Session M1: Poster Session II (5:30 - 7:00PM)

Laser drive development for the APS Dynamic Compression Sector

The Dynamic Compression Sector (DCS) at the APS synchrotron offers unprecedented possibilities for x-ray diffraction and scattering measurements in-situ during dynamic loading, including single-shot data collection with x-ray energies high enough (tens of kV) to study high-Z samples in transmission as well as reflection. Dynamic loading induced by laser ablation is an important component of load generation, as the duration, strain rate, and pressure can be controlled via the energy, spot size, and pulse shape. Using radiation hydrodynamics simulations, validated by experiments at several laser facilities, we have investigated the relationship between irradiance history and pressure for ablative loads designed to induce shock and ramp loading in the nanosecond to microsecond range, and including free ablation and also ablation confined by a transparent substrate. We have investigated the effects of lateral release, which constrains the minimum diameter of the focal spot for a given drive duration. In this way, we are able to relate the desired drive conditions to the total laser energy needed, which dictates the laser technologies suitable for a given type of experiment.   

X-ray Thomson scattering as a temperature probe for gigabar shock experiments

In X-ray Thomson scattering (XRTS), high-resolution spectrometry of probe x-rays scattered from matter gives an elastic (ionic) and an inelastic (electronic) feature, whose location, width, and amplitude can be analyzed for the temperature and density of the electrons. This diagnostic is complementary to traditional, mechanical EOS measurements which do not directly constrain temperature. XRTS has been demonstrated on planar dynamic-loading experiments at the Omega laser, and a spectrometer has been constructed for use at the National Ignition Facility (NIF). We plan to obtain XRTS measurements into the gigabar regime using hohlraum-driven converging shocks at NIF. In these experiments, the radial profile through the sample at any instant of time varies greatly, though the XRTS signal is dominated by the hottest region, which is at the shock front where simultaneous radiography obtains an equation of state measurement. However, the shock signal is potentially obscured by scattering from the preheat shield, comprising a higher-Z dopant than the sample. Thus we are developing an imaging spectrometer, which should enable a spatial unfold of XRTS spectrum, providing a more precise temperature measurement at the shock front and potentially in the converging flow behind the shock.   

Synchronizing flash-melting in a diamond cell with synchrotron X ray diffraction (XRD)

The major challenges in measuring melting temperatures in laser heated diamond cells are sample instability, thermal runaway and chemical reactions. To circumvent these problems, we developed a ``flash heating'' method using a modulated CW fiber laser and fast X ray detection capability at APS (Pilatus 1M detector). As an example, Pt spheres of 5micron diameter were loaded in a single crystal sapphire encapsulation in the diamond cell at 65 GPa and heated in a single flash heating event for 20ms to reach a desired temperature. A CCD spectrometer and the Pilatus were synchronized to measure the temperature and the XRD signal, respectively, when the sample reached the thermal steady state. Each successive flash heating was done at a higher temperature. The integrated XRD pattern, collected during and after (300K) each heating, showed no chemical reaction up to 3639K, the highest temperature reached in the experiment. Pt111 and 200 peak intensity variation showed gradual recrystalization and complete diminishing at about 3600 K, indicating melting. Thus, synchronized flash heating with novel sample encapsulation circumvents previous notorious problems and enables accurate melting temperature measurement in the diamond cell using synchrotron XRD probe.   

New pressure cell for ultrasonic measurements

Ultrasonic interferometry at high pressure remains a technical challenge as the small sample space requires the application of very high-frequency ultrasound [1]. Here we present the design of a new cell developed specifically for ultrasonic measurements of single crystals at low temperatures (2K) and high pressures (5GPa). The design allows greater sample space (compared to a conventional diamond anvil cell) and simultaneous measurement of ultrasonic attenuation and velocities. Coupling the fine transducers to spherical sapphire anvils reduces background and enables different polarizations of the ultrasonic wave to be measured at the same pressure and temperature conditions. The results are used to deduce the elastic, electronic and magnetic properties of a crystal. The finite element analysis of the cell together with the pressure calibration curves and test data taken on UGe$_{2}$ are presented.\\[4pt] [1] Jacobsen S. D. et al. A gigahertz ultrasonic interferometer for the diamond-anvil cell and high-pressure elasticity of some iron-oxide minerals. In: J. Chen et al. (Eds.) Advances in High-Pressure Technology for Geophysical Applications, Elsevier (2005).   

Integration of structure, x-ray radiography, elastic wave velocity, and viscosity measurement in the Paris-Edinburgh Cell

We have integrated a range of techniques for physical property measurement with the energy-dispersive x-ray diffraction (EDXD) technique at the 16BM-B, a white x-ray beamline at the Advanced Photon Source, to promote comprehensive studies of structure-property correlations of liquid and amorphous materials at high-pressure. These include white x-ray radiography, ultrasonic velocity, and falling sphere viscometry techniques. The integration is centered on a Paris-Edinburgh cell to fully utilize the multi-angle EDXD capability with the wide open access. The integrated techniques are particularly useful to study liquid and amorphous materials, for which the integrated facility allows making simultaneous observations of macroscopic phenomena as the direct manifestation of the microscopic structure. The Paris-Edinburgh press enables us to compress large volume samples up to 2 mm in both diameter and length up to $\sim$7 GPa and 2300 K. The resolution of white x-ray radiography is $\sim$4 $\mu $m. The ultrasonic wave velocity measurement can be made for liquid materials as well as amorphous solids. The falling sphere viscometry technique have been developed using high-speed x-ray camera (\textgreater 1000 frame/second), enabling us to investigate viscosity of not only high viscosity melts such as silicates but also low viscosity (\textless 1 mPa s) liquids such as liquid metals and salts.   

Development of multi-component explosive lenses for arbitrary phase velocity generation

The combination of explosives with different detonation velocities and lens-like geometric shaping is a well-established technique for producing structured detonation waves. This technique can be extended to produce nearly arbitrary detonation phase velocities for the purposes of sequentially imploding pressurized tubes or driving Mach disks through high-density metalized explosives. The current study presents the experimental development of accelerating, multi-component lenses designed using simple geometric optics and idealized front curvature. The fast explosive component is either Composition C4 (VOD $=$ 8 km/s) or Primasheet 1000 (VOD $=$ 7 km/s), while the slow component varies from heavily amine-diluted nitromethane (amine mass fraction exceeding 20{\%}) to packed metal and glass particle beds wetted with amine-sensitized nitromethane. The applicability of the geometric optic analog to such highly heterogeneous explosives is also investigated. The multi-layered lens technique is further developed as a means of generating a directed mass and momentum flux of metal particles via Mach-disk formation and jetting in circular and oval planar lenses.   

Investigation of non-uniform materials under pressure

The approach is considered of the investigation of non-uniform (NU) materials at high pressure (P). Under P a material may become NU due to phase transition (PT). At topological insulators the properties may include the contributions both of the bulk states as well as of the surface ones as at NU material etc.. The approach is based on the model of multi-phase system with ordered phase inclusions of variably configuration (A) and concentration (C), and the experimental data are presented for: i) the substances near PT, ii) some ceramics, iii) the certain natural minerals. Si, ZnX, PbX, SmX (X -- Te, Se, S), GaP, iron ores, and (WC)$_{\mathrm{x}}$Co$_{\mathrm{1-x}}$ hard alloys etc. have been investigated under P up to 30 GPa. It was shown that the model allows to describe resistance (R) and thermoelectric power (S), etc. in the vicinity of PT. For hard alloys WC-Co the elastic modulus has been fitted using the model, and A has been estimated to be distinguished from the simple isotropic case. In the iron ores the A and the C of various components (Fe, Fe$_{\mathrm{y}}$O$_{\mathrm{x}}$, MgO, Mg$_{\mathrm{2}}$SiO$_{\mathrm{4}}$, etc.) has been estimated due to the using of the new approach based on the different depth of penetration of X-ray and neutron radiation, and also on different dependences of S, R on C, A.   

Dynamics of shocks in laser-launched flyer plates probed by photon Doppler velocimetry

We have developed a laser-launched flyer plate system that lets us launch Al flyers of varying thicknesses at velocities up to 4 km/s using different duration laser pulses. We probe the launch and impact with a target using an 8 GHz PDV system. These 25-100 micron thick flyers produce shocks lasting a few nanoseconds. The launch process involves generating a shock in the Al foil that rings and damps out. When the flyer impacts a target, a complicated shock waveform is generated including a steady shock and a release wave. The duration of the steady shock, usually thought to be about equal to the shock round-trip time in the flyer plate, turns out to be quite different. These phenomena were studied in detail using PDV, and their dynamics depend a great deal on the launch laser pulse duration and the flyer thickness. Of particular interest is how the viscoelastic relaxation of the polymer PMMA depends on shock duration in the short shock regime.   

Raman Temperature Measurement

We are examining the experimental tradeoffs for the use of the spontaneous Raman Stokes/anti-Stokes intensity ratio as a fundamental temperature measurement at static and dynamic extreme conditions. The tradeoff space includes spatial resolution and temperature range versus vibrational frequency, as well as heating of the sample and nonlinear damage caused by the excitation laser. The experiments are being performed under a range of experimental conditions from picoseconds to seconds and from cryogenic (77 K) to elevated (ca. 1000 K) temperatures. The results are being compared to calculations for transparent metal oxide, polymer, and inorganic materials, with the aim to demonstrate their potential as temperature reporters when used as thin windows on opaque materials.   

Extreme pressure research at the European XFEL

The European XFEL [1] plans to integrate a nanosecond pulse duration laser system into the high energy density experiment (HED) to enable studies of materials at extremely high pressures. Ramp-compression [2] by nanosecond shaped laser pulses will enable to extend the range of high pressure conditions accessible at hard X-ray sources up to 10 Mbar at comparatively low temperatures. A suitable optical laser system with repetition rates of 0.1 and 10 Hz was recently proposed by an international consortium. Probing of the laser generated excited states will be performed with the high energy X-ray free electron laser (FEL). In the energy range between 5 and 25 keV, it will be possible to study samples by X-ray diffraction, X-ray spectroscopy and imaging techniques. Due to the high excitation energies, diffraction patterns will have excellent quality and a wide range of elements ( Z \textgreater 22) will be accessible by X-ray absorption spectroscopy. The high intensity and time structure will enable time-resolved studies of the samples generated during dynamic compression. In addition, the high brilliance and coherence of the FEL radiation will enable spatially resolved studies. \\[4pt] [1] for detailed information about European XFEL see www.xfel.eu\\[0pt] [2] J.-P. Davis, J. Appl. Phys. \textbf{99}, 103512(2006); R. Smith et al., Phys. Rev. Lett. \textbf{102}, 075503(2009); A. Higginbothom et al., Phys. Rev. B \textbf{85}, 024112(2012)   

Extraction of the pressure dependence of the bulk sound velocity of metals from the calculated precompressed Hugoniot in laser-driven shock wave experiments

Recently [1] a novel route to approach the cold compression curve in laser-plasma induced shock waves was suggested. This effect is achieved with a precompression in a diamond anvil cell (DAC). In order to keep the necessary structure of one dimensional shock wave it is required to use a diamond anvil cell with a partially perforated diamond anvil. Precompression pressures of about 50 GPa, that are an order of magnitude higher than the currently reported pressures, are possible to obtain with presently existing diamond anvil cell technology. In this paper, precompressed Hugoniot curves for Al, W and Ta were calculated up to 15 Mbar for different initial pressures reaching to 50 GPa. From the calculated precompressed Hugoniot curves of Al, W and Ta the pressure dependence of the bulk sound velocity was extracted and was used as a consistency check for the calculations' assumptions. It was found that this method provides a good prediction to the pressure dependence of the bulk sound velocity of metals.\\[4pt] [1] N. Nissim, S. Eliezer, M. Werdiger, L. Perelmutter, ``Approaching the ``cold curve'' in laser-driven shock wave experiment of a matter precompressed by a partially perforated diamond anvil,'' Laser and Particle Beams, First view 2012 (to be published in March 2013).   

Characterization of epoxy-based encapsulents

A range of experiments have been performed in order to investigate the effects of strain-rate on the compressive response of both an epoxy resin and an epoxy-based syntactic foam. Strain-rates ranging from the quasi-static (10$^{-4}$ s$^{-1})$ to dynamic (10$^{3}$ s$^{-1})$ regime have been investigated using an Instron 5584 Universal Testing Machine and Split-Hopkinson Pressure Bar (SHPB) apparatus. The effects of temperature (-20 to 80$^{\circ}$C) on the compressive response of the materials have also been investigated. Finally, the experimental results are discussed with reference to the wider challenge of numerical simulation.   

Models of the Dynamic Deformations of Polymers

In the process of deformation under the influence of external loading polymeric mediums show the complicated behavior connected with features of their structure. For amorphous polymers distinguish three physical conditions -- glasslike, highlyelastic and viscoplastic. To each of the listed conditions there corresponds to mikro - meso- and macrostructural mechanisms of irreversible deformation. In the report the review of results of construction of models for the description of dynamic and shock-wave deformation of the polymers which are based on developed authors representations about mechanisms of irreversible deformation is made. Models include the formulation of the equations of conservation laws, considering effect of a relaxation of shear stresses in the process of deformation. For closing of models the equations of states with nonspherical tensor of deformations and relation for time of a relaxation of shear stresses are constructed. With using of the formulated models a number of problems of dynamic and shock wave deformations has been solved. The results are compared with corresponding experimental date. Development of the used approach are in summary discussed. To taking into account memory and fractal properties of real polymers is supposed of derivatives and integrals of a fractional order to use. Examples of constitutive equations with derivatives of a fractional order are presented. This work is supported by the Integration project of the Siberian Branch of the Russian Academy of Science 64 and grant RFBR 12-01-00726.   

