Laser Ignition of Energetic Materials

Table of Contents:
About the Authors xiii Preface xv Acknowledgements xvii 1 Historical Background 1 1.1 Introduction 1 1.2 The Gunpowder Era 2 1.3 Cannons, Muskets and Rockets 2 1.3.1 Musketry 7 1.3.2 Rocketry 9 1.4 Explosive Warheads 9 1.5 Explosives Science 11 Bibliography 14 2 Review of Laser Initiation 17 2.1 Introduction 17 2.2 Initiation Processes 19 2.3 Initiation by Direct Laser Irradiation 21 2.3.1 Laser Power 21 2.3.2 Laser Pulse Duration 22 2.3.3 Absorbing Centres 22 2.3.4 Pressed Density 23 2.3.5 Strength of Confining Container 24 2.3.6 Material Ageing 25 2.3.7 Laser-Induced Electrical Response 25 2.4 Laser-Driven Flyer Plate Initiations 25 2.5 Summary and Research Rationale 27 2.5.1 Rationale for Research 28 Bibliography 29 References 29 3 Lasers and Their Characteristics 35 3.1 Definition of Laser 35 3.2 Concept of Light 36 3.3 Parameters Characterizing Light Sources 39 3.4 Basic Principle of Lasers 45 3.5 Basic Technology of Lasers 47 3.6 Comparison between Laser and Thermal Sources 48 3.7 Suitable Laser Sources for Ignition Applications 49 3.7.1 Nd:YAG Laser 50 3.7.2 Light Emitting Diodes (LEDs) 50 3.7.3 Diode Lasers 52 3.8 Beam Delivery Methods for Laser Ignition 53 3.8.1 Free Space Delivery 53 3.8.2 Fibre Optics Beam Delivery 54 3.9 Laser Safety 57 3.9.1 Laser Interaction with Biological Tissues 57 3.9.2 Precaution against Ocular Hazards 57 Bibliography 59 4 General Characteristics of Energetic Materials 61 4.1 Introduction 61 4.2 The Nature of Explosions 61 4.3 Physical and Chemical Characteristics of Explosives 63 4.4 Fuel and Oxidizer Concept 64 4.4.1 Explosive Mixtures 66 4.4.2 Pyrotechnics 69 4.4.3 Rocket Propellants 73 4.5 Explosive Compounds 74 4.5.1 Chemical Classification 74 4.6 Thermodynamics of Explosions 80 4.6.1 Oxygen Balance 82 Appendix 4.A 83 A.1 Data for Some Explosives 83 A.1.1 TNT (Trinitrotoluene) 83 A.1.2 HNS(Hexanitrostilbene) 83 A.1.3 DATB (1,3,Diamino,2,4,6,trinitrobenzene) 84 A.1.4 TATB (1,3,5,-Triamino-2,4,6-Trinitrobenzene) 84 A.1.5 Picric Acid (2,4,6,trinito- hydroxy benzene) 84 A.1.6 Styphnic Acid (2,4,6,trinito-1,3, dihydroxy benzene) 84 A.1.7 Tetryl or CE (Composition Exploding) 85 A.1.8 PICRITE (Niroguanidine) 85 A.1.9 RDX (Research Department eXplosive) 85 A.1.10 HMX (High Molecular-weight eXplosive) 85 A.1.11 EGDN (Nitroglycol) 86 A.1.12 NG (Nitroglycerine) 86 A.1.13 NC (Nitro-Cellulose) 86 A.1.14 PETN (Pentaerythritol Tetranitrate) 87 A.1.15 Metal Salts 87 A.2 Unusual Explosives 88 A.2.1 Tetrazene 88 Bibliography 89 5 Recent Developments in Explosives 91 5.1 Introduction 91 5.2 Improvements in Explosive Performance 91 5.2.1 Heat of Explosion ΔHc (Q) 91 5.2.2 Density of Explosives 92 5.3 Areas under Development 92 5.3.1 New Requirements for Explosive Compositions 93 5.4 Plastic-Bonded High Explosives 95 5.4.1 Plastic-Bonded Compositions 95 5.4.2 Thermoplastics 96 5.4.3 Thermosetting Materials 96 5.5 Choice of High Explosive for Plastic Bonded Compositions 97 5.6 High-Energy Plastic Matrices 97 5.7 Reduced Sensitivity Explosives 99 5.8 High Positive Enthalpies of Formation Explosives 101 5.8.1 High Nitrogen-Containing Molecules 102 5.8.2 Pure Nitrogen Compounds 102 5.8.3 Other High-Nitrogen Compounds 104 5.8.4 Nitrogen Heterocycles 105 Glossary of Chemical Names for High-Melting-Point Explosives 113 Bibliography 113 References 113 6 Explosion Processes 117 6.1 Introduction 117 6.2 Burning 117 6.3 Detonation 123 6.4 Mechanism of Deflagration to Detonation Transition 124 6.5 Shock-to-Detonation 127 6.6 The Propagation of Detonation 128 6.7 Velocity of Detonation 129 6.7.1 Effect of Density of Loading 131 6.7.2 Effect of Diameter