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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Microclusters of Kinked Silicon Nanowires Synthesized by a Recyclable Iodide Process for High-Performance Lithium-Ion Battery Anodes

Silicon shows great promise as a high-capacity anode material for lithium-ion batteries. Nanostructuring silicon minimizes the impact of fracturing during charging and discharging. However, synthesizing nanostructured silicon typically requires complicated procedures with high manufacturing costs. Additionally, these complicated procedures typically have poor secondary particle formation, a requirement to achieve a high tap density. Here, a cost-effective synthesis procedure which generates nearly ideal secondary particle clusters of nanostructured silicon is developed. The cost-effectiveness is a result of the in operando generation of silicon iodide from iodine gas and low-grade silicon microparticle. Decomposition of silicon iodide into crystalline silicon and iodine gas enables recycling of the iodine gas, allowing for near full reutilization of iodine in the following cycles. Additionally, the optimal nanostructures and microstructures of silicon synthesized by the recyclable iodide decomposition reaction enables 83.6% capacity retention over 1000 cycles. The good performance is a result of well-maintained morphology during cycling, enabling reutilization of the solid electrolyte interphase.

25 ENERGY STORAGE↗
NASA NTRS1978

Floating substrate process: Large-area silicon sheet task low-cost solar array project

Supercooling of silicon-tin alloy melts was studied. Values as high as 78 C at 1100 C and 39 C at 1200 C were observed, corresponding to supersaturation parameter values 0.025 and 0.053 at 1050 C and 1150 C, respectively. The interaction of tin with silane gas streams was investigated over the temperature range 1000 to 1200 C. Single-pass conversion efficiencies exceeding 30% were obtained. The growth habit of spontaneously-nucleated surface growth was determined to be consistent with dendritic and web growth from singly-twinned triangular nucleii. Surface growth of interlocking silicon crystals, thin enough to follow the surface of the liquid and with growth velocity as high as 5 mm/min, was obtained. Large area single-crystal growth along the melt surface was not achieved. Small single-crystal surface growth was obtained which did not propagate beyond a few millimeters.

Garfinkel, M.↗
NASA NTRS1981

Process for purification of silicon

The purification of metallurgically pure silicon having a silicon content of more than 95% by weight is accomplished by leaching with an acidic solution which substantially does not attack silicon. A mechanical treatment leading to continuous particle size reduction of the granulated silicon to be purified is combined with the chemical purification step.

Rath, H. J.↗
NASA NTRS1982

Process Research On Polycrystalline Silicon Material (PROPSM)

The mechanisms limiting performance in polycrystalline silicon was determined. The initial set of experiments in this task entails the fabrication of cells of various thicknesses for four different bulk resistivities between 0.1 and 10 omega-cm. The results for the first two lots are presented.

Wohlgemuth, J. H.↗
NASA NTRS1982

Process Research on Polycrystalline Silicon Material (PROPSM)

The investigation of the performance limiting mechanisms in large grain (greater than 1-2 mm in diameter) polycrystalline silicon was continued by fabricating a set of minicell wafers on a selection of 10 cm x 10 cm wafers. A minicell wafer consists of an array of small (approximately 0.2 sq cm in area) photodiodes which are isolated from one another by a mesa structure. The junction capacitance of each minicell was used to obtain the dopant concentration, and therefore the resistivity, as a function of position across each wafer. The results indicate that there is no significant variation in resistivity with position for any of the polycrystalline wafers, whether Semix or Wacker. However, the resistivity of Semix brick 71-01E did decrease slightly from bottom to top.

Culik, J. S.↗
NASA NTRS1983

Process Research on Polycrystalline Silicon Material (PROPSM)

The performance limiting mechanisms in large grain (greater than 1-2 mm in diameter) polycrystalline silicon was investigated by measuring the illuminated current voltage (I-V) characteristics of the minicell wafer set. The average short circuit current on different wafers is 3 to 14 percent lower than that of single crystal Czochralski silicon. The scatter was typically less than 3 percent. The average open circuit voltage is 20 to 60 mV less than that of single crystal silicon. The scatter in the open circuit voltage of most of the polycrystalline silicon wafers was 15 to 20 mV, although two wafers had significantly greater scatter than this value. The fill factor of both polycrystalline and single crystal silicon cells was typically in the range of 60 to 70 percent; however several polycrystalline silicon wafers have fill factor averages which are somewhat lower and have a significantly larger degree of scatter.

