Search NASA⌕ Search

SEARCH · Search NASA

Results for “Structured packing”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,459 records · Page 81
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

High-performance liquid chromatography of oligoguanylates at high pH

Because of the stable self-structures formed by oligomers of guanosine, standard high-performance liquid chromatography techniques for oligonucleotide fractionation are not applicable. Previously, oligoguanylate separations have been carried out at pH 12 using RPC-5 as the packing material. While RPC-5 provides excellent separations, there are several limitations, including the lack of a commercially available source. This report describes a new anion-exchange high-performance liquid chromatography method using HEMA-IEC BIO Q, which successfully separates different forms of the guanosine monomer as well as longer oligoguanylates. The reproducibility and stability at high pH suggests a versatile role for this material.

Non-NASA Center↗
NASA NTRS2009

Long Cable Deployments During Martian Touchdown: Lessons Learned

The launch of NASA/JPL's next generation Mars rover is planned for the fall of 2011. The landing scheme chosen for this rover represents a step forward in unmanned payload delivery. The rover will be lowered from a rocket powered descent stage and then placed onto the surface while hanging from three bridles. During this touchdown event, the communication between the rover and descent stage is maintained by an electrical umbilical cable which is deployed in parallel with the structural bridles. During the development of the deployment device for the electrical umbilical, many obstacles were identified and overcome. Many of these challenges were due in large part to the helical nature of the packing geometry of the umbilical cable. And although none of these issues resulted in the failure of the design, they increased both development and assembly time. Many of the issues and some of the benefits of a helical deployment were not immediately apparent during the trade studies carried out during the deployment selection process. Tests were conducted upon completion of the device in order to characterize both the deployment and separation characteristics of the cable. Extraction loads were needed for inputs to touchdown models and separation dynamics were required to assess cable-rover recontact risk. Understanding the pros and cons surrounding the deployment of a helically packed cable would most certainly influence the outcome of future trade studies surrounding the selection of cable deployment options.

Mars Science Lab↗
NASA NTRS2023

Progress in Predicting Ionic Cocrystal Formation: The Case of Ammonium Nitrate

In contrast to the mature predictive frameworks applied to neutral cocrystals, ionic cocrystals, those including an ion pair, are difficult to design. Furthermore, they are generally excluded categorically from studies which correlate specific molecular properties to cocrystal formation, leaving the prospective ionic cocrystal engineer with few clear avenues to success. Herein ammonium nitrate, an energetic oxidizing salt, is targeted for cocrystallization in a potential coformer group selected based on likely interactions with the nitrate ion as revealed in the Cambridge Structural Database; six novel ionic cocrystals were discovered. Molecular descriptors previously identified as being related to neutral cocrystal formation were examined across the screening group but showed no relationship with ionic cocrystal formation. High packing coefficient is shown to be a constant among the successful coformers in the set and is utilized to directly target two more successful coformers, bypassing the need for a large screening group.

