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Recovery of MOF-5 from Extreme High-Pressure Conditions Facilitated by a Modern Pressure Transmitting Medium
Here mechanisms underlying the mechanically induced amorphization of metal-organic frameworks (MOFs) are of current interest, and both high-pressure experimentation and molecular dynamics simulations have been used to reveal the fundamentals of load bearing, deformation, and pressure-induced amorphization (PIA) in these highly porous materials. Unfortunately, MOFs are typically highly susceptibility to amorphization, which limits the conditions under which they can be processed and used. However, their flexible structures can be stabilized to high pressures by incorporating guest species into the framework matrix. In this study, a large molecule pressure transmitting medium (DAPHNE 7575 ) is used as a structure-fortifying guest species to stabilize the prototypical MOF -5 to ultra-high pressures ( >9 GPa) and enable the recovery of crystalline material upon decompression. Structural changes associated with the penetration of the pressure transmitting medium on compression are examined using a combination of high pressure synchrotron powder diffraction and molecular dynamics simulations. This work enhances the understanding of PIA in MOFs while showcasing a potential route for the stabilization of MOFs to surprisingly high-pressures.
Measurement component technology. Volume 1: Cryogenic pressure measurement technology, high pressure flange seals, hydrogen embrittlement of pressure transducer material, close coupled versus remote transducer installation and temperature compensation of pressure transducers
The results are presented of an investigation into the availability and performance capability of measurement components in the area of cryogenic temperature, pressure, flow and liquid detection components and high temperature strain gages. In addition, technical subjects allied to the components were researched and discussed. These selected areas of investigation were: (1) high pressure flange seals, (2) hydrogen embrittlement of pressure transducer diaphragms, (3) The effects of close-coupled versus remote transducer installation on pressure measurement, (4) temperature transducer configuration effects on measurements, and (5) techniques in temperature compensation of strain gage pressure transducers. The purpose of the program was to investigate the latest design and application techniques in measurement component technology and to document this information along with recommendations for upgrading measurement component designs for future S-2 derivative applications. Recommendations are provided for upgrading existing state-of-the-art in component design, where required, to satisfy performance requirements of S-2 derivative vehicles.
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.
Phase transitions in ε-FeOOH at high pressure and ambient temperature
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The phase diagram of Ti-6Al-4V at high-pressures and high-temperatures
We report results from a series of diamond-anvil-cell synchrotron x-ray diffraction and large-volume-press experiments, and calculations, to investigate the phase diagram of commercial polycrystalline high-strength Ti-6Al-4V alloy in pressure–temperature space. Up to ~30 GPa and 886 K, Ti-6Al-4V is found to be stable in the hexagonal-close-packed, or α phase. The effect of temperature on the volume expansion and compressibility of α–Ti-6Al-4V is modest. The martensitic α → ω (hexagonal) transition occurs at ~30 GPa, with both phases coexisting until at ~38–40 GPa the transition to the ω phase is completed. Between 300 K and 844 K the α → ω transition appears to be independent of temperature. ω–Ti-6Al-4V is stable to ~91 GPa and 844 K, the highest combined pressure and temperature reached in these experiments. Pressure–volume–temperature equations-of-state for the α and ω phases of Ti-6Al-4V are generated and found to be similar to pure Ti. A pronounced hysteresis is observed in the ω–Ti-6Al-4V on decompression, with the hexagonal structure reverting back to the α phase at pressures below ~9 GPa at room temperature, and at a higher pressure at elevated temperatures. Based on our data, we estimate the Ti-6Al-4V α–β–ω triple point to occur at ~900 K and 30 GPa, in good agreement with our calculations.
High pressure behaviors and novel high-pressure phase of Si 3 N 4 and TiN
Abstract not provided
Stabilization of pentazolate anions in the high-pressure compounds Na 2 N 5 and NaN 5 and in the sodium pentazolate framework NaN 5 ·N 2
Three oxygen-free pentazolate salts Na 2 N 5 , NaN 5 and NaN 5 ·N 2 were synthesized from sodium azide NaN 3 and molecular nitrogen N 2 at 50 GPa.
