Testing the thermal conductivity of energetic materials is a challenge with traditional steady-state techniques, as the required large volumes of material pose undesirable safety risks or the necessary sample geometries are impractical. This often leads to estimation of thermal conductivity in predictive models rather than true measurement.
The dependence of thermal conductivity of a material undergoing an exothermic reaction on local temperature has a significant effect on the critical conditions for thermal ignition. The theory of thermal ignition, whether or not consumption and diffusion of reactant is taken into account, has been commonly analyzed using the traditional grouping of dimensionless parameters suggested by Frank Kamaenetskii.
Canadian Explosives Research Laboratory: Thermal Conductivity of Ammonium Nitrate Emulsion
The use of ammonium nitrate emulsion (ANE) in mines, quarries and construction is well established and ANE’s are, in fact, very insensitive and stable products at standard temperature and pressure of normal manufacturing, especially compared to previously used nitroglycerin-based products. The purpose for studying thermal decomposition behaviour of ANE explosives is due to the continued worldwide occurrence of tragic incidents involving the production, processing and handling of ANE’s.
In order to test the ANE, a small volume test kit was used in order to minimize required material. For the sample testing, about 2.5mL was used which equates to roughly 4 grams of ANE. The sensor was placed inside an oven and a weighted cap was used to ensure that there was complete coverage of the sensor during testing.
The table to the right lists the measured thermal conductivity values for various batches of emulsion with increasing amounts of aluminum and microballoons.
|Additive blended with X3153 (%)||Measurement Temperature (°C)||Thermal Conductivity (W/mK)|
|1% glass microballoons||21||0.414|
|4% glass microballoons||21||0.318|
|6% glass microballoons||23||0.309|
|100% glass microballoons||23||0.021|
Source: Physcical Characterization, Accelerating Rate Calorimetry and Thermal Conductivity of Ammonium Nitrate Emulsion (CANMET, 2007)