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Main The Chemistry of Explosives: RSC
The Chemistry of Explosives: RSCAkhavan, Jacqueline
This concise, easy-to-read book outlines the basic principles needed to understand the chemical mechanisms of explosion. Covering detonation, deflagration, initiation, the latest theories on the production of ""hotspots"", thermochemistry, thermodynamics and kinetics, the text includes detailed formulations and reactions presented with thermochemical calculations to aid understanding. The history, theory and chemical types of explosives are introduced, along with propellants, pyrotechnics and the most up-to-date information on energetic binders for explosive compositions. Covering all aspects of explosive chemistry from history to manufacturing techniques and formulation, The Chemistry of Explosives is a unique text which introduces difficult subjects in a readable manner. Ideal for A-level students and new graduates with no previous knowledge of explosive materials, it will also be useful to anyone needing succinct information on the subject
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The Chemistry of Explosives 3rd Edition Jacqueline Akhavan School of Engineering & Applied Science, Cranfield University, Defence Academy of UK, Swindon, UK ISBN: 978-1-84973-330-4 A catalogue record for this book is available from the British Library r J. Akhavan 2011 All rights reserved Apart from fair dealing for the purposes of research for non-commercial purposes or for private study, criticism or review, as permitted under the Copyright, Designs and Patents Act 1988 and the Copyright and Related Rights Regulations 2003, this publication may not be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of The Royal Society of Chemistry or the copyright owner, or in the case of reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of the licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to The Royal Society of Chemistry at the address printed on this page. The RSC is not responsible for individual opinions expressed in this work. Published by The Royal Society of Chemistry, Thomas Graham House, Science Park, Milton Road, Cambridge CB4 0WF, UK Registered Charity Number 207890 For further information see our web site at www.rsc.org Preface Since the last 12 years of writing the first edition of the Chemistry of Explosives there has been a movement towards safety rather than performance of explosives and this has been reflected in this 3rd edition. The new generation of explosive compositions called Insensitive High Explosives (IHE) have been introduced in Chapter 1 with more detail of their properties in Chapter 2. Another emerging trend in the field of explosives is the effect they have on the environment. This is mainly due to recent legislations and an increase in environmental awareness. Details of the relevant legislations together with the consequences are discussed in Chapter 1. In this 3rd edition the properties for the explosives have been updated using a variety of sources and this has been reflected in the thermochemical calculations. With these main revisions and minor up-dates this 3rd edition should provide the reader with a basic understanding of the chemistry of explosives. This edition is still aimed primarily at A'level students and new graduates who have not previously studied explosive materials, but I hope the more experienced chemist in the explosives industry will also find the book useful. In writing this edition I have taken information from books and journals, and I would like thank those authors whom I have drawn upon in preparing this edition. My last thanks go to my husband Shahriar who has always supported me. The Chemistry of Explosives, 3rd Edition By Jacqueline Akhavan r J. Akhavan 2011 Published by the Royal Society of Chemistry, www.rsc.org v Contents Chapter 1 Introduction to Explosives 1 Development of Blackpowder Development of Nitroglycerine Development of Mercury Fulminate Development of Nitrocellulose Development of Dynamite Development of Ammonium Nitrate Development of Commercial Explosives Development of Permitted Explosives Development of ANFO, Slurry, Emulsion and Blasting Explosives Development of Military Explosives Development of Picric Acid Development of Tetryl Development of TNT Development of Nitroguanidine Development of PETN Development of RDX and HMX Polymer Bonded Explosives Recent Developments Insensitive Munitions and Insensitive High Explosives Explosives and the Environment The Chemistry of Explosives, 3rd Edition By Jacqueline Akhavan r J. Akhavan 2011 Published by the Royal Society of Chemistry, www.rsc.org vii 1 2 3 4 5 5 6 6 7 8 8 9 10 10 11 11 13 16 18 22 viii Chapter 2 Classification of Explosive Materials Explosions Atomic Explosions Physical Explosions Chemical Explosions Chemical Explosives Classification of Chemical Explosives Primary Explosives Secondary Explosives Propellants Chemical Data on Explosive Materials Primary Explosives Mercury Fulminate Lead Azide Lead Styphnate Silver Azide Tetrazene Secondary Explosives Nitroglycerine Nitrocellulose Picric Acid Tetryl TNT Nitroguanidine PETN RDX HMX TATB HNS NTO TNAZ CL-20 Fox-12 (GUDN) DNAN FOX-7 (DADNE) LLM-105 Other Compounds used in Explosive Compositions Contents 27 27 27 28 28 29 29 30 32 33 34 34 34 35 36 37 37 38 38 39 41 42 44 46 46 48 49 50 51 52 53 54 55 56 57 58 58 Contents ix Chapter 3 Combustion, Deflagration and Detonation 60 Combustion Physical and Chemical Aspects of Combustion Combustion of Explosives and Propellants Deflagration Detonation Burning to Detonation Shock to Detonation Propagation of the Detonation Shockwave Effect of Density on the Velocity of Detonation Effect of Diameter of the Explosive Composition on the Velocity of Detonation Effect of Explosive Material on the Velocity of Detonation Classification of Explosives 60 61 61 61 64 64 64 66 68 70 71 72 Chapter 4 Ignition, Initiation and Thermal Decomposition 74 Ignition Hotspots Mechanisms for the Formation of Hotspots Ignition by Impact and Friction Friction Impact Classification of Explosives Initiation Techniques Explosive Train Detonators Igniters Thermal Decomposition 74 75 76 77 77 77 79 82 82 82 83 83 Chapter 5 Thermochemistry of Explosives 85 Oxygen Balance Decomposition Reactions Kistiakowsky–Wilson Rules 85 89 89 x Contents Modified Kistiakowsky–Wilson Rules Springall Roberts Rules Heats of Formation Heat of Explosion Effect of Oxygen Balance Volume of Gaseous Products of Explosion Explosive Power, Power Index and TNT Equivalence Temperature of Chemical Explosion Mixed Explosive Compositions Atomic Composition of the Explosive Mixture Oxygen Balance Decomposition Reaction Heat of Explosion Volume of Gaseous Products Energized Explosives Addition of Aluminium Force and Pressure of Explosion 90 92 93 95 99 100 102 103 106 107 107 109 109 110 111 112 112 Chapter 6 Equilibria and Kinetics of Explosive Reactions 116 Equilibria Products of Decomposition The Water–Gas Equilibrium Heat of Explosion Temperature of Explosion Kinetics of Explosive Reactions Activation Energy Rate of Reaction Kinetics of Thermal Decomposition Measurement of Kinetic Parameters Differential Thermal Analysis Thermogravimetric Analysis Differential Scanning Calorimetry 116 117 118 119 123 124 124 125 126 127 128 129 129 Chapter 7 Manufacture of Explosives 131 Nitration C-Nitration Picric Acid Tetryl TNT (2,4,6-Trinitrotoluene) 131 131 131 133 134 Contents xi TATB (1,3,5-Triamino-2,4,6-trinitrobenzene) HNS (Hexanitrostilbene) O-Nitration Nitroglycerine Nitrocellulose PETN (Pentaerythritol tetranitrate) N-Nitration RDX (Cyclotrimethylenetrinitramine) HMX (Cyclotetramethylenetetranitramine) Nitroguanidine Ammonium Nitrate Primary Explosives Lead Azide Mercury Fulminate Tetrazene Commercial Explosive Compositions Ammonium Nitrate Ammonium Nitrate Slurries Ammonium Nitrate Emulsion Slurries Dynamite Military Explosive Compositions Casting Pressing Ram and Screw Extrusion 135 136 138 138 139 141 143 143 148 148 150 151 151 151 152 154 154 154 155 155 156 156 157 160 Chapter 8 Introduction to Propellants and Pyrotechnics 162 Introduction to Propellants Gun Propellants Performance Composition Single-base Propellants Double-base Propellants Triple-base Propellants Propellant Additives High Energy Propellants Liquid Propellants Composite Propellants Rocket Propellants Performance Composition Double-base Propellants 162 162 162 163 164 165 165 165 165 166 167 167 167 168 168 xii Contents Composite Propellants Liquid Propellants Gas-generating Propellants Introduction to Pyrotechnics Heat-producing Pyrotechnics Primers and First Fires Heat-generating Devices Delay Compositions Smoke-generating Compositions Light-generating Compositions Coloured Light White Light Noise-generating Pyrotechnics Bang Whistle 168 169 170 171 171 171 173 173 174 175 175 176 176 176 177 Bibliography 178 Subject Index 181 CHAPTER 1 Introduction to Explosives DEVELOPMENT OF BLACKPOWDER Blackpowder, also known as gunpowder, was most likely the first explosive composition. In 220 BC an accident was reported involving blackpowder when some Chinese alchemists accidentally made black-powder while separating gold from silver during a lowtemperature reaction. According to Dr Heizo Mambo the alchemists added potassium nitrate [also known as saltpetre (KNO3)] and sulfur to the gold ore in the alchemists' furnace but forgot to add charcoal in the first step of the reaction. Trying to rectify their error they added charcoal in the last step. Unknown to them they had just made blackpowder which resulted in a tremendous explosion. Blackpowder was not introduced into Europe until the 13th century when an English monk called Roger Bacon in 1249 experimented with potassium nitrate and produced blackpowder, and in 1320 a German monk called Berthold Schwartz (although many dispute his existence) studied the writings of Bacon and began to make blackpowder and study its properties. The results of Schwartz's research probably speeded up the adoption of blackpowder in central Europe. By the end of the 13th century many countries were using blackpowder as a military aid to breach the walls of castles and cities. The Chemistry of Explosives, 3rd Edition By Jacqueline Akhavan r J. Akhavan 2011 Published by the Royal Society of Chemistry, www.rsc.org 1 2 Chapter 1 Blackpowder contains a fuel and an oxidizer. The fuel is a powdered mixture of charcoal and sulfur which is mixed with potassium nitrate (oxidizer). The mixing process was improved tremendously in 1425 when the Corning, or granulating, process was developed. Heavy wheels were used to grind and press the fuels and oxidizer into a solid mass, which was subsequently broken down into smaller grains. These grains contained an intimate mixture of the fuels and oxidizer, resulting in a blackpowder which was physically and ballistically superior. Corned blackpowder gradually came into use for small guns and hand grenades during the 15th century and for big guns in the 16th century. Blackpowder mills (using the Corning process) were erected at Rotherhithe and Waltham Abbey in England between 1554 and 1603. The first recording of blackpowder being used in civil engineering was during 1548–1572 for the dredging of the River Niemen in Northern Europe, and in 1627 blackpowder was used as a blasting aid for recovering ore in Hungary. Soon, blackpowder was being used for blasting in Germany, Sweden and other countries. In England, the first use of blackpowder for blasting was in the Cornish copper mines in 1670. Bofors Industries of Sweden was established in 1646 and became the main manufacturer of commercial blackpowder in Europe. DEVELOPMENT OF NITROGLYCERINE By the middle of the 19th century the limitations of blackpowder as a blasting explosive were becoming apparent. Difficult mining and tunnelling operations required a 'better' explosive. In 1846 the Italian, Professor Ascanio Sobrero discovered liquid nitroglycerine [C3H5O3(NO2)3]. He soon became aware of the explosive nature of nitroglycerine and discontinued his investigations. A few years later the Swedish inventor, Immanuel Nobel developed a process for manufacturing nitroglycerine, and in 1863 he erected a small manufacturing plant in Helenborg near Stockholm with his son, Alfred. Their initial manufacturing method was to mix glycerol with a cooled mixture of nitric and sulfuric acids in stone jugs. The mixture was stirred by hand and kept cool by iced water; after the reaction had gone to completion the mixture was poured into excess cold water. The