Modern Military High Explosives WILLIAM H. RINKENBACH and L. F. AUDRIETH Picatinny Arsenal, Dover, New Jersey
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FTER approximately six years of war it is now possible to recognize the basic changes which have taken place in the field of military high explosives since World War I and particularly during the present conflict. World War I was fought with only a few standard high explosives together with some inferior substitutes for these which were used because of material shortages. This paucity of explosives permitted but little choice and no special application for specific purposes. Today the field has been so enlarged with respect to types as well as numbers of available explosives, and the range and specificity of their application, that a new era must be recognized and evaluated. High explosives may be defined as explosives which undergo detonation, as contrasted with the rapid autocombustion of black and smokeless powders. They include: (a) initiators, or explosives which are so sensitive as to undergo detonation when subjected to impact, friction, or flame. They are so called because they can initiate the detonation of (b) bursting charge explosives, which are relatively insensitive to impact, friction, and flame. Initiators are used alone and in primer compositions which are physical mixtures containing in addition certain nonexplosive materials. Bursting charge explosives are used alone, in mixtures with one another, and in such order as to insurean increase in the detonating impulse. This leads to the inclusion in ammunition of the "high explosive train" in which detonation is propagated from the most sensitive, least powelful initiator to the least sensitive, most powerful bursting charge explosive.
explosives studied have been found suitable for military use. Primarily, a high explosive must be entirely satisfactory with respect to: (a) sensitivity-susceptibility to shock and friction, (b) stability-resistance to decomposition or physical change during storage, and ( c ) brisance--shattering power. Secondarily, i t is desirable that an explosive be uonhygroscopic, neutral in chemical reactivity, non-volatile, non-toxic, and of high density. The practicability of producing the explosive on a large scale from available raw materials a t reasonable cost is another important consideration. Failure of the explosive t o meet the secondary requirements limits and perhaps prevents its standardization' and use. The nonfeasibility of manufacture on a large scale frequently is the determining factor for explosives which otherwise are entirely satisfactory. However, in some cases only the inordinate demands incident to war or new technological advances have been required to render explosives suitable for standardizatioh. Since World War I a number of new high explosives have been develooed. and a t the same time it was found that these can b'usdd much more specifically. During the World War but few bombs were used and these haphazardly; the use of explosives to penetrate armor and fortifications was unknown; and the incendiary value of explosives was not utilized. Today explosives are applied so as to obtain the following specific effects against different types of targets. Demolition. Brisance or shattering by fragmentation of explosive components such as shell, grenades, bombs, and mines. Blast effect or destruction by impact of a shock wave Priming , Bursting compos,tlon Initiator Booster charge produced by the explosive in bombs or mines. Penetration. The production of narrow but deep At the time of World War I mercury fulminate was holes in or through armor or concrete. This is accomthe only initiator in extensive use and almost all prim- plished by the shaping of the explosive charge in shell ing compositions were based on it. T N T (trinitro- or grenades, thereby utilizing the Monroe effect. Incadiary. An added effect of demolition explosives toluene) in pressed form was used as a booster, and TNT, ammonium picrate, picric acid, Amatol (TNT- obtained by formulation of the explosive or use of ammonium nitrate mixtures) were the only bursting special metals for the component. The practicability of applying explosives so specicharge explosives. Shell, mines, and grenades were used for general demolition purposes and were loaded fically for the above effects has bad much to do with with whatever explosives were available; ammonium the recent develo~mentand standardization of expicrate was reserved for armor-piercing shell because of 2 The term "standardieation" of an explosive implies that such its insensitivity. Amatol was developed and used a material meets all important requirements with respect to sensitivity, stability, brisance, and functioning characteristics in primarily in order to conserve the limited supply of ammunition and that it has been accepted for use wherever TNT. specified. Each standard explosive is covered by a carefully The fact that so limited a number of high explosives prepared specification which is designed to insure acceptance of a free from objectionable impurities which would interfere was used is due to the stringent standards established material with proper behavior of ammunition in which it is loaded when for military high explosives. Only a few of the many this is subjected to storage, handling, and functioning.
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plosives. Some of the newer explosives which have been used in ammunition are described below.
