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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 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Shifting the MLCT of d 6 metal complexes to the red and NIR

Light-active d 6 -coordination compounds hold great promise for light energy conversion, sensors and therapeutic applications. However, the activity in the red-to-NIR spectral region is highly desirable to convert solar light more efficiently, use low-cost red-light sources and activate these chromophores in biological tissue environment. Due to their versatility, tunability and broad intense absorption, d 6 -coordination compounds with metalto-ligand charge transfer (MLCT) transitions are especially interesting. This review article offers a comprehensive collection of strategies to tune MLCT excited states in d 6 metal complexes and gives insights on group 6 to group 9 transition metals and their respective state-of-the-art MLCT engineering towards red-shifted absorption and emission properties with long-lived excited states. Strategies comprise lowering the π* level of the ligands, destabilizing and mixing of the metal-based HOMO, switching within a group of transition metals, matrix effects and insights into dealing with excited state deactivation in the context of the energy gap law.

Metal to ligand charge transfer (MLCT)↗
DOE OSTI2018

Defect engineering of mesoporous nickel ferrite and its application for highly enhanced water oxidation catalysis

Spinel nickel ferrite (NiFe 2 O 4 ) emerges as a promising low-cost catalyst for water splitting but it usually shows low catalytic activity because of its limited number of active sites and poor conductivity. For the first time, herein we have successfully overcome its weaknesses using defect engineering approach by creating oxygen vacancies in NiFe 2 O 4 . The existence of oxygen vacancy not only shifts up the d-band center, strengthens the adsorption of H 2 O, and thus provides more active catalytic sites, but also tunes the electron configuration and creates massive number of defective donor states in the band gap to facilitate charge transfer processes. The optimal defective catalyst showed significantly enhanced catalytic OER performance with an OER overpotential as low as 0.35 V at 10 mA cm -2 and a Tafel slope of only ~40 mV dec -1 . Moreover, the impressive specific mass and area current density of 17.5 A g -1 and 0.106 A m -2 at 1.58 V vs. Finally, RHE have been achieved, which are ~23 and ~36 times higher than that of defect-free counterpart, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Defect Engineering of Earth-Abundant Solar Absorbers BiSI and BiSeI

Bismuth-based solar absorbers have recently garnered attention due to their promise as cheap, nontoxic, and efficient photovoltaics. To date, however, most show poor efficiencies far below those seen in commercial technologies. In this work, we investigate two such promising materials, BiSI and BiSeI, using relativistic first-principles methods with the aim of identifying their suitability for photovoltaic applications. Both compounds show excellent optoelectronic properties with ideal band gaps and strong optical absorption, leading to high predicted device performance. Using defect analysis, we reveal the electronic and structural effects that can lead to the presence of deep trap states, which may help explain the prior poor performance of these materials. Crucially, detailed mapping of the range of experimentally accessible synthesis conditions allows us to provide strategies to avoid the formation of killer defects in the future.

14 SOLAR ENERGY↗
DOE OSTI2018

Paschen's curve in microgaps with an electrode surface protrusion

Paschen's curve in microgaps with a hemi-ellipsoidal protrusion on the electrode surface is examined using a two-dimensional fluid model. The breakdown voltage is identified when the discharge enters the subnormal region, according to voltage-current characteristics. It is discovered that the breakdown in a microgap with a surface protrusion on the electrode can result in a combined Paschen's curve, which transits from long-gap (distance between the cathode and anode without the presence of protrusion) behavior at low pressure to short-gap (distance between the protrusion apex to the opposite electrode) behavior at high pressure. As gas pressure decreases, the length of the optimal discharge path increases, automatically moving from the top of the protrusion to its side surface and then to the wider non-protrusion electrode gap. The effects of the protrusion height and radius as well as the discharge polarity on the Paschen's curve are viewed in detail. The effects of the protrusion aspect ratio on field enhancement are also considered. Our report provides insights into the design of microgaps with controlled breakdown voltage across many orders in pressure via engineered electrode morphology.

