Surfactant Assisted Self-assembly and Synthesis of Highly Uniform Spherical CL-20 Microparticles
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.307
Surfactant Assisted Self-assembly and Synthesis of Highly Uniform Spherical CL-20 Microparticles Kaifu Bian 1, Leanne Alarid 1, David Rosenberg 1 and Hongyou Fan 1,2,*
1
Sandia National Laboratories, Albuquerque, New Mexico, 87106
2
The University of New Mexico Center for Micro-Engineered Materials, Department of Chemical and Biological Engineering, Albuquerque, New Mexico 87131
ABSTRACT
Morphological control of energetic materials (EM) is highly desired because ill-defined morphology arising from variations in processing method and supplier make it impossible to reproducibly engineer their physicochemical properties. As the most powerful, non nuclear energetic material to date, 2,4,6,8,10,12-hexanitro -2,4,6,8,10,12-hexaazaisowurtzitane (CL20) has been the subject of significant interest for improved applications in military grade explosives. Here we report a new method for recrystallization of CL-20 from irregular bulk EMs using a surfactant assisted self-assembly process to produce uniform spherical micronsized particles. Detailed electron microscopy studies indicate that surfactant plays a critical role in controlling CL-20 morphology. Combined X-ray diffraction and Raman spectroscopy results reveal that the resultant spherical CL-20 particles exhibit an orthorhombic β-phase crystal structure. This material is expected to display enhanced functional reproducibility due to its monodisperse nature as well as decreased shock sensitivity due to their sub-micron particle size.
INTRODUCTION Controlled sensitivity, along with maximized energy content of EMs remains an important aspect of material engineering for guarantee of weapons’ safety and function. The morphology of crystalline energetic materials including crystal size, morphology, microstructure, and purity of polymorphic phase, plays a significant role in determining energetic material performance, which influence their shock sensitivity [1]. CL-20 is an EM compound containing six high energy nitro groups per molecule arranged into a strained cage structure and is capable of releasing vast amounts of stored energy through triggered rapid decomposition [2]. Since its first synthesis in 1989 [3], CL-20 has been the most powerful non-nuclear EM available, ideal for applications in military grade propellants and explosives [4]. Compared to the energetic properties of other commonly used EMs, CL-20 possesses more favorable properties including much larger enthalpy of formation [5], better oxygen balance [6], and higher density. CL-20 showed a 14%
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higher explosive performance than HMX while maintaining nearly equivalent sensitivity [7]. However, CL-20 powder prepared by existing methods consists of irregular crystalline particles [8-11]. Such i
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