Amatol

Amatol

[am-uh-tawl, -tol]
Amatol is a highly explosive material made from a mixture of TNT and ammonium nitrate. Amatol was used extensively during World War I and World War II. It was eventually replaced with alternatives such as Composition B, torpex and tritonal.

Typically, Amatol was used as an explosive in military weapons such as aircraft bombs, shells, depth charges and naval mines. Amatol exploits the synergy between TNT and ammonium nitrate: TNT has a high explosive velocity and good brisance, but is comparatively expensive and complex to manufacture and is also deficient in oxygen. This oxygen deficiency can be seen from the black smoke residue from a pure TNT explosion. When compared to TNT, ammonium nitrate has a fairly low detonation velocity and correspondingly low brisance, but is extremely cheap and easy to manufacture. More importantly, it contains a surplus of oxygen which TNT can use during detonation. Depending on the ratio of ingredients used, Amatol leaves a residue of white or grey smoke after detonation.

Amatol allowed existing supplies of TNT to be "padded out" considerably, with little reduction in the destructive power of the final product, so long as the amount of TNT in the mixture did not fall below 60%. These were highly attractive features during major wars, when there was an insatiable demand for high explosives.

Typical ratios of TNT to ammonium nitrate (by weight) for military Amatol are as follows:

  • 80/20
  • 60/40
  • 50/50 — had a detonation velocity of approximately 6,000 metres per second.
  • 20/80

The Amatol production process is very simple, another reason why it was so popular during major conflicts: TNT is gently heated until it melts, acquiring the physical characteristics of a syrup. Then the correct weight ratio of powdered ammonium nitrate is added and mixed in. Whilst this mixture is still in a molten state, it is poured into empty bomb casings and allowed to cool and solidify. However, the lowest grades of amatol (eg 20/80) could not be produced by casting molten TNT. Instead, flaked TNT was thoroughly mixed with powdered ammonium nitrate and then compressed or extruded.

The colour of Amatol ranges from off-white to slightly yellow or pinkish brown, depending on the mixture used, and remains soft for long periods of storage. It is also hygroscopic, which complicates long-term storage. To prevent moisture problems, amatol charges were coated with a thin layer of pure molten TNT or alternatively bitumen. Long-term storage issues were rarely a problem during major conflicts because munitions charged with amatol were generally used soon after manufacture.

Amatol should not be stored in containers made from copper or brass, as it can form dangerous compounds. It is relatively stable, but may be detonated by severe impact. Primary explosives such as mercury fulminate were often used as a detonator, in combination with an explosive booster charge such as tetryl.

The explosive charges hidden in HMS Campbeltown during the St. Nazaire Raid of 1942 contained amatol. Additionally, the British X class midget submarines which planted explosive charges beneath the German battleship Tirpitz in September 1943 used two "saddle charges" containing a total weight of four tons of Amatol. Warheads for the German V1 flying bomb and V-2 rockets also contained amatol.

Ammonite

Amatol is rarely encountered today, except in legacy munitions or unexploded ordnance. However, a form of amatol still exists under a different name — ammonite. Ammonite is a civilian explosive, generally comprising a 20/80 mixture of TNT and ammonium nitrate. Typically, it is used for quarrying or mining purposes. It is a popular civilian explosive in Eastern Europe and China.

Because the proportion of TNT is significantly lower than in its military counterpart, ammonite has much less destructive power. However, given the particular purposes for which ammonite is used, this is not a problem. In general, a 30 kilogram charge of ammonite is roughly equivalent to 20 kilograms of TNT.

See also

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