| CHAPTER 2 EXPLOSIVES |
| 2C6. Shipboard tests and Inspections of smokeless powder The Bureau of Ordnance Manual gives the required periodic tests and inspections prescribed for smokeless powder aboard ship in order to ensure its safe storage. For each index of powder aboard ship, a sample is provided in a glass bottle with a tight glass stopper, and is stored in the magazine containing that powder index. These magazine samples provide a means for daily visual examination of each powder index on board. A strip of methyl violet paper is kept in each sample bottle. Oxides of nitrogen, emanating as a gas from decomposing smokeless powder, will discolor the paper, changing it from violet to white. Such a change is a warning that the powder in the bottle and the powder of which it is a sample have begun to decompose. Additional signs of decomposition which may be noted by daily visual examination are: 1. Discoloration of grains, especially grains with orange or yellow spots, or grains differing markedly in color. 2. Grains showing fine cracks, especially if they lack their normal gloss. 3. Friable or easily crumbled grains. This applies especially to the discolored spots on grains and to the off-colored grains. 4. The unmistakable presence of nitrous fumes as determined by sight or smell immediately on opening the container. Only in the very worst cases are the reddish-brown colored fumes likely to be visible. Care should be taken not to mistake the normal ether-alcohol odor for the characteristic pungent odor of the oxides of nitrogen. 5. The metal of the container showing signs of a green or white corrosion on the inside. 6. The powder is in a soft or mushy condition. Conditions 1, 2, and 5 indicate some decomposition has taken place, but the powder may still be usable. Surveillance tests should be made immediately to determine the extent of decomposition. Conditions 3 and 4 indicate advanced decomposition; the powder should be turned in to an ammunition depot for disposition. Powder in condition 6 is very dangerous and should be thrown overboard immediately. The surveillance test consists in putting a sample of the powder in a tight, glass-stoppered bottle into an electrically heated surveillance oven, and exposing it to a constant temperature of 65.5 degrees C (150 degrees F.). The sample under test is examined once daily until red fumes appear, or 60 days elapse. If the red fumes appear within a minimum time as specified in OP 4 for that particular powder (for example, 16 days for 5”/38 powder), notify the Bureau of Ordnance and request disposition instructions. If fumes appear after the minimum period specified by OP 4, but before 60 days, the powder is reasonably safe, but surveillance tests must be conducted at frequent intervals. If red fumes do not appear in 60 days, the powder is safe. Surveillance testing equipment is carried at present on relatively few types of ships-BB’s, CA’s, CL’s, CAG’s, AD’s, and several types of carriers. The equipment is optional on AE’s. Other types of ships send samples to ammunition depots for test. In general, Cordite type (triple-base) powders are not tested in surveillance equipment. At present, Cordite powders are subjected to methyl violet paper tests just as pyro powders are. However, because triple-base powders contain less than 20 percent nitrocellulose, and are much more stable than pyro, violet paper is not as reliable an indicator of triple-base propellant stability as it is for pyro powders. Improved indicators and test methods are now under development. 2C7. Black powder Black powder (originally called gunpowder), the oldest of explosives, has undergone little change in its composition from earliest times to the present. It consists of a mechanical mixture of approximately 75 percent saltpeter (sodium nitrate), 15 percent charcoal and 10 percent sulphur, although these proportions may be varied somewhat, depending on the use for which the powder is intended. First used in guns in the early 12th century, black powder was the only propellant for firearms until the latter half of the 19th century, when nitrocellulose powders were developed. Black powder is unsuitable as a propellant for several reasons: 1. It leaves a large amount of residue, thus fouling the gun bore. 2. It makes large quantities of black smoke when it burns. 3. Its high temperature of combustion causes rapid erosion of the gun bore. 4. Its velocity of reaction is too rapid, even with very large granulations. Although black powder possesses practically unlimited chemical stability if stored in airtight containers, it deteriorates irregularly when exposed to moisture, which it absorbs readily. Black powder is not affected by moderately high temperatures, nor is it subject to spontaneous combustion at ordinary storage temperatures. It is, however, highly flammable and very sensitive to friction, shock, sparks, or flame. It is extremely quick and violent in its action when ignited. The larger the granulation of black powder, especially when pressed or cut into pellets, the slower the rate of burning. Black-powder dust is exceedingly dangerous, and its accumulation during the handling of any black powder should be prevented. Black powder is the most dangerous of all explosives handled aboard a man-of-war. The uses of black powder are dependent on the size of its granulations. In the order of decreasing grain size, the types and uses of black powder in the United States Navy are as follows: 1. Grained.