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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 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Strengthening of C/SiC Composites by Electrophoretic Deposition of CNTs on a SiC Coating

The current study reports the enhancement of mechanical properties of carbon fiber-reinforced silicon carbide ceramic matrix composites (C/SiC CMCs) by the application of a carbon nanotube/silicon carbide (CNT/SiC) coating. CNTs were deposited on the surfaces of C/SiC composites using electrophoretic deposition (EPD), after which infiltration by SiC was achieved through a chemical vapor infiltration process. An EPD duration of 5 min was associated with a 40% increase in the ultimate flexural strength relative to that of composites with a pure SiC coating. The observed enhancement was rationalized by the microstructural observations of SiC infiltration into the porous CNT morphology and the subsequent formation of CNT/SiC layers on the surfaces of the composites and by the inherent toughness of the SiC whiskers. The flexural strength decreased with EPD durations greater than 5 min due to the formation of thick CNT meshes, which decreased the open porosity and thereby obstructed further SiC infiltration. This is a viable methodology for the improvement of mechanical properties of CMCs by the introduction of a ceramic coating containing CNT.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
NASA NTRS2003

Structural Anomalies Detected in Ceramic Matrix Composites Using Combined Nondestructive Evaluation and Finite Element Analysis (NDE and FEA)

Most reverse engineering approaches involve imaging or digitizing an object and then creating a computerized reconstruction that can be integrated, in three dimensions, into a particular design environment. The rapid prototyping technique builds high-quality physical prototypes directly from computer-aided design files. This fundamental technique for interpreting and interacting with large data sets is being used here via Velocity2 (an integrated image-processing software, ref. 1) using computed tomography (CT) data to produce a prototype three-dimensional test specimen model for analyses. A study at the NASA Glenn Research Center proposes to use these capabilities to conduct a combined nondestructive evaluation (NDE) and finite element analysis (FEA) to screen pretest and posttest structural anomalies in structural components. A tensile specimen made of silicon nitrite (Si3N4) ceramic matrix composite was considered to evaluate structural durability and deformity. Ceramic matrix composites are being sought as candidate materials to replace nickel-base superalloys for turbine engine applications. They have the unique characteristics of being able to withstand higher operating temperatures and harsh combustion environments. In addition, their low densities relative to metals help reduce component mass (ref. 2). Detailed three-dimensional volume rendering of the tensile test specimen was successfully carried out with Velocity2 (ref. 1) using two-dimensional images that were generated via computed tomography. Subsequent, three-dimensional finite element analyses were performed, and the results obtained were compared with those predicted by NDE-based calculations and experimental tests. It was shown that Velocity2 software can be used to render a three-dimensional object from a series of CT scan images with a minimum level of complexity. The analytical results (ref. 3) show that the high-stress regions correlated well with the damage sites identified by the CT scans and the experimental data. Furthermore, modeling of the voids collected via NDE offered an analytical advantage that resulted in more accurate assessments of the material s structural strength. The top figure shows a CT scan image of the specimen test section illustrating various hidden structural entities in the material and an optical image of the test specimen considered in this study. The bottom figure represents the stress response predicted from the finite element analyses (ref .3 ) for a selected CT slice where it clearly illustrates the correspondence of the high stress risers due to voids in the material with those predicted by the NDE. This study is continuing, and efforts are concentrated on improving the modeling capabilities to imitate the structural anomalies as detected.

Abdul-Aziz, Ali↗
DOE OSTI2019

Progress in development of SiC-based joints resistant to neutron irradiation

This study fills a knowledge gap regarding neutron-irradiation resistance of SiC joints for nuclear applications, by investigating high-dose neutron irradiation effects on the strength of selected joints and low-dose neutron irradiation effects on recently developed joints fabricated by state of the art processing methods. The joining methods used for the high-dose radiation study included pressure-assisted liquid-phase sintering (LPS) of SiC nanopowder, pressureless calcia-alumina glass ceramics joining, and reaction sintering of Ti-Si-C powders with hot-pressing. The joints were neutron-irradiated at 530 °C to 20 displacements per atom (dpa). Other joining methods included low-pressure LPS of cold-pressed SiC green body, pressureless reaction sintered Ti-Si-C powder joint, spark plasma–sintered Ti diffusion bond, and hot-pressed Ti diffusion bond, which were irradiated at ~500 °C to ~2 dpa. There was no notable degradation of torsional strengths of the joints following the high-dose irradiation. The irradiation-induced degradation at low neutron dose was highly dependent on joint type.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Novel yellowish-green emitting luminescence in Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}:Eu{sup 2+} phosphor

