Partial phase behavior of HMX/DMSO solutions

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.