In situ synthesis of hydrophobic coatings: an effective strategy to reduce hygroscopicity and catalyze decomposition of ammonium perchlorate

Abstract

Reducing the hygroscopicity and thermal decomposition temperature of ammonium perchlorate is of great significance for its application in solid rocket propellants. In this work, an in situ chemical precipitation reaction of stearic acid with copper acetate or cobalt acetate was adopted to prepare hydrophobic coatings of AP. The prepared samples were characterized by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, contact angle measurement, differential thermal analysis and thermogravimetric analysis. The results show that a compact and uniform hydrophobic layer of copper stearate (CuSt₂) or cobalt stearate (CoSt₂) is successfully coated on the surface of AP particles. Compared with the raw AP, the contact angles of AP/CuSt₂ and AP/CoSt₂ with a coating content of 10 wt% are increased by 136.2° and 133.6°, respectively. Meanwhile, their moisture contents after being placed at 79 wt% relative humidity for 66 h are only 7.42% and 7.68% of the raw AP case. In addition, the high-temperature decomposition peak temperatures of AP/CuSt₂ and AP/CoSt₂ at the optimum coating content (6 wt%) are lowered by 113.3 °C and 75.8 °C, respectively, revealing that the hydrophobic coatings have high catalytic activity in the decomposition of AP. This research provides a promising strategy for reducing the hygroscopicity and simultaneously improving the thermal performance of AP, and this is also a reference for the modification of other materials.