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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Porous metals from sintering of nanoparticles

A method including encapsulating or capping metallic nanoparticles by a dendrimer or a polymer with binding sites for metal particless or metal ions dispersed in a fluid; modifying the fluid to disrupt the interaction of the dendrimer or polymer with the particles; and subsequently or concomitantly sintering or partially consolidating the zero valent metal. A method including introducing a first metal salt and a second metal salt into a dendrimer or a polymer with binding sites for metals or metal ions; reducing a metal ion of the first metal salt to a zero valent first metal and a metal ion of the second metal salt to a zero valend second metal; disrupting an interaction between the dendrimer or the polymer and the first metal and the second metal; and sintering or partially consolidating the first metal and the second metal.

36 MATERIALS SCIENCE↗
DOE OSTI2023

High-Throughput Electric-Field-Assisted Sintering and Characterization Techniques for Materials Discovery

Despite improvements in computing and modeling capabilities, the performance of new materials, particularly those which deviate greatly in composition from well-studied materials (e.g., high-entropy alloys), can be difficult to simulate given the lack of available experimental property data. While some modeling techniques may attempt to predict the properties of these exotic materials, most are forced to make extrapolations from more traditional materials. To fulfill the need for accelerated material synthesis and property measurement, a high-throughput methodology has been developed. Utilizing electric-field-assisted sintering (EFAS), also known as spark plasma sintering (SPS), equipped with custom tooling, samples of differing alloy compositions can be produced simultaneously as a single alloy array. Several arrays have been produced with compositions spanning the Co-Cr-Fe-Mn-Ni alloy family, including many high-entropy alloys, while the novel array geometry has enabled the samples to be polished and characterized in parallel, using X-ray diffraction, scanning-electron microscopy, and laser-based thermal diffusivity measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Sinter-Resistant Platinum Catalyst Supported by Metal-Organic Framework

Installed on the zirconia nodes of a metal-organic framework (MOF) NU-1000 via targeted vapor-phase synthesis. The catalytic Pt clusters, site-isolated by organic linkers, are shown to exhibit high catalytic activity for ethylene hydrogenation while exhibiting resistance to sintering up to 200 degrees C. In situ IR spectroscopy reveals the presence of both single atoms and few-atom clusters that depend upon synthesis conditions. Operando X-ray absorption spectroscopy and Xray pair distribution analyses reveal unique changes in chemical bonding environment and cluster size stability while on stream. Density functional theory calculations elucidate a favorable reaction pathway for ethylene hydrogenation with the novel catalyst. Lastly, these results provide evidence that atomic layer deposition (ALD) in MOFs is a versatile approach to the rational synthesis of size-selected clusters, including noble metals, on a high surface area support.

36 MATERIALS SCIENCE↗
DOE OSTI2023

The onset of selective laser flash sintering in undoped and doped lanthanum chromite

Previous studies have shown that selective laser flash sintering (SLFS) can be initiated in dielectrics that exhibit ionic or electronic conduction at high temperature. These materials required high laser powers to reach the temperatures where electrical conduction is sufficient to initiate SLFS. In this study, SLFS in lanthanum chromite (LC), an intrinsic electronic conductor with high conductivity, and lanthanum strontium chromite (LSC), which is doped to further increase electronic conductivity, were investigated with a focus on understanding the initiation mechanisms. Results show that the initiation of SLFS in LC and LSC occurs when electronic charge carriers are activated and flow to the electrode where the current is measured. A combination of carriers produced at the electrode, temperature-activated intrinsic charge carriers, and extrinsic charge carriers present in LSC due to doping are responsible for the facile initiation of SLFS.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Manufacturing Li 2 TiO 3 -based tritium breeder materials by volume-controlled spark plasma sintering with an optimized microstructure

