A supercritical antisolvent (SAS) process was used to prepare micronized cyclotrimethylenetrinitramin (RDX). This study examined the influence of different solvents at a fixed temperature (50 °C) and pressure (13.7 or 15 MPa) on the morphology, particle size (PS), and particle size distribution (PSD) using a semicontinuous SAS process. Dimethyl sulfoxide (DMSO), dimethylformamide (DMF), acetone (AC), acetonitrile (ACN), n-methyl 2-pyrrolidone (NMP), and cyclohexanone (CHN) were used as solvents. The recrystallized RDX particles were characterized by scanning electron microscopy (SEM), particle size analyzer (PSA), Fourier transform infrared (FT-IR) spectroscopy, and differential scanning calorimetry (DSC). Depending on the solvent used, the recrystallized RDX particles showed a variety of morphologies, particle sizes, and particle size distributions (PSD). The mean particle size of the recrystallized RDX ranged from 2.6 to 17.7 µm. The enthalpy change (∆H ) 583.4, 847.7, 967.1, 823.9, 1131, and 1620 J/g) for the exothermic decomposition of recrystallized RDX was much higher than that of the unprocessed RDX (∆H ) 381.5 J/g).

This study investigated the micronization of HMX (cyclotetramethylenetetranitramine) using two types of recrystallization methods with supercritical carbon dioxide as an antisolvent, namely, the aerosol solvent extraction system (ASES) and gas antisolvent (GAS) processes. The effects of experimental variables on the recrystallization of β-HMX particles in the GAS process were also studied. In particular, we varied the temperature from 303 to 323 K, used CO 2 feeding rates of 20 and 50 mL 3 min À1 , and varied the agitation speed from 200 to 900 rpm in the GAS process. The precipitated HMX particles were characterized by field-emission scanning electron microscopy (FE-SEM), particle size analysis (PSA), and Fourier transform infrared (FT-IR) spectroscopy. Depending on the organic solvent used and the type of recrystallization method, the precipitated HMX particles showed a variety of morphologies, particle size distributions, and crystal phases. The HMX precipitated by the ASES process was transformed into micronized γor δ-HMX with a volume-mean particle size (D 50 ) of 6.3À32.1 μm. On the other hand, in the case of the GAS process, micronized γor β-HMX was formed, with a volume-mean particle size (D 50 ) of 5.3À37.45 μm. In particular, HMX dissolved in acetone was successfully precipitated to micronized β-HMX with a narrow particle size distribution through the GAS process.

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