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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Influence of strontium on structure, sintering and biodegradation behaviour of CaO-MgO-SrO-SiO2-P2O5-CaF2 glasses

The present study investigates the influence of SrO on structure, apatite forming ability, physico-chemical degradation and sintering behaviour of melt-quenched bioactive glasses with composition: mol.% (36.07 – x) CaO – x SrO - 19.24 MgO – 5.61 P2O5 – 38.49 SiO2 – 0.59 CaF2, where x varies between 0 – 10. The detailed structural analysis of glasses has been made by infra red spectroscopy (FTIR) and magic angle spinning-nuclear magnetic resonance spectroscopy (MAS-NMR). Silicon was predominantly present as Q2 (Si) species while phosphorus was found in orthophosphate type environment in all the investigated glasses. The apatite forming ability of glasses was investigated by immersion of glass powders in simulated body fluid (SBF) for time durations varying between 1 h – 7 days. While increasing Sr2+/Ca2+ ratio in glasses did not affect the structure of glasses significantly, their apatite forming ability was decreased considerably. Further, physico-chemical degradation of glasses has been studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris HCl and citric acid buffer and the possible implications of ion release profile from glasses in different solutions has been discussed. The addition of strontium in glasses led to a 7-fold decrease in chemical degradation of glasses in Tris-HCl. The sintering of glass powders rendered glass-ceramics (GCs) with varying degree of crystallinity and good flexural strength (98-131 MPa) where the mechanical properties depend on the nature and amount of crystalline phases present in GCs.

58 GEOSCIENCES↗
DOE OSTI2025

Inkless, dry printing nanographene via in-Situ Coordinated laser ablation and sintering processes

Printing carbon, such as graphene and other carbon structures, for flexible and printed electronics currently relies on either ink-based printing, laser-induced forward transfer (LIFT), or laser-induced graphitization (LIG) to convert carbon-rich precursor materials, such as polymers, to graphene-like carbon structures. Liquid inks contain toxic solvents, surfactants, and stabilizing additives that degrade electrical conductivity and require high-temperature post-processing. On the other hand, LIG is limited by the substrate. Here, this study introduces an additive manufacturing method for dry-printing carbon nanomaterials, ranging from amorphous carbon to crystalline graphene-like structures, on various substrates. The system utilizes laser ablation of a solid graphite target to create pure carbon nanoparticles in situ and on demand. An inert gas carries the nanoparticles onto the substrate, where they can be deposited either as amorphous structures or laser-sintered in real time to form various graphitic structures. The study of laser processing parameters, specifically fluence and pulse repetition frequency, revealed three unique regimes of nanostructure evolution that influence the morphological and electrical properties of these printed structures. Raman spectroscopy confirmed graphitization with a resistivity slightly higher than that of the bulk graphite target. The conductivity/resistivity could be tuned as a function of sintering laser power. Scanning transmission electron microscopy (STEM) revealed that turbostratic nanographene formed with an interlayer spacing of 0.40 nm. Despite ink-based printing methods, such as screen printing, inkjet printing (IJP), and aerosol jet printing (AJP), this eco-friendly and green manufacturing technique could eliminate toxic chemicals, reduce environmental impact, and enable single-step fabrication of carbon-based devices for applications in wearable sensors, energy storage, flexible electronics, and Internet of Things (IoT) devices.

Additive nanomanufacturing↗
DOE OSTI2010

Coarse-grained computation for particle coagulation and sintering processes by linking Quadrature Method of Moments with Monte-Carlo

The study of particle coagulation and sintering processes is important in a variety of research studies ranging from cell fusion and dust motion to aerosol formation applications. These processes are traditionally simulated using either Monte-Carlo methods or integro-differential equations for particle number density functions. In this paper, we present a computational technique for cases where we believe that accurate closed evolution equations for a finite number of moments of the density function exist in principle, but are not explicitly available. The so-called equation-free computational framework is then employed to numerically obtain the solution of these unavailable closed moment equations by exploiting (through intelligent design of computational experiments) the corresponding fine-scale (here, Monte-Carlo) simulation. We illustrate the use of this method by accelerating the computation of evolving moments of uni- and bivariate particle coagulation and sintering through short simulation bursts of a constant-number Monte-Carlo scheme.

