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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Tuning the extent of porosity and composition of N-doped carbon materials by NaNO3 and its effect on electrochemical activity

Highlights: • One-pot method using cheap NaNO{sub 3} as etching agent was developed to tune the porous structure. • NaNO{sub 3} was added into NaCl/ZnCl{sub 2} (NaCl 80 mol%) to form ionothermal salts. • The resultant carbon possesses a 3D hierarchical structure, with more mesopores ratio than micropores. • When NaNO{sub 3} amount is 5% in the salt mixture, the optimal ORR activity was obtained. - Abstract: A facile one-pot method using NaNO{sub 3} as etching agent in a molten salt medium is developed to tune the porous structure and composition of N-doped carbon materials derived from biomass at high temperatures. SEM and TEM analyses reveal that by increasing the amount of NaNO{sub 3}, the structures of the obtained carbons become more open and graphene-like layers are formed. N{sub 2} adsorption/desorption isotherms show that the hierarchical porous structure could be efficiently tuned by adjusting the amount of NaNO{sub 3} in the salt mixture. It is observed that the specific surface area of the as-prepared N-doped carbon using NaNO{sub 3} can reach 1430.1 m{sup 2} g{sup −1}, a much higher value than that of the sample prepared in the absence of NaNO{sub 3}. The micropore ratio decreases with increased amount of NaNO{sub 3}, from 49.42% to 9.98%. Whilst the surface composition of the obtained carbon materials is affected by NaNO{sub 3}. The N content increases and O decreases respectively, by increasing the amount of NaNO{sub 3}. Analysis on the N 1s high resolution reveals that the sum of pyridinic-N and graphitic-N increased, whereas the sum of pyridinic-N oxide and NO{sub x} decreases from NC-0 to NC-0.75. It is also found that the changes of the porous structure and the oxygen-containing groups from NC-0 to NC-0.75 led to changes in hydrophilicity. When the as-prepared carbon materials are used as catalysts for the oxygen reduction reaction, high catalytic activity values are obtained, sample NC-0.5 shows the best performance due to the porous structure and doping effect of N atoms. More importantly, it is concluded that producing N-doped carbon materials from soybean dregs in molten salt medium using NaNO{sub 3} as etching agent could provide a promising approach for the synthesis of opened N-doped carbons of controlled porous structures and large specific surface areas based on biomass precursors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Modeling of interdendritic porosity defects in an integrated computational materials engineering approach for metal casting

Modeling and simulation of multiphysical phenomena needs to be considered in the design and optimization of mechanical properties of cast components in order to accelerate the introduction of new cast alloys. The data on casting defects, including microstructure features, is crucial for evaluating the final performance-related properties of the component. Here in this paper, the required models for the prediction of interdendritic casting defects, such as microporosity and hot tears, are reviewed. The data on calculated solidification shrinkage is presented and its effects on microporosity levels discussed. Numerical simulation results for microporosity are presented for A356, 356 and 319 aluminum alloys using ProCAST TM software. The calculated pressure drop of the interdendritic liquid was observed to be quite significant and the regions of high-pressure drop can be used as an indicator of the severity of interdendritic microporosity defects.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Porosity and structural parameters of Karelian shungites according to the data of small-angle synchrotron radiation scattering and microscopy

The nanoporosity and structure of natural carbons has been investigated on the example of Karelian carbon-rich shungites by comparing the data of small-angle synchrotron radiation scattering and highresolution microscopy. The analysis of small-angle scattering data is based on the model of scattering spheres with lognormal size distribution. It is found that the structure of samples from the Maksovo and Zazhogino deposits subjected to high temperatures in the geological medium and (also to a lesser extent) a sample from the Shunga deposit can be described as an aggregation of polydisperse scattering spheres with lognormal size distribution; the characteristic scatterer size is determined for them. A comparison with microscopy data shows that these scatterers are mainly associated with pores, and the character of their size distribution is similar to that previously established for nanoglobules in schungites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2003

