The phase diagram of HMX/DMSO and the solvated complex HMX-(DMSO)(2) has be
en investigated by visual observation, high performance liquid chromatograp
hy (HPLC), differential scanning calorimetry (DSC), and optical microscopy.
Visual observations showed the solved complex exhibited an incongruent mel
ting point, i.e., the melting point of the solvated crystal occurs within t
he region of the phase diagram where HMX itself precipitates. If the solvat
ed crystal is removed from solution and heated, it reverts to solid HMX and
DMSO at the peritectic temperature (similar to 70 degrees C). Using HPLC t
he change in concentration of the liquid phase was monitored as a function
of temperature to confirm the phase line of the DMSO/solvated complex based
on visual observation. Polarized light microscopy of the dissolution of se
eded solutions of different concentrations was also used to verify these re
sults. It is possible that a 1 : 1 complex also exists, but no evidence for
such a complex was found in these experiments.