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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Influences and interactions of inundation, peat, and snow on active layer thickness

The effect of three environmental conditions: 1) thickness of organic soil, 2) snow depth, and 3) soil moisture content or water table height above and below the soil surface, on active layer thickness (ALT) are investigated using an ensemble of 1D thermal hydrology models. Sensitivity analyses of the ensemble exposed the isolated influence of each environmental condition on ALT and their multivariate interactions. The primary and interactive influences are illustrated in the form of color maps of ALT change. Results show that organic layer acts as a strong insulator, and its thickness is the dominant control of ALT, but the strength of the effect of organic layer thickness is dependent on the saturation state. Snow depth, subsurface saturation, and ponded water depth are strongly codependent and positively correlated to ALT.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2025

Probing the Effect of Electrode Thermodynamics on Reaction Heterogeneity in Thick Battery Electrodes

Thick electrodes present a viable strategy for enhancing energy density and reducing manufacturing costs of lithium-ion batteries. However, reaction heterogeneity during cycling compromises their rate capability and cycle life. While this nonuniformity is commonly attributed to sluggish charge transport, it is demonstrated here that the thermodynamic properties of the electrode material play an equally critical role. Through combined X-ray fluorescence microscopy and absorption near-edge structure spectroscopy, reaction distributions in LiFePO 4 (LFP) and LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC) thick electrodes with matched porosity and tortuosity are compared. LFP electrodes develop pronounced depth-oriented state-of-charge (SOC) gradients that worsen with increasing discharge rates, whereas NMC maintains much more uniform SOC distributions under such conditions. This difference originates from their distinct SOC dependence of equilibrium potentials and is quantifiable through a dimensionless “reaction uniformity” number. Intriguingly, LFP thick electrodes also exhibit lateral SOC variations that strengthen during slow discharge. In conclusion, the enhanced reaction uniformity in NMC correlates with better active material utilization and slower capacity fade than LFP, highlighting electrode thermodynamics as a key design consideration for thick electrodes.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Thick Binder-Free Electrodes for Li-Ion Battery Fabricated Using Templating Approach and Spark Plasma Sintering Reveals High Areal Capacity

The templating approach is a powerful method for preparing porous electrodes with interconnected well-controlled pore sizes and morphologies. The optimization of the pore architecture design facilitates electrolyte penetration and provides a rapid diffusion path for lithium ions, which becomes even more crucial for thick porous electrodes. In this work, NaCl microsize particles are used as a templating agent for the fabrication of 1 mm thick porous LiFePO 4 and Li 4 Ti 5 O 12 composite electrodes using spark plasma sintering technique. These sintered binder-free electrodes are self-supported and present a large porosity (40%) with relatively uniform pores. The electrochemical performances of half and full batteries reveal a remarkable specific areal capacity (20 mA h cm -2 ), which is 4 times higher than those of 100 µm thick electrodes present in conventional tape-casted Li–ion batteries (5 mA h cm -2 ). The 3D morphological study is carried out using full field transmission X-ray microscopy in microcomputed tomography mode to obtain tortuosity values and pore size distributions leading to a strong correlation with their electrochemical properties. These results also demonstrate that the coupling between the salt templating method and the spark plasma sintering technique turns out to be a promising way to fabricate thick electrodes with high energy density.

25 ENERGY STORAGE↗
DOE OSTI2026

Towards High-Speed friction stir welding of 25 mm Thick AA2139-T8: tool innovation and process development

Joining thick plates (≥ 12 mm) of aluminum (Al) alloys is challenging due to high tool forces, uneven material flow, and non-uniform heat distribution through the material’s thickness. Recent advancements in tool design and welding parameters for friction stir welding (FSW) in thick plates butt joining have encountered a developmental plateau, highlighting the need for innovative approaches to overcome existing limitations. Here, this study focuses on the systematic development of single-pass and double-pass FSW processes for high-strength aluminum alloy AA2139-T8, to improve joint efficiency and enable high-speed welding capabilities. Experimental evidence is presented for a novel tool design with opposing pin threads, enabling high-speed (178 mm/min) single-pass friction stir butt welding of 25 mm thick AA2139-T8. A series of FSW trials was conducted both in air and with a trailing water spray, using steel backing plates (BPs) to investigate the impact of quenching and cooling rates on process response and joint performance. A joint efficiency of 83% was attained using the novel tool features and effectively controlling process forces and thermal boundary conditions.

