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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 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Pressure-Induced Multidimensional Assembly and Sintering of CuInS 2 Nanoparticles into Lamellar Nanosheets with Band Gap Narrowing

Two-dimensional (2D) nanomaterials have fascinating structural, electrical, and optical properties, especially strong excitonic effects due to decreased dielectric screening. However, constructing 2D ultrathin nanomaterials, with the exception of layered materials, remains a challenge. In this work, we successfully realize oriented attachment on guiding one-dimensional chalcopyrite CuInS 2 nanocrystal (NC) formation and 2D assembly into lamellar nanosheets by applying pressure-driven sintering of zero-dimensional CuInS2 nanoparticles (NPs). We discuss the atomic-level mechanism of such phenomena and illustrate a pressure-driven processing diagram that reveals the sintering process of NPs coordinated by pressure and structural transformation. Optical measurements exhibit that the band gap has a narrowing by 0.21 eV compared with the initial 2.03 eV upon decompression to ambient conditions. Our findings represent a significant step forward in gaining an in-depth understanding of the pressure-driven morphology engineering of nanomaterials and provide a promising strategy to prepare 2D NCs, thereby greatly increasing the choice of materials for various applications.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ceria Incorporation in Sinter-Resistant Platinum-Based Catalysts

Platinum group metals (PGM) are widely used for exhaust emission abatement. Sintering during the high-temperature emission control conditions decreases noble metal utilization efficiency. Efficient use of scarce noble metals requires sinter-resistant catalysts. Here we extend an approach to synthesize catalysts consisting of platinum nanoparticles encapsulated in a mixture of cerium and aluminum oxides (Pt@Al 2 O 3 -CeO 2 ). We tested the activity of this catalyst toward carbon monoxide, propene, and propane oxidation chosen as model oxidation reactions for emission control catalysts. Pt@Al 2 O 3 -CeO 2 catalysts demonstrated similar activity and stability upon aging as the comparison system without ceria, Pt@Al 2 O 3 , while maintaining small Pt nanoparticles and ceria crystallites. Additionally, we studied the influence of various thermal treatments on CO oxidation activity and determined that a steam treatment can activate low temperature CO oxidation activity of Pt@Al 2 O 3 -CeO 2 . STEM-EDS analysis revealed that thermal treatments led to the co-location of Pt and CeO 2 and temperature programmed-reduction analysis revealed that the steam treatment specifically enhanced CO oxidation activity through surface reduction of the CeO 2 . As a result, we demonstrate the versatility of this encapsulation approach to generate mixed metal-oxide supports with improved metal-support interactions without hindering nanoparticle stability.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2021

Machine learning-based microstructure prediction during laser sintering of alumina

Abstract Predicting material’s microstructure under new processing conditions is essential in advanced manufacturing and materials science. This is because the material’s microstructure hugely influences the material’s properties. We demonstrate an elegant machine learning algorithm that faithfully predicts the microstructure under new conditions, without the need of knowing the governing laws. We name this algorithm, RCWGAN-GP, which is regression-based conditional generative adversarial networks with Wasserstein loss function and gradient penalty. This algorithm was trained with experimental SEM micrographs from laser-sintered alumina under various laser powers. The RCWGAN-GP realistically regenerates the SEM micrographs under the trained laser powers. Impressively, it also faithfully predicts the alumina’s microstructure under unexplored laser powers. The predicted microstructure features, including the morphology of the sintered particles and the pores, match the experimental SEM micrographs very well. We further quantitatively examined the prediction accuracy of the RCWGAN-GP. We trained the algorithm with computer-created micrograph datasets of secondary-phase growth governed by the well-known Johnson–Mehl–Avrami (JMA) equation. The RCWGAN-GP accurately regenerates the micrographs at the trained time series, in terms of the grains’ shapes, sizes, and spatial distributions. More importantly, the predicted secondary phase fraction accurately follows the JMA curve.

