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NASA NTRS1992

Issues/considerations and performance prediction of LEO protective coatings

Organic materials can be used in low earth orbit for long periods only if they are made to be durable to atomic oxygen in addition to the threats of ultraviolet radiation, micrometeoroid and debris impact, thermal cycling, and charged particle radiation. In many materials applications, it is more cost-effective to utilize atomic oxygen protective coatings over materials which are vulnerable to attack by atomic oxygen rather than developing alternative materials which are inherently durable. Many metal and metal oxide coatings have been shown to be potentially suitable for long term protection of organic polymers in low earth orbit. The protection afforded by thin film coatings on polymeric substrates is highly dependent on the completeness of coverage of the coating. Thus, the prime indicator of durability is the size and abundance of pin windows and scratches in the protective coating. Such defects depend on the deposition technique, smoothness of the surface to be protected, and presence of particulate contaminants. Issues and considerations relevant to substrate preparation, deposition of protective coatings, ground laboratory simulation and evaluation of threats in low earth orbit to protective materials, results of in-space tests, and the use of Monte Carlo modeling techniques to predict in-space durability are presented in graphic form.

Banks, Bruce A.↗

NASA NTRS1999

Envelope structure of deeply embedded young stellar objects in the Serpens Molecular Cloud

Aperture-synthesis and single-dish (sub-) millimeter molecular-line and continuum observations reveal in great detail the envelope structure of deeply embedded young stellar objects (SMM 1 = FIRS 1, SMM 2, SMM 3, SMM 4) in the densely star-forming Serpens Molecular Cloud. SMM 1, 3, and 4 show partially resolved (>2" = 800 AU) continuum emission in the beam of the Owens Valley Millimeter Array at lambda = 3.4-1.4 mm. The continuum visibilities accurately constrain the density structure in the envelopes, which can be described by a radial power law with slope -2.0 +/- 0.5 on scales of 300 to 8000 AU. Inferred envelope masses within a radius of 8000 AU are 8.7, 3.0, and 5.3 Msolar for SMM 1, 3, and 4, respectively. A point source with 20%-30% of the total flux at 1.1 mm is required to fit the observations on long baselines, corresponding to warm envelope material within approximately 100 AU or a circumstellar disk. No continuum emission is detected interferometrically toward SMM 2, corresponding to an upper limit of 0.2 Msolar assuming Td = 24 K. The lack of any compact dust emission suggests that the SMM 2 core does not contain a central protostar. Aperture-synthesis observations of the 13CO, C18O, HCO+, H13CO+, HCN, H13CN, N2H+ 1-0, SiO 2-1, and SO 2(2)-1(1) transitions reveal compact emission toward SMM 1, 3, and 4. SMM 2 shows only a number of clumps scattered throughout the primary field of view, supporting the conclusion that this core does not contain a central star. The compact molecular emission around SMM 1, 3, and 4 traces 5"-10" (2000-4000 AU) diameter cores that correspond to the densest regions of the envelopes, as well as material directly associated with the molecular outflow. Especially prominent are the optically thick HCN and HCO+ lines that show up brightly along the walls of the outflow cavities. SO and SiO trace shocked material, where their abundances may be enhanced by 1-2 orders of magnitude over dark-cloud values. A total of 31 molecular transitions have been observed with the James Clerk Maxwell and Caltech Submillimeter telescopes in the 230, 345, 490, and 690 GHz atmospheric windows toward all four sources, containing, among others, lines of CO, HCO+, HCN, H2CO, SiO, SO, and their isotopomers. These lines show 20-30 km s-1 wide line wings, deep and narrow (1-2 km s-1) self-absorption, and 2-3 km s-1 FWHM line cores. The presence of highly excited lines like 12CO 4-3 and 6-5, 13CO 6-5, and several H2CO transitions indicates the presence of material with temperatures > or approximately 100 K. Monte Carlo calculations of the molecular excitation and line transfer show that the envelope model derived from the dust emission can successfully reproduce the observed line intensities. The depletion of CO in the cold gas is modest compared to values inferred in objects like NGC 1333 IRAS 4, suggesting that the phase of large depletions through the entire envelope is short lived and may be influenced by the local star formation density. Emission in high-excitation lines of CO and H2CO requires the presence of a small amount of approximately 100 K material, comprising less than 1% of the total envelope mass and probably associated with the outflow or the innermost region of the envelope. The derived molecular abundances in the warm (Tkin > 20 K) envelope are similar to those found toward other class 0 YSOs like IRAS 16293-2422, though some species appear enhanced toward SMM 1. Taken together, the presented observations and analysis provide the first comprehensive view of the physical and chemical structure of the envelopes of deeply embedded young stellar objects in a clustered environment on scales between 1000 and 10,000 AU.

