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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Pressure-Resistant Intermediate Valence in the Kondo Insulator SmB 6

Resonant x-ray emission spectroscopy was used to determine the pressure dependence of the f-electron occupancy in the Kondo insulator SmB 6 . Applied pressure reduces the f occupancy, but surprisingly, the material maintains a significant divalent character up to a pressure of at least 35 GPa. Thus, the closure of the resistive activation energy gap and onset of magnetic order are not driven by stabilization of an integer valent state. In conclusion, over the entire pressure range, the material maintains a remarkably stable intermediate valence that can in principle support a nontrivial band structure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Impact of External Pressure and Electrolyte Transport Properties on Lithium Dendrite Growth

Practical implementation of metal anodes in commercial lithium-ion batteries has been limited by the growth of dendritic protrusions, which can cause short-circuits and adversely affect battery safety. The impacts of the physical (such as external pressure and electrolyte shear modulus) and electrochemical (for example, conductivity, diffusivity and transference number) properties of a solid electrolyte on the propensity of lithium dendrite growth are investigated here. It is found that over a range of conditions, there are critical pressures above which growth of lithium dendritic protrusions can be prevented. The magnitude of this critical pressure depends on the elastic modulus of the electrolyte. Plastic deformation of lithium at high pressure results in reduced protrusion growth, which helps in obtaining stable deposition. For the first time, phase maps have been developed based on mechanical and transport properties of electrolytes, indicating conditions under which stable deposition of lithium is possible during long-term operation. Suppression of dendrites by individually altering conductivity, or diffusivity, or transference number, or elastic modulus of the electrolyte appears to be a relatively difficult task. Finally, minor tailoring of the transference number and elastic modulus of present-day polymer electrolytes, in a combined fashion, can lead to dendrite-free deposition of lithium.

25 ENERGY STORAGE↗
DOE OSTI2025

Insights into the hydro-mechanical behavior of a decimeter-scale fracture using the mini-SIMFIP probe

ABSTRACT: Understanding hydro-mechanical couplings in fractured rocks is essential for predicting the rock mass response during high-pressure fluid injection, including the stimulation of enhanced geothermal systems. However, fluid-driven fracture dislocations are challenging to measure due to the need for local displacement data at high fluid pressures. In this study, fluid-driven displacement across a decimeter-scale laboratory fracture was investigated using the mini-SIMFIP (step rate injection method for fracture in-situ properties) probe, which is a smaller version of the SIMFIP tool (Guglielmi et al., 2014). The mini-SIMFIP probe is able to resolve the full 3D displacement vector of a fracture. The probe was installed in one of two boreholes across a decimeter-scale saw-cut granite fracture. Two pressure step injection tests were conducted under the same isotropic stress conditions. By varying injection between the boreholes, we estimated the aperture profile across the fracture. The results show a consistent pressure-dependent opening as long as steady-state flow was maintained. At a certain pressure step, steady-state conditions were no longer achievable and the fracture opened rapidly. The pressure-opening relationship diverged between the two tests and indicated a homogenization of the aperture profile and an increase in the non-linearity of the flow regime.

Osten, J↗
NASA NTRS1983

Body-surface pressure data on two monoplane-wing missile configurations with elliptical cross sections at Mach 2.50

Tabulated body surface pressure data for two monoplane-wing missile configurations are presented and analyzed. Body pressure data are presented for body-alone, body-tail, and body-wing-tail combinations. For the lost combination, data are presented for tail-fin deflection angles of 0 deg and 30 deg to simulate pitch, yaw, and roll control for both configurations. The data cover angles of attack from -5 deg to 25 deg and angles of roll from 0 deg to 90 deg at a Mach number of 2.50 and a Reynolds number of 6.56 x 1,000,000 per meter. Very consistent, systematic trends with angle of attack and angle of roll were observed in the data, and very good symmetry was found at a roll angle of 0 deg. Body pressures depended strongly on the local body cross-section shape, with very little dependence on the upstream shape. Undeflected fins had only a small influence on the pressures on the aft end of the body; however, tail-fin deflections caused large changes in the pressures.

