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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 1,621 records · Page 90
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Sorption Behavior of Iodide Ions on Calcium Silicate Hydrate Formed under the Condition Saturated with Saline Water - 17069

The sorption behavior of iodide ions on calcium-silicate-hydrate (CSH gel) under the condition saturated with saline water was examined by using a Raman spectroscopy and ICP-AES, without drying process. In the sorption experiments, I-127 is a stable isotope was used as an alternative of I-129. CSH gel was synthesized with mixing CaO, SiO{sub 2}, and NaCl solution. The Ca/Si molar ratios of CSH gel were set to 0.4, 0.8, 1.2 and 1.6, and the concentration of NaCl solution was set to 0.6 M for simulating the condition of saline groundwater. The liquid/solid weight ratios of CSH gel were set to 10, 13, 15, 17, and 20, and the total weight of solid phase was 1.5 g. Furthermore, at the preparation of CSH gel, the substance of iodide ions in each sample was adjusted to 15 μmol. The synthesis procedure for all samples was conducted in a glove bag filled with nitrogen gas. The curing period was 7, 14, 30, and 60 days at a room temperature (298 K) with shaking at 120 strokes/min. The results of the sorption experiments, iodide ions adsorbed on CSH gel regardless of the high concentration of NaCl. The concentration of iodide ions in liquid phase was equal to the initial one under all experimental conditions. Moreover, the distribution coefficients, K{sub d}, were kept constant (K{sub d} = 1 mL/g) after 14 days. In the results of Raman analysis, the structure of CSH gel was scarcely influenced by incorporating iodide ions from the viewpoint of the silicate chain. These results suggest that iodide ions will be incorporated into CSH gel with the hydration water without changing its structure. Such effect of CSH gel formed with leaching cementitious constituents around the repository may retard the migration of radionuclide (I-129) in the natural barrier of the radioactive waste disposal system. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

The Effect of Boron and Zirconium on the Structure and Tensile Properties of the Cast Nickel-Based Superalloy ATI 718Plus

The effects of boron and zirconium on cast structure, hardness, and tensile properties of the nickel-based superalloy 718Plus were investigated. For this purpose, five alloys with different contents of boron and zirconium were cast via vacuum induction melting and then purified via vacuum arc remelting. Microstructural analysis by light-optical microscope and scanning electron microscope equipped with energy-dispersive x-ray spectroscopy and phase studies by x-ray diffraction analysis were performed. The results showed that boron and zirconium tend to significantly reduce dendritic arm spacing and increase the amount of Laves, Laves/gamma eutectic, and carbide phases. It was also found that boron led to the formation of B{sub 4}C and (Cr, Fe, Mo, Ni, Ti){sub 3}B{sub 2} phases and zirconium led to the formation of intermetallic phases and ZrC carbide. In the presence of boron and zirconium, the hardness and its difference between dendritic branches and inter-dendritic spaces increased by concentrating such phases as Laves in the inter-dendritic spaces. These elements had a negative effect on tensile properties of the alloy, including ductility and strength, mainly because of the increase in the Laves phase. It should be noted that the largest degradation of the tensile properties occurred in the alloys containing the maximum amount of zirconium.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Design, Fabrication and Test of Composite Curved Frames for Helicopter Fuselage Structure

Aspects of curved beam effects and their importance in designing composite frame structures are discussed. The curved beam effect induces radial flange loadings which in turn causes flange curling. This curling increases the axial flange stresses and induces transverse bending. These effects are more important in composite structures due to their general inability to redistribute stresses by general yielding, such as in metal structures. A detailed finite element analysis was conducted and used in the design of composite curved frame specimens. Five specimens were statically tested and compared with predicted and test strains. The curved frame effects must be accurately accounted for to avoid premature fracture; finite element methods can accurately predict most of the stresses and no elastic relief from curved beam effects occurred in the composite frames tested. Finite element studies are presented for comparative curved beam effects on composite and metal frames.