-Torpedo and depth-charge impulse charges. 2. Granular.-Ignition charges for propellants and for saluting charges. 3. Fine-grain.----Primer charges; expelling charge in illuminating projectiles. 4. Meal.-Pyrotechnics and fuzes. 2C8. Solid rocket propellants Solid rocket propellants are double-base compositions with added ingredients for plasticizing, control of burning rate, and reduction of flash. Gas pressure during burning is about one-tenth of that in a gun barrel, and erosion effect is not important in this application. A typical propellent grain is made up of a composition identified as Type N-2 (JPN), and its main ingredients are nitrocellulose (slightly over 51 per cent) and nitroglycerine (a little less than 43 percent). It also contains two plasticizers to ensure homogeneity of composition (these are diethylphthalate, around 3 percent, and a trace of Candelilla wax), about 1 percent of stabilizer (ethyl centralite), a little over 1 percent of potassium sulfate to reduce flash, and a small amount of carbon black to control burning rate. There are a number of other compositions also used for rocket propellent grains, but they are classified, and this one will serve as a specimen for study. As manufactured, the propellant is produced in the form of a sheet about 5 inches wide, 33 inches long, and 0.06 to 0.09 inch thick. To be converted into the grain which actually goes into the rocket motor, several sheets are rolled into “carpet rolls” and put into a press. Under high temperature and pressure the propellant is extruded from the press through a die that gives it the cruciform (cross-shaped) or hollow cylindrical cross section required for the particular motor concerned. The charge is extruded as a homogeneous length of propellant, which is then cut and trimmed to grains of appropriate length. The grains are then turned in a special lathe to give them the proper dimensions for mounting in the motor. Single extruded rocket propellent grains range in size up to 60 inches in length and 6 inches in diameter. From 1 to 4 grains of ballistite propellant are used as the propelling charge in a rocket motor. The grains are designed to burn at a uniform rate to provide a uniform thrust during burning. In cruciform grains provided with suitable plastic inhibitor strips the burning area, and hence the rate of gas production and the thrust, tend to remain constant throughout the burn time. In hollow cylindrical grains, plastic inhibitors bonded to the grain limit the burning area during the first part of the burn period. Cylindrical grains have holes at regular intervals to equalize the pressures inside and surrounding the cylinder. Single grains for JATO units or for use as missile sustainer propellants are made as large as 25 inches in diameter and 10 feet long. Such grains are made by a casting process, and may contain ingredients other than the double-base mixture described above. D. Service High Explosives and Primary Explosives 2D1. General The list of substances which can be grouped under the term high explosives is a long one which, however, may be materially reduced by eliminating explosives not suited for military purposes. The following conditions must be considered in choosing a military high explosive. Depending upon its use, it must: 1. Have proper insensitivity to withstand: a. Shock of gunfire. b. Shock of impact against armor, if used for projectile filler. c. Shock of handling. 2. Have maximum power. 3. Have stability to withstand adverse storage conditions, heat, moisture, etc. 4. Be easy to handle, load, and manufacture. 5. Produce proper fragmentation. 6. Be cheap and available in quantity. A number of high explosives are derived from coal-tar products. When coal is subjected to destructive distillation, coke, gas, and coal tar are obtained. Coal tar is a heavy liquid of a complex nature, which on further distillation will yield aromatic hydrocarbons (benzene, toluene, xylene, naphthalene, and anthracene) and aromatic alcohols (phenol and cresol). From these substances, or from other substances obtained from them, explosives may be made by nitration. High-explosive charges are usually loaded by melting and pouring, if the kind of explosive substance used permits this treatment. This gives greater density of the charge and hence greater explosive effect in a container of given volume. 