What makes nitroglycerin so dangerous?
Henry Hall
First synthesized in 1847 Italy, nitroglycerin was the first ‘ practical ’ explosive more powerful than the black powder being used in small arms at the time. However, it proved so unstable and energetic that it was not until twenty years later, when Alfred Nobel invented dynamite, that it became safe be put to practical use on a large scale. Indeed, even today nitroglycerin is among the most powerful explosives used industrially; 1 more destructive than TNT and comparable to modern explosives such as RDX, which is used in products such as C4. What is it then that gives nitroglycerin such destructive properties? To answer this question, first we must discuss what constitutes an explosive. There are twomain forms of explosive: high and low explosives. Low explosives were first invented in the form of black powder, a primitive gunpowder. They consist of fuel mixed with a source of oxygen, which allows the combustion to occur at a much faster rate than if it relied on atmospheric oxygen alone. In the case of black powder, sulphur and charcoal serve as fuels, while potassium nitrate is used as an oxygen source, decomposing upon heating to release oxygen, resulting in rapid conflagration of the fuels. A low explosive ‘ deflagrates, ’ meaning that the fuels burn as the reaction front spreads throughout the explosive. This reaction front proceeds at a subsonic speed, hence no shockwave is produced, and the reaction can be described as simply a rapid form of combustion. A large volume of gaseous products is produced through combustion, which when in a confined space can result in extreme build-up of pressure, and consequently result in an explosion. 2 In contrast, a high explosive ‘ detonates, ’ meaning the molecule does not release energy through combustion, but decomposes and in doing so releases a great deal of gas and heat. This rapid release of huge amount of energy into a small volume results in the formation of a supersonic shock wave which propagates throughout the explosive material, causing adjacent molecules to decompose in a similar fashion. This will continue until all explosive material has been detonated. This decomposition occurs much faster than the deflagration seen in low explosives, and in the case of nitroglycerin, the shock wave can travel through the material at around 7.7 km/s. 3
But to understand why nitroglycerin is so sensitive and powerful even compared other high explosives, we must look closer at what it is that allows detonation to occur as opposed to deflagration. When looking at the display formulas of any explosive compounds, one of the most striking features is the abundance of functional groups containing nitrogen and oxygen present in the molecules, and it is primarily the presence of nitrogen that results in the huge amount of energy released upon detonation. When the molecule undergoes decomposition, nitrogen atoms can recombine to form N 2 molecules, in
Skeletal formula of nitroglycerin
Image Source: Wikipedia Nitroglycerin
1 See Encyclopaedia Britannica, Nitroglycerin. 2 See Los Alamos National Laboratory, What is a high explosive? 3 See Encyclopaedia Britannica, Nitroglycerin.
218
Made with FlippingBook - Online catalogs