Ammonium nitrate explosive decomposition

A mixture of 0.5% of potassium permanganate with an ammonium nitrate explosive caused an explosion 7 h later. This was owing to formation and exothermic decomposition of ammonium permanganate, leading to ignition. 

The converse obviously applies to ammonium nitrate explosives, which must not contain any chlorates, since during storage a double exchange reaction may occur resulting in the formation of ammonium chlorate (p. 476, Vol. II), an unstable substance which decomposes spontaneously. A number of patents were taken out between 1880 and 1895, for explosives based on the use of ammonium chlorate or mixtures of ammonium nitrate with potassium or sodium chlorate. Many accidents which occurred through the spontaneous decomposition of these explosives proved the impossibility of using mixtures containing both chlorates and ammonium salts (Hantke [79]). 

The effect of solid particles. In his studies of the detonation products of explosives stemmed in different ways, Audibert [29, 32] paid attention to the fact that in charges insufficiently stemmed a certain amount of the explosive remains in the form of small particles which may undergo further explosive decomposition according to conditions, i.e., temperature and ambient pressure. If these particles are ejected into a space filled with a methane-air mixture they may lead to the explosion of this mixture. The possibility of the existence of particles of undecomposed explosive in ejected detonation products has been disputed by some authors (Segay [33]), but many others have proved that it can occur. T. Urbanski [34] found that a thin layer on the periphery of a cylindrical charge of ammonium nitrate explosive is... 

However, Feick and Hainer [18] consider most of the above figures of the energy of activation are not very accurate as in the period prior to explosion a considerable quantity of ammonium nitrate is evaporated. The authors suggest the following equations for ammonium nitrate thermal decomposition ... 

J.C. Oxley, S.M. Kaushik, N.S. Gilson "Thermal Decomposition of Ammonium Nitrate-Based Composites", Thermochem. Acta, 153 (1989) 269-286. J.C. Oxley, S.M. Kaushik, N.S. Gilson, "Ammonium Nitrate Explosives—Thermal Stability and Compatibility on Small and Large Scale" Thermochem. Acta, 212 (1992) 77-85. 

Dr. Rudolf Meyer was born on 4. 3. 1908 in Spandau (Berlin) and took his degree in Physical Chemistry. He began his initial studies in the area of energetic compounds in connection with his Doctor s degree in 1931 at Professor Boden-stein s Institute in Berlin with a paper on the enthalpy of formation and thermal decomposition of hydrazoic acid. After taking his Doctor s degree, he entered the Dynamit Nobel Company in 1934 as assistant to Dr. Ph. Naoum. He worked there from 1936-1945 on the development of pourable ammonium nitrate explosives and on hollow charges. 

Safety Considerations. Ammonium nitrate can be considered a safe material if treated and handled properly. Potential hazards include those associated with fire, decomposition accompanied by generation of toxic fumes, and explosion. 

Exothermic Decompositions These decompositions are nearly always irreversible. Sohds with such behavior include oxygen-containing salts and such nitrogen compounds as azides and metal styphnates. When several gaseous products are formed, reversal would require an unlikely complex of reactions. Commercial interest in such materials is more in their storage properties than as a source of desirable products, although ammonium nitrate is an important explosive. A few typical exampes will be cited to indicate the ranges of reaction conditions. They are taken from the review by Brown et al. ( Reactions in the Solid State, in Bamford and Tipper, Comprehensive Chemical Kinetics, vol. 22, Elsevier, 1980). 

The decomposition of ammonium nitrate, an explosive, evolves 37.0 kj/mol. Use the reaction given in Problem 45 to calculate the mass of ammonium nitrate (in kilograms) required to produce the same amount of energy as that produced when one milligram of U-235 undergoes fission. 

The action of sodium on ammonium nitrate results in a violent explosion. It is assumed to be caused by the decomposition of a hyponitrite formed as follows ... 

Nickei powder gives rise to dangerous reactions, which has led to accidents with potassium perchlorate (ignition), with chlorine at 600°C (ignition) and with ammonium nitrate at about 200°C (detonation). It catalyses the explosive decomposition of hydrogen peroxide. 

In the other method, particularly popular in Germany, the ammonium nitrate is replaced by an equimolar mixture of ammonium chloride and potassium or sodium nitrate. The reaction between the salts, which gives potassium or sodium chloride and ammonium nitrate or its decomposition products, is relatively slow and does not occur to a marked extent when the explosive is fired in an unconfined condition. This method of working is particularly effective in reducing the power of an explosive in the unconfined condition. Used alone it has not proved popular in Britain, because of the low power which tends to be developed under practical firing conditions. Moreover, the finely divided sodium chloride smoke which is produced by the explosive tends to be unpleasant for the miners. 