NASA Discipline Exobiology↗

DOE OSTI2019

Chemistry Design Towards a Stable Sulfide‐Based Superionic Conductor Li 4 Cu 8 Ge 3 S 12

Abstract Sulfide‐based superionic conductors with high ionic conductivity have been explored as candidates for solid‐state Li batteries. However, moisture hypersensitivity has made their manufacture complicated and costly and also impeded applications in batteries. Now, a sulfide‐based superionic conductor Li 4 Cu 8 Ge 3 S 12 with superior stability was developed based on the hard/soft acid–base theory. The compound is stable in both moist air and aqueous LiOH aqueous solution. The electrochemical stability window was up to 1.5 V. An ionic conductivity of 0.9×10 −4 S cm with low activation energy of 0.33 eV was achieved without any optimization. The material features a rigid Cu‐Ge‐S open framework that increases its stability. Meanwhile, the weak bonding between Li + and the framework promotes ionic conductivity. This work provides a structural configuration in which weak Li bonding in the rigid framework promotes an environment for highly conductive and stable solid‐state electrolytes.

Wang, Yingqi↗

DOE OSTI2019

Chemistry Design Towards a Stable Sulfide-Based Superionic Conductor Li 4 Cu 8 Ge 3 S 12

Sulfide-based superionic conductors with high ionic conductivity have been explored as candidates for solid-state Li batteries. However, moisture hypersensitivity has made their manufacture complicated and costly and also impeded applications in batteries. Now, a sulfide-based superionic conductor Li 4 Cu 8 Ge 3 S 12 with superior stability was developed based on the hard/soft acid–base theory. The compound is stable in both moist air and aqueous LiOH aqueous solution. The electrochemical stability window was up to 1.5 V. An ionic conductivity of 0.9×10 -4 S cm with low activation energy of 0.33 eV was achieved without any optimization. The material features a rigid Cu-Ge-S open framework that increases its stability. Meanwhile, the weak bonding between Li + and the framework promotes ionic conductivity. This work provides a structural configuration in which weak Li bonding in the rigid framework promotes an environment for highly conductive and stable solid-state electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2026

Understanding Adsorption and Reactions at Aqueous Oxide Interfaces with Neural Network Potential Molecular Dynamics

Chemical processes at metal oxide−water interfaces are of central importance in geochemistry, biology, and energy technologies. A better understanding of these processes would allow us to make a significant step toward optimizing and controlling them, which could in turn lead to broader impacts. Computational modeling is indispensable to accomplishing this task because complexity and disorder often make it difficult to extract atomistic information from experiments. Balancing computational cost and accuracy, simulation schemes based on efficient machine learning representations of the potential energy surface (PES) predicted by ab initio calculations have become increasingly popular over the past decade. In particular, several studies have demonstrated the ability of machine learning models to accurately reproduce the complex ab initio PESs of aqueous oxide interfaces, allowing simulations of systems and processes that are not accessible with ab initio methods. In this Account, we review our recent efforts to understand adsorption processes and reactions at aqueous oxide interfaces using deep potential molecular dynamics (DPMD), a simulation scheme employing deep neural networks (DNNs), which has proven to be quite successful in accurately describing many different systems in the condensed phase. After summarizing the DPMD methodology, we first review our work on the acid−base chemistry of oxide surfaces in contact with water, a fundamental characteristic that controls proton transfer and surface charge at the interface. We focus on the aqueous interface of rutile IrO 2 , an oxide material thus far considered the best catalyst for the oxygen evolution reaction (OER). We show that this interface is characterized by a large fraction of dissociated water and a strong Brønsted acidity of the surface sites, in good agreement with the experimentally measured value of the point of zero proton charge. In our second example, we investigate how the adsorption of organic species from ambient air or water affects the structure and wettability of the aqueous interfaces of TiO 2 , a prototypical photocatalytic material. This is a question that is relevant to understanding the UV-induced hydrophilicity of TiO 2 surfaces, a property at the basis of self-cleaning windows and related applications. Specifically focusing on formic and acetic acids, the two most common atmospheric organic acids, our simulations reveal that these acids control the wettability of TiO 2 largely through acid−base chemistry at the interface rather than chemisorption on the oxide surface, a finding that could help improve the design of self-cleaning surfaces and photocatalytic devices. Finally, we review our recent study of methanol at TiO 2 −water interfaces, a system whose interest is largely motivated by the role of methanol in enhancing photocatalytic hydrogen evolution on TiO 2 . Our simulations provide mechanistic insights into the coupled roles of the organic adsorbate and water at the TiO 2 interface, with implications for how methanol enhances the activity of H 2 evolution.

