Investigation of the Formation of Nanoscale 2CL-20 · HMX Cocrystal

Energetic nanoscale 2CL-20∙HMX, a cocrystal of CL-20 (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane) and HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocine) at a 2:1 molar ratio, was prepared by a novel method of bead milling an aqueous suspension of ε-CL-20 and β-HMX. Conversion of the coformers to the cocrystal form was monitored by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis of specimens sampled at various milling times. Complete conversion to the cocrystal form was achieved. Rounded 2CL-20∙HMX cocrystal particles with a mean size below 200 nm were produced. The conversion was further studied by varying the processing variables. A mechanism for the conversion of the coformers to the cocrystalline form is postulated based on the experimental results. As an inherently safe manufacturing method, the aqueous bead milling process has a great potential in advancing the cocrystal research and applications in the field of energetic materials.