Although there are many explosive substances, not all of them are suitable for use as military explosives. Generally, military explosives need to be stabile, thus implying resistance to shock, moisture and other considerations that come about through the nature of their use. They usually need to be capable of being stored for long periods of time without significant deterioration. Some of the explosives included here are not actually used as military explosives today, but were at one time.
An explosive produces a rapid expansion of gases in a very short time. It releases the energy that is stored in the original material in various combinations of the forms of heat, light and its breaking down into gases that occupy a much greater volume than its original form did. The expansion of the gases occurs at a very great speed and they displace great volumes of air. There are fine points to the distinctions between simple explosions and detonations that occur at speeds greater than the speed of sound with resulting shock waves and sonic booms. There are three principle types of explosives: mechanical, chemical and nuclear.
Types of Explosives
Mechanical explosions occur due to physical reactions such as overheating a whole potato in a microwave oven. This phenomenon has few applications in engineered explosives, but sometimes this method is used and in those cases it is usually powered by compressed air.
Explosives are defined as materials (chemical or nuclear) that can be initiated to undergo very rapid, self-propagating decomposition that results in the formation of a more stable material, the liberation of heat, or the development of a sudden pressure effect through the action of heat on produced or adjacent gases. All of these outcomes are the result of the liberation of energy from the original material.
Chemical explosions occur in substances that burn extremely rapidly. Although there are many common substances that can produce respectable explosions such as gasoline, these types of materials are not usually classed as explosives because they must obtain their oxidizer from the air, this being the essence of a non-self-propagating material. Generally, chemical explosives are substances where the fuel and oxidizer are combined in the same material thereby causing the reaction to be self-propagating. While some explosives must be physically confined to obtain detonation others do not.
In the general model sense, a chemical explosive contains both an oxidizer and a reducer. The reducing agent such as a metal ion burns to produce hot gasses. The oxidizer is a radical that gives up oxygen atoms to support the combustion.
Oxidizing agents include nitrates, chlorates, oxides, peroxides, chromates, chlorates and perchlorates. Nitrates are stingy with oxygen while chlorates and perchlorates render all that they contain. Therefore, explosives with chlorates and perchlorates are more efficient and faster-burning but consequently tend to be less-stabile.
There are fine points as to what constitutes a chemical explosive and what does not. For a substance to be classed as an explosive it must decompose or rearrange itself very rapidly upon the application of an initiating force such as shock or heat and its combustion must produce gases and/or heat. In most cases, the amount of gases produced is key because the rapid expansion of gases is the characteristic that makes an explosion. Nevertheless, the heat of combustion is the factor that makes the gases expand rapidly enough to create an explosion. In some cases, the process produces mostly heat and those materials can be exploited for that particular attribute. In the case where gasses result, these factors make the material occupy a much larger volume that it did originally in a very short time.
Classification of Chemical Explosives
Different chemical explosives burn with distinct characteristics and they can be classified according to these properties. High-order explosives detonate. Low-order explosives burn or deflagrate. Primers can either detonate or deflagrate.
High-order explosives detonate. Generally, a detonation is brought about by a shock wave traveling at about or greater than the speed of sound through that particular material. This is generally from between 4,000 to 25,00 feet per second. The shock wave serves to break down the material into its constituent molecular materials. This frees up the fuel and oxidizer which heretofore were chemically bonded and they recombine to form gases, heat, light and other energy. High explosives are usually further categorized into primary and secondary types. Primary explosives can be detonated from a simple source such as a flame, spark or impact. Secondary explosives must have sufficient stimulus to initiate detonation. This is usually in the form of an additional explosive charge that sets up an initiating shock wave. A few of these materials also require a booster charge in addition to an initiator to cause them to detonate.
Low-order explosives are materials that burn very rapidly, a process also known as deflagration. These materials burn at subsonic speeds; therefore, no shock wave occurs. The speed of combustion is less than the speed of sound as measured in that particular material. When heated, the constituent fuel and oxidizer in the material combine to produce heat, light, gaseous and some solid materials. Most low-order explosives must be confined to create an explosion and some of them burn at about the same speed in the open as they do when contained. Some burn much faster and hotter under pressure. Under certain conditions, low-order explosives can be caused to detonate. This probably happens more often by accident than intentionally and can have disastrous results. Extremely fine black powder packed too tightly has been known to do this.
Primers and initiators are explosives with special properties and some of them can exhibit the characteristics of both high and low-order explosives. Most of them are high explosives and they are much more sensitive to friction, heat and shock than other forms of explosives. In some of these materials, physical impact or vibration can cause an explosion. Some are strictly deflagrating, but when confined they detonate. They are usually used in small quantities to initiate an explosion in another explosive material. Some high explosives cannot be detonated without the use of some other explosive to set up an initial shock wave and a few must have a booster charge.
