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DOE OSTI2012

{sup 1}H and {sup 23}Na MAS NMR spectroscopy of cationic species in CO{sub 2} selective alkaline earth metal porous silicoaluminophosphates prepared via liquid and solid state ion exchange

The location of extraframework cations in Sr{sup 2+} and Ba{sup 2+} ion-exchanged SAPO-34 was estimated by means of {sup 1}H and {sup 23}Na MAS NMR spectroscopy and spectral deconvolution. Incorporation of the alkaline earth metal cations onto the SAPO framework was achieved via liquid state ion exchange, coupled partial detemplation/solid-state ion exchange, and combination of both techniques. MAS NMR revealed that the level of ion exchange was limited by the presence of protons and sodium cations near hexagonal prisms (site SI), which are relatively difficult to exchange with the alkaline earth metal due to steric and charge repulsion criteria. In addition, the presence of ammonium cations in the supercages facilitated the exchange of otherwise tenacious hydrogen as corroborated by unit cell compositional data as well as enhanced CO{sub 2} adsorption at low partial pressures. The extraframework ammonium species were produced from partial detemplation of the structure-directing agent employed for the SAPO-34 synthesis, tetraethylammonium. - Graphical abstract: MAS NMR was used to elucidate the position the cationic species in alkaline earth metal exchanged silicoaluminophosphates. These species played a significant role during the ion exchange process and, therefore, the materials ultimate CO{sub 2} adsorption performance. Highlights: Black-Right-Pointing-Pointer Location of extraframework Sr{sup 2+} or Ba{sup 2+} cations was estimated by means of {sup 1}H and {sup 23}Na MAS NMR. Black-Right-Pointing-Pointer Level of Sr{sup 2+} or Ba{sup 2+} ion exchange was limited by the presence of protons and sodium cations. Black-Right-Pointing-Pointer Presence of ammonium cations in the supercages facilitated the exchange. Black-Right-Pointing-Pointer Sr{sup 2+} and Ba{sup 2+} ion exchanged SAPOs are outstanding CO{sub 2} adsorbents.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Stability, Crystal Chemistry, and Magnetism of U 2+ x Ni 21– x \B 6 and Nb 3– y Ni 20+ y B 6 and the Role of Uranium in the Formation of the Quaternary U 2– z Nb z Ni 21 B 6 and U δ Nb 3-δ Ni 20 B 6 Systems

In this work, we investigated the U–Ni–B and Nb–Ni–B systems to search for possible new heavy fermion compounds and superconducting materials. The formation, crystal chemistry, and physical properties of U 2 Ni 21 B 6 and Nb 3– y Ni 20+ y B 6 [ternary derivatives of the cubic Cr 23 C 6 -type ( cF 116, $Fm\bar{3}m$)] have been studied; the formation of the hypothetical “U 3 Ni 20 B 6 ” and “Nb 2 Ni 21 B 6 ” has been disproved. U 2 Ni 21 B 6 [ a = 10.6701(2) Å] crystallizes in the ordered W 2 Cr 21 C 6 -type, whereas Nb 3– y Ni 20+ y B 6 [ a = 10.5842(1) Å] adopts the Mg 3 Ni 20 B 6 -type. Ni in U 2 Ni 21 B 6 can be substituted by U, leading to the solid solution U 2+ x Ni 21– x B 6 (0 ≤ x ≤ 0.3); oppositely, Nb in Nb 3 Ni 20 B 6 is partially replaced by Ni, forming the solution Nb 3– y Ni 20+ y B 6 (0 ≤ y ≤ 0.5), none of them reaching the limit corresponding to the hypothetically ordered “U 3 Ni 20 B 6 ” and “Nb 2 Ni 21 B 6 ”. These results prompted us to investigate quaternary compounds U 2– z Nb z Ni 21 B 6 and U δ Nb 3-δ Ni 20 B 6 : strong competition in the occupancy of the 4 a and 8 c sites by U, Nb, and Ni atoms has been observed, with the 4 a site occupied by U/Ni atoms only and the 8 c site filled by U/Nb atoms only. U 2 Ni 21 B 6 , U 2.3 Ni 20.7 B 6 , and Nb 3 Ni 20 B 6 are Pauli paramagnets. Interestingly, Nb 2.5 Ni 20.5 B 6 shows ferromagnetism with T C ≈ 11 K; the Curie–Weiss fit gives an effective magnetic moment of 2.78 μ B /Ni, suggesting that all Ni atoms in the formula unit contribute to the total magnetic moment. The M(H) data at 2 K further corroborate the ferromagnetic behavior with a saturation moment of 10 μ B /fu (≈0.49 μ B /Ni). The magnetic moment of Ni at the 4 a site induces a moment in all of the Ni atoms of the whole unit cell ( 32f and 48h sites), with all atoms ordering ferromagnetically at 11 K. Density functional theory (DFT) shows that the formation of U 2 Ni 21 B 6 and Nb 3 Ni 20 B 6 is energetically preferred. The various electronic states generating ferromagnetism on Nb 2.5 Ni 20.5 B 6 and Pauli paramagnetism on U 2 Ni 21 B 6 and Nb 3 Ni 20 B 6 have been identified.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Visualizing defects and pore connectivity within metal–organic frameworks by X-ray transmission tomography