42 ENGINEERING↗
DOE OSTI2025

A Design for Remanufacturing Framework Incorporating Identification, Evaluation, and Validation: A Case Study of Hydraulic Manifold

In recent years, academic researchers and engineers in the industry have widely recognized the necessity of integrating remanufacturing considerations into product design iterations to advance sustainability objectives. Acknowledging the importance of design for remanufacturing (DfRem), efforts were made to develop tools and guidelines that could be implemented in practice. However, such methods largely rely upon experiential insights and qualitative assessments, leaving a gap in the ability to quantitatively assess the economic and environmental impacts of design choices. To bridge this gap, we investigate existing efforts and present a framework for DfRem that integrates established design and remanufacturing practices into a cohesive workflow with quantitative assessments. To demonstrate its efficacy for making practical design changes for remanufacturing, we apply the framework to a hydraulic manifold in a transmission system for heavy-duty tractors. Through this industry-relevant case study, we focus on showcasing the practical utility of our framework. Based on the identified design modifications from remanufacturability analysis, we estimate the reductions in life cycle costs, energy consumption, and emissions. Afterward, the modifications are tested using physical experiments with plans for integration into future iterations of the hydraulic manifold design and production. Here, we anticipate this framework can illustrate the process of remanufacturing that ensures improvements in sustainability while maintaining performance and reliability standards.

design for X↗
DOE OSTI2017

Modeling defect and fission gas properties in U-Si fuels

Uranium silicides, in particular U 3 Si 2 , are being explored as an advanced nuclear fuel with increased accident tolerance as well as competitive economics compared to the baseline UO2 fuel. They benefit from high thermal conductivity (metallic) compared to UO 2 fuel (insulator or semi-conductor) used in current Light Water Reactors (LWRs). The U-Si fuels also have higher fissile density. In order to perform meaningful engineering scale nuclear fuel performance simulations, the material properties of the fuel, including the response to irradiation environments, must be known. Unfortunately, the data available for USi fuels are rather limited, in particular for the temperature range where LWRs would operate. The ATF HIP is using multi-scale modeling and simulations to address this knowledge gap.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Modeling defect and fission gas properties in U-Si fuels

Uranium silicides, in particular U 3 Si 2 , are being explored as an advanced nuclear fuel with increased accident tolerance as well as competitive economics compared to the baseline UO 2 fuel. They benefit from high thermal conductivity (metallic) compared to UO 2 fuel (insulator or semi-conductor) used in current Light Water Reactors (LWRs). The U-Si fuels also have higher fissile density. In order to perform meaningful engineering scale nuclear fuel performance simulations, the material properties of the fuel, including the response to irradiation environments, must be known. Unfortunately, the data available for USi fuels are rather limited, in particular for the temperature range where LWRs would operate. The ATF HIP is using multi-scale modeling and simulations to address this knowledge gap.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1992

Development of Thin Film Thermocouples on Ceramic Materials for Advanced Propulsion System Applications

Thin film thermocouples have been developed for use on metal parts in jet engines to 1000 c. However, advanced propulsion systems are being developed that will use ceramic materials and reach higher temperatures. The purpose of this work is to develop thin film thermocouples for use on ceramic materials. The new thin film thermocouples are Pt13Rh/Pt fabricated by the sputtering process. Lead wires are attached using the parallel-gap welding process. The ceramic materials tested are silicon nitride, silicon carbide, aluminum oxide, and mullite. Both steady state and thermal cycling furnace tests were performed in the temperature range to 1500 C. High-heating-rate tests were performed in an arc lamp heat-flux-calibration facility. The fabrication of the thin film thermocouples is described. The thin film thermocouple output was compared to a reference wire thermocouple. Drift of the thin film thermocouples was determined, and causes of drift are discussed. The results of high heating rate tests up to 2500 C/sec are presented. The stability of the ceramic materials is examined. It is concluded that Pt13Rh/Pt thin film thermocouples are capable of meeting lifetime goals of 50 hours or more up to temperature of 1500 C depending on the stability of the particular ceramic substrate.

