A History of Research and a Review of Recent Developments

4
The nature of explosions
or rather an immense fortune. He was unmarried, dogged by ill-health,
pessimistic and cynical, but luckily he combined these features with a powerful
benevolence. When he died in 1896 he left most of his fortune in trust, to form
the Nobel foundation from which international prizes are awarded annually
for Physics, Chemistry, Medicine, Literature and Peace.
The end of the nineteenth century also saw the discovery of a range of
military explosives of great importance. It was found that methyl benzene
(toluene) reacted with nitric acid in the presence of concentrated sulphuric
acid to form trinitrotoluene, more commonly known as TNT. This became
the standard explosive of the First World War, and since then the combination
of liquid TNT with explosives such as RDX or PETN in plastic form has
proved very successful. TNT can be manufactured with relative safety and
economy, and because of its universal use it has become customary to class all
types of explosive (conventional or nuclear) in terms of TNT as a standard.
PETN is pentaery-thritol-tetranitrate and RDX is cyclo-trimethylenetrinotramine.
HBX is a combination of RDX, TNT and Aluminium; pentolite
is a mixture of PETN and TNT in equal parts. Other important families of high
explosive were the Amotal and Ammonal groups, formed by compounding
ammonium nitrate with TNT. Many combinations of nitrates, TNT and
aluminium were tried, giving rise to a range of trade names that need not concern
us. Explosives of all the above types were the main materials for bombs in the
Second World War, and extensive wartime research established a league table
of strengths in terms of peak instantaneous pressure and positive impulse.
The main development in the latter half of the twentieth century has been
‘slurry’ explosive. This began with the mixing of ammonium nitrate and fuel
oil to form ANFO which, although extensively used for quarrying and mining,
was somewhat low in strength and susceptible to the effects of water. These
problems were overcome by combining the ammonium nitrate with sodium
nitrate in a gelled aqueous solution to form a slurry. This is widely used because
it reduces the cost of many of the civil needs for high explosive, and there has
been a noticeable reduction in the use of the nitroglycerines in recent years.
For military purposes, however, the production of TNT-based explosives in
sheet and slab form has continued, and most readers will be aware of the use
by terrorists of sheets of the Czechoslovakian explosive, Semtex.
Military research establishments have also been involved in the development
of fuel-air explosive (FAE), a detonating explosive that draws virtually all of the
required oxygen from the air. Detonation occurs over a large area so that a
greater impulse is generated than with the point detonation of a conventional
high explosive. Research shows that about 42% of the weight of TNT is due to
the oxygen attached to the explosive molecule 12C 6H 2CH 3(NO 2) 3, whereas
47% of the weight of the consumables (fuel and air) in some types of fuel-air
explosive comes from the surrounding air, and does not have to be carried
within the body of the explosive. This means that a given weight of FAE produces
over seven times the energy of TNT, although the peak overpressure is much