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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Local step-flow dynamics in thin film growth with desorption

Desorption of deposited species plays a role in determining the evolution of surface morphology during crystal growth when the desorption time constant is short compared with the time to diffuse to a defect site, step edge, or kink. However, experiments to directly test the predictions of these effects are lacking. Novel techniques such as in situ coherent x-ray scattering can provide significant new information. Herein we present x-ray photon correlation spectroscopy (XPCS) measurements during diindenoperylene (DIP) vapor deposition on thermally oxidized silicon surfaces. DIP forms a nearly complete two-dimensional first layer over the range of temperatures studied (40–120 ⁢°C), followed by mounded growth during subsequent deposition. Local step flow within mounds was observed, and we find that there was a terrace-length-dependent behavior of the step edge dynamics. This led to unstable growth with rapid roughening (β>0.5) and deviation from a symmetric error-function-like height profile. At high temperatures, the grooves between the mounds tend to close up leading to nearly flat polycrystalline films. In conclusion, numerical analysis based on a (1+1)-dimensional model suggests that terrace-length dependent desorption of deposited ad-molecules is an essential cause of the step dynamics, and it influences the morphology evolution.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Sulfurization as a promising surface passivation approach for both n- and p-type Si

Sulfur is shown to be an effective and promising surface passivation element for both n- and p-type Si wafers after reacting in dilute hydrogen sulfide gas (2 - 6% in argon) at 550°C. Effective minority carrier lifetimes of > 2 ms and > 0.25 ms are achieved for n- and p-type Si wafers, respectively, comparable to the industry standard thermal oxide and atomic layer deposited aluminum oxide passivation level. Surface characterization by x-ray photoelectron and emission spectroscopy reveals that sulfur is primarily bonded in a sulfide environment.

42 ENGINEERING↗
DOE OSTI2025

Corrosion of Rare-Earth Disilicate Environmental Barrier Coatings in Gas Turbine Environments—Part 2: Microstructure Model

A model for the volatization of ytterbium disilicate (YbDS) by water vapor is developed. The new model is based on the Deal & Grove theory of the thermal oxidation of silicon [1], generalized here to account for the multi-step, second-order chemical reactions for silica depletion, multi-component mixture effects, and the unsteady porous microstructural evolution of the corroded inner zone. With the new model, the fundamental kinetic rate and standard porous media parameters are determined using the atmospheric steam jet impingement experiment of Ridley & Opila [2] and compared to results from the original Deal & Grove model. Fixing the input parameters in each respective model, a validation study (blind prediction) is presented for the high Reynolds number (1 × 105) and high pressure (14.7 atm) burner rig experiment of Wan et al. [3].

Cha, Chong M [Rolls Royce]↗
DOE OSTI2022

Ultralow 0.034 dB/m loss wafer-scale integrated photonics realizing 720 million Q and 380 μW threshold Brillouin lasing

We demonstrate 0.034 dB/m loss waveguides in a 200-mm wafer-scale, silicon nitride (Si 3 N 4 ) CMOS-foundry-compatible integration platform. We fabricate resonators that measure up to a 720 million intrinsic Q resonator at 1615 nm wavelength with a 258 kHz intrinsic linewidth. This resonator is used to realize a Brillouin laser with an energy-efficient 380 µW threshold power. The performance is achieved by reducing scattering losses through a combination of single-mode TM waveguide design and an etched blanket-layer low-pressure chemical vapor deposition (LPCVD) 80 nm Si 3 N 4 waveguide core combined with thermal oxide lower and tetraethoxysilane plasma-enhanced chemical vapor deposition (TEOS–PECVD) upper oxide cladding. This level of performance will enable photon preservation and energy-efficient generation of the spectrally pure light needed for photonic integration of a wide range of future precision scientific applications, including quantum, precision metrology, and optical atomic clocks.