Graphical abstract: The phosphor has two separated emission centers with the dependent emission intensity on Eu{sup 2+} doping. There is a red-shift in the emission due to energy transfer with increasing the Eu{sup 2+}-doping. - Highlights: • Green-origin-emitting phosphors of Eu{sup 2+}-doped Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16} were firstly prepared by chemical sol–gel method. • The tunable luminescence color was realized by the changing Eu{sup 2+}-doping in Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}. • Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}:Eu{sup 2+} displays two typical luminescence centers with the emission depending on Eu{sup 2+} doping. • Eu{sup 2+}-doped Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16} phosphor has an excellent thermal stability on the temperature quenching. - Abstract: Color tunable green-origin-emitting phosphor of Eu{sup 2+}-doped phosphate-silicate Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16} was prepared by chemical sol–gel method. The X-ray powder diffraction, the photoluminescence excitation and emission spectra, time resolved spectra, and thermal stability were measured. The excitation spectra can well match with the emission light of near UV-LED chips (360–400 nm). The tunable luminescence was realized by changing Eu{sup 2+}-doping concentration. Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}:Eu{sup 2+} displays two typical luminescence centers, which were suggested to originate from two Ca{sup 2+} sites in the host. With increasing Eu{sup 2+} doping concentrations, the green emission band shifts to long wavelength. Energy transfer between the two different Eu{sup 2+} ions is discussed by analyzing the photoluminescence excitation and emission spectra, concentration-dependent luminescence intensity, and lifetimes. The dependence of the luminescence intensity of Ca{sub 7}Si{sub 2}P{sub 2}O{sub 16}:Eu{sup 2+} on temperatures was measured. The activation energy (ΔE) for thermal quenching was reported.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Lithium stoichiometry of solid electrolytes based on tetragonal Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}

Graphical abstract: - Highlights: • We prepared Li{sub x}La{sub 3}Zr{sub 2}O{sub 8.5+0.5x} (x = 6, 7, 8, 9, 10) by the citrate–nitrate method. • We studied phase composition and conductivity of Li{sub x}La{sub 3}Zr{sub 2}O{sub 8.5+0.5x}. • We proposed a simple method to determine the carbonate impurity content in the solid electrolytes. • The synthesized solid electrolytes Li{sub x}La{sub 3}Zr{sub 2}O{sub 8.5+0.5x} (x = 7–9) have 1.32–3.49 wt.% Li{sub 2}CO{sub 3}. • The composition with x = 9 has high total conductivity, 7.5 × 10{sup −6} S cm{sup −1}, at room temperature. - Abstract: Samples of Li{sub x}La{sub 3}Zr{sub 2}O{sub 8.5+0.5x} (x = 6, 7, 8, 9, 10) were synthesized with the citrate–nitrate method. Neutron diffraction studies have shown the presence of lithium carbonate impurities in the synthesized compounds. We propose a simple and effective method to determine the carbonate impurity content in the solid electrolytes. The technique is based on the measurement of the carbon dioxide volume produced from the interaction of the investigated material with acid. Determined in this way, the content of Li{sub 2}CO{sub 3} in the synthesized electrolytes Li{sub 7}La{sub 3}Zr{sub 2}O{sub 12}, Li{sub 8}La{sub 3}Zr{sub 2}O{sub 12.5} and Li{sub 9}La{sub 3}Zr{sub 2}O{sub 13} are 1.32 ± 0.04, 1.95 ± 0.06 and 3.49 ± 0.10 wt.%, respectively. From the obtained data, the actual lithium content per formula unit of complex oxide was calculated for the synthesized compounds. The composition with x = 9 had the highest total conductivity, σ = 7.5 × 10{sup −6} S cm{sup −1}, at room temperature. All the investigated electrolytes have an activation energy of approximately 50 kJ mol{sup −1}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Electrical Transport Properties of Bi{sub 3}TiNbO{sub 9} High-Temperature Piezoceramics

High-density ceramic samples of the Bi{sub 3}TiNbO{sub 9} ferroelectric phase with a layered perovskite-like structure have been produced by tape casting slurry technology and hot pressing processes. The samples have been characterized by X-ray diffraction and dielectric, piezoelectric, and pyroelectric measurements. The results demonstrate that the samples have a well-defined texture due to the preferential orientation of the basal planes of their platelike grains across the pressing axis or along the film casting direction. The Curie temperature of the samples has been determined to be T{sub C} = 1180 K. The samples have anisotropic electrical transport characteristics. Their piezoelectric constants d{sub 33} in directions perpendicular and parallel to the texture plane is 22 and 5 pC/N, respectively. The conclusion has been drawn that the synthesized materials are potentially attractive for producing high-temperature piezoelectric elements.

