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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Magnetism in Solid Oxygen Studied by High-Pressure Neutron Diffraction

This article reviews progress achieved over the last ~ 15 years in our understanding of magnetism in solid oxygen under high pressure with a particular emphasis on the contribution of neutron diffraction in the multi-GPa range. The paper highlights the unexpected complexity of magnetic structures in the δ phase at 5–8 GPa, presents data on the pressure dependence of diffuse scattering in β-O{sub 2} and discusses potential magnetism in ε-O{sub 2}. High-resolution diffraction data of all three solid phases at ambient pressure are presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

A directional microcrack damage theory for brittle solids based on continuous hyperplasticity

We present a novel microcrack-damage theory for brittle solids under compression. Instead of using internal variables like zeroth, second or fourth rank damage tensors, the state of material damage is represented by an internal function that encapsulates the information of direction, density and size of microcracks. Just like other internal variables, the evolution of this state function must obey the second law of thermodynamics for arbitrary loading paths. This is done by casting the model in the framework of continuous hyperplasticity and enforcing a non-negative dissipation rate functional. The proposed framework offers predictions on the continuous evolution of microcrack density and the induced material anisotropy along with the macroscopic stress-strain curves. The use of continuous damage function grants the model significantly enhanced resolution in characterizing the direction-dependent response of cracked solids compared to classical models that are based on damage tensors. Two scenarios are considered in developing the theory, one assumes frictionless cracks and the other incorporates friction between crack surfaces. The results highlight that inelasticity, pressure dependence, and loading-unloading hysteresis exhibited by brittle solids are natural consequences of frictional microcracks. The proposed theory offers a generic and versatile framework to upscale micromechanical processes operating at individual crack scale to explain the macroscopic behavior of cracked solids.

Materials Science↗
DOE OSTI2023

Automated reaction kinetics and network exploration (Arkane): A statistical mechanics, thermodynamics, transition state theory, and master equation software

The open-source statistical mechanics software described here, Arkane–Automated Reaction Kinetics and Network Exploration–facilitates computations of thermodynamic properties of chemical species, high-pressure limit reaction rate coefficients, and pressure-dependent rate coefficient over multi-well molecular potential energy surfaces (PES) including the effects of collisional energy transfer on phenomenological kinetics. Arkane can use estimates to fill in information for molecules or reactions where quantum chemistry information is missing. The software solves the internal energy master equation for complex unimolecular reaction systems. Inputs to the software include converged electronic structure computations performed by the user using a variety of supported software packages (Gaussian, Molpro, Orca, TeraChem, Q-Chem, Psi4). The software outputs high-pressure limit rate coefficients and pressure-dependent phenomenological rate coefficients, as well as computed thermodynamic properties (enthalpy, entropy, and constant pressure heat capacity) with added energy corrections. Some of the key features of Arkane include treatment of 1D, 2D or ND hindered internal rotation modes, treatment of free internal rotation modes, quantum tunneling effect consideration, transition state theory (TST) and Rice-Ramsperger-Kassel-Marcus (RRKM) rate coefficient computations, master equation solution with four implemented methods, inverse-Laplace transform of high-pressure limit rate coefficients into the energy domain, energy corrections based on bond-additivity or isodesmic reactions, automated and efficient PES exploration, and PES sensitivity analysis. The present work describes the design of Arkane, how it should be used, and refers to the theory that it employs. Arkane is distributed via the RMG-Py software suite (https://github.com/ReactionMechanismGenerator/RMG-Py).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2010

Fourier analysis for hydrostatic pressure sensing in a polarization-maintaining photonic crystal fiber

.We measured the hydrostatic pressure dependence of the birefringence and birefringent dispersion of a Sagnac interferometric sensor incorporating a length of highly birefringent photonic crystal fiber using Fourier analysis. Sensitivity of both the phase and chirp spectra to hydrostatic pressure is demonstrated. Using this analysis, phase-based measurements showed a good linearity with an effective sensitivity of 9.45nm/MPa and an accuracy of {+-}7.8kPa using wavelength-encoded data and an effective sensitivity of -55.7cm{sup -1}/MPa and an accuracy of {+-}4.4kPa using wavenumber-encoded data. Chirp-based measurements, though nonlinear in response, showed an improvement in accuracy at certain pressure ranges with an accuracy of {+-}5.5kPa for the full range of measured pressures using wavelength-encoded data and dropping to within {+-}2.5kPa in the range of 0.17 to 0.4MPa using wavenumber-encoded data. Improvements of the accuracy demonstrated the usefulness of implementing chirp-based analysis for sensing purposes.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1997

