Preparation and characterization of ultra-fine ammonium perchlorate crystals using a microfluidic system combined with ultrasonication

The common methods used for the preparation of ultrafine ammonium perchlorate (AP) crystals are physical and recrystallization methods. These methods are associated with several limitations, including strong vibrations or friction during the preparation process that can be hazardous, as well as high energy consumption, high process cost, and rigorous preparation conditions. Thus, there is need for the development of an alternative method for the preparation of ultra-fine AP crystals that is safe and rapid. In this paper, a novel ultrasonic-assisted microfluidic system that ensures the safe and rapid preparation of ultra-fine AP crystals with controllable size and morphology was developed. This approach employs a flow-focused micromixer as a reactor and it favors a high degree of continuous supersaturation that allows the solution and the anti-solvent to mix efficiently, resulting in the formation of smaller-sized particles. The obtained AP crystals were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the effects of flow-focused micromixer size, ultrasonic parameters, surfactant type and content, and anti-solvent ratio on the morphology and the average size of the AP crystals were investigated. The results obtained showed that under optimal preparation conditions, AP crystals with an average particle size of 0.41 µm were rapidly obtained. Therefore, this method provides a safe and rapid synthetic route for the preparation of ultra-fine AP particles. Additionally, it also has potential for application in the preparation of other energetic ultra-fine particles, including CL-20, HMX, and RDX.