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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

High Temperature Protonic Conductors

High Temperature Protonic Conductors (HTPC) with the perovskite structure are envisioned for electrochemical membrane applications such as H2 separation, H2 sensors and fuel cells. Successive membrane commercialization is dependent upon addressing issues with H2 permeation rate and environmental stability with CO2 and H2O. HTPC membranes are conventionally fabricated by solid-state sintering. Grain boundaries and the presence of intergranular second phases reduce the proton mobility by orders of magnitude than the bulk crystalline grain. To enhanced protonic mobility, alternative processing routes were evaluated. A laser melt modulation (LMM) process was utilized to fabricate bulk samples, while pulsed laser deposition (PLD) was utilized to fabricate thin film membranes . Sr3Ca(1+x)Nb(2-x)O9 and SrCe(1-x)Y(x)O3 bulk samples were fabricated by LMM. Thin film BaCe(0.85)Y(0.15)O3 membranes were fabricated by PLD on porous substrates. Electron microscopy with chemical mapping was done to characterize the resultant microstructures. High temperature protonic conduction was measured by impedance spectroscopy in wet air or H2 environments. The results demonstrate the advantage of thin film membranes to thick membranes but also reveal the negative impact of defects or nanoscale domains on protonic conductivity.

Dynys, Fred↗
NASA NTRS1973

Photoemission from CsI - Experiment.

Considerable attention in the investigation was given to the resolution maximization of details in the spectra. Very thin films were used in the measurements, which were conducted at 300 and 77 C with the aid of an improved photoemission apparatus. It was found that the principal features of the photoemission spectra from CsI cannot be explained on the basis of simple transitions from localized ionic states because such a model would predict a doublet instead of the triplet observed in the photoemission data.

Distefano, T. H.↗
NASA NTRS1975

Effects of dc bias on the fabrication of amorphous GdCo RF sputtered films

An investigation has been conducted on the effects of a dc bias field applied to Gd(1-x)Co(x) thin films during RF sputter deposition. Such films may possess uniaxial magnetic anisotropy with easy axis perpendicular to the plane of the film and may be used in magnetic bubble devices. Uniformity in composition, thickness and magnetic properties has been achieved and film composition has been controlled to within one percent. However, significant variations of magnetic properties were observed from film to film.

Bourne, H. C., Jr.↗
NASA NTRS1985

Process development

An overview is given of seven process development activities which were presented at this session. Pulsed excimer laser processing of photovoltaic cells was presented. A different pulsed excimer laser annealing was described using a 50 w laser. Diffusion barrier research focused on lowering the chemical reactivity of amorphous thin film on silicon. In another effort adherent and conductive films were successfully achieved. Other efforts were aimed at achieving a simultaneous front and back junction. Microwave enhanced plasma deposition experiments were performed. An updated version of the Solar Array Manufacturing Industry Costing Standards (SAMICS) was presented, along with a life cycle cost analysis of high efficiency cells. The last presentation was on the evaluation of the ethyl vinyl acetate encapsulating system.

Bickler, D. B.↗
NASA NTRS1987

Preliminary results on CuInSe2/ZnSe solar cells using reactively sputter-deposited ZnSe

In this paper preliminary results on CuInSe2/ZnSe thin film heterojunction photovoltaic devices are presented. High-conductivity ZnSe films were reactively sutter-deposited onto CuInSe2 films and overcoated with ZnO to reduce the sheet resistance. The highest short-circuit current density, as determined from a spectral response weighted for air mass 1.5 global insolation, was 37.4 mA/sq cm. The highest pen-circuit voltage observed was 430 mV.

Nouhi, A.↗
NASA NTRS1988

Molten-salt corrosion of silicon nitride. I - Sodium carbonate. II - Sodium sulfate

An experimental study of the corrosion of Si3N4 under thin films of Na2CO3 at 1000 C has been conducted using both pure Si3N4 and Si3N4 with various additives. The reaction mechanism is shown to consist of: (1) the decomposition of Na2CO3 and the formation of Na2SiO3; (2) rapid oxidation; and (3) the formation of a protective silica layer below the silicate. In the second part, the corrosion mechanism of Si3N4 + Na2SO4/O2 at 1000 C was studied for both pure and additive-containing Si3N4. The reaction of Si3N4 + Na2SO4 was found to involve an initial period of slow weight loss (due to Na2SO4 vaporization and oxidation-dissolution) followed by further oxidation or the near termination of the reaction, depending on the Si3N4 additive.

Fox, Dennis S.↗
NASA NTRS1993

Gelled Electrolytes For Lithium Batteries

Gelled polymer electrolyte consists of polyacrylonitrile (PAN), LiBF4, and propylene carbonate (PC). Thin films of electrolyte found to exhibit stable bulk conductivities of order of 10 to the negative 3rd power S/cm at room temperature. Used in thinfilm rechargeable lithium batteries having energy densities near 150 W h/kg.

