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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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All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

New developments in high pressure x-ray spectroscopy beamline at High Pressure Collaborative Access Team

The 16 ID-D (Insertion Device - D station) beamline of the High Pressure Collaborative Access Team at the Advanced Photon Source is dedicated to high pressure research using X-ray spectroscopy techniques typically integrated with diamond anvil cells. The beamline provides X-rays of 4.5-37 keV, and current available techniques include X-ray emission spectroscopy, inelastic X-ray scattering, and nuclear resonant scattering. Here, the recent developments include a canted undulator upgrade, 17-element analyzer array for inelastic X-ray scattering, and an emission spectrometer using a polycapillary half-lens. Recent development projects and future prospects are also discussed.

47 OTHER INSTRUMENTATION↗
DOE OSTI2015

Saturation curve of SiO{sub 2} component in rutile-type GeO{sub 2}: A recoverable high-temperature pressure standard from 3 GPa to 10 GPa

The accuracy and precision of pressure measurements and the pursuit of reliable and readily available pressure scales at simultaneous high temperatures and pressures are still topics in development in high pressure research despite many years of work. In situ pressure scales based on x-ray diffraction are widely used but require x-ray access, which is lacking outside of x-ray beam lines. Other methods such as fixed points require several experiments to bracket a pressure calibration point. In this study, a recoverable high-temperature pressure gauge for pressures ranging from 3 GPa to 10 GPa is presented. The gauge is based on the pressure-dependent solubility of an SiO{sub 2} component in the rutile-structured phase of GeO{sub 2} (argutite), and is valid when the argutite solid solution coexists with coesite. The solid solution varies strongly in composition, mainly in pressure but also somewhat in temperature, and the compositional variations are easily detected by x-ray diffraction of the recovered products because of significant changes in the lattice parameters. The solid solution is measured here on two isotherms, one at 1200 °C and the other at 1500 °C, and is developed as a pressure gauge by calibrating it against three fixed points for each temperature and against the lattice parameter of MgO measured in situ at a total of three additional points. A somewhat detailed thermodynamic analysis is then presented that allows the pressure gauge to be used at other temperatures. This provides a way to accurately and reproducibly evaluate the pressure in high pressure experiments and applications in this pressure-temperature range, and could potentially be used as a benchmark to compare various other pressure scales under high temperature conditions. - Graphical abstract: The saturation curve of SiO{sub 2} in TiO{sub 2} shows a strong pressure dependence and a strong dependence of unit cell volume on composition. This provides an opportunity to use this saturation curve as a measurement of pressure during a high-pressure experiment. The curve is a sensitive measure of pressure from 3 GPa to 10 GPa at high temperatures. The pressure is derived from lattice parameter measurements on the recovered solid solution, meaning that in-situ measurements are not necessary to evaluate the pressure of the experiment. - Highlights: • The unit cell of a saturated GeO{sub 2}–SiO{sub 2} solid solution is used as a pressure sensor. • We measure nine bracketed pressure points on the GeO{sub 2}–SiO{sub 2} saturation surface. • We provide a pressure calibrant from 3 GPa to 10 GPa at two temperatures. • Four points are measured at 1200 °C and five points at 1500 °C. • A thermodynamic model is developed for use of the calibrant at other temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Acoustic travel time gauges for in-situ determination of pressure and temperature in multi-anvil apparatus

In this study, we developed a new method for in-situ pressure determination in multi-anvil, high-pressure apparatus using an acoustic travel time approach within the framework of acoustoelasticity. The ultrasonic travel times of polycrystalline Al{sub 2}O{sub 3} were calibrated against NaCl pressure scale up to 15 GPa and 900 °C in a Kawai-type double-stage multi-anvil apparatus in conjunction with synchrotron X-radiation, thereby providing a convenient and reliable gauge for pressure determination at ambient and high temperatures. The pressures derived from this new travel time method are in excellent agreement with those from the fixed-point methods. Application of this new pressure gauge in an offline experiment revealed a remarkable agreement of the densities of coesite with those from the previous single crystal compression studies under hydrostatic conditions, thus providing strong validation for the current travel time pressure scale. The travel time approach not only can be used for continuous in-situ pressure determination at room temperature, high temperatures, during compression and decompression, but also bears a unique capability that none of the previous scales can deliver, i.e., simultaneous pressure and temperature determination with a high accuracy (±0.16 GPa in pressure and ±17 °C in temperature). Therefore, the new in-situ Al{sub 2}O{sub 3} pressure gauge is expected to enable new and expanded opportunities for offline laboratory studies of solid and liquid materials under high pressure and high temperature in multi-anvil apparatus.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Mechanical behaviors and phase transition of Ho{sub 2}O{sub 3} nanocrystals under high pressure

Mechanical properties and phase transition often show quite large crystal size dependent behavior, especially at nanoscale under high pressure. Here, we have investigated Ho{sub 2}O{sub 3} nanocrystals with in-situ x-ray diffraction and Raman spectroscopy under high pressure up to 33.5 GPa. When compared to the structural transition routine cubic -> monoclinic -> hexagonal phase in bulk Ho{sub 2}O{sub 3} under high pressure, the nano-sized Ho{sub 2}O{sub 3} shows a much higher onset transition pressure from cubic to monoclinic structure and followed by a pressure-induced-amorphization under compression. The detailed analysis on the Q (Q = 2π/d) dependent bulk moduli reveals the nanosized Ho{sub 2}O{sub 3} particles consist of a clear higher compressible shell and a less compressible core. Insight into these phenomena shed lights on micro-mechanism studies of the mechanical behavior and phase evolution for nanomaterials under high pressure, in general.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Deformation Twinning of a Silver Nanocrystal under High Pressure