Lowry, D. W.↗
DOE OSTI2026

(CrMnCoNiTi) 3 O 4 high-entropy spinel oxide as a high-performance electrode for supercapacitors

In this study, spinel-structured (CrMnCoNiTi)₃O₄ high-entropy oxides (HEOs) have been successfully synthesized using the solution combustion method, and their performance as supercapacitor electrode materials was investigated. These HEOs exhibit excellent performance, stemming from the unique high-entropy effect and lattice distortion. This structure effectively buffers volumetric strain during cycling, conferring the material with extremely high structural stability and specific capacity. The material demonstrates a high specific capacity of 491.5 C∙g⁻¹ at a current density of 0.5 A∙g⁻¹. Furthermore, it shows extraordinary cycling stability: after 10,000 charge/discharge cycles at 5 A∙g⁻¹, the capacity retention rate is 99%, and the Coulombic efficiency consistently remains close to 100%. Ex-situ structural characterizations further reveal that this excellent cycling durability originates from a cooperative multination valence reconstruction mechanism within an entropy-stabilized spinel framework. Additionally, a symmetric supercapacitor assembled using this material and 1 M KOH electrolyte successfully extended the working voltage to 1.2 V. This research highlights the great potential of high-entropy oxides in synergizing high energy density and ultra-long cycling life, laying a solid foundation for the development of next-generation high-performance supercapacitor electrode materials.

High entropy oxides↗
DOE OSTI2019

Effect of Zn Concentration on the Structure, Morphology, and Magnetic Behavior of Ni{sub 1 − x}Zn{sub x}Fe{sub 2}O{sub 4} Ferrofluid

In this work, we investigated the effect of doping zinc ions onto nickel ferrite upon the structure, morphology, and magnetic properties of Ni{sub 1 − x}Zn{sub x}Fe{sub 2}O{sub 4} ferrite nanoparticles (x = 0, 0.25, and 0.75) prepared via co-precipitation method. X-ray diffraction analysis showed the presence of the most intense peak corresponding to the (311) crystallographic orientation of NiFe{sub 2}O{sub 4} cubic spinel phase, and the crystallite size obtained from Scherrer formula increased from 6.8 to 11.2 nm when the Zn concentration increases from x = 0 to x = 0.75. Fourier transform infrared spectroscopy analysis confirmed the presence of a prominent band associated to the vibrations of metal ions, as a feature of spinel ferrite phase formation, observing that their band positions were very sensitive to Zn doping concentration. Transmission electron microscopy studies allowed to determinate that for all Zn concentrations, the particle sizes are around 15 nm. The magnetic properties were studied by using the vibrating sample magnetometer at room temperature. The results reveal superparamagnetic behavior determined by the shape of the hysteresis loop, presenting decreased coercive magnetic field and increased saturation magnetization, with increased zinc concentration. Additionally, from field cooling and zero field cooling curves, we can observe the typical behavior of the blocking process assembly of superparamagnetic nanoparticles. Alternate current susceptibility measurements show that the blocking temperature is frequency dependent and shifts toward higher temperatures by increasing the frequency, a characteristic of superparamagnetic, and glassy systems. Furthermore, τ{sub 0}, related to the jump attempt frequency of the magnetic moment of the nanoparticle between the opposite directions of the magnetization easy axis, is in the range of 2 × 10{sup −10} and 7 × 10{sup −13} s for the three different Zn concentrations, which agrees with characteristic of non-interacting superparamagnetic systems.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Self-consistent quasiparticle G W and hybrid functional calculations for Al/InAs/Al heterojunctions: Band offset and spin-orbit coupling effects

