Explosive crystallization

HNO4 Peroxonitric acid Unstable, explosive crystals, HOONO2 no solid salts known. (For orthonitrates , N04 , i.e. salts of the unknown orthonitric acid H3NO4, see p. 471 -2)... 

Dehnicke, K,Angew. Chem. (Intern. Ed.), 1979,18, 512 Highly explosive crystals. 

An interesting class of molecular crystals are those that easily decompose exothermally i.e., explosive crystals. Some form from small molecules such as lead azide [Pb(N3)2] and ammonium perchlorate (NH4CIO4) and others form moderately large molecules such as RDX (cyclotrimethylenetrinitramine), and PETN (pentaerythritol-tetranitrate). 

Initiation by Electric Fields. Silver Azide can be initiated by DC fields of ca 70v (min field strength for explosion ca 250v/cm) at extremely low current flow (Bowden Yoffe Fast Reactions in Solids Acad Press (1958) p 101). Maycock Grabenstein [Science 152, 508 (1966) CA 65, 562 (1966)] have postulated that piezoelectric effects generated by compressing explosive crystals may generate sufficiently large electric fields to initiate these crystals... 

They subjected to irradiation a number of sensitive explosive crystals (such as Pb, Ag ... 

Friction between the impacting surfaces, explosive crystals, and/or grit particles in the explosive layer. 

The cyclonite was then washed with water and after neutralizing the residual acid with a 5% solution of sodium carbonate it was recrystallized. Initially, cyclonite was crystallized from nitrobenzene. However this proved to be dangerous due to the high boiling point of the solvent after a plant had been destroyed by an explosion, crystallization from acetone was adopted. The spent acid is denitrated, and KHSO ... 

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. 

Phlegmatizers are added to explosives to aid processing and reduce impact and friction sensitivity of highly sensitive explosives. Phlegmatizers can be waxes which lubricate the explosive crystals and act as a binder. 

In order to achieve the maximum velocity of detonation for a homogeneous explosive, it is necessary to consolidate the explosive composition to its maximum density. For a crystalline explosive the density of compaction will depend upon the consolidation technique (i.e. pressing, casting, extrusion, etc.). The limiting density will be the density of the explosive crystal. The velocity of detonation can be calculated from the density of the explosive composition using Equation 3.5,... 

Extruded explosive compositions contain a polymer which binds the explosive crystals together. The polymer acts as an adhesive and helps the explosive composition to retain its shape after extrusion. 

This book outlines the basic principles needed to understand the mechanism of explosions by chemical explosives. The history, theory and chemical types of explosives are introduced, providing the reader with information on the physical parameters of primary and secondary explosives. Thermodynamics, enthalpy, free energy and gas equations are covered together with examples of calculations, leading to the power and temperature of explosions. A very brief introduction to propellants and pyrotechnics is given, more information on these types of explosives should be found from other sources. This second edition introduces the subject of Insensitive Munitions (IM) and the concept of explosive waste recovery. Developments in explosive crystals and formulations have also been updated. This book is aimed primarily at A level students and new graduates who have not previously studied explosive materials, but it should prove useful to others as well. I hope that the more experienced chemist in the explosives industry looking for concise information on the subject will also find this book useful. 

J. Eadie reported in Ref 71 that the shock sensitivity of HMX/wax compacts is found to decrease as the amount of the HMX surface coated with wax increased. This thus indicates that the shock sensitivity depends on the surface area of the reactive expl exposed to reaction products. Similar results were observed 20 years earlier and reported in Ref 26. The following is a quote from this Ref, It was noted in the course of this work that the quantity of inert material per se was not the important factor in the phenomenon of desensitization. As a matter of fact, it was the thoroughness with which the explosive crystals (PETN) were coated that appeared to be an important factor in desensitization. Table 6 contains the results of the impact sensitivity tests conducted on PETN-wax mixts where both the quantity of wax in the mix and the degree of coating on the expl crystal are taken into account... 

Pollock, Slow Decomposition of Explosive Crystals and their Damage by Fission Fragments , Nature 191, 556—59 (1961) 89) F.P. Bowden... 

H.M. Montagu-Pollock, Surface Decomposition of an Explosive Crystal , ProcRoySoc A269, 219-32 (1962) 97) F.P. Bowden ... 

Isotherm fitting forms. There are two published measurements of the room temperature isotherm for /3-HMX. As part of a series of experiments to determine isotherms for various explosive crystals, Olinger, Roof, and Cady reported in 1978 an x-ray determination of the room temperature lattice parameters of / -HMX in the pressure interval 0 < p < 1A1 Gpa [68]. They fit the isotherm to an equation of state (EOS)... 

Fig. 2. SEM micrograph of a rapidly electron-beam-annealed amorphous Si film that was thermally evaporated on a silica substrate. The 20-keV, 1-//A electron beam was focused to 2 /im and raster scanned at a rate of 2.5 cm sec-1, (a) Shows a periodic crescent-shaped explosive crystallization pattern, (b) Two different types of explosive crystallization features appear at slightly higher scan speed.

Rapid scanned laser annealing of a-Si films revealed similar explosive crystallization mechanisms (Bensahel and Auvert, 1983a,b). Experiments... 

Fig. 3. Explosive crystallization in a-Si by rapid argon-laser scanning, (a) At a scan speed of 85 cm sec-1 both explosive solid-phase crystallization and liquid-phase crystallization are exhibited, (b) Two different types of solid phase crystallization are Observed at a scan speed of 900 cm sec 1, (c) The situation is the same as that in (b) but an even higher scan speed of 1000 cm sec 1 is used. [From Bensahel and Auvert (1983b).]...

The initiating explosive material must be specially treated and phleg-matized to avoid the undesired byproduct of smoke and flash. One method achieves this by using an admixture of alkaline earth sulfates or by means of micro-encapsulation of the explosive crystals. 

They subjected to irradiation a number of sensitive explosive crystals (such as Pb, Ag Cd azides, Ag acetylide and nitrogen iodide) by electrons, neutrons, fusion products and X-rays, All these substances were exploded by an intense electron stream but it was shown that this was due to a thermal effect. Fission products exploded nitrogen iodide but in the other substances some changes within the crystals took place but no explosions. The experiments showed that, in general, the activation of a small group of adjacent molecules was not enough to cause explosion... 

Another class of explosives known as polymer bonded explosives (PBXs) was developed to reduce the sensitivity of the explosive crystals by embedding them in a rubber-like polymer, such as polystyrene. PBXs based on RDX and RDX/PETN, and also on HMX were developed (Tables 12.1 and 12.2). Energetic plasticizers have also been developed for PBXs production (Table 12.3). 

The PBXs are powdered explosives to which plastic binders have been added. The binder is usually precipitated out of solution in the preparation process such that it coats the explosive crystals. Agglomerates of these coated crystals form pressing beads. The beads are then either die pressed or isostatically pressed at temperatures as high as 120°C. Pressures from 1 to 20 kpsi then produce pellets, or billets, with densities as high as 97% of the theoretical maximum density (TMD). The billets thus produced have good mechanical strength and can be machined to very close tolerances. Table 4.3 lists various PBXs in common use in the U.S. Department of Energy s (DOE) weapons laboratories. Table... 

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