Allen, J. M.↗
DOE OSTI2022

Molecular insights into the structure-property relationships of 3D printed polyamide reverse-osmosis membrane for desalination

3D-printing is an emerging method for manufacturing polyamide (PA) reserve osmosis (RO) membranes for water treatment and desalination, which can precisely control membrane structural properties, such as thickness, roughness, and resolution. However, the synthesis-structure (i.e., degree of cross-linking (DC), m-phenylenediamine/trimesoyl chloride (MPD/TMC) ratio, and membrane thickness) to property (permeability and water-salt selectivity) relationships for these membranes has not been well understood. At the same time, a microscopic understanding of the physical mechanism of water and salt transport is needed to guide the design of high-performance 3D-printed membranes and improve the printing efficiency. Furthermore, the atomic-scale transport features and energetics of water and salt ions are studied at high pressure for the 3D-printed PA RO membranes with the different DCs and MPD/TMC ratios through non-equilibrium molecular dynamics (NEMD) simulations. Factoring in membrane structure properties, rejection ratio of salt ions and pressure-dependent water flux, 3D-printed PA membranes having an MPD/TMC ratio of 3.0:2.0 and a DC between 80%~90% attains ideal performance: high water flux, high rejection of salt ions, and excellent structural integrity. Mechanistically, water permeability for highly cross-linked PA RO membranes depends on the temporary on-and-off channels that allow water molecules to jump from one cavity to another at high pressure. In addition, higher pressures cause rapid compaction of PA membranes’ free volume and membrane thickness. Membrane failure at high pressure is determined by the DC and MPD/TMC ratios-dependent compressive yield strength. In short, these findings provide physical insights for optimizing existing PA membranes and designing next-generation desalination membranes at the molecular level.

3D-printed PA RO membrane↗
NASA NTRS1982

An investigation of the kinetics of hydrogen chemisorption on iron metal surfaces

The isothermal kinetics of H2, H2S, and O2 chemisorption onto epitaxially grown (III) oriented Fe films were studied. The measurements were made using the techniques of chemisorption induced resistance change and Auger electron spectroscopy (for adsorbed sulfur and oxygen). Also the origin of the chemisorption induced resistance change for these systems and its applicability to kinetic measurements were established. The chemisorption kinetics were interpreted as dissociative chemisorption via an adsorbed molecular species. The applicable rate constants were established. In none of the studies were the rate constants observed to be coverage dependent. By comparing the temperature dependence of the rate constants with absolute rate theory, the binding energies and activation energies of all the kinetic processes were obtained for the H2/Fe system. The initial sticking coefficient was pressure dependent for both the H2/Fe and H2S/Fe systems. This results from the step between the adsorbed molecular state and the dissociated chemisorbed state being the rate limiting step for absorption at certain pressures and temperatures. Estimates were obtained for the temperature dependence of the rate constants for the O2/Fe system.

Shanabarger, M. R.↗
DOE OSTI2023

Real-time (nanoseconds) determination of liquid phase growth during shock-induced melting

Melting of solids is a fundamental natural phenomenon whose pressure dependence has been of interest for nearly a century. However, the temporal evolution of the molten phase under pressure has eluded measurements because of experimental challenges. By using the shock front as a fiducial, we investigated the time-dependent growth of the molten phase in shock-compressed germanium. In situ x-ray diffraction measurements at different times (1 to 6 nanoseconds) behind the shock front quantified the real-time growth of the liquid phase at several peak stresses. These results show that the characteristic time for melting in shock-compressed germanium decreases from ~7.2 nanoseconds at 35 gigapascals to less than 1 nanosecond at 42 gigapascals. Our melting kinetics results suggest the need to consider heterogeneous nucleation as a mechanism for shock-induced melting and provide an approach to measuring melting kinetics in shock-compressed solids.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Negative Medium-Voltage Direct Current Discharges in Air under Simulated Sub-Atmospheric Pressures for All-Electric Aircraft

