What makes nitroglycerin so dangerous?
Now, let us compare the oxygen balance of TNT with that of RDX, which has the chemical formula C 3 H 6 N 6 O 6 , and subsequently a relative molecular mass of 222:
−1600 222
6 2 ) − 6) = −21.6%
× (2(3) + (
Here, we can see that RDX is far less oxygen deficient than TNT, which corresponds to the fact that, although exact figures depend on the techniques used in measurement, RDX has an RFE of around 1.6 compared to TNT. 8
Finally, we will calculate the oxygen balance of nitroglycerin, which has the formula C 3 H 5 N 3 O 9 , and a relative molecular mass of 227:
−1600 227
5 2 ) − 9) = 3.52%
× (2(3) + (
This shows that, unlike TNT and RDX, nitroglycerin in fact has a positive oxygen balance, and so is capable of fully oxidising all its products of decomposition. However, despite having a far superior oxygen balance to RDX, it too only has an RFE of around 1.6. 9 This is because, besides oxygen balance, there are several other factors which determine an explosive’s properties. Among these properties, some of those which have the most significant impact on an explosive’s performance are physical rather than chemical. One of the most influential of these properties is the material’s density, for fairly obvious reasons – the denser an explosive is, the more you can pack into a given volume. As a result, it will take less time for the shockwave to propagate throughout the entire material, leading to complete detonation and release of energy in a shorter time-span, and hence amore powerful shockwave. In addition, a greater mass of explosive can be packed into a given volume, which is useful for applications such as the filling of artillery shells. Differences in densities can help explain why, despite having a much higher oxygen balance, nitroglycerin has a similar relative explosive factor to RDX: 10
Compound
TNT
RDX
Nitroglycerin
Density (g/ml)
1.60
1.78
1.60
Oxygen Balance (%)
-74.0
-21.6
3.52
Relative Effectiveness Factor
1
~1.6
~1.6
As we can see in this table, nitroglycerin has a density similar to that of TNT, as well as a significantly higher oxygen balance, which helps explain why, as an explosive, it’s around 1.6 times more effective. RDX on the other hand has an oxygen balance lower than that of nitroglycerin, but this is offset by its higher density.
8, 9, 10 See Wikipedia TNT Equivalent.
221
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