Mechanical Sensitivity Improvement of CL-20 by Using Crystal Passivation: A Brief Review

Energetic materials (EMs) have important application value in the military and civil fields. But at the same time, EMs will burn or explode when they are impacted or rubbed. 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is one of the typical energetic compounds with high energy, whose density is 2.04 g cm^-3 and velocity of detonation is 9380 m s^-1. However, its high mechanical sensitivity (impact sensitivity and friction sensitivity) has become one of the major problems that limit its application in solid propellants and explosives. Consequently, the mitigation of CL-20's mechanical sensitivity has remained a critical research objective in the field of EMs. In this review, the passivation of CL-20, including crystal control, cocrystallization, surface coating, spheronization, and nanonization, is summarized. Different methods significantly reduce the sensitivity of CL-20, with the lowest impact sensitivity reaching 35 J. In addition, research directions on the passivation of CL-20 in the future were proposed, promoting the application of CL-20 in energetic systems.