08 HYDROGEN↗
DOE OSTI2021

All solid thick oxide cathodes based on low temperature sintering for high energy solid batteries

Solid-state batteries (SSBs) could significantly improve the safety and energy density over conventional liquid cells. One key enabling technology is the use of solid electrolytes. NASICON-type Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) is a very attractive solid-state electrolyte for the cathode side due to its high oxidation potential and high ionic conductivity. The usage, however, is limited by its large interfacial resistance against most of the cathode materials as well as the thermodynamic instability during high temperature sintering needed to achieve high mass density. Here we construct thin, percolative, and mixed conductive interphases through in situ low-melting-point liquid sintering. These mixed conductive interphases drastically improve the kinetics, leading to high-loading solid LATP/LiCoO 2 cathodes achieving capacity loading of up to ~6 mA h cm –2 . The technique is also applicable to Ni-rich cathode materials, achieving up to ~10 mAh cm –2 , which can lead to more than 400 W h kg –1 cells in SSBs. Furthermore, our composite cathodes show a ten-times and three-times area capacity improvement over the state-of-the-art cathodes using oxide and sulfide SSEs, respectively.

25 ENERGY STORAGE↗
DOE OSTI2012

Studies of sintered MRE-Fe-B magnets by DyF 3 addition or diffusion treatment (MRE = Nd + Y + Dy)

Sintered MRE 2 (Fe, Co) 14 B magnets by DyF 3 blending or diffusion treatment were investigated. “Base-line” magnets with a thickness of 1.5 mm were coated (painted) with DyF 3 powder and heated to promote Dy diffusion at 800–900 °C, i.e., “Diffusion” magnets. For comparison, the magnet alloy powder for making Base-line magnets was blended with 3–5 wt.% DyF 3 powder and then made into sintered magnets, i.e., “Blended” magnets. The coercivity and (BH) max of Base-line magnets were 9.7 kOe and 32.7 MGOe, respectively, while the coercivity of Diffusion magnets was increased to 15 kOe and the (BH) max was nearly unchanged at 31.4 MGOe. Blended magnets with 5 wt% DyF 3 had a coercivity of 17.8 kOe, but the (BH) max was reduced to 25.4 MGOe, due to a considerable reduction of remanence. The total Dy concentration in the MRE 2 (Fe, Co) 14 B Diffusion magnets with a β value of -0.5%/°C was 5.3 wt%, while typical commercial Nd-based Nd 2 Fe 14 B magnets require at least 7.5 wt% Dy to achieve the same β. Therefore, the MRE 2 (Fe, Co) 14 B Diffusion magnets exhibited better temperature stability.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Investigation of chemical composition and crystal structure in sintered Ce{sub 15}Nd{sub 15}Fe{sub bal}B{sub 1} magnet

The substitution of cerium, a more abundant rare-earth element, for sintered Nd-Fe-B magnets has drawn intense interest. In the present work, nominal composition of Ce{sub 15}Nd{sub 15}Fe{sub bal}B{sub 1} (wt. %), with cerium constitutes increased to 50% of the total rare-earth content, was used. And Ce-free Nd{sub 30}Fe{sub bal}B{sub 1} (wt. %) was prepared by the same preparation process as comparison. The microstructure of the sintered magnets has been investigated by means of X-ray diffraction and transmission electron microscope. The results show that there are three kinds of RE-rich phases in the same magnet, i.e., fcc-(Ce,Nd)O{sub x} (a=0.547nm), hcp-(Ce,Nd){sub 2}O{sub 3} (a=0.386nm, c=0.604nm) and bcc-(Ce,Nd){sub 2}O{sub 3} (a=1.113nm). Ors of (140)(Ce,Nd){sub 2}Fe{sub 14}B// (1-21)bcc-(Ce,Nd){sub 2}O{sub 3}(∼3°), [001](Ce,Nd){sub 2}Fe{sub 14}B// [-214]bcc-(Ce,Nd){sub 2}O{sub 3}; (01-1)(Ce,Nd){sub 2}Fe{sub 14}B// (101)fcc- (Ce,Nd)O{sub x}(∼2°), [101](Ce,Nd){sub 2}Fe14B// [12-1]fcc-(Ce,Nd)O{sub x} were found through selected area electron diffraction (SAED) analysis. According to the analysis, it can be concluded that cerium has partly substituted for neodymium by occupying the corresponding atom sites in the Ce{sub 15}Nd{sub 15}Fe{sub bal}B{sub 1} magnet, without changing the crystal configuration.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Electron energy loss spectroscopy study of ceria sinters and nanoparticles irradiated with swift heavy ions