Cellular Structures in the Flow Over the Flap of a Two-Element Wing

Flow visualization information and time dependent pressure coefficients were recorded for the flow over a two-element wing. The investigation focused on the stall onset; particularly at a condition where the flow is attached on the main element but separated on the flap. At this condition, spanwise separation cells were visible in the flow over the flap, and time dependent pressure data was measured along the centerline of the separation cell. The flow visualizations indicated that the spanwise occurrence of the separation cells depends on the flap (and not wing) aspect ratio.

Yon, Steven A.↗
DOE OSTI2024

Pressure induced Invar effect in Fe 55 ⁢Ni 45 : An experimental study with nuclear resonant scattering

Pressure-dependent synchrotron x-ray diffraction (XRD), nuclear resonant inelastic x-ray scattering (NRIXS), and nuclear forward scattering (NFS) measurements were made on 57 Fe 55 Ni 45 . XRD measurements were at 298 and 392 K at pressures up to 20 GPa, confirming a pressure-induced Invar effect between 7 and 13 GPa. A decrease of the 57 Fe magnetic moment was found in NFS measurements under pressure, showing an increase in magnetic entropy. The 57 Fe phonon density of states (DOS) was obtained from NRIXS measurements. The low thermal expansion in the high-pressure Invar region originates from a competition between the thermal expansion from spins and phonons as calculated from Maxwell relations. Finally, the longitudinal phonon modes changed their pressure dependence near the Curie transition, which is evidence for a spin-phonon interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Evolution of critical pressure with increasing Fe substitution in the heavy-fermion system URu 2 - x Fe x Si 2

Measurements of electrical resistivity, ρ(T ), were performed under quasihydrostatic pressure up to P ~ 2.2 GPa to determine the pressure dependence of the so-called hidden order (HO) and large-moment antiferromagnetic (LMAFM) phases for the URu 2-x FexSi2 system with x = 0.025, 0.05, 0.10, 0.15, and 0.20. As the Fe concentration (x) is increased, we observed that a smaller amount of external pressure, P c , is required to induce the HO → LMAFM phase transition. A critical pressure of P c ~ 1.2 GPa at x = 0.025 reduces to P c ~ 0 at x = 0.15, suggesting the URu 2-x Fe x Si 2 system is fully expressed in the LMAFM phase for x ≥ x* c = 0.15, where x * c denotes the ambient pressure critical concentration of Fe. Furthermore, when using a bulk modulus calculation to convert x to chemical pressure, P ch (x), we consistently found that the induced HO → LMAFM phase transition occurred at various combinations of x c and P c such that P ch (x c ) + P c ≈ 1.5 GPa, where xc denotes those critical concentrations of Fe that induce the HO→LMAFM phase transition for the URu 2-x Fe x Si 2 compounds under pressure. We performed exponential fits of ρ(T ) in the HO and LMAFM phases in order to determine the pressure dependence of the energy gap, , that opens over part of the Fermi surface in the transition from the paramagnetic (PM) phase to the HO/LMAFM phase at the transition temperature, T 0 . Finally, this change in the pressure variation of Δ(P) at the HO→LMAFM phase transition is consistent with the values of P c determined from the T 0 (P) phase lines at the PM→HO/LMAFM transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Tunneling spectroscopy of Al/AlO{sub x}/Pb subjected to hydrostatic pressure

We develop an experimental tool to investigate high-pressure electronic density of state by combining electron tunneling spectroscopy measurements with high-pressure technique. It is demonstrated that tunneling spectroscopy measurement on Al/AlO{sub x}/Pb junction is systematically subjected to hydrostatic pressure up to 2.2 GPa. Under such high pressure, the normal state junction resistance is sensitive to the applied pressure, reflecting the variation of band structure of the barrier material upon pressures. In superconducting state, the pressure dependence of the energy gap Δ{sub 0}, the gap ratio 2Δ{sub 0}/k{sub B}T{sub c}, and the phonon spectral energy is extracted and compared with those obtained in the limited pressure range. Our experimental results show the accessibility and validity of high pressure tunneling spectroscopy, offering wealthy information about high pressure superconductivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

