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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 OSTI2020

Cold acclimation of mesophyll conductance, bundle‐sheath conductance and leakiness in Miscanthus × giganteus

Summary The cold acclimations of mesophyll conductance ( g m ), bundle‐sheath conductance ( g bs ) and the CO 2 concentrating mechanism (CCM) of C 4 plants have not been well studied. Here, we estimated the temperature response of g m , g bs and leakiness (ϕ), the amount of concentrated CO 2 that escapes the bundle‐sheath cells, for the chilling‐tolerant C 4 plant Miscanthus × giganteus grown at 14 and 25°C. To estimate these parameters, we combined the C 4 ‐enzyme‐limited photosynthesis model and the Δ 13 C discrimination model. These combined models were parameterised using in vitro activities of carbonic anhydrase (CA), pyruvate, phosphate dikinase (PPDK), ribulose‐1,5‐bisphosphate carboxylase/oxygenase (RuBisCO), and phospho enol pyruvate carboxylase (PEPc). Cold‐grown Miscanthus plants increased in vitro activities of RuBisCO and PPDK but decreased PEPc activity compared with warm‐grown plants. Mesophyll conductance and g bs responded strongly to measurement temperatures but did not differ between plants from the two growth temperatures. Furthermore, modelling showed that ϕ increased with measurement temperatures for both cold‐grown and warm‐grown plants, but was only marginally larger in cold‐grown compared with warm‐grown plants. Our results in Miscanthus support that g m and g bs are unresponsive to growth temperature and that the CCM is able to acclimate to cold through increased activity of PPDK and RuBisCO.

Serrano‐Romero, Erika A.↗
DOE OSTI2014

Degradation of transparent conductive properties of undoped ZnO and Ga-doped ZnO films left in atmospheric ambient for several years and trials to recover initial conductance

This study evaluated the long-term stability of the transparent conductive properties of undoped ZnO and Ga-doped ZnO (GZO) films that had been left in an atmospheric ambient environment for 5 to 6 yr. When ZnO films are stored in a clean room with a controlled temperature and humidity of 23 °C and 45%, respectively, throughout the year, the increases in sheet resistance are less than 5% of their initial value. The ZnO films stored in a non-air-conditioned laboratory room, whose temperature varies between 5 and 35 °C and humidity varies between 30% and 70% per year, suffer from increases in the sheet resistance by almost 13%, which is associated with a slight rise in the near-infrared transmittance level. Postannealing of these degraded ZnO films at 150–200 °C recovers the initial conductance by removing the H{sub 2}O molecules that have penetrated the film. One hour of irradiation with electron cyclotron resonance Ar plasma effectively restores the conductive surfaces while maintaining a temperature below 70 °C. The GZO films containing a few weight percent of Ga{sub 2}O{sub 3} are stable even when stored in a non-air-conditioned laboratory room, with changes in the sheet resistance of less than 3%. The GZO films with a Ga{sub 2}O{sub 3} content larger than 10 wt. %, however, exhibit serious degradation probably due to the strong affinity of segregated Ga{sub 2}O{sub 3} domains with H{sub 2}O vapor molecules. Neither postannealing nor Ar plasma irradiation can recover the initial sheet resistance of these GZO films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Measurement of Ionic Conductivity and Electrode Polarization at Low Temperatures on 8YSZ by a DC Technique

Measurement of ionic conductivity and electrode polarization resistance on a 8YSZ sample with platinum paste electrodes was conducted using a DC method with high input impedance meters over a temperature range from 119°C to 589°C. Over the entire temperature range, the meter resistance was much larger than the sample resistance including the polarization resistance. At lower temperatures, a faraday cage was used to minimize noise. The measured polarization resistance was also verified using electrochemical impedance spectroscopy. Ionic conductivity of 8YSZ exhibited Arrhenius behavior with an activation energy of ~1.1 eV, in good agreement with the literature. In the low current regime, electrode kinetics could be described by the linearized form of the Butler-Volmer equation. At higher current densities, electrode kinetics exhibited Tafel behavior. The polarization resistance exhibited Arrhenius behavior with the activation energy ranging between 1.05 and 1.27 eV. The present work shows that electrode polarizations can be investigated using a DC method. The approach may allow study of different electrodes in various atmospheres using one sample.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Electrically conductive carbon fiber layers as lightning strike protection for non-conductive epoxy-based CFRP substrate

