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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Facile synthesis and temperature-dependent luminescence of single-phase dual-emitting CdTe@NaNO{sub 3} composite

Graphical abstract: Single-phase dual-emitting CdTe@NaNO{sub 3} composite was prepared by a facile and efficient aqueous ethanol phase assisted coprecipitation method. Its use in self-referencing luminescent thermometry was tested, by exploiting the temperature-dependence of fluorescence intensity ratio (green/red) in range of 273–473 K. - Highlights: • Single-phase green and red dual-emitting CdTe@NaNO{sub 3} composite was prepared. • CdTe QDs embedded in NaNO{sub 3} matrices exhibit photoluminescence quantum yields of 35%. • Temperature-dependent luminescent properties of CdTe@NaNO{sub 3} composite were studied. • It could be a good candidate for ratiometric temperature sensing with a high relative sensitivity. - Abstract: Single-phase dual-emitting CdTe@NaNO{sub 3} composite was prepared by a facile and efficient aqueous ethanol phase assisted coprecipitation method, providing a new type of solid-state luminescent material with processability, robustness and high luminescence. Cubic-shape Green + Red (G + R) CdTe@NaNO{sub 3} composite particles display single-excitation, dual-emission with two well-resolved, intensity-comparable fluorescence peaks. Its application potential in ratiometric luminescent thermometry was tested, by exploiting the temperature-dependence of fluorescence intensity ratio (green/red) in range of 273–473 K, and the maximum sensitivity is found to be 0.6183% K{sup −1} at 473 K. The results indicate that dual-emitting G + R CdTe@NaNO{sub 3} composite could be considered as potential candidates for ratiometric temperature sensing.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Extending carbon chemistry at high-pressure by synthesis of CaC 2 and Ca 3 C 7 with deprotonated polyacene- and para-poly(indenoindene)-like nanoribbons

Metal carbides are known to contain small carbon units similar to those found in the molecules of methane, acetylene, and allene. However, for numerous binary systems ab initio calculations predict the formation of unusual metal carbides with exotic polycarbon units, [C 6 ] rings, and graphitic carbon sheets at high pressure (HP). Here we report the synthesis and structural characterization of a HP-CaC 2 polymorph and a Ca 3 C7 compound featuring deprotonated polyacene-like and para-poly(indenoindene)-like nanoribbons, respectively. We also demonstrate that carbides with infinite chains of fused [C6] rings can exist even at conditions of deep planetary interiors (~140 GPa and ~3300 K). Hydrolysis of high-pressure carbides may provide a possible abiotic route to polycyclic aromatic hydrocarbons in Universe.

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

Controlling octahedral rotations in a perovskite via strain doping

The perovskite unit cell is the fundamental building block of many functional materials. The manipulation of this crystal structure is known to be of central importance to controlling many technologically promising phenomena related to superconductivity, multiferroicity, mangetoresistivity, and photovoltaics. The broad range of properties that this structure can exhibit is in part due to the centrally coordinated octahedra bond flexibility, which allows for a multitude of distortions from the ideal highly symmetric structure. However, continuous and fine manipulation of these distortions has never been possible. Here, we show that controlled insertion of He atoms into an epitaxial perovskite film can be used to finely tune the lattice symmetry by modifying the local distortions, i.e., octahedral bonding angle and length. Orthorhombic SrRuO 3 films coherently grown on SrTiO 3 substrates are used as a model system. Implanted He atoms are confirmed to induce out-of-plane strain, which provides the ability to controllably shift the bulk-like orthorhombically distorted phase to a tetragonal structure by shifting the oxygen octahedra rotation pattern. Lastly, these results demonstrate that He implantation offers an entirely new pathway to strain engineering of perovskite-based complex oxide thin films, useful for creating new functionalities or properties in perovskite materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Role of dislocations on martensitic transformation temperatures and microstructure: A molecular dynamics study

Microstructure and defects strongly affect martensitic transformations in metallic alloys. Significant progress has been made in understanding the atomic-level processes that control the role of grain boundaries and precipitates in these solid-to-solid phase transformations. Yet, the role of dislocations and their structures on martensitic transformation temperature and the resulting microstructure remains unclear. Therefore, we used large-scale molecular dynamics simulations to study the forward and reverse transformation of a martensitic material modeled after Ni63Al37 under cyclic thermal loading. The simulations reveal that dislocations in the austenite phase act as one-dimensional seeds for the martensite phase, which is present at temperatures significantly above the martensite start value. We find a reduction in the dislocation density during cyclic thermal loading, which results in the increase in martensite and austenite transition temperatures, in agreement with experiments. Importantly, we extracted a critical martensitic nuclei size for developing stable domains and found that relatively low dislocation densities are needed to grow independent martensitic variants resulting in a multi-domain structure.