The increase in the global temperature due to greenhouse gas emissions is a major concern to the world. To achieve the goal of zero emissions by 2050 in the USA the practical realization of all-electric vehicles, particularly all-electric aircraft (AEA), is important. For the design of electrical power systems (EPSs) in all-electric aircraft, a bipolar medium-voltage direct current (MVDC) system of ±5 kV is being investigated. However, several challenges manifest when using such voltages in a low-pressure environment. One of the main challenges is the partial discharge (PD) behavior of the insulation. It is important to study the PD behavior of the insulation by simulating the aviation environment in the lab. This work aimed to study the partial discharge behavior of air under a negative DC voltage in a needle-to-plane electrode geometry by simulating the aviation pressures in the lab. The partial discharge inception voltage (PDIV) and the breakdown voltage (BDV) show an obvious pressure-dependent variation. Regression analysis was performed to better understand the relationship between the PDIV and pressures. Plots were drawn for the average discharge current at each voltage step until breakdown. This paper’s findings can provide valuable insight into the design of EPS for an AEA. To the best of our knowledge, such a study has not been carried out to date.

air discharge↗
NASA NTRS2014

Liquid Oxygen Thermodynamic Vent System Testing with Helium Pressurization

This report presents the results of several thermodynamic vent system (TVS) tests with liquid oxygen plus a test with liquid nitrogen. In all tests, the liquid was heated above its normal boiling point to 111 K for oxygen and 100 K for nitrogen. The elevated temperature was representative of tank conditions for a candidate lunar lander ascent stage. An initial test series was conducted with saturated oxygen liquid and vapor at 0.6 MPa. The initial series was followed by tests where the test tank was pressurized with gaseous helium to 1.4 to 1.6 MPa. For these tests, the helium mole fraction in the ullage was quite high, about 0.57 to 0.62. TVS behavior is different when helium is present than when helium is absent. The tank pressure becomes the sum of the vapor pressure and the partial pressure of helium. Therefore, tank pressure depends not only on temperature, as is the case for a pure liquid-vapor system, but also on helium density (i.e., the mass of helium divided by the ullage volume). Thus, properly controlling TVS operation is more challenging with helium pressurization than without helium pressurization. When helium was present, the liquid temperature would rise with each successive TVS cycle if tank pressure was kept within a constant control band. Alternatively, if the liquid temperature was maintained within a constant TVS control band, the tank pressure would drop with each TVS cycle. The final test series, which was conducted with liquid nitrogen pressurized with helium, demonstrated simultaneous pressure and temperature control during TVS operation. The simultaneous control was achieved by systematic injection of additional helium during each TVS cycle. Adding helium maintained the helium partial pressure as the liquid volume decreased because of TVS operation. The TVS demonstrations with liquid oxygen pressurized with helium were conducted with three different fluid-mixer configurations-a submerged axial jet mixer, a pair of spray hoops in the tank ullage, and combined use of the axial jet and spray hoops. A submerged liquid pump and compact heat exchanger located inside the test tank were used with all the mixer configurations. The initial series without helium and the final series with liquid nitrogen both used the axial jet mixer. The axial jet configuration successfully demonstrated the ability to control tank pressure; but in the normal-gravity environment, the temperature in the upper tank region (ullage and unwetted wall) was not controlled. The spray hoops and axial jet combination also successfully demonstrated pressure control as well as temperature control of the entire tank and contents. The spray-hoops-only configuration was not expected to be a reliable means of tank mixing because there was no direct means to produce liquid circulation. However, surprisingly good results also were obtained with the sprayhoops- only configuration (i.e., performance metrics such as cycle-averaged vent flowrate were similar to those obtained with the other configurations). A simple thermodynamic model was developed that correctly predicted the TVS behavior (temperature rise or pressure drop per TVS cycle) when helium was present in the ullage. The model predictions were correlated over a range of input parameters. The correlations show that temperature rise or pressure drop per cycle was proportional to both helium mole fraction and tank heat input. The response also depended on the tank fill fraction: the temperature rise or pressure drop (per TVS cycle) increased as the ullage volume decreased.

