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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 OSTI2018

Microstructure of Friction Stir Welded AlSi9Mg Cast with 5083 and 2017A Wrought Aluminum Alloys

Wrought aluminum alloys 5083 and 2017A were each joined with cast aluminum alloy AlSi9Mg through friction stir welding in butt weld configurations. For each material system, the wrought and cast alloy positions, i.e., the advancing side or the retreating side, were exchanged between welding trials. The produced weldments were free from cracks and discontinuities. For each alloy configuration, a well-defined nugget comprised of alternating bands of the welded alloys characterized the microstructure. The degree of mixing, however, strongly depended on which wrought alloy was present and on its position during processing. In all cases, the cast AlSi9Mg alloy dominated the weld center regardless of its position during welding. Electron backscattered diffraction analysis showed that the grain size in both alloys (bands) constituting the nugget was similar and that the majority of grain boundaries exhibited a high angle character (20°-60°). Regardless of the alloy, however, all grains were elongated along the direction of the material plastic flow during welding. A numerical simulation of the joining process visualized the material flow patterns and temperature distribution and helped to rationalize the microstructural observations. The hardness profiles across the weld reflected the microstructure formed during welding and correlated well with the temperature changes predicted by the numerical model. Tensile specimens consistently fractured in the cast alloy near the weld nugget.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Dry reforming of methane over CeO 2 -supported Pt-Co catalysts with enhanced activity

Dry reforming of methane provides opportunities of using CH 4 and CO 2 to produce syngas. The PtCo/CeO 2 bimetallic catalyst shows higher activity and H 2 /CO ratio than the corresponding monometallic catalysts, mainly attributed to the synergistic effect of Pt-Co. Structural feature of the PtCo/CeO 2 catalyst was revealed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of adsorbed CO and in situ techniques like X-ray diffraction (XRD), X-ray adsorption fine structure (XAFS) and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS). Pt-Co alloy and separated Co particles co-existed in the bimetallic catalyst, whereas the former was determined as the dominant active structure with a Pt-Co-mixed-surface termination. During reaction, Pt and Co in the alloy structure nearly maintained their metallic state with slight oxygen decoration, yielding oxygen-metal site-pairs (O*-*). Combined kinetic investigations and DFT calculations reveal that the O*-modified catalytic surface of PtCo/CeO 2 promotes CH bond activation with higher entropy contribution (less constraints) to compensate its higher activation barrier. Thermogravimetric analysis (TGA), transmission electron microscope (TEM) and Raman spectroscopy show that the PtCo/CeO 2 catalyst is resistant to coke formation as effectively as Pt/CeO 2 and can be easily regenerated by a mild CO 2 treatment.

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

RLIP76-dependent suppression of PI3K/AKT/Bcl-2 pathway by miR-101 induces apoptosis in prostate cancer

MicroRNA-101 (miR-101) participates in carcinogenesis and tumor progression in various cancers. However, its biological functions in prostate cancer are still unclear. Here, we demonstrate that miR-101 represents a critical role in regulating cell apoptosis in prostate cancer cells. We first demonstrated that miR-101 treatment promoted apoptosis in DU145 and PC3 cells by using flow cytometric analysis and transmission electron microscopy (TEM). To verify the mechanisms, we identified a novel miR-101 target, Ral binding protein 1 (RLIP76). We found miR-101 transfection significantly suppresses RLIP76 expression, which can transactivate phosphorylation of PI3K-Akt signaling, and resulted in an amplification of Bcl2-induced apoptosis. Furthermore, we demonstrated that RLIP76 overexpression could reverse the anti-tumor effects of miR-101 in DU145 and PC3 cells by using flow cytometry assay and MTT assay. Taken together, our results revealed that the effect of miR-101 on prostate cancer cell apoptosis was due to RLIP76 regulation of the PI3K/Akt/Bcl-2 signaling pathway. - Highlights: • miR-101 inhibited prostate cancer cell proliferation and enhanced apoptosis. • miR-101 directly targeted and regulated RLIP76 expression. • miR-101 suppressed PI3K/Akt/Bcl-2 signaling pathway by targeting RLIP76.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Comparison of three-dimensional printing and vacuum freeze-dried techniques for fabricating composite scaffolds