The electronic energy loss spectra of ceria (CeO 2 ) irradiated with swift heavy ions (27 MeV Xe and 946 MeV Au) in the electronic slowing down regime were measured for bulk sintered samples and nanoparticles by using a double Cs-corrected transmission electron microscope. The low-loss region as well as the core-loss region, including the oxygen K-edge and cerium M 4, 5 white lines, were recorded. No strong lattice disorder was found in the low-loss peaks for both types of samples showing the same bulk oxygen plasmon loss peak at about 15 eV. However, there is a clear evidence of cerium reduction to the trivalent oxidation state after irradiation for the sintered samples as shown by the K-edge shape of oxygen and decrease of the Ce M 4 /M 5 intensity ratio. A similar change of the M 4 /M 5 intensity ratio was observed for the irradiated nanoparticles with respect to the virgin sample owing to the high energy input inside the nanograin. The effect of radiation damage on electron energy loss spectroscopy data is analyzed for both types of samples and irradiation conditions.

Crystallographic defects↗
DOE OSTI2019

Reshaping and sintering of 3D fcc metal nanoclusters: Stochastic atomistic modeling with realistic surface diffusion kinetics

Far-from-equilibrium evolution of metallic nanocluster shapes is highly sensitive to the atomistic-level details of surface diffusion for diverse local surface configurations. A stochastic model was developed incorporating realistic values for the multiple diffusion barriers (contrasting previous unrealistic generic prescriptions) based upon insights from homoepitaxial film growth. Kinetic Monte Carlo simulation then elucidates the conversion of Ag nanocubes to Wulff polyhedra mediated by nucleation of new {100} facets, the pinch-off of sufficiently elongated Ag nanorods, and key aspects of sintering for orientationally aligned Ag and Au nanoclusters. In conclusion, the time scale for sintering of Au nanoclusters observed in high-resolution transmission electron microscopy studies was also recovered.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Alumina-based filters made via binder jet 3D printing of alumina powder, colloidal silica infiltration, and sintering

Alumina-based, porous filter media was made via a binder jet 3D printing process consisting of an alumina powder printing step with subsequent heating, colloidal silica infiltration, drying, and sintering to consolidate particles yet retain a net open porous microstructure. The composites made were alumina-silica or alumina-mullite, where the silica sintering aid was used to densify and join the alumina particles. The resulting composite structures had open porosities in the 25–31 vol% range as measured by Archimedes density. Pressure drops were measured across the filter media at constant flow rates to compare disc shapes and complex, 3D printed filters based on the N95 design requirements. Complex, 3D-printed alumina composites were produced with acceptable pressure drops for N95 implementation.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Predicting the Onset of Flash Sintering

Analyzing the temperature trajectory during flash sintering, this study demonstrates that Joule heating alone is responsible for thermal runaway that is the most likely cause for rapid densification. The calculated onset temperature T on is in good agreement with the literature data. As predicted by the analysis the T on data follow a 1/ T on ~log(field) linear dependence, which affords an expeditious means to estimate the activation energy of resistivity/conductivity of the sintered ceramics.

Dong, Yanhao↗
DOE OSTI2015

Development and Durability Testing of a Low‐Temperature Sintering Bi–Si–Zn Oxide Glass Composite Material (GCM) 129 I Waste Form

The capture and safe storage of radiological iodine ( 129 I) from nuclear fuel reprocessing is of concern due to its long half‐life and potential mobility in the environment. The development of durable waste forms in which to store captured iodine requires materials that are both compatible with the iodine capture phases and durable to repository environments. To that end, Sandia is developing a low‐temperature sintering Bi–Si–Zn oxide glass composite material (GCM) waste form and herein presents results of durability testing. Furthermore, durability studies were extended to both the occluded iodine capture material Ag‐Zeolite (Mordenite, MOR) as well as the GCM, synthesized with compositional variations including: amount of Ag flake added, AgI‐MOR particle size in the GCM, and mass loading of I within the AgI‐MOR. Product consistency test (PCT‐B), chemical durability (MCC‐1) tests, and single‐pass flow‐through (SPFT) tests, were performed on both the individual components of the GCM and the completed GCMs. Durability tests indicate low GCM dissolution rates (<10 −3 g/m 2 ·d) across wide variable ranges including: pH, AgI‐MOR loading, I loading, and AgI‐MOR particle size. Results indicate that the Bi–Si–Zn oxide glass matrix sharply limits the release of iodine from the otherwise relatively fast degrading AgI‐MOR getter material. Furthermore, the formation of an amorphous AgI phase during sintering of the GCM results in the limitation of iodine release during waste form degradation. Durability of GCM and release rates approximate those of established nuclear waste glasses, or analogues such as basaltic glass. This suggests that the Bi–Si–Zn GCM is a viable candidate as a repository iodine waste form.