Asteroid density, porosity, and structure

New data from observations of asteroid mutural perturbation events, observations of asteroid satellites, and spacecraft encounters have revolutionized our understanding of asteroid bulk density.

densities↗
DOE OSTI2014

Effects of graphite porosity and anisotropy on measurements of elastic modulus using laser untrasonics

Laser ultrasonic techniques can be used to study the ultrasonic properties of nuclear graphites and can serve as tools in establishing relationships between materials microstructure and the macroscopic stiffnesses of graphite. Establishing structure-property relationships permits improved ultrasonic sensing of graphite microstructural changes related to service-induced degradation. Laser ultrasonic measurements were made using a pulsed Nd:YAG laser source and detection was performed using a Michelson-type interferometer. This source-receiver combination provides for non-contacting, highly linear transduction of broadbanded, ultrasonic pulses permitting simultaneous determination of longitudinal and shear stiffnesses. Measurements show that among the graphites examined, a change in density of 0.26 g/cm3 (average 1.8 g/cm3) results in a change in the longitudinal elastic stiffness of 9.2 GPa (average 11.3 GPa) and 3.2 GPa (average 4.3 GPa) for the shear stiffness. Larger variations in density were produced by controlled oxidation of IG-110 and NBG-18. Shear wave birefringence measurements using laser line sources in IG-110 and PCEA indicate that IG-110 behaves isotropically while PCEA displays texture characteristic of transversely isotropic materials.

ANISOTROPY↗
DOE OSTI2018

Facile Fabrication of Large‐Area Atomically Thin Membranes by Direct Synthesis of Graphene with Nanoscale Porosity

Abstract Direct synthesis of graphene with well‐defined nanoscale pores over large areas can transform the fabrication of nanoporous atomically thin membranes (NATMs) and greatly enhance their potential for practical applications. However, scalable bottom‐up synthesis of continuous sheets of nanoporous graphene that maintain integrity over large areas has not been demonstrated. Here, it is shown that a simple reduction in temperature during chemical vapor deposition (CVD) on Cu induces in‐situ formation of nanoscale defects (≤2–3 nm) in the graphene lattice, enabling direct and scalable synthesis of nanoporous monolayer graphene. By solution‐casting of hierarchically porous polyether sulfone supports on the as‐grown nanoporous CVD graphene, large‐area (>5 cm 2 ) NATMs for dialysis applications are demonstrated. The synthesized NATMs show size‐selective diffusive transport and effective separation of small molecules and salts from a model protein, with ≈2–100× increase in permeance along with selectivity better than or comparable to state‐of‐the‐art commercially available polymeric dialysis membranes. The membranes constitute the largest fully functional NATMs fabricated via bottom‐up nanopore formation, and can be easily scaled up to larger sizes permitted by CVD synthesis. The results highlight synergistic benefits in blending traditional membrane casting with bottom‐up pore creation during graphene CVD for advancing NATMs toward practical applications.

Kidambi, Piran R.↗
DOE OSTI2019

Polymers with Side Chain Porosity for Ultrapermeable and Plasticization Resistant Materials for Gas Separations

Polymer membranes with ultrahigh CO 2 permeabilities and high selectivities are needed to address some of the critical separation challenges related to energy and the environment, especially in natural gas purification and postcombustion carbon capture. However, very few solution-processable, linear polymers are known today that access these types of characteristics, and all of the known structures achieve their separation performance through the design of rigid backbone chemistries that concomitantly increase chain stiffness and interchain spacing, thereby resulting in ultramicroporosity in solid-state chain-entangled films. Herein, the separation performance of a porous polymer obtained via ring-opening metathesis polymerization is reported, which possesses a flexible backbone with rigid, fluorinated side chains. This polymer exhibits ultrahigh CO 2 permeability (>21 000 Barrer) and exceptional plasticization resistance (CO 2 plasticization pressure > 51 bar). Compared to traditional polymers of intrinsic microporosity, the rate of physical aging is slower, especially for gases with small effective diameters (i.e., He, H 2 , and O 2 ). Overall, this structural design strategy, coupled with studies on fluorination, demonstrates a generalizable approach to create new polymers with flexible backbones and pore-forming side chains that have unexplored promise for small-molecule separations.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Engineering Permanent Porosity into Liquids

