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11 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Temperature-Dependent Sheet and Contact Resistivity Measurements on Ag and Ag-Ni Circuit Pastes

The metal circuits and brazes used in electronic, energy conversion, and/or energy storage devices often have difficulty wetting and adhering to ceramic and/or ceramic-passivated metal substrates. Here, a novel Particle Interlayer Directed Wetting and Spreading (PIDWAS) technique is demonstrated that utilizes screen printing, the low wetting angle of silver on nickel, and the high work of adhesion between nickel and various ceramics to produce well-adhered, self-assembled silver patterns on ceramic and/or stainless-steel substrates not normally wet by silver. The resulting Ag-Ni circuits have higher sapphire adhesion strengths (up to 30 MPa on sapphire), higher densities (>97% on sapphire), and similar high-temperature electronic resistivities to those made using commercially-available Heraeus C8710 or DAD-87 silver circuit pastes. Similarly, Ag-Ni brazes between a variety of ceramic and/or stainless-steel substrates have better microstructural stability with rapid thermal cycling, reduction-oxidation cycling, and dual atmosphere isothermal aging than conventional Ag-CuO brazes. In addition, the residual Ni in these Ag-Ni circuits and brazes can be used to chemically getter surface segregated Al, ensuring low contact resistances on a variety of chromia- and/or alumina-passivated stainless steels. Reference: [1] Hu G, Zhou Q, Bhatlawande A, Park J, Termuhlen R, Ma Y, Bieler TR, Yu HC, Qi Y, Hogan T & Nicholas JD. Patterned Nickel Interlayers for Enhanced Silver Wetting, Spreading and Adhesion on Ceramic Substrates. Scripta Materialia, 2021; 196, 113767. 10.1016/j.scriptamat.2021.113767 [2] Park J, Phongpreecha T, Nicholas JD & Qi Y. Enhanced Liquid Metal Wetting on Oxide Surfaces via Patterned Particles. Acta Materialia, 2020; 199, 551-560. 10.1016/j.actamat.2020.08.037

Bhatlawande, Aishwarya↗
DOE OSTI2020

Heterogeneous solute segregation suppresses strain localization in nanocrystalline Ag-Ni alloys

Solute segregation to individual grain boundaries is used by design to produce strong and stable nanocrystalline metallic alloys. Grain-boundary segregation, however, is known to cause adverse embrittlement effects from a strain-localization failure mechanism that imposes significant material limitations for structural applications. Here, using atomistic simulations, it is discovered that heterogeneous Ni segregation in nanocrystalline Ni-mixed Ag alloys dramatically shuts down localized shear bands during plastic deformation, while simultaneously increasing the tensile strength. Nanocrystalline Cu-mixed Ag metals are predicted to exhibit standard homogeneous Cu segregation and a tensile strength that saturates above a solute concentration of 8 at.% due to glass-like shear localization induced by grain boundaries. By contrast, it is found that heterogeneous Ni segregation in nanocrystalline Ag-Ni alloys forms solute-rich clusters along interfaces leading to strain delocalization at high strain and continuous strengthening at high solute concentrations up to 15 at.%. As a result, this study reveals the importance of heterogeneous versus homogeneous segregation behaviors on strain localization and points to a fundamentally new strategy to design failure-resistant nanostructured materials through grain boundary segregation engineering.

36 MATERIALS SCIENCE↗
NASA NTRS1983

Containerless electromagnetic levitation melting of Cu-Fe and Ag-Ni alloys

The feasibility of producing silver or copper alloys containing finely dispersed nickel or iron particles, respectively, by utilizing containerless electromagnetic levitation casting techniques was investigated. A levitation coil was designed to successfully levitate and melt a variety of alloys including Nb-Ge, Cu-Fe, Fe-C, and Ag-Ni. Samples of 70 Cu-30 Fe and 80 Ag-20 Ni (atomic %), prepared by mechanical pressing of the constituent powders, were levitated and heated either to the solid plus liquid range of the alloys or to the fully liquid region. The samples were then solidified by passing helium gas into the bell jar or they were dropped into a quenching oil. The structure of the samples which were heated to the solid plus liquid range consists of uniform distribution of Fe or Ni particle in their respective matrices. A considerable amount of entrapped gas bubbles were contained. Upon heating for longer periods or to higher temperatures, the bubbles coalesced and burst, causing the samples to become fragmented and usually fall out of the coil.