Heterogeneous deformation of metals (copper, tantalum, uranium, titanium) at convergence of cylindrical apertures having small diameters under effect of shock waves

Construction metals undergo loadings of various types during high-velocity deformation. As a result, there are different structural changes and, in particular, varying of mechanical properties. One of these complex structural changes is the process of formation of heterogeneous localized shear bands (LSB) of the twinning nature and the associated temporal decrease of dynamic strength in strong shock waves. The earlier investigations in this area point to the fact that the process of LSB formation has the threshold character, and pressure is the main criterion. So, it is shown in work that LSB formation occurs in coarse-grained copper after effect of shock wave with the amplitude ~28-30 GPa. In this work, within the investigation of convergence of cylindrical channels having small diameters under effect of planar shock waves, it is shown that LSB can be formed in metals, and flow stops being homogeneous at rather low loading level (up to 10 GPa). In this case, the level of plastic strain and its rate are the main factors, which are responsible for heterogeneous deformation. The authors present results of experimental and metallographic researches for some metals, which are copper with various grain sizes, tantalum, uranium, and titanium alloys.   

Laser-driven focusing surface shock waves in glass

Direct real-time visualization of converging surface shock waves in glass is demonstrated in an all-optical experiment. The optical set-up includes an axicon that focuses an intense picosecond excitation pulse into a ring-shaped pattern at the surface of a gold coated glass substrate. Optical excitation induces a surface acoustic wave that propagates in the plane of the sample and converges toward the center resulting in cylindrical focusing of the shock front. The nonlinear evolution of the SAWs and the shock formation is observed at the micro-scale using interferometry with a femtosecond probe pulse at variable delays. A series of images is obtained tracing the converging wave as it collapses in the focal point. The quantitative analysis of the full-field images provides direct information about the surface displacement and the shock velocity. The results open the prospect of spatially resolved studies of shock-compressed materials in a small-scale all-optical experiment.   

Origin of the Volume Collapse under Pressure in Elemental Pr and Gd

Most lanthanide metals exhibit a volume collapse at a critical pressure $P_{c}$. The primary mechanism responsible for this collapse is a matter of debate and may involve the 4$f$ electrons themselves or be the result of simple $s-d$ transfer in the conduction electrons. Possible pressure-induced changes in the 4$f$ electron system include: (i) valence increase, (ii) 4$f $band formation, and (iii) increased 4$f$-conduction electron hybridization leading to Kondo volume collapse. The results of published synchrotron spectroscopic studies at pressures near $P_{c}$ (21 GPa for Pr and 59 GPa for Gd) will be critically examined. Recent high-pressure experiments on the dilute magnetic alloys Y(Pr) and Y(Gd) shed light on the appropriateness of the Kondo volume collapse model for elemental Pr and Gd. In Y(Pr) or Y(Gd) the superconductivity of the Y host is seriously weakened if Kondo pair-breaking is strong. We conclude that pressure-enhanced Kondo binding is indeed responsible for the volume collapse in Pr, whereas in Gd simple $s-d$ electron transfer is the appropriate mechanism.   

High-pressure synthesis of BiFeO$_{3}$-BiAlO$_{3}$ and BiFeO$_{3}$-MnTiO$_{3}$ solid solution

There have been so many investigations for high-pressure synthesis of perovskite-type oxides in the material science field. Multiferroic material is particularly attracted in the field of electronic device materials. BiFeO$_{3}$ (ferroelectric antiferromagnet) is known as the only Bi-contained perovskite which can be synthesized at ambient pressure. We investigated solid solution systems of BiFeO$_{3}$-BiAlO$_{3}$ and BiFeO$_{3}$-MnTiO$_{3}$ under high pressure and high temperature to synthesize a new multiferroic compound in the present study. Chemical reagents of simple oxides were mixed with a mortar as a starting material. The mixture was rapped with a gold foil, and it encased in a cubic pressure-medium with a graphite furnace. High pressure experiments were carried out using two DIA-type high pressure apparatuses installed in Nagoya University. X-ray powder diffraction patterns of all recovered specimens were collected using Cu-K$\alpha $ radiation and magnetic susceptibilities for some of the recovered specimens were measured using a vibrating sample magnetometer. In the system of BiFeO$_{3}$-BiAlO$_{3}$, the BiFeO$_{3}$-type solid solution was only obtained in the both Fe- and Al-rich composition. While in the system of BiFeO$_{3}$-MnTiO$_{3}$, no solid solutions were observed.   

High pressure x-ray diffraction and Raman spectra study of V$_{2}$O$_{3}$

The structural and vibrational properties of V$_{2}$O$_{3}$ have been investigated on basis of synchrotron X-ray diffraction and Raman scattering in a diamond anvil cell. The structure analysis based on the Rietveld refinement methods shows the pressure dependence of V-O and V-V bonding distances. The compressibility of volume and cell axis under different pressure medium is discussed. The pressure dependence of Raman modes was obtained and compared with the existing low temperature measurements. A new high pressure phase of V$_{2}$O$_{3}$ was observed by x-ray diffraction and also predicted by ab initio method. This new phase has similar structure with low temperature phase.   

The effect of high pressure on the density and viscosity of liquid sulfur

Liquid sulfur has attracted attention because it is a complex system that exhibits anomalous properties such as density and viscosity with changes in temperature and pressure. Brazhkin et al. (1991) suggested a first-order liquid-liquid phase transition of liquid sulfur occurs at pressure around 8 GPa. However, no dramatic change accompanying the phase transition has been observed in the previous high pressure viscosity experiment, and this transition is still under debate (Terasaki et al. 2004). Recently, we designed a new method for measuring the density and viscosity of liquid at high pressure using synchrotron radiation and a multi-anvil press (Funakoshi et al. 2012). We successfully obtained the density and viscosity of liquid sulfur and determined the precise compression curve at pressures up to 11 GPa. The density of liquid sulfur showed a smoothly increase and no sharp changes with increasing pressure. This behavior indicates that the long polymeric chain structure of liquid sulfur is continuously compressed after the $\lambda $-transition. However, an abrupt increase in the viscosity was observed around 9 GPa. This remarkable change in the viscosity suggests that a second-order phase transition without structural changes may have occurred in the pressure range.   

Phase Transitions and Melting in Magnesium to 200 GPa and 4500 K

Magnesium is a ``simple'' nearly free-electron metal up to around 100 GPa. Despite similarly-simple group II metals being the subject of numerous studies that have revealed complex high-pressure behaviour, Mg has very few high-pressure diffraction studies, particularly above room temperature. Here we describe such studies to above 200 GPa at 300 K, combined with resistive- and laser-heating experiments to 4500 K and 100 GPa. The hcp-bcc transition at $\sim$50 GPa exhibits a large region of phase co-existence at all temperatures up to 800 K, and the transition pressure is found to decrease with temperature at the rate of $\sim$3.4 GPa per 100 K, somewhat smaller than the rate calculated by Mehta \textit{et al}., [1]. At lower pressures, below the melting curve at 10 GPa, we find the dhcp phase to be stable, in agreement with Errandonea \textit{et al.} [2]. Laser heating studies to 4500 K and 100 GPa show that Mg remains bcc up to the melting curve, our measurement of which is in good agreement with the previous ``speckle'' studies of Errandonea \textit{et al.} [3]. [1] S. Mehta, \textit{et al}., J. Chem. Phys. 125, 194507 (2006). [2] D. Errandonea, \textit{et al}., J. Phys.: Condens. Matter 15 (2003) 1277--1289 [3] D. Errandonea, \textit{et al}. Phys. Rev. B 65, 012108 (2001)   

Angle-Distortion Equations in Special Relativity

Let's consider an object of triangular form $\Delta $\textit{ABC }moving in the direction of its bottom base \textit{BC} (on the $x-$axis), with speed $v$. The side \textit{\textbar BC\textbar }$= \quad \alpha $\textit{ is} contracted with the Lorentz contraction factor $C(v)=\sqrt {1-v^{2}/c^{2}} $ since \textit{BC} is moving along the motion direction, therefore \textit{\textbar B'C'\textbar }$= \quad \alpha C(v). $But the oblique sides \textit{AB }and \textit{CA} are contracted respectively with the oblique-contraction factors \textit{OC(v, B) }and\textit{ OC(v, }$\pi -C),$ where the \textbf{oblique-length contraction factor} is defined as: \[ OC(v,\theta )=\sqrt {C(v)^{2}\cos^{2}\theta +\sin^{2}\theta } . \] In the resulting triangle $\Delta A'B'C'$ one simply applies the Law of Cosine in order to find each distorted angle A', B', and C'. Therefore: \[ A'=\arccos \frac{-\alpha^{2}\cdot C(v)^{2}+\beta^{2}\cdot OC(v,A+B)^{2}+\gamma^{2}\cdot OC(v,B)^{2}}{2\beta \cdot \gamma \cdot OC(v,B)\cdot OC(v,A+B)}, \] \[ B'=\arccos \frac{\alpha^{2}\cdot C(v)^{2}-\beta^{2}\cdot OC(v,A+B)^{2}+\gamma^{2}\cdot OC(v,B)^{2}}{2\alpha \cdot \gamma \cdot C(v)\cdot OC(v,B)}, \] \[ C'=\arccos \frac{\alpha^{2}\cdot C(v)^{2}+\beta^{2}\cdot OC(v,A+B)^{2}-\gamma^{2}\cdot OC(v,B)^{2}}{2\alpha \cdot \beta \cdot C(v)\cdot OC(v,A+B)}. \] The angles A', B', and C' are, in general, different from the original angles$ A, B, $and $ C$ respectively. The distortion of an angle is, in general, different from the distortion of another angle.   

Gahnite under high pressure: A XRD insitu study

Placing P-T-t constraints on planetary differentiation Natural gahnite has the ideal formula ZnAl$_{2}$O$_{4}$. Together with franklinite (ZnFe$_{2}$O$_{4})$ it forms a limited solid solution at high temperatures an occurs as an accessory phase in magmatic and metamorphic rocks, but mainly in the Franklin marble and skarn deposits (Carvalho and Sclar 1988, Frondel and Baum 1974). A natural gahnite sample was investigated with large volume presses at the Synchrotron source DESY. Pressure was stepwise increased to 5 GPa at the MAX80 and 15 GPa at MAX200x and diffraction patterns were collected after each step. The determined volume-pressure-data are fitted to a 2nd and 3rd order Birch-Murnaghan equation of state to obtain the isothermal bulk modulus K$_{\mathrm{T0}}$ and its pressure derivative K'. Isothermal bulk modulus was derived from XRD data. Using a 2nd and 3rd order Birch-Murnaghan equation of state revealed K$_{\mathrm{T02nd}}=$ 207(4) GPa K$_{\mathrm{T03rd}} \quad =$ 204(4) GPa and K' $=$ 4.9(3), respectively. A significant change of the pressure derivatives of C11, C12 and C44 at a pressure of approximately 15 GPa indicates a 2nd order phase transition in gahnite.   

Determination of Equations of State for AlF$_{3}$ and AlI$_{3}$: Semi-empirical Modeling of Extreme Condition Halide Chemistry

Pressure dependent angle-dispersive x-ray powder diffraction measurements of alpha-phase aluminum trifluoride (alpha-AlF$_{3}$) and separately, aluminum triiodide (AlI$_{3}$) were conducted using a diamond-anvil cell. Results at 295 K extend to 50 GPa. The equations of state of AlF$_{3}$ and AlI$_{3}$ were determined through refinements of collected x-ray patterns. The respective bulk moduli and corresponding pressure derivatives using multiple orders of the Birch-Murngahan, Ff, and Gg EoS models will be discussed. Aluminum trifluoride exhibits no pressure induced structural phase transition while the triiodide data reveal a second-order iso-structural rearrangement: Applied stress transformed a monoclinicly distorted face centered cubic (FCC) structure into a perfect FCC structure. Results from semi-empirical thermochemical computations of energetic materials formulated with fluorine containing reactants will be presented.   

In situ high pressure-temperature synchrotron XRD study of Mo with laser-heated diamond anvil cells

In order to understand the behavior of materials at high pressure and high temperature, it is important to have a precise knowledge of pressure ($P)$ -volume ($V)$ -temperature ($T)$ relationship. In this paper, Mo is studied by an integrated technique of diamond anvil cell, laser-heated and synchrotron XRD technologies, providing experimental insight into its behavior at high pressure and temperature. We have measured the cold compression of Mo with the neon pressure media up to 77 GPa, and its thermal expansion up to 94 GPa and 3470 K. The third-order Birch--Murnaghan EoS of Mo at room temperature can be fitted with $K_{0}=$267 GPa, $K_{0}$'$=$3.4, with $V_{0}=$31.32 {\AA}$^{3}$. High temperature data have been treated with both thermodynamic and Mie--Gr\"uneisen-Debye methods for the thermal EoS inversion. The results are self-consistent and in agreement with those obtained by previous theoretical data. The crystal structure of Mo is determined up to 94 GPa and 3470 K and no evidence for the predicted transition to a close-packed face-centered cubic (fcc) phase is found.   

Properties of high density gaseous nitrogen under shock compression in hemispherical geometry

Recent investigations of liquid nitrogen properties under shock compression show compression limit of 4.2 close to of ideal gas $\sigma =$ 4 in pressure region 100 -- 330 GPa and demonstrate an unusual Hugoniot pressure -- density dependence similar to isochoric compression. We performed two experiments with gaseous nitrogen with initial density $\rho _{0} =$ 0.8 g/cm$^{3}$ to confirm previous data on liquid nitrogen. The experiments were conducted using HE shock wave generators of hemispherical geometry. We obtain Hugoniot pressures (190 $\pm$ 5) and (226 $\pm$ 5) GPa, compressions (4,64 $\pm$ 0,47) and (4,42 $\pm$ 0,36), temperatures (37500 $\pm$ 5800) and (45900 $\pm$ 9300) K. Experimental data on gaseous nitrogen agree with that on liquid nitrogen and modified model of compressible covolume.   