Liu, Kaikai (ORCID:0000000213609646)↗
DOE OSTI2020

Novel High Temperature Carbide and Boride Ceramics for Direct Power Extraction Electrode Applications. Final report

The current project aims to develop new carbide and boride ceramic materials that incorporate different metal elements (e.g., (Hf 1-x Zr x )B 2 , also called ceramic solid solutions) and understand the fundamental composition-processing-structure-property relationships for such materials. Specifically, nano powders and related nano-composites for selected mixed metal carbide and boride materials are synthesized from nano-scale mixed precursors obtained from solution-based processing via heat treatment in inert atmosphere. The obtained fine powders were then consolidated into dense ceramics via a novel flash sintering process. The mechanical properties and thermal oxidation resistance for the obtained materials were evaluated for these materials. It was found that different synthesis routes produced powders with somewhat different characteristics in terms of composition and microstructure, which then led to different properties for the final ceramics. The synthesis and processing methods demonstrated in this study might be adopted for developing other similar high temperature ceramics, while the mixed metal or solid solution ceramic materials obtained from this study might be used as hot electrodes for direction power extraction and other energy-related applications.

20 FOSSIL-FUELED POWER PLANTS↗
DOE OSTI2021

A New Route to Quantum-Scale Structures through a Novel Enhanced Germanium Diffusion Mechanism

This project sought to develop a fundamental understanding of the mechanisms underlying a newly observed enhanced germanium (Ge) diffusion process in silicon germanium (SiGe) semiconductor nanostructures during thermal oxidation. Using a combination of oxidationdiffusion experiments, high resolution imaging, and theoretical modeling, a model for the enhanced Ge diffusion mechanism was proposed. Additionally, a nanofabrication approach utilizing this enhanced Ge diffusion mechanism was shown to be applicable to arbitrary 3D shapes, leading to the fabrication of stacked silicon quantum dots embedded in SiGe nanopillars. A new wet etch-based method for preparing 3D nanostructures for highresolution imaging free of obscuring material or damage was also developed. These results enable a new method for the controlled and scalable fabrication of on-chip silicon nanostructures with sub-10 nm dimensions needed for next generation microelectronics, including low energy electronics, quantum computing, sensors, and integrated photonics.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Next Generation Fiber-Encapsulated Nanoscale Hybrid Materials for Direct Air Capture with Selective Water Rejection

Recently, NOHMs sorbents have been demonstrated to be highly stable and tunable for CO2 capture and have negligible vapor pressure, but their main drawbacks are high viscosity and high gas transfer limitation in their neat bulk phase. This project explored gas-assisted electrospinning processing coupled with promising encapsulation matrices such as Polymers with Intrinsic Microporosity (PIM-1) and polyacrylonitrile (PAN)/organopolysilizane (OPSZ) polymer/ceramic hybrid materials, which were demonstrated to be effective novel carriers for the active NOHMs sorbents. These encapsulation materials were evaluated by their thermal stability, hydrophobicity, permeability, and CO2 selectivity. The manufacturing parameters such as component composition and processing solvent were linked to bulk sorbent properties, e.g., surface area, pore volume, fiber thickness, capture capacity, capture kinetics, etc. These investigations resulted in fundamental knowledge and technical know-how that will be useful for scaling up the nanofiber mat contactor design. The encapsulation materials and design has been shown to not only increase the thermal oxidative stability of the NOHMs, but also yield significantly reduced pressure drop and increased performance of large modular air filters. 70 PAN: 30 OPSZ/NIPEI fibers exhibited the highest capture performance with 1.5 mmol CO2/g∙h kinetics the first hour under 100% CO2 condition, followed by 80 PAN: 20 OPSZ/NIPEI and 90 PAN: 10 OPSZ/NIPEI, while 90 PAN: 10 OPSZ/NIPEI fibers performed the best with 0.25 mmol CO2/g∙h of the initial kinetics under 400 ppm CO2 concentration. All the fabricated fibers demonstrated stable capture performances up to 15 cycles of adsorption and desorption. Using encapsulated NOHMs, the study found that the microwave could help regenerate the capture materials within 20 minutes without chemically degrading the materials. A high-level TEA/LCA study was performed to evaluate the feasibility of this technology at scale. These estimates show that the sorbent cost and environmental impact levels are comparable to other existing technologies. Overall, these findings increase the technological feasibility of using liquid-like, low vapor pressure NOHMs as a next generation sorbent for the direct air capture of CO2.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Comparison of Industrialized Late 20th Century Flowsheets for Reprocessing Used Nuclear Fuel

