Jon L. Maienschein

Simulating thermal explosion of cyclotrimethylenetrinitramine-based explosives: Model comparison with experiment

We compare two-dimensional model results with measurements for the thermal, chemical, and mechanical behavior in a thermal explosion experiment. Confined high explosives (HEs) are heated at a rate of 1°C∕h until an explosion is observed. The heating, ignition, and deflagration phases are modeled using an Arbitrarily Lagrangian-Eulerian code (ALE3D) that can handle a wide range of time scales that vary from a structural to a dynamic hydrotime scale. During the preignition phase, quasistatic mechanics and diffusive thermal transfer from a heat source to the HE are coupled with the finite chemical reactions that include both endothermic and exothermic processes. Once the HE ignites, a hydrodynamic calculation is performed as a burn front propagates through the HE. Two cyclotrimethylenetrinitramine-based explosives, C-4 and PBXN-109, are considered, whose chemical-thermal-mechanical models are constructed based on measurements of thermal and mechanical properties along with small scale thermal explosion measu...

Simulating thermal explosion of octahydrotetranitrotetrazine-based explosives: Model comparison with experiment

A model comparison with measurements for the thermal, chemical, and mechanical behaviors in a thermal explosion experiment is presented. Confined high explosives (HEs) are heated at a rate of 1°C∕h until an explosion is observed. The heating, ignition, and deflagration phases are modeled using an arbitrarily Lagrangian-Eulerian (ALE3D) code that can handle a wide range of time scales that vary from a structural to a hydrodynamic time scale. During the preignition phase, quasistatic mechanics and diffusive thermal transfer from a heat source to the HE are coupled with the finite chemical reactions that include both endothermic and exothermic processes. Once the HE ignites, a hydrodynamic calculation is performed as a burn front propagates through the HE. Two octahydrotetranitrotetrazine (HMX)-based explosives, LX-04 and LX-10, are considered, whose chemical-thermal-mechanical models are constructed based on measurements of thermal and mechanical properties along with small-scale thermal explosion measureme...

Shock Sensitivity of LX-04 Containing Delta Phase HMX at Elevated Temperatures

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 duri...

Ammonium perchlorate phase transitions to 26 GPa and 700 K in a diamond anvil cell

Abstract The behavior of ammonium perchlorate (AP) was studied as a function of temperature (to 693 K) and high pressure (to ≈ 26 GPa) in a diamond anvil cell (DAC). At temperatures above the known 513 K orthorhombic-to-cubic phase transition, liquid droplets were observed, and are interpreted as the onset to melting. Mid-infrared FTIR spectra of the residue showed only ammonium perchlorate. At much higher temperatures, gas formation was also seen. Rapid decomposition took place during gas formation in the presence of oxidized steel, but not in the presence of tantalum. The appearance of both liquid and gas is interpreted as corresponding to the solid-liquid and liquid-gas phase lines in the phase diagram of AP.

Increase of tritium permeation through resistant metals at 323 K by lattice defects

We report data on tritium permeation at 323 K and 373 K through annealed and single crystal copper for comparison with our earlier data on unannealed copper, and show that tritium transport along grain boundaries or other lattice defects controls the overall rate at 323 K in unannealed material. Measurements on unannealed and annealed gold foil also indicate the importance of defect transport, although with gold we could not reduce the defect concentration sufficiently to measure permeation through the metal lattice. We also include permeation data on aluminum, molybdenum, tungsten, beryllium, cadmium, iridium, lead, rhenium, and silver; all of these were probably dominated by tritium transport along lattice defects. 24 refs., 3 figs., 3 tabs.

