Effect of Alkyl imidazole ionic liquids C_nmimCl (N = 4, 6, 8) on CL-20 recrystallization

Hexanitrohexaazaisowurtzitane (CL-20) is considered to be a representative high energy density material. It is important to control the microstructure of the crystal during recrystallization to ensure the quality of CL-20. In this study, the effects of different types and concentrations of ionic liquids on CL-20 were investigated by adding them to the solvent or anti-solvent during recrystallization. Three types of ionic liquids acting as a morphology control additive can reduce the crystal size of recrystallized CL-20. Thermal analysis shows that most ionic liquids added to solvents or anti-solvents can increase the transition temperature from the ε crystal to the γ crystal by up to 12.6 °C, and the decomposition peak temperature increases so the thermal stability of CL-20 improves. The heat output increases to 1344 J∙g^－1. When DmimCl is added into the solvent, recrystallized CL-20 has smaller particle size and an octahedral shape without sharp edges or agglomeration. With different concentrations of DmimCl in the solvent, the decomposition peak temperature of recrystallized CL-20 increases more than 6 °C and the heat output is more than 1100 J∙g^－1. Therefore, DmimCl is an ideal morphology control additive.