Physics↗
DOE OSTI2019

Cryogenic specimens for nanoscale characterization of solid–liquid interfaces

We report new cryogenic characterization techniques for exploring the nanoscale structure and chemistry of intact solid–liquid interfaces have recently been developed. These techniques provide high-resolution information about buried interfaces from large samples or devices that cannot be obtained by other means. These advancements were enabled by the development of instrumentation for cryogenic focused ion beam liftout, which allows intact solid–liquid interfaces to be extracted from large samples and thinned to electron-transparent thicknesses for characterization by cryogenic scanning transmission electron microscopy or atom probe tomography. Future implementation of these techniques will complement current strides in imaging of materials in fluid environments by in situ liquid-phase electron microscopy, providing a more complete understanding of the morphology, surface chemistry, and dynamic processes that occur at solid–liquid interfaces.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2024

Quench process modeling & simulation in the heat-treatment of critical aerospace components

To manufacture light-weight, advanced metal alloy components for gas turbine engines, quench heat-treatment processes are typically used. By quenching the component from elevated tempera-tures, the alloy sometimes undergoes a solid-state phase transformation which produces special microstructures with the required, enhanced mechanical properties. However, the quenching can also lead to cracks forming in the component. Addressing the quench cracking problems adds a significant burden to the cost, schedule, and energy demand of manufacture. Currently, optimizing the quench process to mitigate or avoid the cracking is performed largely by trial-and-error, relying heavily on costly experimental (thermocouple) trials to understand the local thermal gradients which cause the cracks to form. In this first part (Phase 1) of the work, high-performance computing is employed to establish the ability of modern CFD (computational fluid dynamics) to alleviate or wholly replace the experimental quenching trials by virtual testing. A baseline CFD model is defined and its accuracy established to be comparable to (and which usually exceeds) the accuracy of existing HTC (heat-transfer correlation) based simulation methods of quenching. As a first-principles based approach, “calibration” of the Baseline CFD model is independent of the quench process itself, but instead relies on the accuracy of the underlying (modeled), generic two-phase fluid processes which cannot be currently resolved by CFD for large, industrial-scale cases. A novel, high-fidelity DNS capability has been developed and verified to examine and further improve upon the mean-field closure submodels on which the Baseline CFD approach is based.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Lab-Scale Development of a Solid Sorbent for CO 2 Capture Process for Coal-Fired Power Plants