The electronic structure of surfaces and interfaces plays a key role in the properties of quantum devices. Here, we study the electronic structure of realistic Al/InAs/Al heterojunctions using a combination of density functional theory with hybrid functionals and state-of-the-art quasiparticle G W (QSGW) calculations. We find a good agreement between QSGW calculations and hybrid functional calculations, which themselves compare favorably well with angle-resolved photoemission spectroscopy experiments. Our paper confirms the need for well-controlled quality of the interfaces to obtain the needed properties of InAs/Al heterojunctions. A detailed analysis of the effects of spin-orbit coupling on the spin splitting of the electronic states shows a linear scaling in k space, related to the two-dimensional nature of some interface states. The good agreement by QSGW and hybrid functional calculations opens the door towards trustable use of an effective approximation to QSGW for studying very large heterojunctions. Published by the American Physical Society 2024

36 MATERIALS SCIENCE↗
DOE OSTI2019

Microstructural Evolution and Toughness of the Various HAZs in 1300-MPa-Grade Ultrahigh-Strength Structural Steel

The effect of heat input on the microstructure and toughness of simulated subregions was investigated by welding thermal simulations and Charpy impact tests. The results indicate that the microstructures of the simulated coarse and fine grain heat affected zone (CGHAZ and FGHAZ) gradually changed from lath martensite to a mixture of lath martensite/lath bainite and finally to granular bainite with the increase in heat input. The microstructure of the simulated intercritical heat affected zone (ICHAZ) was mainly composed of granular bainite and blocky martensite regardless of heat input. When the heat input increased, the toughness of the simulated CGHAZ and ICHAZ continuously decreased. Nevertheless, the simulated FGHAZ still displayed good toughness (53.16 J) due to its fine structure. The occurrence of martensite-austenite (M-A) constituents was the main reason for the decrease in crack initiation energy of the simulated CGHAZ and ICHAZ at high values of heat input, and the toughness deteriorated as the size of M-A constituents increased. It should be noted that high-misorientation packet and block boundaries can effectively deviate or arrest the propagation of microcracks. When the heat input was in the approximate range of 8.63-14.95 kJ cm{sup −1}, all of the simulated subregions exhibited good toughness.

36 MATERIALS SCIENCE↗
NASA NTRS1994

The Roles of Large- and Small-Scale Structures in Turbulent Free Shear Layers

The occurrence of large-scale coherent structures in turbulent free shear flows (especially the planar mixing layer) has been recognized for some time. Indeed, the observation of such structures in mixing layers did much to promote interest in the study of coherent structures in turbulence. It has been widely assumed that the large-scale structures in these flows are responsible for the entrainment of free-stream fluid and the overall growth of the layer, while the small-scale structures provide mixing and dissipation. A model of scalar mixing based on these ideas was proposed for these flows. However, recent experimental and computational evidence suggests that the dominance of the large-scale structures in turbulent mixing layers is not universal. In addition, there is a substantial variation among experiments in several statistical measures of self-similar mixing layers, for example growth rate and velocity variances. To investigate the importance of large-scale structures, several free shear flows (mixing layers and wakes) have been simulated via direct numerical simulation. The simulations are designed to mimic experimental mixing layers in which the splitter plate boundary layers are turbulent. Different levels of two-dimensional forcing are included resulting in large-scale structures of differing strength and importance. These simulations are used to investigate the role of large-scale coherent structures in free shear layers and the effect of these structures on relevant turbulence statistics and scalar mixing. It is found that the statistics and structures in several experiments involving turbulent mixing layers are in better agreement with simulations that do not exhibit dominant large-scale structures than those in which the common mixing layer structures do dominate. It is also found that the level of forcing can have a profound effect on the qualitative and quantitative features of these shear layer, even when they are nominally self-similar.

Moser, Robert D.↗
NASA NTRS1994

Experimental observations of scale effects on bonded and bolted joints in composite structures

The objective is to observe size (scale) effects in (1) fiber dominated laminates and bolted joints, (2) adhesive (matrix) dominated bonded joints with fiber dominated laminate adherends, and (3) matrix dominated laminates. Selected literature on scale effects is reviewed with comments and test data from one source that is analyzed for predicted and actual scale effects utilizing uniaxial loaded static strength, spectrum fatigue residual strength, and spectrum fatigue lifetime test results. Causes of scale effects are discussed, the results are summarized, and conclusions are made.