2D2. TNT (trinitrotoluene) TNT, the most familiar of all military high explosives, is obtained from the nitration of toluene in three successive steps. TNT is a white crystalline substance when pure, and varies in shade from a light yellow to a dirty brown when impurities are present. When pure, it melts at about 80.5 degrees C. (177 degrees F.). TNT is neutral in reaction and, even under unfavorable conditions of moisture and temperature, does not form sensitive compounds by combination with metals. It has high chemical stability even when subjected to temperatures as high as 150 degrees F. for considerable periods of time, and can withstand great variations in temperature. TNT is relatively insensitive to shock, friction, or pressure. When ignited, unconfined, it burns slowly with a dense black smoke and without explosion. However, in a hot fire it will explode with violence. TNT can be melted and cast into any form desired. This property makes it a very convenient substance for explosive charges. The rate of detonation of TNT is about 7,000 meters per second. In a cast form, TNT is rather difficult to detonate and usually requires a booster such as refined granular TNT to provide the shock necessary to ensure complete high-order detonation. TNT is not, however, as insensitive as one may suppose. Small particles of TNT have been known to detonate when scraped with a knife. The presence of moisture in TNT adds greatly to the difficulty of detonating it and probably decreases its explosive force. It is, therefore, of greatest importance that TNT boosters be kept dry. A dark-brown oily liquid frequently separates out of cast TNT, and may exude from the containers after a period of storage. This exudate consists of isomers of TNT and lower nitrotoluenes. (Isomers are substances having the same chemical formula but with molecular arrangements and melting points different from those of the original substance.) Such exudates are relatively insensitive, but when mixed with an absorbent cellulose material, form a low explosive which is easily ignited, burns rapidly, and may even be detonated. An accumulation of exudate is considered both a fire hazard and an explosive hazard. Exudates discovered when cast TNT is inspected should be immediately removed. Large cast TNT charges must not be stowed on wooden or linoleum-covered decks, nor on any material that is likely to absorb the exudates. Exudate may be removed with carbon tetrachloride or alcohol, or, if discovered before it hardens, by water and a stiff brush. Because of its sensitivity, exudate must never be removed by steel scrapers, nor should soap or other alkaline solutions be used to remove it. TNT has many uses. It may provide main disrupting charges in projectiles, torpedo war heads, depth charges, mines, bombs, grenades, boosters, demolition charges, etc. It is more frequently used as a component in other explosives. For fuzes and boosters, only a refined granular or crystalline TNT of high melting point is used. For large charges such as those in mines, bombs, etc., cast TNT of one of the lower grades and lower melting points is ordinarily used. TNT is not sufficiently insensitive to be a satisfactory filler for armor-piercing projectiles. TNT may be mixed with other materials for certain applications. For example, TNT, with its relatively low melting point (80.5° Centigrade when pure) can be cast-loaded-that is, it can be poured into the burster cavity of a projectile and permitted to harden. Many other high explosives have melting points too high for this technique. But by using TNT as a vehicle, it is possible to cast-load a mixture of TNT and some other explosive. Thus a mixture of TNT and RDX (to be discussed below) can be cast-loaded. Two other fairly common mixtures including TNT are amatol and tritonal. Amatol is a mixture of TNT and ammonium nitrate, and is used in large aircraft bombs. The mixture is less expensive than straight TNT. Tritonal is a mixture of TNT and aluminum powder. In this and other mixtures containing aluminum powder, the aluminum has the effect of improving the brisance of the explosive components, although it does not significantly affect the power of the explosive. 2D3. Explosive D (ammonium picrate) This explosive, patented in 1888, was for many years the secret high explosive of the United States. Its particular importance as a military explosive lies in its marked insensitivity to shock and friction. It is only slightly inferior to TNT in explosive strength. It is a crystalline powder of light-yellow color which is loaded in projectiles by pressure tamping. It is only slightly hygroscopic, but, when wet, forms sensitive and dangerous picrates with copper and lead. Although it does not form dangerous compounds with iron, it does cause corrosion; the interiors of projectiles are therefore painted or varnished before being filled. It has high chemical stability, even when subjected for considerable periods of time to temperatures as high as 150° F. It cannot be melted and cast like TNT. Explosive D is made by saturating a hot solution of picric acid (trinitrophenol) with ammonia water (ammonium hydroxide) or ammonia gas. This results in neutralizing the acid, which is shown by the formation of crystals. This solution, when the reaction is complete, is dumped into crystallization tanks, where the ammonium picrate