(278c) Raman Spectroscopy Investigation of Nanoenergetics

Raman spectra for various nanoenergetics and an amorphous nitramine have been obtained and analyzed.  In the case of 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), there was a linear relationship between intensity of Raman spectra and crystal size, and the modes between 120 cm^-1 and 220 cm^-1 were especially affected. The low order modes were eliminated at the smallest sizes and could be recovered with ripening. Octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) likewise, had a linear relationship between intensity of Raman spectra and crystal size, though there was no extraordinary change in lower frequency modes. The Raman spectra intensity of 1,3,5-Trinitroperhydro-1,3,5-triazine (RDX) was not observably affected by crystal size.  In addition to the nitramines, a similar explosive compound, 2,4,6-triamino-1,3,5- trinitrobenzene (TATB), was investigated. A similar, but weaker trend, to that of HMX and CL-20 was observed in TATB. The relationships observed leads to the notion that there is a layer of surface disorder on each material which is inherently different from the bulk amorphous structure (Raman spectra of amorphous HMX:CL-20 are discussed briefly) and that has a thickness dependent on its constituent molecules but unaffected by crystal size.  These results will have practical benefit, not only for allowing facile monitoring of crystal size during manufacturing, but because the 120 cm^-1 and 220 cm^-1 modes could be ‘doorway modes,’ which would make them important for shock induced supersonic reaction.  Furthermore, these findings could lead to deep insights into the general structure of materials.