The stress state in bismuth to 298 GPa and its use as a pressure transmitting medium and pressure marker at multi-megabar pressures
We have conducted diffraction studies of bismuth (Bi) to 298 GPa using both conventional and toroidal diamond anvil cells (DACs) to investigate its suitability as a pressure-transmitting medium (PTM) to such pressures. Using microfocused x-ray beams, we have determined the pressure dependence of the uniaxial stress component (t) in cubic Bi-V from 7 to 298 GPa and find that at 298 GPa, t < 0.5 GPa. Bi-V, therefore, cannot support significant shear stresses, making it an excellent PTM. We have also measured the compressibility of Bi-V against that of copper (Cu) and gold (Au), allowing it to be used as a pressure marker as well as a PTM.
High-Pressure Raman and Infrared Spectroscopic Study of Prehnite
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The relation of the yield stress of high-pressure anvils to the pressure attained at yielding and the ultimate attainable pressure
A sensitive microprofilometer was used to determine the onset of yielding in the anvils of a supported opposed anvil device for the case of 3% cobalt-cemented tungsten carbide as the anvil material. In addition, it is shown how the commencement of yielding in boron carbide pistons, the yield strength being known, can be used to obtain the transition pressure to a conducting phase in gallium phosphide. The transition pressures of bismuth and gallium phosphide are obtained and it is found that these transitions are extremely close to the maximum attainable pressure in, respectively, a maraging steel and a 3% cobalt-cemented tungsten carbide.
Pressure Dome for High-Pressure Electrolyzer
A high-strength, low-weight pressure vessel dome was designed specifically to house a high-pressure [2,000 psi (approx. = 13.8 MPa)] electrolyzer. In operation, the dome is filled with an inert gas pressurized to roughly 100 psi (approx. = 690 kPa) above the high, balanced pressure product oxygen and hydrogen gas streams. The inert gas acts to reduce the clamping load on electrolyzer stack tie bolts since the dome pressure acting axially inward helps offset the outward axial forces from the stack gas pressure. Likewise, radial and circumferential stresses on electrolyzer frames are minimized. Because the dome is operated at a higher pressure than the electrolyzer product gas, any external electrolyzer leak prevents oxygen or hydrogen from leaking into the dome. Instead the affected stack gas stream pressure rises detectably, thereby enabling a system shutdown. All electrical and fluid connections to the stack are made inside the pressure dome and require special plumbing and electrical dome interfaces for this to be accomplished. Further benefits of the dome are that it can act as a containment shield in the unlikely event of a catastrophic failure. Studies indicate that, for a given active area (and hence, cell ID), frame outside diameter must become ever larger to support stresses at higher operating pressures. This can lead to a large footprint and increased costs associated with thicker and/or larger diameter end-plates, tie-rods, and the frames themselves. One solution is to employ rings that fit snugly around the frame. This complicates stack assembly and is sometimes difficult to achieve in practice, as its success is strongly dependent on frame and ring tolerances, gas pressure, and operating temperature. A pressure dome permits an otherwise low-pressure stack to operate at higher pressures without growing the electrolyzer hardware. The pressure dome consists of two machined segments. An O-ring is placed in an O-ring groove in the flange of the bottom segment and is trapped by the flange on the top dome segment when these components are bolted together with high-strength bolts. The pressure dome has several unique features. It is made (to ASME Pressure Vessel guidelines) in a high-strength aluminum alloy with the strength of stainless steel and the weight benefits of aluminum. The flange of the upper dome portion contains specially machined flats for mounting the dome, and other flats dedicated to the special feedthroughs for electrical connections. A pressure dome can be increased in length to house larger stacks (more cells) of the same diameter with the simple addition of a cylindrical segment. To aid in dome assembly, two stainless steel rings are employed. One is used beneath the heads of the high-strength bolts in lieu of individual hardened washers, and another is used instead of individual nuts. Like electrolyzers could be operated at low or high pressures simply by operating the electrolyzer outside or inside a pressurized dome.
