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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 415 records · Page 23
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Interaction of Molecular Hydrogen on α-Pu at 300 K: Nucleation of Hydrides and Pu-Catalyzed Carbides

An α-Pu sample was studied in its “as-received” and “sputtered” state by both X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). Analysis of the “as-received” surface indicated significant carbon and oxygen, with oxygen signal pertaining to plutonium dioxide (PuO 2 ) and sesquioxide (Pu 2 O 3 ). The “sputtered” clean metal surface was then dosed with hydrogen (H 2 ) gas at 300 K and found to nucleate hydride species (PuH x ). Interestingly, H 2 was observed to be critical for nucleation of carbides (Pu x C y ) by acting as a catalyst for Pu’s reaction with background gases. Because Pu metal has a high affinity for oxygen, reoxidation occurred under UHV, forming Pu x O y and disrupting both PuH x and Pu x C y growth. Observations from the experiments were modeled for the α-Pu(020) surface, illustrating the ability of H 2 to readily dissociate onto sputtered and speciated surfaces at 300 K. The projected density of states from these calculations were compared to experiments, showing good agreement between the Pu 5f, 6d, and 7s states and the H 1s, O 2p, and C 2p valence states. Overall, the above results indicated that the formed hydride layer is unstable at 300 K in UHV conditions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Density functional theory-based surrogate kinetic models for heterogeneous reactions of hydrocarbon intermediates on silicon carbide

The increasing demand for high-performance materials in advanced technologies highlights the importance of achieving a fundamental understanding and potential control of silicon carbide (SiC) deposition processes. However, existing models often lack sufficient theoretical detail, relying heavily on empirical data and offering limited predictive capability. In particular, the complex surface chemistry governing SiC growth remains poorly understood. This study addresses these challenges by employing density functional theory (DFT) to investigate key heterogeneous reactions involving hydrocarbon intermediates on SiC surfaces, including dehydrogenation, hydrogenation, and carbon deposition. Transition state searches were conducted to identify reaction pathways and energy barriers. While first-principles calculations offer high accuracy, they are computationally intensive. To extend the utility of these first-principles results, vibrational analyses were performed using phonon-based statistical thermochemistry to compute temperature-dependent reaction rates which were used to develop Arrhenius-type surrogate kinetic models. Furthermore, the resulting framework provides a more rigorous, physically grounded basis for integrating atomistic insights into continuum-scale modeling, ultimately enabling improved prediction and optimization of SiC film growth in high-performance material systems.

Density Functional Theory↗
DOE OSTI2020

Thermal shock resistance of multilayer silicon carbide receiver tubes for 800°C molten salt concentrating solar power application

CSP power tower receiver systems during rapid transient weather periods can be vulnerable to thermal shock conditions from rain that which can facilitate the onset of leaks and failures that can have catastrophic consequences. Silicon carbide (SiC) materials have attractive receiver application characteristics for being light weight, having high-strength and excellent thermal shock resistance performance which make them a particularly good fit for receiver absorber materials in CSP. In this investigation, the performance characteristics of Ceramic Tubular Products (CTP) SiC ceramic matrix composite (CMC), multilayered tubes were explored with respect to thermal shock performance for solar receiver applications in next generation CSP plants. Here, thermal shock testing was performed at the Sandia National Laboratories (SNL) Solar Furnace facility using a dynamic stage and thermal shock tube test setup. The tubes tested under incident solar heat flux of 100 W/cm2 were heated with inner tube temperatures reaching approximately 800 °C, with outer temperatures exceeding or just reaching 1000 El for the multilayer and monolithic SiC tubes respectively. The tubes were then quenched with simulated rain. The tubes were then cooled and subjected to hoop stress analysis using an Instron device to assess their subsequent mechanical strength. Furthermore, the on-sun study experimental results indicate an average of 24.2% and 97% higher hoop strength for the CMC tubes than those composed of monolithic SiC and aluminum oxide (A1203) respectively.

