(424d) Controlling Ammonium Perchlorate Particle Size Distribution, Morphology, and Orientation Via Meniscus Guided Coating (MGC)

The ballistics of solid rocket motors are controlled by the burning rate of the propellant. Ammonium perchlorate (AP) is commonly used in propellant formulations because of its positive oxygen balance, long term stability, and ability to control the burn rate by varying its particle size distribution (PSD). For particle sizes greater than 20 μm, AP undergoes deflagration, and larger PSDs have slower burn rates than smaller PSDs. For particle sizes less than 20 μm, AP is considered a detonable material and presents safety challenges for storage and transportation. For rocket propulsion, controlling the burn rate by tailoring the PSD and transitioning from a deflagration regime to a detonation regime is beneficial to ensure safe storage and transportation, extend flight range, and enhance performance.

Meniscus guided coating (MGC) is a technique that provides a high degree of control over nucleation and growth rates during crystallization, allowing for tunable properties in thin films, as seen for organic semiconductors, active pharmaceutical ingredients, and other energetic materials. In this work, MGC is employed to crystallize AP. Different crystallization pathways created by unique MGC conditions results in variable PSD, morphology, coherence length, and preferential orientation of films as observed via optical microscopy and x-ray diffraction.

Finally, crystallizing AP in the presence of nanoparticles results in encapsulation of nanoparticles within AP crystal domains. Nanoparticle encapsulation also influences the particle size distribution, morphology, and preferential orientation of AP crystals. Functionality of nanoparticles can be leveraged and explored as a mechanism for fracturing AP crystals into smaller PSDs, ultimately transitioning bulk AP crystals from deflagration-preferred pathway ( > 20 μm) during storage and transportation to detonation-preferred pathway ( < 20 μm) when ready for use.