97 MATHEMATICS AND COMPUTING↗
DOE OSTI2019

Reaction-bond composite synthesis of SiC-TiB 2 by spark plasma sintering/field-assisted sintering technology (SPS/FAST)

High-density SiC-TiB 2 composites were fabricated using the displacement reaction spark plasma sintering/field-assisted sintering technology (SPS/FAST) and SiC, B 4 C, TiC, and Si powders. The reaction process was performed in a narrow time frame compared hot pressing. The SiC-TiB 2 composites were sintered with precursor SiC at various pressures to determine the effects of processing with SPS/FAST. The composites completed synthesis during SPS/FAST processing, which occurs more quickly than hot pressing. SEM, STEM, and Raman spectroscopy are used to show the conversion and microstructure. Finally, the composite of 53.6 wt.% SiC and 46.4 wt.% TiB 2 has 99 % theoretical density, hardness of 26.4 GPa, and fracture toughness of 5.12 MPa m 1/2 .

36 MATERIALS SCIENCE↗
DOE OSTI2023

Reactive flash sintering of TiZrN and TiAlN ternary metal nitrides

Here, this study demonstrated the reactive flash sintering (RFS) for two powder mixtures: TiN-ZrN (both conducting) and AlN-TiN (TiN conducting but AlN insulating), targeting ternary metal nitrides (TMN) of Ti 0.5 Zr 0.5 N and Ti 0.5 Al 0.5 N, respectively. A constant volage and pressure (e.g., 8 V DC, ∼15 MPa) at room temperature triggered the flash (current density up to 27 A/mm 2 ) without pre-heating, and the entire RFS process finished in a few minutes. For TiZrN, the flash was instantaneous whereas for TiAlN, there was a long incubation before the flash followed by a quick and dramatic flash. Both conventional ex situ XRD and in situ synchrotron study had been carried out. They showed a uniform Ti 0.57 Zr 0.43 N solution formed in RFS and persisted upon cooling, while (Ti, Al) N solid solution formed at high temperature was not stable and likely went through a very quick phase separation in the cooling process. The final products from RFS had been characterized using SEM/EDS for microstructure. Both TiZrN and TiAlN were dense. Distribution of Ti, Zr, and N was uniform for TiZrN; for TiAlN, Ti and N distribution was uniform, while association of Al with oxygen was observed. TGA-DSC revealed the onset oxidation temperature for TiZrN was comparable to TiN and ZrN, while it was higher by ∼200 °C for TiAlN, likely due to the formation of Al 2 O 3 . In terms of mechanical properties such as hardness or fracture toughness, forming a single-phase solid solution (like TiZrN) does not offer obvious benefits. while large grain size from RFS seemed to be unfavorable. Future optimization of RFS condition and in-depth study by both experiments and simulation are needed to fully understand the composition-processing-structure-property relationships for such TMN from the reactive flash sintering process.