adsorption↗

DOE OSTI2020

Definition of Redox Centers in Reactions of Lithium Intercalation in Li 3 RuO 4 Polymorphs

Cathodes based on layered LiMO 2 are the limiting components in the path toward Li-ion batteries with energy densities suitable for electric vehicles. Introducing an over-stoichiometry of Li increases storage capacity beyond a conventional mechanism of formal transition metal redox. However, the role and fate of the oxide ligands in such intriguing additional capacity remain unclear. This reactivity was predicted in Li 3 RuO 4 , making it a valuable model system. For this study, a comprehensive analysis of the redox activity of both Ru and O under different electrochemical conditions was carried out, and the effect of Li/Ru ordering was evaluated. Li 3 RuO 4 displays highly reversible Li intercalation to Li 4 RuO 4 below 2.5 V vs Li + /Li 0 , with conventional reactivity through the formal Ru 5+ -Ru 4+ couple. In turn, it can also undergo anodic Li extraction at 3.9 V, which involves O states to a much greater extent than Ru. This reaction competes with side processes such as electrolyte decomposition and, to a much lesser extent, oxygen loss. Although the associated capacity is reversible, reintercalation unlocks a different, conventional pathway also involving the formal Ru 5+ -Ru 4+ couple despite operating above 2.5 V, leading to chemical hysteresis. This new pathway is both chemically and electrochemically reversible in subsequent cycles. This work exemplifies both the challenge of stabilizing highly depleted O states, even with 4d metals, and the ability of solids to access the same redox couple at two very different potential windows depending on the underlying structural changes. It highlights the importance of properly defining the covalency of oxides when defining charge compensation in view of the design of materials with high capacity for Li storage.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Epitaxial stabilization of Sr 3 Ir 2 O 7 thin films

Ruddlesden-Popper type Sr n+1 Ir n O 3n+1 compounds are a major focus of condensed matter physics, where the subtle balance between electron-electron correlation, spin–orbit interaction, and crystal field effect brings a host of emergent phenomena. While it is understandable that a canted antiferromagnetic insulating state with an easy-plane anisotropy is developed in Sr 2 IrO 4 as the two-dimensional limit of the series, it is intriguing that bilayer Sr 3 Ir 2 O 7 , with slightly higher effective dimensionality, stabilizes c-axis collinear antiferromagnetism. This also renders Sr 3 Ir 2 O 7 a unique playground to study exotic physics near a critical spin transition point. However, the epitaxial growth of Sr 3 Ir 2 O 7 is still a challenging task because of the narrow growth window. In our research, we have studied the thermodynamic process during the synthesis of Sr 3 Ir 2 O 7 thin films. We expanded the synthesis window by mapping out the relationship between the thin film crystal structure and the gas pressure. Furthermore, our work thus provides a more accessible avenue to stabilize metastable materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Poster — Thur Eve — 40: Automated Quality Assurance for Remote-Afterloading High Dose Rate Brachytherapy

High dose rate (HDR) remote afterloading brachytherapy involves sending a small, high-activity radioactive source attached to a cable to different positions within a hollow applicator implanted in the patient. It is critical that the source position within the applicator and the dwell time of the source are accurate. Daily quality assurance (QA) tests of the positional and dwell time accuracy are essential to ensure that the accuracy of the remote afterloader is not compromised prior to patient treatment. Our centre has developed an automated, video-based QA system for HDR brachytherapy that is dramatically superior to existing diode or film QA solutions in terms of cost, objectivity, positional accuracy, with additional functionalities such as being able to determine source dwell time and transit time of the source. In our system, a video is taken of the brachytherapy source as it is sent out through a position check ruler, with the source visible through a clear window. Using a proprietary image analysis algorithm, the source position is determined with respect to time as it moves to different positions along the check ruler. The total material cost of the video-based system was under $20, consisting of a commercial webcam and adjustable stand. The accuracy of the position measurement is ±0.2 mm, and the time resolution is 30 msec. Additionally, our system is capable of robustly verifying the source transit time and velocity (a test required by the AAPM and CPQR recommendations), which is currently difficult to perform accurately.