Andrew J. Bennett↗
DOE OSTI2023

Study on the Carbon Nanostructures for Nanosized Si Electrodes

Silicon (Si) has been considered as a next-generation anode material due to natural abundance, low operating potential (<0.5 V vs. Li/Li+), and high theoretical specific capacity of 4200 mAh g-1.[1] However, the electrochemical alloying reaction of Si involves large volume changes of 400% during lithiation and delithiation, causing cracking and pulverization of Si.[1] In addition, solid electrolyte interface (SEI) of Si anode experiences constant changes due to unstable SEI reactivity.[2] Considerable efforts have been made to design nanostructured Si materials to address the issues because nanostructuring can relieve the mechanical strain.[3] However, when compared to micrometer-sized active materials having sufficient electrolyte pathway through interparticle space, the nanoparticle (NP)-based electrodes tend to be densely packed. As mass loading is higher and electrode is thicker, ion transport issue can become more severe in the densely packed electrodes.[4] In this work, we will present studies on engineered porosity impacts performance in Si NP electrodes by altering carbon nanostructures. We explore the extreme limit of effectively non-porous electrodes using quasi-spherical, Si NPs, which result in densely packed electrodes when slurry is prepared with conventional carbon black. We engineer porosity using carbon nanostructures including multi-walled carbon nanotubes and carbon nanorods in place of conventional carbon black to create pore structure in Si NP-based electrodes. These experiments provide a correlation between mass loading, porosity and silicon utilization in Si NP-based electrodes. References: [1] C. K. Chan, H. Peng, G. Liu, K. Mcllwrath, X. F. Zhang, R. A. Huggins, Y. Cui, "High-performance lithium battery anodes using silicon nanowires", Nat. Nanotechnol., 2008, 3, 31, [2] J. D. McBrayer, M.-T. F. Rodrigues, M. C. Schulze, D. P. Abraham, C. A. Apblett, I. Bloom, G. M. Carroll, A. M. Coclasure, C. Fang, K. L. Harrison, G. Liu, S. D. Minteer, N. R. Neale, G. M. Veith, C. S. Johnson, J. T. Vaughey, A. K. Burrel, B. Cunningham, "Calendar aging of silicon-containing batteries", Nat. Energy, 2021, 6, 1164, [3] H. Wu, G. Zheng, N. Liu, T. J. Carney, Y. Yang, Y. Cui, "Engineering Empty space between Si Nanoparticles for Lithium-Ion Battery Anodes", Nano Lett., 2012, 12, 904, [4] X. Zhang, Z. Ju, Y. Zhu, K. J. Takeuchi, E. S. Takeuchi, A. C. Marschilok, G. Yu, "Multiscale Understanding and Architecture Design of High Energy/Power Lithium-Ion Battery Electrodes", Adv. Energy Mater., 2021, 11, 2000808

carbon nanostructure↗
DOE OSTI2015

The cluster compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} containing Mo{sub 14} clusters and the new mono- and bi-capped trioctahedral Mo{sub 15} and Mo{sub 16} clusters: Synthesis, crystal structure, and electrical and magnetic properties

Single crystals of the new quaternary compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} were obtained by solid state reaction. The crystal structure was determined by single-crystal X-ray diffraction. In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} crystallizes in the orthorhombic space group Pbca with unit-cell parameters a=9.4432(14) Å, b=11.4828(12) Å, c=20.299(4) Å and Z=4. Full-matrix least-squares refinement on F{sup 2} using 3807 independent reflections for 219 refinable parameters resulted in R{sub 1}=0.0259 and wR{sub 2}=0.0591. The crystal structure contains in addition to Mo{sub 14} clusters the first examples of mono- and bi-capped trioctahedral Mo{sub 14} i.e. Mo{sub 15} and Mo{sub 16} clusters. The oxygen framework derives from a stacking along the a direction of close-packed layers with sequence (…ABAC…). The Mo–Mo distances range between 2.6938(5) and 2.8420(6) Å and the Mo–O distances between 1.879(5) and 2.250(3) Å, as usually observed in molybdenum oxide clusters. The indium atoms form In{sub 4}{sup 6+} bent chains with In–In distances of 2.6682(5) and 2.6622(8) Å and the Ti atoms are in highly distorted octahedral sites of oxygen atoms with Ti–O distances ranging between 1.865(4) and 2.161(4) Å. Magnetic susceptibility measurements confirm the presence of Ti{sup 4+} cations and the absence of localized moments on the Mo network. Electrical resistivity measurements on a single crystal of In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} show a semimetallic behavior. - Graphical abstract: We present here the synthesis, the crystal structure, and the electrical and magnetic properties of the new compound In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} in which Mo{sub 14} clusters coexist statistically with mono- and bi-capped trioctahedral Mo{sub 14} that is Mo{sub 15} and Mo{sub 16} clusters. - Highlights: • Single crystals of In{sub 4}Ti{sub 1.5}Mo{sub 0.5}Mo{sub 14}O{sub 26} were obtained by solid state reaction. • The crystal structure contains Mo{sub 14}, Mo{sub 15} and Mo{sub 16} clusters. • The indium atoms form In{sub 4}{sup 6+} bent chains. • Poorly metallic behavior. • Absence of localized moments on the Mo network as well as on the Ti atoms.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Crystal structure of 4-[benzylideneamino]-3-thiophen-2-yl-methyl-4,5-dihydro-1H-[1,2,4]triazole-5-one