Culik, J. S.↗
NASA NTRS1984

Process Research of Polycrystalline Silicon Material (PROPSM)

An investigation was begun into the usefulness of molecular hydrogen annealing on polycrystalline solar cells. No improvement was realized even after twenty hours of hydrogenation. Thus, samples were chosen on the basis of: (1) low open circuit voltage; (2) low shunt conductance; and (3) high light generated current. These cells were hydrogenated in molecular hydrogen at 300 C. The differences between the before and after hydrogenation values are so slight as to be negligible. These cells have light generated current densities that indicate long minority carrier diffusion lengths. The open circuit voltage appears to be degraded, and quasi-neutral recombination current enhanced. Therefore, molecular hydrogen is not usful for passivating electrically active defects.

Culik, J. S.↗
NASA NTRS1985

Process Research on Polycrystalline Silicon Material (PROPSM)

Results of hydrogen-passivated polycrysalline silicon solar cell research are summarized. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystalline silicon solar cells.

Culik, J. S.↗
NASA NTRS1985

Studies of the Crystallization Process of Aluminum-Silicon Alloys Using a High Temperature Microscope

It is shown that primary silicon crystals grow polyhedral in super-eutectic AlSi melts and that phosphorus additives to the melt confirm the strong seeding capacity. Primary silicon exhibits strong dendritic seeding effects in eutectic silicon phases of various silicon alloys, whereas primary aluminum does not possess this capacity. Sodium addition also produces a dendritic silicon network growth in the interior of the sample that is attributed to the slower silicon diffusion velocity during cooling.

Justi, S.↗
NASA NTRS2015

Silicon Carbide (SiC) Power Processing Unit (PPU) for Hall Effect Thrusters

Arkansas Power Electronics International (APEI), Inc., is developing a high-efficiency, radiation-hardened 3.8-kW SiC power supply for the PPU of Hall effect thrusters. This project specifically targets the design of a PPU for the high-voltage Hall accelerator (HiVHAC) thruster, with target specifications of 80- to 160-V input, 200- to 700-V/5A output, efficiency greater than 96 percent, and peak power density in excess of 2.5 kW/kg. The PPU under development uses SiC junction field-effect transistor power switches, components that APEI, Inc., has irradiated under total ionizing dose conditions to greater than 3 MRad with little to no change in device performance.

Reese, Bradley↗
DOE OSTI2025

Prediction of Silicon Content in a Blast Furnace via Machine Learning: A Comprehensive Processing and Modeling Pipeline

Silicon content plays an important role in determining the operational efficiency of blast furnaces (BFs) and their downstream processes in integrated steelmaking; however, existing sampling methods and first-principles models are somewhat limited in their capability and flexibility. Current data-based prediction models primarily rely on a limited set of manually selected furnace parameters. Additionally, different BFs present a diverse set of operating parameters and state variables that are known to directly influence the hot metal’s silicon content, such as fuel injection, blast temperature, and raw material charge composition, among other process variables that have their own impacts. The expansiveness of the parameter set adds complexity to parameter selection and processing. This highlights the need for a comprehensive methodology to integrate and select from all relevant parameters for accurate silicon content prediction. Providing accurate silicon content predictions would enable operators to adjust furnace conditions dynamically, improving safety and reducing economic risk. To address these issues, a two-stage approach is proposed. First, a generalized data processing scheme is proposed to accommodate diverse furnace parameters. Second, a robust modeling pipeline is used to establish a machine learning (ML) model capable of predicting hot metal silicon content with reasonable accuracy. The method employed herein predicted the average Si content of the upcoming furnace cast with an accuracy of 91% among 200 target predictions for a specific furnace provisioned by the XGBoost model. This prediction is achieved using only the past shift’s operating conditions, which should be available in real time. This performance provides a strong baseline for the modeling approach with potential for further improvement through provision of real-time features.

Chemistry↗
NASA NTRS1982

Producing Cryolite From Waste Sodium Fluoride

Simple chemical process makes synthetic cryolite by utilizing byproducts of one kind of silicon production process. Potential result of commercialization could be economic benefit to silicon industry or to aluminum industry, in which cryolite is used as flux.

Bartlett, R. W.↗
DOE OSTI2023

Ultra‐Low‐Loss Silicon Nitride Photonics Based on Deposited Films Compatible with Foundries

Abstract The fabrication processes of silicon nitride (Si 3 N 4 ) photonic devices used in foundries require low temperature deposition, which typically leads to high propagation losses. Here, it is shown that propagation loss as low as 0.42 dB cm −1 can be achieved using foundry compatible processes by solely reducing waveguide surface roughness. By postprocessing the fabricated devices using rapid thermal anneal (RTA) and furnace anneal, propagation losses down to 0.28 dB cm −1 and 0.06 dB cm −1 , respectively, are achieved. These low losses are comparable to the conventional devices using high temperature, high‐stress LPCVD films. The dispersion of the devices is also tuned, and it is proved that these devices can be used for linear and nonlinear applications. Low threshold parametric oscillation, broadband frequency combs, and narrow‐linewidth laser are demonstrated. This work demonstrates the feasibility of scalable photonic systems based on foundries.