second manufacturing process was to pour glycerol and cooled mixed acids into a conical lead vessel which 3 Introduction to Explosives had perforations in the constriction. The product nitroglycerine flowed through the restrictions into a cold water bath. Both methods involved the washing of nitroglycerine with warm water and a warm alkaline solution to remove the acids. Nobel began to license the construction of nitroglycerine plants which were generally built very close to the site of intended use, as transportation of liquid nitroglycerine tended to generate loss of life and property. The Nobel family suffered many set backs in marketing nitroglycerine because it was prone to accidental initiation, and its initiation in bore holes by blackpowder was unreliable. There were many accidental explosions, one of which destroyed the Nobel factory in 1864 and killed Alfred's brother, Emil. Alfred Nobel in 1864 invented the metal 'blasting cap' detonator which greatly improved the initiation of blackpowder. The detonator contained mercury fulminate [Hg(CNO)2] and was able to replace blackpowder for the initiation of nitroglycerine in bore holes. The mercury fulminate blasting cap produced an initial shock which was transferred to a separate container of nitroglycerine via a fuse, initiating the nitroglycerine. After another major explosion in 1866 which completely demolished the nitroglycerine factory, Alfred turned his attentions into the safety problems of transporting nitroglycerine. To reduce the sensitivity of nitroglycerine Alfred mixed it with an absorbent clay, 'Kieselguhr'. This mixture became known as ghur dynamite and was patented in 1867. Nitroglycerine (1.1) has a great advantage over blackpowder since it contains both fuel and oxidizer elements in the same molecule. This gives the most intimate contact for both components. (1.1) Development of Mercury Fulminate Mercury fulminate was first prepared in the 17th century by the Swedish–German alchemist, Baron Johann Kunkel von Löwenstern. 4 Chapter 1 He obtained this dangerous explosive by treating mercury with nitric acid and alcohol. At that time, Kunkel and other alchemists could not find a use for the explosive and the compound became forgotten until Edward Howard of England rediscovered it between 1799 and 1800. Howard examined the properties of mercury fulminate and proposed its use as a percussion initiator for blackpowder and in 1807 a Scottish Clergyman, Alexander Forsyth patented the device. DEVELOPMENT OF NITROCELLULOSE At the same time as nitroglycerine was being prepared, the nitration of cellulose to produce nitrocellulose (also known as guncotton) was also being undertaken by different workers, notably Schönbein at Basel and Böttger at Frankfurt-am-Main during 1845–47. Earlier in 1833, Braconnot had nitrated starch, and in 1838, Pelouze, continuing the experiments of Braconnot, also nitrated paper, cotton and various other materials but did not realize that he had prepared nitrocellulose. With the announcement by Schönbein in 1846, and in the same year by Böttger that nitrocellulose had been prepared, the names of these two men soon became associated with the discovery and utilization of nitrocellulose. However, the published literature at that time contains papers by several investigators on the nitration of cellulose before the process of Schönbein was known. Many accidents occurred during the preparation of nitrocellulose, and manufacturing plants were destroyed in France, England and Austria. During these years, Sir Frederick Abel was working on the instability problem of nitrocellulose for the British Government at Woolwich and Waltham Abbey, and in 1865 he published his solution to this problem by converting nitrocellulose into a pulp. Abel showed through his process of pulping, boiling and washing that the stability of nitrocellulose could be greatly improved. Nitrocellulose was not used in military and commercial explosives until 1868 when Abel's assistant, E.A. Brown discovered that dry, compressed, highly-nitrated nitrocellulose could be detonated using a mercury fulminate detonator, and wet, compressed nitrocellulose could be exploded by a small quantity of dry nitrocellulose (the principle of a Booster). Thus, large blocks of wet nitrocellulose could be used with comparative safety. Introduction to Explosives 5 Naval vessels were now able to carry 'gun cotton' torpedoes by keeping the major portions of the cargo completely saturated with water. In 1888 Charles E. Munroe noticed that when a block of guncotton with the manufacturer's name stamped into it was detonated with its lettered surface against a metal plate, the letters were indented into the surface of the plate. If letters were raised in relief above the surface of the guncotton then the letters on the plate would also be raised above its surface. This is now known as the Munroe effect. The Munroe effect refers to the partial focusing of blast energy caused by a hollow or void cut into a piece of explosive. DEVELOPMENT OF DYNAMITE In 1875 Alfred Nobel discovered that on mixing nitrocellulose with nitroglycerine a gel was formed. This gel was developed to produce blasting gelatine, gelatine dynamite and later in 1888, ballistite, the first smokeless powder. Ballistite was a mixture of nitrocellulose, nitroglycerine, benzene and camphor. In 1889 a rival product of similar composition to ballistite was patented by the British Government in the names of Abel and Dewar called 'Cordite'. In its various forms Cordite remained the main propellant of the British Forces until the 1930s. In 1867, the Swedish chemists Ohlsson and Norrbin found that the explosive properties of dynamites were enhanced by the addition of ammonium nitrate (NH4NO3). Alfred Nobel subsequently acquired the patent of Ohlsson and Norrbin for ammonium nitrate and used this in his explosive compositions. Development of Ammonium Nitrate Ammonium nitrate was first prepared in 1654 by Glauber but it was not until the beginning of the 19th century when it was considered for use in explosives by Grindel and Robin as a replacement for potassium nitrate in blackpowder. Its explosive properties were also reported in 1849 by Reise and Millon when a mixture of powdered ammonium nitrate and charcoal exploded on heating. Ammonium nitrate was not considered to be an explosive although small fires and explosions involving ammonium nitrate occurred throughout the world. 6 Chapter 1 After the end of World War II, the USA Government began shipments to Europe of so-called Fertilizer Grade Ammonium Nitrate (FGAN), which consisted of grained ammonium nitrate coated with about 0.75% wax and conditioned with about 3.5% clay. Since this material was not considered to be an explosive, no special precautions were taken during its handling and shipment – workmen even smoked during the loading of the material. Numerous shipments were made without trouble prior to 16 and 17 April 1947, when a terrible explosion occurred. The SS Grandchamp and the SS Highflyer, both moored in the harbour of Texas City and loaded with FGAN, blew up. As a consequence of these disasters, a series of investigations was started in the USA in an attempt to determine the possible causes of the explosions. At the same time a more thorough study of the explosive properties of ammonium nitrate and its mixtures with organic and inorganic materials was also conducted. The explosion at Texas City had barely taken place when a similar one aboard the SS Ocean Liberty shook the harbour of Brest in France on 28 July 1947. The investigations showed that ammonium nitrate is much more dangerous than previously thought and more rigid regulations governing its storage, loading and transporting in the USA were promptly put into effect. DEVELOPMENT OF COMMERCIAL EXPLOSIVES Development of Permitted Explosives Until 1870, blackpowder was the only explosive used in coal mining, and several disastrous explosions occurred. Many attempts were made to modify blackpowder; these included mixing blackpowder with 'cooling agents' such as ammonium sulfate, starch, paraffin, etc., and placing a cylinder filled with water into the bore hole containing the black-powder. None of these methods proved to be successful. When nitrocellulose and nitroglycerine were invented, attempts were made to use these as ingredients for coal mining explosives instead of blackpowder but they were found not to be suitable for use in gaseous coal mines. It was not until the development of dynamite and blasting gelatine by Nobel that nitroglycerine-based explosives began to dominate the commercial blasting and mining Introduction to Explosives 7 industries. The growing use of explosives in coal mining brought a corresponding increase in the number of gas and dust explosions, with appalling casualty totals. Some European governments were considering prohibiting the use of explosives in coal mines and resorting to the use of hydraulic devices or compressed air. Before resorting to such drastic measures, some governments decided to appoint scientists, or commissions headed by them, to investigate this problem. Between 1877 and 1880, commissions were created in France, Great Britain, Belgium and Germany. As a result of the work of the French Commission, maximum temperatures were set for explosions in rock blasting and gaseous coal mines. In Germany and England it was recognized that regulating the temperature of the explosion was only one of the factors in making an explosive safe and that other factors should be considered. Consequently, a testing gallery was constructed in 1880 at Gelsenkirchen in Germany in order to test the newly-developed explosives. The testing gallery was intended to imitate as closely as possible the conditions in the mines. A Committee was appointed in England in 1888 and a trial testing gallery at Hebburn Colliery was completed around 1890. After experimenting with various explosives the use of several explosive materials was recommended, mostly based on ammonium nitrate. Explosives which passed the tests were called 'permitted explosives'. Dynamite and blackpowder both failed the tests and were replaced by explosives based on ammonium nitrate. The results obtained by this Committee led to the Coal Mines Regulation Act of 1906. Following this Act, testing galleries were constructed at Woolwich Arsenal and Rotherham in England. Development of ANFO, Slurry, Emulsion and Blasting Explosives By 1913, British coal production reached an all-time peak of 287 million tons, consuming more than 5000 tons of explosives annually and by 1917, 92% of these explosives were based on ammonium nitrate. In order to reduce the cost of explosive compositions the explosives industry added more of the cheaper compound ammonium nitrate to the formulations, but this had an unfortunate side effect of reducing the explosives' waterproofness. This was a significant problem because mines and quarries were often wet and the holes drilled to take the explosives regularly filled with water. Chemists overcame this problem by coating the 8 Chapter 1 ammonium nitrate with various inorganic powders before mixing it with dynamite, and by improving the packaging of the explosives to prevent water ingress. Accidental explosions still occurred involving mining explosives, and in 1950 manufacturers started to develop explosives which were waterproof and solely contained the less hazardous ammonium nitrate. The most notable composition was ANFO (Ammonium Nitrate Fuel Oil). In the 1970s, the USA companies Ireco and DuPont began adding paint-grade aluminium and monomethylamine nitrate (MAN) to their formulations to produce gelled explosives which could detonate more easily. More recent developments concern the production of emulsion explosives which contain droplets of a solution of ammonium nitrate in oil. These emulsions are waterproof because the continuous phase is a layer of oil, and they can readily detonate since the ammonium nitrate and oil are in close contact. Emulsion explosives are safer than dynamite, and are simple and cheap to manufacture. The first emulsion explosive was made by Egly and Neckar in 1964 where they mixed a water solution of ammonium nitrate with oil and an emulsifier using a high shear mixer. They then added crystalline ammonium nitrate to the emulsion. This emulsion explosive had a relatively limited lifetime and an improved and stable emulsion explosive called aquaram was later invented by Bluhm in 1969. Bluhm emulsified a hot water solution of ammonium nitrate and sodium nitrate in mineral oil containing an