It is increasingly clear that CO 2 capture and sequestration (CCS) must play a critical role in curbing worldwide CO 2 emissions to the atmosphere. Development of these technologies to cost-effectively remove CO 2 from coal-fired power plants is very important to mitigating the impact these power plants have within the world’s power generation portfolio. Currently, conventional CO 2 capture technologies, such as aqueous-monoethanolamine based solvent systems, are prohibitively expensive and if implemented could result in a 75 to 100% increase in the cost of electricity for consumers worldwide. Solid sorbent CO 2 capture processes – such as RTI’s 3rd Generation Solid Sorbent CO 2 Capture Process – are promising alternatives to conventional, liquid solvents. Supported amine sorbents – of the nature RTI has developed – are particularly attractive due to their potential for high CO 2 loadings, excellent stability over multiple cycles, reduced corrosivity/volatility and a potential to reduce the regeneration energy needed to carry out CO 2 capture. The remaining challenges for these sorbent processes have provided the framework for the project team’s research and development and target for advancing the technology beyond lab-scale testing. Previous work in this area has failed to adequately address various technology challenges such as sorbent stability and regenerability, sorbent scale-up, improved physical strength and attrition-resistance, proper heat management and temperature control, proper solids handling, as well as the proper coupling of process engineering advancements that are tailored for a promising sorbent technology. Under a cooperative agreement with the US Department of Energy, and part of NETL’s CO 2 Capture Program, RTI has led an effort to address and mitigate the challenges associated with solid sorbent CO 2 capture. The overall objective of this project was to mitigate the technical and economic risks associated with the performance and scale-up of solid sorbent-based CO 2 capture processes, enabling subsequent larger pilot demonstrations and ultimately commercial deployment. An integrated development approach has been a key focus of this project in which sorbent development, process development, and economic analyses have informed each of the other development processes. Development efforts have focused on developing novel hybrid solids-based CO 2 capture sorbents and improving their performance stability, refining process engineering and design, and evaluating the viability of the technology through detailed economic analyses. Sorbent advancements have led to a next generation, commercially-viable CO 2 capture sorbent exhibiting performance stability in various gas environments and a physically strong fluidizable form. The team has reduced sorbent production costs and optimized the production and scale-up of novel metal-organic framework (MOF) hybrid solids-based CO 2 capture sorbents, fluidizable sorbents. Refinement of the process engineering and design at the lab-scale research unit has demonstrated promising CO 2 capture performance in simulated coal-fired flue gas conditions. Long-term testing has informed the project team on the process conditions needed to operate a solids-based system for optimal performance. Data collected from all phases of testing has been used to develop a detailed techno-economic assessment of RTI’s technology. These detailed analyses show that RTI’s technology has significant economic advantages over current amine scrubbing and potential to achieve the DOE’s Carbon Capture Program’s goal of >90% CO 2 capture rate at a cost of almost $40/tonne CO 2 captured by 2025. Through this integrated technology development approach, the project team has advanced RTI’s 3rd generation CO 2 capture technology to TRL-3, according to the DOE/FE definitions for Technology Readiness Levels. At a broader level, this project has advanced the whole of the solid sorbent CO 2 capture field, with advancements in process engineering and design, technical risk mitigation, sorbent scale-up optimization, and an understanding of the commercial viability and applicability of solid sorbent CO 2 capture technologies for the U.S. existing fleet of coal-fired power plants.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2019

Comparative Study of the Effect of Magnetic Nanoparticle CoFe{sub 2}O{sub 4} on Fluctuation-Induced Conductivity of Y-123 and Y-358 Superconductors

In this study, a comparative investigation of the electrical conductivity fluctuations in nano-CoFe{sub 2}O{sub 4} added to Y{sub 3}Ba{sub 5}Cu{sub 8}O{sub 18±x} (Y-358) and YBa{sub 2}Cu{sub 3}O{sub 7−d} (Y-123) products is performed. All products were made using the solid-state reaction process. X-ray powder diffraction (XRD) analyses confirmed the formation of different phases. Scanning electron microscope (SEM) analysis shows the reduction of grain size with increasing the quantity of nano-CoFe{sub 2}O{sub 4} particles for both the Y-123 and Y-358 samples. The decrease of grain size is more accentuated in the case of the Y-358 samples compared with the Y-123 ones. The data of conductivity fluctuations are examined in terms of the derivative of the electrical resistivity with respect to temperature and the logarithmic derivative of the conductivity with regard to temperature. The results illustrate the existence of a transition with two stages; intragrain and intergrain. It is demonstrated that the addition of CoFe{sub 2}O{sub 4} nanoparticles affects the electrical conductivity fluctuations, the values of the critical exponents, and the fluctuation dimensionality in YBCO systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Valorization of GaN based metal-organic chemical vapor deposition dust a semiconductor power device industry waste through mechanochemical oxidation and leaching: A sustainable green process

Dust generated during metal organic vapor deposition (MOCVD) process of GaN based semiconductor power device industry contains significant amounts of gallium and indium. These semiconductor power device industry wastes contain gallium as GaN and Ga{sub 0.97}N{sub 0.9}O{sub 0.09} is a concern for the environment which can add value through recycling. In the present study, this waste is recycled through mechanochemical oxidation and leaching. For quantitative recovery of gallium, two different mechanochemical oxidation leaching process flow sheets are proposed. In one process, first the Ga{sub 0.97}N{sub 0.9}O{sub 0.09} of the MOCVD dust is leached at the optimum condition. Subsequently, the leach residue is mechanochemically treated, followed by oxidative annealing and finally re-leached. In the second process, the MOCVD waste dust is mechanochemically treated, followed by oxidative annealing and finally leached. Both of these treatment processes are competitive with each other, appropriate for gallium leaching and treatment of the waste MOCVD dust. Without mechanochemical oxidation, 40.11 and 1.86 w/w% of gallium and Indium are leached using 4 M HCl, 100 °C and pulp density of 100 kg/m{sup 3,} respectively. After mechanochemical oxidation, both these processes achieved 90 w/w% of gallium and 1.86 w/w% of indium leaching at their optimum condition. - Highlights: • Waste MOCVD dust is treated through mechanochemical leaching. • GaN is hardly leached, and converted to NaGaO{sub 2} through ball milling and annealing. • Process for gallium recovery from waste MOCVD dust has been developed. • Thermal analysis and phase properties of GaN to Ga{sub 2}O{sub 3} and GaN to NaGaO{sub 2} is revealed. • Solid-state chemistry involved in this process is reported.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Methanogenesis and Acetogenesis in Hydrogenotrophy with Carbonate Minerals: Dependence on Mineral Surface Area, Biofilm Growth, and Microbial Community