Multifunctional ceramic breeder materials are highly desirable for the deuterium-tritium fusion to achieve high efficiency in breeding tritium through neutron irradiation of lithium-containing blankets. Li 2 TiO 3 displays unique attributes as a potential ceramic breeder material. An optimized microstructure with three-dimensional interconnected pore structure is required for rapid transport of the tritium for effective fuel cycle, which however enviably results in the degradation of the thermal-mechanical properties of the breeding materials. In this work, nanocrystalline porous Li 2 TiO 3 ceramic pellets with controlled porosities of 14% and 20% are manufactured by volume-controlled spark plasma sintering. An optimized 3D interconnected pore structure is achieved consisting of both micro-sized pores and nano-sized pores embedded in nanocrystalline matrix, which could be beneficial to facilitate easy removal of bred T and He. Further, the 3D interconnected porous structure is well maintained upon isothermal annealing of the SPS-fabricated pellets at relevant operation temperature of the solid breeding materials. Single-phasic porous pellets also display enhanced thermal-mechanical properties, superior to current state-of-the-art materials which establish their potential as a promising tritium breeder material for nuclear fusion applications.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

High-throughput synthesis of high-entropy alloys via parallelized electric field assisted sintering

Materials discovery and design is an expensive and time-consuming process, though necessary to advance many engineering fields. In this work, a novel tooling design is utilized in conjunction with electric field assisted sintering (EFAS) to effectively create a new high-throughput synthesis technique: parallelized EFAS. Through this technique, a wide range of material compositions and geometries can be synthesized in parallel as isolated samples or as part of contiguous arrays. Multiple tooling designs are explored to examine both the flexibility and limitations of the technique. A series of increasing complex alloys is produced simultaneously using in situ alloying, beginning with pure Ni and adding equimolar constituents up to the septenary high-entropy alloy AlCoCrCuFeMnNi. Microstructural characterization reveals each sample is effectively fully dense and chemically homogenous while exhibiting phases in agreement with CALPHAD predictions. Scalability of parallelized EFAS is then experimentally demonstrated and the implications for materials discovery and automation are discussed.

36 - MATERIALS SCIENCE↗
DOE OSTI2022

The influence of the processing parameters on the reactive flash sintering of ZrO 2 -CeO 2

Reactive flash sintering (RFS) is a method that was recently developed to produce dense single-phase bulk ceramic parts through solid-state reactions in a single-step that only takes a few minutes. The influence of the RFS parameters on the phase purity of a simple mixed oxide, (Zr 0.8 ,Ce 0.2 )O 2 , was investigated. Parameters such as furnace temperature, furnace atmosphere, electric current density, and alternating current (AC) or direct current (DC) were examined. It was found that (Zr 0.8 ,Ce 0.2 )O 2 pellets with high densities, above 90% of its theoretical density, can be produced by RFS in a few minutes when RFS occurs under oxidizing atmospheres, AC fields with current densities of 100 mA·mm –2 , and at a furnace temperature of 1200°C. Reducing conditions such as Ar-H 2 atmosphere and DC fields, low furnace temperatures, and low current densities resulted in phase impurities and poor reactions between the ZrO 2 and the CeO 2 powders. These results show that RFS is a useful method to produce mixed oxides, but it is very sensitive to the processing parameters. This is the first time that the influence of most of the RFS processing parameters has been studied systematically. Thus, the present work aims to provide guidelines on selecting the right processing parameters when exploring RFS.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Hybrid Additive Manufacturing and Electric Field-Assisted Sintering of High-temperature Heat Exchangers via Sacrificial Channel Molds

A hybrid manufacturing approach, integrating additive manufacturing (AM) with powder methodology via electric field-assisted sintering (EFAS), was developed for the fabrication of high-temperature compact heat exchangers (CHX) from refractory metals. The methodology employed additively manufactured sacrificial channel molds (SCMs) as shapeholders for CHX channels, which were embedded in metal powders using EFAS. Following embedding, the SCMs were chemically dissolved to form the internal channel network. SCMs were fabricated using both digital light processing (DLP) and direct ink writing (DIW) from chemically reactive, calcium-based ceramic feedstocks with varying ratios of Al2O3 reinforcement. The microstructure, phase composition, and dissolution behavior of both as-printed and embedded SCMs were investigated. The shrinkage behavior of the SCMs embedded in refractory metals, as well as the interfacial characteristics between the SCMs and metal matrix, were studied. The results showed that the SCMs containing sufficient chemical reactive ceramics dissolved effectively before and after embedding. The as-printed SCMs retained the phase composition of their feedstocks, but the embedded SCMs containing calcium-based ceramics and Al2O3 exhibited the formation of calcium aluminates due to high temperature exposure during embedding. Most SCMs exhibited a cellular Al2O3 network filled with Ca-rich ceramics. Shrinkage after embedding was strongly dependent on SCM density, with lower density SCMs exhibiting greater shrinkage. A thin SCM-affected zone was observed at the metal matrix surface, characterized by increased porosity compared to the bulk matrix. This effect was attributed to infiltration of the SCM materials into powder particle boundaries under pressure, followed by their removal during dissolution. This study demonstrates the feasibility of manufacturing CHXs from hard-to-process refractory metals for use in harsh environments.

