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. Described are the results of high temperature equilibrium solvation studies coupled with Fourier transform infrared spectroscopy (FTIR) for the identification of polymorphic conversion. These results are augmented by data in Part II from differential scanning calorimetry (DSC), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and optical hot stage microscopy(6). The thermodynamic stability order of ϵ > γ > α‐hydrate > β is shown, with the epsilon polymorph the most thermodynamically stable phase of HNTW at room temperature. The existence of multiple α‐hydrate phases is shown to complicate the determination of the equilibrium P‐T phase diagram of HNIW.

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.

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Shock initiation experiments on the explosives Composition B and C-4 were performed to obtain in-situ pressure gauge data for the purpose of providing the Ignition and Growth reactive flow model with proper modeling parameters. A 100 mm diameter propellant driven gas gun was utilized to initiate the explosive charges containing manganin piezoresistive pressure gauge packages embedded in the explosive sample. Experimental data provided new information on the shock velocityparticle velocity relationship for each of the investigated material in their respective pressure range. The run-distance-to-detonation points on the Pop-plot for these experiments showed agreement with previously published data, and Ignition and Growth modeling calculations resulted in a good fit to the experimental data. Identical ignition and growth reaction rate parameters were used for C-4 and Composition B, and the Composition B model also included a third reaction rate to simulate the completion of reaction by the TNT component. This model can be applied to shock initiation scenarios that have not or cannot be tested experimentally with a high level of confidence in its predictions.

LX-04 is a widely used HMX-based plastic bonded explosive, which contains 85 weight % HMX and 15 weight % Viton binder. The sensitivity of LX-04 to a single stimulus such as heat, impact, and shock has been previously studied. However, hazard scenarios can involve multiple stimuli, such as heating to temperatures close to thermal explosion conditions followed by fragment impact, producing a shock in the hot explosive. The sensitivity of HMX at elevated temperatures is further complicated by the beta to delta solid-state phase transition, which occurs at approximately 165˚C. This paper presents the results of shock initiation experiments conducted with LX-04 preheated to 190˚C, as well as density measurements and small scale safety test results of the δ phase HMX at room temperature. This work shows that LX-04 at 190˚C is more shock sensitive than LX-04 at 150˚C or 170˚C due to the volume increase during the β to δ solid phase transition, which creates more hot spots, and the faster growth of reaction during shock compression.