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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

The Majorana Demonstrator radioassay program

The Majorana collaboration is constructing the Majorana Demonstrator at the Sanford Underground Research Facility at the Homestake gold mine, in Lead, SD. The apparatus will use Ge detectors, enriched in isotope 76 Ge, to demonstrate the feasibility of a large-scale Ge detector experiment to search for neutrinoless double beta decay. The long half-life of this postulated process requires that the apparatus be extremely low in radioactive isotopes whose decays may produce backgrounds to the search. The radioassay program conducted by the collaboration to ensure that the materials comprising the apparatus are sufficiently pure is described. The resulting measurements from gamma-ray counting, neutron activation and mass spectroscopy of the radioactive-isotope contamination for the materials studied for use in the detector are reported. In conclusion, we interpret these numbers in the context of the expected background for the experiment.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Status of the Majorana Demonstrator

The Majorana Collaboration is constructing the Majorana Demonstrator, an ultra-low background, 40-kg modular high purity Ge detector array to search for neutrinoless double-beta decay in 76 Ge. In view of the next generation of tonne-scale Ge-based neutrinoless double-beta decay searches that will probe the neutrino mass scale in the inverted-hierarchy region, a major goal of the Demonstrator is to demonstrate a path forward to achieving a background rate at or below 1 count/tonne/year in the 4 keV region of interest around the Q-value at 2039 keV. Lastly, the current status of the Demonstrator is discussed, as are plans for its completion.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

A Dark Matter Search with MALBEK

The Majorana Demonstrator is an array of natural and enriched high purity germanium detectors that will search for the neutrinoless double-beta decay of 76Ge and perform a search for weakly interacting massive particles (WIMPs) with masses below 10 GeV. As part of the Majorana research and development efforts, we have deployed a modified, low-background broad energy germanium detector at the Kimballton Underground Research Facility. With its sub-keV energy threshold, this detector is potentially sensitive to non-Standard Model physics, including interactions with WIMPs. We discuss the backgrounds present in the WIMP region of interest and present results from a WIMP search with 221.49 live days of data from this detector.

Giovanetti, G. K.↗
DOE OSTI2015

The MAJORANA DEMONSTRATOR for 0νββ: Current Status and Future Plans

The Majorana Demonstrator will search for neutrinoless-double-beta decay in 76Ge, while establishing the feasibility of a future tonne-scale germanium-based neutrinoless-double-beta decay experiment, and performing searches for new physics beyond the Standard Model. The experiment, currently under construction at the Sanford Underground Research Facility in Lead, SD, will consist of a pair of modular high-purity germanium detector arrays housed inside of a compact copper, lead, and polyethylene shield. Through a combination of strict materials qualifications and assay, low-background design, and powerful background rejection techniques, the Demonstrator aims to achieve a background rate in the neutrinoless-double-beta decay region of interest (ROI) of no more than 3cnts/(ROI-t-y). The current status of the Demonstrator is discussed, as are plans for its completion.

Green, M. P.↗
DOE OSTI2015

Background Model for the Majorana Demonstrator

The Majorana Collaboration is constructing a prototype system containing 40 kg of HPGe detectors to demonstrate the feasibility and potential of a future tonne-scale experiment to search for neutrinoless double-beta (0v BB) decay in 76Ge. In view of the requirement that the next generation of tonne-scale Ge-based 0vBB-decay experiment be capable of probing the neutrino mass scale in the inverted-hierarchy region, a major goal of theMajorana Demonstrator is to demonstrate a path forward to achieving a background rate at or below 1 cnt/(ROI-t-y) in the 4 keV region of interest around the Q-value at 2039 keV. This goal is pursued through a combination of a significant reduction of radioactive impurities in construction materials with analytical methods for background rejection, for example using powerful pulse shape analysis techniques profiting from the p-type point contact HPGe detectors technology. The effectiveness of these methods is assessed using Geant4 simulations of the different background components whose purity levels are constrained from radioassay measurements.