According to an O.S. amendment sheet, the procedure as described [1] is dangerous because the reaction mixture (dicyanodiamide and ammonium nitrate) is similar in composition to commercial blasting explosives. This probably also applies to similar earlier preparations [2]. An earlier procedure which involved heating ammonium thiocyanate, lead nitrate and ammonia demolished a 50 bar autoclave [3], TGA and DTA studies show that air is not involved in the thermal decomposition [4], Explosive properties of the nitrate are detailed [5], An improved process involves catalytic conversion at 90-200°C of a molten mixture of urea and ammonium nitrate to give 92% conversion (on urea) of guanidinium nitrate, recovered by crystallisation. Hazards of alternative processes are listed [6],... 

Decomposition of a 70% nitric acid-ammonium nitrate slurry explosive led to overflow, contact with wood and a fire. This spread to detonators, which initiated detonation of the slurry. 

The nitrate containing 0.1% of ammonium chloride decomposes vigorously below 175°C [1], Presence of 0.1% of calcium chloride or iron(III) chloride in the nitrate lowers its initiation temperature sufficiently to give violent or explosive decomposition. Thermal analysis plots for aluminium chloride, calcium chloride and iron(III) chloride are given [2],... 

A violent explosion in an ammonium nitrate store with sawdust-covered floors (to absorb spillage and prevent sparks) was attributed to local decomposition of the moist nitrate-containing sawdust, leading to temperature rise and spontaneous ignition. The observation of red-brown fumes just before the explosion supports this hypothesis. 

Alone, or Metals, or Metal compounds Mellor, 1940, Vol. 8, 327 1967, Vol. 8, Suppl. 2.2, 84, 96 It is an explosive of positive oxygen balance, less stable than ammonium nitrate, and has been studied in detail. Stable on slow heating to 300°C, it decomposes explosively on rapid heating or under confinement. Presence of zinc, copper, most other metals and their acetylides, nitrides, oxides or sulfides cause flaming decomposition above the m.p. (70°C). Commercial cobalt (cubes) causes an explosion also. 

Heating a mixture of an ammonium salt with a nitrite salt causes a violent explosion on melting [1], owing to formation and decomposition of ammonium nitrite. Salts of other nitrogenous bases behave similarly. Mixtures of ammonium chloride and sodium nitrite are used as commercial explosives [2], Accidental contact of traces of ammonium nitrate with sodium nitrite residues caused wooden decking on a truck to ignite [3],... 

Heating ammonium nitrate can present a severe explosion hazard. When heated above 210°C, its decomposition is exothermic, producing nitrous oxide and water vapor. In closed confinement, heating the molten mass can cause a pressure build-up. Above 300°C, there is rapid evolution of nitrogen, water... 

Some nitric acid is used for the manufacture of explosives and chemicals, but much is converted on-site to the potentially explosive high nitrogen fertilizer ammonium nitrate (Section 2.11). Ammonia gas from the Haber plant is absorbed in aqueous HN03, and the NH4N03 solution is evaporated to a liquid melt (< 8% H20) for crystallization, but care must be taken to keep the pH of the solution above about 4.5 and to exclude any material (chlorides, organic compounds, metals) that might catalyze the explosive decomposition of NH4N03. It is also wise to keep the melt mass low and to vent it to avoid pressure buildup. The solid product should be stored well away from the main plant. 

Chretien and Woringer [34] described the preparation of silver cyanamide from calcium cyanamide by the action of silver nitrate and also described its explosive properties. Montagu-Pollock [35] described a method for growing large crystals of the salt from its aqueous solution in the presence of ammonium nitrate, ammonia and a surface active agent. Bowden and Montagu-Pollock [36] and Montagu-Pollock [35] studied the slow decomposition of the crystals when heated at temperatures from 150 to 360°C. The course of decomposition was studied by electron microscope. 

The system ammonium nitrate, aluminium, nitro compound (e.g. TNT) would be expected to undergo gradual decomposition, e.g. that in stored shells and bombs filled with such mixtures changes would occur, leading to the oxidation of the aluminium. Obviously, a mixture containing oxidized aluminium has lower explosive power than the same mixture containing metallic aluminium. It was therefore very important to determine the mechanism of the oxidation of aluminium. It became apparent that this is caused by impurities in the ammonium nitrate, not by the... 

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