Most modern military low-order explosives are used as propellants. Propellants impart motion to something like a rocket or projectile. They are classified as single-base, double-base and composites. Single-base propellants are the simple forms of nitrocellulose powders. Double-based propellants are nitrocellulose powders that have nitroglycerin added to them thus making them more powerful. Composite propellants are mixtures of fuels and oxidizers that are mostly not nitrocellulose and nitroglycerin.
Propellants can be made to perform differently by varying the physical characteristics of the individual grains because burning is mostly a surface phenomenon. In a degressive powder, the surface area decreases as the powder is consumed. If the grains are made so that each grain has a hole in it, it can then be a neutral powder because as it burns the surface area remains about the same. These are called perforated powders. If the grains have multiple holes, known as multiperforated powders, they can burn progressively meaning that they burn faster as they are consumed. This allows powders to develop more gases after a projectile has begun to move down the barrel of a gun.
Black powder was the first known explosive and it continued to be the main explosive material until the late-1800s. It was called gunpowder until nitrocellulose powder became the most widely used type. After that, nitrocellulose powder was called gunpowder and black powder was called black powder. Black powder is one of the most important substances ever known to mankind because its manufacture brought forth modern chemistry and modern science.
Black powder made with sodium nitrate instead of potassium nitrate was available by 1857. The material was cheaper and more powerful than original black powder and was sometimes called soda powder. Lammot du Pont developed soda powder and it began to be used at about the time of the US Civil war. Soda powder was made in several varieties like one named Mammoth Powder that was designed for large artillery. Its use as a propellant was limited because both more modern artillery and guncotton became available at about the same time. As it turned out, soda powder was mostly used for blasting powder.
Black powder has been largely replaced as a propellant by nitrocellulose powder but it is still widely used for initiating charges, primers and fuzes in military ammunition as well as fireworks, flares and other uses. It is still necessary for antique equipment designed for use with black powder.
Guncotton began to replace black powder as a propellant around the time of the US Civil War in the 1860s. Guncotton was the precursor to nitrocellulose, or modern gunpowder. T. J. Pelouze discovered that cotton became explosive after it was dipped in nitric acid in 1838. Christian Shönbein developed a process of dipping cotton in both nitric and sulfuric acids and then washing out the residue of the acids in 1845. However, the washing process frequently failed to remove all of the acids and the material would occasionally explode spontaneously. This frequently happened for no apparent reason and this characteristic along with the fact that the material was too powerful for most of the guns of the era kept it from being widely adopted as a propellant.
Paul Vieille, a French chemist and physicist solved the problems associated with guncotton by developing processes to remove all of the residual acids from the material and stabilizers such as diphenylamine that kept it from exploding spontaneously. It is no coincidence that Vieille and a partner, Marcellin Berthelot made the important discovery of shock waves in physics.
Nitrocellulose or Smokeless Powder
Smokeless powder is actually nitrocellulose-based powder, the material developed by Paul Vieille in 1884. Nitrocellulose required much more processing than simply dipping cotton in acid and wood pulp soon became the preferred source of raw cellulose. The two sources of raw cellulose have different properties so they are used and blended based upon the intended purpose of the finished product. To make nitrocellulose powder, the nitrocellulose is dissolved in a mixture of ether and alcohol and it becomes a gelatinous mass. When the solvents evaporate, it leaves a hard plastic material. The gelatinous blob is usually rolled into a sheet before it hardens and after it hardens it is cut up into various sized flakes. The cutting is done on machines because the particles are tiny and it takes a great deal of cutting. Furthermore, it just wouldn’t have been the Industrial Revolution if they had cut it by hand. Nitrocellulose was the first reliable and stable gunpowder. It is the principle type of propellant today.
High-order explosives are available in many different forms and they are the most common kind of explosives. They are used for blasting and applications like fragmenting artillery shells and armor piercing ammunition.
EC Powder, or Explosive Company Powder, is a type of modified nitrocellulose powder used for fragmentation charges in grenades and the like. It is coarser than regular smokeless powder and it has additional nitrates added to it.
Dynamite was developed by Immanuel and Alfred Nobel of Sweden through their efforts to find a safe way of using nitroglycerin. Nobel applied nitroglycerin to diatomaceous earth which absorbed it and made it much more stable and safer to handle. This mixture is then wrapped in a paper cover similar to a giant firecracker. However, for the most part, it has to have a blasting cap to set it off. Other fillers can be used as well such as saw dust and other fibers. Dynamite was patented in 1867. There were various attempts to use dynamite as a propellant but it was too powerful. There were also some interesting uses of dynamite in artillery and naval guns. Dynamite cannons were built in the late 1800s and they used compressed air to launch charges of dynamite at targets. This technique was used during the Spanish-American War. Dynamite guns more-or-less disappeared by World War I. Dynamite was also used as a military explosive for blasting. There were several modifications to basic dynamite in subsequent years.