The crystal structure of the title compound C{sub 14}H{sub 12}N{sub 4}OS was determined by the X-ray diffraction method. The compound crystallizes in the triclinic space group <##> } P } 1 }&#x00AF;<!-- ?? --> $ P/bar 1 $ P 1-bar </##> with Z = 2. The molecule is not planar: the dihedral angle between the triazole and thiophene rings is 73.98(2)°, and that between the triazole and benzene rings is 4.05(2)°. The thiophene ring is disordered over two positions, which are approximately parallel and oppositely oriented. The major component refined to a site-occupancy factor of 0.573(3). An intramolecular C-H...O hydrogen bond generates an S(6) ring motif. In the crystal, molecules are linked together by two pairs of N-H...O interactions (to the same O atom as acceptor), forming inversion dimers. The crystal packing is also stabilized by π-π interactions [centroid-centroid distance is 3.978 Å].

36 MATERIALS SCIENCE↗
DOE OSTI2012

Structural studies of high-K{sub u} metastable CoPt thin films with long-range order

The symmetries of CoPt thin films in different phases, including disordered A1, ordered L1{sub 1}, and L1{sub 0} were examined by making measurements along the (10.1) diffraction rod. The films were deposited by sputtering on MgO(111) substrates at different temperatures (T{sub a}). The stacking sequence of close-packed atomic planes in 50 nm-thick samples with T{sub a} {>=} 200 deg. C was identified as ABCABC, indicating that the distribution of defects in the film was random, so the symmetry was preserved with increasing T{sub a}. In the RT-prepared film, a considerable amount of ({approx}62.9 vol.%) disordered CoPt with hexagonal symmetry was detected, vanishing as T{sub a} increased. Defect-induced modification of symmetry was observed in the L1{sub 1} film as its thickness was reduced to 10 nm. A pseudo-hcp component of around 7.1 vol.% was present in the film, as a result of the periodic distribution of defects. The defects in the structure may also explain the broadened magnetic alignment.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Mechanisms of Local Stress Sensing in Multifunctional Polymer Films Using Fluorescent Tetrapod Nanocrystals

Nanoscale stress-sensing can be used across fields ranging from detection of incipient cracks in structural mechanics to monitoring forces in biological tissues. We demonstrate how tetrapod quantum dots (tQDs) embedded in block copolymers act as sensors of tensile/compressive stress. Remarkably, tQDs can detect their own composite dispersion and mechanical properties with a switch in optomechanical response when tQDs are in direct contact. Using experimental characterizations, atomistic simulations and finite-element analyses, we show that under tensile stress, densely packed tQDs exhibit a photoluminescence peak shifted to higher energies ("blue-shift") due to volumetric compressive stress in their core; loosely packed tQDs exhibit a peak shifted to lower energies ("red-shift") from tensile stress in the core. The stress shifts result from the tQD's unique branched morphology in which the CdS arms act as antennas that amplify the stress in the CdSe core. Our nanocomposites exhibit excellent cyclability and scalability with no degraded properties of the host polymer. Colloidal tQDs allow sensing in many materials to potentially enable autoresponsive, smart structural nanocomposites that self-predict upcoming fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2021

New insights into the mechanism governing the elasticity of calcium silicate hydrate gels exposed to high temperature: A molecular dynamics study

When exposed to fire, the integrity of cement-based materials is governed by thermally-induced changes in the mechanical properties of their binding phase, i.e., the calcium–silicate–hydrate (C–S–H) gel. However, the effect of temperature on the structure, density, and mechanical properties of C–S–H remains only partially known. Here, based on reactive molecular dynamics simulations, we reveal the nature of thermally-induced damage in C–S–H gels. In general, we show that, at the atomic scale, exposure to high temperature results in partial dehydration, volumetric shrinkage, disordering, and stiffening in the C–S–H grains. However, we show that the thermal response of C–S–H strongly depends on its chemical composition, wherein C–S–H systems associated with lower Ca/Si molar ratios are able to undergo higher temperatures before amorphization. Based on these results, we demonstrate that the stiffness of C–S–H gels (i.e., including porosity—as probed by nanoindentation) is governed by a competition between the stiffening of the grains and the decrease in packing density—wherein the latter eventually become predominant.