07 ISOTOPE AND RADIATION SOURCES↗

DOE OSTI2023

Composite Cathode Architectures Made By Freeze-Casting for All Solid State Lithium Batteries (CRADA Final Report)

As part of a Battery 500 seedling project, MBRDNA partnered with LBNL and Montana State University (MSU) to develop solid-state batteries based on an Al-substituted LLZO (Li 7 La 3 Zr 2 O 12 ) ceramic ion-conductor. All solid-state lithium batteries are attractive contenders for use as power sources for electric vehicles because of their potential for better safety and higher energy density than state-of-the-art lithium-ion batteries, although they are still at early stages of development. Al-substituted LLZO is one of the most promising solid electrolytes for battery applications based on high ionic conductivity, a wide operating voltage window, and apparent stability vs. reduction by lithium. However, difficulties with processing thin (< 20 $\textit{um}$ and dense LLZO membranes have hampered development of devices based on this material. It is non-compressible and must be sintered at high temperatures to densify components. It is also difficult to maintain contact between the active cathode material and LLZO in the composite cathodes, which is critical for successful operation. This research project aimed to use novel processing methods to overcome these issues. The end result was the first ever-reported truly all solid-state battery based on LLZO operating at room temperature without application of exogenous pressure. During the course of the project, we also identified a number of issues that need to be addressed to improve the technology readiness level of this battery.

25 ENERGY STORAGE↗

NASA NTRS1972

Initiation system for low thrust motor igniter

A test program was carried out to demonstrate an igniter motor initiation system utilizing the bimetallic material Pyrofuze for a solid propellant rocket with controlled low rate of thrust buildup. The program consisted of a series of vacuum ignition tests using a slab burning window motor that simulated the principal initial ballistic parameters of the full scale igniter motor. A Pyrofuze/pyrotechnic igniter system was demonstrated that uses a relatively low electrical current level for initiation and that eliminates the necessity of a pyrotechnic squib, with its accompanying accidental firing hazards and the typical basket of pyrotechnic pellets. The Pyrofuze ignition system does require an initial constraining of the igniter motor nozzle flow, and at the low initiating electrical current level the ignition delay time of this system was found to be quite sensitive to factors affecting local heat generation or loss rates.

Strand, L. D.↗

NASA NTRS1984

Dust streaks on Mars: Colors and photometry

Photometric studies of crater related bright and dark streaks have strongly supported the hypothesis that the bright streaks are excess dust deposits and dark streaks are erosional windows in a partial dust cover. Red-blue (and red-violet) plots show that bright streaks are consistent with mosaics of bright red dust and background material. Here the plains are also consistent with a partial dust cover; the dark streak is the least covered area. Bright and dark streaks both reverse contrast relative to surrounding plains at phase angles over 100 deg in violet filter images. The similar phase behavior of both bright and dark streaks supports the idea that they are both changes in the amount of dust cover. Red-violet plots of bright streaks are most easily explained by mosaics of optically thick dust and plains material. Lengths of bright streaks are independent of their contrasts. This suggests the streak deposition, if in the mosaic patterns indicated above, is a function of available sites of deposition, rather than atmospheric dust loading. Contrasts of dark streaks with plains indicate the plains have fractional dust covers nealy as great as the maximum additional cover in bright streaks. The bright streaks thus store little of the global supply of dust.

Thomas, P.↗

NASA NTRS1984

Noise transmission through an acoustically treated and honeycomb stiffened aircraft sidewall

The noise transmission characteristics of test panels and acoustic treatments representative of an aircraft sidewall are experimentally investigated in the NASA Langley Research Center transmission loss apparatus. The test panels were built to represent a segment sidewall in the propeller plane of a twin-engine, turboprop light aircraft. It is shown that an advanced treatment, which uses honeycomb for structural stiffening of skin panels, has better noise transmission loss characteristics than a conventional treatment. An alternative treatment, using the concept of limp mass and vibration isolation, provides more transmission loss than the advanced treatment for the same total surface mass. Effects on transmission loss of a variety of acoustic treatment materials (acoustic blankets, septa, damping tape, and trim panels) are presented. Damping tape does not provide additional benefit when the other treatment provides a high level of damping. Window units representative of aircraft installations are shown to have low transmission loss relative to a completely treated sidewall.