emulsifier and then sensitised the emulsion by either aerating in a high shear mixer, adding a chemical gassing agent or adding hollow glass microballoons. The addition of ANFO to an emulsion explosive to produce a blasting explosive was first prepared by Clay in 1978. The advantage of blasting explosive was that it did not contain sensitising agents or air bubbles. DEVELOPMENT OF MILITARY EXPLOSIVES Development of Picric Acid Picric acid [(trinitrophenol) (C6H3N3O7)] was found to be a suitable replacement for blackpowder in 1885 by Turpin, and in 1888 blackpowder was replaced by picric acid in British munitions under the name Liddite. Picric acid is probably the earliest known nitrophenol: it is mentioned in the alchemical writings of Glauber 9 Introduction to Explosives as early as 1742. In the second half of the 19th century, picric acid was widely used as a fast dye for silk and wool. It was not until 1830 that the possibility of using picric acid as an explosive was explored by Welter. Designolle and Brugère suggested that picrate salts could be used as a propellant, while in 1871, Abel proposed the use of ammonium picrate as an explosive. In 1873, Sprengel showed that picric acid could be detonated to an explosion and Turpin, utilizing these results, replaced blackpowder with picric acid for the filling of munition shells. In Russia, Panpushko prepared picric acid in 1894 and soon realized its potential as an explosive. Eventually, picric acid (1.2) was accepted all over the world as the basic explosive for military uses. (1.2) Picric acid did have its problems: in the presence of water it caused corrosion of the shells, its salts were quite sensitive and prone to accidental initiation, and picric acid required prolonged heating at high temperatures in order for it to melt. Development of Tetryl An explosive called tetryl was also being developed at the same time as picric acid. Tetryl was first prepared in 1877 by Mertens and its structure established by Romburgh in 1883. Tetryl (1.3) was used as an explosive in 1906, and in the early part of this century it was frequently used as the base charge of blasting caps. (1.3) 10 Chapter 1 Development of TNT Around 1902 the Germans and British had experimented with trinitrotoluene [(TNT) (C7H5N3O6)], first prepared by Wilbrand in 1863. The first detailed study of the preparation of 2,4,6-trinitrotoluene was by Beilstein and Kuhlberh in 1870, when they discovered the isomer 2,4,5-trinitrotoluene. Pure 2,4,6-trinitrotoluene was prepared in 1880 by Hepp and its structure established in 1883 by Claus and Becker. The manufacture of TNT began in Germany in 1891 and in 1899 aluminium was mixed with TNT to produce an explosive composition. In 1902, TNT was adopted for use by the German Army replacing picric acid, and in 1912 the US Army also started to use TNT. By 1914, TNT (1.4) became the standard explosive for all armies during World War I. (1.4) Production of TNT was limited by the availability of toluene from coal tar and it failed to meet demand for the filling of munitions. Use of a mixture of TNT and ammonium nitrate, called amatol, became wide-spread to relieve the shortage of TNT. Underwater explosives used the same formulation with the addition of aluminium and was called aminal. Development of Nitroguanidine The explosive nitroguanidine was also used in World War I by the Germans as an ingredient for bursting charges. It was mixed with ammonium nitrate and paraffin for filling trench mortar shells. Nitroguanidine was also used during World War II and later in triple-base propellants. Nitroguanidine (CH4N4O2) was first prepared by Jousselin in 1877 and its properties investigated by Vieille in 1901. In World War I nitroguanidine was mixed with nitrocellulose and used as a flashless propellant. However, there were problems associated with this composition; nitroguanidine attacked nitrocellulose during Introduction to Explosives 11 its storage. This problem was overcome in 1937 by the company Dynamit AG who developed a propellant composition containing nitroguanidine called 'Gudol Pulver'. Gudol Pulver produced very little smoke, had no evidence of a muzzle flash on firing, and was also found to increase the life of the gun barrel. After World War I, major research programmes were inaugurated to find new and more powerful explosive materials. From these programmes came cyclotrimethylenetrinitramine [(RDX) (C3H6N6O6)] also called Cyclonite or Hexogen, and pentaerythritol tetranitrate [(PETN) (C5H8N4O12)]. Development of PETN PETN was first prepared in 1894 by nitration of pentaerythritol. Commercial production of PETN could not be achieved until formaldehyde and acetaldehyde required in the synthesis of pentaerythritol became readily available about a decade before World War II. During World War II, RDX was utilized more than PETN because PETN was more sensitive to impact and its chemical stability was poor. Explosive compositions containing 50% PETN and 50% TNT were developed and called 'Pentrolit' or 'Pentolite'. This composition was used for filling hand and anti-tank grenades, and detonators. Development of RDX and HMX RDX was first prepared in 1899 by the German, Henning for medicinal use. Its value as an explosive was not recognized until 1920 by Herz. Herz succeeded in preparing RDX by direct nitration of hexamine, but the yields were low and the process was expensive and unattractive for large scale production. Hale, at Picatinny Arsenal in 1925, developed a process for manufacturing RDX which produced yields of 68%. However, no further substantial improvements were made in the manufacture of RDX until 1940 when Meissner developed a continuous method for the manufacture of RDX, and Ross and Schiessler from Canada developed a process which did not require the use of hexamine as a starting material. At the same time, Bachmann developed a manufacturing process for RDX (1.5) from hexamine which gave the greatest yield. 12 Chapter 1 (1.5) Bachmann's products were known as Type B RDX and contained a constant impurity level of 8–12%. The explosive properties of this impurity were later utilized and the explosive HMX, also known as Octogen, was developed. The Bachmann process was adopted in Canada during World War II, and later in the USA by the Tennessee–Eastman Company. This manufacturing process was more economical and also led to the discovery of several new explosives. A manufacturing route for the synthesis of pure RDX (no impurities) was developed by Brockman, and this became known as Type A RDX. In Great Britain the Armament Research Department at Woolwich began developing a manufacturing route for RDX after the publication of Herz's patent in 1920. A small-scale pilot plant producing 75 lbs of RDX per day was installed in 1933 and operated until 1939. Another plant was installed in 1939 at Waltham Abbey and a full-scale plant was erected in 1941 near Bridgewater. RDX was not used as the main filling in British shells and bombs during World War II but was added to TNT to increase the power of the explosive compositions. RDX was used in explosive compositions in Germany, France, Italy, Japan, Russia, USA, Spain and Sweden. Research and development continued throughout World War II to develop new and more powerful explosives and explosive compositions. Torpex (TNT/RDX/aluminium) and cyclotetramethylenetetranitramine, known as Octogen [(HMX) (C4H8N8O8)], became available at the end of World War II. In 1952 an explosive composition called 'Octol' was developed; this contained 75% HMX and 25% TNT. Mouldable plastic explosives were also developed during World War II; these often contained vaseline or gelatinized liquid nitro compounds to give a plastic-like consistency. A summary of explosive compositions used in World War II is presented in Table 1.1. Introduction to Explosives Table 1.1 13 Examples of explosive compositions used in World War II Name Composition Baronal Composition A Composition B (cyclotol) H-6 Minol-2 Pentolites Picratol PIPE PTX-1 PTX-2 PVA-4 RIPE Tetrytols Torpex Barium nitrate, TNT and aluminium 88.3% RDX and 11.7% non-explosive plasticizer RDX, TNT and wax 45% RDX, 30% TNT, 20% aluminium and 5% wax 40% TNT, 40% ammonium nitrate and 20% aluminium 50% PETN and 50% TNT 52% Picric acid and 48% TNT 81% PETN and 19% Gulf Crown E Oil 30% RDX, 50% tetryl and 20% TNT 41–44% RDX, 26–28% PETN and 28–33% TNT 90% RDX, 8% PVA and 2% dibutyl phthalate 85% RDX and 15% Gulf Crown E Oil 70% Tetryl and 30% TNT 42% RDX, 40% TNT and 18% aluminium Polymer Bonded Explosives Polymer bonded explosives (PBXs) were developed to reduce the sensitivity of the newly-synthesized explosive crystals by embedding the explosive crystals in a rubber-like polymeric matrix. The first PBX composition was developed at the Los Alamos Scientific Laboratories in USA in 1952. The composition consisted of RDX crystals embedded in plasticized polystyrene. Since 1952, Lawrence Livermore Laboratories, the US Navy and many other organizations have developed a series of PBX formulations, some of which are listed in Table 1.2. HMX-based PBXs were developed for projectiles and lunar seismic experiments during the 1960s and early 1970s using Teflon (polytetra-fluoroethylene) as the binder. PBXs based on RDX and RDX/PETN have also been developed and are known as Semtex. Development is continuing in this area to produce PBXs which contain polymers that are energetic and will contribute to the explosive performance of the PBX. Inert prepolymers have been substituted by energetic prepolymers [mainly hydroxy terminated polybutadiene (HTPB)] in explosive compositions, in order to increase the explosive performance, without compromising its vulnerability to accidental initiation. In the last ten years it has become apparent that PBXs containing inert or energetic binders are more sensitive to impact compared to traditional explosive 14 Table 1.2 Chapter 1 Examples of PBX compositions, where HMX is cyclotetramethylene-tetranitramine (Octogen), HNS is hexanitrostilbene, PETN is pentaerythritol tetranitrate, RDX is cyclotrimethylenetrinitramine (Hexogen) and TATB is 1,3,5triamino-2,4,6-trinitrobenzene Explosive Binder and plasticizer HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HMX HNS NTO NTO/HMX NTO/HMX NTO/HMX PETN PETN PETN PETN PETN PETN PETN PETN PETN PETN RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX RDX TATB/HMX Acetyl-formyl-2,2-dinitropropanol (DNPAF) and polyurethane Cariflex (thermoplastic elastomer) Hydroxy-terminated polybutadiene (polyurethane) Hydroxy-terminated polyester Kraton (block copolymer of styrene and ethylene–butylene) Nylon (polyamide) Polyester resin–styrene Polyethylene Polyurethane Poly(vinyl) alcohol Poly(vinyl) butyral resin Teflon (polytetrafluoroethylene) Viton (fluoroelastomer) Teflon (polytetrafluoroethylene) Cariflex (block copolymer of butadiene–styrene) Cariflex (block copolymer of butadiene–styrene) Estane (polyester polyurethane copolymer) Hytemp (thermoplastic elastomer) Butyl rubber with acetyl tributylcitrate Epoxy resin–diethylenetriamine Kraton (block copolymer of styrene and ethylene–butylene) Latex with bis-(2-ethylhexyl adipate) Nylon (polyamide) Polyester and styrene copolymer Poly(ethyl acrylate) with dibutyl phthalate Silicone rubber Viton (fluoroelastomer) Teflon (polytetrafluoroethylene) Epoxy ether Exon (polychlorotrifluoroethylene/vinylidine chloride) Hydroxy-terminated polybutadiene (polyurethane) Kel-F (polychlorotrifluoroethylene) Nylon (polyamide) Nylon and aluminium Nitro-fluoroalkyl epoxides Polyacrylate and paraffin Polyamide resin Polyisobutylene/Teflon (polytetrafluoroethylene) Polyester Polystyrene Teflon (polytetrafluoroethylene) Kraton (block copolymer of styrene and ethylene–butylene) 15 Introduction to Explosives compositions. The addition of a plasticizer has reduced the sensitivity of PBXs whilst improving its processability and mechanical properties. Energetic plasticizers have also been developed for PBXs. Examples of energetic polymers and energetic plasticizers under investigation are presented in Tables 1.3 and 1.4, respectively. Table 1.3 Examples of energetic polymers Common name Chemical name GLYN (monomer) Glycidyl nitrate polyGLYN Poly(glycidyl nitrate) NIMMO (monomer) 3-Nitratomethyl-3methyl oxetane polyNIMMO Poly(3-nitratomethyl-3methyl oxetane) GAP Glycidyl azide polymer AMMO (monomer) 3-Azidomethyl-3-methyl oxetane PolyAMMO Poly(3-azidomethyl-3methyl oxetane) BAMO (monomer) 3,3-Bis-azidomethyl oxetane PolyBAMO Poly(3,3-bis-azidomethyl oxetane) Structure 16 Table 1.4 Chapter 1 Examples of energetic plasticizers Common name Chemical name NENAs Alkyl nitratoethyl nitramines EGDN Ethylene glycol dinitrate MTN Metriol trinitrate BTTN Butane-1,2,4-triol trinitrate K10 Mixture of di- and tri-nitroethylbenzene BDNPA/ BDNFA Mixture of bisdinitropropylacetal and bis-dinitropropylformal Structure Recent Developments Recent developments in explosives have seen the production of hexanitrostilbene [(HNS) (C14H6N6O12)] in 1966 by Shipp, and triaminotrinitrobenzene {(TATB) [(NH2)3C6(NO2)3]} in 1978 by Adkins and Norris. Both of these materials are able to withstand relatively high temperatures compared with other explosives. TATB was first prepared in 1888 by Jackson and Wing, who also determined its solubility characteristics. In the 1950s, the USA Naval Ordnance Laboratories recognized TATB as a useful heatresistant explosive, and successful small-scale preparations and synthetic routes for large-scale production were achieved to give high yields. 