This study identified and compared three flowsheets for reprocessing used nuclear fuel (UNF) industrialized in plants in the United Kingdom (the Thermal Oxide Reprocessing Plant), France (UP2-800/UP3) and Japan (the Rokkasho Reprocessing Plant). The study also identified the major implications for a plant in the United States if it were initiated. All flowsheets employed the established Plutonium Uranium Reduction Extraction (PUREX) solvent extraction technology to separate uranium and plutonium from UNF dissolved in nitric acid. However, differences in the approaches to managing iodine-129, tritium and technetium were identified in the flowsheets. A US plant would also need to separate krypton-85 as well as iodine-129 and tritium for immobilization and disposal.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

Upcycling Polyethylene Waste Into Hybrid Graphitic Porous Carbon Materials Used in High-Performance Zinc-Ion Hybrid Capacitors

Polyethylene (PE) waste is a challenge to upcycle into useful materials because this plastic tends to decompose into volatile compounds when heated at relatively low temperatures. In this work, we report a chemical process that addresses this challenge by converting mixtures of linear low-density polyethylene (LLDPE), low-density polyethylene (LDPE), and high-density polyethylene (HDPE) waste into a hybrid graphitic porous carbon (HGPC) that can be used as a zinc-ion hybrid capacitor cathode. The process uses a low temperature thermal oxidation pre-treatment step, with assistance of an inert solid additive (KCl) to increase the effective surface area of the PE melt, to functionalize, cross-link, and stabilize the PE waste followed by carbonization and catalytic graphitization steps at higher temperatures with a potassium carbonate (K2CO3) catalyst. The PE waste derived HPGC (PW-HPGC) has a hybrid structure composed of graphene-like carbon nanosheets grown on the surface of carbon particles, high porosity with the Brunauer–Emmett–Teller (BET) specific surface area up to 1,763 m2g-1, and good graphitic degree with average Raman I2D/IG ratios of 0.53. When used as a cathode material for zinc-ion hybrid capacitors, this PW-HGPC exhibits an excellent specific capacity up to 126.7 mAhg-1 at high mass loading of 10 mgcm-2. Moreover, PW-HGPC exhibits remarkable cycling stability with capacity retention of >94% after 10,000 cycles at a current density of 2.0 A g-1.

hybrid graphitic porous carbon↗
DOE OSTI2020

Disulfonated Poly(arylene ether sulfone) Random Copolymers Containing Hierarchical Iptycene Units for Proton Exchange Membranes

Two series of disulfonated iptycene-based poly(arylene ether sulfone) random copolymers, i.e., TRP-BP (triptycene-based) and PENT-BP (pentiptycene-based), were synthesized via condensation polymerization from disulfonated monomer and comonomers to prepare proton exchange membranes (PEMs) for potential applications in electrochemical devices such as fuel cell. To investigate the effect of iptycene units on membrane performance, these copolymers were systematically varied in composition (i.e., iptycene content) and the degree of sulfonation (i.e., 30–50%), which were characterized comprehensively in terms of water uptake, swelling ratio, oxidative stability, thermal and mechanical properties, and proton conductivity at various temperatures. Comparing to copolymers without iptycene units, TRP-BP and PENT-BP ionomers showed greatly enhanced thermal and oxidative stabilities due to strong intra- and inter-molecular supramolecular interactions induced by hierarchical iptycene units. In addition, the introduction of iptycene units in general provides PEMs with exceptional dimensional stability of low volume swelling ratio at high water uptakes, which is ascribed to the supramolecularly interlocked structure as well as high fractional free volume of iptycene-based polymers. It is demonstrated that the combination of high proton conductivity and good membrane dimension stability is the result of the synergistic effects of multiple factors including free volume (iptycene content), sulfonation degree, hydrophobicity, and swelling behavior (supramolecular interactions).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Reduced metal nanocatalysts for selective electrochemical hydrogenation of biomass-derived 5-(hydroxymethyl)furfural to 2,5-bis(hydroxymethyl)furan in ambient conditions

