Physical Characterization, Accelerating Rate Calorimetry and Thermal Conductivity of Ammonium Nitrate Emulsion

Published with CANMET, Canadian Explosives Research Laboratory, Natural Resources Canada.

Abstract: In the recent years, there have been numerous incidents involving runaway reactions in ammonium nitrate emulsion (ANE) explosives. In most cases, thermal explosions have occurred during abnormal (dry-running or deadheading) pumping operations Current work at the Canadian Explosives Research Laboratory involves assessing the thermal hazards of ANE explosives in order to better understand the effect of their formulation and physical properties on their thermal stability. Since manufacturers’ (proprietary) ANE formulations vary considerably to suit the end-user, multiple small (1-2 kg) batches of ANE were prepared in-house using a standard formula of diesel oil/surfactant/water/ammonium nitrate. We report on the basic physical properties of these ANEs: viscosity, density, water content, emulsion droplet size and size distribution. Additionally, using a recently established technique for measuring the thermal conductivity () of small volumes of energetic materials, the base emulsion and base emulsion blended with sensitizing agents such as aluminum particles or glass microballoons, is reported. The thermal decomposition of these ANEs was characterized using accelerating rate calorimetry (ARC). Preliminary data suggests an interesting correlation between the measured refinement (emulsion droplet size) and the ARC detected onset temperatures for thermal runaway. Correlation of the thermal conductivity measurements with the ARC detected thermal decomposition behavior is also discussed.

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