Holanda, R.↗
DOE OSTI2019

Understanding the Role of Oxygen Vacancy in Visible–Near-Infrared-Light-Absorbing Ferroelectric Perovskite Oxides Created by Off-Stoichiometry

Recently, the visible or even-to-near-infrared light absorbing perovskite ABO 3 solid state solutions, show promising application in solar cells and multienergy harvesters or sensors by simultaneously introducing transition metal and oxygen vacancies. However, the existence of oxygen vacancies fundamentally causes photoexcited carrier trapping and large leakage current. Therefore, it is still challenging to limit oxygen vacancies while maintaining low bandgap and high ferroelectricity. Here, an efficient charge compensation strategy by finely adjusting the ion ratio on the A-site to obtain an oxygen-vacancy-free relaxer ferroelectric is demonstrated in the system of Na x BiyTiO 3 -BaTi 0.5 Ni 0.5 O 3 , where y > x. It is found that the oxygen-vacancy-free composition still yields strong visible-near-infrared-light-absorbing and enhanced photoresponse, in which the photocurrent density doubles from approximate to 0.16 to approximate to 0.32 mu A cm -2 . A new bandgap tuning mechanism is proposed according to the local structural information of Ni ions obtained via extended X-ray absorption fine structure. Moreover, this work succeeds in establishing the relationship between the concentration of oxygen vacancies and ferroelectric/piezoelectric properties of Na x BiyTiO 3 -BaTi 0.5 Ni 0.5 O 3 . Finally, this research points out a promising route to the material design of bandgap engineered ferroelectrics with controlled defects, which is expected to benefit a wide range of functional energy conversion devices.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Heat Transfer Coefficient at Cast-Mold Interface During Centrifugal Casting: Calculation of Air Gap

During centrifugal casting, the thermal resistance at the cast-mold interface represents a main blockage mechanism for heat transfer. In addition to the refractory coating, an air gap begins to form due to the shrinkage of the casting and the mold expansion, under the continuous influence of strong centrifugal forces. Here, the heat transfer coefficient at the cast-mold interface h has been determined from calculations of the air gap thickness d{sub a} based on a plane stress model taking into account thermoelastic stresses, centrifugal forces, plastic deformations, and a temperature-dependent Young’s modulus. The numerical approach proposed here is rather novel and tries to offer an alternative to the empirical formulas usually used in numerical simulations for a description of a time-dependent heat transfer coefficient h. Several numerical tests were performed for different coating thicknesses d{sub C}, rotation rates Ω, and temperatures of solidus T{sub sol}. Results demonstrated that the scenario at the interface is unique for each set of parameters, hindering the possibility of employing empirical formulas without a preceding experiment being performed. Initial values of h are simply equivalent to the ratio of the coating thermal conductivity and its thickness (~ 1000 Wm{sup −2} K{sup −1}). Later, when the air gap is formed, h drops exponentially to values at least one order of magnitude smaller (~ 100 Wm{sup −2} K{sup −1}).

36 MATERIALS SCIENCE↗
DOE OSTI2022

Knowledge-matching based computational framework for genome-scale metabolic model refinement

Genome-scale metabolic models (GEMs) are mathematically structured knowledge base reconstructed from annotated genome of different organisms. With the advancement of next-generation sequencing technology, many organisms have had their genomes sequenced. However, obtaining a high-quality GEM is highly time-consuming, even with the introduction of several genome-scale reconstruction tools that offer automated draft network generation and gap filling. It has been recognized that the iterative process of manual curation and refinement is the limiting step of GEM development, and how to expedite the GEM refinement is still an open question. As cellular metabolism is a complex system with very high degree of freedom and redundancy, the principles and techniques developed in process systems engineering can be adapted to expedite GEM refinement. In this paper we present a knowledge-matching based computation framework for GEM refinement, and demonstrate the effectiveness of the proposed solution using the refinement of a GEM for Clostridium tyrobutyricum.