Flash Sintering↗
DOE OSTI2023

Toughening Sm–Co sintered magnets via microstructure modification with additives

We report the mechanical properties of the brittle Smsingle bondCo permanent magnets are of great practical significance. However, studies on the magnets have mostly focused on their magnetic properties. This paper reports the modified microstructure and refined unimodal grain size, enhanced flexural strength, and magnetic properties of Sm 2 (Co,Fe,Cu,Zr) 17 sintered magnets doped with La 2 O 3 , MgO, and CaF 2 fine particulates. The correlations between microstructure, phase composition, and mechanical and magnetic properties were studied. Doping of a small amount (e.g., 0.5–3 wt%) of La 2 O 3 , MgO, or CaF 2 fine particulates could significantly refine the unimodal grain sizes of the Smsingle bondCo magnets via the Zener pinning effect. Moreover, doping significantly improved the flexural strengths σ of the magnets. For example, the σ values of the magnets with 0.5 wt% MgO, 1 wt% La 2 O 3 , and 1 wt% CaF 2 were approximately 65%, 63%, and 42% higher than that of the reference magnet, respectively. Micromechanical simulations revealed that the fine particles of La 2 O 3 could deflect crack growth, while the CaF 2 particles could attract or arrest cracks during the fracture process. The mechanical strengthening effect was mainly due to grain size refinement. The Smsingle bondCo magnets with 0.5–1.5 wt% CaF2 and 0.5 wt% La 2 O 3 exhibited excellent magnetic properties while doping 1–3 wt% La2O3 and 0.5–3 wt% MgO deteriorated magnetic performance. The rational design of CaF 2 - or La 2 O 3 -doped microstructure can be an economical and effective method for producing toughened Sm–Co sintered magnets with high magnetic performance.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Spark Plasma Sintering of W-UO2 Cermets

About 50 vol.% 3 um depleted uranium dioxide (UO2) powder was encapsulated within a tungsten super alloy matrix produced from sub-micron tungsten powders using the Spark Plasma Sintering (SPS) process. An additive of 25 atom-percent (at.%) rhenium was included within the tungsten matrix to improve the ductility and fracture toughness of the ceramic–metallic (cermet) matrix. Cermet fabrication to 97.9% of the theoretical cermet density was achieved by sintering at 1500 degrees C with 40 MPa of applied pressure for 20 min. The results presented are from the first known trials of W–UO2 and nuclear cermet production via SPS.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Sintering and characterization of SrBi{sub 2}Ta{sub 2}O{sub 9} obtained by high-pressure processing at low temperatures

High-pressure processing is a very attractive approach for the production of materials with new and/or improved properties. In this work, pressures in the order of 7.7 GPa and 2.5 GPa were induced in SrBi{sub 2}Ta{sub 2}O{sub 9} samples at different temperatures placed in a specific reaction cell and generated different effects on phase formation. The microstructural evolution during high-pressure processing was investigated by scanning electron microscopy in association with energy dispersion spectroscopy and with the support of an X-ray diffraction analyzer. Frequency response analysis was used to obtain the dielectric curves by electrochemical impedance spectroscopy. A SrBi{sub 2}Ta{sub 2}O{sub 9} single-phase sample, treated at 2.5 GPa and 900 °C, was used to evaluate the electrical properties, obtaining a dielectric response similar to SrBi{sub 2}Ta{sub 2}O{sub 9} samples sintered by conventional processes at temperatures above 1000 °C. In addition, by this method, it was possible to obtain ceramics with uniform microstructure and a relative density of 93%. - Highlights: • The first production of SrBi{sub 2}Ta{sub 2}O{sub 9} using the technique of high-pressure processing. • The ability to produce single-phase SrBi{sub 2}Ta{sub 2}O{sub 9} treated at 2.5 GPa and 900 °C. • The electrical properties are compatible with SBT sintered at high temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Macroporous glass monoliths prepared from powdered niobium phosphate glass by fast sintering

Macroporous monoliths were prepared by very fast sintering (between 3 and 15 min) of niobophosphate glass powders at low temperature (1018 K) using cellulose as a foaming agent. The porous materials were analyzed by thermal analysis, Raman spectroscopy, scanning electron microscopy and powder X-ray diffraction, and further investigated using X-ray microtomography, a non-destructive technique capable of reconstructing three-dimensional models of samples and providing structural measurements. The progression of the porosity of the monoliths depends on the sintering time (3 to 15 min) and the amount (up to 50% in mass) of cellulose used. The macroporous glass monoliths may find application in integrated chemical systems and in filtering processes.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Nanostructured cobalt powders synthesised by polyol process and consolidated by Spark Plasma Sintering: Microstructure and mechanical properties

