Thermal Instability of Process Chemicals Used In the Manufacture of Commercial Explosives

摘要

The compatibility of ammonium nitrate (AN) and sodium nitrite (NaNO_2) was characterized using various thermal techniques. These two oxidizing chemicals are used in the commercial mining industry. In blasting operations at mine sites, the nitrosation reaction of aqueous NaNO_2 is used to reduce the overall density of AN emulsions (ANEs) by introducing evenly dispersed nitrogen gas bubbles. These microbubbles act as hotspots to facilitate the shock to detonation transition in ANEs. This presentation focuses on the thermal results obtained for powdered AN and NaNO_2, in a scenario for which NaNO_2 may be present at an emulsion manufacturing site before its actual use in ANEs. An unconfined mound of the two dry powders in contact at room temperature and ambient relative humidity did not exhibit self-heating. However, an eventual temperature rise was recorded after the remote addition of a microdroplet of water. Using accelerating rate (ARC) and heat flow (DSC, C80) calorimetries, an exothermic reaction occurring immediately upon sample data acquisition near 50°C was documented for the AN and NaNO_2 mixtures. Sample homogeneity and the method of heating greatly affected the extent of reaction. Nevertheless, a low temperature exothermic reaction was detected in all thermal tests. The AN and NaNO_2 mixture was entirely consumed at the end of some thermal tests. Unmixed samples with low % NaNO_2 tended towards decomposing in two steps: the lower temperature exotherm likely indicating decomposition at the AN/NaNO_2 interface, and the higher temperature exotherm indicating decomposition of any remaining (unreacted) AN. Simultaneous TG-DSC-FTIR-MS experiments were also conducted to explore the reaction pathways of the AN/NaNO_2 interaction. An important finding was that near room temperature and under isothermal conditions, NaNO_2 was shown to react on contact with AN with an induction time of only a few hours.