17 Introduction to Explosives Nitro-1,2,4-triazole-3-one [(NTO) (C2H2N4O3)] is one of the new explosives with high energy and low sensitivity. It has a high heat of reaction and shows autocatalytic behaviour during thermal decomposition. NTO was first reported in 1905 from the nitration of 1,2,4-triazol-3-one. There was renewed interest in NTO in the late 1960s, but it wasn't until 1987 that Lee, Chapman and Coburn reported the explosive properties of NTO. NTO is now widely used in explosive formulations, PBXs, and gas generators for automobile inflatable airbag systems. The salt derivatives of NTO are also insensitive and are potential energetic ballistic additives for solid rocket propellants. 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (C6H6 N12O12) or HNIW, more commonly called CL-20 belongs to the family of high energy dense caged nitramines. CL-20 was first synthesized in 1987 by Arnie Nielsen, and is now being produced at SNPE in France in quantities of 50–100 kg on an industrial pilot scale plant. Nitrocubanes are probably the most powerful explosives with a predicted detonation velocity of 410,000 m s1. Cubanes were first synthesised at the University of Chicago, USA by Eaton and Cole in 1964. The US Army Armament Research Development Centre (ARDEC) then funded development into the formation of octanitrocubane [(ONC) (C8N8O16)] and heptanitrocubane [(HpNC) (C8N7O14)]. ONC and HpNC were successfully synthesised in 1997 and 2000 respectively by Eaton and co-workers. The basic structure of ONC is a cubane molecule where all the hydrogens have been replaced by nitro groups (1.6). HpNC is denser than ONC and predicted to be a more powerful, shockinsensitive explosive. O2N O2N O2N O2N NO2 NO2 O2N O2N NO2 O2N O2N NO2 (1.6) NO2 NO2 NO2 The research into energetic molecules which produce a large amount of gas per unit mass, led to molecular structures which 18 Chapter 1 have a high hydrogen to carbon ratio. Examples of these structures are hydrazinium nitroformate (HNF) and ammonium dinitramide (ADN). The majority of the development of HNF has been carried out in The Netherlands whereas the development of ADN has taken place in Russia, USA and Sweden. ADN is a dense non chlorine containing powerful oxidiser and is an interesting candidate for replacing ammonium perchlorate as an oxidiser for composite propellants. ADN is less sensitive to impact than RDX and HMX, but more sensitive to friction and electrostatic spark. Recent developments in polymeric binders are in the new family of polyphosphazenes. These polymers are highly flexible with very low glass transition temperatures and have a wide range of structures and physical properties. OCH2CF3 P N OCH2CF3 x OR P N OCH2CF3 y OR P OR N z (1.7) Polyphosphazenes (1.7) are polymers containing nitrogen as part of their backbone; they are commonly used in O-rings, pipelines, seals in the oil industry, fuel delivery, and storage systems. Polyphosphazene derivatives are biocompatible, biodegradable, and bioactive, and some of them are being investigated for possible medical applications. In 1995 attempts were made to synthesis energetic polyphosphazenes by Colclough and in 2006 Golding and Trussel patented the synthesis of energetic polyphosphazenes. Their materials possessed high energy density and lower glass transition temperatures than existing materials such as GAP, polyNIMMO and polyGLYN, and could undergo chemical modification to produce a tacky and rubbery polymer which could be used as a binder in PBXs. Examples of some explosive molecules under development are presented in Table 1.5. A summary of the significant discoveries in the history of explosives throughout the world is presented in Table 1.6. Insensitive Munitions and Insensitive High Explosives In an effort to improve munitions survivability and safety, several countries established a policy requiring all new munitions be capable of withstanding accidents, fires, or enemy attack. One method 19 Introduction to Explosives Table 1.5 Examples of explosive molecules under development Common name Chemical name NTO 5-Nitro-1,2,4-triazol-3-one ADN Ammonium dinitramide TNAZ 1,3,3-Trinitroazetidine CL-20 2,4,6,8,10,12-Hexanitro2,4,6,8,10,12hexaazaisowurtzitane Structure O2N N O2N N N N N O2N HNF Hydrazinium nitroformate N NO2 H N–NH C(NO ) O2N NO2 NO2 O2N ONC Octanitrocubane NO2 NO2 O2N O2N NO2 O2N NO2 O2N HpNC Heptanitrocubane O2N O2N H2N DAF NO2 NO2 NO2 NH2 3,4-Diaminofurazan N N O 20 Table 1.6 Chapter 1 Some significant discoveries in the history of incendiaries, fireworks, blackpowder and explosives Date Explosive 220 BC 222–235 AD Chinese alchemists accidentally made blackpowder. Alexander VI of the Roman Empire called a ball of quicklime and asphalt 'automatic fire' which spontaneously ignited on coming into contact with water. Arabs used blackpowder at the siege of Mecca. The Chinese invented the 'Fire Ball' which is made of an explosive composition similar to blackpowder. The Chinese built a blackpowder plant in Pein King. The Chinese started to make fireworks. Roger Bacon first made blackpowder in England. The German, Schwartz studied blackpowder and helped it to be introduced into central Europe. Corning, or granulating, process was developed. The Hungarian, Kaspar Weindl used blackpowder in blasting. Swedish Bofors Industries began to manufacture blackpowder. Preparation of ammonium nitrate was undertaken by Glauber. The German, Kunkel prepared mercury fulminate. Glauber prepared picric acid. Welter explored the use of picric acid in explosives. The Frenchman, Pelouze carried out nitration of paper and cotton. Schönbein and Böttger nitrated cellulose to produce guncotton. The Italian, Sobrero discovered liquid nitroglycerine. Reise and Millon reported that a mixture of charcoal and ammonium nitrate exploded on heating. The Swedish inventor, Nobel manufactured nitroglycerine. The German, Wilbrand prepared TNT. Schultze prepared nitrocellulose propellants. Nitrocellulose propellants were also prepared by Vieile. Nobel developed the mercury fulminate detonator. An increase in the stability of nitrocellulose was achieved by Abel. Nobel invented Dynamite. The Swedish chemists, Ohlsson and Norrbin added ammonium nitrate to dynamites. Brown discovered that dry, compressed guncotton could be detonated. Brown also found that wet, compressed nitrocellulose could be exploded by a small quantity of dry nitrocellulose. Abel proposed that ammonium picrate could be used as an explosive. Sprengel showed that picric acid could be detonated. Nobel mixed nitroglycerine with nitrocellulose to form a gel. Mertens first prepared tetryl. Nobel manufactured Ammoniun Nitrate Gelatine Dynamite. The German, Hepp prepared pure 2,4,6-trinitrotoluene (TNT). The structure of tetryl was established by Romburgh. The structure of TNT was established by Claus and Becker. Turpin replaced blackpowder with picric acid. 690 940 1040 1169–1189 1249 1320 1425 1627 1646 1654 1690 1742 1830 1838 1846 1846 1849 1863 1863 1864 1864 1864 1865 1867 1867 1868 1868 1871 1873 1875 1877 1879 1880 1883 1883 1885 Introduction to Explosives Table 1.6 21 Continued Date Explosive 1888 1888 1888 1889 1891 1894 1894 1899 1899 1900 1902 1905 1906 1912 1920 1925 1940 Jackson and Wing first prepared TATB. Picric acid was used in British Munitions called Liddite. Nobel invented Ballistite. The British scientists, Abel and Dewar patented Cordite. Manufacture of TNT began in Germany. The Russian, Panpushko prepared picric acid. Preparation of PETN was carried out in Germany. Preparation of RDX for medicinal use was achieved by Henning. Aluminium was mixed with TNT in Germany. Preparation of nitroguanidine was developed by Jousselin. The German Army replaced picric acid with TNT. NTO was first reported from the nitration of 1,2,4-triazol-3-one. Tetryl was used as an explosive. The US Army started to use TNT in munitions. Preparation of RDX by the German, Herz. Preparation of a large quantity of RDX in the USA. Meissner developed the continuous method for the manufacture of RDX. Bachmann developed the manufacturing process for RDX. Bachmann prepared HMX. PBXs were first prepared containing RDX, polystyrene and dioctyl phthalate in the USA. Octols were formulated. Slurry explosives were developed by the American, Cook. Cubanes were first synthesised at the University of Chicago, USA by Eaton and Cole. HNS was prepared by Shipp. The USA companies, Ireco and Dupont produced a gel explosive by adding paint-grade aluminium and MAN to ANFO. Adkins and Norris prepared TATB. TNAZ was first prepared at Fluorochem Inc. Lee, Chapman and Coburn reported the explosive properties of NTO. CL20 was first synthesized by Arnie Nielsen. ONC was successfully synthesised by Eaton and coworkers. HpNC was successfully synthesised by Eaton and coworkers. 1940 1943 1952 1952 1957 1964 1966 1970 1978 1983 1987 1987 1997 2000 of addressing this requirement was the use of ''Insensitive Munitions'' (IM). An IM is one that will not detonate under any condition other than its intended use. If it is struck by fragments from an explosion or hit by a bullet, it will not detonate. It also will not detonate if it is in close proximity to a target that is hit. In extreme temperatures, the IM will only burn. This increased safety allows greater numbers of munitions to be packaged, handled, stored, and transported in smaller containers. 22 Chapter 1 Three approaches are taken when designing IMs: Firstly, the high energy device can be protected and transported with an external protection of some kind. Some munition shipping containers are designed to provide a degree of protection and thermal insulation. Secondly, the casings of high energy devices can be designed in such a way as to allow venting or some other form of pressure relief in a fire. Lastly, the chemistry of the high energy fill is chosen to provide a higher degree of stability, for example by using insensitive high explosives (IHE). The IHE must be powerful enough to do the job and at the same time insensitive enough to prevent accidental explosion, for example CL-20 has an energy density at least 15% greater than that of HMX but it is not an IHE due to its sensitivity to impact, whereas LLM-105 [2,6-Pyrazinediamine, 3,5-dinitro-1-oxide (C4H4N6O5)] has 60% more energy than TNT and is classed as an IHE. TATB is a reasonably powerful high explosive who's thermal and shock stability is considerably greater than that of any other known material of comparable energy and is therefore a good candidate for IHE. In the late 1990s Groupe SNPE, (France's state-owned producer of space and military propellants and explosives) produced a reduced sensitive form of RDX (RS-RDX) for use in IHE formulations. Other manufacturers soon produced forms of RS-RDX such as I RDX (Insensitive RDX) and Grade A RDX. A version of RS-HMX has also been manufactured in Norway by Chemring Nobel AS. Examples of IHE formulations are presented in Table 1.7. Explosives and the Environment Up until the mid-1980s, surplus and unserviceable energetic materials, munitions and propellants were either dumped at sea or destroyed by open burning and open detonation. Sea dumping, open burning and open detonation were the preferred disposal techniques because of their simplicity, low cost, effectiveness and safety. However, concern has grown in recent years over the protection of human health and the environment and it is generally accepted that sea dumping, open burning and open detonation activities have the potential to cause harm. As a result, sea dumping is now banned while open burning and open detonation operations are becoming