Equations of state for hydrocodes

The equation of state (EOS) governing the system of gas dynamic equations defines significantly accuracy and reliability of results of numerical modeling. In our report, we will formulate main mathematical and physical demands to wide-range EOS for hydrocodes. Our semi-empirical EOS model fully assigns the free energy thermodynamic potential for metals over entire phase diagram region of practical interest. It accounts for solid, liquid, plasma states as well as two-phase regions of melting and evaporation. Available now are wide-range multi-phase EOS for 30 simple and transition metals of the most practical interest. Their direct usage in computer codes leads to complicated and not economy calculations, so they are usually involved in numerical modeling in tabular form. The EOS code for calculation of tables can produce the complete set of thermodynamic derivatives (such as pressure, sound velocity, heat capacity) using any one of input pairs: volume-temperature, volume-internal energy or volume-pressure. The input grid can be linear, logarithmic or arbitrary; each point in 2D output tables is marked by symbol which indicates the physical state, such as solid, liquid, gas, plasma or mesh. We also present in our talk estimations of shock melting and evaporating and importance of these effects for results of numerical modeling.   

Reversible pressure-induced polymerization of C$_{60}$, C$_{70}$ doped ferrocene

C$_{60}$, C$_{70}$ combined with organometallic donors can form a wide variety of donor-acceptor complexes and only relatively weak van der Waals interactions and charge transfer between them. Ferrocene (Fc) is an example with the tunable degree of charge transfer to C$_{60}$/C$_{70}$ and offers us a good model to study the effect of charge transfer on the polymerization of fullerenes. Pressure can modify the intermolecular distance and thus affect the charge transfer between host and guest. It is expected that the interaction can be tuned by applying pressure and further affect the polymerization of fullerenes. In-situ high pressure Raman, IR and XRD studies are used to investigate the phase transitions of C$_{60}$/C$_{70}$(Fc)$_{2}$. We find that the charge transfer interaction is strengthened under pressure and the polymer chain is formed in C$_{60}$(Fc)$_{2}$ at 5GPa, while dimer phase and 1D/2D polymers are formed in C$_{70}$(Fc)$_{2}$ at 3GPa and at 8GPa, respectively. Only certain fullerene molecules take part in this reaction due to the layered structure of the samples. These transitions are quite different from those of pure C$_{60}$/C$_{70}$ because of the intercalated Fc. The observed polymerization is reversible and can be related to the overridden steric repulsion of counter ions and the tunable charge transfer at high pressure.   

High pressure study of RNi intermetallics (R$=$Dy, Gd)

The structural, electronic and magnetic properties of RNi's (R$=$Dy, Gd) have been analyzed using \textit{ab-initio }full-potential linear augmented plane wave method within the density functional formalism. Spin polarized GGA$+$U approximations based on exchange-correlation energy optimization has been used for the calculation of total energy of the systems. Under compression, DyNi undergoes a first--order structural phase transformation from ambient FeB to CsCl phase at 18.4 GPa while GdNi transform its structure from CrB to CsCl phase at 3.73 GPa. The calculated magnetic moment for R$^{3+}$ ions are obtained as 9.3 $\mu$B and 7 $\mu$B, respectively, in DyNi and GdNi. The results are closer to the experimental values (10 $\mu$B for Dy$^{3+}$ and 7 $\mu$B for Gd$^{3+})$. Details related to structural, electronic and magnetic properties are reported, theoretically, for the first time for DyNi intermetallic compound. The equilibrium lattice constants are in good agreement with their experimental data. Our calculation shows that both the intermetallic compounds are metallic in nature.   

Phase Decomposition of Rare Earth Apatite and Formation of Perovskite Rare Earth Silicate at High Pressure and High Temperature Conditions

The crystal structure of rare earth apatite was studied at high pressure and room temperature conditions. A reversible subtle phase transition was found at pressure. The high-pressure phase has also a hexagonal unit cell but with a lower symmetry reduced from \textit{P6}$_{3}/m$ to \textit{P6}$_{3}$. Due to the symmetry change, the high-pressure phase has an unusual lower bulk modulus as compared with the corresponding ambient structure. Laser heating of La-Si-O apatite at high pressure conditions revealed that apatite structure is not stable at temperatures higher than 1500 K and decomposes into two different phases. The decomposed phase is a perovskite-type structure. Alkaline earth silicate minerals can easily form the 6-coordianted high-pressure phase in the deep earth environment. However, a rare earth silicate with the perovskite structure has not been previously reported. The experimental results also suggest that the La$_{0.67}$SiO$_{3}$ perovskite structure is at least partially quenchable.   

High energy-resolution electron energy-loss spectroscopy and x-ray emission spectroscopy studies of amorphous diamond transformed from neutron-irradiated graphite

Specimens for transmission electron microscopy were prepared from amorphous diamond, which was synthesized from neutron-irradiated graphite by shock compression. High energy resolution EELS measurements were performed by using a monochromator transmission electron microscope (TEM). XES measurements were performed by using a wavelength-dispersive type spectrometer for soft x-ray attached to the monochromator TEM. A volume plasmon peak of am-DIA is observed at 32.5 eV, which is slightly located at lower energy than that of c-DIA. Since the plasmon energy is dominantly proportional to square root of valence electron density, the lower plasmon energy of am-DIA indicates that the valence electron density of am-DIA is smaller than that of c-DIA. Also, it is revealed that the band gap energy of am-DIA is 4.0 eV, which shows good agreement with the estimation of 3.9 eV from the onset energy of valence-electron excitation spectrum.   

Pressure-induced phase transition in $\gamma $-MnOOH

At ambient conditions manganite, $\gamma $-MnOOH, crystallizes in space group P2$_{\mathrm{1}}$/c (Kohler et al. 1997). A high pressure study by Suzuki (2006) up to 9 GPa gave a bulk modulus of 91(2) GPa, when the data was fitted with a 2$^{\mathrm{nd}}$ order Birch-Murnaghan equation of state. Preliminary DFT calculation predicted a phase transition to an orthorhombic space group at pressures above 15 GPa. In order to test the prediction, natural $\gamma $-MnOOH was ground to powder and compressed in a DAC up to 70 GPa. Lattice parameters were determined from X-ray patterns recorded at the Extreme Conditions Beamline P02.2@PETRA III. A structural phase transition into an orthorhombic phase was observed at 47 GPa. The bulk modulus of the ambient pressure phase is 98(3) GPa with K$' = $ 7.7(3). Currently, DFT$+$U calculations are carried out to understand the compression mechanism and the phase transition. Funding by the BMBF (project 05K10RFA) is gratefully acknowledged. We thank DESY Photon Science for beam time and Hanns-Peter Liermann and his team for support. Kohler T. et al, J Solid State Chemistry, 1997, 133, 486-500. Suzuki A., SPring-8 Exp. Report, 2006, 2006A1464.   

Molybdenum Sound Velocity and Shear Strength Softening

We recently carried out a series of light-gas gun experiments to measure molybdenum acoustic sound speed up to 5 Mbars on the Hugoniot. Our measured sound speeds increase linearly with pressure up to 2.6 Mbars and taper off near the melting pressure. The gradual leveling off of sound speed suggests a possible loss of shear strength near the melt. A linear extrapolation of our data to zero pressure is in good agreement with the sound speed measured at ambient condition. The results indicate that molybdenum remains in the bcc phase on the Hugoniot up to the melting pressure. There is no bcc solid phase transition on the Hugoniot as previously reported.   

Bcc-fcc structure transition of Te

A group 16 element, tellurium (Te) undergoes numerous structural phase transitions under high pressure. Up to now, five different crystalline modifications have been identified at pressure up to 36 GPa: trigonal (Te-I at ambient pressure), monoclinic (Te-II at 4 GPa), incommensurate monoclinic (Te-III at 4.5 GPa), beta-Po type (Te-IV at 23 GPa and 473 K) and bcc (Te-V at 29 GPa). The pressure-induced successive structural phase transitions are accompanied by an increase in the coordination number of Te atoms: 2-4-6-8. Therefore, a transition to the structure with larger coordination number such as fcc or hcp is expected with further compression. In this paper, in order to explore the post-bcc phase, the synchrotron radiation x-ray powder diffraction experiments of Te at pressure up to 255 GPa and at room temperature have been carried out and the bcc-fcc structure transition is reported.   

Electrical properties (ZrO$_{2}+$Y$_{2}$O$_{3})+$Al$_{2}$O$_{3}$ at high pressures

We studied electrical resistance (ZrO$_{2}+$Y$_{2}$O$_{3})+$Al$_{2}$O$_{3}$ at the pressures 22 - 50 GPa and temperatures 77 - 400 K. Measurements were made with samples containing 80\% (ZrO$_{2}+$\textit{3mol{\%}}Y$_{2}$O$_{3})+$ 20{\%}Al$_{2}$O$_{3}$. The d.c. conductivity measurements were carried out in a diamond anvil cell (DAC) with anvils of the ``rounded cone-plane'' (Verechagin--Yakovlev) type made of synthetic carbonado-type diamonds, consisting of dielectric grains of synthetic diamonds in layers of conducting materials. These anvils are relatively good conductors, thus permitting measurement of the resistances of samples placed between the anvils in the DAC by using the anvils as the electrical contacts to the sample At a pressures of about 28-30 GPa the (ZrO$_{2}+$Y$_{2}$O$_{3})+$Al$_{2}$O$_{3}$ resistance decreases by 3-4 orders of magnitude. The temperature dependences of the resistance exhibits a metal-like character (with the positive temperature coefficient).   

High Pressure Raman and X-ray diffraction studies on MoS$_{2}$ up to 51 GPa

Molybdenum disulphide (MoS$_{2})$ is technologically important material which finds potential applications as high temperature lubricant, universal joint in ultra high vacuum chambers and in photovoltaic devices. Recent studies show excellent antishock or shock-absorbing property under very high shock wave pressures of 25 GPa and temperature up to 1,000$^{\circ}$C. We have investigated the structural stability of MoS$_{2}$ under high pressure conditions up to 51 GPa using synchrotron x-ray diffraction (XRD) in an angle dispersive geometry and a diamond anvil cell using Ne pressure medium. Raman spectra were collected up to 30 GPa. Furthermore, we have also performed high temperature x-ray diffraction up to 450$^{\circ}$C at ambient pressure conditions. Analysis of both XRD and Raman data indicate a pressure induced phase transition occurring above 20 GPa from the ambient hexagonal to a possible high pressure orthorhombic phase. The results will be presented in detail.   

Coupling of strong elastic shock with supersonic melting front produced by ultrashort laser pulse

Generation of ultrashort shock elastic and plastic waves by femtosecond laser pulses in Al and Ni films is investigated by two-temperature hydrodynamics (2T-HD) and molecular dynamics (MD) methods. Ultrafast laser heating of metals is approximately isochoric during first several picoseconds. It leads to significant overheating of surface layer above the equilibrium melting line $T_{\mathrm{m}}(P)$, causing the melting front to propagate with supersonic speed as deep as a local degree of overheating drops to $\sim$1.2. After that the melting front decelerates quickly and a compression wave leaves the heated surface layer. Because the melting transition occurs at isochoric compression, the pressure and temperature at a solid-liquid interface in a moment when the melting front stops are independent on laser energy absorbed in metals. If absorbed energy exceeds some threshold, the compression wave splits into elastic and plastic shock waves. Evolution of those waves, including their coupling with the melting front at early stage and emission of rarefaction and compression elastic pulses by a plastic front, was studied by both 2T-HD and MD simulation. It was shown that the elastic precursor has a fluence-independent amplitude; whereas the plastic front undergoes significant attenuation during propagation and may fully decay within a metal film.   

Structural and superconducting properties of Bi$_{1-x}$Sb$_{x}$ under high pressure

We have studied pressure-induced superconductivity and structural phase transition in bismuth-antimony alloy (Bi$_{1-x}$Sb$_{x}$), which is a substitutional solid solution over the full composition range. Bi$_{1-x}$Sb$_{x}$ crystallizes in the A7-structure with space-group $R${\=3}$m$ at ambient condition and shows pressure-induced structural changes similar to those of pure Bi and Sb: the A7-structure -- the incommensurate host-guest composite structure with super space-group $I$4'/$mcm(00\gamma)$ (the HP-composite phase) -- the body-centered cubic one with $Im${\=3}$m$ (bcc). In the composition of $x=0.08$, these two phase transitions occur above 3 and 10 GPa, respectively. In pure Bi and Sb, the superconductivity is observed in these high-pressure phases. To investigate the superconducting transition in $x=0.08$, we performed the electrical resistivity measurement at low temperature under high pressure up to 12 GPa using modified Bridgman anvil cell. The superconducting transition is observed above 2.7 GPa with the transition temperature $T_c=7.0$ K. Furthermore, $T_c$ discontinuously increases up to 8.5 K at 9.7 GPa. As compared to the structural change, the superconductivities observed at 2.7 and 9.7 GPa are attributed to the HP-composite structure and bcc, respectively.   