36 - MATERIALS SCIENCE↗
DOE OSTI2021

Fast and Scalable Synthesis of LiNi 0.5 Mn 1.5 O 4 Cathode by Sol–Gel-Assisted Microwave Sintering

High-voltage spinel LiNi 0.5 Mn 1.5 O 4 (LNMO) is a promising cathode material for high-energy-density and high-power-density lithium-ion batteries (LIBs). The high cost of the currently available LIBs needs to be addressed urgently for wide application in the transport sector (electric vehicles, buses) and large-scale energy storage systems (ESS). Of significance, herein, novel fast and scalable microwave-assisted synthesis of LNMO is reported, which leads to a production cost cut. X-ray diffraction (XRD) analysis confirms the formation of the desired phase with high crystallinity. Field emission scanning (FE-SEM) and transmission electron microscopy (TEM) analyses indicate that the synthesized phase is of nanometric size (50–150 nm) due to an extremely short sintering time (20 min). The material synthesized at 750 °C shows a higher initial discharge capacity (130 mA h g -1 ) than that synthesized at 650 °C (115 mA h g -1 ). The materials heat treated at higher temperatures show better electrochemical performance in terms of initial capacity, rate capability, and improved cycling. The improved electrochemical performance of LNMO at 750 °C is attributed to the formation of a stable crystal structure, low charge transfer resistance at the electrode/electrolyte interface, high electrical conductivity due to the presence of a disorder structure, and improved ionic diffusivity.

25 ENERGY STORAGE↗
DOE OSTI2018

Dwell Time Influence on Spark Plasma-Sintered MgB{sub 2}

Samples of MgB{sub 2} with relative density above 95% were obtained by spark plasma sintering (SPS) at 1150 °C for a heating time of 100 °C/min and a maximum pressure of 95 MPa. Dwell time was of 1, 4, 7, 10, and 20 min. Samples show that dwell time has a low influence on superconducting characteristics. However, small differences were observed and they are discussed from the viewpoint of density, structural, microstructural, critical current density, irreversibility field, and pinning type. The dominant contribution for all investigated samples is given by point and δT{sub c} pinning.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ex Situ Spark Plasma Sintering of Short Powder-in-Tube MgB{sub 2} Tapes with Open and Closed Ends

Short powder-in-tube tapes of MgB{sub 2} in the Fe sheath were fabricated by ex situ route from a commercial powder containing some free Mg and MgO impurity phases. The final heat treatment was performed by spark plasma sintering (SPS). Tapes were with open (OT) or closed (CT) endings. Closed endings were made by folding and pressing. The MgB{sub 2} core of the OT sample has shown a higher low-field critical current density, a higher maximum pinning force, a slightly higher disorder, smaller average MgB{sub 2} crystallite size, a weak contact between Fe and MgB{sub 2} core, and more macro-flux jumps. The upper and irreversibility fields were similar for OT and CT samples. In the center of the MgB{sub 2} cores, the detected impurity phase is MgO, while at the interface with Fe, MgB{sub 4} also occurs. Impurity phases found at interface, MgO and MgB{sub 4}, are present in the center of the bulk SPSed samples. Reactions and pinning-force-related parameters are discussed with respect to Mg behavior influenced by condition of endings. It is inferred that the presence of free Mg in the raw MgB{sub 2} powder has an important contribution to observed differences, and its removal or control is recommended.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Progress in Critical Current Density (J{sub c}) in Sintered MgB{sub 2} Bulks