A large amount of electrically conductive fillers is needed to enhance a Carbon Fiber Reinforced Plastics (CFRP) electrical conductivity enough to withstand lightning strikes of peak currents. However, such large alien constituents hamper the inherent good mechanical properties of CFRP structures. In this work, a solution has been proposed to retain both desired properties in a CFRP laminate. Layer-wise hybrid laminate has been demonstrated as a solution for lightning strike protection of Carbon Fiber Reinforced Plastics (CFRP). Top few layers of a hybrid laminate are prepared using electrically conductive polymer-based resin (CF/C-POLY) to provide effective dissipation of lightning current while epoxy-based CFRP substrate (CF/Epoxy) provides the main structural strength. An insulating adhesive layer is used to bond CF/C-POLY and CF/Epoxy to prepare the laminate. The hybrid laminates were tested for their effectiveness against lightning strikes. Laminates were struck by modified lightning waveform of component A with peak current of -14 kA and -40 kA. The performance of the laminates against lightning strike were evaluated using high speed camera, high-speed and thermal camera. It is found that CF/C-POLY layer successfully defended the main structural component i.e. CF/Epoxy from lightning direct damage.

36 MATERIALS SCIENCE↗
NASA NTRS1980

Thermal conduction in a composite circular cylinder - A new technique for thermal conductivity measurements of lunar core samples

A technique is described for the measurement of the thermal conductivity of lunar core samples. According to their technique, the core sample is heated radiatively from the outside at a known rate, the temperature is measured at the surface of the core-tube, and the thermal conductivity of the sample is determined by comparing the measured temperature with the theory. The corresponding problems for a composite slab or sphere were solved and the solutions are presented for possible future application to the thermal conductivity measurements. The experimental apparatus construction and procedure are examined as well as the number of precautions taken to preserve the sample from disturbances and to improve the measurement results.

Horal, K.↗
NASA NTRS2001

Method of forming electronically conducting polymers on conducting and nonconducting substrates

The present invention provides electronically conducting polymer films formed from photosensitive formulations of pyrrole and an electron acceptor that have been selectively exposed to UV light, laser light, or electron beams. The formulations may include photoinitiators, flexibilizers, solvents and the like. These solutions can be used in applications including printed circuit boards and through-hole plating and enable direct metallization processes on non-conducting substrates. After forming the conductive polymer patterns, a printed wiring board can be formed by sensitizing the polymer with palladium and electrolytically depositing copper.

Murphy, Oliver J.↗
DOE OSTI2018

Ultralow Thermal Conductivity in Diamond-Like Semiconductors: Selective Scattering of Phonons from Antisite Defects

In this work, we discover anomalously low lattice thermal conductivity (<0.25 W/mK at 300 degrees C) in the Hg-containing quaternary diamond-like semiconductors within the Cu2IIBIVTe4 (IIB: Zn, Cd, Hg) (IV: Si, Ge, Sn) set of compositions. Using high-temperature X-ray diffraction, resonant ultrasound spectroscopy, and transport properties, we uncover the critical role of the antisite defects HgCu and CuHg on phonon transport within the Hg-containing systems. Despite the differences in chemistry between Hg and Cu, the high concentration of these antisite defects emerges from the energetic proximity of the kesterite and stannite cation motifs. Our phonon calculations reveal that heavier group IIB elements not only introduce low-lying optical modes, but the subsequent antisite defects also possess unusually strong point defect phonon scattering power. The scattering strength stems from the fundamentally different vibrational modes supported by the constituent elements (e.g., Hg and Cu). Despite the significant impact on the thermal properties, antisite defects do not negatively impact the mobility (>50 cm2/(Vs) at 300 degrees C) in Hg-containing systems, leading to predicted zT > 1.5 in Cu2HgGeTe4 and Cu2HgSnTe4 under optimized doping. In addition to introducing a potentially new p-type thermoelectric material, this work provides (1) a strategy to use the proximity of phase transitions to increase point defect phonon scattering, and (2) a means to quantify the power of a given point defect through inexpensive phonon calculations.

14 SOLAR ENERGY↗
DOE OSTI2018

Thermoelectric Material SnPb 2 Bi 2 S 6 : The 4,4 L Member of Lillianite Homologous Series with Low Lattice Thermal Conductivity

Although the binary sulfides Bi 2 S 3 , PbS, and SnS have attracted extensive interest as thermoelectric materials, no quaternary sulfides containing Sn/Pb/Bi/S elements have been reported. In this paper, we report the synthesis of a new quaternary sulfide, SnPb 2 Bi 2 S 6 , which crystallizes in the orthorhombic space group Pnma with unit cell parameters of a = 20.5458(12) Å, b = 4.0925(4) Å, c = 13.3219(10) Å. SnPb 2 Bi 2 S 6 has a lillianite-type crystal structure consisting of two alternately aligned NaCl-type structural motifs separated by a mirror plane of PbS 7 monocapped trigonal prisms. In the lillianite homologous series, SnPb 2 Bi 2 S 6 can be classified as 4,4L, where the superscripted numbers indicate the maximum numbers of edge-sharing octahedra in the two adjacent NaCl-shaped slabs along the diagonal direction. The obtained SnPb 2 Bi 2 S 6 phase exhibited good thermal stability up to 1000 K and n-type degenerate semiconducting behavior, with a power factor of 3.7 μW cm -1 K -2 at 773 K. Notably, this compound exhibited a very low lattice thermal conductivity of 0.69-0.92 W m -1 K -1 at 300-1000 K. Theoretical calculations revealed that the low thermal conductivity is caused by the complex crystal structure and the related elastic properties of a low Debye temperature, low phonon velocity, and large Grüneisen parameters. A reasonable figure of merit (ZT) of ~0.3 was obtained at 770 K.