Thermodynamic vent system↗
DOE OSTI2025

Pressure-Modulated Energy Transfer Dynamics in Mn 2+ -Doped CdS/ZnS Core/Shell Quantum Dots

Transition metal doping in semiconductor quantum dots (QDs) significantly impacts their optical properties, thus expanding the range of their potential optoelectronic applications. This study investigates the pressure-dependent energy transfer dynamics in Mn 2+ -doped CdS/ZnS core/shell QDs, focusing on how external hydrostatic pressure modulates these dynamics and optical properties. By synthesizing Mn 2+ -doped QDs with varying Mn 2+ doping concentrations, we explore the effects of the pressure on photoluminescence (PL) spectra and energy transfer efficiency. Our study reveals that increasing pressure induces a blueshift in the QD host bandgap PL and a redshift in the Mn 2+ dopant PL. The pressure-induced shifts highlight a unique modulation mechanism where the energy transfer efficiency decreases with pressure due to reduced wave function overlap between host excitons and Mn 2+ dopants. Detailed analysis of the PL quantum yields and energy transfer rate constants provides insights into these dynamics, suggesting that the pressure can effectively and reversibly regulate the energy transfer efficiencies and rates. In conclusion, these results have implications for developing pressure-sensitive configurable devices and exploring pressure-induced phenomena in doped nanomaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Mass spectrometric investigation of high-mass neutral species in the downstream region of Ar/CH{sub 4} plasmas

Mass analysis was carried out on neutral species in the downstream region of Ar/CH{sub 4} plasmas. The ionization of the neutral species by Li{sup +} attachment, which can inhibit the fragmentation accompanied by ionization in most cases, successfully led to the observation of high-mass neutral hydrocarbons containing up to twenty-seven carbon atoms. Pure Ar and Ar/H{sub 2} plasmas were also used to investigate the influence of sputtering of an amorphous hydrocarbon (a-C:H) film deposited during the generation of the Ar/CH{sub 4} plasmas. In addition, time dependence of intensity in several neutral species accompanied by the growth of the a-C:H film and its CH{sub 4} partial pressure dependence were observed for the first time. On the basis of the present experimental results, the desorption of high-mass neutral molecules from the film to the gas phase is concluded.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Superconductivity on the Verge of a Pressure-Induced Lifshitz Transition in CaFe{sub 2}As{sub 2}: an Interpretation Within the Eliashberg Theory

In a recent paper, we presented the first directional point-contact Andreev reflection spectroscopy (PCARS) measurements on CaFe{sub 2}As{sub 2} crystals under quasi-hydrostatic pressure and discussed the pressure dependence of the gaps and the critical temperature. While T{sub c} exhibits a well-known smooth dependence and a broad maximum at about 0.6 GPa, both gaps increase very sharply in a small pressure range between 0.5 and 0.6 GPa, leading to a doubling of the ratio 2Δ{sub 2}/k{sub B}T{sub c} and a quadruplication of the ratio 2Δ{sub 1}/k{sub B}T{sub c}, Δ{sub 1} and Δ{sub 2} being the small and large gap, respectively. This peculiar behavior is likely to be related to a sharp change in the lattice structure that, in turn, produces a 2D-3D topological transition in the hole-like Fermi surface sheet. In this work, we show that, within an effective three-band Eliashberg theory for the electron-spin fluctuation coupling (s± symmetry), these results can be rationalized as being due to a large increase of the electron-boson coupling, which mimics the effects of a boost mechanism for the coupling related to the underlying Lifshitz transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

A study of tantalum pentoxide Ta 2 O 5 structures up to 28 GPa

In this study, tantalum pentoxide Ta 2 O 5 with the orthorhombic L-Ta 2 O 5 structure has been experimentally studied up to 28.3 GPa (at ambient temperature) using synchrotron angle-dispersive powder X-ray diffraction (XRD). The ambient pressure phase remains stable up to 25 GPa where with increased pressure a crystalline to amorphous phase transition occurs. A detailed equation of state (EOS), including pressure dependent lattice parameters, is reported. The results of this study were compared with a previous high-pressure XRD study by Li et al. A clear discrepancy between the ambient-pressure crystal structures and, consequently, the reported EOSs between the two studies was revealed. Finally, he origin of this discrepancy is attributed to two different crystal structures used to index the XRD patterns.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Proton transfer reactions from H3/+/ ions to N2, O2, and CO molecules