TNT, or trinitrotoluene, is the most important military explosive. TNT was discovered in 1863 as a dye agent. It was not used as an explosive until 1904. It became popular as a military explosive during World War I and it became the standard military explosive by World War II. The power of other explosives is frequently expressed as an equivalent amount of TNT. It can be cast easily by melting the material and then it can be poured into shells. It is very stable and can be stored for long periods. It is extremely moisture resistant and is not likely to be detonated by physical shock.
RDX, an acronym for Research Department Explosive, is chemically named cyclotrimethylenetrinitramine. It is a handy and versatile material for bringing about all kinds of destruction that was discovered by Hans Henning of Germany in 1899. It is called hexogen in some locales. It was not widely used until World War II. It is fairly sensitive and it can be made into many different plastic explosives. It is frequently used in blasting caps and percussion-type explosives.
PETN, or penthrite, which is more properly called pentaerythritol tetranitrate is probably the least stable of the modern military explosives, but it does have a long shelf life. It was first used after World War I and it is closely related to nitroglycerin. PETN is usually in the form of clear crystals in a water solution. It is easily detonated and it is used in blasting caps and other types of initiators.
RDX and PETN Blends
RDX and PETN are usually mixed with other explosives in their actual applications. They can then be cast and molded into various shapes to fit into weapons like artillery shells and the like. They are frequently mixed with TNT in ratios around 50%. This makes the TNT easier to detonate and makes the more sensitive compounds PETN and RDX safer to handle.
Tetryl, or trinitrophenylmethylnitramine, has various common names such as nitramine, tetralite, and tetril. It is fairly sensitive and it can be initiated from flame, friction, shock, or sparks. Tetryl is commonly used as a booster explosive where stable explosives need more than simply an initiator to cause them to detonate. It is no longer manufactured in the United States and it is an environmental hazard. Æ
Tetrytol is a mixture of tetryl and TNT. It is used for casting into artillery shells and the like.
Nitrostarch is similar to nitrocellulose and is sometimes used as a substitute for TNT, but it is less powerful. It cannot be made to gel and it is not soluble in water. It will dissolve in acetone and alcohol-ether mixtures.
Explosive D, or ammonium picrate, is the most stable of military explosives. Since physical shock does not set it off easily, it is used in artillery shells and armor penetrating ammunition where an explosive charge must endure a great amount of physical shock before detonation.
Picric Acid is one of the oldest explosives and it found uses in early artillery shells as the bursting charge and it is also useful as a primer and initiator. It is not widely used today because it is fairly sensitive and better substances are available for most applications.
Ammonium Nitrate is an explosive that is also useful for fertilizer. It is not used much as a military explosive in its simpler forms, but when mixed with other explosives like TNT it is encountered frequently in military explosives. It has been around since the mid-1800s, but early problems with moisture kept it from being widely used as an explosive. These problems were solved through various means and today ammonium nitrate is usually manufactured in prills, or small round pellets. It is formulated this way so that it will flow freely when used for fertilizer. Ammonium Nitrate can be combined with various other explosives and it is very stable. Therefore, it needs a substantial charge to cause it to detonate.
Amatol is a mixture of TNT and ammonium nitrate. It is usually made from between 50-50 to 80-20 TNT and ammonium nitrate. It was discovered that this mixture was nearly as powerful as pure TNT and it made scarce supplies of expensive TNT go much further during World War I. It is used in artillery shells and for similar applications.
ANFO is an acronym for Ammonium Nitrate Fuel Oil mixture. This mixture is used in blasting. Many uses of ammonium nitrate as an explosive are facilitated by the addition of about 6% #2 fuel oil which, among other things, helps keep it dry. ANFO was developed for use in mining, but its usefulness for other applications is now appreciated.
Composition Explosives are a variety of plastic explosives that are designated by acronyms like C1, C2, C3, C4, CA, CB and etcetera. These are plastic demolition explosives that are made from various explosives like RDX and PETN blended with other agents like waxes, oils and plasticizers to produce explosives that exhibit special qualities for specific applications. C-2 is a particularly useful military version and C4 is a mixture of RDX and PETN. The main difference between the various mixtures is that they remain useful through different temperature ranges.
