 84A.1.4 TATB (1,3,5,-Triamino-2,4,6-Trinitrobenzene) 84A.1.5 Picric Acid (2,4,6,trinito- hydroxy benzene) 84A.1.6 Styphnic Acid (2,4,6,trinito-1,3, dihydroxy benzene) 84A.1.7 Tetryl or CE (Composition Exploding) 85A.1.8 PICRITE (Niroguanidine) 85A.1.9 RDX (Research Department eXplosive) 85A.1.10 HMX (High Molecular-weight eXplosive) 85A.1.11 EGDN (Nitroglycol) 86A.1.12 NG (Nitroglycerine) 86A.1.13 NC (Nitro-Cellulose) 86A.1.14 PETN (Pentaerythritol Tetranitrate) 87A.1.15 Metal Salts 87A.2 Unusual Explosives 88A.2.1 Tetrazene 88Bibliography 895 Recent Developments in Explosives 915.1 Introduction 915.2 Improvements in Explosive Performance 915.2.1 Heat of Explosion ΔHc (Q) 915.2.2 Density of Explosives 925.3 Areas under Development 925.3.1 New Requirements for Explosive Compositions 935.4 Plastic-Bonded High Explosives 955.4.1 Plastic-Bonded Compositions 955.4.2 Thermoplastics 965.4.3 Thermosetting Materials 965.5 Choice of High Explosive for Plastic Bonded Compositions 975.6 High-Energy Plastic Matrices 975.7 Reduced Sensitivity Explosives 995.8 High Positive Enthalpies of Formation Explosives 1015.8.1 High Nitrogen-Containing Molecules 1025.8.2 Pure Nitrogen Compounds 1025.8.3 Other High-Nitrogen Compounds 1045.8.4 Nitrogen Heterocycles 105Glossary of Chemical Names for High-Melting-Point Explosives 113Bibliography 113References 1136 Explosion Processes 1176.1 Introduction 1176.2 Burning 1176.3 Detonation 1236.4 Mechanism of Deflagration to Detonation Transition 1246.5 Shock-to-Detonation 1276.6 The Propagation of Detonation 1286.7 Velocity of Detonation 1296.7.1 Effect of Density of Loading 1316.7.2 Effect of Diameter of Charge 1316.7.3 Degree of Confinement 1316.7.4 Effect of Strength of Detonator 1326.8 The Measurement of Detonation Velocity 1336.9 Classifications of Explosives and Pyrotechnics by Functions and Sensitivity 1336.10 The Effects of High Explosives 1356.10.1 Energy Distribution in Explosions 1356.11 Explosive Power 1376.12 Calculation of Q and V from Thermochemistry of Explosives 1386.12.1 General Considerations 1386.12.2 Energy of Decomposition 1386.12.3 Products of the Explosion Process 1396.13 Kistiakowsky - Wilson Rules 1406.14 Additional Equilibria 1416.15 Energy Released on Detonation 1426.16 Volume of Gases Produced during Explosion 1446.17 Explosive Power 1456.17.1 Improving Explosives Power 1466.18 Shockwave Effects 1476.19 Appendices: Measurement of Velocity of Detonation 149Appendix 6.A: Dautriche Method 149Appendix 6.B: The Rotating Mirror Streak Camera Method 151Appendix 6.C: The Continuous Wire Method 152Appendix 6.D: The Event Circuit 152Bibliography 153References 1537 Decomposition Processes and Initiation of Energetic Materials 1557.1 Effect of Heat on Explosives 1557.2 Decomposition Mechanisms 1627.2.1 Thermal Decomposition Mechanism of TNT 1637.2.2 Non-Aromatic Nitro Compounds 1647.2.3 Nitro Ester Thermal Decomposition 1677.2.4 Nitramine Thermal Decomposition 1687.2.5 Photon-Induced Decomposition Mechanisms 1697.3 Practical Initiation Techniques 1727.3.1 Methods of Initiation 1737.3.2 Direct Heating 1747.3.3 Mechanical Methods 1757.3.4 Electrical Systems 1777.3.5 Chemical Reaction 1777.3.6 Initiation by Shockwave 1787.4 Classification of Explosives by Ease of Initiation 1787.5 Initiatory Explosives 1797.5.1 Primary Explosive Compounds 1797.5.2 Primer Usage 1817.6 Igniters and Detonators 1827.7 Explosive Trains 1837.7.1 Explosive Trains in Commercial Blasting 187Bibliography 190References 1908 Developments in Alternative Primary Explosives 1938.1 Safe Handling of Novel Primers 1938.2 Introduction 1938.3 Totally Organic 1948.4 Simple Salts of Organics 1998.5 Transition Metal Complexes and Salts 2028.6 Enhancement of Laser Sensitivity 206References 207Appendix 8.A: Properties of Novel Primer Explosives 211Appendix 8.B: Molecular Structures of Some New Primer Compounds 213Purely Organic Primers 2139 Optical and Thermal Properties of Energetic Materials 2219.1 Optical Properties 2219.1.1 Introduction 2219.1.2 Theoretical Considerations 2229.1.3 Practical Considerations 2259.1.4 Examples of Absorption Spectra 2269.2 Thermal Properties 2319.2.1 Introduction 2319.2.2 Heat Capacity 2329.2.3 Thermal Conductivity 2329.2.4 Thermal Diffusivity 233References 23410 Theoretical Aspects of Laser Interaction with Energetic Materials 23510.1 Introduction 23510.2 Parameters Relevant to Laser Interaction 23610.2.1 Laser Parameters 23610.2.2 Material Parameters 23610.3 Mathematical Formalism 23710.3.1 Basic Concept 23710.3.2 Optical Absorption 23810.3.3 Optical Reflection 24010.4 Heat Transfer Theory 240References 24511 Laser Ignition – Practical Considerations 24711.1 Introduction 24711.1.1 Laser Source 24811.1.2 Beam Delivery System 24911.2 Laser Driven Flyer Plate 24911.3 Direct Laser Ignition 25011.3.1 Explosives 25111.3.2 Propellants 25911.3.3 LI of Pyrotechnic Materials 263References 26712 Conclusions and Future Prospect 26912.1 Introduction 26912.2 Theoretical Considerations 26912.3 Lasers 27012.4 Optical and Thermal Properties of Energetic Materials 27112.5 State of the Art: Laser Ignition 27112.6 Future Prospect 272References 274Index 275