Low Density Ammonium Nitrate (LDAN) Porosity Control Agents
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 two states of concern are the alpha-rhombic and the beta-rhombic states in the temperature range most normally encountered under typical ambient conditions. These states can convert from one to the other upon temperature / pressure changes with resulting volume changes, which in turn can cause disruptions to the crystalline structure and lead to the production of dust / fines. Water is thought to “catalyze” these phase transitions.
Low density ammonium nitrate (LDAN) used in the production of blasting agents is very susceptible to product degradation as a result of these phase transitions. Explosive grade ammonium nitrate needs adequate porosity to ensure complete detonation. Production of excess fines results in density increases which can ultimately lead to failure of the product as a blasting agent.
ArrMaz’s GALORYL® AT porosity control agents are usually introduced to the ammonium nitrate melt prior to its solidification into prills. They 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 prills. Reduction in moisture levels is thought to assist in the formation of a metastable transition between the two rhombic forms outlined above resulting in the main “destructive” phase transition being pushed to a higher temperature.