In this study, the performances of different preparation methods of the scaffolds were analyzed for chondrocyte tissue engineering. Silk fibroin/collagen (SF/C) was fabricated using a vacuum freeze-dried technique and by 3D printing. The porosity, water absorption expansion rates, mechanical properties, and pore sizes of the resulting materials were evaluated. The proliferation and metabolism of the cells was detected at different time points using an MTT assay. Cell morphologies and distributions were observed by histological analysis and scanning electron microscopy (SEM). The porosity, water absorption expansion rate, and Young’s modulus of the material obtained via 3D printing were significantly higher than those obtained by the freeze-dried method, while the pore size did not differ significantly between the two methods. MTT assay results showed that the metabolism of cells seeded on the 3D printed scaffolds was more viable than the metabolism on the freeze-dried material. H&E staining of the scaffolds revealed that the number of cells in the 3D printed scaffold was higher in comparison to a similar measurement on the freeze-dried material. Consequently, stem cells grew well inside the 3D printed scaffolds, as measured by SEM, while the internal structure of the freeze-dried scaffold was disordered. Compared with the freeze-dried technique, the 3D printed scaffold exhibited better overall performance and was more suitable for cartilage tissue engineering. - Highlights: • Silk fibroin/collagen was fabricated using 3D printing. • Physical characterization and Cell compatibility were compared. • 3D printed scaffold exhibited better overall performance.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

In vitro large scale production of megakaryocytes to functional platelets from human hematopoietic stem cells

Highlights: • Human HSCs were isolated from donor, showed positive to CD34 and CD133 and negative to CD90 and CD73. • These HSCs were induced in novel PI-LC and PII-LC to MKs and platelets differentiation. • The PII-LC (contains andrographolide) showed high MKs production as evidence from flow cytometry and CFU-MK. • The DNA ploidy also showed up to 32 N polyploidy in PII-LC induced MKs compared to PI-LC. • Further, western blotting and qRT-PCR showed high expression of MKs specific genes in PII-LC induced MKs. Megakaryocytopoiesis results in the formation of platelets, which are essential for hemostasis. Decreased production or increased destruction of platelets can cause thrombocytopenia, in which platelet transfusion is the mode of treatment. The present study is aimed in generation of megakaryocytes (MKs) and platelet from human hematopoietic stem cells (HSCs). The purity of HSCs was assessed through Flow cytometry and immunocytochemistry (ICC) studies. These pure HSCs were induced with thrombopoietin (TPO), similarly with Andrographis paniculata extract (APE) for 21 days to generate MKs. The APE is mainly composed of andrographolide which stimulates TPO from the liver, and this binds to CD110 present on the surface of HSCs and triggers the proliferation of HSCs and initiate higher MKs population subsequently, a large number of platelets. The results of the present study showed increased proliferation of HSCs grown in the presence of APE and revealed a high population of CD41a and CD42b positive MKs as enumerated by Flow cytometry compared with TPO induced MKs. These results also concurred with qRT-PCR and western blot analysis. The scanning electron microscopy (SEM) revealed the morphology of differentiated MKs and platelets were similar to human blood platelets. The differentiated MKs in APE exhibited polyploidy up to 32 N while TPO induced MKs showed polyploidy of 8 N, these results corroborated with colony forming unit assay. On thrombin stimulation, high expression of P-selectin (CD62p) and fibrinogen binding were detected in APE induced platelets. Autologous transplantation of platelets generated from APE may be a useful option in thrombocytopenia condition.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Characterization of a sustainable sulfur polymer concrete using activated fillers