Mesoscale modeling of deflagration-induced deconsolidation in polymer-bonded explosives

Initially undamaged polymer-bonded explosives can transition from conductive burning to more violent convective burning via rapid deconsolidation at higher pressures. The pressure-dependent infiltration of cracks and pores, i.e., damage, by product gases at the burn-front is a key step in the transition to convective burning. However, the relative influence of pre-existing damage and the evolution of deflagration-induced damage during the transition to convective burning is not well understood. The objective of this study is to investigate the role of microstructure and initial pressurization on deconsolidation. We performed simulations using the multi-physics hydrocode, ALE3D. HMX-Viton A served as our model explosive. A Prout-Tompkins chemical kinetic model, Vielles Law pressure-dependent burning, Gruneisen equation-of-state, and simplified strength model were used for the HMX. The propensity for deconsolidation increased with increasing defect size and decreasing initial pressurization, as measured by the increase in burning surface area. These studies are important because they enable the development of continuum-scale damage models and the design of inherently safer explosives.

Thermal crystalline-to-amorphous transition of beryllium hydride

Abstract An irreversible thermally induced solid-state phase change in crystalline beryllium hydride has been discovered, with the product being amorphous or glassy beryllium hydride. The phase change was observed using simultaneous differential thermal analysis/thermogravimetric analysis and using X-ray diffraction. The phase change takes place at 485–550 K, just below the thermal decomposition temperature of 570 K. There is slight decomposition of the beryllium hydride during the phase change of about 5±2%. The enthalpy change associated with the phase transition is 2.3±0.7 kJ mol−1.

Synthesis and properties of a low density, high porosity lithium hydride-beryllium hydride foam

Abstract We have developed a low density (30–670 kg m −3 ), high porosity (up to 96%) foam containing lithium hydride (LiH) and amorphous beryllium hydride (BeH 2 ). The composition of the foam can be varied, but the most vigorous foaming reaction is observed with equimolar mixtures of LiH and BeH 2 . We discuss several ways to synthesize the foam, and report on physical properties such as the density, the open and closed porosity, the pore size distribution, the uniformity of foam density and the foam sensitivity to moisture. Hydrogen and organic contaminants in the BeH 2 are evolved during the foaming reaction and apparently provide the force needed to expand the plastic reaction mass into a foam. Simultaneous differential thermal analysis-thermogravimetric analysis show that the reaction is endothermic with very little mass loss. The presence of LiBeH 3 as either a reaction intermediate or a final product is suggested by the fact that the most vigorous foaming occurs with equimolar mixtures of LiH and BeH 2 . This foam may be attractive as the X-ray scattering element in the Thomson scattering polarimeter as proposed for inclusion in the High Throughput X-ray Spectroscopy Space Mission sponsored by the European Scientific Agency.

DEFLAGRATION RATES OF SECONDARY EXPLOSIVES UNDER STATIC MPA - GPA PRESSURE

We provide measurements of the chemical reaction propagation rate (RPR) as a function of pressure using diamond anvil cell (DAC) and strand burner technologies. Materials investigated include HMX and RDX crystalline powders, LX‐04 (85% HMX and 15% Viton A), and Composition B (63% RDX, 36% TNT, 1% wax). The anomalous correspondence between crystal structure, including in some instances isostructural phase transitions, on pressure dependent RPRs of HMX and RDX are correlated to confocal micro‐Raman spectroscopic results. The contrast between DAC GPa and strand burner MPa regime measurements yield insight into explosive material burn phenomena. Here we highlight physicochemical mechanisms that appear to affect the deflagration rate of precompressed energetic materials.

Reactions of lithium hydride and beryllium hydride: thermal studies and identification of products

Abstract Using simultaneous differential thermal analysis and thermogravimetric analysis, and powder X-ray diffraction, we determined that the reactions of lithium hydride and beryllium hydride follow the pathway for reaction mixtures containing less than 66.6 mol.% LiH, and for reaction mixtures containing 66.6 mol.% LiH or more. LiBeH 3 undergoes fusion at 430 K. Li 2 BeH 4 has two thermal transitions at 550 K and 660 K; the first may be intramolecular rearrangement and the second may be fusion. The two products are indistinguishable by powder X-ray diffraction.