Preparation of porous ammonium dinitramide crystals and efficient catalytic decomposition of corresponding iron oxide assembled composite particles†

In this work, highly spherical and porous ammonium dinitramide (ADN) crystals were prepared using the solvent–antisolvent crystallization method. To explore the growth mechanism of ADN crystals in different solvent environments, we adjusted the supersaturation of the solution by varying the stirring speed and flow rate. The growth process and internal morphology of the particles reflected the crystal growth mechanism: small ADN particles followed the traditional nucleation and growth process, while larger ADN particles underwent particle aggregation, filling-in-growth and wearing into spherical shapes. By combining the crystal growth mechanism of this method, iron oxide (Fe₂O₃) was introduced during the ADN crystallization process, successfully constructing ADN@Fe₂O₃ composite microparticles with the inorganic host crystal encapsulating the guest. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to verify the structure of ADN@Fe₂O₃, and the results showed that Fe₂O₃ was successfully encapsulated in ADN particles without affecting the crystal structure of ADN. The thermal decomposition behavior of the composite microparticles was compared with that of the physical mixture using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), confirming the superior catalytic effect of Fe₂O₃ in this composite form. The apparent activation energy at the initial stage of decomposition decreased from 194.39 kJ mol⁻¹ to 174.76 kJ mol⁻¹. The crystal growth mechanism revealed in this work can be extended to the preparation of other spherical crystal materials and provides a general and effective new approach for constructing composite energetic particles with unique structures and excellent decomposition performance.