Sulfur polymer concrete (SPC) is a thermoplastic composite concrete consisting of chemically modified sulfur polymer and aggregates. This study focused on the characterization of a new SPC that has been developed as a sustainable construction material. It is made from industrial by-product sulfur that is modified with activated fillers of fly ash, petroleum refinery residual oil, and sand. Unlike conventional sulfur polymer cements made using dicyclopentadiene as a chemical modifier, the use of inexpensive industrial by-products enables the new SPC to cost-effectively produce sustainable, low-carbon, thermoplastic binder that can compete with conventional hydraulic cement concretes. A series of characterization analyses was conducted including thermal analysis, X-ray diffraction, and spatially-resolved Xray absorption spectroscopy to confirm the polymerization of sulfur induced from the presence of the oil. In addition, mechanical testing, internal pore structure analysis, and scanning electron microscope studies evaluate the performance of this new SPC as a sustainable construction material with a reduced environmental impact.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

The influence of substrate moisture preparation on bond strength of concrete overlays and the microstructure of the OTZ

The influence of substrate moisture preparation on the direct shear bond strength of composite substrate-overlay specimens was evaluated. The substrate surface was exposed to four different moisture conditions prior to overlay application. A quantitative analysis of backscattered electron images of the microstructure of the overlay transition zone was carried out to quantify its properties along the interface and help analyse the results of the shear bond testing. The results show that pre-wetting the substrate surface prior to application of the overlay provides no added benefit towards increasing the bond strength and may in some cases reduce bond strength significantly. The microstructural investigations confirmed that pre-saturated substrates increase the w/c ratio and the porosity in the overlay transition zone (OTZ), which was found to have a thickness of about 100 μm. The OTZ in overlays cast on dry substrate surfaces had lower porosity and an increased amount of anhydrous cement.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Interaction between dissolution and precipitation during olivine carbonation: Implications for CO 2 mineralization

Large-scale carbonation of olivine is considered a promising approach for in situ mineral carbonation, offering a permanent and stable method for CO 2 storage. A critical aspect of this process is understanding how dissolution and precipitation interact, as this could drive fracturing and enhance further reactions. In this study, we conducted carbonation experiments on olivine using CO 2 -saturated aqueous solutions of NaHCO 3 and NaCl. Two experimental setups were used: one representing an open geochemical system and the other a closed system, corresponding to reaction-limited and flow-limited scenarios, respectively. Further, post-reaction textural analysis using scanning electron microscopy (SEM) revealed surface coatings of reaction products in the closed system, while etch pits and etch channels were prevalent in the open system. Although no direct evidence of reaction-driven fracturing was observed, etch pits and etch channels may serve as initiation points for subcritical crack formation and growth, potentially maintaining permeability and exposing new unreacted surfaces. Using linear elastic fracture mechanics (LEFM) model, we estimate that microcracks could propagate under a pressure of 0.1 GPa if reaction products accumulate within the etch pits. Our findings offer new insights into the mechanisms governing olivine carbonation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Theoretical kinetics predictions for NH 2 + HO 2

Recent modeling studies of NH 3 oxidation, which are motivated by the prospective role of ammonia as a zero-carbon fuel, have indicated significant discrepancies between existing literature mechanisms. In this study high level theoretical kinetics predictions have been obtained for the reaction of NH 2 with HO 2 , which has previously been highlighted as an important reaction with high sensitivity and high uncertainty. The potential energy surface is explored with coupled cluster calculations including large basis sets and high-level corrections to yield high accuracy (~0.2 kcal/mol) estimates of the stationary point energies. Variational transition state theory is used to predict the microcanonical rate constants, which are then incorporated in master equation treatments of the temperature and pressure dependent kinetics. For the radical-radical channels, the microcanonical rates are obtained from variable reaction coordinate transition state theory implementing directly evaluated multireference electronic energies. The analysis yields predictions for the total rate constant as well as the branching to the NH 3 + O 2 , H 2 NO + OH, and HNO + H 2 O channels. Rate constants are also reported for the H 2 NO + OH reaction as they arise naturally from the analysis. The rate constant and branching fraction determined in this work for the NH 2 + HO 2 reaction deviate significantly from values used in most previous modeling studies. The fact that the main product channel is chain terminating, rather than propagating, has strong implications for modeling NH 3 ignition and oxidation, in particular at intermediate temperatures and elevated pressure.