increasingly restricted. Countries such as Germany and the Netherlands prohibit open burning and open 23 Introduction to Explosives Table 1.7 Examples of insensitive high explosives (IHE) formulations where CAB is cellulose acetate butyrate, DNAN is 2,4dinitroanisole, HTPB is hydroxyterminated polybutadiene, IPDI is isophorone diisocyanate and Kel F 800 is chlorotrifluoroethylene-co-vinylidene fluoride polymer Name Explosive \%wt LX-17 PAX-2A(1) 92.5 TATB 85 HMX PAX-21 36 RDX 34 DNAN N/A DNAN PAX-24 PAX-25 PAX-26 20 RDX 40 DNAN PAX-40 65 HMX 35 DNAN 65 RDX 35 DNAN 27 NTO 20 RDX 47 NTO 5 RDX PBXW-124 PBXW-122 7.5 Kel-F 800 1.6 CAB 9 K10 Other ingredients\%wt N/A Carbon 30 Ammonium perchlorate n-methyl nitroaniline Ammonium perchlorate n-methyl nitroaniline Ammonium perchlorate n-methyl nitroaniline Aluminium Ammonium perchlorate n-methyl nitroaniline 20 Aluminium 20 Ammonium perchlorate n-methyl nitroaniline n-methyl nitroaniline N/A RDX N/A DNAN N/A DNAN PAX-28 PAX-41 Binder+ Plasticizer \%wt Nitroaniline 5 HTPB 7 IPDI 5 HTPB 7 IPDI 20 Aluminium 20 Ammonium perchlorate 15 Aluminium 20 Ammonium perchlorate detonation activities and others restrict it, for example in the US and Canada. There is a concern however, that activities in the past have lead to contamination of the land, soil and water. There are various explosive related activities that can contribute to contaminating land, soil and water these include manufacturing plants, firing ranges, open burning, open detonation and munitions which have been left in the ground from previous conflicts i.e. World War I and II. For example in 1914–1918 in the UK, waste containing picric acid from the manufacture of explosives were placed in abandoned chalk pits and in early 1920's water from a nearby well was reported to have a yellow tint. By 1942 the pollutant had migrated at least a mile as indicated by another contaminated well. From 1939 until 1955 water samples around the 24 Chapter 1 area were reported to have this characteristic yellow picric acid tint. Studies have been conducted on the effect TNT, RDX, HMX and other explosives have on the environment. TNT has been found to be soluble in water and has a tendency to degrade by photolysis, whereas RDX and HMX are less soluble in water and therefore leach out of the soil to groundwater (see Table 1.8). In order to reduce, control and monitor explosive waste, environmental Table 1.8 Explosives properties that can effect the environment Explosive Environmental Properties* Environmental Consequences* TNT Fast dissolution rate, adsorbs strongly to soil but also degrades readily. Depending on soil characteristics, these breakdown products are either more mobile than or have a similar mobility to TNT. TNT can be taken up by plants from contaminated soil, including edible varieties of garden plants, aquatic and wetland plants, trees, and can accumulate in plant roots. RDX Dissolves very slowly in water, does not adsorb strongly to soil and migrates further in contaminant plumes in groundwater. It is not bioaccumulative in plant or animal tissues but can be taken up by plants from contaminated soils, thus small amounts could be transferred up the food chain Adsorbs to soil to a lesser degree than TNT, is more soluble than RDX and is resistant to biodegradation in aquifers. Degradation and its breakdown products have rarely been found in the environment. Lethal concentration of TNT to plants in water is 5000 mg L1. Phytotoxicity from contaminated soil is dependant on soil properties, for example, plant yields are significantly reduced in silty soils when TNT concentrations reach 200 mg kg1 but no effects are observed at concentrations of less than 400 mg kg1 in clay. Laboratory research has also shown that TNT concentrations in soil greater than 9000 mg kg1 result in no surviving earthworms, whilst male animals treated with high doses of TNT have developed serious reproductive system effects. Plant species have been found to die in RDX contaminated soils at concentrations of 580 mg kg1. Studies into the phytotoxicity of RDX indicate a lethal concentration in water of 5 to 6 mg L1 with stunted growth of emergent species experienced at concentrations of 1.5 mg L1. Potential to cause liver and central nervous system damage but it is not known whether it causes cancer or reproductive problems in animals. HMX *Some of this information is taken from Warde, C, Lee, R and Baker, A, 2007. 25 Introduction to Explosives legislations have been implemented. These legislations include the Water Resources Act, Groundwater Regulation and Environmental Protection Act (see Table 1.9). With regards to the future, explosives may be made 'greener' by using less toxic reagents and solvents, and having a reduced environmental impact. The term 'green chemistry' was first used by Anastas and Warner in 1998 where toxic or noxious reagents Table 1.9 Environmental legislations which has an impact on explosive waste Environmental Legislation Comment Water Resources Act 1991 and Water Act 2003 It is an offence to cause or knowingly permit poisonous, noxious or polluting matter, or any solid waste matter, to enter controlled waters (which include groundwater). A list of materials that must be either prevented from reaching groundwater (red list) or whose introduction to groundwater should be reduced (grey list). Explosive compounds are not included on these lists but certain metals such as lead, copper, zinc and cadmium are. This defines the term contaminated land, where there is a release of substances that can cause harm. This prevents the release of toxic substances to the atmosphere. Groundwater Regulations 1998 Environmental Protection Act 1990 Waste Incineration Directive 2000 Table 1.10 Examples of processes for the recovery of explosives from the casing Removal of Explosive from casing Melt out and filtration Cryogenic wash-out High pressure water jet Induction heating Microwave melt out Ammonia washout Supercritical solvent extraction Explosive Status TNT, TNT/RDX TNT, TNT/RDX, PBX TNT, TNT/RDX, HMX, RDX, PBX TNT, TNT/RDX TNT, TNT/RDX TNT, TNT/RDX TNT, TNT/RDX, RDX, HMX, PBX Current Practice Current Practice Current Practice Current Practice Development Development Research 26 Chapter 1 are replaced with more environmentally acceptable ones, whilst minimizing waste and energy and maximising product yield. One way of making explosives greener is to reduce its environmental impact by recycling the explosives. This has been achieved with TNT where TNT based compositions are melted using a hot water bath. The recovered TNT is then solidified and re-used. However with the new IHE compositions containing PBXs this method is not viable. Methods are therefore being developed to remove the waste explosive compositions safely from the casing using mechanical methods or high-pressure water jet. The recovered material then has to be disposed of or recycled. Table 1.10 lists details of current and future technologies for the recovery of explosives. CHAPTER 2 Classification of Explosive Materials EXPLOSIONS An explosion occurs when a large amount of energy is suddenly released. This energy may come from an over-pressurized steam boiler, or from the products of a chemical reaction involving explosive materials, or from a nuclear reaction which is uncontrolled. In order for an explosion to occur there must be a local accumulation of energy at the site of the explosion which is suddenly released. This release of energy can be dissipated as blast waves, propulsion of debris, or by the emission of thermal and ionizing radiation. These types of explosion can be divided into three groups; physical explosions such as the over-pressurized steam boiler, chemical explosions as in the chemical reactions of explosive compositions, and atomic explosions. Atomic Explosions The energy produced from an atomic or nuclear explosion is a million to a billion times greater than the energy produced from a chemical explosion. The shockwaves from an atomic explosion are similar to those produced by a chemical explosion but will last longer and have a higher pressure in the positive pulse and a lower pressure in the negative phase. The heavy flux of neutrons produced from an atomic explosion would be fatal to anybody near The Chemistry of Explosives, 3rd Edition By Jacqueline Akhavan r J. Akhavan 2011 Published by the Royal Society of Chemistry, www.rsc.org 27 28 Chapter 2 the explosion, whereas those who are some distance from the explosion would be harmed by the gamma radiation. Atomic explosions also emit intense infra-red and ultra-violet radiation. Physical Explosions A physical explosion can arise when a substance whilst being compressed undergoes a rapid physical transformation. At the same time, the potential energy of the substance is rapidly transformed into kinetic energy, and its temperature rises rapidly, resulting in the production of a shockwave in the surrounding medium. An example of a physical explosion is the eruption of the Krakatoa volcano in 1883. During this eruption a large quantity of molten lava spilled into the ocean causing about 1 cubic mile of sea water to vapourize. This rapid vaporization created a blast wave which could by heard up to 3000 miles away. Chemical Explosions A chemical explosion is the result of a chemical reaction or change of state which occurs over an exceedingly short space of time with the generation of a large amount of heat and generally a large quantity of gas. Chemical explosions are produced by compositions which contain explosive compounds and which are compressed together but do not necessarily need to be confined. During a chemical explosion an extremely rapid exothermic transformation takes place resulting in the formation of very hot gases and vapours. Owing to the extreme rapidity of the reaction (onehundredth of a second), the gases do not expand instantaneously but remain for a fraction of a second inside the container occupying the volume that was once occupied by the explosive charge. As this space is extremely small and the temperature of explosion is extremely high (several thousands of degrees), the resultant pressure is therefore very high (several hundreds of atmospheres) – high enough to produce a 'blast wave' which will break the walls of the container and cause damage to the surrounding objects. If the blast wave is strong enough, damage to distant objects can also occur. The types of explosion described in this book are based on the explosions caused by the chemical reaction of explosive compositions. Classification of Explosive Materials 29 CHEMICAL EXPLOSIVES The majority of substances which are classed as chemical explosives generally contain oxygen, nitrogen and oxidizable elements (fuels) such as carbon and hydrogen. The oxygen is generally attached to nitrogen, as in the groups NO, NO2 and NO3. The exception to this rule are azides, such as lead azide (PbN6), and nitrogen compounds such as nitrogen triiodide (NI3) and azoimide (NH3NI3), which contain no oxygen. In the event of a chemical reaction, the nitrogen and oxygen molecules separate and then unite with the fuel components as shown in Reaction 2.1. (2.1) During the reaction large quantities of energy are liberated, generally accompanied by the evolution of hot gases. The heat given out during the reaction (heat of reaction) is the difference between the heat required to break up the explosive molecule into its elements and the heat released on recombination of these elements to form CO2, H2O, N2, etc. Classification of Chemical Explosives Classification of explosives has been undertaken by many scientists throughout this century, and explosives have been classified with respect to their chemical nature and to their performance and uses. Chemical explosives can be divided into two groups depending on their chemical nature; those that are classed as substances which are explosive, and those that are explosive mixtures such as blackpowder. Substances that are explosive contain molecular groups which have explosive properties. Examples of these molecular groups are: (1) nitro compounds; (2) nitric esters; (3) nitramines; 30 Chapter 2 (4) derivatives of chloric and perchloric acids; (5) azides; (6) various compounds capable of producing an explosion, for example, fulminates, acetylides, nitrogen-rich compounds such as tetrazene, peroxides and ozonides, etc. A systematic approach to the relationship between the explosive properties of a molecule and its structure was proposed by van't Hoff in 1909 and Plets in 1953. According to Plets, the explosive properties of any substance depend upon the presence of definite structural groupings. Plets divided explosives into eight classes as shown in Table 2.1. Classifying explosives by the presence of certain molecular groups does not give any information on the performance of the explosive. A far better way of classification is by performance and uses. Using this classification, explosives can be divided into three classes; (i) primary explosives, (ii) secondary explosives, and (iii) propellants as shown in Figure 2.1. PRIMARY EXPLOSIVES Primary explosives (also known as primary high explosives) differ from secondary explosives in that they undergo a very rapid transition from burning to detonation and have the ability to transmit the detonation to less sensitive explosives. Primary explosives will detonate when they are subjected to heat or shock. On detonation the molecules in the explosive dissociate and produce a tremendous amount of heat and/or shock. This will in turn initiate a second, Table 2.1 Classification of explosive substances by their molecular groups Group Explosive compounds –O–O– and –O–O–O– –OClO2 and –OClO3 –N–X2 NO2 and –ONO2 –N¼N– and –N¼N¼N– –N¼C –CRC– M–C Inorganic and organic peroxides and ozonides Inorganic and organic chlorates and perchlorates Where X is a halogen Inorganic and organic substances Inorganic and organic azides Fulminates Acetylene and metal acetylides Metal bonded with carbon in some organometallic compounds Classification of Explosive Materials Figure 2.1 Classification of explosive substances. 