The thermal stability of the polymorphs of hexanitrohexaazaisowurtzitane, part II

Solid‐solid phase transitions in the α‐, β‐, γ‐, and ϵ‐polymorphs of 2,4,6,8,10,12‐hexanitrohexaazaisowurtzitane (HNIW) have been studied as a function of temperature. Techniques employed include differential scanning calorimetry (DSC), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and hot stage microscope analysis. Fourier transform infrared spectroscopy (FTIR) was used to identify results of polymorphic conversion. Results corroborate those(2) of Part I that the existence of multiple α‐hydrate phases complicates definition of the HNIW P‐T phase diagram. A high temperature endothermic DSC response was determined by FTIR spectroscopy to be the β → γ transition, not a conversion to a new high temperature “delta” phase. The role of water in the shifting this conversion to higher temperature is discussed.