Abbaschian, G. J.↗
DOE OSTI2025

Porous Interlayers that Getter Surface-Segregating Species for Improved Silver Wetting, Adhesion, and Electrical Contact on Stainless Steel SOFC Components

Here, porous nickel interlayers or porous platinum interlayers were shown to promote the wetting, spreading, and adhesion of silver on alumina-forming ferritic stainless steel (AFFSS) and chromia-forming ferritic stainless steel (CFFSS). These interlayers resulted in dense, crack-free AFFSS|Ag-Ni|CFFSS and AFFSS|Ag-Pt|CFFSS braze joints that, after 300 h in 650 °C air, displayed shear strengths up to 70 MPa similar to, or larger than, those of AFFSS|Ag-CuO|CFFSS or AFFSS|Ag|CFFSS joints subjected to identical treatment. Similarly, after exposure to 25 cycles of (50 switches between) 12 h of 650 °C air and 12 h of 650 °C 4%H 2 –96%N 2 , AFFSS|Ag-Ni|CFFSS and AFFSS|Ag-Pt|CFFSS braze joints displayed shear strengths significantly larger than those of AFFSS|Ag-CuO|CFFSS or AFFSS|Ag|CFFSS joints subjected to identical treatment. In addition, nickel and platinum were found to chemically getter surface-segregating steel constituents, particularly Al from the AFFSS. As a result, Ag-Ni and Ag-Pt electrical contact resistances on AFFSS and CFFSS substrates were several orders of magnitude lower than those of conventional Ag-CuO reactive air brazes or Heraeus C8710 Ag contact pastes. Together, these results suggest that Ag-Pt and especially Ag-Ni may be useful for the fabrication of durable joints, seals, and/or electrical contacts in electrical/electrochemical devices exposed to high temperatures and/or variable oxygen partial pressure environments.

36 MATERIALS SCIENCE↗
NASA NTRS1996

Development of Uniform Microstructures in Immiscible Alloys by Processing in a Low-Gravity Environment

Highly segregated macrostructures tend to develop during processing of hypermonotectic alloys because of the density difference existing between the two liquid phases. The approximately 4.6 seconds of low-gravity provided by Marshall Space Flight Center's 105 meter drop tube was utilized to minimize density-driven separation and promote uniform microstructures in hypermonotectic Ag-Ni and Ag-Mn alloys. For the Ag-Ni alloys a numerical model was developed to track heat flow and solidification of the bi-metal drop configuration. Results, potential applications, and future work are presented.

Grugel, R. N.↗
NASA NTRS1977

Analytical study of space processing of immiscible materials for superconductors and electrical contacts

The results of a study conducted to determine the role space processing or materials research in space plays in the superconductor and electrical contact industries are presented. Visits were made to manufacturers, users, and research organizations connected with these products to provide information about the potential benefits of the space environment and to exchange views on the utilization of space facilities for manufacture, process development, or research. In addition, space experiments were suggested which could result in improved terrestrial processes or products. Notable examples of these are, in the case of superconductors, the development of Nb-bronze alloys (Tsuei alloys) and, in the electrical contact field, the production of Ag-Ni or Ag-metal oxide alloys with controlled microstructure for research and development activities as well as for product development. A preliminary experimental effort to produce and evaluate rapidly cooled Pb-Zn and Cu-Nb-Sn alloys in order to understand the relationship between microstructure and superconducting properties and to simulate the fine structure potentially achievable by space processing was also described.

Gelles, S. H.↗
NASA NTRS1984

Technique for the efficient and reproducible fabrication of electromagnetic levitation coils

A technique has been developed for fabricating electromagnetic induction coils in a reproducible manner. The process utilizes a split mandrel that can be disassembled to remove the mandrel from the coil. The technique has increased coil production rates by a factor of 8 over the freehand winding method. The success rate for producing a functional levitation coil has been increased from 50 percent to 95 percent. The levitation coil designed during this work has successfully levitated and melted a variety of alloys including Cu, Ag, Ag-Ni, Cu-Fe, Fe-C, and Nb-Ge. W was also levitated but not melted at temperatures as high as 2700 C. The highest sample melt temperature achieved was 2400 C for the Nb-Ge samples.

Ethridge, E. C.↗
DOE OSTI2020

Synthesis and Characterization of Pd-based Nanomaterials

Bimetallic nanoparticles (BNPs) consist of two different types of metals or alloys that are bonded together. Unique properties such as optical, electronic, thermal, and catalytic effects differ for each type of BNP. Important BNPs range from Au-Pd, Ag- Pt, Au-Pt, and Ag-Ni. Pd bimetallic nanoparticles are of interest due to their many applications such as catalysis and sensing. Bimetallic catalysts have increase reaction rates and have improved catalyst stability through the geometry and ligand distribution. Pd nanoparticles are considered to be a strong catalyst due to their high activity at low temperatures and high tolerance to moisture. The catalytic properties of bimetallic nanoparticles depend on the structural properties such as size and shape. Core-shell, hollow structure, and multi-shell alloy are three possible structures nanoparticles can form as bimetallic catalysts. BNPs can be synthesized through different methods to control the size, shape, and structure. To obtain different morphologies, a variety of methods can be performed. Different methods can range from the usage of the glancing angle deposition (GLAD) to the galvanic replacement reaction, but the methods all depend on the properties of the metals. The galvanic displacement reaction was the method used to obtain Pd-based nanoparticles. This reaction is best know for obtaining hollow shaped NPs. To determine what redox process was preformed, the activity series of metals was used. From the activity series of metals, silver (Ag) was selected to preform Pd-based nanoparticles. Objectives: Synthesize Ag nanoparticles and Ag-Pd nanoparticles to understand the morphology. Characterize the synthesized nanoparticles using scanning electron microscopy (SEM), phase analysis light scattering (PALS), dynamic light scattering (DLS), energy dispersive X-ray spectroscopy (EDS), and UV-Vis spectroscopy. Results: In the UV-Vis spectrum, the Ag-Pd bimetallic NP's plasmon band decreased as the volume of palladium increased. The surface charge increases as the concentration of palladium increases. The Pd{sup 2+} ions interact with the sodium citrate surface, and decrease the negative charge. Conclusion: Ag-Pd nanoparticles were successfully created and stabilized with sodium citrate. The addition of Pd decreased the prominent plasmon band of the Ag nanoparticles. The SEM analysis showed that Ag nanoparticles had a well-defined structure, while the Ag-Pd nanoparticles showed hollow and rough structure. The EDX analysis confirmed the presence of silver and palladium. This material can be used in many industrial and research fields such as organic synthesis, fuel cells, and environmental sensing and remediation.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2020