In-situ study of rules of nanostructure evolution, severe plastic deformations, and friction under high pressure

Severe plastic deformations under high pressure are used to produce nanostructured materials but were studied ex-situ. Rough diamond anvils are introduced to reach maximum friction equal to yield strength in shear and the first in-situ study of the evolution of the pressure-dependent yield strength and radial distribution of nanostructural parameters are performed for severely pre-deformed Zr. ω-Zr behaves like perfectly plastic, isotropic, and strain-path-independent and reaches steady values of the crystallite size and dislocation density, which are pressure-, strain- and strain-path-independent. However, steady states for a-Zr obtained with smooth and rough anvils are different, causing major challenge in plasticity theory. In-situ study of severe plastic deformation of α-Zr with rough diamond anvils revealed that pressure-dependent yield strength, crystallite size, and dislocation density are getting steady and plastic strain- and strain-path-independent.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Low frequency pressure modulation of indium antimonide

A lumped parameter resonator capable of generating megapascal pressures at low frequency (kilohertz) is described. Accelerometers are used to determine the applied pressure, and are calibrated with a piezoelectric sample. A laser diagnostic was also developed to measure the pressure in semiconductor samples through the band gap pressure dependence. In addition, the laser diagnostic has been used to measure the attenuation coefficient {alpha} of commercially available indium antimonide (InSb) wafers. The resonator and laser diagnostic have been used with InSb samples to verify the pressure response.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1972

Effect of velocity-changing collisions on the output of a gas laser.

A theoretical model for the pressure dependence of the intensity of a gas laser is presented in which only velocity-changing collisions with foreign-gas atoms are included. This is a special case where the phase shifts are the same for the two atomic-laser levels or are so small that deflections are the dominant effect of collisions. A collision model for hard-sphere repulsive interactions is derived and the collision parameters, persistence of velocity and collision frequency, are assumed to be independent of velocity. The collision theory is applied to a third-order expansion of the polarization in powers of the cavity electric field (weak-signal theory). The resulting expression for the intensity shows strong pressure dependence. The collisions reduce the amount of saturation and the laser intensity increases with pressure in a characteristic fashion.

Borenstein, M.↗
DOE OSTI2019

Kinetic Study of the OH + Ethylene Reaction using Frequency Modulated Laser Absorption Spectroscopy

The pressure dependence of the OH + C 2 H 4 addition reaction has been investigated using frequency modulated laser absorption spectroscopy to monitor OH kinetics. Bimolecular rate coefficients for the title reaction are reported in argon bath gas at room temperature and total pressures ranging from 2–361Torr. The pressure dependent rate coefficients measured here agree well with the majority of published kinetic studies under similar conditions. Previous high-level ab initio calculations have identified a pre-reaction complex on the OH + C 2 H 4 potential energy surface. In conclusion, the influence of this complex on the OH + C 2 H 4 kinetics has been investigated using one-dimensional master equation analyses of the current and previous experimental measurements

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

MESOSCALE MODELING OF DEFLAGRATION-INDUCED DECONSOLIDATION IN POLYMER-BONDED EXPLOSIVES

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

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

High-pressure behavior of amorphous selenium from ultrasonic measurements and Raman spectroscopy

The high-pressure behavior of melt-quenched amorphous selenium (a-Se) has been investigated via ultrasonic measurements and Raman scattering at room temperature. The ultrasonic measurements were conducted on a-Se in a multi-anvil apparatus with two different sample assemblies at pressures of up to 4.5 and 4.8 GPa. We discovered that similar kinks occur in the slopes of the pressure dependence characteristics of the travel time and the sound velocity in both shear and longitudinal waves in the 2.0–2.5 GPa range. These kinks are independent of the sample assemblies, indicating an intrinsic transformation of the a-Se. Additionally, we deduced the pressure-volume relationship of a-Se from the sound velocity characteristics using the Birch–Murnaghan equation of state, and the results agreed well with those of previous reports. In situ high-pressure Raman scattering measurements of a-Se were conducted in a diamond anvil cell with an 830 nm excitation line up to a pressure of 4.3 GPa. We found that the characteristic band of a-Se at ∼250 cm{sup −1} experienced a smooth shift to a lower frequency with pressure, but a sharp slope change in the band intensity versus pressure occurred near 2.5 GPa. The results of X-ray diffraction and differential scanning calorimetry measurements indicate that the samples remain in their amorphous states after decompression. Thus, we proposed that the abnormal compression behavior of a-Se in the 2.0–2.5 GPa range can be attributed to pressure-induced local atomic reconfiguration, implying an amorphous-amorphous transition of the elementary selenium.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1970

