Porosity Control for Enhanced Performance | specialtysurfactants.arkema.com

Ammonium nitrate (AN) continues to be widely used as a low-cost blasting agent. It is inherently unstable, and a total of five different crystalline states have been identified over cooling from the molten state to -16°C.

The transition point at 32°C causes the most concern as it occurs in the temperature range most normally encountered under typical ambient conditions. As the temperature passes through this transition point from 1 phase to another, volume changes occur, ultimately leading to the generation of dust/fines. Water is thought to “catalyze” these phase transitions.

Low-density ammonium nitrate (LDAN), also known as industrial grade ammonium nitrate (IGAN), as used in the production of blasting agents, is very susceptible to product degradation due to these phase transitions. Explosive-grade ammonium nitrate needs adequate porosity to ensure complete detonation. Production of excess fines may result in density increases which can ultimately lead to the failure of the product as a blasting agent.

During ammonium nitrate production, Arkema’s Galoryl^® AT porosity control agents are introduced to the ammonium nitrate melt prior to its solidification into prills and are designed to lower the surface tension of the melt resulting in spherical droplets. They improve drying characteristics and help the ammonium nitrate crystallize as small rather than large needles, thus improving the strength (reducing friability or fragility) and structural integrity of the resulting porous prilled ammonium nitrate. A reduction in moisture levels is thought to assist in forming a metastable transition between the two rhombic forms around the 32°C transition point, resulting in the main “destructive” phase transition being pushed to a higher temperature.