Bulk nanostructured cobalt was processed using a bottom-up strategy. Nanostructured particle agglomerates of about 50 and 240 nm in diameter were synthesised using a polyol route and subsequently consolidated by Spark Plasma Sintering (SPS). The microstructure of the starting powders and of the processed bulk samples was studied and characterised by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns of the as-prepared powders showed predominantly a face centred cubic (fcc) crystalline phase, whereas both fcc and hexagonal close packed (hcp) phases were found within the consolidated samples. A sample with the highest relative mass density (94.5%) was obtained from the small powder particles. TEM observations revealed a lamellar substructure with a high density of nanotwins and stacking faults in every grain in the sample with the highest density. Brillouin light scattering (BLS) and quasistatic compression tests were used to investigate the mechanical properties of the consolidated samples. The two techniques yielded Young modulus values of 168 GPa and 130 GPa, respectively, in the sample with the highest density. This sample also exhibited a yield stress higher than 1 GPa after the compression test, which is mainly attributed to the lamellar-like structure occurring in almost every grain of the polycrystalline aggregate. - Highlights: Black-Right-Pointing-Pointer Cobalt nanoparticles produced by the polyol process present mainly the fcc metastable phase. Black-Right-Pointing-Pointer Bulk nanostructured cobalt is obtained from the nano-particles by Spark Plasma Sintering consolidation. Black-Right-Pointing-Pointer Nanotwins and stacking faults are present in every grain of the more dense sample. Black-Right-Pointing-Pointer Yield strength and plastic domain may be varied depending on the nanoparticle size and the porosity of the consolidated material.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Development of an in-situ multi-component reinforced Al-based metal matrix composite by direct metal laser sintering technique — Optimization of process parameters

In the present investigation, an in-situ multi-component reinforced aluminum based metal matrix composite was fabricated by the combination of self-propagating high-temperature synthesis and direct metal laser sintering process. The different mixtures of Al, TiO{sub 2} and B{sub 4}C powders were used to initiate and maintain the self-propagating high-temperature synthesis by laser during the sintering process. It was found from the X-ray diffraction analysis and scanning electron microscopy that the reinforcements like Al{sub 2}O{sub 3}, TiC, and TiB{sub 2} were formed in the composite. The scanning electron microscopy revealed the distribution of the reinforcement phases in the composite and phase identities. The variable parameters such as powder layer thickness, laser power, scanning speed, hatching distance and composition of the powder mixture were optimized for higher density, lower porosity and higher microhardness using Taguchi method. Experimental investigation shows that the density of the specimen mainly depends upon the hatching distance, composition and layer thickness. On the other hand, hatching distance, layer thickness and laser power are the significant parameters which influence the porosity. The composition, laser power and layer thickness are the key influencing parameters for microhardness. - Highlights: • The reinforcements such as Al{sub 2}O{sub 3}, TiC, and TiB{sub 2} were produced in Al-MMC through SHS. • The density is mainly influenced by the material composition and hatching distance. • Hatching distance is the major influencing parameter on porosity. • The material composition is the significant parameter to enhance the microhardness. • The SEM micrographs reveal the distribution of TiC, TiB{sub 2} and Al{sub 2}O{sub 3} in the composite.

36 MATERIALS SCIENCE↗
DOE OSTI2014

High energy X-ray diffraction study of a dental ceramics–titanium functional gradient material prepared by field assisted sintering technique

A functional gradient material with eleven layers composed of a dental ceramics and titanium was successfully consolidated using field assisted sintering technique in a two-step sintering process. High energy X-ray diffraction studies on the gradient were performed at High Energy Material Science beamline at Desy in Hamburg. Phase composition, crystal unit edges and lattice mismatch along the gradient were determined applying Rietveld refinement procedure. Phase analysis revealed that the main crystalline phase present in the gradient is α-Ti. Crystallinity increases stepwisely along the gradient with a decreasing increment between every next layer, following rather the weight fraction of titanium. The crystal unit edge a of titanium remains approximately constant with a value of 2.9686(1) Å, while c is reduced with increasing amount of titanium. In the layer with pure titanium the crystal unit edge c is constant with a value of 4.7174(2) Å. The lattice mismatch leading to an internal stress was calculated over the whole gradient. It was found that the maximal internal stress in titanium embedded in the studied gradient is significantly smaller than its yield strength, which implies that the structure of titanium along the whole gradient is mechanically stable. - Highlights: • High energy XRD studies of dental ceramics–Ti gradient material consolidated by FAST. • Phase composition, crystallinity and lattice parameters are determined. • Crystallinity increases stepwisely along the gradient following weight fraction of Ti. • Lattice mismatch leading to internal stress is calculated over the whole gradient. • Internal stress in α-Ti embedded in the gradient is smaller than its yield strength.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Isothermal and cyclic oxidation behaviours of MoSi2 with additions of B at 1250 °C prepared by spark plasma sintering

