the surface area of the reactants and hence oxidation will occur quicker
and therefore a more efficient explosion.
If the proportions of the different mixtures are controlled, then
different explosions can be made varying in their magnitude. Also using
different oxidisers can change the rate at which oxidation happens to
increase the explosion magnitude.
“The Gun Powder that was used for centuries is a mixture of powdered
potassium nitrate”. (Article 1 ~ Conkering cordite)
This was known as black powder in its
compressed form. The problem
armies faced by around 1815, was the
huge amounts of smoke that was
released. (see fig 2.5)
This was a huge disadvantage in war as the friendly fire rate increased.
Surprise attacks increased as smoke gave up the positions of
troops and snipers. Consequently, generals could not issue appropriate
orders.
An explosive that produced little or no smoke was eagerly awaited. In
1846, Dr Christian Schonbein accidentally discovered nitrocellulose, a
chemical that changed the world of warfare due to the lack of smoke
from the gun powder.
This was used as the main ingredient in gunpowder which replaced black
powder. The new explosive could also be detonated by percussion and
therefore a lighted fuse was not needed and hence more powder could be
used per shell.
Nitrocellulose lead to explosive shells replacing cannon balls and bullets
replacing musket balls.
Bullets and shells are made by cordite. Cordite was made by propanone.
But in the First World War, the British were running out of shells due to
the short supply of propanone. The existing source of propanone was from
the anaerobic dry distillation of wood and imports from Germany and
USA. Britain was at war with Germany and supplies were low. Weizmann
discovered that propanone could be made by the fermentation of starch
in maize. This was adopted and ships imported maize from USA. But
because many ships were been sunk by Germans, the maize was needed as food.
”Therefore conkers were used as a source of propanone to replace
maize. Even though they were not as efficient, a year later they were not
needed as the war had ended.”
"Acetone." Microsoft® Encarta® 2006 [DVD]. Redmond, WA: Microsoft Corporation, 2005.
Both the explosives rely on oxidation and hence there being instant
oxygen available for a great explosion. Therefore compounds with lots of
oxygen in them were often used, (see fig3)
As you can see from the formula on
the left, there are 11 oxygen atoms
which make this a very good explosive.
Nitroglycerine, a material that was unpredictable in its explosive nature.
This meant it was extremely unsafe. At around 1861, a chemist and
another scientist died because of this random explosive nature.
Alfred Nobel made this explosive safe by mixing it with kieselguhr to
make a paste that could be shaped into rods. These would only explode
when deliberately detonated. (SEE Fig 4)
“These rods became famous as sticks of dynamite and
were the first safe high explosive.” (Article 2 ~ Nitroglycerine) (SEE Fig 4)
Nitroglycerine is a high explosive because the time it (the reactants) takes to
decompose is extremely fast and it produces insanely high temperatures and pressures.
Black powder is a low explosive as it takes more time than a high explosive
to burn, and it produces lower pressures than that of high explosives like
Nitroglycerine.
Explosive reactions need to take place very quickly and have to be
exothermic. This also means that the products should mostly be gasses.
“Either by a fuse or another small explosion, the reaction will be triggered.”
"Nitroglycerine (explosive)." Microsoft® Encarta® 2006 [DVD]. Redmond, WA: Microsoft Corporation, 2005.
No oxygen from the air is needed with good explosives as the reactants
contain lots of oxygen atoms. Due to the exothermic burning, there is
a dramatic increase in temperature and pressure of the surroundings. As
the reaction is confined to an extremely small space, there will be an
explosion.
The above is the structural formula for Nitroglycerine
(Article 2 ~ Nitroglycerine Pg 9 ~ GI Brown)
High explosives like Nitroglycerine are extremely efficient as the
reactions are extremely quick and under very high exothermic
conditions. (SEE FIG 6)
“The power of an explosive depends more on the rate at which the energy
is released than on the total amount of energy”.
(Article 2 ~ Nitroglycerine Pg 11 ~ GI Brown)
Therefore High explosives tend to result in the most efficient explosions.
Despite being used for explosives, Nitroglycerine is used to cure Angina, a disease
of the heart.
Ascanio Sobrero discovered Nitroglycerine and its unreliable tendency to explode.
Many people who experimented with it have been killed and thoughts that the
chemical would have any practical uses was discarded.
But later on, Thomas Brunton found that Nitroglycerine had similar a structure to
amyl nitrate and hence they were both used to cure angina.
Workers who handle the chemical were exposed to severe headaches when away
from it, and so they always carried some of the explosives with them!
Therefore the development of Nitroglycerine as a medicine and explosive required
lots of research and many people were certainly injured or even killed in the
experiments.
References:
Article 1, Conkering cordite, Wilson Flood, Volume 10, Number 2, November 2000.
Article 2, Nitroglycerine, GI Brown, Volume 9, Number 2 of Chemistry Review, Nov 1999.
(visited 4th March 06)
http:// (visited 3rd March 06)
(VISITED 5TH March)
"Nitroglycerine (explosive)." Microsoft® Encarta® 2006 [DVD]. Redmond, WA: Microsoft
Corporation, 2005.
"Acetone." Microsoft® Encarta® 2006 [DVD]. Redmond, WA: Microsoft Corporation, 2005.