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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.

Ammonium perchlorate is an important oxidizer in solid rocket propellants, underwater explosives and pyrotechnics. The crystal quality of ammonium perchlorate has an important impact on its application in these fields. In this work, a dropwise cooling crystallization method was proposed to crystallize ammonium perchlorate in gas–liquid two-phase suspension systems. Compared with the typical cooling crystallization method, dropwise cooling crystallization is favorable to control supersaturation and then control the shape and size of ammonium perchlorate crystals. The prepared samples were characterized by scanning electron microscopy, optical microscopy, laser particle distribution measurement, thermogravimetric analysis and powder X-ray diffraction. It is clearly shown that the as-prepared ammonium perchlorate crystals exhibit a high-index faced polyhedron morphology with a uniform shape and a narrow particle size distribution, the size of which can be controlled within the range of 13.64 μm to 50.33 μm. In addition, the gas-phase medium plays a good role in mixing, and it is found that higher gas-phase medium flow rates and higher feed rates of concentrated ammonium perchlorate solution result in a smaller average size of ammonium perchlorate crystals. Moreover, the crystallization method proposed in this study also has a good effect on the crystallization of sodium nitrate and ammonium chloride. This research provides a reference for the crystallization of other crystalline materials in crystal engineering.

A combined zero-valent iron (ZVI) reduction and Fenton oxidation process was tested for the pretreatment of 2,4-dinitroanisole (DNAN) producing wastewater. Operating conditions were optimized and overall performance of the combined process was evaluated. For ZVI process, almost complete reduction of nitroaromatic compounds was observed at empty bed contact time (EBCT) of 8 h. For Fenton process, the optimal pH, H 2 O 2 to Fe(II) molar ratio, H 2 O 2 dosage and hydraulic retention time (HRT) were found to be 3.0, 15, 0.216 mol/L and 5 h, respectively. After pretreatment by the combined ZVI-Fenton process under the optimal conditions, aromatic organic compound removal was as high as 77.2%, while the majority of COD remained to be further treated by sequent biological process. The combined anaerobic-aerobic process consisted of an anaerobic baffled reactor (ABR) and a moving-bed biofilm reactor (MBBR) was operated for 3 months, fed with ZVI-Fenton effluent. The results revealed that the coupled ZVI-Fenton-ABR-MBBR system was significantly efficient in terms of correcting the effluent's main parameters of relevance, mainly aromatic compounds concentration, COD concentration, color and acute toxicity. These results indicate that the combined ZVI-Fenton process offers bright prospects for the pretreatment of wastewater containing nitroaromatic compounds.