The production, storage, and use of hydrogen are anticipated to grow substantially to achieve energy and climate goals. Consequently, microbial communities in many terrestrial and subsurface Earth environments could be exposed to elevated hydrogen concentrations. Hydrogen stimulates metabolic processes that reduce aqueous chemical species, such as bicarbonate or sulfate, that can exchange with solid mineral phases, but the controls on microbial hydrogenotrophy with mineral sources of electron acceptors are not fully understood. Herein, we applied laboratory experiments and biogeochemical modeling to study the response of a natural microbial community to an elevated partial pressure of hydrogen in the presence of carbonate minerals of varying composition, solubility, and size. Experimental incubations and simulation results showed that hydrogen consumption by microbial communities was initially dominated by sulfate reduction and, subsequently, transitioned to acetogenesis and methanogenesis. The rates of acetogenesis and methanogenesis were not correlated with the solubility of carbonate minerals. Instead, we observed strong linear correlations between the rates and surface area of carbonate minerals. Methane and acetate production slowed down in all incubations after about 2 weeks of incubation, although biogeochemical modeling predicted that the metabolic processes were not thermodynamically limited. Electron microscopy and infrared spectroscopy showed that biofilms with diverse microorganisms grew on the carbonates during this period. The methane δ13C value significantly increased, consistent with slower growth at elevated pH. This work highlights that microbial communities form biofilm on carbonate mineral surfaces as a response to hydrogen and that biofilm formation could pose a strong kinetic limitation to hydrogenotrophic metabolism utilizing carbonate minerals.

Acetobacterium↗
DOE OSTI2014

LABORATORY OPTIMIZATION TESTS OF TECHNETIUM DECONTAMINATION OF HANFORD WASTE TREATMENT PLANT LOW ACTIVITY WASTE OFF-GAS CONDENSATE SIMULANT