Selective electrochemical hydrogenation (ECH) of biomass-derived unsaturated organic molecules has enormous potential for sustainable chemical production. However, an efficient catalyst is essential to perform an ECH reaction consisting of superior product selectivity and a higher conversion rate. Here, we examined the ECH performance of reduced metal nanostructures, i.e., reduced Ag (rAg) and reduced copper (rCu) prepared via electrochemical or thermal oxidation and electrochemical reduction process, respectively. Surface morphological analysis suggests the formation of nanocoral and entangled nanowire structure formation for rAg and rCu catalysts. rCu exhibits a slight enhancement in ECH reaction performance in comparison to the pristine Cu. However, the rAg exhibits more than two times higher ECH performance without compromising the selectivity for 5-(HydroxyMethyl) Furfural (HMF) to 2,5-bis(HydroxyMethyl)-Furan (BHMF) formation in comparison to the Ag film. Moreover, a similar ECH current density was recorded at a reduced working potential of 220 mV for rAg. This high performance of rAg is attributed to the formation of new catalytically active sites during the Ag oxidation and reduction processes. This study demonstrates that rAg can potentially be used for the ECH process with minimum energy consumption and a higher production rate.

2,5- bis(hydroxymethyl)furan (BHMF)↗
NASA NTRS1973

Thermally resistant polymers for fuel tank sealants

Imide-linked perfluoroalkylene ether polymers, that were developed for the high temperature fuel tank sealant application, are discussed. Modifications of polymer structure and properties were realized through use of a new aromatic dianhydride intermediate containing an ether-linked perfluoroalkylene segment. Tests of thermal, oxidative and hydrolytic stability, fuel resistance, and adhesion are discussed along with tensile strength and elongation results. Efforts to effect a low temperature condensation of amic acid prepolymer to form imide links inside are described.

Webster, J. A.↗
NASA NTRS1973

Flame retardant polyphosphazenes

Six polyphosphazene compositions were prepared by reaction of three bis-tertiary phosphines with two phenyl-s-triazine derived diazides. All six polyphosphazenes produced were completely characterized, four of them were furthermore subjected to isothermal gravimetric analysis, smoke density measurements, flammability and oxidative thermal degradation testing. The results of the characterization studies indicate that only low molecular weight oligomers, possibly of a cyclic structure, were obtained in the polymerization reactions. Despite this, however, two of the materials showed no weight loss after 96 hr at 200 C, one did not autoignite at 500 C in air, and all four self extinguished when exposed to a flame as soon as contact between flame and resin was lost. The only toxic decomposition products to be concerned about were found to be hydrogen cyanide and benzene. Under the conditions employed it was proven, however, that the quantities of toxic products are greatly reduced if no ignition takes place, e.g., if thermal decomposition proceeds at a sufficiently low rate.

Paciorek, K. L.↗
NASA NTRS1974

Polyimide resin composites via in situ polymerization of monomeric reactants

Thermo-oxidatively stable polyimide/graphite-fiber composites were prepared using a unique in situ polymerization of monomeric reactants directly on reinforcing fibers. This was accomplished by using an aromatic diamine and two ester-acids in a methyl alcohol solvent, rather than a previously synthesized prepolymer varnish, as with other A-type polyimides. A die molding procedure was developed and a composite property characterization conducted with high modulus graphite fiber tow. Flexure, tensile, compressive, and shear tests were conducted at temperatures from 72 to 650 F on laminates before and after exposures at the given temperatures in an air environment for times up to 1000 hours. The composite material was determined to be oxidatively, thermally, and hydrolytically stable.

Cavano, P. J.↗
NASA NTRS1975

Flame resistant nontoxic polymer development

A number of homopolymers, copolymers, and terpolymers were synthesized employing styrene and four derivatives of diphenyl-p-styrylphosphine. The various polymeric compositions were prepared by two processes, (1) monomer bulk polymerizations and (2) substitution of preformed polydiphenyl-p-styrylphosphine. Results indicate that the majority of the compositions exhibit superior melting and flame retardant characteristics as compared to polystyrene, but are inferior in molding and film forming capability. Terpolymerization appears to result in the materials with the best overall combination of properties. Toxicological evaluation of three representative basic compositions in the form of molded washers showed that no mortalities occurred among the test animals exposed to the products of the oxidative thermal decomposition of the three materials.

Paciorek, K. L.↗
NASA NTRS1975

Time dependent breakdown in silicon dioxide films

An investigation was conducted regarding the possible existence of a time-dependent breakdown mechanism in thermal oxides of the type used as gate oxide in MOS circuits. Questions of device fabrication are discussed along with details concerning breakdown measurements and the determination of C-V characteristics. A relatively large prebreakdown current observed in one of the cases is related to the time-dependent breakdown.

Svensson, C.↗