Cuesta, C.↗
DOE OSTI2018

Changes in Electronic Structure upon Li Deintercalation from LiCoPO 4 Derivatives

On the path toward the design of Li-ion batteries with increased energy densities, efforts are focused on the development of positive electrodes that can maximize the voltage of the full cell. However, the development of novel materials that operate at high voltage, while also showing high efficiency and meeting strict safety standards, is an ongoing challenge. LiCoPO 4 is being explored as a possible candidate, as the Co 2+/3+ redox couple operates at 4.8 V versus Li + /Li 0 . The presence of phosphate groups is typically expected to stabilize the compound against oxygen loss, yet the changes in Co-O bonding upon Li extraction have not been ascertained. In addition, LiCoPO 4 is riddled with problems relating to poor transport and strain in the crystal structure of the delithiated phase, which handicap its use as a high-voltage electrode. In this work, substituting ions to generate Li 1.025 Co 0.84 Fe 0.10 Cr 0.05 Si 0.01 (PO 4 ) 1.025 is found to stabilize both the electronic structure and crystal structure and, therefore, substantially improve the ability to fully utilize the redox capacity of the material. A thorough study by spectroscopic tools, combined with computations of the electronic structure, was used to probe changes in chemical bonding. The measurements revealed the existence of redox gradients between surface and bulk that are common in other materials that react at high potential. Lastly, the study offers a comprehensive understanding of the fundamental reactions in LiCoPO 4 -type frameworks, while further demonstrating that ion substitution is an effective tool for improving their performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Understanding and Mitigating Stickiness in Biochar Produced through Acid Hydrolysis and Dehydration

Levulinic acid is a platform chemical with significant potential for conversion into a wide range of biobased chemicals and fuels. A common process for producing levulinic acid from lignocellulosic feedstocks involves acid hydrolysis and dehydration (AHDH), where hexose polymers are hydrolyzed into monomeric sugars and subsequently dehydrated to levulinic acid and formic acid in the presence of dilute sulfuric acid. However, scaling the AHDH process is challenging because of the formation of byproducts such as sticky biochar, which accumulates in continuous-flow reactors, reducing effective reaction volume and increasing process downtime. This study investigates the effect of a chemical preconditioning step on mitigating sticky biochar formation. Woody biomass was preconditioned at 170 °C with 0.26 wt % sulfuric acid for 30 min, resulting in substantial removal of hemicellulose and acid-soluble lignin. AHDH of these preconditioned solids produced biochar that did not adhere to reactor surfaces. TGA analysis confirmed that the chemical preconditioning step minimized interactions between hemicellulose-derived degradation products and lignin side chains, reducing sticky char formation. Additionally, the study observed a 6% higher yield of organic acids from softwood species compared to hardwoods, with bark content shown to negatively impact yield. These findings suggest that targeted preconditioning of lignocellulosic biomass can enhance reactor operability and improve organic acid production efficiency in AHDH processes.

biopolymers↗
DOE OSTI2015

Conformation-Dependent Photostability among and within Single Conjugated Polymers

The relationship between photostability and conformation of 2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) conjugated polymers was studied via excitation polarization modulation depth (M) measurements. Upon partial photobleaching, M distributions of collapsed, highly ordered MEH-PPV molecules shifted toward lower values. Conversely, M distributions of MEH-PPV molecules with random coil conformations moved toward higher values after partial photobleaching. Monte Carlo simulations of randomly distributed dipole moments along polymer chains subjected to partial photobleaching revealed that a statistical effect leads to an increase in peak M value. Decreases in M values seen experimentally in the population of MEH-PPV molecules with high M values, however, are due to conformation-dependent photostability within single MEH-PPV polymers. Here, we show that, while folded MEH-PPV molecules are relatively more photostable than extended MEH-PPV molecules in an ensemble, extended portions of particular molecules are more photostable than folded domains within single MEH-PPV molecules.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Effects of Controlled Crystalline Surface of Hydroxyapatite on Methane Oxidation Reactions