Nagasubramanian, Ganesan↗
NASA NTRS2004

Advanced Adiabatic Demagnetization Refrigerators for Continuous Cooling

The research at Houston was focused on optimizing the design of superconducting magnets for advanced adiabatic demagnetization refrigerators (ADRs), assessing the feasibility of using high temperature superconducting (HTS) magnets in ADRs in the future, and developing techniques to deposit HTS thin and thick films on high strength, low thermal conductivity substrates for HTS magnet leads. Several approaches have been tested for the suggested superconducting magnets.

Chu, Paul C. W.↗
NASA NTRS2004

Direct Electrolytic Deposition of Mats of Mn(x)O(y) Nanowires

Mats of free-standing manganese oxide (MnxOy) nanowires have been fabricated as experimental electrode materials for rechargeable electrochemical power cells and capacitors. Because they are free-standing, the wires in these mats are electrochemically accessible. The advantage of the mat-of-nanowires configuration, relative to other configurations of electrode materials, arises from the combination of narrowness and high areal number density of the wires. This combination offers both high surface areas for contact with electrolytes and short paths for diffusion of ions into and out of the electrodes, thereby making it possible to charge and discharge at rates higher than would otherwise be possible and, consequently, to achieve greater power densities. The nanowires are fabricated in an electrolytic process in which there is no need for an electrode binder material. Moreover, there is no need to incorporate an electrically conductive additive into the electrode material; the only electrically conductive material that must be added is a thin substrate contact film at the anchored ends of the nanowires. Hence, the mass fraction of active electrode material is close to 100 percent, as compared with about 85 percent in conventional electrodes made from a slurry of active electrode material, binder, and conductive additive pressed onto a metal foil. The locations and sizes of the nanowires are defined by holes in templates in the form of commercially available porous alumina membranes. In experiments to demonstrate the present process, alumina membranes of various pore sizes and degrees of porosity were used. First, a film of Au was sputtered onto one side of each membrane. The membranes were then attached, variously, to carbon tape or a gold substrate by use of silver or carbon paste. Once thus attached, the membranes were immersed in a plating solution comprising 0.01 M MnSO4 + 0.03 M (NH4)2SO4. The pH of the solution was kept constant at 8 by addition of H2SO4 or NH4OH as needed. Mn(x)O(y) nanowires were potentiostatically electrodeposited in the pores in the alumina templates. Depending on the anodic deposition potentials, Mn(x)O(y) was deposited in various oxidation states [divalent (Mn3O4), trivalent (Mn2O3), or tetravalent (MnO2)]. The Mn(x)O(y) wires were made free-standing (see figure) by dissolving the alumina templates, variously, in KOH or NaOH at a concentration of 20 volume percent.

Myung, Nosang↗
NASA NTRS2004

Polyimide/Carbon Nanotube Composite Films for Electrostatic Charge Mitigation

Low color, space environmentally durable polymeric films with sufficient electrical conductivity to mitigate electrostatic charge (ESC) build-up have potential applications on large, deployable, ultra-light weight Gossamer spacecraft as thin film membranes on antennas, solar sails, thermal/optical coatings, multi-layer insulation blankets, etc.. The challenge has been to develop a method to impart robust electrical conductivity into these materials without increasing solar absorptivity (alpha ) or decreasing optical transparency or film flexibility. Since these spacecraft will require significant compaction prior to launch, the film portion of the spacecraft will require folding. The state-of-the-art clear, conductive coating (e.g. indium-tin-oxide, ITO) is brittle and cannot tolerate folding. In this report, doping a polymer with single-walled carbon nanotubes (SWNTs) using two different methods afforded materials with good flexibility and surface conductivities in the range sufficient for ESC mitigation. A coating method afforded materials with minimal effects on the mechanical, optical, and thermo-optical properties as compared to dispersal of SWNTs in the matrix. The chemistry and physical properties of these nanocomposites are discussed.

Smith, Joseph G., Jr.↗
NASA NTRS1989

Comparisons of boundary-layer transition measurement techniques in the Langley Unitary Plan wind tunnel

Four different boundary-layer transition detection techniques, namely liquid crystals, very thin hot films, IR photography, and an optical interferometer, were compared using the same flat plate model for the same tunnel conditions. The comparisons, conducted at NASA-Langley, involved not only their sensitivity to transition but also their ease of use. The thin films, as expected, gave excellent quantitative information and were used as the standard for evaluating the other techniques. Both the liquid crystals and IR photography were able to detect transition before the boundary-layer intermittency factor had reached 50 percent. The optical interferometer was unsuccessful. Conditions sampled included a range of Mach numbers from 1.5 to 2.5 and unit Reynolds numbers from 1.0 to 4.0 million/foot.