36 MATERIALS SCIENCE↗
NASA NTRS1983

Energy Recovery System

Cogeneration system is one in which the energy ordinarily wasted in an industrial process is recovered and reused to create a second form of energy. Such an energy recovery system is in use at Crane Company's plant in Ferguson, KY, which manufactures ceramic bathroom fixtures. Crane's system captures hot stack gases from the company's four ceramic kilns and uses them to produce electrical power for plant operations.

Source record↗
DOE OSTI2025

Maturing ceramic am and establishing a qualification framework at los alamos national laboratory

We successfully produced specimens made from porcelain resin (Tethon3D) in three different orientations (Z=45mm, Z=4mm and Z=3mm) without any cracks or delamination, both before and after post-processing. Four-point flexural tests were conducted on these specimens. Among the three orientations, specimens printed in the Z=4mm direction showed the best flexural strength, followed by Z=3mm and Z=45mm.

36 MATERIALS SCIENCE↗
NASA NTRS1983

Development of metallization process: FSA project, cell and module formation research area

This experiment is involved in determining bulk resistivity values for different past concentrations. Experiments were performed on silicon Cz and non-Cz wafers. To determine bulk resistivity more accurately, pastes were printed on ceramic substrates. Contact resistance was determined by measuring the voltage drop at constant current. Because of irregularity of grid profiles, accurate determination of cross sections of grid lines is difficult. The bulk resistivity is accurate when the resistivity of the metallization is much less than that of the layer beneath it. When the resistivity of the metal approaches that of the substrate, the actual resistivity will be larger than the measured value.

Garcia, A., III↗
NASA NTRS1989

Microgravity processing of particulate reinforced metal matrix composites

The elimination of such gravity-related effects as buoyancy-driven sedimentation can yield more homogeneous microstructures in composite materials whose individual constituents have widely differing densities. A comparison of composite samples consisting of particulate ceramics in a nickel aluminide matrix solidified under gravity levels ranging from 0.01 to 1.8 G indicates that the G force normal to the growth direction plays a fundamental role in determining the distribution of the reinforcement in the matrix. Composites with extremely uniform microstructures can be produced by these methods.

Morel, Donald E.↗
NASA NTRS2015

A Fully Non-Metallic Gas Turbine Engine Enabled by Additive Manufacturing

The Non-Metallic Gas Turbine Engine project, funded by NASA Aeronautics Research Institute, represents the first comprehensive evaluation of emerging materials and manufacturing technologies that will enable fully nonmetallic gas turbine engines. This will be achieved by assessing the feasibility of using additive manufacturing technologies to fabricate polymer matrix composite and ceramic matrix composite turbine engine components. The benefits include: 50 weight reduction compared to metallic parts, reduced manufacturing costs, reduced part count and rapid design iterations. Two high payoff metallic components have been identified for replacement with PMCs and will be fabricated using fused deposition modeling (FDM) with high temperature polymer filaments. The CMC effort uses a binder jet process to fabricate silicon carbide test coupons and demonstration articles. Microstructural analysis and mechanical testing will be conducted on the PMC and CMC materials. System studies will assess the benefits of fully nonmetallic gas turbine engine in terms of fuel burn, emissions, reduction of part count, and cost. The research project includes a multidisciplinary, multiorganization NASA - industry team that includes experts in ceramic materials and CMCs, polymers and PMCs, structural engineering, additive manufacturing, engine design and analysis, and system analysis.

Ceramics↗
DOE OSTI2018

Impedance Spectroscopy Study of the Electrical Properties of Cation-Substituted Barium Hexaaluminate Ceramics

We report on the behavior of frequency and temperature dependences of the impedance of a measuring cell in the form of a parallel-plate capacitor filled with barium hexaaluminate ceramics with four aluminum cations replaced by iron (BaO · 2Fe{sub 2}O{sub 3} · 4Al{sub 2}O{sub 3}). The measurements have been performed in the frequency range of 0.5–10{sup 8} Hz at temperatures of 20-375°C. A technique for determining the electrical properties of the investigated ceramics is proposed, which is based on an equivalent electric circuit allowing the recorded impedance spectra to be approximated with sufficiently high accuracy. The established spectral features are indicative of the presence of two electric relaxation times different from each other by three orders of magnitude. This fact is explained by the difference between the charge transport processes in the bulk of crystallites and thin intercrystallite spacers, for which the charge activation energies have been determined.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Influence of the Cobalt Content on the Strength Properties of Tungsten Carbide Ceramics under Dynamic Loads

