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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Controlled surface segregation leads to efficient coke-resistant nickel/platinum bimetallic catalysts for the dry reforming of methane

Surface composition and structure are of vital importance for heterogeneous catalysts, especially for bimetallic catalysts, which often vary as a function of reaction conditions (known as surface segregation). The preparation of bimetallic catalysts with controlled metal surface composition and structure is very challenging. In this study, we synthesize a series of Ni/Pt bimetallic catalysts with controlled metal surface composition and structure using a method derived from surface organometallic chemistry. The evolution of the surface composition and structure of the obtained bimetallic catalysts under simulated reaction conditions is investigated by various techniques, which include CO-probe IR spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, extended X-ray absorption fine structure analysis, X-ray absorption near-edge structure analysis, XRD, and X-ray photoelectron spectroscopy. It is demonstrated that the structure of the bimetallic catalyst is evolved from Pt monolayer island-modified Ni nanoparticles to core–shell bimetallic nanoparticles composed of a Ni-rich core and a Ni/Pt alloy shell upon thermal treatment. As a result, these catalysts are active for the dry reforming of methane, and their catalytic activities, stabilities, and carbon formation vary with their surface composition and structure.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Dry Sliding Wear Resistance of Cobalt Boride Coatings Formed on ASTM F1537 Alloy

New results about the wear resistance of CoB-Co{sub 2}B coatings under dry sliding conditions were estimated in this work. The cobalt boride coatings were developed at the surface of the ASTM F1537 alloy by means of the powder-pack boriding process using two experimental conditions: 1223 K with 6 h of exposure and 1273 K with 10 h of exposure. Before the sliding wear tests, Vickers depth-sensing microindentation tests were conducted on the cross section of the cobalt boride coatings to estimate the distribution of hardness, Young’s modulus, and residual stresses. Otherwise, the sliding wear tests were performed on both boriding conditions and on the untreated material, using a ball-on-flat configuration comprised of an alumina ball as a counterpart with applied loads between 5 and 20 N. The wear rates of the borided ASTM F1537 alloy were ranged between 4.02 and 8.91 × 10{sup −6} mm{sup 3} N{sup −1} m{sup −1} compared with the values of the untreated material (13.90 and 15.78 × 10{sup −6} mm{sup 3} N{sup −1} m{sup −1}) for the overall set of experimental conditions; nevertheless, the influence of boriding conditions (1273 K with 10 h of exposure) tended to increase the CoB coating thickness, developing a more brittle layer that decreased the sliding wear resistance at the surface of the borided ASTM F1537 alloy. Finally, the presence of failure mechanisms on the surface of the wear tracks was analyzed for both borided ASTM F1537 alloy and untreated material.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Demonstration of Selective Single-Barium Ion Detection with Dry Diazacrown Ether Naphthalimide Turn-on Chemosensors

Single-molecule fluorescence imaging (SMFI) of gas-phase ions has been proposed for “barium tagging,” a burgeoning area of research in particle physics to detect individual barium daughter ions. This has potential to significantly enhance the sensitivity of searches for neutrinoless double-beta decay (0νββ) that is obscured by background radiation events. The chemistry required to make such sensitive detection of Ba 2+ by SMFI in dry Xe gas at solid interfaces has implications for solid-phase detection methods but has not been demonstrated. Here, we synthesized simple, robust, and effective Ba 2+ -selective chemosensors capable of function within ultrapure high-pressure 136 Xe gas. Turn-on fluorescent naphthalimide-(di)azacrown ether chemosensors were Ba 2+ -selective and achieved SMFI in a polyacrylamide matrix. Here, fluorescence and NMR experiments supported a photoinduced electron transfer mechanism for turn-on sensing. Ba 2+ selectivity was achieved with computational calculations correctly predicting the fluorescence responses of sensors to barium, mercury, and potassium ions. With these molecules, dry-phase single-Ba 2+ ion imaging with turn-on fluorescence was realized using an oil-free microscopy technique for the first time—a significant advance toward single-Ba 2+ ion detection within large volumes of 136 Xe, plausibly enabling a background-independent technique to search for the hypothetical process of 0νββ.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Development of a Freeze-Dried CRISPR-Cas12 Sensor for Detecting Wolbachia in the Secondary Science Classroom