The present paper focuses on methods of further improving the flux pinning and critical current density of disk-shaped MgB{sub 2} bulk superconductors by adding excess Mg metal in combination with an optimum silver content and optimized processing conditions. Bulk MgB{sub 2} samples were produced by in situ solid-state reaction in Ar gas ambient using high purity commercial powders of Mg metal and 1.5 wt% carbon-coated amorphous B powders mixed in a fixed ratio of Mg/B = 1.1:2. Further, 4 wt% silver was added to improve flux pinning as well as mechanical performance of the bulk MgB{sub 2} material. The magnetization measurements confirmed a sharp superconducting transition with T{sub c,onset} at around 37 K, which is only by 1 K lower than in bulk MgB{sub 2} material produced without carbon-coated amorphous boron. The critical current density (J{sub c}) values significantly improved in the MgB{sub 2} material with 4 wt% of silver and 1.5 wt% of carbon-coated amorphous boron, sintered at 775 {sup ∘}C for 3 h. At 20 K, this sample showed J{sub c} at around 500 and 350 kA/cm{sup 2} in the self-field and 1 T, respectively, which makes it suitable for several industrial applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Structural, Morphological, Electrical and Magnetic Properties of Yttrium-Substituted Co-Zn Ferrites Synthesized by Double Sintering Technique

A series of rare earth Y{sup 3+} ion substituted Co-Zn ferrites Co{sub 0.5}Zn{sub 0.5}Y{sub x}Fe{sub 2-x}O{sub 4} (x = 0.00 to 0.08 in step of 0.02) have been synthesized by conventional double sintering technique from the oxide powders of Co, Zn, Fe, and Y. The XRD, FESEM, EDS, DC resistivity, dielectric measurements, VSM, and Curie temperature (T{sub c}) analysis have been used to investigate structural, morphological, electrical, and magnetic properties. Single phase of cubic spinel structure has been confirmed up to x < 0.06, and a small amount of secondary phase YFeO{sub 3} has also been detected for x > 0.06. The lattice parameter initially decreases than increases with yttrium concentrations. The FESEM image shows that the grains and grain boundaries are distinct and uniformly distributed and the purity has also been endorsed from the EDS spectra. The average grain size decreases at x = 0.02 and then increases with Y substitution. The long range mobility of charge carriers and presence of localized charge carriers with retreat from the Debye-like behavior in the compositions have been explored using electric modulus and impedance. The magnetic strength diminishes owing to existence of magnetic dilution in the A-B interactions subsequent to the T{sub c} declines with the x contents. The value of saturation magnetization decreases with increasing Y{sup 3+} contents that indicates that the domain wall motion become tougher due to substitution of foreign ions Y{sup 3+} that possess larger ionic radius. Therefore, the Y{sup 3+} substituted Co{sub 0.5}Zn{sub 0.5}Y{sub x}Fe{sub 2-x}O{sub 4} (x = 0.00 to 0.08 in step of 0.02) ferrites with high resistivity and low losses has implications to be used in high frequency and power supply devices applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Large-scale dissolution of sintered Mo disks

Non-uranium production of 99 Mo via neutron capture or by photonuclear reaction using an electron accelerator is receiving considerable attention. For commercial production of 99 Mo, post-irradiation processes must incorporate a robust design for easy scale-up. Once developed, large-scale chemical processes must be optimized for hot-cell operations and potential automation. In this work, we present experimental results on the large-scale dissolution of sintered Mo disks using three 50% hydrogen peroxides from different suppliers. Dissolution rates obtained for 600-g Mo batches and potential reasons for different dissolution behaviors is discussed.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

Current-Assisted Diffusion Bonding of Extruded Ti-22Al-25Nb Alloy by Spark Plasma Sintering: Interfacial Microstructure and Mechanical Properties