Grimes, Glenn C.↗
NASA NTRS1993

Effects of precipitation on the thermodynamic structure of the trade wind boundary layer

A model of the thermodynamic structure of the trade wind boundary layer is formulated to include the parameterization of precipitation in relatively shallow clouds. Although the area-averaged simulated precipitation rates are relatively small (less than 1 mm/day), the inclusion of precipitation has an appreciable effect on the predicted thermodynamic structure. The cloud layer structure simulated with precipitation is warmer, drier, and more stable than that simulated without precipitation. The simulated inversion height is lowered by as much as 60 mbar when precipitation is included.

Albrecht, Bruce A.↗
DOE OSTI2022

Magnetic control over the fundamental structure of atomic wires

When reducing the size of materials towards the nanoscale, magnetic properties can emerge due to structural variations. Here, we show the reverse effect, where the structure of nanomaterials is controlled by magnetic manipulations. Using the break-junction technique, we find that the interatomic distance in platinum atomic wires is shorter or longer by up to ~20%, when a magnetic field is applied parallel or perpendicular to the wires during their formation, respectively. The magnetic field direction also affects the wire length, where longer (shorter) wires are formed under a parallel (perpendicular) field. Our experimental analysis, supported by calculations, indicates that the direction of the applied magnetic field promotes the formation of suspended atomic wires with a specific magnetization orientation associated with typical orbital characteristics, interatomic distance, and stability. A similar effect is found for various metal and metal-oxide atomic wires, demonstrating that magnetic fields can control the atomistic structure of different nanomaterials when applied during their formation stage.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Stable Water Isotopes Reveal Effects of Intermediate Disturbance and Canopy Structure on Forest Water Cycling

Forests play an important role in the climate system and link water fluxes between the land surface and the atmosphere. Here we compare water vapor isotopes in two adjacent forest sites in the northern lower peninsula of Michigan to understand the effects of intermediate disturbance and canopy structure on forest water cycling. One site is dominated by aspen and birch and has a thick, closed canopy. All of the aspen and birch were killed at the second site. As a result, the disturbed site has a more open-canopy structure. From our comparison, we found that both the species of tree and the spacing around trees are important controls on forest water cycling. With more space between trees, air mixes more freely into the canopy, which dries the forest air. Alternatively, air may be poorly mixed within and above thick, closed canopies.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2022

Effect of iron redox ratio on the structures of boroaluminosilicate glasses

Iron oxide is commonly found in natural or industrial glass compositions and can exist as ferrous (Fe 2+ ) or ferric (Fe 3+ ) species, with their ratios depending on glass composition, temperature, pressure and the redox reactions during the glass forming process. The iron redox ratio plays an important role on silicate glass structures and consequently various properties. This work aims to study the effect of iron oxide, and particularly the iron redox ratio, on the structures of borosilicate and boroaluminosilicate glasses using molecular dynamics simulations with newly developed iron potential parameters that are compatible with the borosilicate potentials. The results provide detailed cation coordination states of both iron species and the effect of redox ratio on boron coordination and other structural features. Particularly, competition for charge compensating modifier cations (such as Na + ) among the fourfold-coordinated cations such as B 3+ , Al 3+ , and Fe 3+ is investigated by calculating the cation–cation pair distribution functions and coordination preferential ratios. The results show that the trivalent ferric ions, with a shorter Fe–O bond distance and better defined first coordiation shell with mainly four-fold coordination, act as a glass former whereas the divalent ferrous ions mainly play the role of glass modifier. The ferrous/ferric ratio (Fe 2+ /Fe 3+ ) was found to affect the glass chemistry and hence glass properties by regulating the amount of four-coordinated boron, the fraction of non-briding oxygen and other features. Finally, the results are compared with available experimental data to gain insights of the complex structures and charge compensation schemes of the glass system.

