Polymethylhydrosiloxane-Coated Ammonium Dinitramide: A Simple Strategy to Moisture-Resistant and Insensitive Energetic Microspheres

Ammonium dinitramide (ADN) is a promising, environmentally friendly oxidizer for next-generation solid propellants. However, its high hygroscopicity and sensitivity to mechanical stimuli significantly hinder its practical applications. Here, ADN–polymethylhydrosiloxane (ADN–PMHS) composite microspheres were prepared via solvent–antisolvent crystallization, followed by a simple surface coating step. The morphology, chemical structure, thermal behavior, hygroscopicity, and mechanical sensitivity of the coated microspheres were systematically characterized. Results revealed that PMHS formed a uniform, continuous hydrophobic layer on the ADN crystal surfaces, yielding well-dispersed spherical particles. At an optimal PMHS content of 0.5 wt % (ADN–0.5%PMHS), the composite exhibited 54.8% lower moisture uptake after 25 h at 60% relative humidity and a 1.6 times reduction in impact sensitivity compared with raw ADN. Moreover, the activation energy increased from 164.44 to 184.96 kJ/mol, indicating improved thermal stability, while the decomposition temperature remained nearly unchanged. These findings demonstrate that ADN–0.5%PMHS microspheres possess enhanced moisture resistance, mechanical insensitivity, and thermal stability, making them highly attractive for advanced, environmentally sustainable solid-propellant formulations.