Research Progress on the Physicochemical Mechanisms of Mechanical Sensitivity of Nitramine Crystals

Nitramine crystals, notably 1, 3, 5-trinitro-1, 3, 5-triazacyclohexane (RDX), 1, 3, 5, 7-tetranitro-1, 3, 5, 7-tetrazocane (HMX), and 2, 4, 6, 8, 10, 12-hexanitro-2, 4, 6, 8, 10, 12-hexaazaisowurtzitane (CL-20), are widely recognized as cornerstone materials in advanced energetic formulations due to their unparalleled energy density and combustion performance. However, the intrinsic mechanical sensitivity of high-energy nitramines-particularly CL-20-poses critical safety challenges during synthesis, transportation, and deployment. Recent advancements in crystal engineering and interfacial chemistry have demonstrated that precision control over crystal morphology, defect architecture, and surface passivation can significantly enhance stability while mitigating unintended initiation risks. This chapter reviews the physicochemical origins of mechanical sensitivity, such as crystal morphology, particle size, and internal defects (e.g., vacancies, dislocations, cracks, and voids). These structural imperfections act as precursors to hotspot formation, where localized energy accumulation under mechanical stimuli (e.g., impact and friction) triggers exothermic decomposition cascades. Desensitization techniques, including recrystallization, coating, cocrystallization, and hybrid modification, are evaluated for their effectiveness in reducing sensitivity by optimizing crystal structures and suppressing hotspot generation. Central to this discussion is the hotspot theory, which delineates the multiscale energy conversion cascade (mechanical ? thermal ? chemical) and quantifies the roles of void collapse, anisotropic thermal transport, and crystallographic orientation in governing initiation thresholds. Simulation insights into bond rupture energetics (e.g., cleavage and HONO elimination) reveal how defect topology modulates decomposition kinetics at the molecular level.