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Results for “metal sintering”

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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Investigation of UO 2 doped with Fe 2 O 3 sintered under a reducing atmosphere

Nuclear fuel produced with trace amounts of transition metal additives is of potential interest for introducing intentional signatures for accelerating nuclear forensics. In this work, we investigate the effects on microstructure, grain size, crystal structure, and stoichiometry when trace amounts of Fe in the form of Fe 2 O 3 are added to UO 2 . Sintering of compacts with different concentrations, from 250 to 3000 ppmw, was performed under a reducing atmosphere at 1773 K. The persistence of the taggant during the fuel fabrication process as well as its impact on grain size, crystal lattice, and first-neighbor chemistry was evaluated using inductively coupled plasma–optical emission spectroscopy, powder X-ray diffraction (pXRD), Raman spectroscopy, scanning electron microscopy–backscatter electron spectroscopy, energy dispersive spectroscopy, and thermogravimetric analysis. We observed that a negligible amount of Fe was lost during sintering. Our results indicate that the feedstock, Fe 2 O 3 transforms into Fe and FeO under the test sintering conditions. For all compositions, metallic Fe precipitate was found in grain boundaries as a secondary phase. In conclusion, the potential incorporation of ionic Fe into the UO 2 unit cell was determined by pXRD and Raman spectra.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1993

Non-destructive, ultra-low resistance, thermally stable contacts for use on shallow junction InP solar cells

Contact formation to InP is plagued by violent metal-semiconductor intermixing that takes place during the contact sintering process. Because of this the InP solar cell cannot be sintered after contact deposition. This results in cell contact resistances that are orders of magnitude higher than those that could be achieved if sintering could be performed in a non-destructive manner. We report here on a truly unique contact system involving Au and Ge, which is easily fabricated, which exhibits extremely low values of contact resistivity, and in which there is virtually no metal-semiconductor interdiffusion, even after extended sintering. We present a description of this contact system and suggest possible mechanisms to explain the observed behavior.

Weizer, V. G.↗
DOE OSTI2024

Acetylene ligands stabilize atomically dispersed supported rhodium complexes under harsh conditions

Facile sintering of atomically dispersed supported noble metal catalysts at catalytically relevant temperatures, particularly under reducing conditions, poses a challenge for their practical applications. Some ligands, such as carbonyls, aid in improving the stability at the expense of severely suppressing the catalytic activity. In this work, we demonstrate that substitution of the carbonyl ligands with reactive acetylene ligands can maintain the atomic dispersion of the supported mononuclear rhodium complex under harsh reducing conditions (>573 K), as confirmed by in-situ X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies. In contrast, the supported rhodium carbonyl complex aggregates into nanoclusters under identical conditions. Furthermore, our results indicate that the acetylene ligands provide this anti-sintering ability while retaining the hydrogenation activity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1977

Design, fabrication, and evaluation of charge-coupled devices with aluminum-anodized-aluminum gates

A 4-phase, 49 1/2 bit CCD shift register was designed and fabricated using two levels of aluminum metallization with anodic Al2O3 insulation separating the layers. Test circuitry was also designed and constructed. A numerical analysis of an MOS-RC transmission line was made and results are given to characterize performance for various conductivities. The electrical design of the CCD included a low-noise dual-gate input and a balanced floating diffusion output circuit. Metallization was accomplished both by low voltage DC sputtering and thermal evaporation. The audization was according to published procedures using a buffered tartaric acid bath. Approximately 20 wafers were processed with 50 complete chips per wafer. All devices failed by shorting between the metal levels at some point. Experimental procedures eliminated temperature effects from sintering and drying, anodic oxide thickness, edge effects, photoresist stripping procedures, and metallization techniques as the primary causes of failure. It was believed from a study of SEM images that protuberances (hillocks) grow up from the first level metal through the oxide either causing a direct short or producing a weak, highly stressed insulation point which fails at low voltage. The cause of these hillocks is unknown; however, they have been observed to grow during temperature excursions to 470 C.