Metal–Organic Frameworks (MOFs) have the potential to change the landscape of molecular separations in chemical processes owing to their ability of selectively binding molecules. Their molecular sorting properties generally rely on the micro- and meso-pore structure, as well as on the presence of coordinatively unsaturated sites that interact with the different chemical species present in the feed. In this work, we show a first-of-its-kind tomographic imaging of the crystal morphology of a metal– organic framework by means of transmission X-ray microscopy (TXM), including a detailed data reconstruction and processing approach. Corroboration with Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) images shows the potential of this strategy for further (non-destructively) assessing the inner architecture of MOF crystals. By doing this, we have unraveled the presence of large voids in the internal structure of a MIL-47(V) crystal, which are typically thought of as rather homogeneous lattices. This challenges the established opinion that hydrothermal syntheses yield relatively defect-free material and sheds further light on the internal morphology of crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Effect of pressure on heterocyclic compounds: Pyrimidine and s-triazine

We have examined the high-pressure behaviors of six-membered heterocyclic compounds of pyrimidine and s-triazine up to 26 and 26.5 GPa, respectively. Pyrimidine crystallizes in Pna2{sub 1} symmetry (phase I) with the freezing pressure of 0.3 GPa, and transforms to another phase (phase II) at 1.1 GPa. Raman spectra of several compression-decompression cycles demonstrate there is a critical pressure of 15.5 GPa for pyrimidine. Pyrimidine returns back to its original liquid state as long as the highest pressure is below 15.1 GPa. Rupture of the aromatic ring is observed once pressure exceeds 15.5 GPa during a compression-decompression cycle, evidenced by the amorphous characteristics of the recovered sample. As for s-triazine, the phase transition from R-3c to C2/c is well reproduced at 0.6 GPa, in comparison with previous Raman data. Detailed Raman scattering experiments corroborate the critical pressure for s-triazine may locate at 14.5 GPa. That is, the compression is reversible below 14.3 GPa, whereas chemical reaction with ring opening is detected when the final pressure is above 14.5 GPa. During compression, the complete amorphization pressure for pyrimidine and s-triazine is identified as 22.4 and 15.2 GPa, respectively, based on disappearance of Raman lattice modes. Synchrotron X-ray diffraction patterns and Fourier transform infrared spectra of recovered samples indicate the products in two cases comprise of extended nitrogen-rich amorphous hydrogenated carbon (a-C:H:N)

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Self-assembled peptide nanotubes as electronic materials: An evaluation from first-principles calculations

In this letter, we report on the evaluation of diphenylalanine (FF), dityrosine (YY), and phenylalanine-tryptophan (FW) self-assembled peptide nanotube structures for electronics and photonics applications. Realistic bulk peptide nanotube material models were used in density functional theory calculations to mimic the well-ordered tubular nanostructures. Importantly, validated functionals were applied, specifically by using a London dispersion correction to model intertube interactions and a range-separated hybrid functional for accurate bandgap calculations. Bandgaps were found consistent with available experimental data for FF, and also corroborate the higher conductance reported for FW in comparison to FF peptide nanotubes. Interestingly, the predicted bandgap for the YY tubular nanostructure was found to be slightly higher than that of FW, suggesting higher conductance as well. In addition, the band structure calculations along the high symmetry line of nanotube axis revealed a direct bandgap for FF. The results enhance our understanding of the electronic properties of these material systems and will pave the way into their application in devices.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2024

