Detonation in Ammonium Nitrate

Abstract

IT has been appreciated for many years^1–5 that ammonium nitrate, even when free from combustible material, can detonate. This is not surprising, since the products of decomposition must be entirely gaseous and have substantially less energy of formation than the original substance. For example, if the nitrogen is not oxidized, the energy released at constant volume, with water in the vapour phase, is 380 cal./gm. or 8.7 kcal. per mole of gas. This is, of course, rather low compared with typical values for explosives, which lie in the range 20–50 kcal./mole gas. The temperatures and pressures reached in the detonation wave will therefore also be relatively low, and one might expect the substance to detonate with difficulty and only under good confinement. This is found to be so. For normal material at densities around 1 gm./cm.³, cartridge diameters of many inches or heavy metal tubes are necessary^6,7, and even then the measured speeds are much lower than the maximum values calculated for products N₂ + 2H₂O + ½O₂. This has led eome authors⁸ to conclude that an equilibrium involving oxides of nitrogen is more appropriate, and that the release of energy is of order 230 cal./gm.