Transitions from Separately Crystallized CL-20 and HMX to CL-20/HMX Cocrystal Based on Solvent Media

Cocrystallization is a helpful method for explosives improvement. However, lack of knowledge of the formation mechanism leads to low efficiency in cocrystal preparation. In order to enhance the understanding of the cocrystal formation mechanism, the formation process of CL-20/HMX cocrystals are investigated by using the X-ray diffraction qualitative/quantitative analysis and scanning electron microscopy methods in anhydrous acetone, acetone/H2O solvent, and slightly soluble-medium transition experiments. We find that the formation process of CL-20/HMX cocrystal experiences significant phase transition from CL-20 and HMX separated precipitations to CL-20/HMX cocrystal in acetone solvent, and also in slightly soluble medium. The solvent media and tiny active secondary nuclei are necessary in the phase transition process. On the basis of this paper, we have a more profound understanding of the formation mechanism of cocrystals. It is helpful to select more suitable experimental conditions and make access to excellent cocrystals more efficient.