Larmor power limit for cyclotron radiation of relativistic particles in a waveguide

Cyclotron radiation emission spectroscopy (CRES) is a modern technique for high-precision energy spectroscopy, in which the energy of a charged particle in a magnetic field is measured via the frequency of the emitted cyclotron radiation. The He6-CRES collaboration aims to use CRES to probe beyond the standard model physics at the TeV scale by performing high-resolution and low-background beta-decay spectroscopy of 6 He and 19 Ne. Having demonstrated the first observation of individual, high-energy (0.1–2.5 MeV) positrons and electrons via their cyclotron radiation, the experiment provides a novel window into the radiation of relativistic charged particles in a waveguide via the time-derivative (slope) of the cyclotron radiation frequency, df c /dt. We show that analytic predictions for the total cyclotron radiation power emitted by a charged particle in circular and rectangular waveguides are approximately consistent with the Larmor formula, each scaling with the Lorentz factor of the underlying e ± as γ 4 . This hypothesis is corroborated with experimental CRES slope data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2020

Phosphorus alleviation of nitrogen‐suppressed methane sink in global grasslands

Abstract Grassland ecosystems account for more than 10% of the global CH 4 sink in soils. A 4‐year field experiment found that addition of P alone did not affect CH 4 uptake and experimental addition of N alone significantly suppressed CH 4 uptake, whereas concurrent N and P additions suppressed CH 4 uptake to a lesser degree. A meta‐analysis including 382 data points in global grasslands corroborated these findings. Global extrapolation with an empirical modelling approach estimated that contemporary N addition suppresses CH 4 sink in global grassland by 11.4% and concurrent N and P deposition alleviates this suppression to 5.8%. The P alleviation of N‐suppressed CH 4 sink is primarily attributed to substrate competition, defined as the competition between ammonium and CH 4 for the methane mono‐oxygenase enzyme. The N and P impacts on CH 4 uptake indicate that projected increases in N and P depositions might substantially affect CH 4 uptake and alter the global CH 4 cycle.

Zhang, Lihua↗

DOE OSTI2012

The Surprising Occurrence of Non-Steady-State Growth of Divergent Lamellar Decomposition Products in Uranium-Niobium Alloys: A Preliminary Report

Metastable materials are all expected to decompose sooner or later, but sometimes the kinetic paths they travel confound standard textbook explanations. Such is the case for supersaturated uranium-niobium alloy microstructures that transform to lamellar products in the 300-647 ºC temperature range. An experimental study of these isothermal transformation kinetics is reported here for U-5.5Nb and U-7.5Nb alloys. About 85 specimens from each alloy were isothermally aged at eight temperatures for durations spanning five orders of magnitude, up to two years. The volume fractions and growth rates of fine-spacing discontinuous precipitation (DP) and coarse-spacing discontinuous coarsening (DC) lamellar reaction products were directly measured by quantitative metallography. This study was enhanced by explicit consideration of the DP initiation site during measurements: (1) prior matrix grain boundaries (the usual site found in every alloy that produces DP) and (2) carbide inclusions (a rarely-encountered site). This constitutes the first systematic study of inclusion-nucleated DP in any alloy system. The growth rates were measured by the robust method of Cahn and Hagel (1963). The measurements were taken across the entire span of fraction transformed, giving the best opportunity to discriminate between typical vs. anomalous growth behavior. In both alloys the growth rates for DP and DC are constant at the lowest aging temperatures (300-400ºC), in line with standard explanations. The growth rates, however, noticeably diminish with reaction time at the higher aging temperatures (450-625ºC), dropping by an order of magnitude or more. These results corroborate as-yet unpublished data of divergent lamellar spacings (i.e., increase of the spacing with reaction time) observed at the same higher aging temperatures. These surprising results are rationalized in terms of kinetic competition for chemical driving force between the lamellar and precursor nonlamellar reactions on comparable time scales. In previous studies divergent lamellar products occurred only in transformations involving diffusion of both interstitial and substitutional elements. Since the same phenomena are now seen in a purely substitutional system like U-Nb, it is likely that divergent and time-varying lamellar reactions may be more prevalent in other substitutional alloy systems than previously thought.

