Lattice Dynamics of Heated Nitramines.
DELAWARE UNIV NEWARK DEPT OF CHEMISTRY
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The laser Raman spectra of the four known polymorphs of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine HMX have been recorded. Comparison of the spectra show that beta-HMX contains a different ring conformation than do alpha, gamma and delta-HMX. Alpha, gamma and delta-HMX have conformations which are similar to one another. The phase transition behavior between the polymorph forms was studied at slow heating rates and the results with transition temperatures being given parenthetically are beta to delta or 140 C, alpha to delta147-160C, gamma to delta 205C. For rapid heating rates 50 Csec. the results are beta to delta 175 C, beta to delta or 175 C, alpha to beta or 185 C and gamma to delta or 170 C. The transition times at 25 C are delta to alpha 24 hrs., delta to beta 24 hrs., gamma to beta 12 mo., alpha to beta 12 mo.. Gamma-HMX appears to contain more anharmonicity in its vibrational motions and this may explain why it does not form thermally from the other polymorphs, but readily converts to delta-HMX upon heating. Research on RDX heating rates and polymorphs has been undertaken, recently, along with spectral examination of the decomposition products of HMX.
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