Highlights: • A Mo-Si-B alloy is obtained when fine Mo-Si-B powder is sintered. • SPS Mo-Si-B alloy consists of fine MoSi{sub 2}, Mo{sub 2}B{sub 5}, MoB and SiO{sub 2} phases. • Increasing B content reduces incubation stage of oxide layer but increases mass gain. • SPS sample made from finer alloy powder has better oxidation resistance. • Spilling of SiO{sub 2} in SPS sample acts as a “Mechanical locking” on oxide layer. - Abstract: Mo-Si-B alloys were obtained by spark plasma sintering (SPS) using Mo-57Si-10B and Mo-52Si-15B alloy powders, and the effects of the B content and powder size on the isothermal and cyclic oxidation behaviours of the Mo-Si-B alloys at 1250 °C were investigated. A SiO{sub 2} phase was introduced during the SPS process and the Mo-Si-B alloys consisted of a fine MoSi{sub 2}/Mo{sub 2}B{sub 5}/MoB/SiO{sub 2} microstructure. Under isothermal and cyclic oxidation conditions, the kinetic curves of the SPS Mo-Si-B alloys exhibited parabolic time dependence on the weight gain. The increase in the nominal B caused a decrease in the incubation stage of the formation of continuously protective borosilicate layer but increased the mass gain due to the higher fluidity of the borosilicate layer. The SiO{sub 2} phase was found to supply the borosilicate layer with a “Mechanical locking” mechanism through the spilling of the SiO{sub 2} phase in the SPS samples, especially under the cyclic oxidation condition.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Low-temperature sintering and compatibility with silver electrode of Ba{sub 4}MgTi{sub 11}O{sub 27} microwave dielectric ceramic

Ba{sub 4}MgTi{sub 11}O{sub 27} microwave dielectric ceramic was investigated using X-ray diffraction, scanning electron microscopy and dielectric measurement. The pure Ba{sub 4}MgTi{sub 11}O{sub 27} ceramic shows a high sintering temperature ({approx}1275 {sup o}C) and good microwave dielectric properties as Q x f of 19,630 GHz, {epsilon}{sub r} of 36.1, {tau}{sub f} of 14.6 ppm/{sup o}C. It was found that the addition of BaCu(B{sub 2}O{sub 5}) (BCB) can effectively lower the sintering temperature from 1275 to 925 {sup o}C, and does not induce much degradation of the microwave dielectric properties. The BCB-doped Ba{sub 4}MgTi{sub 11}O{sub 27} ceramics can be compatible with Ag electrode, which makes it a promising ceramic for LTCC technology application.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Graphene addition to MgB{sub 2} superconductor obtained by ex-situ spark plasma sintering technique