Gassaway, J. D.↗
DOE OSTI2021

Unconventional Materials Processing Using Spark Plasma Sintering

Spark plasma sintering (SPS) has gained recognition in the last 20 years for its rapid densification of hard-to-sinter conventional and advanced materials, including metals, ceramics, polymers, and composites. Herein, we describe the unconventional usages of the SPS technique developed in the field. The potential of various new modifications in the SPS technique, from pressureless to the integration of a novel gas quenching system to extrusion, has led to SPS’ evolution into a completely new manufacturing tool. The SPS technique’s modifications have broadened its usability from merely a densification tool to the fabrication of complex-shaped components, advanced functional materials, functionally gradient materials, interconnected materials, and porous filter materials for real-life applications. The broader application achieved by modification of the SPS technique can provide an alternative to conventional powder metallurgy methods as a scalable manufacturing process. The future challenges and opportunities in this emerging research field have also been identified and presented.

36 MATERIALS SCIENCE↗
DOE OSTI2021

On the Origin of Sinter‐Resistance and Catalyst Accessibility in Raspberry‐Colloid‐Templated Catalyst Design

Abstract Nanoparticle (NP) sintering is a major cause of the deactivation of supported catalysts. Raspberry‐colloid‐templated (RCT) catalysts are an emerging class of materials that show an unprecedented level of sinter‐resistance and exhibit high catalytic activity. Here a comprehensive study of the origin of NP stability and accessibility in RCT catalysts using theoretical modeling, 3D electron microscopy, and epitaxial overgrowth is reported. The approach is showcased for silica‐based RCT catalysts containing dilute Pd‐in‐Au NPs previously used in hydrogenation and oxidation catalysis. Modeling of the contact line of the silica precursor infiltrating into the assembled raspberry colloids suggests that a large part of the particles must be embedded into silica, which is confirmed by quantitative visualization of >200 individual NPs by dual‐axis electron tomography. The RCT catalysts have a unique structure in which all NPs reside at the pore wall but have >50% of their surface embedded in the matrix, giving rise to the strongly enhanced thermal and mechanical stability. Importantly, epitaxial overgrowth of Ag on the supported NPs reveals that not only the NP surface exposed to the pore but the embedded interface as well remained chemically accessible. This mechanistic understanding provides valuable guidance in the design of stable catalytic materials.

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

Autonomous Aerosol and Plasma Co‐Jet Printing of Metallic Devices at Ambient Temperature

Abstract Additive manufacturing of metallic materials holds the potential to revolutionize the fabrication of functional devices unattainable via traditional methods. Despite recent advancements, printing metallic materials typically requires thermal processing at elevated temperatures to form dense structures with desired properties, which presents a major challenge for direct printing and integration with temperature‐sensitive materials. Herein, a unique co‐jet printing (CJP) method is reported integrating an aerosol jet and a non‐thermal, atmospheric pressure plasma jet to enable concurrent aerosol deposition of metal nanoparticle inks and in situ sintering at ambient temperature. A machine learning algorithm is integrated with the CJP to perform real‐time defect detection and autonomous correction, enhancing the yield of printed films with high electrical conductivity from 44% to 94%. Concurrent printing and sintering eliminate the need for post‐printing processing, reducing the overall manufacturing time by multiple folds depending on product size. CJP enables direct printing of functional devices on a variety of temperature‐sensitive materials including biological materials. Direct printing of hydration sensors on living plant leaves is demonstrated for long‐duration monitoring of hydration level in the plant. The versatile CJP method opens tremendous opportunities to harmoniously integrate abiotic and biotic materials for emerging applications in wearable/implantable devices and biohybrid systems.

Du, Yipu [Department of Aerospace and Mechanical E↗
NASA NTRS1974

Preparation and evaluation of thin-film sodium tungsten bronzes

Thin films of sodium tungsten bronze (NaxWO3) were investigated as reversible sodium ion electrodes for solid electrolytes. The films were made by electron beam evaporation of the three phases, W metal, Na2WO4, and WO3, followed by sintering. The substrates were sodium beta alumina disks and glass slides. X-ray diffraction analyses of the films showed that sintering in dry nitrogen with prior exposure to air lead to mixed phases. Sintering in vacuum with no air exposure produced tetragonal I bronze with a nominal composition of Na0.31WO3, single phase within the limits of X-ray diffraction detectability. The films were uniform and adherent on sodium beta alumina substrates. The ac and dc conductivities of the beta alumina were measured with the sodium tungsten bronze films as electrodes. These experiments indicated that the tetragonal I bronze electrodes were not completely reversible. This may have resulted from sodium ion blocking within the bronze film or at the bronze beta alumina interface. Methods for attempting to make more completely reversible electrodes are suggested.

