(712d) Particle Design of HMX Using Supercritical Anti-Solvent Processes

HMX (Cyclotrimethylenetrinitramine) is a widely used explosive for military and civil use. Like all the other explosives, the performance and stability of HMX depend on its particle properties, especially size and morphology. Firstly, among the four polymorphs of HMX, β–HMX is desired because it shows greatest performance and stability due to its highest density and stability. On the other hand, the effect of particle size on the performance and stability of HMX is still controversial. However, preparation of nano-energetic materials itself is of great interest because it is a state of the art technology. Supercritical anti-solvent process can be used for the recrystallization of HMX because nano- or microparticles production is possible using this process. Two widely used supercritical anti-solvent processes, ASES (Aerosol Solvent Extraction System) process and GAS (Gas Anti-Solvent) process, were used in this work. It was found that the morphology and crystal phase of HMX is tunable by using different processes and solvents. β-HMX was obtained by GAS process when acetone, dimethyl sulfoxide , cyclohexanone, and γ-butyrolactone were used as the solvents. Also, it was found that additives can be used to change the crystal phase of HMX. Crystal phase changed from α to γ when PVA (polyvinyl alcohol) was co-precipitated using ASES process where dimethyl sulfoxide is used as the solvent. Under all the experimental conditions for GAS process, size reduction from the original mean particle size of 100μm to nearly 10μm was observed. When ASES process was used, although β-HMX was not obtained, nano- or microcrystals of other forms were obtained. The effects of operating parameters such as CO₂ addition rate, temperature, initial solution concentration, and stirring rate on the particle size were investigated for the case of recrystallization into β-HMX using GAS process and acetone as the solvent.