Ji, Xingchen↗
NASA NTRS1980

Tribological properties of silicon carbide in metal removal process

Material properties are considered as they relate to adhesion, friction, and wear of single crystal silicon carbide in contact with metals and alloys that are likely to be involved in a metal removal process such as grinding. Metal removal from adhesion between sliding surfaces in contact and metal removal as a result of the silicon carbide sliding against a metal, indenting into it, and plowing a series of grooves or furrows are discussed. Fracture and deformation characteristics of the silicon carbide surface are also covered. The adhesion, friction, and metal transfer to silicon carbide is related to the relative chemical activity of the metals. The more active the metal, the higher the adhesion and friction, and the greater the metal transfer to silicon carbide. Atomic size and content of alloying elements play a dominant role in controlling adhesion, friction, and abrasive wear properties of alloys. The friction and abrasive wear (metal removal) decrease linearly as the shear strength of the bulk metal increases. They decrease as the solute to solvent atomic radius ratio increases or decreases linearly from unity, and with an increase of solute content. The surface fracture of silicon carbide is due to cleavages of 0001, 10(-1)0, and/or 11(-2)0 planes.

Miyoshi, K.↗
NASA NTRS1980

Characterization of silicon-gate CMOS/SOS integrated circuits processed with ion implantation

The double layer metallization technology applied on p type silicon gate CMOS/SOS integrated circuits is described. A smooth metal surface was obtained by using the 2% Si-sputtered Al. More than 10% probe yield was achieved on solar cell controller circuit TCS136 (or MSFC-SC101). Reliability tests were performed on 15 arrays at 150 C. Only three arrays failed during the burn in, and 18 arrays out of 22 functioning arrays maintained the leakage current below 100 milli-A. Analysis indicates that this technology will be a viable process if the metal short circuit problem between the two metals can be reduced.

Woo, D. S.↗
NASA NTRS1989

Effect of processing on fracture toughness of silicon carbide as determined by Vickers indentations

Several alpha-SiC materials were processed by hot isostatic pressing (HIPing) and by sintering an alpha-SiC powder containing boron and carbon. Several beta-SiC materials were processed by HIPing a beta-SiC powder with boron and carbon additions. The fracture toughnesses K(sub 1c) of these beta- and alpha-SiC materials were estimated from measurements of Vickers indentations. The three formulas used to estimate K(sub 1c) from the indentation fracture patterns resulted in three ranges of K(sub 1c) estimates. Furthermore, each formula measured the effects of processing differently. All three estimates indicated that fine-grained HIPed alpha-SiC has a higher K(sub 1c) than coarsed-grained sintered alpha-SiC. Hot isostatically pressed beta-SiC, which had an ultrafine grain structure, exhibited a K(sub 1c) comparable to that of HIPed alpha-SiC.

Dannels, Christine M.↗
DOE OSTI2025

Additive manufacturing of high‐density silicon carbide ceramics through post‐processing spark plasma sintering

This research advances the field of additive manufacturing (AM) of silicon carbide (SiC) ceramics by integrating spark plasma sintering (SPS) to enhance material density, mechanical strength, and thermal properties. Traditional AM techniques struggle to achieve the high‐density SiC required for demanding applications, such as aerospace engineering, where high thermal conductivity and mechanical strength are paramount. Here, our study addresses these challenges by incorporating SPS as a post‐processing step, achieving near‐theoretical maximum densities and significantly reducing porosity, thereby resulting in outstanding thermal conductivity in SiC ceramics. We developed a specialized SiC ink optimized for 3D printing, ensuring structural integrity after deposition through tailored rheological properties. The application of SPS facilitates rapid, uniform sintering, essential for attaining superior density, mechanical properties, and thermal performance. Our experimental results, confirmed through scanning electron microscopy analysis, demonstrate significant microstructural properties, mechanical strength, and thermal conductivity, showcasing the effectiveness of integrating SPS in AM processes. This innovative approach not only expands the capabilities of AM in producing complex, high‐density ceramic structures but also broadens the potential applications of SiC in demanding environments.

36 MATERIALS SCIENCE↗