AA2139-T8↗
DOE OSTI2016

Deuteron irradiation of W and WO 3 for production of high specific activity 186 Re: Challenges associated with thick target preparation

This investigation evaluated target fabrication and beam parameters for scale-up production of high specific activity 186 Re using deuteron irradiation of enriched 186 W via the 186 W(d,2n) 186 Re reaction. Thick W and WO 3 targets were prepared, characterized and evaluated in deuteron irradiations. Full-thickness targets, as determined using SRIM, were prepared by uniaxi-ally pressing powdered natural abundance W and WO 3 , or 96.86% enriched 186 W, into Al target supports. Alternatively, thick targets were prepared by pressing 186 W between two layers of graphite powder or by placing pre-sintered (1105°C, 12 hours) natural abundance WO 3 pellets into an Al target support. Assessments of structural integrity were made on each target pre-pared. Prior to irradiation, material composition analyses were conducted using SEM, XRD, and Raman spectroscopy. With-in a minimum of 24 hours post irradiation, gamma-ray spectroscopy was performed on all targets to assess production yields and radionuclidic byproducts. Problems were encountered with the structural integrity of some pressed W and WO 3 pellets before and during irradiation, and target material characterization results could be correlated with the structural integrity of the pressed target pellets. Under the conditions studied, the findings suggest that all WO 3 targets prepared and studied were unacceptable. By contrast, 186W metal was found to be a viable target material for 186 Re production. Lastly, thick targets prepared with powdered 186W pressed between layers of graphite provided a particularly robust target configuration.

43 PARTICLE ACCELERATORS↗
DOE OSTI2023

Exact solution of burst pressure for thick-walled pipes using the flow theory of plasticity

This paper develops an exact solution of burst pressure for defect-free, thick-walled pipes using the flow theory of plasticity in terms of the average shear stress yield criterion (or Zhu-Leis yield criterion). The pipe steel is assumed to obey the power-law strain hardening rule, and large plastic deformation is described by the finite strain theory. On this basis, internal pressure is obtained as a power series function of the effective strains on the inside and outside surfaces of the thick-walled pipe with use of the second Bernoulli numbers. At burst failure, the Zhu-Leis flow solution of burst pressure is determined as a power series solution, and the burst effective strains, the burst effective stresses, and the burst pressure are functions of the diameter ratio (D o / D i ), strain hardening exponent (n), and ultimate tensile strength (UTS). Similarly, the Tresca and von Mises flow solutions of burst pressure are also determined as a power series solution in terms of the Tresca and von Mises yield criteria. A general closed-from exact solution of burst pressure is then proposed for the three yield criteria, and the results showed that the proposed exact solution matches well with the power series solution for each yield criterion. Moreover, the von Mises flow solution is an upper bound prediction, the Tresca flow solution is a lower bound prediction, and the Zhu-Leis flow solution is an intermediate prediction that agrees well with the finite element analysis results of burst pressure for thick-walled pipes. Furthermore, two datasets of full-scale burst tests are then utilized to evaluate and validate the proposed flow solutions of burst pressure for both thin and thick-walled pipes.

42 ENGINEERING↗
DOE OSTI2016

Preparation of ultra-thin and high-quality WO{sub 3} compact layers and comparision of WO{sub 3} and TiO{sub 2} compact layer thickness in planar perovskite solar cells

In this paper, the ultra-thin and high-quality WO{sub 3} compact layers were successfully prepared by spin-coating-pyrolysis method using the tungsten isopropoxide solution in isopropanol. The influence of WO{sub 3} and TiO{sub 2} compact layer thickness on the photovoltaic performance of planar perovskite solar cells was systematically compared, and the interface charge transfer and recombination in planar perovskite solar cells with TiO{sub 2} compact layer was analyzed by electrochemical impedance spectroscopy. The results revealed that the optimum thickness of WO{sub 3} and TiO{sub 2} compact layer was 15 nm and 60 nm. The planar perovskite solar cell with 15 nm WO{sub 3} compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO{sub 2} compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency. - Graphical abstract: The planar perovskite solar cell with 15 nm WO{sub 3} compact layer gave a 9.69% average and 10.14% maximum photoelectric conversion efficiency, whereas the planar perovskite solar cell with 60 nm TiO{sub 2} compact layer achieved a 11.79% average and 12.64% maximum photoelectric conversion efficiency. Display Omitted - Highlights: • Preparation of ultra-thin and high-quality WO{sub 3} compact layers. • Perovskite solar cell with 15 nm-thick WO{sub 3} compact layer achieved PCE of 10.14%. • Perovskite solar cell with 60 nm-thick TiO{sub 2} compact layer achieved PCE of 12.64%.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Activation energy and carriers dynamics of multilayer CdTe/ZnTe quantum dots with different ZnTe separation layer thicknesses

