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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

Sintering Behaviors of ZrC, NbC, and TaC Mono-and Binary Carbides

Nuclear Thermal Propulsion (NTP) has undergone development as an alternate in-space propulsion system to traditional chemical propulsion methods since the 1950s. In an NTP system, the energy released from fission in the core is utilized as the heat source to directly heat a propellant for propulsion, rather than chemical combustion in a traditional rocket. NTP has many desirable capabilities including flexible mission launch dates and reduced transit times due to it’s capability for high specific impulse. One of the main challenges with NTP systems is the structural integrity of the fuel. The fuel form required in the reactor core must withstand temperatures above 2700 Kelvin. Ceramic-metallic matrix fuel, ceramic-ceramic matrix fuel, and solid solution carbide fuels are the three strongest candidates for the extreme environments. Solid solution carbides have the potential to exhibit promising behavior as a fuel form in an NTP system. Of the multiple refractory metal carbides of interest, here we focus on zirconium carbide (ZrC), niobium carbide (NbC), and tantalum carbide (TaC). ZrC, NbC, and TaC powders were consolidated in monocarbide (ZrC, NbC, and TaC) and bi-carbide (ZrC-NbC, ZrC-TaC, NbC-TaC) forms using spark plasma sintering (SPS). In addition to the pure endpoint carbides, the examined compositions of the various bi-carbides ranged from 25-75 mol%. The sintering temperatures, pressures, and hold times were varied to determine the ideal sintering conditions. Grain size analysis, Archimedes’ density, scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersion spectroscopy (EDS) were used to determine and characterize the grain size, ideal density, porosity, phase stability, and chemical composition of each sample. The data from each sample was then used to generate a Master Sintering Curve (MSC) unique to each monocarbide or bi-carbide.

nuclear thermal propulsion↗
NASA NTRS2023

Homogeneity Study of ZrC, NbC, and TaC Binary Carbide Fuels for the Application of Nuclear Thermal Propulsion

In alignment with NASA and DARPA goals, efforts towards Nuclear Thermal Propulsion (NTP) have increased in recent years. As progress is made, a main challenge still exists; the fuel in an NTP system must survive the extreme environment experienced during operating conditions. Three fuel forms have been studied including a ceramic-metallic matrix, a ceramic-ceramic matrix, and solid solution carbides. Solid solution carbides were studied previously as a fuel for NTP and was shown to be a promising technology; however, the programs were canceled before demonstration in an NTP engine test. Of the refractory metal carbides of interest, zirconium carbide (ZrC), niobium carbide (NbC) and tantalum carbide (TaC) were studied. ZrC, NbC, and TaC powders were consolidated in monocarbide (ZrC, NbC, TaC) and bi-carbide (ZrC-NbC, ZrC-TaC, NbC-TaC) forms using spark plasma sintering (SPS), with 50-50 mol% compositions of the bi-carbides of interest. The time and temperature conditions to achieve a completely homogeneous solid solution for the mixed carbides is of interest for NTP fuel applications, since this homogeneity is considered to be essential for this fuel form. Homogeneity is typically not achieved during sintering, as surface diffusion (predominant for sintering to near ideal density) tends to occur at lower temperatures than bulk volumetric diffusion (required for solute interdiffusion to achieve a homogeneous solid solution). High temperature isochronal annealing was performed to identify the conditions to achieve a chemically homogeneous sample. The solute interpenetration vs annealing temperature was quantified using energy dispersion spectroscopy (EDS) in a scanning electron microscope (SEM). X-ray diffraction (XRD) was used to accurately measure the phase stability and lattice parameter as a function of annealing conditions. The diffusion data from each sample was then used to determine self-diffusion coefficients for interdiffusion of the Nb, Zr, and Ta solutes and compared to existing literature values. The minimum annealing conditions to achieve complete chemical homogeneity for each carbide was determined.

nuclear thermal propulsion↗
NASA NTRS2003

NBC detection in air and water

Participating in a Navy STTR project to develop a system capable of the 'real-time' detection and quanitification of nuclear, biological and chemical (NBC) warfare agents, and of related industrial chemicals including NBC agent synthesis by-products in water and in air immediately above the water's surface. This project uses JPL's Soft Ionization Membrane (SIM) technology which totally ionizes molecules without fragmentation (a process that can markedly improve the sensitivity and specificity of molecule compostition identification), and JPL's Rotating Field Mass Spectrometer (RFMS) technology which has large enough dynamic mass range to enable detection of nuclear materials as well as biological and chemical agents. This Navy project integrates these JPL Environmental Monitoring UnitS (REMUS) an autonomous underwater vehicle (AUV). It is anticipated that the REMUS AUV will be capable of 'real-time' detection and quantification of NBC warefare agents.

