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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 1,315 records · Page 73
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Elevated temperature tribology of cobalt and tantalum-based alloys

This paper describes the friction and wear behavior of a Co–Cr alloy sliding on a Ta–W alloy. Measurements were performed in a pin-on-flat configuration with a hemispherically tipped Co-base alloy pin sliding on a Ta–W alloy flat from ambient to 430°C. Focused ion beam-scanning electron microscopy (FIB-SEM) and cross-sectional transmission electron microscopy (TEM) were used to identify the friction-induced changes to the chemistry and crystal structure in the subsurface regions of wear tracks. During sliding contact, transfer of material varied as a function of the test temperature, either from pin-to-flat, flat-to-pin, or both, resulting in either wear loss and/or volume gain. Friction coefficients (μ) and wear rates also varied as a function of test temperature. The lowest friction coefficient (μ=0.25) and wear rate (1×10 –4 mm 3 /N•m) were observed at 430°C in argon atmosphere. This was attributed to the formation of a Co-base metal oxide layer (glaze), predominantly (Co, Cr)O with Rocksalt crystal structure, on the pin surface. Part of this oxide film transferred to the wear track on Ta–W, providing a self-mated oxide-on-oxide contact. Once the oxide glaze is formed, it is able to provide friction reduction for the entire temperature range of this study, ambient to 430°C. Furthermore, the results of this study indicate that glazing the surfaces of Haynes alloys with continuous layers of cobalt chrome oxide prior to wear could protect the cladded surfaces from damage.

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

Tribochemical changes of alloy 800HT under sliding contact at elevated temperature in impure helium environment

This work investigates the chemical changes of the surface of Alloy 800HT during sliding contact under helium atmosphere in the presence of impurities at 750 °C, which is of interest for the nuclear industry. The alloy samples are exposed to helium (He) atmosphere at high temperature for long duration of 500 h to identify the chemical and topographical changes of the alloy surface. The oxidation rate constant is reported based on the weight change data. For the tribo-experimental samples, the surfaces inside and outside the wear track are studied thoroughly using techniques such as secondary electron microscopy, energy dispersive spectroscopy, x-ray diffraction, Raman spectroscopy and secondary ion mass spectroscopy. The formation and evolution of surface oxides are discussed in He atmosphere, compared with air. The presence of Fe-rich thin layer of oxide on top of a thicker Cr-rich oxide and a mixed spinel-based inner layer on the bulk is found. The persistent presence of thicker Fe3O4 in the wear track in high temperature air proved to be the reason of lower friction property. Pre-oxidation of the samples in air or He does not improve but worsen the tribological behavior in He atmosphere.

36 MATERIALS SCIENCE↗
DOE OSTI2025

A theoretical study of the upper bound of surface elevation variance in the Phillips initial stage during wind-wave generation

The resonance mechanism in the initial of wind-wave generation proposed by Phillips is a foundation of wind-wave generation theory, but a precise theoretical quantification of wave energy growth in this initial stage has not been obtained yet after more than six decades of research. In this study, we aim to address this knowledge gap by developing an analytical approach based on a novel complex analysis method to theoretically investigate the temporal evolution of the wave energy in the Phillips initial stage. We quantitatively derive and analyse the growth behaviour of the surface wave energy and obtain an analytical solution for its upper bound. Our result highlights the crucial effects of surface tension. Because the phase velocity of gravity–capillary waves has a minimal value at a critical wavenumber, gravity–capillary waves and gravity waves (which neglect surface tension) exhibit distinct resonance curve properties and wave energy growth behaviours. For gravity waves, the resonance curve extends indefinitely; for gravity–capillary waves, it either forms a finite-length curve or does not exist, depending on the wind speed. The leading-order term of the upper-bound solution of the energy of gravity waves increases linearly over time, while for gravity–capillary waves, the term increases linearly over time under strong wind conditions but remains finite under weak wind conditions. This theoretical study provides an analytical framework for the generation of wind-waves in the Phillips initial stage, which may inspire further theoretical, numerical and experimental research.

58 GEOSCIENCES↗
DOE OSTI2018

Surface Structural and Chemical Evolution of Layered LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) under High Voltage and Elevated Temperature Conditions