Hall, R. M.↗
NASA NTRS1990

Microwave Conductivity of Laser Ablated YBa2Cu3O7-delta Superconducting Films and Its Relation to Microstrip Transmission Line Performance

We report on the values of the microwave conductivity in the normal (sigma(subN)) and superconducting (sigma*=sigma(sub1)-j sigma(sub2)) states of two laser ablated YBa2CU3O7(sigma) thin films at 35 GHz, in the temperature range from 20 to 300 K. The films 0.7 and 0.4 micrometers) were deposited on LaA10(sub3) by laser ablation. The conductivity was obtained from the microwave power transmitted through the films and assuming a two-fluid model. Values of sigma(subN) approximately 2.3 X 10(exp5) S/m at room temperature for both films, and of sigma(sub1) approximately 6.3 X 10(exp5) and 4.6 X 10(exp5) S/m at temperatures around 80 K were obtained for the 0.7 and 0.4 micrometer films respectively. For sigma(sub2) values of 4.9 X 10(exp6) and 5.4 X 10(exp6) S/m were obtained for the 0.7 and 0.4 micrometer films at 80 K. The expected conductor losses and Q-factor of a superconducting ring resonator were calculated using these conductivity values. The theoretical values were then compared with the experimental results obtained for a resonator fabricated from one of these films.

Bhasin, K. B.↗
NASA NTRS2007

Absorber Materials for Transition-Edge Sensor X-ray Microcalorimeters

Arrays of superconducting transition-edge sensors (TES) can provide high spatial and energy resolution necessary for x-ray astronomy. High quantum efficiency and uniformity of response can be achieved with a suitable absorber material, in which absorber x-ray stopping power, heat capacity, and thermal conductivity are relevant parameters. Here we compare these parameters for bismuth and gold. We have fabricated electroplated gold, electroplated gold/electroplated bismuth, and evaporated gold/evaporated bismuth 8x8 absorber arrays and find that a correlation exists between the residual resistance ratio (RRR) and thin film microstructure. This finding indicates that we can tailor absorber material conductivity via microstructure alteration, so as to permit absorber thermalization on timescales suitable for high energy resolution x-ray microcalorimetry. We show that by incorporating absorbers possessing large grain size, including electroplated gold and electroplated gold/electroplated bismuth, into our current Mo/Au TES, devices with tunable heat capacity and energy resolution of 2.3 eV (gold) and 2.1 eV (gold/bismuth) FWHM at 6 keV have been fabricated.

Brown, Ari-David↗
NASA NTRSDate not supplied

Quantifying Primary Arc-Induced Degradation of Perovskite Solar Cells

Primary arcing induced by spacecraft charging presents a significant hazard to thin film solar cells if left unchecked. Here, we present the results of a preliminary effort to quantify the impacts of primary arcing to perovskite solar cells. Solar cells operating in a charged environment are susceptible to electrostatic discharges known as arcing. While primary arcs are not generally considered a major concern for traditional space PV, for thin film cells, these can induce significant heating and subsequent damage. We conducted ESD testing in a LEO-like plasma in the National Plasma Interaction Facility at NASA Glenn Research Center to quantify impacts to cell performance by arcing. The perovskites tested saw a decrease of short circuit current with an increased number of arcs, averaging a relative change of 73.89 ± 15.90% after 60 total arcs supplied a cumulative energy dose of 76.12 mJ to the string. Ongoing work entails testing with larger perovskite data sets and expanding to include additional thin film cell technologies to demonstrate the risk unmitigated primary arcing presents.

primary arcing↗
NASA NTRS1990

Effects of 12-Crown-4 ether on the ionic conductivity and electrode kinetics of electrolytes in polyethylene oxide

Results are described of investigations of the electrical and electrochemical properties of thin films of polyethylene oxide (PEO) electrolytes with and without 12-Crown-4 ether (12Cr4) as a function of temperature and in the frequency regime 100 kHz-0.1 Hz. These measurements were made for LiCF3SO3, LiBF4, and LiClO4 salts. At a given temperature, the bulk conductivity, sigma, (S/cm), for a particular salt, depends on the 12Cr4 concentration with sigma reaching a maximum at about 3 mM 12Cr4. Of the three salts studied, the sigma is the highest for PEO/LiBF4 with 3 mM 12Cr4. The ac and dc measurements yield a lower charge transfer resistance for 12Cr4-incorporated samples than for samples without. Plating/stripping of Li occurs at a potential closer to Li(+)/Li for 12Cr4 samples than those without. The conductivities of a thin (about 100 microns) and a thick (400 microns) films are similar.

Nagasubramanian, G.↗
NASA NTRS1977

A three dimensional dynamic study of electrostatic charging in materials

A description is given of the physical models employed in the NASCAP (NASA Charging Analyzer Program) code, and several test cases are presented. NASCAP dynamically simulates the charging of an object made of conducting segments which may be entirely or partially covered with thin dielectric films. The object may be subject to either ground test or space user-specified environments. The simulation alternately treats (1) the tendency of materials to accumulate and emit charge when subject to plasma environment, and (2) the consequent response of the charged particle environment to an object's electrostatic field. Parameterized formulations of the emission properties of materials subject to bombardment by electrons, protons, and sunlight are presented. Values of the parameters are suggested for clean aluminum, Al2O3, clean magnesium, MgO, SiO2 kapton, and teflon. A discussion of conductivity in thin dielectrics subject to radiation and high fields is given, together with a sample calculation.

Katz, I.↗