The possibility of engineering well-defined pores into liquid materials is fascinating from both a conceptual and an applications point of view. Although the concept of porous liquids was proposed in 2007, these materials had remained hypothetical due to the technical challenges associated with their synthesis. Over the past five years, however, reports of the successful construction of porous liquids based on existing porous scaffolds, such as coordination cages, organic cages, metal–organic frameworks, porous carbons, zeolites, and porous polymers, have started to emerge. Here, the focus is on these early reports of porous liquids as prototypes in the field, classified according to the previously defined types of porous liquids. Particular attention will be paid to design strategies and structure–property relationships. Porous liquids have already exhibited promising applications in gas storage, transportation, and chemical separations. Furthermore, they show great potential for use in the chemical industry. The challenges of preparation, scale-up, volatility, thermal and chemical stability, and competition with porous solids will also be discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Precision Calcination Mechanism of CaCO 3 to High-Porosity Nanoscale CaO CO 2 Sorbent Revealed by Direct In Situ Observations

Deploying energy storage and carbon capture at scale is hindered by the substantial endothermic penalty of decomposing CaCO 3 to CaO and CO 2 , and the rapid loss of CO 2 absorption capacity by CaO sorbent particles due to sintering at the high requisite decomposition temperatures. The decomposition reaction mechanism underlying sorbent deactivation remains unclear at the atomic level and nanoscale due to past reliance on postmortem characterization methods with insufficient spatial and temporal resolution. Thus, elucidating the important CaCO 3 decomposition reaction pathway requires direct observation by time-resolved (sub-)nanoscale methods. Here, chemical and structural dynamics during the decomposition of CaCO 3 nanoparticles to nanoporous CaO particles comprising high-surface-area CaO nanocrystallites are examined. Comparing in situ transmission electron microscopy (TEM) and synchrotron X-ray diffraction experiments gives key insights into the dynamics of nanoparticle calcination, involving anisotropic CaCO 3 thermal distortion before conversion to thermally dilated energetically stable CaO crystallites. Time-resolved TEM uncovered a novel CaO formation mechanism involving heterogeneous nucleation at extended CaCO 3 defects followed by sweeping reaction front motion across the initial CaCO 3 particle. These observations clarify longstanding, yet incomplete, reaction mechanisms and kinetic models lacking accurate information about (sub-)nanoscale dynamics, while also demonstrating calcination of CaCO 3 without sintering through rapid heating and precise temperature control.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ambient Electrosynthesis of Ammonia: Electrode Porosity and Composition Engineering

Ammonia, a key precursor for fertilizer production, convenient hydrogen carrier, and emerging clean fuel, plays a pivotal role in sustaining life on Earth. Currently, the main route for NH 3 synthesis is by the heterogeneous catalytic Haber–Bosch process (N 2 +3 H 2 →2 NH 3 ), which proceeds under extreme conditions of temperature and pressure with a very large carbon footprint. Herein we report that a pristine nitrogen–doped nanoporous graphitic carbon membrane (NCM) can electrochemically convert N 2 into NH 3 in an acidic aqueous solution under ambient conditions. The Faradaic efficiency and rate of production of NH 3 on the NCM electrode reach 5.2 % and 0.08 g m –2 h –1 , respectively. Functionalization of the NCM with Au nanoparticles dramatically enhances these performance metrics to 22 % and 0.36 gm –2 h –1 , respectively. In conclusion, as this system offers the potential to be scaled to industrial levels it is highly likely that it might displace the century-old Haber–Bosch process.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