Joint Acceptance Attenuation Factor of Integrated Pressure with Unsteady Pressure-Sensitive Paint Measurements
The Unsteady Pressure-Sensitive Paint (uPSP) is widely used to measure the surface pressure of scaled models in wind tunnel tests. Compared to the conventional pressure transducers, uPSP has the advantage of high spatial resolution. With multiple high-speed Complementary Metal Oxide Superconductor (CMOS) cameras, the uPSP data collected with the camera pixels are mapped to the surface grid of the scaled model and converted to pressure. The shot noise is the dominant component of the noise in the uPSP measurement. The integrated pressure is usually computed on the grid nodes of a user-defined patch. The effect of shot noise is reduced in the integrated pressure on the patch; however, the measurement of the aerodynamic pressure may also be attenuated by the decorrelation of the flow pressure field being measured. This paper discusses the Joint Acceptance Attenuation Factor (JAAF) of the integrated pressure with uPSP measurements. The JAAF, a function of frequency, is defined as the ratio of the Power Spectral Density (PSD) of the integrated aerodynamic pressure on the patch to the average PSD of the aerodynamic pressure on the grid nodes of the patch. In this paper, the JAAF is investigated for the integrated pressure on rectangular patches, whose edges are defined in the direction along the streamline or across the streamline. Based on the assumption that the surface pressure field can be described by the Corcos model, the closed-form formulas to compute the JAAFs of the integrated pressure on the discrete grid nodes of a rectangular patch and over the continuous area of a rectangular patch are derived respectively. It is shown that the JAAF of the integrated pressure over the continuous area of a rectangular patch is the limit of that on discrete nodes of the rectangular patch when the number of nodes in each row or column goes to infinity. The closed-form formulas of the JAAF derived in this paper, with estimated parameters of the model, are verified with the measurements of the uPSP and the conventional pressure transducer collected in the Space Launch System Ascent Unsteady Aerodynamics Test at NASA Ames Research Center in November 2017. The closed-form formulas of the JAAF of the integrated pressure on the rectangular patches, based on the Corcos model, provide an efficient method to estimate the attenuation of integration by the decorrelation of the flow pressure field and set references for the comparison of the spectrum of the integrated uPSP measurements and the conventional pressure transducer measurements. The work described in this paper is a part of NASA’s development of a new state-of-the-art uPSP capability in production wind tunnels. Funding was provided by the NASA Aerosciences Evaluation and Test Capabilities Portfolio Office.
Joint Acceptance Attenuation Factor of Integrated Pressure with Unsteady Pressure-Sensitive Paint Measurements
The Unsteady Pressure-Sensitive Paint (uPSP) is widely used to measure the surface pressure of scaled models in wind tunnel tests. Compared to the conventional pressure transducers, uPSP has the advantage of high spatial resolution. With multiple high-speed Complementary Metal Oxide Superconductor (CMOS) cameras, the uPSP data collected with the camera pixels are mapped to the surface grid of the scaled model and converted to pressure. The shot noise is the dominant component of the noise in the uPSP measurement. The integrated pressure is usually computed on the grid nodes of a user-defined patch. The effect of shot noise is reduced in the integrated pressure on the patch; however, the measurement of the aerodynamic pressure may also be attenuated by the decorrelation of the flow pressure field being measured. This paper discusses the Joint Acceptance Attenuation Factor (JAAF) of the integrated pressure with uPSP measurements. The JAAF, a function of frequency, is defined as the ratio of the Power Spectral Density (PSD) of the integrated aerodynamic pressure on the patch to the average PSD of the aerodynamic pressure on the grid nodes of the patch. In this paper, the JAAF is investigated for the integrated pressure on rectangular patches, whose edges are defined in the direction along the streamline or across the streamline. Based on the assumption that the surface pressure field can be described by the Corcos model, the closed-form formulas to compute the JAAFs of the integrated pressure on the discrete grid nodes of a rectangular patch and over the continuous area of a rectangular patch are derived respectively. It is shown that the JAAF of the integrated pressure over the continuous area of a rectangular patch is the limit of that on discrete nodes of the rectangular patch when the number of nodes in each row or column goes to infinity. The closed-form formulas of the JAAF derived in this paper, with estimated parameters of the model, are verified with the measurements of the uPSP and the conventional pressure transducer collected in the Space Launch System Ascent Unsteady Aerodynamics Test at NASA Ames Research Center in November 2017. The closed-form formulas of the JAAF of the integrated pressure on the rectangular patches, based on the Corcos model, provide an efficient method to estimate the attenuation of integration by the decorrelation of the flow pressure field and set references for the comparison of the spectrum of the integrated uPSP measurements and the conventional pressure transducer measurements. The work described in this paper is a part of NASA’s development of a new state-of-the-art uPSP capability in production wind tunnels. Funding was provided by the NASA Aerosciences Evaluation and Test Capabilities Portfolio Office.
