Chemical kinetic thermal decomposition models of pressed solid high explosives containing octahydro-1,3,5,7tetranitro-1,3,5,7-tetrazocine (HMX) and triaminotrinitrobenzene (TATB), which accurately calculate the times to explosion at various initial temperatures measured in the one-dimensional time to explosion (ODTX) test, are extended to higher temperatures to predict the critical temperatures, times to explosion, and dimensions of the impact-and shock-induced hot spots that are known to control the ignition of exothermic reaction in solid explosives. The effects of hot spot geometry and surrounding temperature on the critical hot spot conditions are investigated. Since hot spot temperatures and dimensions cannot be measured experimentally, these estimated temperatures, sizes, and times required for exothermic chemical reaction provide a means to evaluate proposed physical mechanisms of hot spot formation in accident scenarios involving impact (friction and shear) and shock compression of solid explosives.
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.
We investigate the effects of shock pressure and pore morphology on the formation and growth of hot spots in HMX (octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine). Both non‐reactive and reactive ALE3D simulations are used in these studies. Our non‐reactive simulations show a viscous‐dominated pore collapse mode at lower shock pressures (2–10 GPa) with shear band formation and a hydrodynamic‐dominated mode at higher shock pressures (20‐40 GPa) due to bulk melting. When normalized by bulk shock heating, viscous‐dominated pore collapse modes are more efficient at generating hot spots. Pore morphology influences the post‐collapse temperature distributions and reaction rate for a fixed pore area and shock pressure. We find that multiple surface pores at the binder‐grain interface tend to react the fastest. Due to their upstream location in the HMX grain, the surface pores collapse sooner than interior pores; thus, the extent of reaction will generally favor these morphologies because they have more time to grow. In general, multiple smaller hot spots tend to react faster than a single larger hot spot because they accelerate one another's burning. The rank order of morphology effects, however, is not the same for non‐reactive and reactive simulations. For example, while multiple surface pores produce the highest reaction rates they do not produce the highest (non‐reactive) hot spot temperatures. Our numerical studies provide insights on hot spot mechanisms in lieu of direct measurements and can be used to develop advanced shock initiation models.
The theory for solvated excess electrons described in an earlier paper is now applied numerically. For the simple model of an electron excluded from spherical regions of radius d surrounding each of the particles in a hard sphere fluid, our results exhibit a rich behavior. At all temperatures for which λe ≫σ, where λe is the thermal wavelength of the electron and σ is the diameter of the hard sphere fluid particles, we find a relatively narrow transition region of solvent densities below which the solvated electron is extended and above which the electron is localized. For λe =10σ and d=σ/2, localization occurs near the solvent density 0.15σ−3. Both the width and location of the transition region increase with decreasing λe (i.e., increasing temperature). When λe =6σ, the region is broad, barely discernible, and located near 0.3σ−3 when d=σ/2. For λe ≲5σ, no precipitous behavior is found as density is increased and the electron passes from extended to localized behavior. The localized electron is characterized by a condition of ground state dominance, and this behavior leads to a density dependence of the electron-solvent pair structure that is very different than the dependence found when the electron is delocalized and extended. We estimate the behavior of the friction constant for the electron and find a change in direction of its temperature dependence as one passes from the localization to delocalized case. We discuss how the location of the localization depends upon model parameters and temperature, and we provide qualitative explanations of our results in terms of structural principles associated with the fact that the delocalized electron has a distribution of spatially large fluctuations while the localized electron does not fluctuate over large distances and is characterized by primarily one length scale, its range of self-correlations. The equations central to our theory embody these principles.
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