Microchannel-confined crystallization: shape-controlled continuous preparation of a high-quality CL-20/HMX cocrystal

Abstract

Further towards the fast, continuous, efficient and scaled-up production of energetic cocrystals, a microchannel-confined crystallization strategy has been developed to prepare a high-quality CL-20/HMX cocrystal with desired shape and size. Applying the flow-focusing microchannel, the mixing efficiency of solution and antisolvent and supersaturation were facilely regulated through changing the solution concentration and flow rate ratio of the solution and antisolvent. At the solution concentration of 0.25 mol L⁻¹ and flow rate ratio of 1 : 6, a pure CL-20/HMX cocrystal with a cube-shaped appearance and a particle diameter D (4, 3) of 21.8 μm has been obtained, overcoming the problem easy to crystallize in platelet morphology. This cocrystal presents a sharp decomposition within a very narrow temperature range (245.1 °C to 246.2 °C) and a peak temperature of 245.4 °C, close to that of raw CL-20, showing a quick energy release rate. TG-FTIR and thermal analysis illustrate that its thermal behavior under isothermal conditions is determined by the decomposition of the least stable CL-20 molecules. A high density of 1.9552 ± 0.0014 g cm⁻³ at room temperature, few internal defects and friction impact sensitivity, even lower than that of raw HMX, mean high crystal quality of the CL-20/HMX cocrystal.