36 MATERIALS SCIENCE↗
NASA NTRS2018

Super Ball Bot - Structures for Planetary Landing and Exploration

Small, light-weight and low-cost missions will become increasingly important to NASA's exploration goals for our solar system. Ideally teams of dozens or even hundreds of small, collapsable robots, weighing only a few kilograms a piece, will be conveniently packed during launch and would reliably separate and unpack at their destination. Such teams will allow rapid, reliable in-situ exploration of hazardous destination such as Titan, where imprecise terrain knowledge and unstable precipitation cycles make single-robot exploration problematic. Unfortunately landing many lightweight conventional robots is difficult with conventional technology. Current robot designs are delicate, requiring combinations of devices such as parachutes, retrorockets and impact balloons to minimize impact forces and to place a robot in a proper orientation. Instead we propose to develop a radically different robot based on a "tensegrity" built purely upon tensile and compression elements. These robots can be light-weight, absorb strong impacts, are redundant against single-point failures, can recover from different landing orientations and are easy to collapse and uncollapse. We believe tensegrity robot technology can play a critical role in future planetary exploration.

Agogino, Adrian K.↗
NASA NTRS2018

Development of an Inflatable Airlock for a Deep Space Gateway

Inflatable structures technology utilizes high-strength fabric materials and internal pressure to create a stiffened pressure vessel that can replace traditional metallic primary structure in a habitable spacecraft. The flexibility of fabric structures allows them to be compactly stowed for launch and expanded in space, providing significant launch volume savings. The unique construction and design flexibility of these structures can be customized for a variety of uses in space including landing bags, decelerators, long duration in-space and planetary surface habitats, and even airlocks. An airlock is often a required component of a crewed spacecraft to allow for maintenance and human exploration outside of the vehicle. Airlock designs in use today rely on complex hatches and seals connected by metallic walls. Recent developments towards the design of an inflatable airlock structure show feasibility and a significant launch volume savings over a traditional metallic design. This paper will provide a high-level summary of these projects and the current state-of-the-art in inflatable airlock development with additional references and detail about previous and on-going research, providing guidance for the design of a softgoods airlock system. The use of inflatables in space has been in development since the 1960’s for both habitats and airlocks. The first ever EVA was conducted by the USSR in 1965 using an inflatable airlock known as the Volga. This airlock was attached to the Voskhod 2 spacecraft and turned the vehicle into a dual chamber airlock. The airlock was successfully deployed, used and jettisoned after Alexey Leonov’s historic spacewalk. Additional work on human-rated inflatable structures was not continued until the late 1990’s when NASA-JSC led an effort to demonstrate these structures as feasible long-term pressurized elements with the TransHab project. The technology developed and pioneered during this project led to multiple patents and proven feasibility that inflatables could be used for large habitable structures. Following TransHab, Bigelow Aerospace continued the development of inflatable structures with technical support from NASA. This partnership eventually led to the successful flight certification, launch, attachment and deployment of the Bigelow Expandable Activities Module (BEAM) on the ISS in 2016. Inflatable and expandable airlock structures have undergone various detailed feasibility studies and testing for over 15 years, most notably with the Advanced Inflatable Airlock (AIA), Dual-Chamber Hybrid Inflatable Suitlock (DCIS), Minimalistic Advanced Soft Hatch (MASH), and Lightweight External Inflatable Airlock (LEIA). During this time, full-scale articles have been built and pressure-tested, and mock-ups and demonstrators have been constructed and evaluated. During the 2001-2003 timeframe, the AIA concept was matured through requirements development, conceptual design, subscale and full-scale engineering breadboards subjecting various test articles to deployment and pressure testing up to four times operating pressure. These tests proved the feasibility of successful deployment and structural integrity of an inflatable crewlock. Additional testing was performed in the ensuing years, as funding permitted, to further refine additional structural and deployment concepts and to understand the EVA crewmember interfaces, hatches and EVA support equipment interfaces that would be required for a fully functioning airlock. This work resulted in a refinement of the structural requirements and an accounting of the systems needed in an inflatable airlock. In 2014, the MASH project developed an ultra-lightweight airlock concept with a fabric hatch that utilized a unique pressure vessel shape to minimize structural loads around a linear seal. The concept uses an automated zipper-like seal that allows for crew egress/ingress. Most of the development work on the project thus far has focused on the design, analysis and testing of the primary structure and the zipper-like seal system is in the preliminary stages of development with a successful proof-of-concept test. As part of the 2017 LEIA effort, studies were conducted on EVA crewmember interfaces on the inside of an inflatable airlock. These efforts included the design of an internal secondary structure and placement of handholds and foot restraints to enable hatch opening, closing and translation through the airlock. Structural design, analysis and testing was completed on several secondary structure candidates. Crew interface testing was also completed using an inflatable crewlock mockup and the JSC Active Response Gravity Offload System (ARGOS) to simulate the movement of an EVA crewmember through an inflatable crewlock in microgravity. The results of these tests helped demonstrate the feasibility of utilizing an inflatable structure as an airlock and informed the required volume, hatch size, and configuration and location of translation aids for crewmembers in a microgravity crewlock. The ISS Quest airlock uses a dual-chamber design with isolated compartments known as the equipment-lock and the crewlock. The equipment-lock houses the Servicing, Performance and Checkout Equipment (SPCE) items (suit batteries, consumables, etc.) while the crewlock has limited internal hardware and is the nominally depressurized compartment during US EVAs. While inflatable dual chamber airlocks have been studied, the current state of the art emphasizes an inflatable crewlock-type structure attached to a rigid equipment-lock type or habitat structure. Since a large portion of the hardware in the equipment-lock are rigid components and connectors that are installed on the ground - and an inflatable structure does not achieve full structural capabilities until pressurized in space - a depressurized fabric structure cannot provide the capabilities of a full equipment-lock. The use of an inflatable as a crewlock, however, provides all the required capabilities for EVA operations in a small launch package that offers significant volume savings over a metallic crewlock. The functions of a traditional equipment lock, including the SPCE, could be provided by a spacecraft’s habitat module or node and not necessarily in a separate equipment lock. An inflatable crewlock would be attached to the vehicle and launched in a packed and compressed state, saving volume under the launch shroud and mass for the overall airlock element compared to a rigid crewlock. Work is currently underway to continue development of an inflatable airlock with a variety of focus areas including the consideration of crew-induced loads and interfaces, the design and development of an internal sub-structure to provide translation aids and restraints, the thermal considerations of a fabric shell depressurized during an EVA, the micrometeorite environment in deep space, and the packaging and deployment of an inflatable airlock.