31 32 Chapter 2 more stable explosive. For these reasons, they are used in initiating devices. The reaction scheme for the decomposition of the primary explosive lead azide is given in Reaction 2.2. 1=2PbN 6 ! 1=2Pb2þ þ N3 ! 1=2Pb þ N2 þ N (2:2) This reaction is endothermic, taking in 213 kJ of energy. According to Reaction 2.2, one atom of nitrogen is expelled from the N3 ion. This nitrogen then reacts with another N3 ion to form two molecules of nitrogen as shown in Reaction 2.3. 1=2PbN 6 þ N ! 1=2Pb2þ þ N3 þ N ! 1=2Pb þ 2N2 (2:3) Reaction 2.3 is highly exothermic, producing 657 kJ of energy. The decomposition of one N3 group may involve 2–3 neighbouring N3 groups. If these groups decompose simultaneously, the decomposition of 22 N3 ions may occur. Thus the rapid transition of lead azide to detonation may be accounted for by the fact that decomposition of a small number of molecules of lead azide may induce an explosion in a sufficiently large number of N3 ions to cause the explosion of the whole mass. Primary explosives differ considerably in their sensitivity to heat and in the amount of heat they produce on detonation. The heat and shock on detonation can vary but is comparable to that for secondary explosives. Their detonation velocities are in the range of 3500–5500 m s1. Primary explosives have a high degree of sensitivity to initiation through shock, friction, electric spark or high temperatures and explode whether they are confined or unconfined. Typical primary explosives which are widely used are lead azide, lead styphnate (trinitroresorcinate), lead mononitroresorcinate (LMNR), potassium dinitrobenzofurozan (KDNBF) and barium styphnate. Other primary explosive materials which are not frequently used today are mercury azide and mercury fulminate. SECONDARY EXPLOSIVES Secondary explosives (also known as high explosives) differ from primary explosives in that they cannot be detonated readily by heat or shock and are generally more powerful than primary explosives. Secondary explosives are less sensitive than primary explosives and Classification of Explosive Materials 33 can only be initiated to detonation by the shock produced by the explosion of a primary explosive. On initiation, the secondary explosive compositions dissociate almost instantaneously into other more stable components. An example of this is shown in Reaction 2.4. C3 H6 N6 O6 ! 3CO þ 3H2 O þ 3N2 (2:4) RDX (C3H6N6O6) will explode violently if stimulated with a primary explosive. The molecular structure breaks down on explosion leaving, momentarily, a disorganized mass of atoms. These immediately recombine to give predominantly gaseous products evolving a considerable amount of heat. The detonation is so fast that a shockwave is generated that acts on its surroundings with great brisance (or shattering effect) before the pressure of the exerted gas can take effect. Some secondary explosives are so stable that rifle bullets can be fired through them or they can be set on fire without detonating. The more stable explosives which detonate at very high velocities exert a much greater force during their detonation than the explosive materials used to initiate them. Values of their detonation velocities are in the range of 5500–9000 m s1. Examples of secondary explosives are TNT, tetryl, picric acid, nitrocellulose, nitroglycerine, nitroguanidine, RDX, HMX and TATB. Examples of commercial secondary explosives are blasting gelatine, guhr dynamite and 60% gelatine dynamite. PROPELLANTS Propellants are combustible materials containing within themselves all the oxygen needed for their combustion. Propellants only burn and do not explode; burning usually proceeds rather violently and is accompanied by a flame or sparks and a hissing or crackling sound, but not by a sharp, loud bang as in the case of detonating explosives. Propellants can be initiated by a flame or spark, and change from a solid to a gaseous state relatively slowly, i.e. in a matter of milliseconds. Examples of propellants are blackpowder, smokeless propellant, blasting explosives and ammonium nitrate explosives, which do not contain nitroglycerine or other aromatic nitro compounds. 34 Chapter 2 CHEMICAL DATA ON EXPLOSIVE MATERIALS Primary Explosives Mercury Fulminate. Mercury fulminate (C2N2O2Hg) (2.1) is obtained by treating a solution of mercuric nitrate with alcohol in nitric acid. (2.1) This reaction, together with its products, has been studied by a number of chemists, including Liebig, who gave an account of the elementary chemical composition of fulminate in 1823. The mechanism of the reaction which results in the formation of mercury fulminate was reported by Wieland and by Solonina in 1909 and 1910, respectively. The most important explosive property of mercury fulminate is that after initiation it will easily detonate. On detonation, it decomposes to stable products as shown in Reaction 2.5. ðCNOÞ2 Hg ! 2CO þ N2 þ Hg (2:5) Mercury fulminate is sensitive to impact and friction, and is easily detonated by sparks and flames. It is desensitized by the addition of water but is very sensitive to sunlight and decomposes with the evolution of gas. Some of the properties of mercury fulminate are presented in Table 2.2. Table 2.2 Properties of mercury fulminate Characteristics Explosive material Colour Grey, pale brown or white crystalline solid 284.624 160 90 170 4.42 +267.99 +272.92 Molecular weight Melting temperature/1C Decomposition temperature/1C Thermal ignition temperature/1C Density at 20 1C/g cm3 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Classification of Explosive Materials 35 Lead Azide. Lead azide (PbN6) (2.2) was first prepared by Curtius in 1891. (2.2) Curtius added lead acetate to a solution of sodium or ammonium azide resulting in the formation of lead azide. In 1893, the Prussian Government carried out an investigation into using lead azide as an explosive in detonators, when a fatal accident occurred and stopped all experimental work in this area. No further work was carried out on lead azide until 1907 when Wöhler suggested that lead azide could replace mercury fulminate as a detonator. The manufacture of lead azide for military and commercial primary explosives did not commence until 1920 because of the hazardous nature of the pure crystalline material. Lead azide has a good shelf life in dry conditions, but is unstable in the presence of moisture, oxidizing agents and ammonia. It is less sensitive to impact than mercury fulminate, but is more sensitive to friction. Lead azide is widely used in detonators because of its high capacity for initiating other secondary explosives to detonation. On a weight basis, it is superior to mercury fulminate in this role. However, since lead azide is not particularly susceptible to initiation by impact it is not used alone in initiator components. Instead, it is used with lead styphnate and aluminium (ASA mixtures) for military detonators, in a mixture with tetrazene, and in a composite arrangement topped with a more sensitive composition. Lead azide can exist in two allotropic forms; the more stable a-form which is orthorhombic, and the b-form which is monoclinic. The a-form is prepared by rapidly stirring a solution of sodium azide with a solution of lead acetate or lead nitrate, whereas the b-form is prepared by slow diffusion of sodium azide in lead nitrate solutions. The b-form has a tendency to revert to the a-form when its crystals are added to a solution containing either the a-form crystals or a lead salt. If the b-form crystals are left at a temperature of B160 1C they will also convert to the a-form. Some of the properties of lead azide are presented in Table 2.3. 36 Table 2.3 Chapter 2 Properties of lead azide Characteristics Explosive material Colour Molecular weight Decomposition temperature/1C Boiling point/1C Thermal ignition temperature/1C Density at 20 1C/g cm3 a-form orthorhombic b-form monoclinic Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Colourless to white crystalline solid 291.24 190 350 327–360 4.17 4.93 +468.61 +476.06 Lead Styphnate. Lead styphnate (2.3), also known as lead 2,4,6trinitroresorcinate (C6H3N3O8 Pb), is usually prepared by adding a solution of lead nitrate to magnesium styphnate. Lead styphnate is practically insoluble in water and most organic solvents. It is very stable at room- and elevated-temperatures (e.g. 75 1C) and is non-hygroscopic. Lead styphnate is exceptionally resistant towards nuclear radiation and can easily be ignited by a flame or electric spark. It is very sensitive to the discharge of static electricity and many accidents have occurred during its preparation. Attempts have been made to reduce its sensitiveness1 to static discharge by adding graphite, but so far this has been unsuccessful and lead styphnate continues to be very dangerous to handle. OH O2N NO2 Pb(II) OH NO2 (2.3) Lead styphnate is a weak primary explosive because of its high metal content (44.5%) and therefore is not used in the filling of detonators. It is used in ignition caps, and in the ASA (i.e. lead azide, lead styphnate and aluminium) mixtures for detonators. Some of its properties are shown in Table 2.4. 1 In this book the term 'sensitiveness' is used to describe the response of an explosive to accidental initiation, i.e. friction, impact, etc., whereas 'sensitivity' is used when the explosive is initiated by non-accidental methods, i.e. shock from a primary explosive. 