Highlights: • Graphene-added dense MgB{sub 2} was prepared by ex-situ spark plasma sintering. • There is a limited interaction between graphene and MgB{sub 2}. • Addition of graphene (G) shows a small enhancement of J{sub c} and μ{sub 0}H{sub irr}. • G is one of the least effective C-containing additions. - Abstract: Graphene nanopowder (G) with average thickness particle size of about 6–8 nm was added to MgB{sub 2} commercial powder. Starting composition was (MgB{sub 2}){sub (1−x)}(G){sub x}, x = 0.0125, 0.025, 0.05. Processing was performed by Spark Plasma Sintering (SPS) technique. All added samples have high density (above 95%). The critical temperature (T{sub c}) and the lattice parameter a (c-axis lattice parameter is constant) show a small variation suggesting that carbon substitution for boron is low. TEM observations show the presence of un-reacted graphene plates supporting the T{sub c} and structural results. It also indicates that G-addition does not modify the MgB{sub 2} microstructure. Despite this, there is an optimum doped sample (MgB{sub 2}){sub 0.9875}(G){sub 0.0125} for which the critical current density at temperatures below 25 K is slightly higher at high magnetic fields than for the pristine sample. The addition of G is found as one of the least effective C-source additions enhancing J{sub c}. We discuss results as being strongly related to variation of the residual stress.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Multicycle flash sintering of cubic Y 2 O 3 -stabilized ZrO 2 : An in situ energy dispersive synchrotron x-ray diffraction study with high temporal resolution

The current induced unit cell volume changes, (111) Bragg peak full width at half maximum (FWHM) and its integrated intensity in 8 % Y 2 O 3 stabilized ZrO 2 (8 %YSZ) solid state electrolyte was monitored during a triple-flash sintering experiment by in situ energy dispersive x-ray diffraction using a polychromatic synchrotron probe (max, photon energy 200 keV) with 2 second temporal resolution. The first spontaneous singularity in the unit cell volume (+0.54 %) was observed at 899 °C under 15 V/mm applied field intensity, which was associated with 13 mA/mm 2 current draw and an increase in density to 97 %. Following anelastic relaxation of the unit cell volume under open circuit conditions, the same applied field was applied twice in a row which resulted in additional induced singularities at 925 °C (+0.48 %) and 944 °C (+0.42 %). A floating baseline, which was above the thermal expansion baseline, was observed from 833 to 969 °C and was attributed to Joule heating. In conclusion, the singularity at 899 °C is associated with a sharp change in (111) FWHM and a 34 % decrease in integrated peak area that was attributed to changes in the distribution of oxygen vacancies and the changes in their concentration as induced by the applied field in the spontaneous transient stage of flash sintering.

36 MATERIALS SCIENCE↗
DOE OSTI2018

In situ X-ray characterization of uranium dioxide during flash sintering

The in situ response of stoichiometric and non-stoichiometric uranium dioxide during flash sintering is examined using high energy X-ray diffraction. Our results show that the onset of flash is driven by an increase in temperature and controlled by the applied field with no evidence of an accumulation of defects. The incubation time, that is the time after the application of the field before the flash occurs, is found to be material specific with hyper-stoichiometric samples requiring lower fields to flash. For low current/voltage fields we quantify very little change in the atomic and microstructure of the different uranium dioxide samples post-flash. Microstructural changes are identified for high fields and currents, where joule heating and sample temperatures are high, resulting in the complete transformation of the U 4 O 9 phase. Our results highlight the usefulness of high energy X-ray characterization in understanding the subtle structural changes that occur during the flash sintering process.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Revealing the Structural Evolution and Phase Transformation of O3-Type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 Cathode Material on Sintering and Cycling Processes

O-type layered oxide cathode materials can be easily synthesized for a full sodium stoichiometry with high specific capacity, but they all suffer from a capacity fade on cycling. The sintering process control and optimization are critical to ensure a high quality and consistency of the prepared cathode materials with stable structure. Herein, in situ high-energy X-ray diffraction (HEXRD) was first employed to investigate the phase evolution of the oxides during the sintering process of O3-type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 . The in situ HEXRD and both operando Bragg coherent diffraction (BCXD) and coherent multicrystal diffraction (CMCD) were utilized to investigate the phase transformation of the cathode materials during the sodiation/desodiation process. A composite structure comprised of O-type and P-type oxides was formed after the initial electrochemical activation of the cathode material, resulting in good structural and electrochemical stability. This finding implies that strain engineering can be a new design philosophy for the development of next generation high-performance sodium ion cathodes.

25 ENERGY STORAGE↗