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

Dynamical responses of constrained pipe conveying fluids and its dependence on the modeling of the contact force

Accurately modeling the impact force used in the analysis of loosely constrained cantilevered pipes conveying fluid is imperative. If little information is known of the motion-limiting constraints used in experiments, the analysis of the system may yield inaccurate predictions. Here in this work, multiple forcing representations of the impact force are defined and analyzed for a cantilevered pipe that conveys fluid. Depending on the representation of the impact force, the dynamics of the pipe can vary greatly when only the stiffness of the constraints is known from experiments. Three gap sizes of the constraints are analyzed, and the representation of the impact force used to analyze the system is found to significantly affect the response of the pipe at each gap size. An investigation on the effects of the vibro-impact force representation is performed through using basin of attraction analysis and nonlinear characterization of the system’s response.

42 ENGINEERING↗
DOE OSTI2015

Continuously adjustable, molecular-sieving “gate” on 5A zeolite for distinguishing small organic molecules by size

Zeolites/molecular sieves with uniform, molecular-sized pores are important for many adsorption-based separation processes. Pore size gaps, however, exist in the current zeolite family. This leads to a great challenge of separating molecules with size differences at ~0.01 nm level. Here, we report a novel concept, pore misalignment, to form a continuously adjustable, molecular-sieving “gate” at the 5A zeolite pore entrance without sacrificing the internal capacity. Misalignment of the micropores of the alumina coating with the 5A zeolite pores was related with and facilely adjusted by the coating thickness. For the first time, organic molecules with sub-0.01 nm size differences were effectively distinguished via appropriate misalignment. Lastly, this novel concept may have great potential to fill the pore size gaps of the zeolite family and realize size-selective adsorption separation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Elucidating molecular scale interactions underlying the freezing behavior of salt solutions in silica nanopores

Elucidating the influence of nanoscale confinement on the freezing behavior of salt solutions is of fundamental interest to environmental security and materials science and engineering. Specific structural information such as the coordination environment of ions in confined aqueous medium, effects on the extended hexagonal network of water molecules and their mutual non-bonding interactions in confinement are sparse in the literature along with the change in the dynamical characteristics of water in the presence of ions. To address these knowledge gaps, the current study is focused on investigating the influence of reduced dimensionality arising from nanoscale confinement on the structural evolution of salt solutions on freezing and the associated fluid–surface interactions. In this regard, operando wide-angle X-ray scattering (WAXS) measurements and classical molecular dynamics (MD) simulations are conducted with water and 0.5 M CaCl 2 , MgCl 2 and KCl solutions confined in 4 nm sized SBA-15 silica pores upon cooling from 300 K to 200 K. The freezing point of the salt solutions is depressed to 235 K which is about 10 K lower than that of confined water. The translational dynamics of confined salt solutions indicates shifts in the fragile-to-strong dynamical crossover to a lower temperature compared to pure water. The strong electrostatic attraction between the cations and the surrounding water molecules contributes to the freezing point depression in confined salt solutions. These insights unlock the molecular-scale basis and mechanisms underlying the freezing behavior of confined salt solutions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Memristive devices from ZnO nanowire bundles and meshes

Here, we report two types of memristive devices made of ZnO nanowire assemblies and Ag electrodes: nanowire-bundle and nanowire-mesh memristors. Although constructed with the same materials, these devices exhibit different characteristics. Nanowire-bundle memristors have small On/Off ratios and feature stable hysteresis under X-ray irradiation. Nanowire-mesh memristors show large On/Off ratios and multiple distinct states. We attribute the switching in bundle nanowires to the modification of the Schottky barrier by the mobile Ag ions and the stability of hysteresis to the ability of the bundles to retain Ag in the alleys between nanowires, as confirmed by first-principles calculations and energy dispersive x-ray measurements. For nanowire-mesh memristors, the high On/Off ratio leads us to attribute the switching mechanism to the formation and dissolution of Ag bridges in the nano-gaps at the intersections of nanowires.

