Activation energy explosives

Nitrocellulose is among the least stable of common explosives. At 125°C it decomposes autocatalyticaHy to CO, CO2, H2O, N2, and NO, primarily as a result of hydrolysis of the ester and intermolecular oxidation of the anhydroglucose rings. At 50°C the rate of decomposition of purified nitrocellulose is about 4.5 x 10 %/h, increasing by a factor of about 3.5 for each 10°C rise in temperature. Many values have been reported for the activation energy, E, and Arrhenius frequency factor, Z, of nitrocellulose. Typical values foiE and Z are 205 kj/mol (49 kcal/mol) and 10.21, respectively. The addition of... 

Polymerizing, Decomposing, and Rearranging Substances Most of these substances are stable under normal conditions or with an added inhibitor, but can energetically self-react with the input of thermal, mechanical, or other form of energy sufficient to overcome its activation energy barrier (see Sec. 4, Reaction Kinetics, Reactor Design, and Thermodynamics). The rate of self-reaction can vary from imperceptibly slow to violently explosive, and is likely to accelerate if the reaction is exothermic or self-catalytic. 

Fortunately, explosives have an activation energy, so it takes some energy to get the reaction started. Usually, what starts the reaction is heat, but it can be a physical shock for especially sensitive explosives like liquid nitroglycerin. 

ANTA (114) readily forms a stable anion on reaction with bases like sodium ethoxide and this anion has been used as a nucleophile for the synthesis of many ANTA derivatives. Laval and co-workers synthesizedDANTNP (116) (calculated VOD 8120 m/s, = 1.84 g/cm, m.p. > 330 °C) from the reaction of 4,6-dichloro-5-nitropyrimidine (115) with two equivalents of ANTA (114) in the presence of sodium ethoxide. Agrawal and co-workers studied the thermal and explosive properties of both ANTA and DANTNP and suggested their use for applications in propellant/explosive formulations where insensitivity coupled with thermal stability is of prime importance. The activation energies of ANTA and DANTNP indicate that DANTNP is more thermally stable than ANTA. 

Extensive theoretical and experimental thermodynamic studies have been carried out on the explosive 1,4,5,8-tetranitro-l,4,5,8-tetraazadecalin (TNAD 104). Much of the data are summarized in a 2005 publication <2005IJQ(102)398> in which detailed decomposition profiles are proposed, although additional theoretical studies have been reported since <2006PCB10651>. The first step activation energy is lower for /ra r-104 than for the cis-form (18,5 vs. 33.3kJmoP )-... 

The paper of Gordon describes a model for diffusion-controlled reaction based on the "hole concept in liquids of Jost (Ref 1, p 459). in which the activation energy for diffusion is equated simply to pV. The marked effect of density, therefore, results from the strong dependence of pressure on density (p varying about as the density cubed) and the appearance of this factor in an exponential term. On this basis, Gordon derived an approximate expression for dependence of detonation velocity D on explosive density pQ. This equation is given on pp 833 and 836 of Gordon s paper. From this expression the critical diameter dc for composite explosives is related to an exponential function of density by ... 

The activation energy for Reaction (2) is 18-19 kcal/mole. It has been assumed that this is the energy required to remove ammonia from the surface of the solid NH3 -NI3. After removal of the ammonia the Nl3 that is left is unstable and decomposes with the liberation of heat. The explosion then grows from this hot region the reactions proposed being either... 

The induction time t is of particular interest, since it can be compared to the induction time computed for an adiabatic thermal explosion (See Ref 6, pp 173—74 or Eq 6 of Article on Hot Spots, p H172-R) to provide a check on the correctness of the supposition that the input shock"generates a thermal explosion (at the shock entry face). Unfortunately, an exact quantitative treatment of the induction times of shock-generated thermal explosions suffers from a) uncertainty of the shockgenerated temperature in the LE and b) uncertainty in the Arrhenius kinetic parameters (activation energy and pre-exponential factor) (See Kinetics in this Vol)... 

A comparative evaluation of heat sensitivity of different explosives can be obtained by determining (a) explosion delay (TD) or induction period (b) explosion temperature ( T) and (c) activation energy ( a) which are related to each other. 

Activation Energy It is experimentally seen that the explosion delay (ED) for the build-up of an explosion decreases with an increase in temperature. Therefore, energy of activation (IQ can be calculated on the basis of a relationship between the experimentally obtained ED and the absolute temperature of the Wood s metal bath. This relationship is expressed by an Arrhenius type of equation, that is, (Equation 3.3) ... 

Isothermal DSC was used to determine the kinetic parameters for thermal decomposition of 2,4,6-TNT and it was found that molten TNT shows a temperature-dependent explosion delay prior to its exothermic decomposition. The rate constant of exothermic decomposition and activation energies of explosion delay and exothermic decomposition were also reported [42]. Similarly, House and Zack... 

In a nutshell, it may be concluded that DTA, DSC and TGA have been used mainly to determine the thermal properties of explosives like melting points, thermal stability, kinetics of thermal decomposition and temperatures of initiation and ignition etc. Further, the properties which can be calculated quantitatively from the experimentally obtained values are reaction rates, activation energies and heats of explosion. DTA data of some explosives are given [46] in Table 3.6. 

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