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

Reverse martensitic transformation on the corrosion behavior of a 2304 lean duplex stainless steel

This study investigates the influence of the reverse martensitic transformation on the corrosion behavior of 2304 lean duplex stainless steel (LDSS) at low temperatures (400–600°C). The steel underwent cold rolling, followed by isochronal annealing for 0.5 h. Phase transformations and microstructures were analyzed using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Corrosion resistance was evaluated using a syringe cell with cyclic potentiodynamic polarization in 0.6 M NaCl solution and double-loop electrochemical potentiokinetic reactivation in 0.5 M H 2 SO 4 + 0.001 M KSCN solution. A bimodal breakdown potential behavior, associated with either pitting or transpassivity, was observed in the as-received (AR) and samples annealed at 400°C. Pitting in the AR sample was associated with Al–Mg–Si–Ca–O inclusions, while pitting on the samples annealed at 400°C was linked to local reduced passive film resistance. Severe cold rolling enhanced the pitting resistance of 2304 LDSS. Selective electrochemical etching revealed preferential corrosion at phase interfaces and within the austenite phase. Additionally, annealing at 500°C to 600°C led to a marked decrease in pitting resistance and increased sensitization. Electron backscatter diffraction analysis of the corroded pits in the annealed specimens indicated that pits tend to nucleate and grow in α'-martensite/austenite regions. Furthermore, the nanostructure formed during low-temperature reversion, characterized by dislocation-cell martensite with high dislocation density and stacking faults, may adversely affect corrosion resistance due to heterogeneities associated with alloying element redistribution.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Distinguishing interfacial double layer and oxide-based capacitance on gold and pre-oxidized Fe-Cr in 1-ethyl-3-methylimidazolium methanesulfonate room temperature ionic liquid aqueous mixture

The frequency-dependent impedance of a metal/oxide/room temperature ionic liquid (RTIL) interface was separated into oxide layer (C ox ) and double layer (C dl ) capacitances using electrochemical impedance spectroscopy (EIS). A pre-formed oxide of known initial thickness on Fe-20 at.% Cr was investigated in 1-ethyl-3-methylimidazolium methanesulfonate ([Emim][MeSO 3 ]) RTIL + aqueous mixtures. The oxide thickness was calculated from C ox using the complex capacitance representation and the power-law model. The result was additionally verified by cross-sectional analysis using transmission electron microscopy. The C dl calculated from the constant-phase element (CPE) was distinguishable from C ox for Fe-20Cr, which enables monitoring of the interfaces of structural metals with oxide layers in RTILs containing water.

Constant-phase element↗
DOE OSTI2025

A microstructural signature of the coesite-quartz transformation: New insights from high-pressure experiments and EBSD

Ultra-high pressure (UHP) metamorphism is difficult to identify in continental crust as few petrological barometers are suitable for dominantly felsic lithologies. In such cases, burial to extreme depths is commonly identified through the preservation of coesite, a high-pressure polymorph of SiO 2 that typically forms at depths exceeding ∼ 100 km (i.e., > 2 GPa pressure). Unfortunately, coesite readily transforms to quartz upon exhumation, meaning that UHP terranes may often be overlooked. While some studies have suggested that quartz may inherit an orientation signature indicative of former coesite, both the specific nature of this signature and the conditions favouring its development remain uncertain. Here, to address this problem, we combine electron backscatter diffraction analysis of natural and experimental samples to explore microstructural evolution across the coesite-quartz phase transformation. We demonstrate that neighbouring domains of quartz commonly feature an 84 ± 4° rotation of [c] axes around the pole of a common {m} plane. This orientation relationship is a product of epitaxy, whereby the {$11\bar{2}2$} Japan twin plane in quartz nucleates on the (010) plane in coesite. In supercell simulations, the nucleation of Japan twins can be explained by the energetically favourable alignment of quartz tetrahedra on parental coesite tetrahedra. Through experiments, we demonstrate that this signature emerges over a broad range of conditions, regardless of the availability of nucleation sites (e.g., grain boundaries) or the density of crystal lattice defects (e.g., dislocations). Overall, our work provides a quantitative and unambiguous tool for identifying UHP terranes from quartz in isolation.