Deep Space Exploration↗
DOE OSTI2023

Structure, Dynamics, and Hydrogen Transport in Amorphous Polymers: An Analysis of the Interplay between Free Volume Element Distribution and Local Segmental Dynamics from Molecular Dynamics Simulations

Polymers are attractive membrane materials owing to their mechanical robustness and relatively inexpensive fabrication. An important indicator of membrane performance are free volume elements (FVE): microporous void spaces created by the inefficient packing of bulky groups along the polymer chain. FVEs tend to degrade over time, as polymer chains reorganize irreversibly. While it is widely accepted that polymer flexibility has an impact on membrane transport properties, the molecular nature of this impact is still not well understood. By the establishment of a correlation between local chain dynamics and the distribution of free volume elements (FVEs), penetrant transport can be regulated more efficiently in amorphous polymer membranes. In this work, we implement all-atom molecular dynamics (MD) simulations to explore the relationship between chain dynamics and free volume in three polymers with different levels of backbone flexibility: polymethylpentene (PMP), polystyrene (PS), and HAB-6FDA thermally rearranged polymer (TRP). We construct these polymers at different temperatures and examine how temperature impacts the FVE distribution and segmental mobility. Our analysis shows that chain segments near FVEs have higher mobility compared with the atoms in the bulk; the extent of this difference increases with chain flexibility. Increasing the chain flexibility by increasing the temperature results in a broader FVE distribution. Rigid polymers such as TRP show the most robust FVE distribution and are not significantly affected by the temperature change. To capture penetrant diffusion through the polymer matrix, hydrogen is inserted and the diffusion is measured at different temperatures; hydrogen mobility is influenced by the FVE structure and overall mobility of polymer chains. Lastly, at low temperatures, hydrogen mobility is influenced by void distribution, while at high temperatures, polymer dynamics dictate hydrogen transport.