Kautz, H. E.↗
NASA NTRS1993

Study on the mechanism of liquid phase sintering (M-12)

The objectives were to (1) obtain the data representing the growth rate of solid particles in a liquid matrix without the effect of gravity; and (2) reveal the growth behavior of solid particles during liquid phase sintering using the data obtained. Nickel and tungsten are used as the constituent materials in liquid phase sintering. The properties of the constituent metals are given. When a compact of the mixture of tungsten and nickel powders is heated and kept at 1550 C, nickel melts down but tungsten stays solid. As the density of tungsten is much greater than that of nickel, the sedimentation of tungsten particles occurs in the experiment on Earth. The difference between the experiments on Earth and in space is illustrated. The tungsten particles sink to the bottom and are brought into contact with each other. The resulting pressure at the contact point causes the accelerated dissolution of tungsten. Consequently, flat surfaces are formed at the contact sites. As a result of dissolution and reprecipitation of tungsten, the shape of particles changes to a polygon. This phenomenon is called 'flattening.' An example of flattening of tungsten particles is shown. Thus, the data obtained by the experiment on Earth may not represent the exact growth behavior of the solid particles in a liquid matrix. If the experiments were done in a microgravity environment, the data corresponding to the theoretical growth behavior of solid particles could be achieved.

Kohara, S.↗
DOE OSTI2022

Enhanced Oxygen Activation Achieved by Robust Single Chromium Atom-Derived Catalysts in Aerobic Oxidative Desulfurization

Oxidative desulfurization (ODS) plays critical roles in the production of high-quality sulfur impurity-free fuels, especially procedures using molecular oxygen as the sole oxidant. However, the state-of-the-art systems still rely on noble metal nanocatalysts, with deactivation issues caused by coking and sintering still present. In this work, leveraging the merits of single-atom catalysts (SACs) with earth-abundant metal cores and robust nanoporous supports, a series of catalysts composed of homogeneously distributed single chromium atoms anchored on multiwalled carbon nanotubes were fabricated and deployed to catalyze the aerobic ODS transformation. Adopting aromatic sulfur compound (ASC)-containing alkanes as a model system with molecular oxygen as the oxidant, efficient oxygen-to-active O 2 •– transformation and subsequent ASCs-to-sulfone conversion have been achieved, with the former benefiting from the chromium-active sites and the latter arising from the robust, nanoporous, and π-conjugated architecture of the supports. The attractive catalytic performance and cycling stability of the chromium-based SACs make them promising candidates in practical sulfur species removal from liquid fuels, supplying an alternative guidance on the catalyst design toward cost-effective and energy-efficient ODS procedures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS1984

Method of forming a relatively stable slip of silicon metal particles and yttrium containing particles

The method concerns forming a relatively stable slip of silicon metal particles and yttrium containing particles. In one embodiment, a casting slip of silicon metal particles is formed in water. Particles of a yttrium containing sintering aid are added to the casting slip. The yttrium containing sintering aid is a compound which has at least some solubility in water to form Y.sup.+3 ions which have a high potential for totally flocculating the silicon metal particles into a semiporous solid. A small amount of a fluoride salt is added to the casting slip which contains the yttrium containing sintering aid. The fluoride salt is one which will produce fluoride anions when dissolved in water. The small amount of the fluoride anions produced are effective to suppress the flocculation of the silicon metal particles by the Y.sup.+3 ions so that all particles remain in suspension in the casting slip and the casting slip has both an increased shelf life and can be used to cast articles having a relatively thick cross-section. The pH of the casting slip is maintained in a range from 7.5 to 9. Preferably, the fluoride salt used is one which is based on a monovalent cation such as sodium or ammonia. The steps of adding the yttrium containing sintering aid and the fluoride salt may be interchanged if desired, and the salt may be added to a solution containing the sintering aid prior to addition of the silicon metal particles.