37 Classification of Explosive Materials Table 2.4 Properties of lead styphnate (lead 2,4,6-trinitroresorcinate) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Decomposition temperature/1C Thermal ignition temperature/1C Density at 20 1C/g cm3 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Orange-yellow to dark brown crystalline solid 468.305 260–310 235 330 3.02 –836.80 –818.22 Table 2.5 Properties of silver azide Characteristics Explosive material Colour Molecular weight Melting temperature/1C Boiling temperature/1C Density at 20 1C/g cm3 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Fine white crystalline solid 149.888 252 297 5.1 +308.78 +312.50 Silver Azide. Silver azide (AgN3) (2.4) is manufactured in the same way as lead azide, by the action of sodium azide on silver nitrate in an aqueous solution. (2.4) Silver azide is slightly hygroscopic and is a very vigorous initiator, almost as efficient as lead azide. Like lead azide, silver azide decomposes under the influence of ultra-violet irradiation. If the intensity of radiation is sufficiently high the crystals may explode by photochemical decomposition. The ignition temperature and sensitiveness to impact of silver azide are lower than that of lead azide. Some of its properties are presented in Table 2.5. Tetrazene. Tetrazene or tetrazolyl guanyltetrazene hydrate (C2H6N10 H2O) (2.5) was first prepared by Hoffmann and Roth in 1910 by the action of a neutral solution of sodium nitrite on 38 Chapter 2 aminoguanidine salts. In 1921, Rathsburg suggested the use of tetrazene in explosive compositions. N N N NH2 C N N N C NH2 H2O . NH NH (2.5) Tetrazene is slightly hygroscopic and stable at ambient temperatures. It hydrolyses in boiling water evolving nitrogen gas. Its ignition temperature is lower than that for mercury fulminate and it is slightly more sensitive to impact than mercury fulminate. The detonation properties of tetrazene depend on the density of the material, i.e. its compaction. Tetrazene will detonate when it is not compacted but when pressed it produces a weaker detonation. These compaction properties make the transition from burning to detonation very difficult. Therefore, tetrazene is unsuitable for filling detonators. Tetrazene is used in ignition caps where a small amount is added to the explosive composition to improve its sensitivity to percussion and friction. Some of the properties of tetrazene are given in Table 2.6. Secondary Explosives Nitroglycerine. Nitroglycerine (C3H5N3O9) (2.6) was first prepared by the Italian, Ascanio Sobrero in 1846 by adding glycerol to a mixture of sulfuric and nitric acids. In 1863, a laboratory plant was set up to manufacture nitroglycerine by the Nobel family. In 1882, the Boutmy–Faucher process for the manufacture of Table 2.6 Properties of tetrazene Characteristics Explosive material Colour Molecular weight Melting temperature/1C Decomposition temperature/1C Thermal ignition temperature/1C Density at 20 1C/g cm3 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Light colourless or pale yellow crystalline solid 188.152 140–160 100 140 1.7 +189.12 +212.59 39 Classification of Explosive Materials nitroglycerine was developed in France and also adopted in England. (2.6) Nitroglycerine is a very powerful secondary explosive with a high brisance, i.e. shattering effect, and it is one of the most important and frequently-used components for gelatinous commercial explosives. Nitroglycerine also provides a source of high energy in propellant compositions, and in combination with nitrocellulose and stabilizers it is the principal component of explosive powders and solid rocket propellants. Nitroglycerine is toxic to handle, causes headaches, and yields toxic products on detonation. It is insoluble in water but readily dissolves in most organic solvents and in a large number of aromatic nitro compounds, and forms a gel with nitrocellulose. The acid-free product is very stable, but exceedingly sensitive to impact. Some of the properties of nitroglycerine are presented in Table 2.7. Nitrocellulose. Nitrocellulose (2.7) was discovered by C.F. Schönbeim at Basel and R. Böttger at Frankfurt-am-Main during 1845–47. The stability of nitrocellulose was improved by Table 2.7 Properties of nitroglycerine Characteristics Explosive material Colour Molecular weight Melting temperature/1C Thermal ignition temperature/1C Boiling point/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Yellow oil 227.087 10.2–13.8 200 218 145.7* 1.593 135.8* –370.70 –349.66 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). 40 Chapter 2 Abel in 1865 and its detonation properties were developed by Abel's assistant, Brown. (2.7) The name, nitrocellulose does not refer to a single type of molecular compound but is a generic term denoting a family of compounds. The customary way to define its composition is to express the nitrogen content as a percentage by weight. The number of nitrate groups present in nitrocellulose can be calculated using Equation 2.1, where N is the percentage of nitrogen calculated from chemical analysis. y¼ 162N 1400 45N ð2:1Þ If the structure for the unit cell of cellulose (2.8) is written as C6H7O2(OH)3, then nitrocellulose can be written as C6H7O2(OH)x (ONO2)y, where x + y = 3. (2.8) 41 Classification of Explosive Materials A product containing on average two nitrate groups, i.e. [C6H7O2(OH)1(ONO2)2], will contain 11.11% nitrogen as shown in Equation 2.2. 162N 1400 45N 2ð1400 45NÞ ¼ 162N 2800 90N ¼ 162N 2¼ ð2:2Þ 11:1 ¼ N A product containing three nitrate groups, i.e. [C6H7O2(ONO2)3], will therefore contain 14.14% nitrogen. In practice, nitrocellulose compositions used in explosive applications vary from 10 to 13.5% of nitrogen. Nitrocellulose materials prepared from cotton are fluffy white solids, which do not melt but ignite in the region of 180 1C. They are sensitive to initiation by percussion or electrostatic discharge and can be desensitized by the addition of water. The thermal stability of nitrocellulose decreases with increasing nitrogen content. The chemical stability of nitrocellulose depends on the removal of all traces of acid in the manufacturing process. Cellulose is insoluble in organic solvents, whereas nitrocellulose dissolves in organic solvents to form a gel. The gel has good physical properties due to the polymeric nature of nitrocellulose, and is an essential feature of gun propellants, double-base rocket propellants, gelatine and semi-gelatine commercial blasting explosives. Some of the properties of nitrocellulose are presented in Table 2.8. Picric Acid. Glauber in 1742 reacted nitric acid with wool or horn and produced picric acid in the form of lead or potassium Table 2.8 Properties of nitrocellulose Characteristics Explosive material Colour Molecular weight Melting temperature/1C Thermal ignition temperature/1C Boiling point/1C Density at 251/g cm3 Enthalpy of formation/kJ mol1 Energy of formation/kJ mol1 White fibres 297.106 (14.14%N) 150–169 (decomp) o100 190 1.66 max value by pressing –652.66 (14.14%N) –626.64 (14.14%N) 42 Chapter 2 picrate. In 1771, Woulfe prepared picric acid by treating indigo with nitric acid, and in 1778 Haussmann isolated picric acid also known as 2,4,6-trinitrophenol (C6H3N3O7) (2.9). (2.9) Other early experimenters obtained picric acid by nitrating various organic substances such as silk, natural resins, etc. The correct empirical formula for picric acid was determined by Laurent in 1841 who prepared the acid by reacting phenol with nitric acid and isolated dinitrophenol which was formed in an intermediate stage of the reaction. Picric acid is a strong acid, very toxic, soluble in hot water, alcohol, ether, benzene and acetone, and is a fast yellow dye for silk and wool. It attacks common metals, except for aluminium and tin, and produces salts which are very explosive. The explosive power of picric acid is somewhat superior to that of TNT, both with regard to the strength and the velocity of detonation. Picric acid was used in grenade and mine fillings and had a tendency to form impact-sensitive metal salts (picrates) with the metal walls of the shells. The filling of mines and grenades was also a hazardous process, since relatively high temperatures were needed to melt the picric acid. Some of the properties of picric acid are presented in Table 2.9. Tetryl. Tetryl (2.10), also known as 2,4,6-trinitrophenylmethylnitramine (C7H5N5O8), was first obtained by Mertens in 1877 and its structure determined by Romburgh in 1883. (2.10) 43 Classification of Explosive Materials Table 2.9 Properties of picric acid (2,4,6-trinitrophenol) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Thermal ignition temperature/1C Boiling point/1C Flash point/1C Density at 19 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Yellow crystalline solid 229.106 121.8–122.4 300 160–198 (decomp) 133.9* 1.767 123.3* –214.35 –198.24 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). Table 2.10 Properties of tetryl Characteristics Explosive material Colour Molecular weight Melting temperature/1C Decomposition temperature/1C Thermal ignition temperature/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Light yellow crystalline solid 287.145 129.5 162 187 258.4* 1.731 159.2* +33.89 +56.19 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). Tetryl has been used as an explosive since 1906. In the early part of this century it was frequently used as the base charge of blasting caps but is now replaced by PETN or RDX. During World War II, it was used as a component of explosive mixtures. Tetryl is a pale yellow, crystalline solid with a melting temperature of 129 1C. It is moderately sensitive to initiation by friction and percussion, and is used in the form of pressed pellets as primers for explosive compositions which are less sensitive to initiation. It is slightly more sensitive than picric acid, and considerably more sensitive than TNT. Tetryl is quite toxic to handle and is now being replaced by RDX and wax (called Debrix). Some of the properties of tetryl are presented in Table 2.10. 44 Chapter 2 TNT. Trinitrotoluene (C7H5N3O6) can exist as six different isomers. The isomer that is used in the explosives industry is the symmetrical isomer 2,4,6-trinitrotoluene (2.11). For convenience, the 2,4,6-isomer will be referred to in this book as TNT. (2.11) TNT was first prepared in 1863 by Wilbrand and its isomers discovered in 1870 by Beilstein and Kuhlberg. Pure TNT (2,4,6trinitrotoluene isomer) was prepared by Hepp in 1880 and its structure determined by Claus and Becker in 1883. The development of TNT throughout the 19th and 20th centuries is summarized in Table 2.11. TNT is almost insoluble in water, sparingly soluble in alcohol and will dissolve in benzene, toluene and acetone. It will darken in sunlight and is unstable in alkalis and amines. Some of the properties of TNT are presented in Table 2.12. TNT has a number of advantages which have made it widely used in military explosives before World War I and up to the present time. These include low manufacturing costs and cheap raw materials, safety of handling, a low sensitivity to impact and friction, and a fairly high explosive power. TNT also has good chemical and thermal stability, low volatility and hygroscopicity, good compatibility with other explosives, a low melting point for casting, and moderate toxicity. TNT is by far the most important explosive for blasting charges. It is widely used in commercial explosives and is much safer to produce and handle than nitroglycerine and picric acid. A lower grade of TNT can be used for commercial explosives, whereas the military grade is very pure. TNT can be loaded into shells by casting as well as pressing. It can be used on its own or by mixing with other components such as ammonium nitrate to give amatols, aluminium powder to give tritonal, RDX to give cyclonite and composition B. One of the major disadvantages of TNT is the exudation (leaching out) of the isomers of dinitrotoluenes and trinitrotoluenes. Even a minute quantity of these substances can result 45 Classification of Explosive Materials Table 2.11 Date Summary of the development of TNT (2,4,6-trinitrotoluene) throughout the 19th and 20th centuries Developments 1837 1841 1863 1870 1880 1882 1883 1891 1899 1900 Pelletier and Walter first prepared toluene. Mononitrated toluene was prepared. Wilbrand prepared crude TNT. Beilstein and Kuhlberg discovered the isomer 2,4,5-trinitrotoluene. Hepp prepared pure TNT (2,4,6-trinitrotoluene). The 2,3,4-trinitrotoluene isomer prepared. Claus and Becker determined structure of 2,4,6-trinitrotoluene. TNT was manufactured in Germany. Aluminium was added to TNT for use as explosives. Improved production of raw materials for TNT therefore reducing its cost. 1902 TNT replaced picric acid in the German Army. 1912 Use of TNT began in the US Army. 1913 Reduction in price of raw material (nitric acid) by the commercialization of the Haber–Bosch process for ammonia synthesis. 1914 Will determined structures of isomers 2,3,4- and 2,4,5-trinitrotoluene. 1914–18 Standard explosive for World War I. Production limited by availability of toluene from coal tar. To relieve shortage, TNT was mixed with ammonium nitrate to give amatols, and aluminium to produce tritonals. 1903–40 TNT was mixed with RDX to give cyclotols. 1939–45 During World War II, an improved process was developed for producing petroleum naphthas ensuring unlimited quantities of toluene. Purification techniques were improved for TNT. Composites mixtures of TNT–PETN, TNT–RDX, TNT–tetryl, TNT–ammonium picrate, TNT–aluminium, etc., were prepared. 1952 TNT was mixed with HMX to give octols. 1966 Shipp prepared HNS from TNT. 1968 Continuous production of TNT in the USA. 1978 Adkins and Norris prepared TATB from TNT. Table 2.12 Properties of TNT (2,4,6-trinitrotoluene) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Thermal ignition temperature/1C Boiling point/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Pale yellow crystalline solid 227.133 80.7 300 345–373 167.1* 1.654 141.2* –62.07 –45.44 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). 