We studied the optical properties of multilayer CdTe/ZnTe quantum dots (QDs) with various ZnTe separation layer thicknesses on GaAs substrates. The low temperature photoluminescence (PL) spectra show that the excitonic peaks in multilayer CdTe/ZnTe QDs shift to higher energy levels, and PL peak intensities increase with increasing ZnTe separation layer thickness. This is because of increasing uncoupling and because there are many more carriers confined in the QDs with wider separation layers. Temperature-dependent PL measurements showed that the activation energies of the confined electrons in the multilayer CdTe/ZnTe QDs decreases with decreasing ZnTe separation layer thickness. The time-resolved PL spectra show increasing carrier decay times with decreasing ZnTe separation layer thickness, due to increasing coupling between QDs with narrower separation layers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Impact of MgO thickness on the perpendicular magnetic anisotropy of Mo/Co2FeAl/MgO/Mo multilayers with improved annealing stability

Highlights: • Robust PMA is demonstrated for thermally stable Mo/Co{sub 2}FeAl(CFA)/MgO/Mo multilayer. • Thickness of CFA and MgO over-layer plays a main role in achieving the strong PMA. • Significant PMA energy of K{sub eff} ≈ 1.67 × 10{sup 6} erg/cm{sup 3} is achieved for film annealed at 400 °C. • Co and/or Fe – 3d{sub Z}{sup 2} and O-2P{sub Z} orbital hybridization at interface is the origin for PMA. - Abstract: In this study, an interfacial perpendicular magnetic anisotropy (PMA) is achieved in Mo/Co{sub 2}FeAl (CFA)/MgO/Mo multilayer with good thermal stability up to 400 °C by tuning the annealing temperature and film thickness of CFA and MgO. For an optimized CFA film thickness (1.0 nm) and annealing temperature (400 °C), the CFA/MgO interface plays a main role in achieving the strong PMA property when the MgO film thickness was tuned from 0.5 nm to 2.0 nm. The effective perpendicular magnetic anisotropy energy density (K{sub eff}) is approximately 1.67 × 10{sup 6} erg/cc when t{sub MgO} = 2 nm. Surface morphology and surface roughness changes in the films are investigated by atomic force microscopy (AFM). An enhancement in surface smoothness is observed for the annealed films. X-ray photoelectron spectroscopy (XPS) reveals that the strong PMA in Mo/CFA/MgO is originated from the adequate oxidation of Co and Fe at CFA/MgO interface.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Thickness and uniformity mapping of thin foils using resistive silicon detectors

Alpha energy loss is a common tool used for measuring target thicknesses. However, these measurements are often made without position information, which either forfeits knowledge of material uniformity and local thickness or requires a prohibitive number of measurements per target to partially recover this information. In consideration of this, a method for measuring position-dependent thicknesses is described in this work; by using the position-sensitivity of the dual-axis duo-lateral (DADL) silicon detector, thicknesses across the entire face of the material can be measured to sub-mm precision with a single measurement. Several examples are presented using a number of targets with varying characteristics, which altogether demonstrate the precision, accuracy, and versatility of this technique.

Foil uniformity↗
DOE OSTI2025

Experimental study of energy-dependent angular broadening of MeV electron beams for high-resolution imaging in thick samples

In scanning transmission electron microscopy (STEM), spatial resolution is primarily influenced by the projected size of the electron probe within the specimen. In thin samples, a large semi-convergence angle enables a tightly focused beam and sub-nanometer resolution. However, in thick specimens, resolution is fundamentally limited by transverse beam broadening from multiple large-angle scattering events—for example, a probe with 10 mrad angular divergence can broaden by ∼100 nm over a 10 μm path. Since this broadening scales inversely with beam energy, MeV-STEM offers a promising route for high-resolution imaging in thick materials. To quantitatively assess this effect, we performed high-precision measurements at UCLA’s PEGASUS beamline, characterizing beam divergence and intensity profiles for 3–8 MeV electrons transmitted through a wedged-silicon sample of varying thickness. Our results reconcile discrepancies among analytical models and validate Monte Carlo simulations. Here, we find that increasing beam energy from 3.0 to 5.8 MeV reduces angular broadening by a factor of 2.6, with diminishing returns observed at 7.6 MeV. These findings provide a quantitative framework for optimizing MeV-STEM parameters in high-resolution imaging of thick biological and microelectronic specimens, and for guiding beam energy selection in other advanced imaging modes beyond STEM.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Thickness-Dependent Cross-Plane Thermal Conductivity Measurements of Exfoliated Hexagonal Boron Nitride