Phase changes induced by guest ordering of filled ice Ih structure of methane hydrate under high pressure and low temperature

Orientational ordering of guest methane molecules in a filled ice Ih structure of methane hydrate (MH-FIIhS) was observed above 20GPa by our previous Raman study, whereas change in a fundamental structure was not detected by XRD. In this study, in-situ XRD studies were performed in the temperature range from 300 to70 K at the pressures up to 57 GPa. The results revealed that the lattice parameters changed continuously with increasing pressure, however, clear changes in axes ratios were shown. At about 20 GPa the slopes of axis ratios, b/c and c/a, changed abruptly at room temperature. The Raman spectroscopy showed split of CH vibration mode of the methane molecules, which indicates the orientational ordering of the guest methane molecules, at the almost same pressure. These results demonstrated that the changes in axis ratio were caused by orientational ordering of the guest molecules. Similar changes in the axis ratios and split of CH vibration mode were observed at low temperature regions. The regions of the guest-ordered phase and the guest-rotated phase were roughly estimated from the experimental results.   

Sound velocity determination of PbTe under pressure

Recent investigations\footnote{S. V. Ovsyannikov and V. V. Shchennikov, Appl. Phys. Lett. 90, 122103 (2007).} of PbTe have revealed interesting high pressure transitions resulting in improved thermoelectric performance. High pressure sound velocities of PbTe have been measured to 14 GPa using an ultrasonic interferometric method.\footnote{B. Li, I. Jackson, T. Gasparik, and R. C. Liebermann, Phys. Earth Planet. Int. 98, 79 (1996).} Elastic moduli and their pressure derivatives for phases in this range have been obtained using a finite strain approach. From this, an estimate of the acoustic phonon contribution to the thermal conductivity is made. By combining this with previous determinations of the thermal conductivity due to electrons, a significantly lower value than the previously determined total thermal conductivity is found. This is interpreted as evidence for coupling between the low-lying transverse optic (TO) and longitudinal acoustic (LA) modes allowing transfer of thermal energy between them. The application of pressure causes energy transference between the optical modes and electron population, which is likely the cause of the increased thermoelectric efficiency in the intermediate Pbnm state.   

Study of electric properties of amorphous AgGe$_{\mathrm{1+x}}$As$_{\mathrm{1-x}}$S$_{3}$ with content of carbon nanotubes

Multicomponent copper and silver chalcogenides have been known as promising materials for scientific and applied purposes. These materials are also under intense investigation for application in a phase-change random access memory [1]. In order to obtain materials with a high ionic conductivity component, glassy silver chalcogenides AgGe$_{\mathrm{1+x}}$As$_{\mathrm{1-x}}$S$_{3}$ with the addition of nanotubes were synthesized. In this work the study of electrical properties of the amorphous chalcogenide AgGe$_{1.4}$As$_{0.6}$S$_{3}$ (x$=$0.4) with carbon nanotube content at a frequency of the alternating-current electric field varying from 1 Hz to 5 MHz and on direct current at ambient pressure and at pressure up to 30 GPa are presented. The ion transport was confirmed by means DC measurements in cells with blocking ion component of conductivity electrodes. An evaluation of the proportion of ionic conductivity can make a preliminary conclusion that the ionic component of the conductivity of at least 98{\%}. Analyze of the baric dependences of AC properties have shown that the dielectric loss tangent and the real part of an admittance of the AgGe$_{1.4}$As$_{0.6}$S$_{3}$ with carbon nanotube content compound exponentially increase with a pressure increase from 1 up to 30 GPa. \\[4pt] [1] R. Waser and M. Aono, Nature Mater. 6, 833, 2007.   

Pressure effects on superconductivity in LaFeAsO$_{1-\delta}$

Pressure effects on superconductivity in LaFeAsO$_{1-\delta}$ oxypnictide were studied using piston-cylinder type pressure cell. LaFeAsO$_{1-\delta}$ has been recognized as one of the typical FeAs-based superconductor since the discovery of superconductivity in LaFeAs(O, F). Oxygen deficiency in LaFeAsO leads doping and causes superconductivity. Pressure dependence of the superconducting transition temperature of LaFeAsO$_{0.7}$ was clarified by electrical resistivity measurement up to the pressure of $P=$2.5 GPa. The sample of LaFeAsO$_{0.7}$ was prepared by high pressure synthesis technique. Using a cubic-anvil-type apparatus the sample was sintered at 1250$^{\circ}$C under the pressure of 3 GPa. Oxygen deficiency was estimated from the nominal composition of starting materials. At ambient pressure, LaFeAsO$_{0.7}$ shows superconducting transition at $T_{\mathrm{c}}$ = 21.8 K. With increasing pressure, $T_{\mathrm{c}}$ increased almost linearly with coefficient of d$T_{\mathrm{c}}$/d$P$ = 2.6 K/GPa. The pressure dependence of $T_{\mathrm{c}}$ in LaFeAsO$_{0.7}$ is similar to that of an under doped sample in the LaFeAs(O, F) system.   

Pressure Effect on Superconductivity of Rhenium

Rhenium metal is often used as a gasket material in high pressure experiments using DACs. It has been known that Re become a superconductor with superconducting transition temperature $T_{c}$ of 1.6-2.8 K at ambient pressure [1]. Although, pressure dependence of $T_{c}$, have not been studied in detail over 2 GPa [1]. It's important to study pressure effect on $T_{c}$ of Re in two points. First is that hard simple elements Os, W, Ir and Re are known to superconduct with very low $T_{c}$s at ambient pressure, but high pressure properties of their $T_{c}$ have not been well studies so far. Another point is a technical aspect. In the studies of superconductivity under high pressures, we employ electrical resistance and magnetic susceptibility measurements to detect superconductivity. Superconducting Re-gasket below 4 K masks superconducting signal of sample in magnetic susceptibility measurements. In electrical resistance measurements, if the electric circuit has a short with~Re-gasket, superconducting transition comes to be mixed in measured data. We present pressure dependence of $T_{c}$ of rhenium up to 65 GPa measured using a DAC. We observed $T_{c}$ increases in pressure range of 0-10 GPa and it gradually decreased with applied pressure. \\[4pt] [1] C.W. Chu et al., Phys. Rev. Lett. 20, 198 (1968)   

Pressure-induced superconductivity in non-stoichiometric bismuth telluride Bi$_{35}$Te$_{65}$

Stoichiometric bismuth telluride (Bi$_2$Te$_3$), which is a $p$-type semiconductor, has the rhombohedral structure with space group $R$-3$m$ at ambient condition. We have previously reported that pressure-induced superconductivity of stoichiometric $p$-type Bi$_2$Te$_3$ occurs in the high-pressure phases which appear above 8 GPa. The transport properties of Bi$_2$Te$_3$, however, depend on the atomic composition; the dominant charge carriers change from hole to electron above 63at.\% Te. In this study, we performed the electrical resistivity measurement and the x-ray diffraction study of non-stoichiometric $n$-type Bi$_{35}$Te$_{65}$ under high pressure to investigate pressure-induced superconductivity and structural phase transition. Bi$_{35}$Te$_{65}$ has also the $R$-3$m$ structure at ambient condition. It remains stable up to 9 GPa at room temperature. The superconducting transition is observed at 6 GPa below 2.9 K. There is no obvious anomaly indicating structural phase transition in both pressure dependence of the electrical resistivity at pressures up to 6 GPa and temperature dependence of it at 6 GPa. It suggests that the superconducting transition at 6 GPa of Bi$_{35}$Te$_{65}$ occurs in the $R$-3$m$ structure.   

Parameterization of classical force fields in the context of high pressure calculations

Activation volumes and volume profiles of chemical reactions are concepts widely used in high pressure reaction kinetics. We have recently shown that these quantities can be calculated using molecular dynamics (MD) simulations with accuracy comparable to that of the experiment. The major challenge in performing such calculations comes from the fact that standard MD force fields are parameterized for stable species and, therefore, are not directly usable for transient points along the reaction coordinate. We propose a consistent scheme of parameterization for such species based on fitting force field potentials to quantum mechanical deformation energies, and show that MD simulations with these parameters produce molar volumes of quality comparable to that of OPLS and the experiment.   

MD studies of electron transfer at ambient and elevated pressures

The effect of pressure on the rate constants of outer-sphere electron transfer reactions has often been described using the Marcus-Hush theory.\footnote{R.A. Marcus. J. Chem. Phys. \textbf{24}, 966 (1956); \textbf{24}, 979 (1956); \textbf{26}, 867 (1957). Discuss. Faraday Soc. \textbf{29}, 21 (1960). Faraday Discuss. Chem. Soc. \textbf{74},7 (1982); N.S. Hush. Trans. Faraday Soc. \textbf{57}, 557 (1961).} This theory agrees well with experiment when internal reorganization of the ionic system is negligible,\footnote{T.W. Swaddle. Inorg. Chem. \textbf{29}, 5017 (1990).} however it does not offer a recipe for calculation of the effects that result from significant solute restructuring. We have recently developed a molecular dynamics technique that accurately describes structural dependence of molecular volumes in non-polar and weakly polar systems. We are now extending this approach to the case of highly polar ionic systems where both solvent and solute restructuring components are important. For this purpose we construct pressure-dependent two-dimensional surfaces for electron transfer reactions in coordinate system composed of interionic distance and Marcus-type solvent polarization coordinate, and use these surfaces to describe pressure effects on reaction kinetics.   

Effect of high pressure on reaction profiles and energy surfaces

Both experiment and first principles calculations unequivocally indicate that properties of elements and their compounds undergo a tremendous transformation at ultra-high pressures exceeding 100 GPa due to the fact that the difference between intra- and intermolecular interactions disappears under such conditions. Yet, even at much milder pressures of 5-30 GPa, when molecules still retain their individual identity, their chemical properties and reactivity change dramatically. Although first principles MD is perfectly suitable and, in fact, is being increasingly used to describe these systems, its applications are severely restricted by their size and complexity. Since, as long as transition state theory remains valid, the reaction kinetics and mechanisms can be described in terms of the free energy surfaces (FESs) of the solvated reaction systems, we propose to use classical molecular dynamics to describe effects of high pressure on condensed-phase FESs by calculating effects of solvation on the quantum mechanical gas-phase potential energy surfaces. We also show that high-pressure free energy surface G(\textbf{x};P) (\textbf{x} is a multidimensional geometrical parameter) is well approximated by equation G(\textbf{x};P) $\approx $ G(\textbf{x};0) $+$ PV(\textbf{x}), where G(\textbf{x};0) is the zero-pressure free energy surface and V(\textbf{x}) is the volume of reaction system in configuration x.   

Structural and Vibrational Properties of Nitrogen-Hydrogen Mixtures at High Pressure

The chemistry and equations of state of simple molecular systems (e.g. N2, H2, H2O, CO2, CH4 etc.) in the dense fluid state are of extreme importance to planetary astrophysics and are model systems for understanding the effects of pressure on chemical bonding, reactivity in the solid solution and potentially new routes to pressure-induced metallization. Here, we present the first comprehensive study of the binary N2/H2 system in the diamond anvil cell using Raman spectroscopy, synchrotron infrared micro-spectroscopy and visual observation. We find a eutectic-type binary phase diagram with two stable high-pressure compounds which we identify as (N2)6(H2)7 (R-3m) and N2(H2)2 (Pm-3m) using single-crystal x-ray diffraction. The former has a novel rhombohedral structure in which groups of hydrogen molecules are contained by the nitrogen lattice. We discuss further infrared absorption studies on this compound, including evidence for a gradual transformation from van der Waals to ionic interactions with pressure. A phase transition to an ionic compound with the same stoichiometry is observed at 55 GPa. Compression of this compound was carried out up to 200 GPa to investigate possible metallization.   

High-pressure Brillouin study on plastic crystals of neopentane and adamantane

Spherical top molecules neopentane and adamantane with Td symmetry crystallize face centered cubic (fcc) plastic crystals in which molecules are rather freely rotating at fcc lattice points. In the case of fcc plastic crystalline methane, the value of elastic anisotropy $A$ is above 5 which is large than $A$ $\sim$ 2.5 of rare gas solids without molecular rotation, and shows strong pressure dependence because of the enhancement of the molecular rotation-translation (R-T) coupling by compression. Therefore, the purpose of the present study is to carry out the high-pressure Brillouin measurements for the fcc plastic crystals of neopentane and adamantane up to 0.75 and 0.5 GPa, respectively, and to clarify the dependence of the R-T coupling on pressure and molecular weight. The obtained value of $A$ of fcc neopentane is 6.1 at 0.18 GPa and steeply increase up to 12.8 at 0.72 GPa. This remarkably large $A$ values and its strong pressure dependence indicate that the R-T coupling effect in the plastic phase of neopentane is obviously large in comparison with methane. On the other hand, the plastic crystal of adamantane shows almost constant ($A =$ 2.5) which is nearly the same as the rare gas solids, suggesting no R-T coupling effect.   

High-pressure Raman study of fully deuterated methane hydrate

Methane hydrate (MH: CH$_{4}$-$n$H$_{2}$O) crystallizes in a cubic structure I (sI) which consists of hydrogen-bonded water cages which enclathrate methane molecules as guests. With increasing pressure, the initial sI of MH transforms to a hexagonal structure H (sH) at 0.9 GPa, and eventually to an orthorhombic cage-less structure O at 1.9 GPa. The sH consists of three small S1, two small S2, and one large LL water cages in a hexagonal unit cell. The previous high-pressure Raman measurements for C-H stretching vibration of MH-sH indicated that the capacity of methane molecules in the large LL cage abruptly increased at 1.3 GPa, and its occupation number of methane molecule was about 2.5 above 1.3 GPa. However, this result disagrees with the previous high-pressure neutron diffraction experiments for sH of fully deutarated methane hydrate (FDMH: CD$_{4}$-$n$D$_{2}$O). To solve this discrepancy, we have carried out the high pressure Raman measurements for C-D stretching vibration in the sI and sH phases of FDMH. As a result, we have obtained the different Raman spectral patterns between FDMH and MH, which suggests that the occupancy of CD$_{4}$ in water cages is somewhat different from CH$_{4}$.   