Based on the registration and analysis of the full wave profiles, the Hugoniot elastic limit and spall strength of ceramics based on tungsten carbide with different cobalt content are measured. We also study the influence of the cobalt content on the mechanical characteristics of tungsten carbide such as hardness, fracture strength, Young’s modulus, shear modulus, and sound velocity. It is shown that in the process of spalling, the failure stresses grow and the dynamic elastic limit decreases almost linearly within the scatter of their values with growing cobalt content; moreover, the value of the Hugoniot elastic limit is abruptly practically halved as the cobalt content grows from 0 to 2 wt %.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS2008

Effect of Excess Lead and Bismuth Content on the Electrical Properties of High-Temperature Bismuth Scandium Lead Titanate Ceramics

Aeronautic and aerospace applications require piezoelectric materials that can operate at high temperatures. The air-breathing aeronautic engines can use piezoelectric actuators for active combustion control for fuel modulation to mitigate thermo-acoustic instabilities and/or gas flow control to improve efficiency. The principal challenge for the insertion of piezoelectric materials is their limitation for upper use temperature and this limitation is due low Curie temperature and increasing conductivity. We investigated processing, microstructure and property relationship of (1-x)BiScO3-(x)PbTiO3 (BS-PT) composition as a promising high temperature piezoelectric. The effect of excess Pb and Bi and their partitioning in grain boundaries were studied using impedance spectroscopy, ferroelectric, and piezoelectric measurement techniques. Excess Pb addition increased the grain boundary conduction and the grain boundary area (average grain size was 24.8 m, and 1.3 m for compositions with 0at.% and 5at.% excess Pb, respectively) resulting in ceramics with higher AC conductivity (tan d= 0.9 and 1.7 for 0at.% and 5at.% excess Pb at 350 C and at 10kHz) that were not resistive enough to pole. Excess Bi addition increased the resistivity (rho= 4.1x10(exp 10) Omega cm and 19.6 x10(exp 10) Omega.cm for compositions with 0at.% and 5at.% excess Bi, respectively), improved poling, and increased the piezoelectric coefficient from 137 to 197 pC/N for 5at.% excess Bi addition. In addition, loss tangent decreased more than one order of magnitude at elevated temperatures (greater than 300 C). For all compositions the activation energy of the conducting species was similar (approximately equal to 0.35-0.40 eV) and indicated electronic conduction.

Sehirlioglu, Alp↗
DOE OSTI2015

Characterization of high level nuclear waste glass samples following extended melter idling

The Savannah River Site Defense Waste Processing Facility (DWPF) melter was recently idled with glass remaining in the melt pool and riser for approximately three months. This situation presented a unique opportunity to collect and analyze glass samples since outages of this duration are uncommon. The objective of this study was to obtain insight into the potential for crystal formation in the glass resulting from an extended idling period. The results will be used to support development of a crystal-tolerant approach for operation of the high-level waste melter at the Hanford Tank Waste Treatment and Immobilization Plant (WTP). Two glass pour stream samples were collected from DWPF when the melter was restarted after idling for three months. The samples did not contain crystallization that was detectible by X-ray diffraction. Electron microscopy identified occasional spinel and noble metal crystals of no practical significance. Occasional platinum particles were observed by microscopy as an artifact of the sample collection method. Reduction/oxidation measurements showed that the pour stream glasses were fully oxidized, which was expected after the extended idling period. Chemical analysis of the pour stream glasses revealed slight differences in the concentrations of some oxides relative to analyses of the melter feed composition prior to the idling period. While these differences may be within the analytical error of the laboratories, the trends indicate that there may have been some amount of volatility associated with some of the glass components, and that there may have been interaction of the glass with the refractory components of the melter. These changes in composition, although small, can be attributed to the idling of the melter for an extended period. The changes in glass composition resulted in a 70-100 °C increase in the predicted spinel liquidus temperature (TL) for the pour stream glass samples relative to the analysis of the melter feed prior to the outage. This indicates that the potential for spinel crystallization increased as a result of idling for an extended period. However, the predicted TL of the pour stream glasses remained 150-200 °C below the mean melt pool temperature of about 1125 °C during the idling period. Given the change in predicted TL over the three month outage, the results indicate that it is important to have a thorough understanding of spinel crystallization within the melter for WTP to operate with a volume percent crystallization constraint. This knowledge will enable process control routines to be developed that avoid bulk crystallization in the melter and allow for recovery from off-normal events. The current WTP crystal-tolerant glass program will develop an improved understanding of spinel crystallization in the WTP melter to allow for operation at maximum waste loading in glass composition systems limited by predictions of spinel crystallization.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