14 SOLAR ENERGY↗
DOE OSTI2024

Sound speed measurements in shock compressed cemented tungsten carbide: Evolution of elastic moduli with damage at pressures to 100 GPa

The motivation of the present study is to gain insights into the evolution of elastic properties of cemented tungsten carbides (WC) shock compressed to 100 GPa. Seven plate impact experiments—two front surface impact and five release wave overtake—are conducted to make simultaneous measurements of Hugoniot states and longitudinal sound speeds in shocked WC with 3.7wt.% cobalt binder. The sound speeds along with estimates for bulk sound speeds, obtained using the Birch–Murnaghan EoS, are analyzed to determine the elastic moduli—longitudinal, bulk, and shear—as a function of Hugoniot stress. The longitudinal and bulk sound speeds at Hugoniot states of interest are found to increase linearly with longitudinal stress. Consistent with the increase in sound speeds, the longitudinal and bulk moduli also increase with Hugoniot stress; however, the increase in longitudinal modulus is modest when compared to predictions of theoretical models that account for pressure and temperature dependence of elastic moduli, but with no damage. The shear moduli remain nearly constant at ~318 GPa over the range of Hugoniot states investigated. These values are, however, much lower than those predicted by the Steinberg–Guinan model with no damage. Poisson’s ratio decreases initially from its ambient value of 0.208 to ~0.199 for Hugoniot stress ≤10 GPa indicating consolidation of the WC microstructure with low initial stress; however, with an increase in Hugoniot stress to ~100 GPa, Poisson’s ratio increases to ~0.317, indicating degradation of shear moduli with increasing stress. The product of density and Grüneisen parameter (ρΓ), after an initial spike, remains nearly constant for volumetric strains ≥0.07. The maximum average temperature rise is estimated to be ~286°C at the highest Hugoniot stress employed in the study.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Multiscale Modeling of the Mechanical Response of Silicon Carbide Composite Within the Accelerated Fuel Qualification Framework

The accelerated fuel qualification (AFQ) framework has been used for the initial development of multiscale modeling of silicon carbide (SiC) fiber reinforced composite (SiC-SiC). The AFQ framework provides a methodology to leverage physics-informed multiscale modeling along with a reduced set of empirical test data to reduce the time and cost of licensing and qualification of new nuclear fuel systems while maintaining the overall nuclear power plant safety case. SiC-SiC is being proposed for in-core applications, most notably fuel cladding, for current and next-generation nuclear reactors because of its high temperature stability, irradiation tolerance, and ability to withstand many accident conditions. As these composites exhibit multiscale architectures and complex microstructure-based fracture mechanics, it is an appealing use case for the AFQ methodology. While the end goal of this work is a single multiscale model that can be used for predictive in-core performance, current focus is on the individual various length scale models. Four individual models have been initially developed from microscale to engineering system level to capture key physics-based effects across different length scales. These models include a microscale homogenized tow model, a mesoscale fast Fourier transform–based weave model that integrates the homogenized tow model, a mesoscale finite element–based weave model, and a system-level BISON fuel performance model. Results of these models have undergone an initial comparison with separate-effects test data showing a good match to experimental results. By using the AFQ framework during model development, several near-term benefits have been secured including a reduction in development time for the SiC-SiC cladding, more targeted irradiation testing, and a better understanding of uncertainty.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Investigation of Ion-Irradiated Beryllium Carbide (Be 2 C) for High-Temperature Nuclear Reactor Moderators

Beryllium carbide (Be 2 C) is an attractive alternative to graphite as a moderator material because of its high melting point, moderating efficiency, and theoretical environmental compatibility in MSRs, FHRs and HTGRs. However, its behavior under neutron irradiation is not yet known. Research on otherwise promising beryllium compounds are restricted because of the toxic nature of the material. For this work, a novel experiment was designed to safely irradiate beryllium-containing samples at The Michigan Ion Beam Laboratory (MIBL). Using this new capability, Be 2 C samples were irradiated with 9 MeV C 3+ ions from 2 dpa to 30 dpa, at temperatures up to 500 °C. Samples were characterized to investigate radiation tolerance. No evidence of phase precipitation, dislocation loops, or amorphization was observed up to 30 dpa, suggesting good radiation tolerance. One sample left in air for ~3 months oxidized slowly and lost structural integrity, while a sample kept in argon did not, suggesting that Be 2 C is not suitable for service in moist environments, but maintains its integrity in dry environments.