Tetryl, 2,4,6-trinitrophenylmethylnitramine, was developed originally for use as a booster explosive. While INITIATORS less stable, it is much more sensitive Lead azide, PbNe, has replaced almost entirely the to initiation and has greater brisNO2 mercury fulminate formerly used in detonators. Mer- ance than TNT. It is somewhat less cury fulminate was of less than a desirable order of sensitive to impact and friction than stability, required the use of the semistrategic raw PETN and Cyclonite, and is used in detonators and material mercury, and had to be manufactured in rela- boosters without the addition of a desensitizing agent. tively small batches. Lead azide is of remarkable In mixture with TNT it is used in bursting charges for stability, involves no strategic raw material, and can be mines and other special components. manufactured in larger batches. The problem of proBinary BxpZosines. In addition to the individual ducing azide which is of uniform and controlled sensi- compounds which are explosives, there have been detivity has been solved by the addition of small percent- veloped binary explosives which consist of mixtures of ages of agents which modify the crystal form. Lead these with TNT. PETN, Cyclonite, Tetryl, etc., all azide is a more effective initiator than mercury ful- are more brisant than TNT, but have melting points minate for the more sensitive explosives used in de- considerably above the maximum temperature of 100°C tonators and boosters and those detonated directly practicable in melt- or cast-loading. The demands of modern warfare require that the loading of shell, bombs, by the action of an initiator. Dkodinitrofihenol has been less of a reand mines be on a mass-production scale. This has been placement than lead azide for mercury fulmet by the development of the mixtures mentioned minate, but has been used to some extent. O,N above. The admixture of TNT also s w e s to overcome It is of acceptable stability, is not unduly the undesirable sensitivity of PETN, Cyclonite, Tetryl, sensitive to shock, and is more efficient than etc., since TNT is much less sensitive than these. The NOa lead azide as an initiator of detonation; but proportions of the TNT and other explosives are varied its density when loaded under pressure is so somewhat to meet the particular loading, tactical, and much less than that of either lead azide or mercury other requirements involved. The binary explosives fulminate that much less diazodinitrophenol can be are manufactured by melting TNT, adding the other loaded in a standard component. Diazodinitrophenol explosive, mixing, and pouring the slurry into the shell, is unique among initiators in that its rate of detonation bomb, or mine. While partial solution and the formaand brisance ar.e so great as to be approximately equal tion of a eutectic are involved to a greater or less exto those of TNT. Other initiators have much lower tent in most binary systems, the net effect is to susrate and brisance values. pend the particles of the more sensitive explosive in a magma of less sensitive TNT. The binary explosives BURSTING CHARGE EXPLOSIVES so obtained are of acceptable sensitivity, have considerPETN, pentaerythritol tetranitrate, C(CHSNO~)~,ably greater brisance than TNT, and are only slightly has been developed since World War I from a labora- less stable than the less stable ingredient. Explosives having marked blast effects are obtained tory chemical to a material produced on a tonnage basis. It is the most brisant and sensitive of the by adding metallic aluminum to castable single-inbursting charge explosives used in ammunition, and gredient or binary explosives. Such explosives also has a high rate of detonation. While of acceptable have distinct incendiary value, which can be increased stability, i t is less stable than TNT, Cyclonite, or by the utilization of bomb and grenade cases of magTetryl. Because of its sensitivity to impact and fric- nesium-aluminum alloy. In addition to the foregoing there have been detion, it is loaded as such only in detonators, where only small quantities are involved. For use as a booster veloped a considerable number of single-ingredient and explosive, a bursting charge, or a plastic demolition multi-component explosive compositions, the identities explosive, it is desensitized by the addition of a wax or of which are confidential. The development of new explosives has been accomby admixture with TNT. panied by the development of improved methods of Cyclonite, cyclotrimethylene trimanufacturing these and older explosives. An example nitramine, aIso has undergone deof this is found in the case of TNT. During World War velopment from a material produced o t ~N , N. I there was such a shortage of TNT in all the warring with difficulty on a small scale to one I I countries that i t was diluted with other materials and manufactured on a plant scale by new \/ inferior substitutes were used. This was due to the methods. It is almost as brisant and N.NO* limited production of toluene in the coal-tar industry. sensitive as PETN, but is essentially The present production of toluene from petroleum has as stable as TNT. It is used chiefly in bursting charge and plastic demolition explosives removed this limitation, and new developments in when desensitized by admixture with TNT, wax, or oily nitration and purification techniques have enabled plant materials. It has also been used, in the same manner, units to produce approximately five times as much TNT per day as formerly. The vast production and as a booster explosive.
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startlingly reduced cost of T N T today makes i t the "universal solvent" in the field of explosives. With the growing scale and complexity of the manufacture and loading of military high explosives there has been a corresponding increase in the requirements to be met and the technology involved. Because of the extremes of climate under which they are used, loaded explosives must function a t temperatures as low as -50°F., must not exude any partially melted charge a t 170°F.,and must not be desensitized by extreme conditions of temperature and humidity. The elimination or control of impurities incident to meeting these requirements, and the control of physical conditions required for:maximum quality loading, have necessitated refinements which a few years ago were undreamed of but today constitute accepted and inexpensive routine. The present availability of new explosives of great brisance and enhanced blast effect, and the highly specific application of these, have resulted in a breaking of the stalemate between offense and defense which formerly was possible. Explosives are now used suc-
cessfully to destroy defenses which only recently were impregnable. As shown by the results of the recent war in Europe, offensecan dispose of the best defense available and the major problems of warfare with respect to explosives are logistic and strategic. This should not he interpreted as meaning that the ultimate developments in explosives have been achieved or that further developments are not needed. New needs are arising under the exigencies of warfare, and these must he met by new developments. New fields of the science of explosives are now envisioned, and research in these directions may bring developments even more startling than those of the past 25 The recent revelation of the development, use, and general nature of the atomic energy bomb provided a striking illustration of the successful utilization of new saentific concepts in the field of explosives. This culmination of the scientific war effort, which astounded the world and probably saved untold lives, may well serve as a springboard for further advances in the arts of peace as well as the field of military explosives.