The Measurement of Pressure Through Tubes in Pressure Distribution Tests
The tests described in this report were made to determine the error caused by using small tubes to connect orifices on the surface of aircraft to central pressure capsules in making pressure distribution tests. Aluminum tubes of 3/16-inch inside diameter were used to determine this error. Lengths from 20 feet to 226 feet and pressures whose maxima varied from 2 inches to 140 inches of water were used. Single-pressure impulses for which the time of rise of pressure from zero to a maximum varied from 0.25 second to 3 seconds were investigated. The results show that the pressure recorded at the capsule on the far end of the tube lags behind the pressure at the orifice end and experiences also a change in magnitude. For the values used in these tests the time lag and pressure change vary principally with the time of rise of pressure from zero to a maximum and the tube length. Curves are constructed showing the time lag and pressure change. Empirical formulas are also given for computing the time lag. Analysis of pressure distribution tests made on airplanes in flight shows that the recorded pressures are slightly higher than the pressures at the orifice and that the time lag is negligible. The apparent increase in pressure is usually within the experimental error, but in the case of the modern pursuit type of airplane the pressure increase may be 5 per cent. For pressure-distribution tests on airships the analysis shows that the time lag and pressure change may be neglected.
Shape Dependence of Pressure-Induced Phase Transition in CdS Semiconductor Nanocrystals
Understanding structural stability and phase transformation of nanoparticles under high pressure is of great scientific interest, as it is one of the crucial factors for design, synthesis, and application of materials. Even though high-pressure research on nanomaterials has been widely conducted, their shape-dependent phase transition behavior still remains unclear. Examples of phase transitions of CdS nanoparticles are very limited, despite the fact that it is one of the most studied wide band gap semiconductors. Here we have employed in-situ synchrotron wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM) to investigate the high-pressure behaviors of CdS nanoparticles as a function of particle shapes. We observed that CdS nanoparticles transform from wurtzite to rocksalt phase at elevated pressure in comparison to their bulk counterpart. Phase transitions also vary with particle shape—rod-shaped particles show a partially reversible phase transition and the onset of the structural phase transition pressure decreases with decreasing surface-to-volume ratios, while spherical particles undergo irreversible phase transition with relatively low phase transition pressure. Additionally, TEM images of spherical particles exhibited sintering-induced morphology change after high-pressure compression. Calculations of the bulk modulus reveals that spheres are more compressible than rods in the wurtzite phase. These results indicate that the shape of the particle plays an important role in determining their high-pressure properties. Our study provides important insights into understanding of the phase-structure-property relationship, guiding future design and synthesis of nanoparticles for promising applications.
Pressure-Application Device for Testing Pressure Sensors
A portable pressure-application device has been designed and built for use in testing and calibrating piezoelectric pressure transducers in the field. The device generates pressure pulses of known amplitude. A pressure pulse (in contradistinction to a steady pressure) is needed because in the presence of a steady pressure, the electrical output of a piezoelectric pressure transducer decays rapidly with time. The device includes a stainless- steel compressed-air-storage cylinder of 500 cu cm volume. A manual hand pump with check valves and a pressure gauge are located at one end of the cylinder. A three-way solenoid valve that controls the release of pressurized air is located at the other end of the cylinder. Power for the device is provided by a 3.7-V cordless-telephone battery. The valve is controlled by means of a pushbutton switch, which activates a 5 V to +/-15 V DC-to-DC converter that powers the solenoid. The outlet of the solenoid valve is connected to the pressure transducer to be tested. Before the solenoid is energized, the transducer to be tested is at atmospheric pressure. When the solenoid is actuated by the push button, pressurized air from inside the cylinder is applied to the transducer. Once the pushbutton is released, the cylinder pressure is removed from the transducer and the pressurized air applied to the transducer is vented, bringing the transducer back to atmospheric pressure. Before this device was used for actual calibration, its accuracy was checked with a NIST (National Institute of Standards and Technology) traceable calibrator and commercially calibrated pressure transducers. This work was done by Wanda Solano of Stennis Space Center and Greg Richardson of Lockheed Martin Corp.