The Hanford Waste Treatment and Immobilization Plant (WTP) Low Activity Waste (LAW) vitrification facility will generate an aqueous condensate recycle stream (LAW Off-Gas Condensate) from the off-gas system. The baseline plan for disposition of this stream is to send it to the WTP Pretreatment Facility, where it will be blended with LAW, concentrated by evaporation and recycled to the LAW vitrification facility again. Alternate disposition of this stream would eliminate recycling of problematic components, and would enable de-coupled operation of the LAW melter and the Pretreatment Facilities. Eliminating this stream from recycling within WTP would also decrease the LAW vitrification mission duration and quantity of glass waste. This LAW Off-Gas Condensate stream contains components that are volatile at melter temperatures and are problematic for the glass waste form. Because this stream recycles within WTP, these components accumulate in the Condensate stream, exacerbating their impact on the number of LAW glass containers that must be produced. Approximately 32% of the sodium in Supplemental LAW comes from glass formers used to make the extra glass to dilute the halides to acceptable concentrations in the LAW glass, and diverting the stream reduces the halides in the recycled Condensate and is a key outcome of this work. Additionally, under possible scenarios where the LAW vitrification facility commences operation prior to the WTP Pretreatment facility, identifying a disposition path becomes vitally important. This task examines the potential treatment of this stream to remove radionuclides and subsequently disposition the decontaminated stream elsewhere, such as the Effluent Treatment Facility (ETF), for example. The treatment process envisioned is very similar to that used for the Actinide Removal Process (ARP) that has been operating for years at the Savannah River Site (SRS), and focuses on using mature radionuclide removal technologies that are also compatible with longterm tank storage and immobilization methods. For this new application, testing is needed to demonstrate acceptable treatment sorbents and precipitating agents and measure decontamination factors for additional radionuclides in this unique waste stream. The origin of this LAW Off-Gas Condensate stream will be the liquids from the Submerged Bed Scrubber (SBS) and the Wet Electrostatic Precipitator (WESP) from the LAW melter off-gas system. The stream is expected to be a dilute salt solution with near neutral pH, and will likely contain some insoluble solids from melter carryover. The soluble components are expected to be mostly sodium and ammonium salts of nitrate, chloride, and fluoride. This stream has not been generated yet and will not be available until the WTP begins operation, but a simulant has been produced based on models, calculations, and comparison with pilot-scale tests. One of the radionuclides that is volatile and expected to be in greatest abundance in this LAW Off-Gas Condensate stream is Technetium-99 ({sup 99}Tc). Technetium will not be removed from the aqueous waste in the Hanford WTP, and will primarily end up immobilized in the LAW glass by repeated recycle of the off-gas condensate into the LAW melter. Other radionuclides that are low but are also expected to be in measurable concentration in the LAW Off-Gas Condensate are {sup 129}I, {sup 90}Sr, {sup 137}Cs, {sup 241}Pu, and {sup 241}Am. These are present due to their partial volatility and some entrainment in the off-gas system. This report discusses results of optimized {sup 99}Tc decontamination testing of the simulant. Testing examined use of inorganic reducing agents for {sup 99}Tc. Testing focused on minimizing the quantity of sorbents/reactants added, and minimizing mixing time to reach the decontamination targets in this simulant formulation. Stannous chloride and ferrous sulfate were tested as reducing agents to determine the minimum needed to convert soluble pertechnetate to the insoluble technetium dioxide. The reducing agents were tried with and without sorbents. The sorbents, hydroxyapatite and sodium oxalate, were expected to sorb the precipitated technetium dioxide and facilitate removal. The Phase 1 tests examined a broad range of conditions and used the initial baseline simulant. The Phase 2 tests narrowed the conditions based on Phase 1 results, and used a slightly modified simulant. Test results indicate that excellent removal of {sup 99}Tc was achieved using SnCl{sub 2} as a reductant, and was effective with or without sorption onto hydroxyapatite. This reaction worked even in the presence of air (which could oxidize the stannous ion) and at room temperature. This process was very effective at neutral pH, with a Decontamination Factor (DF) >199 in one hour with only 1 g/L of SnCl{sub 2}. Prior work had shown that it was much less effective at alkaline pH. The only deleterious effect observed was that the chromium co-precipitates with the {sup 99}c during the SnCl{sub 2} reduction. This effect was anticipated, and would have to be considered when managing disposition paths of this stream. Reduction using FeSO{sub 4} was not effective at removing {sup 99}Tc, but did remove the Cr. Chromium is present due to partial volatility and entrainment in the off-gas, and is highly oxidizing, so would be expected to react with reducing agents more quickly than pertechnetate. Testing showed that sufficient reducing agent must be added to completely reduce the chromium before the technetium is reduced and removed. Other radionuclides are also present in this off-gas condensate stream. To enable sending this stream to the Hanford ETF, and thereby divert it from the recycle where it impacts the LAW glass volume, several of these also need to be removed. Samples from optimized conditions were also measured for actinide removal in order to examine the effect of the Tc-removal process on the actinides. Plutonium was also removed by the SnCl{sub 2} precipitation process. Results of this separation testing indicate that sorption/precipitation is a viable concept and has the potential to decontaminate the {sup 99}Tc from the stream, allowing it to be diverted away from WTP and thus eliminating the impact of the recycled halides and sulfate on the LAW glass volume. Based on the results, a possible treatment scenario could involve the use of a reductive precipitation agent (SnCl{sub 2}) with or without sorbent at neutral pH to remove the Tc. Although hydroxyapatite was not necessary to effect the {sup 99}Tc removal, it may be beneficial in solid-liquid separations. Other testing will examine removal of the other radionuclides. This testing was the second phase of testing, which aimed at optimizing the process by examining the minimum amount of reductant needed and the minimum reaction time. Although results indicated that SnCl{sub 2} was effective, further work on a pH-adjusted Fe(SO{sub 4}) mixture are needed. Additional tasks are needed to examine removal of the other radionuclides, solid-liquid separation technologies, slurry rheology measurements, composition variability impacts, corrosion and erosion, and slurry storage and immobilization.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2023

