Ammonal is an explosive made up of ammonium nitrate, trinitrotoluene (TNT), and aluminium powder.
The ammonium nitrate functions as an oxidizer and aluminium as a power enhancer. To some extent the aluminium makes it more sensitive to detonation. The use of the relatively cheap ammonium nitrate and aluminium makes it a replacement for pure TNT.
The mixture can suffer humidity because ammonium nitrate is highly hygroscopic. Ammonal burns vigorously when open to the air, but detonates when confined inside some form of casing.
The detonation velocity of ammonal is approximately 4,400 metres per second or 9,842 miles per hour.
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From early 1916 the British Army employed ammonal for their mines during World War I, starting with the Hawthorn Ridge mine during the Battle of the Somme. Three of the mines used at the Battle of Messines which were exploded at the start of the Third Battle of Ypres contained 30,000 lbs (over 13.6 metric tons) of ammonal, a fourth contained 20,000 lbs (over 9 metric tons). 1917 – World War I: The British Army detonated 19 ammonal mines under the German lines, killing 10,000 in the deadliest non-nuclear man-made explosion in history. Ammonal used for military mining purposes was generally contained within metal cans or rubberised bags to prevent moisture ingress problems. The composition of ammonal used at Messines was 65% ammonium nitrate, 17% aluminum, 15% TNT and 3% charcoal.[1]
Not all of the mines that had been laid at Messines were detonated. Two of the original 21 mines were not ignited because they were outside the area of the offensive. On 17 July 1955, a lightning strike set off one of the remaining mines. There were no human casualties, but one cow was killed. The 21st mine is believed to have been found,[2] but no attempt has been made to remove it. It is possible that the one unexploded mine was dismantled, because German tunnellers were coming too close to the chamber.
Ammonal remains in use as an industrial explosive. Typically, it is used for quarrying or mining purposes.
An ammonal mixture previously used in hand grenades and shells has the proportions (by mass):[3]