Spectroscopic Studies of Cyclopentane under Extreme Conditions and Implications for the P-T Phase Diagram

Infrared (IR) spectroscopy and Raman scattering combined with diamond anvil cell (DAC) and cryogenic techniques have been employed to investigate cyclopentane up to 4 GPa in the temperature range of 100-350 K and isothermal compression up to 84 GPa at room temperature. Four phases including liquid, plastic phases I and II, and truly crystalline phase III are clearly identified in the P-T range studied based on the changes of the ring breathing mode and CH$_{2}$ rocking modes. The phase diagram is extended to the pressure and temperature range of 0 -- 4.0 GPa and 105 -- 350 K. Further compression at room temperature up to 84 GPa, another high-pressure phase (IV) is observed based on the appearance of low frequency peaks related to the lattice vibrational modes in the synchrotron far-IR spectra. The spectroscopic results indicate that cyclopentane persists the orientation ordered crystalline phase up to 84 GPa at room temperature.   

Fe$_{4}$O$_{5}$: HP-HT synthesis and properties

Recently, a new iron oxide, Fe$_{4}$O$_{5}$ has been synthesized at high-pressure high-temperature (HP-HT) conditions [1,2]. In this work using multi-anvil large-volume cells we investigated the synthesis conditions of Fe$_{4}$O$_{5}$ in wide ranges pressures of 9-24 GPa and temperatures of 900-1800 C. We have prepared both single crystals and bulk polycrystalline samples of Fe$_{4}$O$_{5}$. We investigated the chemical composition and the microstructure of Fe$_{4}$O$_{5}$. From a single-crystal diffraction study we have refined the crystal structure of Fe$_{4}$O$_{5}$. We have studied compressibility of Fe$_{4}$O$_{5}$ up to 50 GPa. In addition, we studied magnetic, optical and electronic transport properties of Fe$_{4}$O$_{5}$ at ambient pressure. These studies included magnetic susceptibility, magnetization, Mossbauer spectroscopy, Raman and Infra-red spectroscopy, electrical resistivity. We have performed also calculations of the lattice stability and electronic band structure of Fe$_{4}$O$_{5}$\\[4pt] [1] B. Lavina, et al., Proc Nat. Acad. Sci. US 108, 17281 (2011).\\[0pt] [2] A. B Woodland, et al., Am. Miner. 97, 1808 (2012).   

Shear-induced phase transition of disordered nanocrystalline hexagonal boron nitride at room temperature

Disordered hexagonal boron nitride (hBN) is an important precursor material for the synthesis of super-hard materials, wurtzitic BN (wBN) and cubic BN. However, the phase transformations from disordered hBN were only achieved at high temperatures under high pressures. By applying large shear by rotational diamond anvil cell, we observed the phase transition from disordered nanocrystalline hBN to wBN at room temperature under a moderate pressure of 6.7 GPa. Yet, under hydrostatic compression to 52.8 GPa, the same hBN sample did not transform to wBN. Our results demonstrate a potential of low pressure-room temperature synthesis of super-hard materials under plastic shear from disordered or amorphous precursors.   

Pressure-induced structural transformations of 1D nanostructured TiO$_{2}$

Nanostructured materials especially semiconductors in different morphologies such as dots, wires, belts and tubes are of fundamental importance because of their wide range of tunable electrical, optical and mechanical properties. Investigations of the structures and phase transformations of nanomaterials under high pressures have received increasing attention. This is because, in addition to composition and synthetic routes, high pressure provides an additional effective driving force to produce new structures and, therefore, new nanomaterial properties. Using vibrational spectroscopy and synchrotron X-ray probes, in particular, we have studied several nanostructured TiO$_{2}$ materials under high pressure in situ to explore their high-pressure behaviors in terms of transformation pressures, phase stability regions and compressibility. Interesting size dependent phase transitions were observed in all those nanomaterials comparing with the corresponding bulk materials.   

High-pressure Phase Transition of Hexagonal Silver Sulfide Nano Platelets

Silver sulfide (Ag2S) is a narrow band gap semiconducto. Due to the excellent photoelectric and thermoelectric properties, silver sulfide has been widely used in the field of photocell, photoconductive devices and infrared detectors. Recent years, the discovery of fast ionic conductivity of silver sulfide at high temperature, making it became the research focus once again. Previous studies is limited to the temperature-induced phase transitions, the study of pressure-induced phase transition has not been reported. In order to study the pressure-induced phase transition properties of silver sulfide, the high-pressure synchrotron radiation XRD study on hexagonal silver sulfide nanoplates was carried out. Silver sulfide sample was in the morphology of regular hexagonal nanoplate, with an average diameter of 20nm. High-pressure synchrotron radiation XRD experiments shows that, under high-pressure, the diffraction peaks of silver sulfide are broadening. When the pressure reaches 12.4GPa, the sample transformed into amorphous state gradually and kept the amorphous state until the end of experiment, the highest attainable pressure was 29.4GPa. After the sample quenched to the initial pressure, it returned to the initial monoclinic $\alpha $-Ag2S phase, phase transformation was reversible.   

Superconductivity of Mg/MgO interface formed by shock-wave pressure

Instability of the non-equilibrium superconducting Mg/MgO-interface under normal conditions has motivated our attempt to create it using shock-wave pressure. During the shock-wave impact, a stroke applied to the sample creates a series of strong high-pressure shock-waves propagating throughout the sample due to relative displacements of local parts of the sample material. Highly non-equilibrium conditions thus realized, can stimulate phase transitions or mechanochemical reactions inaccessible in a static pressure mode. Furthermore, the energy of the shock wave rapidly propagating through the sample within 10$^{\mathrm{-6}}$ -- 10$^{\mathrm{-9}}$ s, leads to local non-equilibrium overheat of the sample's regions at the shock wavefront, followed by their rapid cooling (quenching) as the shock-wave is passed. Such quenching can provide room-temperature stabilization of metastable non-equilibrium phases, unstable otherwise under normal conditions. A mixture of Mg and MgO has been subjected to a shock-wave pressure of $\simeq $20 GPa. The ac susceptibility measurements of the product has revealed a metastable superconductivity with Tc $\approx $ 30 K. Comparison of the ac susceptibility and the dc magnetization measurements infers that the superconductivity arises within the interfacial layer formed between metallic Mg and its oxide due to the shock-wave.   

Regenerated Spider Silk Possess Mechanical Properties of Super- and Cyclic Contraction in Response to Environmental Humidity

Major Ampullate (MA) spider silk is among the most impressive biomaterials due to its unparalleled mechanical properties, such as super-contraction and cyclic response to changes in humidity. Electro-spinning enables the generation of engineered silk fibers with controlled parameters and dimentions for various medical and commercial applications. However, their applications hinge on the ability to reproduce the mechanical properties such as a precise expansion-contraction response existed in natural silk fibers. Here, we successfully reproduced MA spider-silk fibers from solutions of natural MA silk proteins via electrospinning, which exhibit the super-contraction and cyclic response to humidity change in a manner mirroring the natural fibers.   

Investigation of ultrafast relaxation in terrestrial and meteoric Fe-Ni

The ablation and breakup of meteorites upon entry into the Earth's atmosphere is an important challenge of global relevance. However, large thermal gradients, coupled with complex stoichiometry of Fe-Ni based meteorites, lead to difficulties in accurately modeling the breakup process. Ultrafast compression experiments are being conducted to better understand the effect of microstucture and temperature on the behavior of dislocation mechanisms in Fe-rich materials. The Janus laser at the Jupiter Laser Facility (LLNL) has been employed to drive pressures up to 50 GPa into thin foil targets composed of Fe and 0-25{\%} atomic composition of Ni. Targets have been prepared from meteorites harvested from Diablo Canyon and the Gibeon crater, as well as Fe-Ni synthesized to yield similar stoichiometry. A new target holder has been used to pre-heat/cool targets in the range of 77-600K. Line-imaging VISAR and X-ray diffraction are employed to provide measure of distinct features linked to the onset of stress relaxation as well as to examine the effects of impurities on the $\alpha $ - $\varepsilon $ phase transformation. In this poster, we present preliminary data of the effect of temperature and impurity content on the peak elastic state of Fe-Ni alloys under laser-driven shock compression.   

Shock Thermodynamics of Mantle Rocks: Rockport Fayalite

In order to address questions related to giant impacts and impact cratering on terrestrial planets, we need robust equations of state (EOS) and thermodynamic data for major mantle minerals (e.g., the olivine series and enstatite) and rocks under a wide range of pressure-temperature conditions. It is important to accurately characterize the amount of impact-induced heating that occurs in order to understand a range of planetary problems, including the mechanics of basin formation, the formation of the Martian crustal dichotomy, the origin of Earth's moon, and the depths of magma oceans on the early Earth during accretion. The long-term goal of this work is to develop comprehensive EOS for the most important mantle minerals for use in impact modeling and to understand the heterogeneous distribution of shock and post-shock temperatures in rocks. Here we present the results from new post-shock temperature experiments on fine-grained Rockport fayalite rock and comparisons to previous post-shock measurements on rocks and minerals. Multi-band pyrometry data indicate that the post-shock temperature field is very heterogeneous in Rockport fayalite. We observe multi-wave shock profiles with VISAR in the mixed-phase region on the Hugoniot, which have not been previously recognized.   

High Pressure Synchrotron X-ray diffraction and Raman Scattering Studies of Ammonium Azide

High-pressure in situ X-ray powder diffraction and Raman scattering studies on NH$_{4}$N$_{3}$ have been conducted up to 50.5 GPa and 48 GPa, respectively. The compressibility of orthorhombic phase is isotropic due to the orientation of azide anions. The hydrogen bonding weaken with increasing pressure due to the bending of N$-$H$\cdot\cdot\cdot$N bonding, leading to the increase of N$-$H stretch frequency and rotation of azide anions at \textit{2b} and \textit{4h} Wyckoff positions up to 2.9 GPa. The rotation of azide anions obviously influences the intermolecular interactions along $c$ axis in orthorhombic phase. The pressure induced phase transition involves a proximity of $a$ and $c$, temporally assigned as a reversible second-order orthorhombic-to-tetragonal transition. The bulk modulus of the orthorhombic phases are determined to be $K_{OT} = $ 24.5$\pm$3.5 GPa with $K_{OT}' = $ 3.4$\pm$3.2.   

A view on the functioning mechanism of EBW detonation - Part 1: Electrical Characterisation

This paper is the first of three characterising the initiation of PETN in an exploding bridgewire detonator to understand the underlying mechanism. The approach taken was to understand the transfer of energy through the system, beginning with the fireset / bridgewire interactions. The measurement of current, time to bridgewire burst and the transient voltage across the bridgewire at burst have enabled the determination of the energy used in bursting the bridgewire. This in turn has lead to the calculation of the energy efficiency of the fireset bridgewire system and an estimate of the energy delivered post bridgewire burst. It was postulated that this post-burst energy was responsible for the decrease in detonator function time as the firing energy is increased from threshold to all-fire levels. A fireset was designed to allow the post burst energy to be diverted away from the detonator, thus permitting the effect of the post burst energy on detonator function time to be quantified. The results of the experimental work will be presented, together with the implications for the initiation mechanism of PETN in an exploding bridgewire detonator.   

Shock Initiation Thresholds of Various Energetic Materials

Shock initiation threshold data for several energetic materials has been analyzed for both short-pulses and long, sustained shocks. In the limit of long duration shocks, the critical pressure for initiation is governed by the balance between chemical energy release in the vicinity of hotspots and thermal dissipation which cools the hotspot and can quench reactions. The observed trends in critical pressure from one material to the next are related to the thermophysical properties and chemical reaction kinetics of each material. Scaling analysis, combined with hydrocode simulations of collapsing pores has confirmed these trends; however large uncertainty in the reaction kinetics under shock loading prevents an accurate quantitative description of hotspot ignition. For a given pore diameter, scaling analysis allows a quick estimate of the temperature at which the reaction rate will exceed the rate of thermal dissipation. Using published thermophysical property data and reaction kinetics we found that the trend in critical hotspot temperatures for several common materials (e.g. PETN, HMX, HNS, and TATB) matches the observed trend in initiation sensitivity. The hydrocode simulations of pore collapse provide a link between the critical temperature and the initial shock pressure. For these simulations we have used recently published QMD-based equations of state for the fully-dense, crystalline phase and have included the effects of variable specific heat, viscous dissipation, and plastic work. These results will be presented and the need for physically-meaningful reaction rates will be emphasized.   

X-ray diffraction studies of Mg$_{2}$Si and Ag-doped Mg$_{2}$Si under pressure

The magnesium disilicide (Mg$_{2}$Si) is one of the thermoelectric material in 500-800 K temperature rage. The ${p}$- and ${n}$-Mg$_{2}$Si materials are necessary for the high-performance thermoelectric device, however Mg$_{2}$Si is ${n}$-type semiconductor and stable ${p}$-type Mg$_{2}$Si has not developed. Because it was reported that Ag-dope Mg$_{2}$Si was ${p}$-type Mg$_{2}$Si, we performed the X-ray diffraction studies of Mg$_{2}$Si and Ag-doped Mg$_{2}$Si under high-pressure at NE-5C beam line (PF-AR). Four samples which were a high-purity Mg$_{2}$Si powder, a mixture of Mg and Si powders, and Ag-doped these powders were papered. Mg$_{2}$Si decomposed with increasing temperature, and new peaks of MgO and SiO$_{2}$ appeared beyond 673 K. The Mg$_{2}$Si with Ag also decomposed and the oxide peaks appeared, and Ag peaks did not disappear. In the case of Mg and Si powder, Mg$_{2}$Si was synthesized at 573 K and Mg peaks disappeared with increasing temperature but MgO or SiO$_{2}$ peaks did not appeared. In the case of Ag-doped Mg and Si powder, Mg$_{2}$Si was synthesized at 523 K, and Ag peaks disappeared at 823 K and MgO or SiO$_{2}$ peaks did not also appeared. The result means the possibility of the synthesis of Ag-doped Mg$_{2}$Si under pressure.   