Hydroxyapatite (HAP, Ca 10 (PO 4 ) 6 (OH) 2 ) has a hexagonal prismatic structure that exposes two crystalline surfaces: prism-faceted a- and basal-faceted c-surfaces. Here, the predominant exposure of c-surface was controlled, and its influences in methane oxidation reactions (combustion and oxidative coupling over HAP and lead-substituted HAP (Pb-HAP), respectively) were studied. The c-surface exposure was realized by crystal orientation in HAP-based catalyst film, which was created by an electrochemical deposition of HAP seeds on a titanium substrate, followed by hydrothermal crystallization and peeling off of the crystalline films from the substrate. In comparison to a-surface that is prevalently exposed in unoriented HAP-based catalysts, the c-surface (i.e., (002) crystalline plane) of HAP-based catalysts exhibited up to 47-fold enhancement in areal rate in both reactions. The distinct catalytic activity between these two crystalline surfaces is attributed to the preferential formation of oxide ions and vacancies on c-surfaces. The oxide ions and vacancies in turns function as actives sites for promoting methane activation and complete oxidation into CO 2 . Density functional theory calculations confirmed the close relationship between different catalytic activities in c-surface of oriented and a-surface of unoriented HAP through the tendency of vacancy formation. Without the presence of vacancies, the methyl or methylene group after methane activation forms ethane or ethylene via coupling. The present study explored the effects of HAP crystal orientation in methane oxidation reactions, which revealed distinct catalytic behaviors of crystal surfaces in HAP-based materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Localizing Exciton Recombination Sites in Conformationally Distinct Single Conjugated Polymers by Super-resolution Fluorescence Imaging

To thoroughly elucidate how molecular conformation and photophysical properties of conjugated polymers (CPs) are related requires simultaneous probing of both. Here, previous efforts used fluorescence imaging with one nanometer accuracy (FIONA) to image CPs, which allowed simultaneous estimation of molecular conformation and probing of fluorescence intensity decay. We show that calculating the molecular radius of gyration for putative folded and unfolded poly(2-methoxy-5-(2'-ethylhexyloxy)1,4-phenylenevinylene) (MEH-PPV) molecules using FIONA underestimates molecular extension by averaging over emitters during localization. In contrast, employing algorithms based on single molecule high resolution imaging with photobleaching (SHRImP), including an approach we term all-frames SHRImP, allows localization of individual emitters. SHRImP processing corroborates that compact MEH-PPV molecules have distinct photophysical properties from extended ones. Estimated radii of gyration for isolated 168 kDa MEH-PPV molecules immobilized in polystyrene and exhibiting either stepwise or continuous intensity decays are found to be 12.6 and 25.3 nm, respectively, while the distance between exciton recombination sites is estimated to be ~10 nm independent of molecular conformation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Origin of High Activity and Durability of Twisty Nanowire Alloy Catalysts under Oxygen Reduction and Fuel Cell Operating Conditions

The ability to control the surface composition and morphology of alloy catalysts is critical for achieving high activity and durability of catalysts for oxygen reduction reaction (ORR) and fuel cells. Here, this report describes an efficient surfactant-free synthesis route for producing a twisty nanowire (TNW) shaped platinum–iron (PtFe) alloy catalyst (denoted as PtFe TNWs) with controllable bimetallic compositions. PtFe TNWs with an optimal initial composition of ~24% Pt are shown to exhibit the highest mass activity (3.4 A/mg Pt , ~20 times higher than that of commercial Pt catalyst) and the highest durability (<2% loss of activity after 40000 cycles and <30% loss after 120000 cycles) among all PtFe-based nanocatalysts under ORR or fuel cell operating conditions reported so far. Using ex situ and in situ synchrotron X-ray diffraction coupled with atomic pair distribution function (PDF) analysis and 3D modeling, the PtFe TNWs are shown to exhibit mixed face-centered cubic (fcc)-body-centered cubic (bcc) alloy structure and a significant lattice strain. A striking finding is that the activity strongly depends on the composition of the as-synthesized catalysts and this dependence remains unchanged despite the evolution of the composition of the different catalysts and their lattice constants under ORR or fuel cell operating conditions. Notably, dealloying under fuel cell operating condition starts at phase-segregated domain sites leading to a final fcc alloy structure with subtle differences in surface morphology. Due to a subsequent realloying and the morphology of TNWs, the surface lattice strain observed with the as-synthesized catalysts is largely preserved. This strain and the particular facets exhibited by the TNWs are believed to be responsible for the observed activity and durability enhancements. These findings provide new insights into the correlation between the structure, activity, and durability of nanoalloy catalysts and are expected to energize the ongoing effort to develop highly active and durable low-Pt-content nanowire catalysts by controlling their alloy structure and morphology.