crystallizes out. The crystals are removed, drained, and screened. The powder is then ready for packing. Explosive D is used primarily as a burster charge for large-caliber armor-piercing projectiles, and armor-piercing bombs, as it will withstand the shock of impact against any thickness of armor. The advantage of this is, of course, that the armor-piercing projectile will have partially or completely penetrated the plate before it is detonated by the fuze action. Aboard ship, Explosive D is found only in loaded projectiles or bombs and requires no special care, except to see that the projectile rooms are kept thoroughly dry and at moderate temperatures. In case of fire in the vicinity of projectiles, care should be taken that they do not become heated to a high temperature. No special tests or inspections of Explosive D are required afloat. 2D4. Tetryl (trinitrophenylmethyltrinitramlne) This high explosive is another aromatic nitrocompound. It is a yellow crystalline substance usually produced by the nitration of dimethylaniline. Tetryl is more powerful than TNT and more sensitive to shock. It is stable at all ordinary temperatures, melting at 130 degrees C. (266 degrees F.). Tetryl is an excellent explosive for booster charges, especially in mines and torpedo war heads, which do not have to undergo the heavy shock of firing. Sometimes a mixture of tetryl and a primary explosive is used as a detonator. 2D5. RDX This high explosive, known also as “Cyclonite” and “Hexogen”, is a fairly recent development. It is a fairly sensitive explosive, and is more powerful than either TNT or Explosive D. It is produced by the nitration of hexamethylenetetramine, an organic compound derived from ammonia and formaldehyde. Purification is accomplished by crystallization from acetone. The crystals are then coated with beeswax or similar waxes to reduce the sensitivity of the material. In this form, RDX is insensitive enough to permit handling. Further additions of less sensitive materials are necessary before it can be used as a military explosive. The forms in which it appears in service are: 1. Composition A. A mixture of about 91 percent RDX and 9 percent beeswax or synthetic wax. Since this composition has about the same sensitivity as Explosive D but is more powerful, it is now being used as a projectile filler in place of Explosive D. 2. Composition B. A mixture of about 60 percent RDX, 40 percent TNT, and less than 1 percent wax. It is used as a projectile and bomb filler. 3. Composition C. A plastic mixture of about 90 percent RDX and 10 percent emulsifying oil-used to advantage as a demolition explosive because of its plastic form. 2D6. HBX There are in service use two varieties of HBX- HBX-1 and HBX-3. HBX-1 is a cast explosive, consisting of a mixture of RDX, TNT, aluminum powder, and a desensitizer composed chiefly of wax. It is stable, relatively insensitive to impact, and more powerful than TNT. It is used in rocket heads as a burster charge. HBX-3 differs from HBX-1 in having a much larger proportion of aluminum powder to increase its brisance. It is otherwise similar to HBX-1, but has much greater destructive effect underwater. It is therefore used in depth charges and other underwater explosive devices. 2D7. Primary explosives Primary explosives are used in the early part of the explosive train, where sensitivity is important. For many years fulminate of mercury was the most important explosive used for this purpose. Because of its relatively poor keeping qualities, particularly under higher temperatures and in the presence of even a small amount of moisture, it is gradually being eliminated. Ammunition now being procured does not contain mercury fulminate. The important primary explosives used in U. S. naval ammunition today are lead azide, lead styphnate, DDNP, tetracene, and nitromannite. To ignite a propellant, the primary elements in an explosive train must produce a hot flame of sufficient temperature, size, and duration for reliable action. To detonate a high explosive, the primary elements in the train must produce a shock sufficient to detonate the succeeding elements. The primary explosives mentioned above are used in these applications. Detonators and primers differ chiefly in the auxiliary ingredients used to produce the effects desired. Thus, oxidizing agents such as nitrates or chlorates are added to increase impulse (shock effect) and sensitivity; abrasives like ground or powdered glass increase sensitivity to firing pin action; fuels such as antimony tri sulfide increase flame energy. Explosive binders like nitrocellulose or nitrostarch are used to provide structure for the primary mixture and to hold it in place, and graphite or other electrical conductors are used to increase conductivity for electrical initiation. These components are used in various combinations, depending on the characteristics desired in the initiator. For details concerning specific primary explosives and the design of explosive trains, see the Ordnance Explosive Designer’s Handbook, published by the Navy as NOLR/1111. |