42 ENGINEERING↗
DOE OSTI2023

Unveiling the structure and electronic characteristics of amorphous GeS for high performance threshold switching

Ovonic threshold switching selectors are widely studied owing to the essential application in high density phase-change memory. Amorphous GeS is proposed as a potential candidate for the excellent performance. However, the knowledge of amorphous GeS is still insufficient up to date. Here, we have studied the structure and electronic characteristics of GeS in the amorphization process, by using ab initio molecular dynamics simulations. The results indicate that the amorphous GeS is mainly made up of Ge–S bonds. The Ge- and S-centered clusters are dominantly in the form of octahedral structures in liquid GeS. Furthermore, during the amorphization process, most of Ge-centered clusters become highly coordinated octahedrons while a small number of Ge-centered clusters change to tetrahedrons, and the S-centered clusters deviate from the octahedral structure gradually. In addition, the large bandgap and the relatively small mid-gap states in amorphous GeS lead to a high switching voltage.

42 ENGINEERING↗
DOE OSTI2013

Safety of Hydrogen Systems Installed in Outdoor Enclosures

The Hydrogen Safety Panel brings a broad cross-section of expertise from the industrial, government, and academic sectors to help advise the U.S. Department of Energy’s (DOE) Fuel Cell Technologies Office through its work in hydrogen safety, codes, and standards. The Panel’s initiatives in reviewing safety plans, conducting safety evaluations, identifying safety-related technical data gaps, and supporting safety knowledge tools and databases cover the gamut from research and development to demonstration and deployment. The Panel’s recent work has focused on the safe deployment of hydrogen and fuel cell systems in support of DOE efforts to accelerate fuel cell commercialization in early market applications: vehicle refueling, material handling equipment, backup power for warehouses and telecommunication sites, and portable power devices. This paper resulted from observations and considerations stemming from the Panel’s work on early market applications. This paper focuses on hydrogen system components that are installed in outdoor enclosures. These enclosures might alternatively be called “cabinets,” but for simplicity, they are all referred to as “enclosures” in this paper. These enclosures can provide a space where a flammable mixture of hydrogen and air might accumulate, creating the potential for a fire or explosion should an ignition occur. If the enclosure is large enough for a person to enter, and ventilation is inadequate, the hydrogen concentration could be high enough to asphyxiate a person who entered the space. Manufacturers, users, and government authorities rely on requirements described in codes to guide safe design and installation of such systems. Except for small enclosures used for hydrogen gas cylinders (gas cabinets), fuel cell power systems, and the enclosures that most people would describe as buildings, there are no hydrogen safety requirements for these enclosures, leaving gaps that must be addressed. This paper proposes that a technical basis be developed to enable code bodies to write requirements for the range of enclosures from the smallest to the largest.

08 HYDROGEN↗
DOE OSTI2020

Wind Turbine Lightning Mitigation System Radar Cross Section Reduction

Modern wind turbines employ Lightning Mitigation Systems (LMSs) in order to reduce costly damages caused by lightning strikes. Lightning strikes on wind turbines occur frequently making LMS configurations a necessity. An LMS for a single turbine includes, among other equipment, cables running inside each blade, along the entire blade length. These cables are connected to various metallic receptors on the outside surface of the blades. The LMS cables can act as significant electromagnetic scatterers which may cause interference to radar systems. This interference may be mitigated by reducing the Radar Cross-Section (RCS) of the wind turbine's LMS. This report investigates proposed modifications to LMS cables in order to reduce the RCS when illuminated by Re locatable Over the Horizon Radar (ROTHR) systems which operate in the HF band (3 - 30 MHz). The proposed modifications include breaking up the LMS cables using spark gap connections, and changing the orientation of the LMS cable within the turbine blade. Both simulated analyses of such RCS mitigation techniques is provided as well as recommendations on further research.

17 WIND ENERGY↗