25 ENERGY STORAGE↗
DOE OSTI2024

Electrochemical Synthesis of Zeolite Coatings with Controlled Crystal Polymorphism and Self-Regulating Growth

Zeolite coatings are studied as molecular sieves for membrane separation, membrane reactors, and chemical sensor applications. They are also studied as anticorrosive films for metals and alloys, antimicrobial and hydrophobic films for heating, ventilation, and air conditioning, and dielectrics for semiconductor applications. Zeolite coatings are synthesized by hydrothermal, ionothermal, and dry-gel conversion approaches, which require high process temperatures and lengthy times (ranging from hours to days). Here, we report the first zeolite coatings synthesized via electrochemical deposition on a cathodic electrode, with controlled crystal polymorphism achieved within subhourly duration. We demonstrate this approach by developing sodium zeolite (e.g., sodalite (SOD), NaA (LTA), and Linde Type N (LTN)) coatings on a titanium electrode and extending the synthesis method to porous stainless steel. The coating morphology and crystallinity depend on the temperature, time, and applied current. The coating thickness is independent of the applied current, showing the presence of a self-regulating mechanism to ensure a uniform coating thickness across the metal surface. The electrochemical zeolite growth mechanism was elucidated with high-resolution transmission electron microscopy, and applications of the resultant zeolite coatings for oil/water separation and ethanol/water pervaporation were exploited. Electrochemical synthesis represents a novel, simple, fast, and environmentally friendly approach to preparing zeolite coatings. It can potentially be generalized for developing zeolite materials with diverse framework structures, morphologies, and orientations for substrates with complicated geometries.

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

Surface oxygenation of multicomponent nanoparticles toward active and stable oxidation catalysts

Abstract The need for active and stable oxidation catalysts is driven by the demands in production of valuable chemicals, remediation of hydrocarbon pollutants and energy sustainability. Traditional approaches focus on oxygen-activating oxides as support which provides the oxygen activation at the catalyst-support peripheral interface. Here we report a new approach to oxidation catalysts for total oxidation of hydrocarbons (e.g., propane) by surface oxygenation of platinum (Pt)-alloyed multicomponent nanoparticles (e.g., platinum-nickel cobalt (Pt–NiCo)). The in-situ/operando time-resolved studies, including high-energy synchrotron X-ray diffraction and diffuse reflectance infrared Fourier transform spectroscopy, demonstrate the formation of oxygenated Pt–NiOCoO surface layer and disordered ternary alloy core. The results reveal largely-irregular oscillatory kinetics associated with the dynamic lattice expansion/shrinking, ordering/disordering, and formation of surface-oxygenated sites and intermediates. The catalytic synergy is responsible for reduction of the oxidation temperature by ~100 °C and the high stability under 800 °C hydrothermal aging in comparison with Pt, and may represent a paradigm shift in the design of self-supported catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Catalytic Oxidation of Propane over Palladium Alloyed with Gold: An Assessment of the Chemical and Intermediate Species

Understanding the catalytic oxidation of propane is important for developing catalysts not only for catalytic oxidation of hydrocarbons in emission systems but also for selective oxidation in the chemical processing industry. For palladium-based catalysts, little is known about the identification of the chemical or intermediate species involved in propane oxidation. We describe herein findings of an investigation of the catalytic oxidation of propane over supported palladium nanoalloys with different compositions of gold (Pd n Au 100–n ), focusing on probing the chemical or intermediate species on the catalysts in correlation with the bimetallic composition and the alloying phase structure. In addition to an enhanced catalytic activity, a strong dependence of the catalytic activity on the bimetallic composition was revealed, displaying an activity maximum at a Pd : Au ratio of 50 : 50 in terms of reaction temperature. This dependence is also reflected by its dependence on the thermochemical treatment conditions. While the activity for nanoalloys with n ~ 50 showed little change after the thermochemical treatment under oxygen, the activities for nanoalloys with n < 50 and n > 50 showed opposite trends. Importantly, this catalytic synergy is linked to the subtle differences of chemical and intermediate species which have been identified for the catalysts with different bimetallic compositions by in situ measurements using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). For the catalytic oxidation of propane over the highly-active catalyst with a Pd : Au ratio of 50 : 50, the major species identified include acetate and bicarbonate, showing subtle differences in comparison with the identification of bicarbonate and formate for the catalyst with <50% Au (with a lower activity) and the absence of apparent species for the catalyst with >50% Au (activity is largely absent). The alloying of 50% Au in Pd is believed to increase the oxophilicity of Pd, which facilitates the first carbon–carbon bond cleavage and oxygenation of propane. Finally, the implications of the findings on the catalytic synergy of Pd alloyed with Au and the design of active Pd alloy catalysts are also discussed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