This work reports new insights into structural and chemical evolution of surface phases of LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) held at constant high voltages (up to 4.75 V) as well as high temperatures (60 °C) by correlating crystal structure using high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imaging with chemistry using electron energy loss spectroscopy (EELS). We also followed the Al distribution within individual NCA particles by X-ray energy dispersive spectroscopy (EDS). The progression of these phases as a function of distance from the edge shows simultaneous evolution of crystal structures and chemistry from rocksalt to layered, forming a complete solid solution. We have also observed an extended disordered phase with rocksalt (Fm3m) symmetry in which quantitative electron energy loss spectroscopy reveals it to be an oxygen deficient cation disordered phase with chemical characteristics, as determined by EELS, similar to spinel. The formation of these disordered phases with cation and oxygen vacancies has been driven by surface oxygen loss caused by reactions with the electrolyte followed by cation migration from the octahedral 3a M (M = Ni, Co, Al) layer to the octahedral 3b Li layer. These surface rocksalt phases are not fully dense as they contain Al and Li as well as a high concentration of cation and oxygen vacancies. After discharge, Li is detected within these phases indicative that Li transport has occurred through these rocksalt phases. At 60 °C and 4.75 V a very large impedance rise is observed leading to complete cell irreversibility which is caused by significant metal dissolution from the cathode and formation of surface porosity. In the near surface region of some particles, a phase transformation from R3m (O3) to P3m1 (O1) is also observed which has become thermodynamically stable from complete delithiation as well as from local Al surface depletion.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Electronic Structure and Safety Insights into Prussian Blue Analog Cathode Behavior at Elevated Temperatures in Sodium-Ion Batteries

Prussian blue analogs (PBAs) represent promising cathode materials for sodium-ion batteries (SIBs) due to their high theoretical capacity, open framework structure, and use of earth-abundant elements. However, the high-temperature structural evolution, water content effects, and thermal safety of PBAs, particularly in charged states, remain poorly understood, hindering their practical deployment. Here, we investigate Na 2 Fe[Fe(CN) 6 ]·2H 2 O using thermogravimetric analysis (TGA), ex situ and in situ temperature-dependent X-ray absorption spectroscopy (XAS), and accelerated rate calorimetry (ARC). TGA and ex situ XAS confirm water loss between 150 and 200 °C, resulting in Fe 2+ oxidation, enhanced local symmetry, and uniform redox behavior that improves electrochemical performance. In situ XAS reveals irreversible structural changes above 240 °C, including ligand loss, Fe site distortion, and increased disorder, while ARC on charged electrodes shows minimal self-heating rates (<0.1 °C/min) up to 300 °C, indicating exceptional thermal stability without lattice oxygen release. These insights elucidate PBA thermal dynamics, demonstrating improved electrochemical performance of water-deficient PBAs and informing future material design and safety assessment for SIB applications.

batteries↗
DOE OSTI2025

Rational Electrolyte Design for Elevated-Temperature and Thermally Stable Lithium-Ion Batteries with Nickel-Rich Cathodes

As the energy density of lithium-ion batteries (LIBs) increases, the shortened cycle life and the increased safety hazard of LIBs are drawing increasing concerns. To address such challenges, a series of localized high-concentration electrolytes (LHCEs) based on a solvating-solvent mixture of tetramethylene sulfone and trimethyl phosphate and a high flash-point diluent 1H,1H,5H-octafluoropentyl 1,1,2,2-tetrafluoroethyl ether were designed. The LHCEs exhibited non-flammability and greatly suppressed heat release at high temperatures, which would potentially improve the safety performance of the LIBs. Moreover, the optimal LHCE achieved capacity retentions of 87.1% and 81.7% in graphite||LiNi 0.8 Mn 0.1 Co 0.1 O 2 cells after 500 cycles at 25 °C and 45 °C, respectively, which were significantly better than the conventional electrolyte, whose capacity retentions were only 75.2% and 38.5% under the same condition. Mechanistic studies revealed that the LHCE not only formed a more robust solid electrolyte interphase, but also exhibited improved anodic stability, compared with the conventional electrolyte. Further, this work sheds light in rational electrolyte design for high energy density LIBs with high battery performance and low safety concerns.

25 ENERGY STORAGE↗
DOE OSTI2019

Elevated Stability and Efficiency of Solar Cells via Ordered Alloy Co-Acceptors

Power conversion efficiency (PCE) and long-term stability are the two key parameters of photovoltaic devices to meet standards for commercial use. In this Letter, an ordered alloyed co-acceptor by incorporating PC 61 BM and CO i 8DFIC is obtained. This ordered alloy structure increases the light absorption by producing a shoulder peak at 935 nm and improves electron mobility from 1.51 × 10 –5 to 8.91 × 10 –4 cm 2 V –1 s –1 by PC 61 BM interacting with the end group of CO i 8DFIC and connecting adjacent CO i 8DFIC molecules. Consequently, the PCE is enhanced from 10.80 to 14.22%, enhancement of about 32%. Even further, the device stability is improved due to the fact that the alloy fixes the morphology of the active layer. As a result, after keeping for 7200 h, about 10 months, the PCE of those solar cells is retained at 13.2%, corresponding to a PCE loss of only 5.7%, while the PCE loss in the binary control device is up to 33.3%.

14 SOLAR ENERGY↗