molecules↗
DOE OSTI2020

Materials Data on NbC by Materials Project

NbC is Halite, Rock Salt structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Nb4+ is bonded to six equivalent C4- atoms to form a mixture of corner and edge-sharing NbC6 octahedra. The corner-sharing octahedral tilt angles are 0°. All Nb–C bond lengths are 2.25 Å. C4- is bonded to six equivalent Nb4+ atoms to form a mixture of corner and edge-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 0°.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbC by Materials Project

NbC is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Nb4+ is bonded to six equivalent C4- atoms to form a mixture of edge, face, and corner-sharing NbC6 octahedra. The corner-sharing octahedral tilt angles are 47°. All Nb–C bond lengths are 2.29 Å. C4- is bonded to six equivalent Nb4+ atoms to form a mixture of distorted edge and corner-sharing CNb6 pentagonal pyramids.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbC by Materials Project

NbC is Zincblende, Sphalerite structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Nb4+ is bonded to four equivalent C4- atoms to form corner-sharing NbC4 tetrahedra. All Nb–C bond lengths are 2.10 Å. C4- is bonded to four equivalent Nb4+ atoms to form corner-sharing CNb4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbC by Materials Project

NbC is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Nb4+ is bonded in a body-centered cubic geometry to eight equivalent C4- atoms. All Nb–C bond lengths are 2.43 Å. C4- is bonded in a body-centered cubic geometry to eight equivalent Nb4+ atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on NbC by Materials Project

NbC is Molybdenum Carbide MAX Phase-like structured and crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Nb4+ is bonded to six equivalent C4- atoms to form a mixture of distorted corner and edge-sharing NbC6 pentagonal pyramids. All Nb–C bond lengths are 2.25 Å. C4- is bonded to six equivalent Nb4+ atoms to form a mixture of corner, edge, and face-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 47°.

36 MATERIALS SCIENCE↗
NASA NTRS1972

Ordering Effects in NbC and TaC

By means of transmission electron microscopy and electron diffraction, evidence has been obtained for the existence of long range carbon atom ordering in single-crystal niobium carbide that has a carbon-to-metal ratio close to the integral composition Nb6C5. The ordering, which gives rise to superlattice and domain structures similar to those observed in V6C5, appears, however, only in samples that have been cooled slowly through the order-disorder temperature of 1025 C. In TaC of similar composition, the ordering, although present, remains very imperfect even after the crystals are subjected to the same thermal treatment. The results are interpreted in terms of the electronic structure of the transition metal carbides as it is currently understood, and their relevance to the mechanical properties of NbC and TaC are discussed.

Venables, J. D.↗
NASA NTRS1988

NBC boil-off calorimeter for measuring thermal conductivity of insulating materials

Modern temperature, pressure and flow sensors along with a high speed digital control system have been incorporated into an existing thermal conductivity apparatus (ASTM C745). The system has also been modified to include the use of liquid helium as the refrigerant, if desired. The apparatus can be used to study thermal conductivity in the temperature range from 4 K to room temperature. Preliminary results on insulating materials indicate that the system update has significantly improved the precision and operational characteristics of the apparatus. Basic principles of operation, sources of system error and the reduction of system error by application of digital control and modern sensors are discussed. Preliminary data are presented.

Dube, W. P.↗
NASA NTRS1995

Rings of the North Brazil Current: Their structure and behavior inferred from observations and a numerical simulation

Large anticyclonic rings are shed from the retroflecting North Brazil Current (NBC) near 8 deg N in the tropical western Atlantic. New subsurface velocity and temperature measurements within three such rings are presented here and are found to be consistent with previous in situ and remotely sensed NBC ring measurements. A high-resolution numerical model of the Atlantic Ocean forced by monthly wind stress and an imposed meridional overturning cell is found to shed NBC rings that approximate those observed. The model rings are more surface-intensified than those observed and somewhat smaller in diameter. Both observed and modeled NBC rings move northwestward along the coast of South America with a speed of 8-16 cm/s, considerably slower than predicted by analytical theories describing westward ring propagation. At least 2-3 rings per year separate from the NBC retroflection. Annually, 1-3 rings translate intact from their formation region near 50 deg W to the islands of the southeastern Caribbean, where they disintegrate after a lifetime of about 100 days. This study is the first to make use of subsurface temperature and velocity data to compute the volume of the anomalous ring core. NBC rings may be responsible for 3-4 Sv of direct mass transport across the equatorial-tropical gyre boundary or 20-25% of the total upper ocean cross-gyre transport required by the Atlantic meridional overturning cell. Translating NBC rings may contribute 20% of the total meridional heat transport by the ocean at this latitude.

Fratantoni, David M.↗