Humidity induced agglomeration and caking behavior of ammonium perchlorate

Abstract

Ammonium perchlorate (AP) is an oxidizer used in explosives, fireworks and rocket motors. Due to its hygroscopic nature, it forms agglomerate and solid cake under humid conditions. This creates considerable problem during processing and handling of AP powder. Characterization of agglomeration and caking tendencies in these powders can be helpful in understanding and mitigating such issues. In this study, humidity induced agglomeration and caking behaviour of AP is investigated by static and dynamic test methodologies provided by Powder Rheometer. Caking propensity of AP at different relative humidity (RH) conditions was characterized by Flow Energy (FE), Basic Flowability Energy (BFE), Conditioned Bulk density (CBD), cohesion coefficient, Unconfined Yield Strength (UYS), Flow Function Coefficient (ff c ). Although, the results from both static and dynamic tests followed a similar pattern, it also highlighted that sometimes these tests may give different results because of different stress states involved. Shear test result shows increasing trend of cohesion coefficient, unconfined yield strength (UYS) indicating poor flow with increasing humidity while flow energy increased upto 75% RH and then reduced, indicating moisture related changes in the sample. Also a reduction in the bulk densities of RH conditioned powders is observed beyond a certain RH due to changes in the powder packing behaviour caused by the formation of aggregates. This is implicated with the increased interparticle capillary force along with the partial dissolution of surfaces and fusion of particles which ultimately lead to agglomeration and caking of AP particles.