The rate constants for proton transfer from H3(+) ions to N2, O2, and CO have been measured as function of hydrogen-buffer-gas partial pressure. The rate constant for proton transfer from H3(+) to N2 shows a very large pressure dependence, increasing from 1.0 by 10 to the -9th power cu cm/s at low H2 partial pressures to 1.7 by 10 to the -9th power cu cm/s at high H2 partial pressures. The rate constants for proton transfer from H3(+) to O2 and CO are constant with partial pressure of H2. The roles of excess vibrational energy in H3(+) ions and of equilibrium between forward and back reactions are discussed. Back reaction is observed only for the reaction of H3(+) ions with O2, and an equilibrium constant of 2.0 (plus or minus 0.4) at 298 K has been determined. From these data, the proton affinity of O2 is deduced to be 0.47 (plus or minus 0.11) kcal/mole higher than that of H2.

Kim, J. K.↗
DOE OSTI2016

Spatially coherent high-order harmonics generated at optimal high gas pressure with high-intensity one- or two-color laser pulses

Here, we investigate the gas-pressure dependence of macroscopic harmonic spectra generated in a high-ionization medium using intense 800-nm laser pulses. The harmonics obtained at the optimal pressure show good spatial coherence with small divergence (less than 2 mrad) in the far field. By analyzing the evolution of the laser's electric field as it propagates, we find that dynamic phase matching conditions are fulfilled in the second half of the gas cell and that harmonic yields do not depend on the position of the gas cell with respect to the focusing position. We also demonstrate that harmonic yields at the optimal pressure can be further enhanced by increasing input laser energy or by adding a few percent of second or third harmonic to the fundamental.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

X-ray Diffraction, Lattice Structure, and Equation of State of PdH x and PdD x to Megabar Pressures

High-pressure X-ray diffraction of PdH x and PdD x demonstrates that these materials remain in a face-centered cubic (fcc, $Fm\bar{3m}$) structure to megabar pressures at room temperature. The volumes indicate stoichiometric compositions under pressure with x = 1 for both materials. No indication of any phase transition was observed up to the highest pressures reached in the experiments. A third-order Birch–Murnaghan equation of state used to fit the pressure–volume data gives V 0 = 10.73 (±0.03) cm 3 /mol, K 0 = 147 (±11) GPa, and K 0 ' = 4.7 (±0.5), whereas a Vinet fit gives V 0 = 10.74 (±0.03) cm 3 /mol, K 0 = 143 (±11) GPa, and K 0 ' = 5.1 (±0.5), for the combined data for both PdH x and PdD x . Here, the results are used to obtain the pressure dependence of the effective volume of H and D atoms in PdH x and PdD x to megabar pressures for comparison with other simple hydrides with implications for superconductivity in this class of materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Origin of Pressure-induced Superconducting Phase in K x Fe 2-y Se 2 studied by Synchrotron X-ray Diffraction and Spectroscopy

Pressure dependence of the electronic and crystal structures of K x Fe 2–y Se 2 , which has pressure-induced two superconducting domes of SC I and SC II, was investigated by x-ray emission spectroscopy and diffraction. X-ray diffraction data show that compressibility along the c-axis changes around 12 GPa, where a new superconducting phase of SC II appears. This suggests a possible tetragonal to collapsed tetragonal phase transition. X-ray emission spectroscopy data also shows the change in the electronic structure around 12 GPa. These results can be explained by the scenario that the two SC domes under pressure originate from the change of Fermi surface topology. Lastly, our results here show the pronounced increase of the density of states near the Fermi surface under pressure with a structural phase transition, which can help address our fundamental understanding for the appearance of the SC II phase.

36 MATERIALS SCIENCE↗