Mowry, Curtis D.↗
DOE OSTI2015

Onset Criterion for Flash Sintering

When the sample temperature is warm enough so that the Joule heating takes over the environment's radiation heating as the dominant heating means, thermal runaway follows and flash sintering is triggered. This condition accurately predicts the reported onset temperature T on of all the constant‐field ( E ) experiments on flash sintering, performed under a constant heating rate. The predicted linear ln( E 2 / T on 4 ) versus T on −1 relation determines the activation energy and the relative ranking of the electrical conductivity of the tested materials.

Dong, Yanhao↗
DOE OSTI2017

Cold sintering process of Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 solid electrolyte

Abstract The recently developed technique of cold sintering process (CSP) enables densification of ceramics at low temperatures, i.e., <300°C. CSP employs a transient aqueous solvent to enable liquid phase‐assisted densification through mediating the dissolution‐precipitation process under a uniaxial applied pressure. Using CSP in this study, 80% dense Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) electrolytes were obtained at 120°C in 20 minutes. After a 5 minute belt furnace treatment at 650°C, 50°C above the crystallization onset, Li‐ion conductivity was 5.4 × 10 −5 S/cm at 25°C. Another route to high ionic conductivities ~10 −4 S/cm at 25°C is through a composite LAGP ‐ (PVDF‐HFP) co‐sintered system that was soaked in a liquid electrolyte. After soaking 95, 90, 80, 70, and 60 vol% LAGP in 1 M LiPF 6 EC‐DMC (50:50 vol%) at 25°C, Li‐ion conductivities were 1.0 × 10 −4 S/cm at 25°C with 5 to 10 wt% liquid electrolyte. This paper focuses on the microstructural development and impedance contributions within solid electrolytes processed by (i) Crystallization of bulk glasses, (ii) CSP of ceramics, and (iii) CSP of ceramic‐polymer composites. CSP may offer a new route to enable multilayer battery technology by avoiding the detrimental effects of high temperature heat treatments.

Berbano, Seth S.↗
DOE OSTI2020

Direct selective laser sintering of hexagonal barium titanate ceramics

Abstract A direct selective laser sintering (SLS) process was combined with a laser preheating procedure to decrease the temperature gradient and thermal stress, which was demonstrated as a promising approach for additive manufacturing of BaTiO 3 ceramics. The phase compositions in BaTiO 3 ceramics fabricated by SLS were investigated by X‐ray and neutron diffractions. The surface morphologies and cross‐section microstructures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). A dense hexagonal h‐BaTiO 3 layer was formed on the surface and extended to a depth of 500 μm, with a relative density higher than 97% and absence of pores or microcracks. SLS resulted in the formation of the high‐temperature phase, h‐BaTiO 3 , which was retained at room temperature possibly due to the high cooling rate. The grain boundaries of SLSed h‐BaTiO 3 ceramics consist of a Ti‐rich secondary phase. Compared with that of the pressureless sintered t‐BaTiO 3 ceramics, the Vickers hardness of SLSed h‐BaTiO 3 is 70% higher.