22 - GENERAL STUDIES OF NUCLEAR REACTORS↗
DOE OSTI2025

High pressure Raman spectroscopy of boron-rich boron carbides up to 50 GPa

We investigated the effects of increased boron content on the resistance to non-hydrostatic stress-induced (NHSI) local amorphous zones in boron-rich boron carbide (BxC) compounds. Using high-pressure Raman spectroscopy, we subjected B 4.3 C, B 6.4 C, and B 10.4 C to pressures up to 50 GPa and monitored their responses. Our results show that higher boron content delays the onset of NHSI local amorphous zone formation, shifting it from 35 GPa in B 4.3 C to approximately 50 GPa in B 10.4 C. This enhanced resistance is attributed to a reduction in the formation of the B 12 (CCC) polytype, which is susceptible to amorphization, and the greater flexibility of B–B–B chains. Furthermore, alternative mechanisms, such as boron vacancy-driven C–C bond formation, provide additional insights into defect-mediated structural changes that may influence the amorphization process. In conclusion, these findings highlight the dual role of boron content and defect mechanisms in improving the structural stability of B x C materials under extreme environments.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Ultrathick Boron Carbide Coatings for Nuclear Fusion Targets

Boron carbide is an attractive ablator for next-generation inertial confinement fusion (ICF) targets. Here we describe several aspects of our ongoing systematic studies of the deposition and processing of B 4 C coatings for ICF targets. We show that residual compressive stress in films can be reduced and the deposition rate increased by N-doping. Further, we also demonstrate successful Si substrate etching and surface polishing and discuss remaining challenges and offer potential solutions to the buildup of particulates in the deposition chamber during prolonged coating runs, control of nodular growth defects, and lateral nonuniformity of film properties for deposition conditions with relatively low target-to-substrate distances.

36 MATERIALS SCIENCE↗
DOE OSTI2025

High-Rate Sputter Deposition of Ultrathick Boron Carbide Coatings on Rolling Spherical Substrates

Amorphous boron carbide (B 4 C) is a promising next-generation ablator material for inertial confinement fusion. However, the deposition of ultrathick B4C coatings with submicron-scale density uniformity on spherical substrates, as required for ablator shell fabrication, remains challenging. Here, in this study, we use direct current magnetron sputtering to deposit B 4 C onto 2-mm-diameter Si spheres rolling in a dish-shaped substrate holder. High deposition rates of ∼3 μm/h are achieved. Ultrathick films have a columnar microstructure, with the column width determined by the density of nodular defects. Nodular defect nucleation is dominated by the pickup of particulates from the holder during substrate rolling. We demonstrate the fabrication of a hollow B 4 C spherical shell with a wall thickness of 80 μm. Also demonstrated is the laser machining of holes in the B 4 C coating, which is necessary for both the chemical removal of the Si template and the attachment of a fusion fuel fill tube.

Inertial confinement fusion targets↗
DOE OSTI2023

Atomistic simulation of brittle-to-ductile transition in silicon carbide embedded with nano-sized helium bubbles

In this study, the tensile response of cubic silicon carbide (SiC) bulk containing cavities (voids and He bubbles) has been investigated using molecular dynamic simulations. The formation of cavities in SiC leads to a significant degradation in the mechanical properties of SiC with more influence on material fracture than initial elastic deformation. The brittle-to-ductile transition occurs in cavity-embedded SiC as the pressure in He bubbles increases. This is associated with the deformation mechanism that bond breaking at a low He bubble pressure transfers to extensive dislocation activities at a higher He bubble pressure. The cavities can effectively concentrate stress around them in the direction perpendicular to the tension, which leads to preferred cracking in the region with a higher tensile stress. The failure mechanism as revealed by this study improves understanding of property degradation in SiC that may be useful for applications of SiC in advanced nuclear energy systems.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Evaluation of silicon carbide as a divertor armor material in DIII-D H-mode discharges

Silicon carbide (SiC) represents a promising but largely untested plasma-facing material (PFM) for next-step fusion devices. In this work, an analytic mixed-material erosion model is developed by calculating the physical (via SDTrimSP) and chemical (via empirical scalings) sputtering yield from SiC, Si, and C. The Si content in the near-surface SiC layer is predicted to increase during D plasma bombardment due to more efficient physical and chemical sputtering of C relative to Si. Silicon erosion from SiC thereby occurs primarily from sputtering of the enriched Si layer, rather than directly from the SiC itself. SiC coatings on ATJ graphite, manufactured via chemical vapor deposition, were exposed to repeated H-mode plasma discharges in the DIII-D tokamak to test this model. The qualitative trends from analytic modeling are reproduced by the experimental measurements, obtained via spectroscopic inference using the S/XB method. Quantitatively the model slightly under-predicts measured erosion rates, which is attributed to uncertainties in the ion impact angle distribution, as well as the effect of edge-localized modes. After exposure, minimal changes to the macroscopic or microscopic surface morphology of the SiC coatings were observed. Compositional analysis reveals Si enrichment of about 10%, in line with expectations from the erosion model. Extrapolating to a DEMO-type device, an order-of-magnitude decrease in impurity sourcing, and up to a factor of 2 decrease in impurity radiation, is expected with SiC walls, relative to graphite, if low C plasma impurity content can be achieved. Furthermore, these favorable erosion properties motivate further investigations of SiC as a low-Z, non-metallic PFM.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2025

