Thermal stability and sensitivity of energetic formulations
Explosive mixtures have found widespread use in both military applications and as a component of improvised explosive devices (IEDs). Knowledge of how the components of these formulations interact with each other will benefit both military and anti-terrorism organizations. Since there are significant differences in the explosive properties desired by the military verses those involved in illicit activities, it is important to study both military and improvised formulations. ^ The use of improvised explosive devices by terrorist organizations is a significant problem that has resulted in destruction of property and loss of both military and civilian lives in countries throughout the world. There are many different materials that can be used to make home-made explosives (HMEs), but they are often combinations of a fuel and an oxidizer. These materials are popular because they are generally readily available due to their use in various industrial and household processes. Knowledge of which fuel/oxidizer combinations are potentially dangerous can help anti-terrorist organizations focus resources on detecting potential threats and preventing the use of potential HME components. In the first manuscript, titled "Fuel-oxidizer Mixtures: Their Stabilities and Burn Characteristics", various fuel-oxidizer combinations were examined by differential scanning calorimetry (DSC) and simultaneous differential scanning calorimetry/thermogravimetric analysis (SDT). It was found that the reaction between the fuel and the oxidizer was generally triggered by a thermal event such as a melt, phase change, or decomposition. When the fuel used was a polyalcohol or sulfur, the triggering event was often the melt of the fuel, which usually occurred at a lower temperature than that of the oxidizer. However, three of the oxidizers, potassium nitrate, potassium perchlorate, and ammonium perchlorate, generally did not react until they had undergone a phase change or began to decompose, and as a result, reactions with these oxidizers tended to occur at much higher temperatures. Reactions with hydrocarbon fuels containing fewer or no alcohol groups also tended to react at higher temperatures. Regardless of the fuel used, the mixtures containing potassium chlorate, ammonium perchlorate and ammonium nitrate generally released the greatest amount of heat, around 2000 J/g, while mixtures containing potassium dichromate were the least energetic, generally releasing less than 200 J/g. For some formulations, reactions did not occur until temperatures higher than 500°C. In order to reach higher temperatures, it was necessary to use unsealed samples in the SDT rather than the sealed capillaries used in the DSC. It was noted that when samples were not in sealed capillaries, other processes such as sublimation effectively competed with the exothermic reactions experienced by the formulations. As a result, the heat release values obtained by SDT for some formulations were artificially low. ^ The second manuscript "Thermal Stability Studies on IMX-101 (Dinitroanisole/Nitroguanidine/NTO)" examines the interactions among the components of an insensitive munitions formulation, IMX-101, which has been developed and qualified for use as a replacement for TNT (2,4,6-trinitrotoluene). IMX-101 contains the energetic materials 2,4-dinitroanisole (DNAN), nitroguanidine (NQ), and 3-nitro-1,2,4-triazol-5-one (NTO). DNAN is a nitroarene that is very similar in structure to TNT, but with only two nitro groups, and with an anisole functional group in place of the methyl group in TNT. 2,4-Dinitrotoluene (DNT), which also contains only two nitro groups, is even more similar to TNT, because it is a toluene rather than an anisole. DSC and isothermal analyses were used to compare DNAN and DNT, to see if increased thermal stability made the use of DNAN more appealing than DNT in IMX-101 and other insensitive munitions formulations. The isothermal studies showed that neat DNAN was more stable than neat DNT. However, when mixed with either or both of the other components of the IMX-101 formulation, the thermal stability of both DNAN and DNT was decreased, with a greater impact on DNAN. The thermal decomposition of both DNAN and DNT was significantly accelerated by the presence of NQ. NTO also enhanced the decomposition of both nitroarenes, but this compound had a significantly greater impact on DNAN than on DNT. An examination of the decomposition products from the various mixtures showed that 2,4-dinitroaniline (DNA) was produced from the decomposition of both DNAN and DNT with either of the two additives; DNA was not observed during the neat decomposition of either nitroarene. It was thought that ammonia, which has been detected in either gaseous form or as ammonium ions during decomposition studies on both NQ and NTO, might be one cause of the decreased stability imparted to the nitroarenes by the two additives. Heating DNAN and DNT in the presence of ammonia generated from ammonium carbonate produced dinitroaniline and had an accelerating effect on the decomposition of the two nitroarenes, with the greater impact, both in the acceleration level and the amount of dinitroaniline produced, on DNAN. ^
Chemistry, Physical|Engineering, Chemical
Maria A Donnelly,
"Thermal stability and sensitivity of energetic formulations"
Dissertations and Master's Theses (Campus Access).