Training the future synthetic biology workforce requires the opportunity for students to be exposed to biotechnology concepts and activities in secondary education. Detecting Wolbachia bacteria in arthropods using polymerase chain reaction (PCR) has become a common way for secondary students to investigate and apply recombinant DNA technology in the science classroom. Despite this important activity, cutting-edge biotechnologies such as clustered regularly interspaced short palindromic repeat (CRISPR)-based diagnostics have yet to be widely implemented in the classroom. To address this gap, we present a freeze-dried CRISPR-Cas12 sensing reaction to complement traditional recombinant DNA technology education and teach synthetic biology concepts. The reactions accurately detect Wolbachia from arthropod-derived PCR samples in under 2 h and can be stored at room temperature for over a month without appreciable degradation. Here, the reactions are easy-to-use and cost less than $40 to implement for a classroom of 22 students including the cost of reusable equipment. We see these freeze-dried CRISPR-Cas12 reactions as an accessible way to incorporate synthetic biology education into the existing biology curriculum, which will expand biology educational opportunities in science, technology, engineering, and mathematics.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2017

Tree water dynamics in a drying and warming world: Future tree water dynamics

Disentangling the relative impacts of precipitation reduction and vapour pressure deficit (VPD) on plant water dynamics and determining whether acclimation may influence these patterns in the future is an important challenge. Here, we report sap flux density (FD), stomatal conductance (Gs), hydraulic conductivity (KL) and xylem anatomy in piñon pine (Pinus edulis) and juniper (Juniperus monosperma) trees subjected to five years of precipitation reduction, atmospheric warming (elevated VPD) and their combined effects. No acclimation occurred under precipitation reduction: lower Gs and FD were found for both species compared to ambient conditions. Warming reduced the sensibility of stomata to VPD for both species but resulted in the maintenance of Gs and FD to ambient levels only for piñon. For juniper, reduced soil moisture under warming negated benefits of stomatal adjustments and resulted in reduced FD, Gs and KL. Although reduced stomatal sensitivity to VPD also occurred under combined stresses, reductions in Gs, FD and KL took place to similar levels as under single stresses for both species. Our results show that stomatal conductance adjustments to high VPD could minimize but not entirely prevent additive effects of warming and drying on water use and carbon acquisition of trees in semi-arid regions.

Grossiord, Charlotte↗
DOE OSTI2020

Analysis of Planar-Cavity Receiver Reactor for Solar Thermochemical Dry-Reforming

Concentrating solar thermal (CST) systems can be leveraged to provide not only heat for power generation, but also for energy storage and thermochemical fuel production. Such solar thermochemical processes have been studied conceptually, from solar thermochemical hydrogen production (STCH) and thermochemical energy storage (TCES), to gasification, reforming, and fuel upgrading by various means. The solar receiver and reactor are critical components in the conversion of solar energy into chemical energy in the form of 'solar fuels'. For effective conversion of solar energy within a coupled solar receiver-reactor, extremely high temperatures are required, thereby demanding a high solar concentration ratio (CR) for efficient operation. This creates a design challenge for the receiver-reactor, as many thermochemical processes involve gas or gas-solid systems that are limited by low heat transfer coefficients. A unique receiver design is proposed that has the potential to incorporate various high-temperature thermochemical processes such as TCES-assisted power generation, methane reforming, or STCH processes. Modeling this receiver and its potential applications requires a full three-dimensional model that accurately captures the interconnected effects of receiver geometry, spatial solar irradiance, complex radiation, reaction kinetics, fluid dynamics, and heat transfer. In this paper we analyze a CST system integrated with this unique planar-cavity receiver-reactor design using the developed model. The model presented in this paper showed where improved thermal management was needed to achieve suitable receiver performance when a dry-methane reforming process is implemented.

14 SOLAR ENERGY↗
DOE OSTI2019

Impact of Ni and Mg Loadings on Dry Reforming Performance of Pt/Ceria-Zirconia Catalysts

The isolated effects of Ni and Mg on a series of Pt/Ce 0.6 Zr 0.4 O 2 (CZO) reforming catalysts were evaluated and used to formulate an improved catalyst with both Ni and Mg present. The dry reforming reaction results indicate that Ni enhances the CH 4 conversion at low temperatures while Mg improves the H 2 :CO ratio and stability, but requires high temperatures to reach similar conversions. The detection of coke (5.5 X 10 -4 g/g cat •h) over the 2.7Ni-CZO sample led to the examination of the 2.7Ni-0.50Mg-CZO sample. The catalyst activity results and the absence of coke formation over the 2.7Ni-0.50Mg-CZO sample confirmed that both Ni and Mg are needed to obtain a balance between catalyst activity and stability. The catalysts tested yielded low temperature activity with 10 % CH 4 conversions at temperature <500 °C. Furthermore, this work provides key insights into the proper design of low temperature reforming catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Aluminum Spent Fuel Performance in Dry Storage Task 4 Aluminum Oxide Sampling of ATR Dry Stored Fuel