Amorphization and siliconization of silicon carbide as a first wall material

The understanding and prediction of silicon carbide (SiC) material evolution exposed to SOL plasma conditions is of prime interest because SiC represents a promising main chamber wall plasma-facing material for next-step fusion devices (low hydrogenic diffusion, good mechanical and thermal properties under neutron irradiation). Gross and net Si erosion rates from SiC surfaces in contact with a well-diagnosed L-mode plasma in the DIII-D tokamak have been simulated and the surface concentrations of impurities have been tracked as a function of time. Coupled simulation of surface model and impurity transport demonstrates amorphization of crystalline SiC exposed to L-mode plasma due to the accumulation of displacement damages under ion irradiation. This affects the lifetime of SiC plasma facing components. Surface evolution is tightly coupled to impurity transport in the plasma and therefore needs to be integrated with impurity transport simulations to effectively predict Si erosion rates and sub-surface concentrations as a function of time. The simulation workflow couples a semi-analytical surface model to the impurity transport code GITR. The surface model is a homogeneous mixed-material model that tracks physical & chemical sputtering and reflection of impurities. Gross erosion is primarily influenced by the background plasma parameters and redeposition patterns are mainly influenced by the prompt redeposition due to the gyro-orbits of impurity ions. Although crystalline form of SiC is preferable for fusion wall applications because of resistance to neutron irradiation, this work indicates that crystalline SiC will undergo amorphization under D plasma contact with implications of higher sputtering and fuel retention. These results direct us to explore the effects of amorphization on crystalline SiC and further the physics basis of SiC usage as first wall material for fusion environments.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2023

An Effective Current Balancing Method for Inverters With Paralleled Silicon Carbide Power Modules

Silicon carbide (SiC) MOSFET has many superior characteristics in high power applications. Paralleling the SiC devices is an effective approach to increase the current capacity of the system, which also leads to current sharing issues. In this article, both transient and steady-state current sharing issues are studied for the high-power grid-tied inverters with paralleled SiC modules with an effective current balancing strategy proposed to address both issues simultaneously. The steady-state imbalance current due to the parameter mismatch is suppressed by the self-inductance of power cables used for paralleling connection. With the elimination of steady-state imbalance current, the transient imbalance current sensing is much simplified and can be realized by using low-cost current sensors. With the sensed imbalance current, a closed-loop control approach is proposed to adjust the modulation reference signal for each module to mitigate the remaining transient imbalance current. Furthermore, the proposed method is straightforward to implement with enhanced compatibility and flexibility compared to existing methods. Experimental studies are performed using inverters with 2 and 4 power modules paralleled in each phase to demonstrate the effectiveness of the proposed method.

42 ENGINEERING↗
DOE OSTI2020

Busbar Design and Optimization for Voltage Overshoot Mitigation of a Silicon Carbide High-Power Three-Phase T-Type Inverter

The silicon carbide (SiC) devices have faster switching speed than that of the conventional silicon (Si) devices, which however may cause excessive device voltage overshoot. Larger gate resistance can help to restrain the overshoot, it however slows down the switching speed and increases switching losses. There are other methods that can mitigate the voltage overshoot, e.g., using low-inductance busbars, adding snubber circuits, etc. In this article, the busbar design for a 250-kW SiC three-level T-type inverter is investigated. The current commutation loops (CCLs) are first analyzed using a single-phase equivalent circuit. Then the detailed busbar design methods, especially a 3-D busbar design concept, are proposed to select the optimal stacking order for the multilayer laminated busbar and to address constraints posed by the physical terminal arrangements of SiC modules and dc-link capacitors. The stray inductance in each CCL is extracted via a finite element analysis and validated on the actual inverter busbar prototypes using an impedance analyzer. To further minimize the busbar stray inductance, a hybrid busbar structure with printed circuit board based buffer circuit using high-frequency decoupling capacitors is designed and evaluated in this article. Lastly, the effectiveness of the designed busbars as well as the buffer circuit are validated using experimental studies.