Materials Data on NiAg3 by Materials Project

Ni1Ag3 is alpha La-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ni is bonded to twelve Ag atoms to form NiAg12 cuboctahedra that share corners with four equivalent NiAg12 cuboctahedra, corners with eight equivalent AgNi4Ag8 cuboctahedra, edges with eight equivalent NiAg12 cuboctahedra, edges with sixteen equivalent AgNi4Ag8 cuboctahedra, faces with four equivalent NiAg12 cuboctahedra, and faces with fourteen AgNi4Ag8 cuboctahedra. There are eight shorter (2.83 Å) and four longer (2.84 Å) Ni–Ag bond lengths. There are two inequivalent Ag sites. In the first Ag site, Ag is bonded to four equivalent Ni and eight Ag atoms to form AgNi4Ag8 cuboctahedra that share corners with twelve equivalent AgNi4Ag8 cuboctahedra, edges with eight equivalent NiAg12 cuboctahedra, edges with sixteen AgNi4Ag8 cuboctahedra, faces with four equivalent NiAg12 cuboctahedra, and faces with fourteen AgNi4Ag8 cuboctahedra. There are four shorter (2.83 Å) and four longer (2.84 Å) Ag–Ag bond lengths. In the second Ag site, Ag is bonded to four equivalent Ni and eight equivalent Ag atoms to form AgNi4Ag8 cuboctahedra that share corners with four equivalent AgNi4Ag8 cuboctahedra, corners with eight equivalent NiAg12 cuboctahedra, edges with twenty-four AgNi4Ag8 cuboctahedra, faces with six equivalent NiAg12 cuboctahedra, and faces with twelve AgNi4Ag8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NiAg3 by Materials Project

Ni1Ag3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ni is bonded to twelve equivalent Ag atoms to form NiAg12 cuboctahedra that share corners with twelve equivalent NiAg12 cuboctahedra, edges with twenty-four equivalent AgNi4Ag8 cuboctahedra, faces with six equivalent NiAg12 cuboctahedra, and faces with twelve equivalent AgNi4Ag8 cuboctahedra. All Ni–Ag bond lengths are 2.83 Å. Ag is bonded to four equivalent Ni and eight equivalent Ag atoms to form AgNi4Ag8 cuboctahedra that share corners with twelve equivalent AgNi4Ag8 cuboctahedra, edges with eight equivalent NiAg12 cuboctahedra, edges with sixteen equivalent AgNi4Ag8 cuboctahedra, faces with four equivalent NiAg12 cuboctahedra, and faces with fourteen equivalent AgNi4Ag8 cuboctahedra. All Ag–Ag bond lengths are 2.83 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Ni3Ag by Materials Project

Ni3Ag1 is alpha La-derived structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. there are two inequivalent Ni sites. In the first Ni site, Ni is bonded to eight Ni and four equivalent Ag atoms to form NiNi8Ag4 cuboctahedra that share corners with twelve equivalent NiNi8Ag4 cuboctahedra, edges with eight equivalent AgNi12 cuboctahedra, edges with sixteen NiNi8Ag4 cuboctahedra, faces with four equivalent AgNi12 cuboctahedra, and faces with fourteen NiNi8Ag4 cuboctahedra. There are four shorter (2.60 Å) and four longer (2.61 Å) Ni–Ni bond lengths. All Ni–Ag bond lengths are 2.61 Å. In the second Ni site, Ni is bonded to eight equivalent Ni and four equivalent Ag atoms to form NiNi8Ag4 cuboctahedra that share corners with four equivalent NiNi8Ag4 cuboctahedra, corners with eight equivalent AgNi12 cuboctahedra, edges with twenty-four NiNi8Ag4 cuboctahedra, faces with six equivalent AgNi12 cuboctahedra, and faces with twelve NiNi8Ag4 cuboctahedra. All Ni–Ag bond lengths are 2.60 Å. Ag is bonded to twelve Ni atoms to form AgNi12 cuboctahedra that share corners with four equivalent AgNi12 cuboctahedra, corners with eight equivalent NiNi8Ag4 cuboctahedra, edges with eight equivalent AgNi12 cuboctahedra, edges with sixteen equivalent NiNi8Ag4 cuboctahedra, faces with four equivalent AgNi12 cuboctahedra, and faces with fourteen NiNi8Ag4 cuboctahedra.

36 MATERIALS SCIENCE↗