Model-Based Development of a Small-Scale Experiment for Non-Shock Ignition of High Explosives

We demonstrate a model-based approach for developing small-scale experiments for non-shock ignition of high explosives (HEs) that are representative of abnormal environmental conditions. While small-scale experiments are often favored over large-scale testing since costs are lower and samples sizes are amenable to early stage HE formulation, concerns remain about the ability to predict full-scale non-shock ignition response. Our approach is to perform simulations of full-scale systems (i.e., Skid test) to identify the localized material extrema states (e.g., pressure, pressure duration, shear stress, strain-rate) underlying the non-shock ignition mechanism. The extrema states then provide a metric for iterative model-based development of small-scale experiments using a drop-hammer system. We performed these simulations using the HERMES (High Explosive Response to MEchanical Stimuli) model in the multiphysics code, ALE3D. Optimized experimental geometries reach 10s MPa pressures over 1-3 ms durations while inducing a large degree of shear. The results of the experimental development and the effects of design variations on non-shock initiation response of Comp B will be presented.   

Equation of State for Detonation Product Gases

Based on the empirical linear relationship between detonation velocity and loading density, an approximate description for the Chapman-Jouguet state for detonation product gases of solid phase high explosives has been developed. Provided that the Gr\"{u}neisen parameter is a function only of volume, systematic and closed system of equations for the Gr\"{u}neisen parameter and CJ volume have been formulated. These equations were obtained by combining this approximation with the Jones-Stanyukovich-Manson relation together with JWL isentrope for detonation of crystal density PETN. A thermodynamic identity between the Gr\"{u}neisen parameter and another non-dimensional material parameter introduced by Wu and Jing can be used to derive the enthalpy-pressure-volume equation of state for detonation gases. This Wu-Jing parameter is found to be the ratio of the Gr\"{u}neisen parameter and the adiabatic index. Behavior of this parameter as a function of pressure was calculated and revealed that their change with pressure is very gradual. By using this equation of state, several isentropes down from the Chapman-Jouguet states reached by four different lower initial density PETN have been calculated and compared with available cylinder expansion tests.   

Effect of the oxygen balance on ignition and detonation properties of liquid explosive mixtures

The objective is to compare ignition and detonation properties of various liquid high explosives having negative up to positive oxygen balance (OB): nitromethane (OB \textless 0), saccharose and hydrogen peroxide based mixture (quasi nil OB), hydrogen peroxide with more than 90{\%} purity (OB \textgreater 0). The decomposition kinetic rates and the equations of state (EOS) for the liquid mixtures and detonation products (DP) are the input data for a detonation model. EOS are theoretically determined using the Woolfolk et al universal liquid polar shock law and thermochemical computations for DP. The decomposition kinetic rate laws are determined to reproduce the shock to detonation transition for the mixtures submitted to planar plate impacts. Such a model is not sufficient to compute open field explosions. The aerial overpressure is well reproduced in the first microseconds, however, after it becomes worse at large expansion of the fireball and the impulse is underestimated. The problem of the DP EOS alone is that it takes into account only the detonation, the secondary combustion DP -- air being not considered. To solve this problem a secondary combustion model has been developed to take into account the OB effect. The detonation model has been validated on planar plate impact experiments. The secondary combustion parameters were deduced from thermochemical computations. The whole model has been used to predict the effects of the oxygen balance on open air blast effects of spherical charges.   

The Deflagration of Energetic Crystals at Pressures above the Weak Shock Limit

The response of inert solid to shock loading may be divided into two regimes of contrasting behaviour. In the lower of these, the material deforms in a regime below the theoretical strength of the material where deformation is triggered at discrete flaws within the microstructure at grain boundaries, second-phase particles, or vacancies within the lattice at the higher pressures. There comes a point however, where the theoretical strength of the material is overcome and response becomes truly homogeneous behind the shock front and this point corresponds to the limit of weak shock behaviour within the crystal. Recent work of Zaug discussing burning rate of HMX as a function of pressure is reviewed and the onset of rapid deflagration is shown to commence as the WSL is exceeded. Implications for the shock response of energetic materials are discussed.   

Shock initiation sensitivity and Hugoniot-based equation of state of Composition-B obtained using \textit{in situ} electromagnetic gauging

Composition-B (Comp-B) is a solid cast explosive comprised of 59.5 wt {\%} cyclotrimethylene-trinitramine (RDX), 39.5 wt{\%} 2,4,6-trinitrotoluene (TNT), and 1 wt{\%} wax. Its initial density depends on formulation method and as a result, the detonation properties of Comp-B have generally been studied at densities of 1.69 g/cm$^{3}$ and 1.72 g/cm$^{3}$. The shock initiation sensitivity (Pop-plot) of Comp-B has been reported previously; obtained using both explosively-driven wedge tests and embedded manganin gauge techniques. We describe the results of a series of gas-gun-driven plate-impact initiation experiments on Comp-B ($\rho_{0} = $1.72 g/cm$^{3})$ using embedded electromagnetic gauges to obtain \textit{in situ} particle velocity wave profiles at 10 Lagrangian positions in each experiment. From the wave profiles, an unreacted Hugoniot locus, the run-distance-to-detonation, and initiation waveforms are obtained in each experiment. The results indicate that Comp-B at $\rho_{0} = $1.72 g/cm$^{3}$ is more sensitive than reported previously. Comparisons are made of the new Hugoniot states with an earlier Hugoniot-based EOS. Measurements of the detonation wave profile using photonic Doppler velocimetry are also presented and discussed in the context of ZND detonation theory.   

Pressure-Induced Irreversible Phase Transition in the Energetic Material Urea Nitrate

The behavior of energetic material Urea Nitrate ((NH$_{2})_{2}$COH$^{+}$ $\cdot$ NO$_{3}^{-}$, UN) has been investigated up to the pressure of $\sim$26 GPa. UN exhibits the typical supramolecular structure with uronium cation and nitrate anion held together by multiple hydrogen bonds in the layer. Both Raman and XRD data provide obvious evidence for the distorted phase transition in the pressure range $\sim$9--15 GPa. Further analysis indicates phase II has \textit{Pc} symmetry. The mechanism for the phase transition involves collapse of the initial 2D supramolecular structure to 3D hydrogen-bonded networks in phase \textit{Pc}. Importantly, the transition is irreversible and leads to a large reduction in volume on release of pressure. The density in phase \textit{Pc} has been increased by $\sim$11.8{\%} compared to the phase $P$2$_{1}$/$c$ under ambient conditions and therefore phase \textit{Pc} is expected to have much higher detonation power. This study opens new opportunities for preparing energetic materials with high density combining supramolecular chemistry with high-pressure techniques. Corresponding author. E-mail: zoubo@jlu.edu.cn Reference: JPCC. 2013, 117, 152.   

Comparison of Internal-Blast Explosive Performance in Small- and Large-Scale Tests

Small-scale internal blast measurements were correlated with large-scale test data. Highly confined small explosive samples \textless 0.5 g were subjected to the output from a PETN detonator while enclosed in a 3-liter chamber. Large-scale tests up to 22.7 kg were generally unconfined and shot in a 180-m$^{\mathrm{3}}$ chamber. When sample mass was expressed as total sample energy/chamber volume, theoretical peak quasi-static blast pressures for both small and large-scale tests fell on the same curve. Blast explosives may comprise high levels of fuels and reactive materials to enhance or control the release of energy, and may be insensitive and slow-reacting, with performance that may not scale well to small size tests. High confinement of a small sample can compensate for low sensitivity, but at the expense of heat loss to the metal confinement. This heat loss can be measured to improve the correlation between large and small-scale measurements, unless the released energy becomes too low to sustain complete reaction of the sample, either with itself or with air in the chamber.   

Features of the Valorization of Single and Double Based Powders for Codetonation in Emulsion Explosives

In this work, features of the thermal and detonation behavior of compositions resulting from the mixture of single and double based gun powder within ammonium nitrate (AN) based emulsion explosives are shown. That includes results of thermodynamic-equilibrium calculations of the detonation velocity, the chemical compatibility assessment through differential scanning calorimetry [DSC] and thermo gravimetric analysis [TGA], the experimental determination of the detonation velocity and a comparative evaluation of the shock sensitivity using a modified version of the ``gap-test''. DSC/TGA results for the compositions and for the individual components overlap until the beginning of the thermal decomposition which is an indication of the absence of formation of any new chemical specimens and so of the capability of the composition components. After the beginning of the thermal decomposition it can be seen that the rate of mass loss is much higher for the compositions with gun powder than for the sole emulsion explosive. Both, theoretical and experimental, values of the detonation velocity have shown to be higher for the powdered compositions than for the pure emulsion explosive. Shock sensitivity assessment have ended-up with a slightly bigger sensitivity for the compositions with double based gun powder when compared to the single based compositions or to the pure emulsion.   

The Shock Response of Space Bears: The Ability of Life to Survive Some of the Most Extreme Environments Known to Man

There have been many recent discoveries of life forms living in environments previously thought to be completely uninhabitable. One particularly interesting discovery of this na- ture is the space bear or tardigrade. The name space bear is a colloquialism applied to the tardigrades because of a recent investigation which saw them being exposed to the vacuum of space and intense solar radiation, and surviving. Tardigrades have the ability to dehy- drate themselves, entering a state called cryptobiosis. This state enables them to survive in the vacuum of space. A single stage gas gun has been employed to uniaxially shock load and subsequently recover tardigrades in both regular and cryptobiotic states. Loading histories were calculated via hydrocode modelling. Survival data is presented comparing shocked and control samples for tardigrades both in normal and cryptobiotic states.   

Mechanical response of porcine skin under compression from low to high strain rates

Uniaxial compression experiments were performed on fresh porcine skin samples at different strain rates to study the stress-strain response. Low strain rate experiments were performed with an Instron 5566, while high strain rates were achieved using a Split Hopkinson Pressure Bar system. Magnesium bars and semiconductor strain gauges were used respectively to maximize the signal transmission from porcine skin to the output bar and to allow the signal measurement. Skin samples were harvested from different area of the animal to investigate the heterogeneity of such material. The experimental results showed that the mechanical response of skin in compression is strongly dependent on the strain rate of loading and on the location from which the samples were collected. Specimens collected from the rump showed a stiffer response compared to samples harvested from the thigh. Finally, a histological analysis of the samples post compression was carried out to examine the extent of tissue damage as a function of strain rate.   

Cylindrical shock waves and dynamic phenomena induced in solids by intense proton beams

The accidental impact of hadron beams on matter can induce intense shockwaves along with complex dynamic phenomena (phase transitions, extended density changes, explosions and fragment projections). These events have been successfully modeled resorting to wave propagation codes; to produce accurate results, however, these programs require reliable material constitutive models that are often scarce and inaccurate. A complex and innovative experiment was carried out at CERN to benchmark existing material constitutive models and possibly derive new ones. The test setup, aimed at the characterization of six different materials impacted by 440 GeV intense proton pulses, allowed to generate cylindrical shockwaves on material specimens and to observe the effects induced by their propagation. This method, a combination between numerical simulations and an experimental technique, permitting to tune the intensity, location and timing of the beam-deposited energy, may allow to study the effects induced by internal, quasi-instantaneous loadings in domains well beyond particle physics (accidents in nuclear facilities, internal explosions, high pressure blasts etc.), particularly when relatively little explored cylindrical shockwaves are generated.   

Strength and Sintering Effects at Ejection of Explosively Driven Sand

A description of sand response to extreme loads is very important for the evaluation of the sand ejecta effects to civilian and military targets. Sand is a complex material to simulate because of its porosity. With porous materials it is very hard to achieve the inter-phase equilibrium in shock waves. A previously developed two-phase model with strength has been implemented in CTH and applied to quartz sand. It has been shown that the Hugoniot abnormality known from the literature for highly porous silica is adequately described with the material non-equilibrium approach. Several models available in CTH may describe the flash X-ray observations available in the literature for the sand ejecta due to explosion of buried charges. However, a test-calculation divergence is noticeable when considering different burial depths. This is attributed to the material property variations due to the thermal sintering effects of the sand particles. Dynamic flash X-ray observations of aluminium plates loaded by ejected sand have been conducted, which has confirmed the material property variations in the ejected material. CTH calculations with a sintering kinetic implemented in the two-phase model improve description of the present tests and the sand ejecta tests at different burial depths.   

Impact on porous targets: penetration, crater formation, target compaction and ejection

Using a granular-mechanics code, we study the impact of a sphere into a porous adhesive granular target, consisting of monodisperse silica grains. The model includes elastic repulsive, adhesive and dissipative forces, as well as sliding, rolling and twisting friction. Impact velocities up to 30 m/s, and target filling factors (densities) between 19{\%} and 35{\%} have been systematically studied. We find that the projectile is stopped by an effective drag force which is proportional to the square of its velocity. Target adhesion influences projectile stopping only below a critical velocity, which increases with adhesion. The penetration depth depends approximately logarithmically on the impact velocity, and is inversely proportional to the target density. The excavated crater is of conical form and is surrounded by a compaction zone, whose width increases, but whose maximum value decreases with increasing target density. Grain ejection increases in proportion with impactor velocity and the angular distribution of the ejecta has a maximum around 45 degrees respect to the surface normal.   