Nondestructively Visualizing and Understanding the Mechano-Electro-chemical Origins of “Soft Short” and “Creeping” in All-Solid-State Batteries

All-solid-state Li-metal batteries (ASLMBs) represent a significant breakthrough in the quest to overcome limitations associated with traditional Li-ion batteries, particularly in energy density and safety aspects. However, widespread implementation is stymied due to a lack of profound understanding of the complex mechano-electro-chemical behavior of Li metal in the ASLMBs. Herein, operando neutron imaging and X-ray computed tomography (XCT) are leveraged to nondestructively visualize Li behaviors within ASLMBs. This approach offers real-time observations of Li evolutions, both pre- and post- occurrence of a “soft short”. The coordination of 2D neutron radiography and 3D neutron tomography enables charting of the terrain of Li metal deformation operando. Concurrently, XCT offers a 3D insight into the internal structure of the battery following a “soft short”. Despite the manifestation of a “soft short”, the persistence of Faradaic processes is observed. To study the elusive “soft short”, phase field modeling is coupled with electrochemistry and solid mechanics theory. The research unravels how external pressure curbs dendrite growth, potentially leading to dendrite fractures and thus uncovering the origins of both “soft” and “hard” shorts in ASLMBs. Furthermore, by harnessing finite element modeling, it dive deeper into the mechanical deformation and the fluidity of Li metal.

25 ENERGY STORAGE↗
DOE OSTI2015

Experimental evidence of the generation of gaseous SiO as precursor for the growth of SiO x nanowires

The vapor–liquid–solid process is a fundamental and widely used mechanism for the growth of nanowires. In this article, experimental observations have been carried out to explain the growth mechanism of silicon-based nanowires using a solid-bulk silicon source as unique precursor. In addition, the synthesis consisted of a thermal treatment at 900°C under an Ar-H 2 atmosphere with a low residual O 2 concentration. Lastly, the presence of SiO in gaseous phase, originated via the active oxidation of the Si substrate, is shown as the principal factor responsible for the nanowires growth, via a process commonly termed as solid–vapor–liquid–solid.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural and cyclic volta metric investigations on BIPBVOX solid electrolyte synthesized by ethylene glycol–citric acid sol–gel route

Samples of BIPBVOX.x (Bi{sub 2}V{sub 1–x}Pb{sub x}O{sub 5.5–x/2}) in the composition range 0.05 ≤ x ≤ 0.20 were prepared by ethylene glycol– citric acid sol–gel synthesis route. Structural investigations were carried out by X–ray diffraction, DTA. The highly conducting γ′– phase was effectively stabilized at room temperature for compositions with x ≥ 0.17. Cyclic voltammetric measurements showed reversible redox reactions of vanadium and irreversible redox reaction of Bi{sup 3+} in the BIPBVOX system during the first cathodic and anodic sweep. However, a higher stability against the reduction of Bi{sup 3+} to metallic bismuth was seen for x=0.20.

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

High Thermoelectric Performance in Supersaturated Solid Solutions and Nanostructured n-Type PbTe-GeTe

Sb-doped and GeTe-alloyed n-type thermoelectric materials that show an excellent figure of merit ZT in the intermediate temperature range (400–800 K) are reported. The synergistic effect of favorable changes to the band structure resulting in high Seebeck coefficient and enhanced phonon scattering by point defects and nanoscale precipitates resulting in reduction of thermal conductivity are demonstrated. The samples can be tuned as single-phase solid solution (SS) or two-phase system with nanoscale precipitates (Nano) based on the annealing processes. The GeTe alloying results in band structure modification by widening the bandgap and increasing the density-ofstates effective mass of PbTe, resulting in significantly enhanced Seebeck coefficients. The nanoscale precipitates can improve the power factor in the low temperature range and further reduce the lattice thermal conductivity (κ lat ). Specifically, the Seebeck coefficient of Pb 0.988 Sb 0.012 Te–13%GeTe–Nano approaches -280 μV K -1 at 673 K with a low κ lat of 0.56 W m -1 K -1 at 573 K. Consequently, a peak ZT value of 1.38 is achieved at 623 K. Furthermore, a high average ZT avg value of ≈1.04 is obtained in the temperature range from 300 to 773 K for n-type Pb 0.988 Sb 0.012 Te–13%GeTe–Nano.