Dickie, Ray A.↗
DOE OSTI2024

Uniaxial compressive creep tests by spark plasma sintering of 70% theoretical density α -uranium and U-10Zr

Metallic fuels hold numerous advantages over conventional uranium dioxide fuels and are a key component of several liquid metal-cooled advanced reactor concepts including sodium fast reactors. These fuels undergo rapid swelling during early burnup; consequently, they spend most of their reactor lifetime in a porous state. The presence of this porosity alters many of the mechanical properties of the fuel including creep impacting fuel deformation during axial swelling. This work investigates the creep behavior of the porous fuel using a spark plasma sintering technique. Creep tests were performed for the first time on porous α-phase uranium and uranium with 10 wt. % zirconium (U-10Zr) samples. The samples of α-phase uranium and U-10Zr were fabricated from depleted uranium by spark plasma sintering and subjected to uniaxial compressive creep testing. Calculated stress exponents were found to be 2.6±1.6 and 5.7±1.4 for α-U and U-10Zr, respectively, and calculated activation energies were found to be 61.6±1.1kJ/mol for α-U. The creep data were also used to evaluate existing porosity inclusive in creep models.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1983

Radiant heating tests of several liquid metal heat-pipe sandwich panels

Integral heat pipe sandwich panels, which synergistically combine the thermal efficiency of heat pipes and the structural efficiency of honeycomb sandwich construction, were conceived as a means of alleviating thermal stress problems in the Langley Scramjet Engine. Test panels which utilized two different wickable honeycomb cores, facesheets with screen mesh sintered to the internal surfaces, and a liquid metal working fluid (either sodium or potassium) were tested by radiant heating at various heat load levels. The heat pipe panels reduced maximum temperature differences by 31 percent with sodium working fluid and 45 percent with potassium working fluid. Results indicate that a heat pipe sandwich panel is a potential, simple solution to the engine thermal stress problem. Other interesting applications of the concept include: cold plates for electronic component and circuit card cooling, radiators for large space platforms, low distortion large area structures (e.g., space antennas) and laser mirrors.

Camarda, C. J.↗
DOE OSTI2023

Screen printable copper pastes for silicon solar cells

The current work demonstrates the successful metallization of a PERC silicon solar cell with screen-printable copper (Cu) paste that is sintered at elevated temperature in air atmosphere. The existing state of the art in Silicon (Si) solar cell metallization is silver (Ag) paste; Cu cost is 1/100th the cost of Ag and has a comparable conductivity. However, Cu undergoes rapid oxidation at elevated temperatures and the high diffusion of Cu into Si restricts its usage in the metallization of silicon solar cells. In this paper, a Cu paste containing a proprietary mixture of antioxidant additives and diffusion inhibitors was used to make front gridlines on PERC cells. The Cu-printed cells were fired in an IR belt furnace with a peak temperature of 576°C in air atmosphere. The solar cells discussed here reached an efficiency of 19%, which is 88% of the efficiency measured for a commercial Ag-printed cell. The working devices were further characterized using STEM, EDX, ToF-SIMS and long-term suns-V oc studies demonstrating an absence of Cu diffusion. Furthermore, thermally stressing the Cu-printed solar cells yielded a reduction of less than 1.9% of the initial pseudo fill factor (pFF) after 1000 hours at 200°C. Here, the shunt resistance of cells monitored over 3 years remained within 2.5% of its initial value, which demonstrates the effectiveness of the Cu diffusion barrier.

14 SOLAR ENERGY↗
NASA NTRS1983

Radiant heating tests of several liquid metal heat-pipe sandwich panels

Integral heat-pipe sandwich panels, which synergistically combine the thermal efficiency of heat pipes and the structural efficiency of honeycomb sandwich construction, were conceived as a means of alleviating thermal stress problems in the Langley Scramjet Engine. Test panels which utilized two different wickable honeycomb cores, facesheets with screen mesh sintered to the internal surfaces, and a liquid metal working fluid (either sodium or potassium) were tested by radiant heating at various heat-load levels. The heat-pipe panels reduced maximum temperature differences by 31 percent with sodium working fluid and 45 percent with potassium working fluid. Results indicate that a heat-pipe sandwich panel is a potential, simple solution to the engine thermal stress problem. Other interesting applications of the concept include: cold plates for electronic component and circuit card cooling, radiators for large space platforms, low-distortion large area structures (e.g., space antennas) and laser mirrors.

Camarda, C. J.↗