Application of supercritical carbon dioxide in energetic materials processes: A review

The preparation of micro- and nanostructured energetic materials has recently drawn considerable attention as a potential method that can be used to obtain energy release more rapidly than conventional materials. Formation of solid particles with well-defined properties (e.g., particle size, particle size distribution, particle shape) and free of solvent inclusions for production of energetic materials using compressed gases were studied. It is possible to process moderately solids, like energetic materials that are difficult to comminute due to their sensitivity to mechanical or thermal stress. The characteristics of compressed gases allow the variation of morphology of solid particles in a wide range. It is possible to produce crystalline particles with a small size and narrow size distribution without defects (i.e., free of solvent inclusions). In this paper, the different processes to form very fine particles of explosives and propellant with supercritical fluids are reviewed. The first method is the RESS (rapid expansion of supercritical solutions) process, the formation of particles results from the rapid expansion of a supercritical solution. The second process is the GAS (gas anti-solvent) process that uses a high compressed fluid as anti-solvent to decrease the solvent power of a common solvent and thus to recrystallize the solid. Another process is PGSS (particles from gas-saturated solutions suspension). This process allows the formation of particles from a great variety of substances that are not required to be soluble in supercritical. carbon dioxide. In this paper, the solubility of some explosives such as RDX, TNT, and HMX in the supercritical carbon dioxide is discussed. On the other hand, we show that these techniques are applicable for production of very fine particles of energetic materials using a range of supercritical solvents; thus, very fine particles of energetic materials such as TNT, RDX, HMX, and nitroguanidine could be produced by these methods. Also, application of supercritical fluid for particle coating granulation of sensitive energetic materials is discussed.