36 MATERIALS SCIENCE↗

DOE OSTI2022

Impact of modifier-rich coatings on the ionic transport of glasses [Poster]

Ionic conduction in silicate glasses is mainly influenced by the nature, concentration, and mobility of the network-modifying (NWM) cations. The electrical conduction in SLS is dominated by the ionic migration of sodium moving from the anode to the cathode. An activation energy for this conduction process was calculated to be 0.82eV and in good agreement with values previously reported. The conduction process associated to the leakage current and relaxation peak in TSDC for HPFS is attributed to conduction between nonbridging oxygen hole centers (NBOHC). It is suggested that ≡Si-OH = ≡Si-O - + H 0 under thermo-electric poling, promoting hole or proton injection from the anode and responsible for the 1.5eV relaxation peak. No previous TSDC data have been found to corroborate this mechanism. The higher activation energy and lower current intensity for the coated HPFS might be attributed to a lower concentration of NBOHC after heat treatment (Si-OH + OH-Si = SiO-Si + H 2 O). This could explain the TSDC signal around room temperature for the coated HPFS. Another possible explanation could be a redox reaction at the anode region dominating the current response.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Non-Linear Langevin and Fractional Fokker–Planck Equations for Anomalous Diffusion by Lévy Stable Processes

The numerical solutions to a non-linear Fractional Fokker–Planck (FFP) equation are studied estimating the generalized diffusion coefficients. The aim is to model anomalous diffusion using an FFP description with fractional velocity derivatives and Langevin dynamics where Lévy fluctuations are introduced to model the effect of non-local transport due to fractional diffusion in velocity space. Distribution functions are found using numerical means for varying degrees of fractionality of the stable Lévy distribution as solutions to the FFP equation. The statistical properties of the distribution functions are assessed by a generalized normalized expectation measure and entropy and modified transport coefficient. The transport coefficient significantly increases with decreasing fractality which is corroborated by analysis of experimental data.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1989

Low frequency oscillations in total ozone measurements

Low frequency oscillations with periods of approximately one to two months are found in eight years of global grids of total ozone data from the Total Ozone Mapping Spectrometer (TOMS) satellite instrument. The low frequency oscillations corroborate earlier analyses based on four years of data. In addition, both annual and seasonal one-point correlation maps based on the 8-year TOMS data are presented. The results clearly show a standing dipole in ozone perturbations, oscillating with 35 to 50 day periods over the equatorial Indian Ocean-west Pacific region. This contrasts with the eastward moving dipole reported in other data sets. The standing ozone dipole appears to be a dynamical feature associated with vertical atmospheric motions. Consistent with prior analyses based on lower stratospheric temperature fields, large-scale standing patterns are also found in the extratropics of both hemispheres, correlated with ozone fluctuations over the equatorial west Pacific. In the Northern Hemisphere, a standing pattern is observed extending from the tropical Indian Ocean to the north Pacific, across North America, and down to the equatorial Atlantic Ocean region. This feature is most pronounced in the NH summer.

Gao, X. H.↗

NASA NTRS1990

Low-frequency oscillations in total ozone measurements

Gao, X. H.↗

NASA NTRS1976

Secular acceleration of Phobos and Q of Mars

Reductions of Mariner 9 TV data of Phobos and Deimos tend to corroborate the existence of a secular acceleration of Phobos commensurate with two recently reported values based on a reprocessing of earth-based data. These values of secular acceleration have been used together with Mariner 9 data on the physical size of Phobos and earth-based photoelectric observations which infer a carbonaceous composition for Phobos to place upper and lower bounds of 50 and 150, respectively, on the tidal dissipation function of Mars. The corresponding upper and lower bounds on the tidal lag angle are 0.19 and 0.57 deg.

Smith, J. C.↗

NASA NTRS1987

Recent data quality and earth science results from the Landsat thematic mapper

The results of the NASA Landsat Image Data Quality Analysis (LIDQA) program are reviewed. Landsat-4 and Landsat-5 TM data quality with regard to image geometry and radiometry are discussed. The results indicate that the TM provides excellent imagery that can be used in the form of satellite image maps meeting cartographic standards at scales of 1:100,000 or smaller. These data can be used to locate features or guide the revision or updating of maps for scales up to 1:24,000. The TM sensor is also providing data of good radiometric quality and stability, with radiometric uncertainties of 1 percent or smaller. The temperature dependence in the absolute radiometry is on the order of 1 to 5 percent of full scale. In terms of bidirectional reflectance estimated at the satellite, the error is estimated at under 6 percent and commonly 3 percent. Preliminary results also corroborate the utility of the TM data for geological or geographical studies.