An overview on the effect of manufacturing on the shock response of polymers

Polymers are widely employed in areas as diverse as consumer goods and explosives (matrix materials). The consequent commercial interest has led to a continual drive to improve material properties - e.g. via either manufacturing techniques or more fundamental improvements in the understanding of the underlying chemistry. It has been shown previously that chemical compositions can affect the shock profile of the polymer Poly-Methyl Methacrylate (PMMA). To this end the composition will change over time as new formulations are brought to market, for example due to the inclusion of additives that will increase the lifetime of the product. Significantly such changes may not affect the material properties at lower strain rates. At the higher strain rates these subtle difference can lead to larger discrepancies in the shock profiles. In this study comparisons of PMMA have been made between newly sourced and ``legacy'' material studied previously in the literature.   

Experimental study on shear failure of polypropylene under shock loading

The impact response of crystallized polypropylene under combined compression and shear loading was studied by using the inclined gas gun and the IMPS system. The experimental results show that the transverse wave velocity increases nonlinearly with the impact velocity, indicating that its shear behavior is strongly related to the hydrostatic pressure. Remarkable shear wave attenuation occurs near the impact surface when the impact velocity and inclination angle reach the critical value. The micro-observation of recovered samples with a polarized optical microscope reveals that there exists a melting layer of about 2-3 $\mu$m thick, i.e. adiabatic shear failure layer, very near the impact surface (about 5$\mu$m) which causes the shear wave attenuation.   

Shock Properties of Anisotropic Polymers

The effect of anisotropy in polymer materials caused by the alignment of polymer chains during manufacture and processing has been previously investigated at low strain rates by multiple authors, however the effect of molecular orientation at higher strain rates and shock loading is an area of active research. This work presents experimental results on the effect of molecular orientation on shock propagation in polycarbonate. The Us -- Up Hugoniot has been measured for varying degrees of chain alignment. Polycarbonate is an amorphous polymer which does not exhibit cross-linking, allowing the study and modeling of the material to be simplified. Birefringence is used to study the initial anisotropy of the material before loading. During loading optical techniques are used to characterize shock behavior, namely line VISAR, Het-V/PDV and high-speed imaging. The influence of chain orientation on birefringence will be discussed, in particular the effectiveness of high speed imaging in conjunction with birefringence as a method of qualitatively analyzing shock induced anisotropy in optically transparent polymers.   

Rate Dependent Shear Failure and the Scaling Effect in Long Rod Penetration

Long rod penetration tests show a scaling effect that cannot be explained by rate dependent strength. We propose here that this scaling effect may be explained by rate dependent failure. We start by revisiting the well known result, that long rod penetration efficiency depends on the strain to failure of both projectile and target materials. We then make the strain to failure depend on strain rate, using the overstress concept. In this way the effective strain to failure increases with strain rate. As strain rate increases with decreasing scale, we get that penetration efficiency decreases with decreasing scale, as observed in tests. In the paper we show results of hydrocode runs that demonstrate the relation between strain rate sensitivity of the strain to failure, and the scaling effect in long rod penetration.   

Modeling Combined Tension-Shear Failure of Ductile Materials

Failure of ductile materials is usually expressed in terms of effective plastic strain. Ductile materials can fail by two different failure modes, shear failure and tensile failure. Under dynamic loading shear failure has to do with shear localization and formation of adiabatic shear bands. In these bands plastic strain rate is very high, dissipative heating is extensive, and shear strength is lost. Shear localization starts at a certain value of effective plastic strain, when thermal softening overcomes strain hardening. Shear failure is therefore represented in terms of effective plastic strain. On the other hand, tensile failure comes about by void growth under tension. For voids in a tension field there is a threshold state of the remote field for which voids grow spontaneously (cavitation), and the material there fails. Cavitation depends on the remote field stress components and on the flow stress. In this way failure in tension is related to shear strength and to failure in shear. Here we first evaluate the cavitation threshold for different remote field situations, using 2D numerical simulations with a hydrocode. We then use the results to compute examples of rate dependent tension-shear failure of a ductile material.   

Evolution of shock compression waves in a SiC ceramic

The objective of this study was to estimate possible contribution of stress relaxation into the response of hard ceramic materials to high-rate compression and tension. With this goal, the free surface velocity histories have been measured for plane SiC ceramic samples of 3.07 g/cm$^{\mathrm{3}}$ density subjected to impact by a flyer plate. The sample thickness was varied from 0.5 mm up to 8.3 mm. The peak shock stress was in a range of 17.9 - 21.9 GPa. The Hugoniot elastic limit (HEL) is in a range of 8.34 to 8.72 GPa for this material, the spall strength value is 0.5 to 0.62 GPa. Both the HEL and the spall strength are in reasonable agreement with literature data for SiC ceramics of corresponding density. Measurements have not revealed any decay of the elastic precursor wave. Moreover, it has been found the evolution of the compression wave is practically self-similar and is well described by the simple wave approach. It follows from these observations the stress relaxation does not provide significant contribution into the response of hard ceramic materials to shock-wave loading. The ramped transition from elastic to plastic wave is caused by strain hardening of the material and by successive involving of grains of various orientations into the inelastic deformation process.   

Numerical-theoretical analysis of destruction of liquid drop under effect of air shock wave

Direct numerical simulation of liquid fragmentation in gas flow is rather complicated. It is caused by the need for specifying a large number of points, and, therefore, use of superpower computers. On the other hand, surface tension is the characteristic, which determines drop sizes. It is very difficult to simulate this characteristic in calculations. When using the presently available techniques, numerical calculations reproduce some moments of interaction between liquid and air shock wave only at the qualitative level. However, these calculations allow obtaining the change of strain rate average in drop volume versus time, and finally estimating the average particle sizes. We performed similar calculations for drops with different initial diameters. It allowed estimating the influence of scale effect on average size of particles and their final distribution in sizes. Results of the numerical-theoretical investigations are compared to results of experiments, which were performed in VNIIEF.   

Probabilistic Approach to Numerical Simulation of Fracture

The natural heterogeneity of real materials structure influencing on distribution of material physicomechanical characteristics (PMC) is one of the factors determining character of destruction. The introduction of the given factor in the equations of mechanics of a deformable solid is possible at use probabilistic laws of distribution PMC on volume of a considered design. There are problems where the fragmentation is mainly probabilistic process: explosive destruction axisymmetric shells where character of blasting fragmentation are beforehand unknown. Determining influence of heterogeneity of material structure is shown as well in problems punching thin barrier. In order that simulated process of a fragmentation reflected a real picture of behavior of the destroyed bodies, it is necessary to bring in casual distribution of initial deviations strength properties from rating value to PMC of a body. In work the explosive fragmentation of the shells, a fragmentation of a barrier and an shell after barrier piercing, punching thin barrier on a normal and under an angle, crushing of metal rings, process of high-speed impact of the laminated - spaced barrier with the steel spheres is considered.   

Intragranular fracture and frictional effects in granular materials under pressure-shear loading

Research efforts have been undertaken in recent years to investigate the dynamic behavior of granular materials. Many of the investigations have been experimental in nature, consisting of several rounds of Kolsky bar tests on sand with varying moisture content and confining pressures as well as traditional plate impact. More recently, pressure-shear experiments on both sand and granular tungsten carbide have been performed. In order to investigate the mesoscale physics that affect the bulk response observed in experiments, we have undertaken a computational simulation effort. The simulations are conducted using a massively parallel computational peridynamics code capable of modeling many thousand individual grains at high resolution resulting in simulations that consist of several million degrees of freedom. Individual intragranular fracture and discrete contact with friction are modeled explicitly in the simulations. Thus, these simulations treat aspects of the problem that were not represented well in previous mesoscale simulations with Eulerian hydrocodes. Results from these simulations are compared with results from pressure-shear experiments on sand and granular tungsten carbide. A discussion of the effects of fracture and friction on force chain formation and bulk wave propagation in the samples is included.   

Molecular Dynamics Modelling of Laser-Pulse Compression of a Ta single crystal with dislocations

The nanoindentation of a defect-free Ta [001] single crystal is studied by Molecular Dynamics simulations. The potential by Li et al [PRB 67 (2003)], an EFS potential [J Phys Condens Matter 18(2006)], and a recent EAM potential by Ravelo et al [AIP Conf Proc 1426 (2012)] are tested and their results analyzed in terms of dislocation slip planes. Dislocations emitted from the indented zone interact forming prismatic loops. The Ta dislocated structure is then subjected to shock compression induced by a piston hitting the sample at various speeds. The shock-induced dislocation generation and motion mechanisms are studied in order to compare to on-going experiments.   

Dynamic Fracture of Borosilicate Glass with Plasma Confinement geometry in Pure Water by Laser-induced Shock Wave

In order to characterize dynamic fracture of borosilicate glass, we performed laser-shock-experiments of both an aluminum-ablator mounted glass and a glass with plasma confinement geometry in pure water by Q-switched Nd$^{3+}$:YAG laser. The incident beam with 440 mJ were focused onto the target approximately 300 $\mu $m in diameter. The dynamic fracture of the glass targets is observed with high-speed digital framing-camera photography. For the aluminum-ablator mounted glass, propagation of the shock wave in water was observed, and the shock-wave velocity is obtained to be 1.65 $\pm$ 0.02 km/s using image processing. Shock-pressure applied the target is estimated to be 180 MPa by Hugoniot relation. For the glass with plasma confinement geometry, generation of the micro-fragments from the rear side of the target was observed. This result indicates that shock-induced fragmentation by laser irradiation is enhanced by the plasma confinement effect. The soft-recovered fragments are separated according the size with PET mesh having deferent mesh size. As a result, the glass with plasma confinement geometry generated smaller fragment than the aluminum-ablator mounted glass.   

Study on the selectivity of damage nucleation at the boundaries of ductile metal

Voids nucleation is the first stage of fracture in ductile materials. The location and number of nucleation is the key to predict when and where the fracture will take place. Studies show that the nucleation mainly occurs at the grain boundaries in high-purity polycrystalline metals. However, the nucleation and growth does not occur uniformly. This project seeks to test the response of large-grain polycrystalline metal samples with different grain boundary structure under the same loading conditions and then recovers the samples. The resulting tensile damage in the recovered samples is examined by optical, electronic backscatter diffraction analysis of the technology (EBSD), and transmission electron microscopy (TEM). The distribution and mechanism of the nucleation will be studied at different grain boundaries, and a nucleation model will be established for finite element analysis, which can be used to predict the damage nucleation at complex grain boundary conditions (including textured polycrystalline). Finally, the result will be verified by experiment.   

Spall and Damage Behavior of Intrinsically-Reinforced Bulk Metallic Glass Composites

We have performed uniaxial-strain plate-impact experiments to study the strength and spall damage of bulk metallic glass-matrix composites (BMGMCs). BMGMCs counteract the brittle nature of monolithic BMGs through in-situ formed crystalline dendrites which increases toughness and ductility. Applications for micrometeoroid shielding, kinetic energy penetrators (KEP) and armor shielding raises the question of the dynamic stability of BMGMCs. Multicomponent Ti-based BMGMCs were investigated using uniaxial-strain plate-impact experiments to examine the phase stability of the dendrite-reinforced BMGMCs under high pressure and their high strain-rate deformation and failure response. The experiments involve impact of 303 stainless steel flyer plate on 303 stainless steel sample holder containing two BMGMC samples at varying velocities. The Hugoniot Elastic Limit (HEL) and the spall strength of the BMGMC samples was determined using velocity interferometry system for any reflector (VISAR). Post-mortem microstructural characterization is done the on the recovered sample and correlated with the measured damage response. The results obtained to date will be presented.   

Strength and destruction of flat ampoules during shock--wave tests

Devices with nondestructive plane ampoules which permit testing specimens with volume up to 35 cm$^{3}$ under different conditions of explosive action with the intensity up to 100 GPa included are developed. Strength properties of ampoules made of different steels are evaluated under dynamic loading. These devices and ampoules are used for study of physical and chemical processes, which occur in substances under pulse effects of high strain rate, pressures and temperatures. The most promising materials are determined. Schemes are presented for flat recovery ampoule and loading devices required for providing the following loading conditions: 10 GPa $\le $ P $\le $ 100 GPa; 0.5 $\mu $s $\le \quad \tau \quad \le $ 5 $\mu $s. Peculiarities are described for application of the considered recovery ampoules: \begin{itemize} \item to test samples, which undergo volume reduction; \item to test fusible samples; \item to test samples when loading by oblique shock wave. \end{itemize}   

On the importance of the 7.62 mm FFV bullet jacket during penetration

While a critical part of the bullet structure, relatively little attention has traditionally been paid to the effects of the jacket during penetration. Recent work has suggested that the jacket of a 7.62 mm FFV projectile measurably affects penetration into ceramic-faced targets. In this study a series of both forwards and reverse ballistics shots employing 7.62 mm FFV rounds accelerated into at c.a. 830 m/s (and vice-versa) were undertaken. The various FFV rounds were prepared with differing degrees of jacket modification about their tip. Penetration mechanisms were interrogated using a multi-channel flash X-ray system; while a series of depth-of-penetration tests provided a route to quantitatively assess the contribution of the jacket to penetration.   