of Charge 131 6.7.3 Degree of Confinement 131 6.7.4 Effect of Strength of Detonator 132 6.8 The Measurement of Detonation Velocity 133 6.9 Classifications of Explosives and Pyrotechnics by Functions and Sensitivity 133 6.10 The Effects of High Explosives 135 6.10.1 Energy Distribution in Explosions 135 6.11 Explosive Power 137 6.12 Calculation of Q and V from Thermochemistry of Explosives 138 6.12.1 General Considerations 138 6.12.2 Energy of Decomposition 138 6.12.3 Products of the Explosion Process 139 6.13 Kistiakowsky - Wilson Rules 140 6.14 Additional Equilibria 141 6.15 Energy Released on Detonation 142 6.16 Volume of Gases Produced during Explosion 144 6.17 Explosive Power 145 6.17.1 Improving Explosives Power 146 6.18 Shockwave Effects 147 6.19 Appendices: Measurement of Velocity of Detonation 149 Appendix 6.A: Dautriche Method 149 Appendix 6.B: The Rotating Mirror Streak Camera Method 151 Appendix 6.C: The Continuous Wire Method 152 Appendix 6.D: The Event Circuit 152 Bibliography 153 References 153 7 Decomposition Processes and Initiation of Energetic Materials 155 7.1 Effect of Heat on Explosives 155 7.2 Decomposition Mechanisms 162 7.2.1 Thermal Decomposition Mechanism of TNT 163 7.2.2 Non-Aromatic Nitro Compounds 164 7.2.3 Nitro Ester Thermal Decomposition 167 7.2.4 Nitramine Thermal Decomposition 168 7.2.5 Photon-Induced Decomposition Mechanisms 169 7.3 Practical Initiation Techniques 172 7.3.1 Methods of Initiation 173 7.3.2 Direct Heating 174 7.3.3 Mechanical Methods 175 7.3.4 Electrical Systems 177 7.3.5 Chemical Reaction 177 7.3.6 Initiation by Shockwave 178 7.4 Classification of Explosives by Ease of Initiation 178 7.5 Initiatory Explosives 179 7.5.1 Primary Explosive Compounds 179 7.5.2 Primer Usage 181 7.6 Igniters and Detonators 182 7.7 Explosive Trains 183 7.7.1 Explosive Trains in Commercial Blasting 187 Bibliography 190 References 190 8 Developments in Alternative Primary Explosives 193 8.1 Safe Handling of Novel Primers 193 8.2 Introduction 193 8.3 Totally Organic 194 8.4 Simple Salts of Organics 199 8.5 Transition Metal Complexes and Salts 202 8.6 Enhancement of Laser Sensitivity 206 References 207 Appendix 8.A: Properties of Novel Primer Explosives 211 Appendix 8.B: Molecular Structures of Some New Primer Compounds 213 Purely Organic Primers 213 9 Optical and Thermal Properties of Energetic Materials 221 9.1 Optical Properties 221 9.1.1 Introduction 221 9.1.2 Theoretical Considerations 222 9.1.3 Practical Considerations 225 9.1.4 Examples of Absorption Spectra 226 9.2 Thermal Properties 231 9.2.1 Introduction 231 9.2.2 Heat Capacity 232 9.2.3 Thermal Conductivity 232 9.2.4 Thermal Diffusivity 233 References 234 10 Theoretical Aspects of Laser Interaction with Energetic Materials 235 10.1 Introduction 235 10.2 Parameters Relevant to Laser Interaction 236 10.2.1 Laser Parameters 236 10.2.2 Material Parameters 236 10.3 Mathematical Formalism 237 10.3.1 Basic Concept 237 10.3.2 Optical Absorption 238 10.3.3 Optical Reflection 240 10.4 Heat Transfer Theory 240 References 245 11 Laser Ignition – Practical Considerations 247 11.1 Introduction 247 11.1.1 Laser Source 248 11.1.2 Beam Delivery System 249 11.2 Laser Driven Flyer Plate 249 11.3 Direct Laser Ignition 250 11.3.1 Explosives 251 11.3.2 Propellants 259 11.3.3 LI of Pyrotechnic Materials 263 References 267 12 Conclusions and Future Prospect 269 12.1 Introduction 269 12.2 Theoretical Considerations 269 12.3 Lasers 270 12.4 Optical and Thermal Properties of Energetic Materials 271 12.5 State of the Art: Laser Ignition 271 12.6 Future Prospect 272 References 274 Index 275

About the Author :
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.