42 ENGINEERING↗
DOE OSTI2020

Observed volatilization behavior of silicon carbide in flowing hydrogen above 2000 K

In this work, the intrinsic compatibility of silicon carbide (SiC) and hydrogen (H 2 ) at high temperatures (2000-2473 K) and pressure near one atmosphere was evaluated through a combination of thermodynamic calculations and hot hydrogen exposure testing. Thermodynamic calculations predict the decomposition of SiC in a hydrogen environment to form free silicon (Si) and free carbon (C). Free Si is predicted to vaporize from the surface as a volatile species, while free C may interact with H 2 to form the hydrocarbons CH 4 (T < 2100 K) or C 2 H 2 (T > 2100 K). Coupons of high purity chemical vapor deposition (CVD) β-SiC were exposed to slowly flowing hydrogen at temperatures ranging between 2000 and 2473 K. SiC experienced active attack as the result of H 2 exposure, exhibiting linear weight loss kinetics and an Arrhenius dependence of weight loss on exposure temperature. The linear volatilization constant was experimentally evaluated to correspond with an activation energy of 370 ± 18 kJ/mol. Due to the dependence of observed corrosion rates on gas velocity, corrosion of SiC in flowing H 2 was determined to be governed by external mass transfer of volatile Si species through the boundary layer. Experimentally derived mass losses were in good agreement with mass losses predicted by a boundary layer limited gas diffusion model.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Environmental stability of additively manufactured siliconized silicon carbide for applications in hybrid energy systems

A key consideration for the successful operation of hybrid energy systems will be the environmental stability of materials used for their construction, particularly when experiencing service environments containing water vapor at high temperatures. Here, we report results from the characterization of siliconized silicon carbide (Si-SiC) prepared via binder jet additive manufacturing and reactive silicon melt infiltration after being exposed to environments representative of those in solid oxide fuel cell (SOFC) anodes, and to exhaust gases inside a microturbine operating on natural gas. In both cases, it was found that oxide scales formed on the surface and that these scales were dense, continuous, and well-bonded to the substrates, although there was evidence of transverse and longitudinal cracking most likely as a result of mismatches in the thermal expansion of the scale and the substrate. Measured values of the thickness of the oxide scale were compared to those predicted by parabolic oxidation kinetics of silicon, but the potential effects of silica volatilization induced by water vapor, and silica reduction when exposed to hydrogen are discussed. The overall results showed that the oxide scale is expected to be protective under the conditions of hybrid power generation systems.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Selective laser sintering and spark plasma sintering of (Zr,Nb,Ta,Ti,W)C compositionally complex carbide ceramics

Abstract Two advanced manufacturing processes, spark plasma sintering (SPS) and selective laser sintering (SLS), have been developed for synthesis of (Zr,Nb,Ta,Ti,W)C compositionally complex carbide (CCC) via reactive sintering of a powder mixture of constitute monocarbides. X‐ray diffraction analysis confirmed that the single‐phase CCC can be formed by both SPS and SLS. While a homogenous microstructure with uniform metal element distributions was developed during SPS, three‐layer microstructures with a thin TiC‐rich layer and two TaC‐rich layers along with a TiO 2 ‐rich surface layer containing W nanoparticles were formed during SLS. In addition, cellular structures with W, Zr, and Ti element segregation and dislocations on cell boundaries were observed in the SLS‐CCC sample, indicating the effect of nonequilibrium conditions on microstructure formation during laser melting followed by rapid cooling and solidification process. Compared to the SPS‐CCC sample, the SLS‐CCC showed enhanced hardness and reduced thermal conductivity, which may be related to their unique cellular structures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Boron carbide films with reduced nodular defect density deposited by full-face erosion radio-frequency magnetron sputtering

Boron carbide coatings deposited by sputtering with conventional planar magnetrons exhibit nodular growth defects. Here, we demonstrate that the density of nodular defects in B 4 C films can be greatly reduced by using a full-face-erosion magnetron source that achieves a more uniform target erosion by sweeping the confining magnetic field over the target surface. Here, we systematically study properties of B 4 C films deposited on substrates with different tilt angles and demonstrate deposition of ultrathick films with compressive residual stress below 200MPa.

36 MATERIALS SCIENCE↗