A study of the elastic precursor in thin Zr and Ta foils

The evolution of the elastic precursor with strain rate and distance contains rich information regarding the origins of yielding under intense dynamic loading. Such information is necessary for the development of new dislocation-based strength models. In this work we extend study of elastic precursor behavior in zirconium and tantalum foils down to 25 $\mu$m to address the role of reduced thickness and crystal symmetry on the kinetics of stress relaxation. Using a newly constructed mesoscale gas launcher, high purity Zr and Ta targets ranging in thickness from 6 mm down to 25 $\mu$m have been impacted at velocities of $\sim$500 m/s. A combination of line-imaging VISAR and frequency-shifted PDV were employed to measure the particle velocity at a windowed interface. Features of the elastic precursor in the breakout profiles, such as the peak elastic state and yield drop, were used to infer the kinetics of incipient relaxation processes. In future work, these results will be used to further validate the D3P code currently under development.   

Monte Carlo calculations of liquid metals surface tension

Large scale molecular dynamics (MD) simulations have been performed in our group to study and to model the ejecta production from the dynamic fragmentation of shock-loaded metals under melt conditions. Those microscopic simulations show that the modeling of such phenomena using hydrodynamic codes will imply the understanding of the physics occurring at the surface of the liquid fragments. Thus, it appears that surface tension will be one of the overriding properties to be taken into account in the hydrodynamic codes. As a consequence, we report here Monte Carlo calculations of surface tension of liquid metals using both mechanical and thermodynamic approaches.   

Atomistic Mechanism of Plastic Deformation During Nano-indentation of Titanium Aluminide

The mechanisms governing defect nucleation in solids are of great interest in all material science branches. Atomistic computer simulations such as Molecular Dynamics (MD), has been providing more understanding of subsurface deformations, bringing out details of atomic structures and dynamics of defects within the material. In the present work we show the first simulation measurements within an atomistic resolution of the mechanical properties of titanium aluminide intermetallic compound (TiAl), which is a promising candidate for high temperature applications with remarkable properties, such as: attractive combination of low density, high melting temperature, high elastic modulus, and strength retention at elevated temperatures, besides its good creep properties. Through calculations of local pressure, local shear stress and spatial rearrangements of atoms beneath the indenter, it was possible to quantify the indentation damage on the structure. We have founded that prismatic dislocations mediate the emission and interaction of dislocations and the activated slip planes are associated with the Thompson tetrahedron. Furthermore, using the load-penetration depth response, we were able to estimate the elastic modulus and the hardness of the TiAl alloy. All our findings are in well agreement with experimental results.   

Theoretical determination of anisotropic thermal conductivity for crystalline 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)

Bond stretching and three-center angle bending potentials have been developed to extend an existing rigid-bond TATB molecular dynamics (MD) force field (FF) for simulations requiring fully flexible molecules. The FF potentials were fit to experimental vibrational spectra and electronic structure predictions of vibrational normal modes and frequencies using a combination of zero Kelvin eigenmode analysis for the isolated molecule and finite-temperature power spectra for the isolated molecule and bulk crystal. Crystal structures computed using the revised FF are in good agreement with results from other computational models and experimental data. A non-equilibrium MD method was used to obtain the room temperature, atmospheric pressure thermal conductivity along three directions in a well-defined, non-orthogonal basis. The thermal conductivity was found to be significantly anisotropic with values of 1.13 $\pm$ 0.07, 1.07 $\pm$ 0.07 and 0.65 $\pm$ 0.03 W m-1 K-1 for directions nominally parallel to the a, b, and c crystal directions, respectively.   

High pressure XAS and XMCD studies on the ODE beam line at SOLEIL

X-ray Absorption Spectroscopy (XAS) is a very useful probe to obtain local information in materials science. It is suitable for a variety of compounds, since a long-range order is not required. Matsushita has been the first to propose an alternative to the classical method of recording absorption spectra: the dispersive set-up. Instead of scanning the energy step by step, only one crystal is used and bent in such a way that it directly opens an energy range and focuses the beam. Since then, a few beam lines have been developed on this idea, the ODE beam line of the SOLEIL Synchrotron is one of them. Absorption measurements using this set-up present the advantages to be very fast (down to a few $\mu$s) and very stable, since no mechanical movements are required. These characteristics make the dispersive XAS technique suitable for investigating small samples, following kinetics and measuring small signal to noise ratio (down to 10$^{-5})$. Thanks to its focusing optics, the dispersive set-up is very well adapted to high pressure, the sample chamber being typically of about 100$\mu$m in diameter and 20 $\mu$m in thickness. Moreover, the ODE beam line is built on a bending magnet allowing a circular polarization of the beam, hence providing X-ray Magnetic Circular Dichroism (XMCD) measurements. In this poster, we will present some XMCD and fast kinetic results recently obtained and the last improvements of the ODE beam line.   

Methods for processing experimental data in microwave diagnostics of shock waves and detonation

Microwave interferometry is a promising method of unperturbing diagnostics of short-time processes. It is a bit less effective than the optical methods in accuracy, but it provides a researcher with more capabilities, in particular, for measurements in optically opaque media. The classic methods for processing experimental interferograms using extremums allow to obtain data on motion of investigated objects with the resolution of a quarter of wavelength of probing radiation. It is insufficient for majority of practical applications. Use of the mathematical methods for processing output signals of the receiver allows to improve the method resolution significantly and to obtain motion measurement errors of 0.05\textellipsis 0.1 of wavelength or even less. This paper presents schemes of conduction and brief description of the methods for processing a series of tests, which were performed in RFNC-VNIIEF with use of radio interferometer having length of wave of probing radiation $\lambda =$3.2$_{\mathrm{~}}$mm, namely: \begin{itemize} \item to measure velocity of stationary detonation; \item to measure depth of detonation initiation by shock wave; \item to investigate shock compressibility of dielectric materials; \item to investigate dynamics of constructions. \end{itemize}   

Advanced target configurations for gigabar equation of state experiments at the National Ignition Facility

The initial version of the converging-shock equation of state (EOS) platform demonstrated at NIF used a configuration based as closely as possible on inertial confinement fusion (ICF) targets. The success of this platform and the accuracy of the design simulations gives confidence that future experiments can be more flexible in both the hohlraum and target configurations. Changes in the target will enable significant improvements in EOS measurements. The first targets used a proven ICF ablator design, and the sample was a uniform sphere of CH-based plastic. As well as optimizing designs for other sample compositions, we are developing methods of fabricating samples with buried radiographic marker layers--a narrow layer with a high-Z dopant--using direct ink writing and electrophoretic deposition. The incorporation of multiple marker layers is an important step forward in converging shock experiments. The particle speed can be measured directly as the shock passes, and an average compression and opacity can be determined directly from the separation between markers and local x-ray attenuation. The markers can also be used to improve the precision of the radiographic unfold used to reconstruct the spatial dependence of the compression and opacity profiles.   

High-pressure and high-temperature mineral-fluid interface cell for high-resolution x-ray reflectivity measurement

Ordering of water at the mineral-fluid interface is a fundamental process governing mineral hydration, ion-adsorption, dissolution, growth, and charge transfers across the mineral surface. However, the influence of pressure and temperature on this fundamental process is still largely unknown. The experimental determination is limited due to the lack of a sample cell which can properly handle the pressure and temperature of the fluidic component and simultaneously allow measurement of the interfacial structure, e.g., by high-resolution x-ray reflectivity. We recently developed a new high-pressure and high-temperature mineral-fluid interface cell to achieve the high-resolution x-ray reflectivity measurement from single crystalline mineral surfaces under the PT conditions of fluid up to $\sim$750 K and $\sim$40 MPa. The interfacial structures at single crystal mineral surfaces interacting with various hydrothermal fluids will promote our understanding of the molecular aspects of hydrous alteration processes of rocks in deep Earth environments. The application can be extended to mineral surface sciences, geological carbon sequestration, and nuclear engineering.   

Explosive Welding of Pipes

For connection by welding it is suggested to use the explosive welding method. This method is rather new. Nevertheless, it has become commonly used among the technological developments. This method can be advantageous (saving material and physical resources) comparing to its statical analogs (electron-beam welding, argon-arc welding, plasma welding, gas welding, etc.), in particular, in hard-to-reach areas due to their geographic and climatic conditions. Explosive welding of cylindrical surfaces is performed by launching of welded layer along longitudinal axis of construction. During this procedure, it is required to provide reliable resistance against radial convergent strains. The traditional method is application of fillers of pipe cavity, which are dense cylindrical objects having special designs. However, when connecting pipes consecutively in pipelines by explosive welding, removal of the fillers becomes difficult and sometimes impossible. The suggestion is to use water as filler. The principle of non-compressibility of liquid under quasi-dynamic loading is used. In one-dimensional gasdynamic and elastic-plastic calculations we determined non-deformed mass of water (perturbations, which are moving in the axial direction with sound velocity, should not reach the layer end boundaries for 5-7 circulations of shock waves in the radial direction). Linear dimension of the water layer from the zone of pipe coupling along axis in each direction is $\ge $ 2R, where R is the internal radius of pipe.   

Textile dry cleaning in high pressure CO$_{2}$

High-pressure carbon dioxide (CO$_{2})$ is one of the most suitable replacements for perchloroethylene (PER), a common but harmful textile dry cleaning solvent. Previous studies have indicated that the particulate soil removal with CO$_{2}$ is lower compared to that with PER, because of the lesser amount of mechanical action in CO$_{2}$. Furthermore, there is a lack of understanding of textile-dirt-CO$_{2}$ interaction. It is the objective of this study to get an insight in the mechanical forces that play a role in CO$_{2}$ dry cleaning and to use this information to improve the CO$_{2}$ washing performance. Various mechanical actions were investigated with the experiments in an \textit{in-situ} high pressure observation cell. Textiles stained with different kinds of particulate soils were washed in CO$_{2}$. The washing results show that the combination of rotating and vertical action gives the highest cleaning performance and liquid CO$_{2}$ spray may be a suitable additional mechanism to increase the cleaning performance.   

Combined Laser Ultrasonics, Laser Heating and Raman Scattering in Diamond Anvil Cell System

We developed a unique and multifunctional in-situ measurement system under high pressure equipped with laser ultrasonics system,\footnote{N. Chigarev, P. Zinin, M. Li-Chung, G. Amulele, A. Bulou, V. Gusev, Appl. Phys. Lett. \textbf{93}, 181905 (2008).} Raman device, and laser heating system (LH-LU-DAC) at the University of Hawaii. The system consists of four components: (1) LU-DAC system (probe and pump lasers, photodetector, and oscilloscope); (2) a fiber laser (1064 nm), which is designed to allow precise control of the total power in the range from 2 to 100W by changing the diode current, for heating samples; (3) a spectrometer for measuring the temperature of the sample (using Black body radiation), fluorescence spectrum (spectrum of the ruby for pressure measurement), and Raman scattering measurements inside DAC under high pressure and high temperature (HPHT) conditions; and (4) an optical system for focusing laser beams (pump, probe, and 100W CW lasers) on the sample in DAC and for imaging a sample inside the DAC. The system allows us to: (a) measure acoustical properties of materials under HPHT; (b) synthesize new phases under HPHT; and (c) measure Raman scattering under HPHT conditions for detection of phase transition.   

Use of Microwave Technique for Study of Isentropic Detonation Products Expansion

Application of the microwave technique for research of explosives and their detonation products can give a number of advantages as compared to the other experimental techniques. This technique makes it possible to perform a continuous recording of the shock and detonation waves motion directly in explosive. A significant advantage of the technique consists in absence of influence on investigated process, because there are no any sensors, optic fiber etc. in an explosive volume. The microwave technique was used for isentropic detonation products expansion study of HMX/TATB-based explosive compound. For determination of states on the expansion adiabat of detonation products, the experimental series was conducted. In these experiments we recorded time dependences of the shock wave velocities in dielectric microwave-transparent barriers, which were in contact with explosive samples. A low power 94 GHz quadrature interferometer was used. The conducted experiments showed that the use of microwave technique gives a big amount of interesting experimental data with a considerable research simplification.   

Finite Element Based Optimization of Material Parameters for Enhanced Ballistic Protection

The threat imposed by terrorist attacks is a major hazard for military installations, vehicles and other items. The large amounts of firearms and projectiles that are available, pose serious threats to military forces and even civilian facilities. An important task for international research and development is to avert danger to life and limb. This work will evaluate the effect of modern armor with numerical simulations. It will also provide a brief overview of ballistic tests in order to offer some basic knowledge of the subject, serving as a basis for the comparison of simulation results. The objective of this work is to develop and improve the modern armor used in the security sector. Numerical simulations should replace the expensive ballistic tests and find vulnerabilities of items and structures. By progressively changing the material parameters, the armor is to be optimized. Using a sensitivity analysis, information regarding decisive variables is yielded and vulnerabilities are easily found and eliminated afterwards. To facilitate the simulation, advanced numerical techniques have been employed in the analyses.   

Peculiarities of spall fracture of beryllium

Authors of this work performed investigations of spall fracture in a beryllium sample with diameter 90 mm and thickness 20 mm when loading HE charge made of TG 5/5 with thicknesses of 12 and 100 mm, HMX with thickness of 100 mm by detonation wave. Spall fracture was formed in the sample during its release into air gap. Laser interferometer Visar was used to measure velocity profile at the free boundary, thickness of the spall layer was measured by the technique of two-frame pulse X-ray radiography, the manganin gauge technique was used to measure profile of the shock-wave pulse in the fluoroplastic base when decelerating the beryllium spall layer, the technique of electrocontact gauge was used for determination of location of the spall layer at two times. When TG 5/5 thicknesses were 12 and 100 mm, it was revealed that the spall layer thickness, which was measured after its traveling the distance of 8 mm, was nearly unchanged. It was equal to 1.8 and 2.1 mm, respectively. It was observed in the test with a charge made of HMX that, depending on traveled distance \textbf{x}, thickness of the spall layer $\delta$ under the condition of absence of tensile stresses is continuously decreasing.