Crystal structure↗
DOE OSTI2018

Influence of Nonstoichiometry on Proton Conductivity in Thin-Film Yttrium-Doped Barium Zirconate

Proton-conducting perovskites have been widely studied because of their potential application as solid electrolytes in intermediate temperature solid oxide fuel cells. Structural and chemical heterogeneities can develop during synthesis, device fabrication, or service, which can profoundly affect proton transport. Here, we use time-resolved Kelvin probe force microscopy, scanning transmission electron microscopy, atom probe tomography, and density functional theory calculations to intentionally introduce Ba-deficient planar and spherical defects and link the resultant atomic structure with proton transport behavior in both stoichiometric and nonstoichiometric epitaxial, yttrium-doped barium zirconate thin films. The defects were intentionally induced through high-temperature annealing treatment, while maintaining the epitaxial single crystalline structure of the films, with an overall relaxation in the atomic structure. As a result, the annealed samples showed smaller magnitudes of local lattice distortions because of the formation of proton polarons, thereby leading to decreased proton-trapping effect. This resulted in a decrease in the activation energy for proton transport, leading to faster proton transport.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Enhanced Out-of-Plane Conductivity and Photovoltaic Performance in n = 1 Layered Perovskites through Organic Cation Design

Layered perovskites with the formula (R–NH 3 ) 2 PbI 4 have excellent environmental stability but poor photovoltaic function due to the preferential orientation of the semiconducting layer parallel to the substrate and the typically insulating nature of the R–NH 3 + cation. Here, we report a series of these n = 1 layered perovskites with the form (aromatic-O-linker-NH 3 ) 2 PbI 4 where the aromatic moiety is naphthalene, pyrene, or perylene and the linker is ethyl, propyl, or butyl. These materials achieve enhanced conductivity perpendicular to the inorganic layers due to better energy level matching between the inorganic layers and organic galleries. The enhanced conductivity and visible absorption of these materials led to a champion power conversion efficiency of 1.38%, which is the highest value reported for any n = 1 layered perovskite, and it is an order of magnitude higher efficiency than any other n = 1 layered perovskite oriented with layers parallel to the substrate. Furthermore, these findings demonstrate the importance of leveraging the electronic character of the organic cation to improve optoelectronic properties and thus the photovoltaic performance of these chemically stable low n layered perovskites.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Significant Reduction of Lattice Thermal Conductivity by the Electron-Phonon Interaction in Silicon with High Carrier Concentrations: A First-Principles Study

The electron-phonon interaction is well known to create major resistance to electron transport in metals and semiconductors, whereas fewer studies are directed to its effect on phonon transport, especially in semiconductors. Herein we calculate the phonon lifetimes due to scattering with electrons (or holes), combine them with the intrinsic lifetimes due to the anharmonic phonon-phonon interaction, all from first principles, and evaluate the effect of the electron-phonon interaction on the lattice thermal conductivity of silicon. Unexpectedly, we find a significant reduction of the lattice thermal conductivity at room temperature as the carrier concentration goes above 1019 cm –3 (the reduction reaches up to 45% in p-type silicon at around 1021 cm –3 ), a range of great technological relevance to thermoelectric materials.

42 ENGINEERING↗
DOE OSTI2014

Ignition Sensitivity and Electrical Conductivity of a Composite Energetic Material with Conductive Nanofillers

The safe handling of powdered composite energetic materials requires an understanding of their response to electrostatic ignition stimuli. A binary composite comprised of Al and polytetrafluoroethylene (PTFE) was tailored for ESD ignition sensitivity with varied concentrations of highly conductive nanofillers. The goal was to control the ESD ignition response of the Al+PTFE with small concentrations of nanofillers that may not significantly affect the overall combustion performance of the mixture. The nanofillers examined include carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs). Adding CNTs created percolation at a lower volumetric percentage than GNPs and were found to be the controlling nanofiller, creating percolation for the mixture containing both CNTs and GNPs. Various mixing methods were examined. Ignition was achieved only for adding nanofillers at a volumetric percentage and mixing method that led to a bulk conductivity of approximately 5x10-3 ?S/cm.

36 MATERIALS SCIENCE↗