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

Effective interactions between nanoparticles: Creating temperature-independent solvation environments for self-assembly

The extent to which solvent-mediated effective interactions between nanoparticles can be predicted based on structure and associated thermodynamic estimators for bulk solvents and for solvation of single and pairs of nanoparticles is studied here. As a test of the approach, we analyse the strategy for creating temperature-independent solvent environments using a series of homologous chain fluids as solvents, as suggested by an experimental paper [M. I. Bodnarchuk et al., J. Am. Chem. Soc. 132, 11967 (2010)]. Our conclusions are based on molecular dynamics simulations of Au{sub 140}(SC{sub 10}H{sub 21}){sub 62} nanoparticles in n-alkane solvents, specifically hexane, octane, decane and dodecane, using the TraPPE-UA potential to model the alkanes and alkylthiols. The 140-atom gold core of the nanocrystal is held rigid in a truncated octahedral geometry and the gold-thiolate interaction is modeled using a Morse potential. The experimental observation was that the structural and rheological properties of n-alkane solvents are constant over a temperature range determined by equivalent solvent vapour pressures. We show that this is a consequence of the fact that long chain alkane liquids behave to a good approximation as simple liquids formed by packing of monomeric methyl/methylene units. Over the corresponding temperature range (233–361 K), the solvation environment is approximately constant at the single and pair nanoparticle levels under good solvent conditions. However, quantitative variations of the order of 10%–20% do exist in various quantities, such as molar volume of solute at infinite dilution, entropy of solvation, and onset distance for soft repulsions. In the opposite limit of a poor solvent, represented by vacuum in this study, the effective interactions between nanoparticles are no longer temperature-independent with attractive interactions increasing by up to 50% on decreasing the temperature from 361 K to 290 K, accompanied by an increase in emergent anisotropy due to correlation of mass dipoles on the two nanoparticles. One expects therefore that during self-assembly using solvent evaporation, temperature can be used as a structure-directing factor as long as good solvent conditions are maintained. It also suggests that disordered configurations may emerge as solvent quality decreases due to increasing role of short-range attractions and ligand fluctuation-driven anisotropy. The possibilities of using structural estimators of various thermodynamic quantities to analyse the interplay of ligand fluctuations and solvent quality in self-assembly as well as to design solvation environments are discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Phase Transition of H 2 in Subnanometer Pores Observed at 75 K

In this paper, we report a phase transition in H 2 adsorbed in a locally graphitic Saran carbon with subnanometer pores 0.5–0.65 nm in width, in which two layers of hydrogen can just barely squeeze, provided they pack tightly. The phase transition is observed at 75 K, temperatures far higher than other systems in which an adsorbent is known to increase phase transition temperatures: for instance, H 2 melts at 14 K in the bulk, but at 20 K on graphite because the solid H 2 is stabilized by the surface structure. Here we observe a transition at 75 K and 77–200 bar: from a low-temperature, low-density phase to a high-temperature, higher density phase. We model the low-density phase as a monolayer commensurate solid composed mostly of para-H 2 (the ground nuclear spin state, S = 0) and the high-density phase as an orientationally ordered bilayer commensurate solid composed mostly of ortho-H 2 (S = 1). We attribute the increase in density with temperature to the fact that the oblong ortho-H 2 can pack more densely. The transition is observed using two experiments. The high-density phase is associated with an increase in neutron backscatter by a factor of 7.0 ± 0.1. Normally, hydrogen produces no backscatter (scattering angle >90°). This backscatter appears along with a discontinuous increase in the excitation mass from 1.2 amu to 21.0 ± 2.3 amu, which we associate with collective nuclear spin excitations in the orientationally ordered phase. Film densities were measured using hydrogen adsorption. Finally, no phase transition was observed in H 2 adsorbed in control activated carbon materials.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A Comparative Study of Phosphoric Acid-doped m-PBI Membranes