Submicrometer-thick layers of hexagonal boron nitride (hBN) exhibit high in-plane thermal conductivity and useful optical properties, and serve as dielectric encapsulation layers with low electrostatic inhomogeneity for graphene devices. Despite the promising applications of hBN as a heat spreader, the thickness dependence of its cross-plane thermal conductivity is not known, and the cross-plane phonon mean free paths (MFPs) have not been measured. We measure the cross-plane thermal conductivity of hBN flakes exfoliated from bulk crystals. We find that submicrometer thick flakes exhibit thermal conductivities up to 8.1 ± 0.5 W m –1 K –1 at 295 K, which exceeds previously reported bulk values by more than 60%. Surprisingly, the average phonon mean free path is found to be several hundred nanometers at room temperature, a factor of 5 larger than previous predictions. When planar twist interfaces are introduced into the crystal by mechanically stacking multiple thin flakes, the cross-plane thermal conductivity of the stack is found to be a factor of 7 below that of individual flakes with similar total thickness, thus providing strong evidence that phonon scattering at twist boundaries limits the maximum phonon MFPs. These results have important implications for hBN integration in nanoelectronics and improve our understanding of thermal transport in twodimensional materials.

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

Shell Thickness and Heterogeneity Dependence of Triplet Energy Transfer between Core–Shell Quantum Dots and Adsorbed Molecules

Quantum dot (QD)-sensitized triplet energy transfer (TET) has found promising applications in photon upconversion and photocatalysis. However, the underlying mechanism of TET in the QD-acceptor complex remains unclear despite the well-developed TET theory for the molecular donor–acceptor systems. Herein, the coupling strength of TET from CdSe/CdS core–shell QDs to 9-anthracene carboxylic acid (ACA) was studied by measuring the TET rate as a function of shell thickness with time-resolved photoluminescence. The change of TET-coupling strength with increasing shell thickness was further compared to those of electron and hole transfers from QDs so that we could test whether QD-sensitized TET is mediated by the charge transfer virtual state and can be considered as simultaneous electron and hole transfers as in molecular donor–acceptor systems. The measured coupling strength of TET from the CdSe/CdS QD decreases exponentially with the CdS shell thickness r: |V|(r) = |V|(0)e –βr , with an exponential decay factor β of 0.19 Å –1 , which is smaller than the sum of the measured decay factors for electron transfer to methyl viologen (0.18 Å –1 ) and hole transfer to phenothiazine (0.29 Å –1 ) from the same QD. This inconsistency is explained by the broadening of QD shell thicknesses in the distance dependence study, which significantly modifies the TET-coupling strength and driving force, resulting in a shallower distance dependence of the TET rate constants. This study sheds light on the fundamental mechanisms of QD-sensitized TET reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Detecting Permafrost Active Layer Thickness Change From Nonlinear Baseflow Recession

We report permafrost underlies about one fifth of the global land area and affects ground stability, freshwater runoff, soil chemistry, and surface-atmosphere gas exchange. The depth of thawed ground overlying permafrost (active layer thickness) has broadly increased across the Arctic in recent decades, coincident with a period of increased streamflow, especially the lowest flows (baseflow). Mechanistic links between active layer thickness and baseflow have recently been explored using linear reservoir theory, but most watersheds behave as nonlinear reservoirs. We derive theoretical nonlinear relationships between long-term average saturated soil thickness $\bar{η}$(proxy for active layer thickness) and long-term average baseflow. When applied to 38 years of daily streamflow data for the Kuparuk River basin on the North Slope of Alaska, the theory predicts $\bar{η}$ increased 0.17 ± 0.22[2σ] cm a -1 between 1983 and 2020 (6.4 ± cm total). The rate of increase nearly doubled to 0.29 ± 0.31 cm a -1 between 1990 and 2020, during which time local field measurements from Circumpolar Active Layer Monitoring sites indicate the active layer increased 0.31 ± 0.22 cm a -1 . The predicted rate of increase more than doubled again between 2002 and 2020, outpacing a near doubling of observed active layer thickening, consistent with trends in terrestrial water storage inferred from Gravity Recovery and Climate Experiment satellite gravimetry and Modern-Era Retrospective Analysis for Research and Applications climate reanalysis. Overall, hydrologic change is accelerating in the Kuparuk River basin, and we provide a theoretical framework for estimating basin-scale changes in active layer water storage from streamflow measurements.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Thickness dependent structural, optical and electrical properties of CuIn{sub 0.8}Ga{sub 0.2}Se{sub 2} thin films deposited by pulsed laser deposition

