Military explosives casting

Pentaerythritol tetranitrate (PETN) (3) is a powerful explosive which exhibits considerable brisance on detonation (VOD 8310 m/s at = 1.77 g/cm ). It is the most stable and least reactive of the common nitrate ester explosives. The relatively high sensitivity of PETN to friction and impact means that it is usually desensitized with phlegmatizers like wax and the product is used in detonation cord, boosters and as a base charge in detonators. Pentaerythritol tetranitrate can be mixed with synthetic polymers to form plastic bonded explosives (PBXs) like detasheet and Semtex-IA. A cast mixture of PETN and TNT in equal proportions is known as pentolite and has seen wide use as a military explosive and in booster charges. The physical, chemical and explosive properties of PETN commend its use as a high explosive. 

Explosives Sensitivity Data. Card-gap and projectile sensitivity, data are presented by Watson (Ref 1) for a wide variety of expl compns tested at the USBurMines laboratories in more or less standard test geometries. The results of both tests are in good agreement in that they provide the same sensitivity ordering fbr different subclasses of expls. Least sensitive were homogeneous liquids that did not exhibit a tendency, to undergo low-velocity detonation, AN-FO (Ammonium Nitrate-Fuel Oil), and most cast military expls. Of intermediate sensitivity were pressed and powdered military expls, cast Pentolite, permissible and nonpetmissible water-based expls, and one commercial two-component expl. The most sensitive were permissible and nonpermissible Dynamites and expls susceptible to low-velocity detonations Refs I) R.W. Watson, 1 Card-Gap and Projectile Impact Sensitivity Measurements, A Compilation , USBurMines Information Circular 1C 8605(1973)... 

Trinitrotoluene (TNT) was the most commonly used conventional military explosive during the twentieth century. Although it had been used extensively in the dye industry during late 1800s, it was not adopted for use as a military explosive until 1902, when the German army used it to replace picric acid. TNT was first used in warfare during the Russo-Japanese War (1904-1905). The US Army began its use in 1912. After an economical process was developed for the nitration of toluene, TNT became the chief artillery ammunition in World War I (1914—1918). The most valuable property of TNT is that it can be safely melted and cast alone or with other explosives as a slurry. 

Most military explosives are solid compounds which are manufactured in granular form, with bulk densities of less than 1 g cm-3. These granular compounds are then mixed with other explosive or inert additives to give explosive compositions with densities between 1.5 and 1.7 g cm 3. The explosive compositions are then cast, pressed or extruded into their final form. 

A list of US military explosives which are cast-loaded is given in Vol 2, pp C83 R ... 

TNT is one of the important materials used for not only explosives for industry but also military explosives for blasting charges. Since metals are not corroded by TNT, it is cast directly into metal cases as well as pressed into warhead shells. In order to gain high explosive characteristics, TNT is mixed with other materials, such as AN, Tetryl, PETN, A1 powder, and nitramine partides121. The mixture of TNT and AN is named Amatol has a TNT/AN mass fraction ratio ranging from 0.5/0.5 to 0.2/0.8. The mixture of TNT and AN is melted and then cast. The mixture of TNT and A1 named Tritonal has a mass fraction ratio of TNT/A1 = 0.8/0.2. The mixture of TNT and HMX is named Octol composed of the mass fraction ratio of TNT/H MX ranging from 0.3/0.7 to 0.25/0.75. The maximum detonation velocity, 8600 m/s, is obtained when the density is 1800 kg/m3. 

Aromatic nitro compormds, primarily 2,4,6-TNT, have long use as military explosives and commercial application in cast boosters to initiate insensitive blasting agents. In the laboratory, TNT maybe encountered as prills, flake, or a cast solid ranging in color from light yellow to brown. Acetone solutions of TNT slowly develop a pink color and red is produced with ethanolic KOH. Numerous TLC systems have been described for the identification of TNT, usually with visualization by alcoholic KOH. TLC or GC-MS identification of minor products, other isomers of TNT or DNT, provides information to establish a potential common source. The use of isotope ratio MS is now being explored for this purpose. GC or LC-TEA readily identifies TNT. Combinations of TNT and NH4NO3, known as Amatols , have been used as military explosives to conserve TNT and could be encountered in old military ordnance. 

TNT is the most widely used military explosive in history. The reasons for its popularity are its low cost and simplicity of preparation, safe handling (low sensitivity to impact and friction), relatively high explosive power (yet good chemical and thermal stability), low volatility and toxicity, compatibility with other explosives, and a low melting point, allowing for melt-casted formulations. 

TNT is one of the least sensitive of military explosives only ammonium picrate, nitroguanidine, and ammonium nitrate are less sensitive. Impact tests yield high values relative to other military explosives, but impact sensitivity increases sharply with increasing temperature, as shown in table 8-56. Diminishing sensitivity has been reported down to- 196°C. Gap and projectile test results indicate cast TNT is less sensitive than the pressed materiel. Test results from the mod-... 

TNT (2,4,6-trinitrotoluene) is widely used as both an industrial and a military explosive. TNT releases no more energy per kilogram than old-fashioned gunpowder, but it is more stable, and it has other useful properties, such as the ability to be melted and cast into desired shapes. 

Pure PETN is too sensitive to friction and impact for direct application for military purposes. It can usefully be mixed with plasticised nitrocellulose, or with synthetic rubbers to obtain plastic or mouldable explosives. The commonest application, however, is in conjunction with TNT in the form of pentolites. Pentolites are usually obtained by incorporating PETN into molten TNT. A small amount of the PETN goes into solution, but the bulk remains suspended in the liquid and the whole mix can suitably be used in preparing cast charges. Pentolites containing 20-50% PETN are the commonest in practice. 

The two principal loading techniques are casting and pressing. All expls in common military use can be pressed, however, those that are castable are usually cast because of the greater convenience and flexibility of this process. As a rule of thumb, main bursting charges of large cal munitions are cast while small explosive components (initiators to boosters) are pressed... 

Composition D-2, This composition consists of a mixture of desensitizing wax 84, lecithin 2 Nitrocellulose 14%. It is prepared by melting mixing the ingredients in the above amounts When the mixture is uniform and free from any visible impurities, it is cast in the form of slabs not more than 2 inches thick, or in the form of pellets not more than 2 "x 2 " in size. Composition D-2 is used to emulsify desensitize solid explosives or mixtures of explosives. The detailed US Military requirements of Composition D-2 are given in Ref 2, where the tests are also described... 

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