Salomonson, Vincent V.↗

NASA NTRS1986

Radiometric responsivity determination for Feature Identification and Location Experiment (FILE) flown on space shuttle mission

A procedure was developed to obtain the radiometric (radiance) responsivity of the Feature Identification and Local Experiment (FILE) instrument in preparation for its flight on Space Shuttle Mission 41-G (November 1984). This instrument was designed to obtain Earth feature radiance data in spectral bands centered at 0.65 and 0.85 microns, along with corroborative color and color-infrared photographs, and to collect data to evaluate a technique for in-orbit autonomous classification of the Earth's primary features. The calibration process incorporated both solar radiance measurements and radiative transfer model predictions in estimating expected radiance inputs to the FILE on the Shuttle. The measured data are compared with the model predictions, and the differences observed are discussed. Application of the calibration procedure to the FILE over an 18-month period indicated a constant responsivity characteristic. This report documents the calibration procedure and the associated radiometric measurements and predictions that were part of the instrument preparation for flight.

Wilson, R. G.↗

DOE OSTI2019

Elucidating the nature of crystallization kinetics in Zr 46 Cu 46 Al 8 metallic glass through simultaneous WAXS/SAXS measurements

Simultaneous wide- and small-angle X-ray scattering (WAXS/SAXS) measurements were performed to investigate the low-temperature crystallization kinetics of Zr 46 Cu 46 Al 8 bulk metallic glass during isothermal annealing. Quantitative analysis of the WAXS intensity data indicated that the crystallization process was dominated by steady-state homogeneous nucleation and three-dimensional diffusion-controlled growth. This observation was corroborated by quantitative analysis of the SAXS data showing a saturation of the growth of nanoscale crystallites. Comparison of simultaneously measured WAXS and SAXS data showed evidence of composition fluctuation prior to crystallization, suggesting that the crystallization was facilitated by nanoscale phase separation which established regions of favorable compositions catalyzing crystallization. The temperature dependence of crystallization mechanisms and the resulting microstructures in metallic glass are discussed.

36 MATERIALS SCIENCE↗

NASA NTRS1972

Circulation of Prince William Sound

The author has identified the following significant results. Visual examination of the available ERTS-1 and NASA NP-3 aircraft imagery has suggested that sediment-laden plumes from rivers may be useful in tracking surface circulation over the regions where these plumes retain their visible identities. Plumes of ice derived from tidewater glaciers are highly visible on the ERTS-1 imagery, but are generally of too small an areal extent to be useful in tracing surface circulation. Shore-fast ice is also highly visible on the ERTS-1 data. Practical scientific results include a corroboration of the westward flow just offshore in the Gulf of Alaska with inflow through Hinchinbrook Entrance into Prince William Sound. The tracer in this case was the Copper River Plume, which originates at the mouth of the Copper River east of Prince William Sound. A single partial image of Port Valdez, in northeastern Prince William Sound, suggests by the visible suspended sediment distribution that surface circulation there was cyclonic, as deduced previously from oceanographic baseline data. Surf along the shoreline of the Gulf of Alaska is highly visible on ERTS-1 imagery.

Muench, R. D.↗

NASA NTRS1987

Low-frequency atmospheric oscillations over the southeastern Pacific

A 40-50 day atmospheric oscillation has recently been reported in the southeastern Pacific based on analyses of satellite-derived microwave brightness temperature data. Prior to this, such oscillations have not been generally recognized in this region. The purpose of this note is to provide corroboration of the microwave analyses from an independent data set, four years of rawinsonde data from Easter Island. Significant spectral peaks with period 45-53 days were found in the zonal wind near the jet core (300-200 mb) and in the temperature on the underside of the jet. The signal is also present in the 100 mb temperature as shown by strong coherence between 100 and 400 mb temperature perturbations. Direct comparison of the 100 mb temperature perturbations and the microwave data shows good agreement. There is also an indication of a lower frequency signal, about 65-84 day period, in the meridional wind at 1000 mb. This signal appears to be vertically evanescent with maximum amplitude at the surface.

Graves, Charles E.↗