Grosveld, F. W.↗

NASA NTRS1986

Retractable Sun Shade

Window-shade type spring roller contains blanket, taken up by rotating cylindrical frame and held by frame over area to be shaded. Blanket made of tough, opaque polyimide material. Readily unfurled by mechanism to protect space it encloses from Sun. Blanket forms arched canopy over space and allows full access to it from below. When shading not needed, retracted mechanism stores blanket compactly. Developed for protecting sensitive Space Shuttle payloads from direct sunlight while cargo-bay doors open. Adapted to shading of greenhouses, swimming pools, and boats.

Frank, A.↗

NASA NTRS1990

Pressure-Measuring Diaphragm Transmits Optical Signals

Proposed sapphire diaphragm performs two functions in instrumented research engine or pressure vessel. Serves both as pressure sensor and as window for observation, optical probing, or optical transmission of other measurements. Deflections of sapphire diaphragm alters resistances of strain gauges mounted around its periphery. At same time, transparent material enables optical measurements of conditions in chamber. Additional information obtained about conditions in chamber without need for additional sensor mounts.

Hill, Arthur J.↗

NASA NTRS1990

Hypervelocity impact testing of non-metallic materials

A comparative analysis of impact damage in composite and ceramic specimens and in geometrically similar aluminum specimens is performed to determine the advantages and disadvantages of employing certain composite and ceramic materials in the design of structural wall systems for long-duration spacecraft. A similar analysis of the damage in single panel lexan and multi-plane glass windows shows that glass window systems are rather resilent under hypervelocity impact loadings. It is concluded that thin Kevlar 49, IM6/3501-6 graphite/epoxy, and alumina panels offer no advantage over equivalent aluminum 6061-T6 panels in reducing the penetration threat of hypervelocity projectiles.

Schonberg, William P.↗

NASA NTRS1996

STS-79 Flight Day 6

On this sixth day of the STS-79 mission, the flight crew, Cmdr. William F. Readdy, Pilot Terrence W. Wilcutt, Mission Specialists, Thomas D. Akers, Shannon Lucid, Jay Apt, and Carl E. Walz, continue activities aboard Atlantis/Mir as the nine astronauts and cosmonauts work in their second full day of docked operations. The continuing transfer of logistical supplies and scientific hardware can be seen proceeding smoothly. Apt and Walz once again worked with the Active Rack Isolation System experiment to replace a broken pushrod. With that complete, Apt monitors the ARIS experiment as Readdy and Korzun fire small maneuvering jets on their spacecraft to test the ability of ARIS to damp out any disturbances created by the firings. Walz also is continuing his work with the Mechanics of Granular Materials experiment in Atlantis' double Spacehab module. The astronauts used the large format IMAX camera to conduct a photographic survey of Mir from the Shuttle's flight deck windows while Akers shot IMAX movie scenes of Readdy, Wilcutt, and Korzun in the Spektr module.

Source record↗

NASA NTRS1999

IRIS Mariner 9 Data Revisited: An Instrumental Effect - 1

Small spurious features are present in data from the Mariner 9 Infrared Interferometer Spectrometer (IRIS). These represent a low amplitude replication of the spectrum with a doubled wavenumber scale. This replication arises principally from an internal reflection of the interferogram at the input window. An algorithm is provided to correct for the effect, which is at the 2% level. We believe that the small error in the uncorrected spectra does not materially affect previous results; however, it may be significant for some future studies at short wavelengths. The IRIS spectra are also affected by a coding error in the original calibration that results in only positive radiances. This reduces the effectiveness of averaging spectra to improve the signal to noise ratio at small signal levels.

Formisano, V.↗

NASA NTRSDate not supplied

Understanding Thermal Stability in Zirconia-Based Aerogels

For lightweight, thermal insulation needs above 1000ºC, the high surface to volume ratios of ceramic-based aerogels are practically unparalleled. Yet realizing the full potential of aerogel-based thermal protection systems requires not only increased thermal stability, but also a broadened menu of stabilizing mechanisms. Here we will review our recent efforts to understand the impact of synthetic parameters and dopant chemistry on the evolution of zirconia-based ceramics. A broad parametric window for thermal stability is established, in which the more sensitive variable of composition has been probed. However, dopant chemistry is actually an aggregate for many closely related material parameters including surface energy, enthalpy of formation, each of which may contribute uniquely to aerogel destabilization. A truly predictive design framework for ceramic-based aerogels requires further decoupling of these underlying properties through systematic and comprehensive evaluation of thermodynamic properties.

aerogel↗