36 MATERIALS SCIENCE↗
DOE OSTI2017

The effect of fuel staging on the structure and instability characteristics of swirl-stabilized flames in a lean premixed multi-nozzle can combustor

Fuel staging is a commonly used strategy in the operation of gas turbine engines. In multinozzle combustor configurations, this is achieved by varying fuel flow rate to different nozzles. The effect of fuel staging on flame structure and self-excited instabilities is investigated in a research can combustor employing five swirl-stabilized, lean-premixed nozzles. At an operating condition where all nozzles are fueled equally and the combustor undergoes a self-excited instability, fuel staging successfully suppresses the instability: both when overall equivalence ratio is increased by staging as well as when overall equivalence ratio is kept constant while staging. Increased fuel staging changes the distribution of time-averaged heat release rate in the regions where adjacent flames interact and reduces the amplitudes of heat release rate fluctuations in those regions. Increased fuel staging also causes a breakup in the monotonic phase behavior that is characteristic of convective disturbances that travel along a flame. In particular, heat release rate fluctuations in the middle flame and flame–flame interaction region are out-of-phase with those in the outer flames, resulting in a cancelation of the global heat release rate oscillations. The Rayleigh integral distribution within the combustor shows that during a self-excited instability, the regions of highest heat release rate fluctuation are in phase-with the combustor pressure fluctuation. In conclusion, when staging fuel is introduced, these regions fluctuate out-of-phase with the pressure fluctuation, further illustrating that fuel staging suppresses instabilities through a phase cancelation mechanism.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2018

A Method For Determining The Radially-Averaged Effective Impact Area For An Aircraft Crash Into A Structure

This report presents a methodology for deriving the equations which can be used for calculating the radially-averaged effective impact area for a theoretical aircraft crash into a structure. Conventionally, a maximum effective impact area has been used in calculating the probability of an aircraft crash into a structure. Whereas the maximum effective impact area is specific to a single direction of flight, the radially-averaged effective impact area takes into consideration the real life random nature of the direction of flight with respect to a structure. Since the radially-averaged effective impact area is less than the maximum effective impact area, the resulting calculated probability of an aircraft crash into a structure is reduced.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Effects of topography on tropical forest structure depend on climate context

Abstract Topography affects abiotic conditions which can influence the structure, function and dynamics of ecological communities. An increasing number of studies have demonstrated biological consequences of fine‐scale topographic heterogeneity but we have a limited understanding of how these effects depend on the climate context. We merged high‐resolution (1 m 2 ) data on topography and canopy height derived from airborne lidar with ground‐based data from 15 forest plots in Puerto Rico distributed along a precipitation gradient spanning c . 800–3,500 mm/year. Ground‐based data included species composition, estimated above‐ground biomass (AGB), and two key functional traits (wood density and leaf mass per area, LMA) that reflect resource‐use strategies and a trade‐off between hydraulic safety and hydraulic efficiency. We used hierarchical Bayesian models to evaluate how the interaction between topography × climate is related to metrics of forest structure (i.e. canopy height and AGB), as well as taxonomic and functional alpha‐ and beta‐diversity. Fine‐scale topography (characterized with the topographic wetness index, TWI) significantly affected forest structure and the strength (and in some cases direction) of these effects varied across the precipitation gradient. In all plots, canopy height increased with topographic wetness but the effect was much stronger in dry compared to wet forest plots. In dry forest plots, topographically wetter microsites also had higher levels of AGB but in wet forest plots, topographically drier microsites had higher AGB. Fine‐scale topography influenced functional composition but had only weak or non‐significant effects on taxonomic and functional alpha‐ and beta‐diversity. For instance, community‐weighted wood density followed a similar pattern to AGB across plots. We also found a marginally significant association between variation of wood density and topographic heterogeneity that depended on climate context. Synthesis . The effects of fine‐scale topographic heterogeneity on tropical forest structure and composition depend on the climate context. Our study demonstrates how a stronger integration of topographic heterogeneity across precipitation gradients could improve estimates of forest structure and biomass, and may provide insight to the ways that topography might mediate species responses to drought and climate change.

Muscarella, Robert↗