CuIn{sub 0.8}Ga{sub 0.2}Se{sub 2} (CIGS) polycrystalline thin films have been deposited on soda lime glass substrate at different deposition time by pulsed laser deposition. The effect of thickness on structural, surface morphological, optical and electrical properties of thin films were investigated by X-ray diffractometer (XRD), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), UV-Vis-NIR spectrophotometer and electrical measurement unit. XRD study reveals that all deposited films are polycrystalline in nature and have tetragonal phase of CIGS. Crystallinity of CIGS films has been found to improve with increase in thickness of CIGS films as evidenced by sharp XRD peaks for (112) orientation. Grain size and rms surface roughness of CIGS films have been found to be increased with increase in thickness. All the deposited CIGS films exhibit direct band gap semiconducting behaviour with ∼10{sup 6} cm{sup −1} absorption co-efficient. Optical band gap and resistivity of CIGS films have been found to decrease with increase in thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Annealing temperature and thickness dependence of magnetic properties in epitaxial L1{sub 0}-Mn{sub 1.4}Ga films

Mn{sub 1.4}Ga films with high perpendicular magnetic anisotropy and high crystalline quality were grown on MgO substrates with Cr buffer layer using molecular beam epitaxy. The crystalline structure and the surface morphology of the films have been systematically investigated as functions of in-situ annealing temperature (T{sub a}) and film thickness. It is found that the magnetic properties can be largely tuned by adjusting T{sub a}. As T{sub a} increases, both saturation magnetization (M{sub s}) and uniaxial perpendicular magnetic anisotropy constant (K{sub u}) increase to the maximum values of 612 emu/cc and 18 Merg/cc at 300 °C, respectively, and then decrease. The morphology also changes with T{sub a}, showing a minimum roughness of 2.2 Å at T{sub a} = 450 °C. On the other hand, as the thickness increases, M{sub s} and K{sub u} increase while coercivity decreases, which indicates there is a magnetic dead layer with a thickness of about 1.5 nm at the interfaces. The detailed examination on the surface morphology of the films with various thicknesses shows a complicated film growth process, which can be understood from the relaxation mechanism of the interfacial strain.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Study of pipe thickness loss using a neutron radiography method

The purpose of this preliminary work is to study for thickness changes in objects using neutron radiography. In doing the project, the technique for the radiography was studied. The experiment was done at NUR-2 facility at TRIGA research reactor in Malaysian Nuclear Agency, Malaysia. Test samples of varying materials were used in this project. The samples were radiographed using direct technique. Radiographic images were recorded using Nitrocellulose film. The films obtained were digitized to processed and analyzed. Digital processing is done on the images using software Isee!. The images were processed to produce better image for analysis. The thickness changes in the image were measured to be compared with real thickness of the objects. From the data collected, percentages difference between measured and real thickness are below than 2%. This is considerably very low variation from original values. Therefore, verifying the neutron radiography technique used in this project.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗
DOE OSTI2014

Terahertz inline wall thickness monitoring system for plastic pipe extrusion

Conventional and commercially available inline wall thickness monitoring systems for pipe extrusion are usually based on ultrasonic or x-ray technology. Disadvantages of ultrasonic systems are the usual need of water as a coupling media and the high damping in thick walled or foamed pipes. For x-ray systems special safety requirements have to be taken into account because of the ionizing radiation. The terahertz (THz) technology offers a novel approach to solve these problems. THz waves have many properties which are suitable for the non-destructive testing of plastics. The absorption of electrical isolators is typically very low and the radiation is non-ionizing in comparison to x-rays. Through the electromagnetic origin of the THz waves they can be used for contact free measurements. Foams show a much lower absorption in contrast to acoustic waves. The developed system uses THz pulses which are generated by stimulating photoconductive switches with femtosecond laser pulses. The time of flight of THz pulses can be determined with a resolution in the magnitude of several ten femtoseconds. Hence the thickness of an object like plastic pipes can be determined with a high accuracy by measuring the time delay between two reflections on materials interfaces e.g. at the pipe's inner and outer surface, similar to the ultrasonic technique. Knowing the refractive index of the sample the absolute layer thickness from the transit time difference can be calculated easily. This method in principle also allows the measurement of multilayer systems and the characterization of foamed pipes.

36 MATERIALS SCIENCE↗