Zhang, Xiang↗
DOE OSTI2023

Phase evolution during conventional and reactive flash sintering of (Mg,Ni,Co,Cu,Zn)O via in situ X-ray diffraction

Reactive flash sintering (RFS) enables the simultaneous synthesis and sintering of ceramics and has been shown to affect the reaction pathway of different materials. Herein, in situ synchrotron X-ray diffraction (XRD) is used to investigate the (Mg,Ni,Co,Cu,Zn)O entropy-stabilized oxide formation during: (i) conventional heating and (ii) RFS under current rate-controlled mode. The same reaction pathway is verified in both instances: the starting rock-salt (RS), spinel (Co 3 O 4 ), tenorite (CuO), and wurtzite (ZnO) phases transform into a single RS phase with a (1 1 1) to (2 0 0) intensity ratio of 0.67, consistent with a random distribution of the cations into the structure. Pt lattice peak shift from the XRD patterns is used as standard to monitor the sample surface temperature, revealing a strong endothermic reaction during the RS single-phase formation (Pt peaks shift toward higher angles while increasing sample temperature/current density). Furthermore, in RFS, the single-phase RS structure is formed in just 60 s at a furnace temperature of 600°C and a current rate of 220 mA mm -2 /min. Therefore, RFS greatly accelerates the synthesis of (Mg,Ni,Co,Cu,Zn)O, however, it does not play a role in the reaction pathway for this material formation.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Using in situ UO 2 bicrystal sintering to understand grain boundary dislocation nucleation kinetics and creep

Capillary evolution at bicrystal UO 2 grain boundaries is characterized using in situ transmission electron microscopy. The discontinuous nature of the densification process, both particle rotation and axial strain, along with the large activation stress for densification support a hypothesis that grain boundary strain in UO 2 follows nucleation rate limited kinetics at low to intermediate stresses, that is, less than ≈ 10 8 PA. Further, the temperature dependence of the average activation stress for sintering agrees well with analysis of bulk sintering data and creep data reported within the literature when analyzed in the context of a grain boundary dislocation nucleation rate limited kinetic model.

36 MATERIALS SCIENCE↗
DOE OSTI2017

SrZrO 3 Formation at the Interlayer/Electrolyte Interface during (La 1-x Sr x ) 1-δ Co 1-y Fe y O 3 Cathode Sintering

This work probes the formation of SrZrO 3 at the SDC/YSZ interface (Sm doped ceria, SDC; Y stabilized zirconia, YSZ) during (La 1-x Sr x ) 1-δ Co1 -y Fe y O 3 (LSCF) cathode sintering. SEM/EDS and grazing incidence X-ray diffraction results of annealed LSCF and YSZ samples reveal that even without physical contact between LSCF and YSZ, SrZrO 3 was formed on the surface of YSZ, preferentially at the grain boundaries. It was suspected that the SrZrO 3 formation is due to the Sr-containing gas species diffused through the pores of the SDC layer and reacted with the YSZ electrolyte. Computational thermodynamics was adopted to predict the gas species formed in air during sintering by using the La-Sr-Co-Fe-O-H thermodynamic database. Sr(OH) 2 is identified as the dominant Sr-containing gas species under the experimental conditions. In addition, it was found that A-site deficiency in LSCF could effectively suppress the SrZrO 3 formation while a dense and pore-free SDC interlayer is required to totally block the SrZrO 3 formation. As a result, cell performance was significantly improved for a cell with a dense SDC interlayer fabricated by pulsed laser deposition, due to elimination of SrZrO 3 formation and therefore reduced interfacial resistance.

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

Melt-Pool Temperature and Size Measurement During Direct Laser Sintering

Additive manufacturing has demonstrated the ability to fabricate complex geometries and components not possible with conventional casting and machining. In many cases, industry has demonstrated the ability to fabricate complex geometries with improved efficiency and performance. However, qualification and certification of processes is challenging, leaving companies to focus on certification of material though design allowable based approaches. This significantly reduces the business case for additive manufacturing. Therefore, real time monitoring of the melt pool can be used to detect the development of flaws, such as porosity or un-sintered powder and aid in the certification process. Characteristics of the melt pool in the Direct Laser Sintering (DLS) process is also of great interest to modelers who are developing simulation models needed to improve and perfect the DLS process. Such models could provide a means to rapidly develop the optimum processing parameters for new alloy powders and optimize processing parameters for specific part geometries. Stratonics’ ThermaViz system will be integrated with the Renishaw DLS system in order to demonstrate its ability to measure melt pool size, shape and temperature. These results will be compared with data from an existing IR camera to determine the best approach for the determination of these critical parameters.

42 ENGINEERING↗