Phosphoric acid (PA)-doped m-polybenzimidazole (PBI) membranes used in high temperature fuel cells and hydrogen pumps were prepared by a conventional imbibing process and a sol-gel fabrication process. A comparative study was conducted to investigate the critical properties of PA doping levels, ionic conductivities, mechanical properties, and molecular ordering. This systematic study found that sol-gel PA-doped m-PBI membranes were able to absorb higher acid doping levels and to achieve higher ionic conductivities than conventionally imbibed membranes when treated in an equivalent manner. Even at similar acid loadings, the sol-gel membranes exhibited higher ionic conductivities. Heat treatment of conventionally imbibed membranes with 29wt% solids caused a significant reduction in mechanical properties; conversely, sol-gel membranes exhibited an enhancement in mechanical properties. From X-ray structural studies and atomistic simulations, both conventionally imbibed and sol-gel membranes exhibited d-spacings of 3.5 and 4.6 , which were tentatively attributed to parallel ring stacking and staggered side-to-side packing, respectively, of the imidazole rings in these aromatic hetercyclic polymers. An anisotropic staggered side-to-side chain packing present in the conventional membranes may be root to the reduction in mechanical properties.

fuel cells↗
DOE OSTI2019

Extended range X-ray pair distribution functions

Here we describe a dual detector system for high-energy X-ray, simultaneous, small and wide-angle X-ray scattering (SAXS and WAXS), designed to extract extended-range pair distribution functions (ER-PDF) for disordered materials. The hardware and software provides continuous reciprocal space coverage over atomic to nanometer length-scales. Details of the varying resolution, splicing of data and normalization on an absolute scale are outlined. In addition, the combination of SAXS and WAXS theory is considered with a view to enabling a direct Fourier transformation of the structure factor spanning multiple length-scales into real space. Important distinctions between the ER-PDF and the pair distance distribution function (PDDF) representations are demonstrated. It is shown that when the SAXS intensity in the structure factor, S(Q), is similar to the WAXS intensity, the contributions to the ER-PDF are minimal. However, when the SAXS S(Q) intensities are substantially stronger than the WAXS, the ER-PDF can provide important structural information on the local, intermediate and nanometer length-scales. Notably, the ER-PDF method provides direct information on particle sizes and their density distributions, overcoming the limitations of PDDF analysis for densely packed systems.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Observation and characterization of the smallest borospherene, B{sub 28}{sup −} and B{sub 28}

Free-standing boron nanocages or borospherenes have been observed recently for B{sub 40}{sup −} and B{sub 40}. There is evidence that a family of borospherenes may exist. However, the smallest borospherene is still not known. Here, we report experimental and computational evidence of a seashell-like borospherene cage for B{sub 28}{sup −} and B{sub 28}. Photoelectron spectrum of B{sub 28}{sup −} indicated contributions from different isomers. Theoretical calculations showed that the seashell-like B{sub 28}{sup −} borospherene is competing for the global minimum with a planar isomer and it is shown to be present in the cluster beam, contributing to the observed photoelectron spectrum. The seashell structure is found to be the global minimum for neutral B{sub 28} and the B{sub 28}{sup −} cage represents the smallest borospherene observed to date. It is composed of two triangular close-packed B{sub 15} sheets, interconnected via the three corners by sharing two boron atoms. The B{sub 28} borospherene was found to obey the 2(n + 1){sup 2} electron-counting rule for spherical aromaticity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Structural and magnetic properties of the new cobaltate series (BaSr)4-xLa2xCo4O15

We report the structural and magnetic properties of a new class of cobaltates with the chemical formula (BaSr)4-xLa2xCo4O15 (x = 0, 0.5 and 1). These compounds crystallize in a hexagonal structure in which cobalt ions are distributed among two distinct crystallographic sites with dierent oxygen coordination. Three Co{O tetrahedra and one octahedron are linked by shared oxygen atoms to form Co4O15 clusters, which are packed together into a honeycomb-like network. Partial substitution of Sr and/or Ba atoms by La allows one to adjust the degree of Co valence mixing, but all compositions remain subject to a random distribution of charge. Magnetic susceptibility together with neutron scattering measurements reveal that all studied specimens are characterized by competing ferro- and antiferro-magnetic exchange interactions that give rise to a three dimensional Heisenberg spin-glass state. Neutron spectroscopy shows a clear trend of slowing down of spindynamics upon increasing La concentration, suggesting a reduction in charge randomness in the doped samples.

Garlea, Elena↗