Milestone report on sampling of long-term dry-stored ATR spent fuel elements. It describes tooling, sample acquisition methods and analysis of the aluminum oxide samples by scanning electron microscopy, thermogravimetric analysis, X-ray diffraction and transmission electron microscopy. The observations provide input to projections on controls necessary for maintaining the integrity of the fuel during extended interim storage.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2019

Rethinking surface reactions in nanoscale dry processes toward atomic precision and beyond: a physics and chemistry perspective

In this review, we discuss the progress of emerging dry processes with atomic precision. Researchers in the field of plasma processing and surface science have addressed the increasingly challenging demands of material selectivity by utilization of synergistic enhancement of etching or deposition. The discussion encompasses major challenges in the plasma science and technology community. Here, the focus of the review is advances in atomic layer etching and area-selective deposition with activation or deactivation, especially in terms of materials scaling and variety. Control of high-aspect-ratio feature fabrication in semiconductor manufacturing and etched shapes of interior features at the nanoscale are needed. Issues related to profile distortion have received much attention. State-of-the-art techniques used in semiconductor manufacturing are reviewed and future challenges are outlined.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Enhanced Dry Reforming of Methane on Ni and Ni-Pt Catalysts Synthesized by Atomic Layer Deposition

Atomic layer deposition (ALD) was used to deposit Ni and Pt on alumina supports to form monometallic and bimetallic catalysts with initial particle sizes of 1–2.4 nm. The ALD catalysts were more active (per mass of metal) than catalysts prepared by incipient wetness (IW) for dry reforming of methane (DRM), and they did not form carbon whiskers during reaction due to their sufficiently small size. Catalysts modified by Pt ALD had higher rates of reaction per mass of metal and inhibited coking, whereas NiPt catalysts synthesized by IW still formed carbon whiskers. Temperature-programmed reduction of Ni catalysts modified by Pt ALD indicated the presence of bimetallic interaction. Density functional theory calculations suggested that under reaction conditions, the NiPt surfaces form Ni-terminated surfaces that are associated with higher DRM rates (due to their C and O adsorption energies, as well as the CO formation and CH4 dissociation energies).

Environmental Molecular Sciences Laboratory↗
DOE OSTI2015

Dry (Mg,Fe)SiO 3 perovskite in the Earth's lower mantle

Combined synthesis experiments and first-principles calculations show that MgSiO 3 -perovskite with minor Al or Fe does not incorporate significant OH under lower mantle conditions. Perovskite, stishovite, and residual melt were synthesized from natural Bamble enstatite samples (Mg/(Fe+Mg) = 0.89 and 0.93; Al 2 O 3 < 0.1 wt% with 35 and 2065 ppm wt H 2 O, respectively) in the laser-heated diamond anvil cell at 1600-2000 K and 25-65 GPa. Combined Fourier transform infrared (FTIR) spectroscopy, x-ray diffraction, and ex-situ transmission electron microscopy (TEM) analysis demonstrates little difference in the resulting perovskite as a function of initial water content. Four distinct OH vibrational stretching bands are evident upon cooling below 100 K (3576, 3378, 3274, and 3078 cm -1 ), suggesting 4 potential bonding sites for OH in perovskite with a maximum water content of 220 ppm wt H 2 O, and likely no more than 10 ppm wt H 2 O. Complementary, Fe-free, first-principles calculations predict multiple potential bonding sites for hydrogen in perovskite, each with significant solution enthalpy (0.2 eV/defect). We calculate that perovskite can dissolve less than 37 ppm wt H 2 O (400 ppm H/Si) at the top of the lower mantle, decreasing to 31 ppm wt H 2 O (340 ppm H/Si) at 125 GPa and 3000 K in the absence of a melt or fluid phase. Here, we propose that these results resolve a long-standing debate of the perovskite melting curve and explain the order of magnitude increase in viscosity from upper to lower mantle.

58 GEOSCIENCES↗