What makes nitroglycerin explosive

Nitroglycerine is extremely sensitive to shock and in the early days, when impure nitroglycerine was used, it was very difficult to predict under which conditions nitroglycerine would explode.

Alfred Nobel studied these problems in detail, and was the first to produce nitroglycerine on an industrial scale. His first major invention was a blasting cap igniter , a wooden plug filled with black gunpowder, which could be detonated by lighting a fuse.

This in turn, caused an explosion of the surrounding nitroglycerine. Sobrero, like Nobel, was a chemist who studied with professor J. Pelouze in Paris, according to the Nobel Prize website.

The oil this produced was incredibly explosive, writes Nobel biographer Kenne Fant, and Sobrero considered it too destructive and volatile to have any practical uses. He had a long interest in the use of explosives, the encyclopedia writes, influenced by the family business selling explosive mines and other equipment.

In the early s, having completed his education, he began experimenting with explosives. The solution he devised was a small wooden detonator with a black powder charge that was placed in a metal container full of nitroglycerin. It is the speed of the decomposition reaction which makes nitroglycerin such a violent explosive. Unlike burning, which can only travel as fast as the flame front can move through the material, high explosives are decomposed almost instantaneously by a supersonic shock wave passing through the material.

This instantaneous destruction of all the molecules in the sample is called a detonation , and the rapid expansion of hot gases that results is what causes the destructive blast. In fact, 4 moles of nitroglycerin produces 35 moles of hot gases.

One advantage that nitroglycerin has over some other high explosives, like TNT, is that no solid forms of carbon in the form of soot or smoke is produced when it is detonated. This allows nitroglycerin to be used to make 'smokeless powders', which is of great advantage to artillery or naval gunners whose field of vision does not then become obscured during battle by clouds of billowing smoke.

Nitroglycerin has one major disadvantage, however - it is very, very unstable. To be a useful explosive, a substance has to be able to withstand, without detonating, the jolts and bumps both of its manufacture, and of its transportation to where it will be used.

Clearly, nitroglycerin is far too dangerous for this, and many people lost their lives in the last century trying to use nitroglycerin for peaceful purposes like quarrying.