Polymer degradation rate control of hybrid rocket combustion

Polymer degradation to small fragments is treated as a rate controlling step in hybrid rocket combustion. Both numerical and approximate analytical solutions of the complete energy and polymer chain bond conservation equations for the condensed phase are obtained. Comparison with inert atmosphere data is very good. It is found that the intersect of curves of pyrolysis rate versus interface temperature for hybrid combustors, with the thermal degradation theory, falls at a pyrolysis rate very close to that for which a pressure dependence begins to be observable. Since simple thermal degradation cannot give sufficient depolymerization at higher pyrolysis rates, it is suggested that oxidative catalysis of the process occurs at the surface, giving a first order dependence on reactive species concentration at the wall. Estimates of the ratio of this activation energy and interface temperature are in agreement with best fit procedures for hybrid combustion data. Requisite active species concentrations and flux are shown to be compatible with turbulent transport. Pressure dependence of hybrid rocket fuel regression rate is thus shown to be describable in a consistent manner in terms of reactive species catalysis of polymer degradation.

Stickler, D. B.↗
DOE OSTI2014

Secondary channels in the thermal decomposition of monomethylhydrazine (CH 3 NHNH 2 )

Mass spectrometric observations in a very low pressure pyrolysis study of the decomposition of the prototypical rocket fuel monomethylhydrazine (MMH) indicated a dominant role for the molecular channels producing NH 3 and H 2 and their coproducts. In contrast, a recent ab initio transition state theory based master equation theoretical study indicated that simple N–N and C–N bond fissions dominate the kinetics. In this work, the possible role of molecular decomposition channels in MMH is explored further through additional investigations of the potential energy surface. These investigations consider the role of triplet channels, of roaming radical channels, and of some previously unexplored pathways for molecular decomposition. New ab initio transition state theory based master equation calculations provide revised predictions for the temperature and pressure dependence of the MMH decomposition kinetics that are in excellent agreement with recent shock tube measurements. These calculations continue to suggest only a very limited contribution from the molecular elimination channels. A roaming pathway is suggested to provide the dominant route for direct formation of ammonia. The possible role of secondary abstraction reactions in the very-low-pressure pyrolysis experiments is briefly discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Large deformation and gas retention during cookoff of a plastic bonded explosive (PBX 9407)

Here, we have used several configurations of the Sandia Instrumented Thermal Ignition (SITI) experiment to develop a pressure-dependent, four-step ignition model for a plastic bonded explosive (PBX 9407) consisting of 94 wt.% RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and a 6 wt.% VCTFE binder (vinyl chloride/chlorotrifluoroethylene copolymer). The four steps include desorption of water, decomposition of RDX to form equilibrium products, pressure-dependent decomposition of RDX forming equilibrium products, and decomposition of the binder to form hydrogen chloride and a nonvolatile residue (NVR). We address drying, binder decomposition, and decomposition of the RDX component from the pristine state through the melt and into ignition. We used Latin Hypercube Sampling (LHS) of the parameters to determine the sensitivity of the model to variation in the parameters. We also successfully validated the model using one-dimensional time-to-explosion (ODTX and P-ODTX) data from a different laboratory. Our SITI test matrix included 1) different densities ranging from 0.7 to 1.63 g/cm 3 , 2) free gas volumes ranging from 1.2 to 38 cm 3 , and 3) boundary temperatures ranging from 170 to 190 °C. We measured internal temperatures using embedded thermocouples at various radial locations as well as pressure using tubing that was connected from the free gas volume (ullage) to a pressure gauge. We also measured gas flow from our vented experiments. A borescope was included to obtain in situ video during some SITI experiments. We observed significant changes in the explosive volume prior to ignition. Our model, in conjunction with data observations, imply that internal accumulation of decomposition gases in high density PBX 9407 (90% of the theoretical maximum density) can contribute to significant strain whether or not the experiment is vented or sealed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