Fragmentation of Ammonium Nitrate Particles under Thermal Cycling

AbstractAmmonium nitrate finds application in explosives and chlorine‐free slow‐burning propellants. Different phases are known for this ammonium salt, each of them featured by peculiar bulk densities. As a consequence, the variation of storage temperature induces processes of expansion‐contraction in the crystals, unless specific stabilization is performed. In this paper, a batch of raw ammonium nitrate particles has been thermally cycled between −30 °C to +60 °C and analyzed. Microscopic observations, particle size measurement, and X‐ray microtomography showed that the particles undergo a progressive fragmentation process, with opening of internal cracks and voids. The tested material halved its mass‐mean diameter after five thermal cycles. As a term of comparison, a phase‐stabilized ammonium nitrate batch was tested under the same conditions, showing no effect