Spark plasma sintering (SPS) technology was used to current-assisted bond extruded Ti-22Al-25Nb alloy. The effects of bonding temperature (920-980 °C) and bonding time (10-30 min) on the microstructure evolution and shear strength of this alloy were investigated systematically. The temperature distribution in the specimen during the current-assisted bonding process was also analyzed by numerical simulation. It is noted that the highest temperature was obtained at the bonding interface. As the bonding temperature and bonding time increased, the voids in the interface shrank increasingly until they vanished. A complete metallurgical bonding interface could be produced at 960 °C/20 min/10 MPa, exhibiting the highest shear strength of 269.3 MPa. In addition, the shear strength of the bonded specimen depended on its interfacial microstructure. With increased bonding temperature, the fracture mode transformed from the intergranular fracture at the bonding interface to the cleavage fracture in the substrate.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructures and Mechanical Behavior of Ti{sub 3}SiC{sub 2}/Al{sub 2}O{sub 3}-Ni Composites Synthesized by Pulse Discharge Sintering

High-purity Ti{sub 3}SiC{sub 2} and Ti{sub 3}SiC{sub 2}/Al{sub 2}O{sub 3}-Ni composites with different Al{sub 2}O{sub 3}-Ni contents were fabricated using pulse discharge sintering (PDS) of a mechanical alloyed powder mixture. The synthesis process of monolithic Ti{sub 3}SiC{sub 2} was studied through displacement temperature–time (DTT) curve, displacement rate–time and displacement rate–temperature diagrams obtained during the PDS process. It was found that TiC{sub x} and Ti{sub 5}Si{sub 3}C{sub y} are the intermediate phases and the PDS process completed after 20 min at 1350 °C. The results showed that in Ti{sub 3}SiC{sub 2}/Al{sub 2}O{sub 3}-Ni composite, the Ni part of Al{sub 2}O{sub 3}-Ni leads to decomposition of Ti{sub 3}SiC{sub 2} to TiC{sub x}, Ti{sub 5}Si{sub 3}C{sub y} and Ni(Si){sub x}. No evidence was detected in the reaction between Al{sub 2}O{sub 3} and Ti{sub 3}SiC{sub 2}. The density and hardness of the composites are higher than monolithic Ti{sub 3}SiC{sub 2} due to the production of reinforcing phases. The composite showed lower flexural strength and higher compressive strength than monolithic Ti{sub 3}SiC{sub 2}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Ablation and Oxidation Behaviors of SiC Coatings on Graphite Prepared by Slurry Sintering and Pack Cementation

SiC coatings were generated on graphite using slurry sintering (SS) and pack cementation (PC). The samples’ ablation features were assessed by an oxyacetylene torch. The rates of mass ablation of the PC–SiC and SS–SiC coatings were approximated 2.17 × 10{sup −3} and 9.52 × 10{sup −3} g s{sup −1}, respectively, decreased by 84.1 and 29.6% compared to the uncoated samples. It was mainly attributed to the formation of a SiO{sub 2} layer on the surface. The continuous SiO{sub 2} molten film formed via the PC–SiC oxidation generates a sealing mechanism which can be an obstacle against the oxygen diffusion and hinder more ablation. This is while discontinuous SiO{sub 2} film formed from the thin SS–SiC cannot protect the graphite effectively. The non-isothermal oxidation test shows that without the SiC coating, the sample weight is lost largely from 25 to 1500 °C, and its weight loss was 2.2% after the TGA. However, after coating, the samples possessed excellent oxidation protection and weight losses of SS–SiC and PC–SiC coatings are down to 1.3 and 0.6%, respectively. The more oxidation of the graphite substrate occurred due to the formation of macrocracks in the coating during the TGA and also the formation of holes on SiO{sub 2} glass layer owing to release of CO or CO{sub 2}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Structural Evolution in Mechanically Alloyed and Spark Plasma Sintered Iron–0.15 wt.% MWCNT Composite

High-energy ball milling (HEBM) of mixtures of iron powder and multi-walled carbon nanotube (MWCNT) has been performed in an attempt to synthesize nano-grained steel. Even after exposure to a harsh HEBM conditions, the MWCNTs are seen to have retained their structural identity, and therefore, an MWCNT-reinforced steel matrix composite could be finally produced. Moreover, the study has revealed that the minor addition of copper leads to a significant reduction in grain size of ferrite in the so-produced steel matrix–MWCNT composite. It is also noticed that the fine grain structure of ferrite remains intact even after consolidation of the powder composite by spark plasma sintering, followed by hot forging. The micro-hardness values obtained for the composites (with/without copper) are observed as comparable with the submicron-grained steels, so far reported in the literature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