Initiating explosives are very sensitive and that is why they are used - to set off an explosion in a less sensitive material. Although they explode easily, their explosions are usually not as powerful as other explosives. That is why they are not usually used as explosives themselves. Because of their sensitivity, they are usually only kept in small quantities and well away from other explosives.
Mercury fulminate had been known of for a long time before the late-1800s. It was one of the first materials used for initiating charges, primers and detonators. It is extremely sensitive and has been replaced in many applications for that reason.
Lead Azide is a whitish crystalline substance that is less sensitive than mercury fulminate. It is used for primers and other initiating charges and is one of the principle materials used in fuzes and detonators for large ammunition today.
Metals can be explosively welded together, a process discovered through the use of artillery. The way that this was discovered was that various types of driving bands and seals have been used over the years to improve the fit of artillery shells in the bore of the gun. Sometimes this was in the form of a plate. Copper plates were used because they are soft metal and thus preserve the bore of the gun. However, it was discovered that the plates became permanently fused to the projectile after firing. The process is capable of bonding metals together that are metallurgically incompatible. Metal blanks for United States sandwich coins are made this way.
Nuclear explosives are the most powerful types and there are several different varieties of explosive devices based upon the mechanics of the explosion.
Atomic bombs, or fission, explosions occur when a fissionable material is manipulated so that a neutron is bombarded into the nucleus of a fissionable material and the nucleus then splits into two new nuclei. A great amount of thermal energy and gamma rays are given off and there are at least two additional neutrons produced as well. These new neutrons are likely to strike another nucleus and the process repeats in a chain reaction where nearly all of the fissionable material is consumed provided that there is sufficient mass of fissionable material to create a sustainable reaction.
Gun-Type Atomic Bombs
Gun-type atomic bombs operate by bombarding two pieces of fissionable material that are individually too small to sustain a nuclear reaction into each other at great speed. These pieces would ideally weigh less than about one pound / 0.45kg. The apparatus used to facilitate this reaction is similar to a gun barrel where the materials are fired at each other like artillery projectiles and collide inside the barrel. When the two pieces of material collide with sufficient speed, they form a supercritical mass provided that the combined mass will be enough to sustain a nuclear reaction. This is a fission reaction and uranium-235 can be used for the fissionable material. The explosive force of a 2.2 pound / 1kg bomb of this type is comparable to exploding about 17,000 tons of TNT. An atomic bomb of this type, named Little Boy, was exploded at 1900 feet / 579 meters altitude over Hiroshima, Japan, on 06 August 1945 at 08:15. It exploded with a force greater than the equivalent of about 15,000 tons of TNT and this was the first actual use of an atomic bomb in warfare.
Implosion-Type Atomic Bombs
Implosion-type atomic bombs operate by surrounding fissionable material with conventional high-explosives in a strong container with the simplest form being spherical. The fissionable material must be of sufficient size to create a critical mass and is positioned as a sphere in the center of the container. The conventional explosives are positioned around this sphere and can be in the form of a shell around it or a large number of individual charges. The explosives are detonated at exactly the same time so that it causes the core of fissionable material to compress. If enough explosives are used in a strong enough container, it causes the fissionable material to compress to the point that its density becomes so great that it explodes releasing enormous amounts of energy. This type of atomic bomb can be made from plutonium-239 and a bomb of this type, named Fat Man, was first used in warfare at Nagasaki, Japan on 09 August 1945 at 11:02. It had the equivalent destructive force of 21,000 tons of TNT and exploded at 1650 feet / 503 meters altitude.
Thermonuclear bombs operate on energy released from a fusion reaction where hydrogen isotopes, usually an interaction of deuterium and tritium, combine to produce helium atoms. Because the light materials must overcome the repellent forces of their protons this can only occur at extremely high temperatures (millions of degrees). A thermonuclear explosion occurs in several stages. The first stages are an implosion-type of fission bomb. However, the fission bomb is exploded inside of a uranium reflector that directs the force of the fission explosion back onto the fusion materials thereby directing enough heat and energy onto them to initiate a fusion reaction. The fusion explosion then affects the uranium reflector causing it to fission also. This adds to the explosion and also creates materials that form fallout. Thermonuclear bombs can be many times more powerful than fission-type bombs and their equivalent energy is usually expressed in megatons of TNT. The USA exploded the first thermonuclear bomb on 01 November 1952 on Enewetak atoll in the Pacific.
Neutron bombs are thermonuclear devices where the uranium reflector is absent and they produce a much smaller blast. However, they produce an enormous amount of neutrons that shower an area with lethal doses of radiation. They are sometimes called enhanced radiation warheads. Allegedly, the effects are limited to an area of a few hundred yards.