Within a high-pressure environment, crystal deformation is controlled by complex processes such as dislocation motion, twinning, and phase transitions, which change materials' microscopic morphology and alter their properties. Understanding a crystal's response to external stress provides a unique opportunity for rational tailoring of its functionalities. It is very challenging to track the strain evolution and physical deformation from a single nanoscale crystal under high-pressure stress. Here, we report an in situ three-dimensional mapping of morphology and strain evolutions in a single-crystal silver nanocube within a high-pressure environment using the Bragg Coherent Diffractive Imaging (CDI) method. We observed a continuous lattice distortion, followed by a deformation twining process at a constant pressure. The ability to visualize stress-introduced deformation of nanocrystals with high spatial resolution and prominent strain sensitivity provides an important route for interpreting and engineering novel properties of nanomaterials.

coherent diffractive imaging↗
DOE OSTI2015

Analysis of Dynamic Stress in The Reactor Core Barrel Due to the Pressure Pulsations

This article presents vibrations analysis of the reactor core barrel caused by pressure pulsations induced by the main coolant pump. For this purpose, the calculations of the pressure distribution in the annulus between the core barrel and the reactor pressure vessel, bounded above by a separating ring were performed. Using transfer matrix method is obtained the solution of two-dimensional problem of pressure pulsations in the annulus between reactor core barrel and reactor vessel. The calculation results are compared with the pulsation pressure measurements made at commissioning unit 2 of the South Ukraine Nuclear Power Station. The distribution of pressure over the height of core barrel was obtained, which makes possible to estimate its strength for variant deformation of the core barrel as a beam, and in the case of deformation of the core barrel as a shell. The calculation results are used to assess the reliability of core barrel pre-load, which clamps the core barrel flange in place at the top, at full power operating. (author)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Melting of Magnesium Borohydride under High Hydrogen Pressure: Thermodynamic Stability and Effects of Nanoconfinement

The thermodynamic stability and melting point of magnesium borohydride were probed under hydrogen pressures up to 1000 bar (100 MPa) and temperatures up to 400 °C. At 400 °C, Mg(BH4)2 was found to be chemically stable between 700 and 1000 bar H2, whereas under 350 bar H2 or lower pressures, the bulk material partially decomposed into MgH2 and MgB12H12. The melting point of solvent-free Mg(BH4)2 was estimated to be 367-375 °C, which was above previously reported values by 40-90 °C. Our results indicated that a high hydrogen backpressure is needed to prevent the decomposition of Mg(BH4)2 before measuring the melting point and that molten Mg(BH4)2 can exist as a stable liquid phase between 367 and 400 °C under hydrogen overpressures of 700 bar or above. The occurrence of a pure molten Mg(BH4)2 phase enabled efficient melt-infiltration of Mg(BH4)2 into the pores of porous templated carbons (CMK-3 and CMK-8) and graphene aerogels. Both transmission electron microscopy and small-angle X-ray scattering confirmed efficient incorporation of the borohydride into the carbon pores. The Mg(BH4)2@carbon samples exhibited comparable hydrogen capacities to bulk Mg(BH4)2 upon desorption up to 390 °C based on the mass of the active component; the onset of hydrogen release was reduced by 15-25 °C compared to the bulk. Importantly, melt-infiltration under hydrogen pressure was shown to be an efficient way to introduce metal borohydrides into the pores of carbon-based materials, helping to prevent particle agglomeration and formation of stable closo-polyborate byproducts.

White, James L.↗
DOE OSTI2016

Hydrogen bond effects on compressional behavior of isotypic minerals: high-pressure polymorphism of cristobalite-like Be(OH) 2

Three isotypic crystals, SiO 2 (α-cristobalite), ε-Zn(OH) 2 (wülfingite), and Be(OH) 2 (β-behoite), with topologically identical frameworks of corner-connected tetrahedra, undergo displacive compression-driven phase transitions at similar pressures (1.5–2.0 GPa), but each transition is characterized by a different mechanism resulting in different structural modifications. In this study, we report the crystal structure of the high-pressure γ-phase of beryllium hydroxide and compare it with the high-pressure structures of the other two minerals. In Be(OH) 2 , the transition from the ambient β-behoite phase with the orthorhombic space group P2 1 2 1 2 1 and ambient unit cell parameters a = 4.5403(4) Å, b = 4.6253(5) Å, c = 7.0599(7) Å, to the high-pressure orthorhombic γ-polymorph with space group Fdd2 and unit cell parameters (at 5.3(1) GPa) a = 5.738(2) Å, b = 6.260(3) Å, c = 7.200(4) Å takes place between 1.7 and 3.6 GPa. This transition is essentially second order, is accompanied by a negligible volume discontinuity, and exhibits both displacive and reversible character. The mechanism of the phase transition results in a change to the hydrogen bond connectivities and rotation of the BeO 4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Pressure-induced phase coexistence in BaFe{sub 1.8}Co{sub 0.2}As{sub 2}

We report high-pressure powder synchrotron X-ray diffraction measurements of overdoped BaFe{sub 1.8}Co{sub 0.2}As{sub 2} under quasi-hydrostatic pressure up to 40.1 GPa. Our results indicate that a tetragonal (T) to collapsed tetragonal (CT) phase transition occurs at 16.8 GPa and the two phase coexist until 30 GPa, which has not been previously observed in iron arsenide compounds. Both the lattice parameters a and c show discontinuous change for the T and CT phases. The decrease of the c lattice parameter is as large as 12.2% owing to the uniaxial pressure effect. The axial ratio c/a of the T phase exhibits similar features to the other 122-type compounds below 16.8 GPa, whereas there is a very small increase with increasing pressure in the two phase coexistence region. Because of the relationship between the axial ratio and superconductivity, the abnormal expansion may be related to the sudden increase of the strength of antiferromagnetic spin fluctuations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