46 Chapter 2 in exudation. This often occurs in the storage of projectiles containing TNT, particularly in the summer time. The main disadvantage caused by exudation is the formation of cracks and cavities leading to premature detonation and a reduction in its density. Migration of the isomers to the screw thread of the fuse will form 'fire channels'. These fire channels can lead to accidental ignition of the charge. If the migrating products penetrate the detonating fuse, malfunctioning of the ammunition components can occur. Nitroguanidine. Nitroguanidine (2.12), also known as picrite (CH4N4O2), was first prepared by Jousselin in 1877 by dissolving dry guanidine nitrate in fuming nitric acid and passing nitrous oxide through the solution. The solution was poured into water and a precipitate was obtained which Jousselin called 'nitrosoguanidine', but which was later determined to be nitroguanidine by Thiele. (2.12) Nitroguanidine is relatively stable below its melting point but decomposes immediately on melting to form ammonia, water vapour and solid products. The gases from the decomposition of nitroguanidine are far less erosive than gases from other similar explosives. Nitroguanidine is soluble in hot water and alkalis, and insoluble in ethers and cold water. It has a high velocity of detonation, a low heat and temperature of explosion, and a high density. Some of the properties of nitroguanidine are given in Table 2.13. Nitroguanidine can be used as a secondary explosive but is also suitable for use in flashless propellants as it possesses a low heat and temperature of explosion. These propellants contain a mixture of nitroguanidine, nitrocellulose, nitroglycerine and nitrodiethyleneglycol which together form a colloidal gel. Nitroguanidine does not dissolve in the gel, but becomes embedded as a fine dispersion. This type of colloidal propellant has the advantage of reducing the erosion of the gun barrel compared with conventional propellants. PETN. PETN (2.13), also known as pentaerythritol tetranitrate (C5H8N4O12), is the most stable and the least reactive of the 47 Classification of Explosive Materials Table 2.13 Properties of nitroguanidine Characteristics Explosive material Colour White fibre-like crystalline solid 104.068 Molecular weight Melting temperature/1C a-form b-form Decomposition temperature/1C Boiling point at 760 Torr/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 232 232 232 219.3* 86.5* 1.77 51.8* –92.05 –79.66 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). explosive nitric esters. It is insoluble in water, sparingly soluble in alcohol, ether and benzene, and soluble in acetone and methyl acetate. It shows no trace of decomposition when stored for a long time at 100 1C. It is relatively insensitive to friction but is very sensitive to initiation by a primary explosive. (2.13) PETN is a powerful secondary explosive and has a great shattering effect. It is used in commercial blasting caps, detonation cords and boosters. PETN is not used in its pure form because it is too sensitive to friction and impact. It is therefore usually mixed with plasticized nitrocellulose, or with synthetic rubbers to form polymer bonded explosives (PBXs). The most common form of explosive composition containing PETN is called Pentolite, which is a mixture of 20–50% PETN and TNT. PETN can also be formed into a rubber-like sheet and used in metal-forming, metal cladding and metal-hardening processes. PETN can also be incorporated into gelatinous industrial explosives. In military applications PETN has been largely replaced by RDX since RDX is more thermally stable and has a longer shelf life. Some of the properties of PETN are given in Table 2.14. 48 Table 2.14 Chapter 2 Properties of PETN (pentaerythritol tetranitrate) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Thermal ignition temperature/1C Boiling point/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Colourless crystalline solid 316.138 142.9 202 180 198.8* 1.778 187.6* –530.53 –500.82 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). RDX. RDX (2.14), also known as Hexogen, Cyclonite and cyclotrimethylenetrinitramine (C3H6N6O6), was first prepared in 1899 by Henning for medicinal use and used as an explosive in 1920 by Herz. The properties and preparation of RDX were fully developed during World War II. (2.14) RDX is a white, crystalline solid with a melting temperature of 204 1C. It attained military importance during World War II since it is more chemically and thermally stable than PETN and has a lower sensitiveness. Pure RDX is very sensitive to initiation by impact and friction and is desensitized by coating the crystals with wax, oils or grease. It can also be compounded with mineral jelly and similar materials to give plastic explosives. Insensitive explosive compositions containing RDX can be achieved by embedding the RDX crystals in a polymeric matrix. This type of composition is known as a polymer bonded explosive (PBX) and is less sensitive to accidental initiation. RDX has a high chemical stability and great explosive power compared with TNT and picric acid. It is difficult to dissolve RDX in organic liquids but it can be recrystallized from acetone. It has a 49 Classification of Explosive Materials Table 2.15 Properties of RDX (cyclotrimethylenetrinitramine) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Type A RDX Type B RDX Decomposition temperature/1C Thermal ignition temperature/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 White crystalline solid 222.117 202–204 192–193 213 210 405.6* 1.816 117.0* +70.29 +92.59 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). high melting point which makes it difficult to use in casting. However, when it is mixed with TNT, which has a low melting temperature, a pourable mixture can be obtained. Some of the properties of RDX are presented in Table 2.15. HMX. HMX (2.15), also known as Octogen and cyclotetramethylenetetranitramine (C4H8N8O8), is a white, crystalline substance which appears in four different crystalline forms differing from one another in their density and sensitiveness to impact. The b-form, which is least sensitive to impact, is employed in secondary explosives. (2.15) HMX is non-hygroscopic and insoluble in water. It behaves like RDX with respect to its chemical reactivity and solubility in organic solvents. However, HMX is more resistant to attack by sodium hydroxide and is more soluble in 55% nitric acid, and 50 Table 2.16 Chapter 2 Properties of HMX (cyclotetramethylenetetranitramine) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Decomposition temperature/1C Thermal ignition temperature/1C Flash point/1C Density at 20 1C and 760 Torr/g cm3 a-form b-form g-form d-form Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 White crystalline solid 296.156 275–280 280 335 501.8* 1.87 1.96 1.82 1.78 151.7* +75.02 +104.73 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). 2-nitropropane than RDX. In some instances, HMX needs to be separated from RDX and the reactions described above are employed for the separation. As an explosive, HMX is superior to RDX in that its ignition temperature is higher and its chemical stability is greater; however, the explosive power of HMX is somewhat less than RDX. Some of the properties of HMX are presented in Table 2.16. TATB. TATB (2.16) is also known as 1,3,5-triamino-2,4,6-trinitrobenzene (C6H6N6O6) and was first obtained in 1888 by Jackson and Wing. (2.16) It is a yellow-brown coloured substance which decomposes rapidly just below its melting temperature. It has excellent thermal stability in the range 260–290 1C and is known as a heat-resistant explosive. Some of the properties of TATB are given in Table 2.17. 51 Classification of Explosive Materials Table 2.17 Properties of TATB (1,3,5-triamino-2,4,6-trinitrobenzene) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Decomposition temperature/1C Thermal ignition temperature/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Yellow-brown crystalline solid 258.15 448.5 >350 384 358.7* 1.937 131.7* –154.18 –132.51 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). Figure 2.2 Configuration of the TATB molecule. The structure of TATB contains many unusual features. The unit cell of TATB consists of molecules arranged in planar sheets. These sheets are held together by strong intra- and intermolecular hydrogen bonding, resulting in a graphite-like lattice structure with lubricating and elastic properties as shown in Figure 2.2. HNS. HNS [hexanitrostilbene (C14H6N6O12)] (2.17) is known as a heat-resistant explosive and is also resistant to radiation. It is practically insensitive to an electric spark and is less sensitive 52 Table 2.18 Chapter 2 Properties of HNS (hexanitrostilbene) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Decomposition temperature/1C Thermal ignition temperature/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 Yellow crystalline solid 450.235 318 318 325 275.4* 1.745 243.6* +78.24 +107.95 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). to impact than tetryl. Some of the properties of HNS are shown in Table 2.18. (2.17) HNS is used in heat-resistant booster explosives and has been used in the stage separation in space rockets and for seismic experiments on the moon. NTO. NTO [5-nitro-1,2,4-triazole-3-one (C2H2N4O3)] (2.18) is a new energetic material with attractive characteristics and high performance. It has a high heat of reaction and is less sensitive and more stable than RDX. O NH C NO2 HN N C (2.18) NTO is being developed in many areas these include i) a substitute for ammonium perchlorate or ammonium nitrate in solid rocket propellants, since it does not liberate undesirable products such as HCl and has quite a high burn rate compared to ammonium perchlorate and ammonium nitrate, ii) used as a burning rate 53 Classification of Explosive Materials Table 2.19 Properties of NTO (5-nitro-1,2,4-triazole-3-one) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Decomposition temperature/1C Thermal ignition temperature/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 White 130.06 270–271 273 258–280 1.92 52.7 –100.8 modifier for composite propellants, iii) replacing RDX and HMX in composite solid propellants, and iv) improving the performance of gun propellants. Some of the properties of NTO are given in Table 2.19. TNAZ. TNAZ (2.19) is also known as 1,3,3-trinitroazetidine (C3H4N4O6) and was first prepared in 1983 at Fluorochem Inc. It is reported to be more thermally stable than RDX but more reactive than HMX. Pure TNAZ is more shock sensitive than the explosives based on HMX but less sensitive than analogous PETN. It can be used as a castable explosive and as an ingredient in solid rocket and gun propellant. NO2 N CH2 H2C C O2N NO2 (2.19) TNAZ is a white crystalline solid and is soluble in acetone, methanol, ethanol, tetrachloromethane and cyclohexane. It has a relatively high vapour pressure and the solidification of its melt is accompanied by a high volume contraction resulting in the formation of shrinkage cavities giving 10–12% porosity. TNAZ exists in two crystal structures, the higher density crystal structure is more stable than the lower density crystal structure. The size of the crystals can be controlled by crystallizing TNAZ from a saturated solution of TNAZ and using an ultra-centrifuge, where the formation of defects in the crystal is minimised. An addition of 5–25% wt 54 Table 2.20 Chapter 2 Eutectic mixtures of TNAZ Additive Melting point of additive/1C Melting point of eutectic/1C TNAZ content in eutectic/mol% TNT Tetryl HMX 80.8 129.5 275 60.0 81.4 95.9 63.3–65.0 65.0 97.9 Table 2.21 Properties of TNAZ (1,3,3-trinitroazetidine) Characteristics Explosive material Colour Molecular weight Melting temperature/1C Boiling point/1C Flash point/1C Density at 20 1C/g cm3 Molar volume at 20 1C and 760 Torr/cm3 mol1 Enthalpy of formation/kJ mol1 Energy formation/kJ mol1 White crystalline solid 192.088 101 252 (decomp) 270.5* 1.7 104.3* +33.64 +50.96 *Calculated using Advanced Chemistry Development (ACD/Labs) Software V11.02 (r 1994–2010 ACD/Labs). of a nitroaromatic amine to TNAZ can reduce the shock sensitivity of TNAZ. This is due to the additive acting as nucleation sites for TNAZ when it is crystallised from the melt, resulting in a more homogeneous structure. TNAZ forms eutectic mixtures with some energetic materials, the details are presented in Table 2.20. Some properties of TNAZ are shown in Table 2.21. CL-20. CL-20 (2.20) also known as HNIW [2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (C6H6N12O12)] belongs to the