Explosives are substances which, when suitably initiated, undergo a rapid release of chemical energy that converts the explosive into hot gas under extreme pressure. These explosive residues can drive a projectile or shatter nearby objects through their shock effect. Explosives have been an important part of warfare since gunpowder was introduced into renaissance Europe, and they reached a high degree of sophistication during the Second World War.
Explosives can be broken down into two broad categories. Low explosives, often referred to as propellants, are combustible chemical mixtures such as gunpowder or nitrocellulose. They do not usually produce a shock effect unless ignited in a confined space. The burning region of the propellant spreads through heat conduction at less than the speed of sound. In technical language, the burn front is a subsonic deflagration front. The relatively gentle combustion of propellants makes them ideal for driving projectiles, such as bullets, shells, or rockets, and this had become their chief military function by the time of the Second World War.
Black powder had long been abandoned by the time
of the Pacific War, and most propellants were nitrocellulose or
mixtures of nitrocellulose with nitroglycerine and nitroguanadine.
Potassium sulphate or similar compounds were sometimes added to reduce
the visible flash produced by the propellant. Nitrocellulose was
usually manufactured by treating cotton with hot nitric and sulphuric
acid. The nitric acid combined with the cellulose in the cotton while
the sulphuric acid acted as a catalyst.
High explosives are chemicals or chemical mixtures that burn so rapidly that the burning region spreads as a shock wave moving at supersonic speeds. In technical language, the burn front is a supersonic detonation front. High explosives produce a shock effect even when unconfined, although a confined explosion is usually somewhat more powerful. Curiously, many high explosives will burn without detonating. These so-called insensitive explosives are relatively safe to handle and are preferred for the bulk of the explosive charge in munitions. They must be initiated using a small quantity of more sensitive explosive that can be set off by heat or impact.
At the start of the Pacific War, high explosives
were dominated by two families of chemicals. Aliphatic explosives, of
which the most important was nitroglycerine, could be produced from
animal or vegetable fat treated with a mixture of hot nitric and
sulphuric acids. Nitroglycerine is a powerful but extremely unstable
explosive liquid, which can be stabilized by absorbing the liquid into
various inert substances such as wood pulp or diatomaceous earth. The
resulting product, dynamite, was widely used in civil engineering but
saw little use in munitions.
Aromatic explosives are a large family of benzene
derivatives. Of these, the most important was trinitrotoluene or TNT,
which is an excellent, inexpensive explosive. It is relatively
insensitive, and it melts well below its detonation temperature. This
makes TNT ideal for explosive castings, by itself or as a mixture with
other explosives. Like nitroglycerine, TNT is produced by treating
toluene with a hot mixture of nitric and sulphuric acids.
TNT contains insufficient oxygen to fully oxidize the carbon in the compound when it is detonated. As a result, TNT explosions produce a smoky black fireball. Amatol is a mixture of TNT with ammonium nitrate that adds enough oxygen to fully oxidize the carbon in the TNT, yielding a more powerful explosive mixture that does not produce black smoke. It was widely used in both wars. Baratol, which uses barium nitrate in place of ammonium nitrate, was used in the standard British Mills hand grenade. Minol is a powerful but somewhat sensitive mixture of TNT, ammonium nitrate, and powdered aluminum that was used in naval mines.
Picric acid (trinitrophenol) is another aromatic
explosive closely related to TNT. It was the chief ingredient of
Shellite, which was widely used in British naval munitions. However,
picric acid is highly toxic, and it has a nasty habit of slowly
corroding any metal it is in contact with to produce extremely
sensitive metal picrates. As a result, older munitions containing
picric acid could be very unsafe to handle. Ammonium picrate (Explosive
D or dunnite) is much less sensitive than picric acid, is not as
corrosive, and was extensively used in U.S. Navy munitions.
RDX (Cyclonite) is an aromatic explosive that went into mass production just as war broke out in Europe. It is very insensitive and significantly more powerful than TNT but somewhat more expensive to manufacture. It was widely used as a mixture with TNT known as Composition B. It was also used in Torpex, a mixture of RDX, TNT, and powdered aluminum whose explosive characteristics were ideal for use in mines and torpedoes.
PETN is a very powerful but somewhat sensitive aliphatic explosive. It was used in light antiaircraft shells as a mixture with TNT (Pentolite) that greatly reduced its sensitivity.
Trinitoaniline (Picramide) was used by the Japanese in naval shells. It is an aromatic explosive similar to TNT. The Japanese also used picric acid in naval shells and PETN or a mixture of TNT and powdered aluminum in light antiaircraft shells.
Detonators
for high explosives contained a small amount of a highly sensitive
explosive. Detonator explosives included lead
azide or lead styphnate. Lead azide is an inorganic compound of lead
and nitrogen, while lead styphnate is a compount of lead with styphnic
acid, a sensitive aromatic explosive related to TNT. Mecury fulminate also saw use in
detonators, as was tetryl, which is chemically similar to ammonium
picrate.
References
The Pacific War Online Encyclopedia
(c) 2008 by Kent G.
Budge. Index