Coesite↗
DOE OSTI2019

Real-time visualization of impact damage in monolithic silicon carbide and fibrous silicon carbide ceramic composite

Impact resistance from foreign debris is a critical requirement for brittle ceramic and ceramic composite materials intended for use in the hot-section of gas turbine engines. A design to mitigate against such impact failures necessitates a detailed understanding of the driving failure mechanisms. The present study introduces a unique time-resolved experimental method which advances the latter effort. Specifically, a pulsed synchrotron X-ray source, in phase contrast imaging (PCI) configuration, is used as a medium, to visually characterize the evolution of damage inside the target materials during impact. As a proof of concept, two types of ceramic materials were tested: monolithic silicon carbide and fibrous silicon carbide composite. Impact was performed using a light-gas gun and 1.5 mm diameter spheres of partially stabilized zirconia (PSZ) and silicon nitride (Si 3 N 4 ). The retrieved dynamic X-ray image sequences provided clear outlines of the damage features. In the case of the monolithic ceramic, the impact by a PSZ projectile initially produced a cone crack and complete failure resulted by extension of a median crack. By contrast, the fibrous composite deformed readily prior to cone crack formation. Nearly identical damage features were observed in the monolith for the Si 3 N 4 projectile, with the exception of the added vertical tensile crack. For this same projectile, the fibrous ceramic showed very limited surface deformation and enhanced cone cracking and kinking of laminates along the crack path. The latter response is attributed to the change in projectile properties. Some of the target materials were recovered, and post-mortem analysis via scanning electron microscopy (SEM) showed correlation with observed X-ray damage profiles. Furthermore, simple Hertzian contact was used to estimate damage for the elastic portion of impact. This approach was found to yield a reasonable match with experimental results for the surface displacement near the contact interface.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural representation of additively manufactured 316L austenitic stainless steel

Three 316L stainless steel materials are studied and reported upon; wrought, as-built additively manufactured (AM), and heat-treated AM material. The AM material was produced from the laser engineered net shaping (LENS) process. Macroscopic uniaxial compression stress-strain curves were obtained for all three materials. The curves were similar for the wrought and heat-treated AM materials but the as-built AM material demonstrated approximately 1.7 times greater flow stress at any given level of strain than the other two materials. Electron-backscatter diffraction analysis of the materials also showed that the microstructures of the three materials differed; with complex grain morphology for the as-built AM material. The mean grain size of each of the three materials also differed. Furthermore, the initial dislocation density was also measured with neutron diffraction and line-profile analysis for both wrought and as-built AM materials with the density in the AM material approximately 2.5 times greater.

36 MATERIALS SCIENCE↗
DOE OSTI2018

In-situ visualizing atomic structural evolution during crystallization in ternary Zr Cu Al bulk metallic glasses