36 MATERIALS SCIENCE↗
DOE OSTI2018

First-Principles and Thermodynamic Simulation of Elastiс Stress Effect on Energy of Hydrogen Dissolution in Alpha Iron

Mobile hydrogen, when dissolving in metals, redistributes due to the density gradients and elastic stresses, and enables destruction processes or phase transformations in local volumes of a solvent metal. It is rather important in solid state physics to investigate these interactions. The first-principle calculations performed in terms of the density functional theory, are used for thermodynamic simulation of the elastic stress effect on the energy of hydrogen dissolution in α-Fe crystal lattice. The paper presents investigations of the total energy of Fe–H system depending on the lattice parameter. As a result, the relation is obtained between the hydrogen dissolution energy and stress. A good agreement is shown between the existing data and simulation results. The extended equation is suggested for the chemical potential of hydrogen atom in iron within the local stress field. Two parameters affecting the hydrogen distribution are compared, namely local stress and phase transformations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Grain boundary facilitated dissolution of nanocrystalline NpO 2 (s) from legacy waste processing

Dissolution of actinide dioxides, including neptunium dioxide (NpO 2 (s)), is paramount for the prediction of the environmental fate of nuclear materials. Quantifying dissolution rates, as well as understanding qualitative dissolution mechanisms, informs performance assessment for geologic disposal of spent nuclear fuel and management of legacy radioactive waste. The aim of this research was to measure the dissolution rate of nanocrystalline NpO 2 (s), produced through legacy nuclear waste processing, under oxidizing conditions, as well as to characterize surface alteration to the material. The solid phase was characterized using electron microscopy techniques (SEM/STEM) and X-ray photoelectron spectroscopy (XPS), indicating preferential dissolution of Np-hydroxide contained in the grain boundaries of NpO 2 (s) and fragmentation of grains from the matrix. The oxidative dissolution was monitored over 40 weeks, yielding a two-step kinetic dissolution model involving hydration of NpO 2 (s) and subsequent oxidation and dissolution of the hydroxide phase. Here, the proposed dissolution models for nanocrystalline NpO 2 (s) suggest that microstructural features such as grain boundaries are key factors affecting dissolution, including release of colloidal particles, and ultimately, environmental fate and transport of nuclear materials.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Interactions Between Fe(III)-oxides and Fe(III)-phyllosilicates During Microbial Reduction 2: Natural Subsurface Sediments

Dissimilatory microbial reduction of solid-phase Fe(III)-oxides and Fe(III)-bearing phyllosilicates (Fe(III)-phyllosilicates) is an important process in anoxic soils, sediments, and subsurface materials. Although various studies have documented the relative extent of microbial reduction of single-phase Fe(III)-oxides and Fe(III)-phyllosilicates, detailed information is not available on interaction between these two processes in situations where both phases are available for microbial reduction. The goal of this research was to use the model dissimilatory iron-reducing bacterium (DIRB) Geobacter sulfurreducens to study Fe(III)-oxide vs. Fe(III)-phyllosilicate reduction in a range of subsurface materials and Fe(III)-oxide stripped versions of the materials. Low temperature (12K) Mossbauer spectroscopy was used to infer changes in the relative abundances of Fe(III)-oxide, Fe(III)-phyllosilicate, and phyllosilicate-associated Fe(II) (Fe(II)-phyllosilicate). A Fe partitioning model was employed to analyze the fate of Fe(II) and assess the potential for abiotic Fe(II)-catalyzed reduction of Fe(III)-phyllosilicates. The results showed that in most cases Fe(III)- oxide utilization dominated (70-100 %) bulk Fe(III) reduction activity, and that electron transfer from oxide-derived Fe(II) played only a minor role (ca. 10-20 %) in Fe partitioning. In addition, the extent of Fe(III)-oxide reduction was positively correlated to surface area-normalized cation exchange capacity and the phyllosilicate-Fe(III)/total Fe(III) ratio, which suggests that the phyllosilicates in the natural sediments promoted Fe(III)-oxide reduction by binding of oxide-derived Fe(II), thereby enhancing Fe(III)-oxide reduction by reducing or delaying the inhibitory effect that Fe(II) accumulation on oxide and DIRB cell surfaces has on Fe(III)-oxide reduction. In general our results suggest that although Fe(III)-oxide reduction is likely to dominate bulk Fe(III) reduction in most subsurface sediments, Fe(II) binding by phyllosilicates is likely to play a key role in controlling the long-term kinetics of Fe(III)-oxide reduction.

Wu, T.↗