Water (H{sub 2}O) and nitrogen (N{sub 2}) are major detonation products of high explosives and it has long been conjectured that they may phase segregate at high enough temperatures and pressures to influence detonation properties of common explosives. We analyze the phase diagram of H{sub 2}O-N{sub 2} mixtures using a thermodynamic theory for polar-nonpolar mixtures and find that phase segregation is unlikely to occur above approximately 1600K. Therefore, H{sub 2}O-N{sub 2} immiscibility is not likely to be relevant for detonation predictions. We propose instead that the high pressure ionic dissociation of water plays an important role in detonation, and model it using a new ionic thermodynamics. We employ this model in chemical equilibrium calculations of standard high explosives, e.g. PETN, HMX and RDX, and find that it performs very well under a wide range of conditions. Thus, although it may require further development, it is likely that explicitly ionic thermodynamics will become a standard tool for explosives modeling.

We investigate the spin transport and interfacial magnetism of magnetic tunnel junctions with highly spin polarized LSMO and Fe3O4 electrodes and a ferrimagnetic NiFe2O4 (NFO) barrier layer. The spin dependent transport can be understood in terms of magnon-assisted spin dependent tunneling where the magnons are excited in the barrier layer itself. The NFO/Fe3O4 interface displays strong magnetic coupling, while the LSMO/NFO interface exhibits clear decoupling as determined by a combination of X-ray absorption spectroscopy and X-ray magnetic circular dichroism. This decoupling allows for distinct parallel and antiparallel electrode states in this all-magnetic trilayer. The spin transport of these devices, dominated by the NFO barrier layer magnetism, leads to a symmetric bias dependence of the junction magnetoresistance at all temperatures.

Elucidation of geodynamic, geochemical, and shock induced processes is limited by challenges to accurately determine molecular fluid equations of state (EOS). High pressure liquid state reactions of carbon species underlie physiochemical mechanisms such as differentiation of planetary interiors, deep carbon sequestration, propellant deflagration, and shock chemistry. In this proceedings paper we introduce a versatile photoacoustic technique developed to measure accurate and precise speeds of sound (SoS) of high pressure molecular fluids and fluid mixtures. SoS of an intermediate boron oxide, HBO{sub 2} are measured up to 0.5 GPa along the 277 C isotherm. A polarized exponential-6 interatomic potential form, parameterized using our SoS data, enables EOS determinations and corresponding semi-empirical evaluations of >2000 C thermodynamic states including energy release from bororganic formulations. Our thermochemical model propitiously predicts boronated hydrocarbon shock Hugoniot results.

Although useful information can be gleaned from 2D and even 1D simulations of slapper type initiation systems, these systems are inherently three-dimensional and therefore require full 3D representation to model all relevant details. Further, such representation provides additional insight into optimizing the design of such devices from a first-principles perspective and can thereby reduce experimental costs. We discuss in this paper several ongoing efforts in modeling these systems, our pursuit of validation, and extension of these methods to other systems. Our results show the substantial dependence upon highly accurate global equations of state and resistivity models in these analyses.

We discuss our measurements of the chemical reaction propagation rate as a function of pressure. Materials investigated have included CL-20, HMX, TATB, and RDX crystalline powders, LX-04, Comp B, and nitromethane. The anomalous correspondence between crystal structure, including in some instances isostructural phase transitions, on pressure-dependant RPRs of TATB, HMX, Nitromethane, CL-20, and PETN have been elucidated using micro-IR and -Raman spectroscopies. Here we specifically highlight pressure-dependent physicochemical mechanisms affecting the deflagration rate of nitromethane and epsilon-CL-20. We find that pressure induced splitting of symmetric stretch NO{sub 2} vibrations can signal the onset of increasingly more rapid combustion reactions.

An anisotropic constitutive model for the long term dimensional stability of insensitive high explosives is proposed. Elastic, creep, thermal, and ratchet growth strains are developed. Pressure and temperature effects are considered. The constitutive model is implemented in an implicit finite element code and compared to a variety of experimental data.

The Probabilistic Shock Threshold Criterion (PSTC) Project at LLNL develops phenomenological criteria for estimating safety or performance margin on high explosive (HE) initiation in the shock initiation regime, creating tools for safety assessment and design of initiation systems and HE trains in general. Until recently, there has been little foundation for probabilistic assessment of HE initiation scenarios. This work attempts to use probabilistic information that is available from both historic and ongoing tests to develop a basis for such assessment. Current PSTC approaches start with the functional form of the James Initiation Criterion as a backbone, and generalize to include varying areas of initiation and provide a probabilistic response based on test data for 1.8 g/cc (Ultrafine) 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) and LX-17 (92.5% TATB, 7.5% Kel-F 800 binder). Application of the PSTC methodology is presented investigating the safety and performance of a flying plate detonator and the margin of an Ultrafine TATB booster initiating LX-17.

Plutonium(VI) sorption on the surface of well-characterized synthetic manganese-substituted goethite minerals (Fe1-xMnxOOH) was studied using X-ray absorption spectroscopy. We chose to study the influence of manganese as a minor component in goethite, because goethite rarely exists as a pure phase in nature. Manganese X-ray absorption near-edge structure measurements indicated that essentially all the Mn in the goethite existed as Mn(III), even though Mn was added during mineral synthesis as Mn(II). Importantly, energy dispersive X-ray analysis demonstrated that Mn did not exist as discrete phases and that it was homogeneously mixed into the goethite to within the limit of detection of the method. Furthermore, Mössbauer spectra demonstrated that all Fe existed as Fe(III), with no Fe(II) present. Plutonium(VI) sorption experiments were conducted open to air and no attempt was made to exclude carbonate. The use of X-ray absorption spectroscopy allows us to directly and unambiguously measure the oxidation state of plutonium in situ at the mineral surface. Plutonium X-ray absorption near-edge structure measurements carried out on these samples showed that Pu(VI) was reduced to Pu(IV) upon contact with the mineral. This reduction appears to be strongly correlated with mineral solution pH, coinciding with pH transitions across the point of zero charge …

Article discusses genomic and coexpression analyses predicting multiple genes involved in triterpene saponin biosynthesis in Medicago truncatula.