A well-designed experimental method has been presented to in-situ visualize the amorphous-to-crystalline phase transformation of two glass formers at the atomic length scale in the supercooled liquid region using a high voltage electron microscopy (HVEM). Analysis of the HVEM high-resolution images, supported by the in situ synchrotron diffraction, further confirms previous observations of distinctively different crystallization pathways in the two Zr-Cu-Al alloys. Moreover, the HVEM results illustrate that isolated distributed nanocrystals with mutual orientation easily grew up from the Zr 56 Cu 36 Al 8 , an average glass former, which follows a classical crystallization pathway; while density population poorly ordered atomic clusters with large misorientation suspended the growth in the Zr 46 Cu 46 Al 8 , a good glass former, which might follow an unusual crystallization pathway. In addition, in-situ synchrotron diffraction measurements confirm that the Zr 56 Cu 36 Al 8 alloy finally crystallized into an extended structure, in contrast, the final crystalline product of Zr 46 Cu 46 Al 8 alloy possesses a damped structure. Our study provides a detailed microscopic understanding of the crystallization behaviors in the supercooled liquids, showing that the density population nucleation site with large misorientation and the confined final crystalline structure contribute to the stability of Zr-Cu-Al supercooled liquids.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Phase degradation in B x Ga 1–x N films grown at low temperature by metalorganic vapor phase epitaxy

Using metalorganic vapor phase epitaxy, a comprehensive study of B x Ga 1-x N growth on GaN and AlN templates is described. BGaN growth at high-temperature and high-pressure results in rough surfaces and poor boron incorporation efficiency, while growth at low-temperature and low-pressure (750–900 °C and 20 Torr) using nitrogen carrier gas results in improved surface morphology and boron incorporation up to ~7.4% as determined by nuclear reaction analysis. However, further structural analysis by transmission electron microscopy and x-ray pole figures points to severe degradation of the high boron composition films, into a twinned cubic structure with a high density of stacking faults and little or no room temperature photoluminescence emission. Films with <1% triethylboron (TEB) flow show more intense, narrower x-ray diffraction peaks, near-band-edge photoluminescence emission at ~362 nm, and primarily wurtzite-phase structure in the x-ray pole figures. For films with >1% TEB flow, the crystal structure becomes dominated by the cubic phase. As a result, only when the TEB flow is zero (pure GaN), does the cubic phase entirely disappear from the x-ray pole figure, suggesting that under these growth conditions even very low boron compositions lead to mixed crystalline phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Analysis of the $\tilde{A}$ - $\tilde{X}$ bands of the Ethynyl Radical near 1.48 μm and Re-evaluation of ~X State Energies

Here, we report the observation and analysis of spectra in part of the near-infrared spectrum of C 2 H, originating in rotational levels in the ground and lowest two excited bending vibrational levels of the ground $\tilde{X}$ 2 Σ+ state. In the analysis, we have combined present and previously reported high resolution spectroscopic data for the lower levels involved in the transitions to determine significantly improved molecular constants to describe the fine and hyperfine split rotational levels of the radical in the zero point, v 2 = 1 and the 2 Σ+ component of v 2 = 2. Two of the upper state vibronic levels involved had not been observed previously. The data and analysis indicate the electronic wavefunction character changes with bending vibrational excitation in the ground state and provide avenues for future measurements of reactivity of the radical as a function of vibrational excitation.

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

Large elastic strains and ductile necking of W nanowires embedded in TiNi matrix

The deformation behaviors of W nanowires embedded in a TiNi matrix were investigated by means of in-situ synchrotron high energy X-ray diffraction (HEXRD) and in-situ transmission electron microscopy (TEM) analysis during tensile deformation. The HEXRD measurement indicated that the W nanowires exhibited an average lattice strain of about 1.50 %, whereas the TEM examination revealed a local elastic strain of about 4.59 % in areas adjacent to the TiNi matrix where stress-induced martensitic transformation occurred. This strain corresponds to a stress of ~15 GPa for the W nanowires. In addition, in areas adjacent to the TiNi matrix where plastic deformation and cracking were generated, the W nanowire showed significant ductile necking with ~80 % reduction in cross-section area. In conclusion, the ductile necking of W nanowire is attributed to the lack of protection from the stress-induced martensitic transformation of the TiNi matrix.

36 MATERIALS SCIENCE↗