Energy Science Laboratories (United States)

This paper reports an effective approach we have developed to sputter nanoporous single-phase La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) thin-film cathodes using glancing angle deposition (GLAD), which leverages the self-shadowing effect to engineer nanocolumnar architectures with high porosity. By systematically tuning the sputtering pressure and film thickness, we achieved precise control over the cathode morphology, resulting in tunable porosity and triple-phase boundary (TPB) density. The GLAD-fabricated LSCF cathode deposited at 0.40Pa exhibited a nanocolumnar porosity of 21.5%, compared to 7.5% for a conventionally sputtered LSCF film. At a thickness of 240nm, this cathode achieved a polarization resistance of 6.4 Ω cm2 at 500 °C, in contrast to 32.9 Ω cm2 for its conventionally sputtered counterpart. Electrochemical analysis attributed this improvement to enhanced gas diffusion and surface exchange properties enabled by the nanocolumnar architecture. An anodized aluminum oxide (AAO)-supported thin-film SOFC (TF-SOFC) integrating the optimized GLAD-fabricated LSCF cathode (with yttria-stabilized zirconia (YSZ) electrolyte and nickel-yttrium doped ceria (YDC) anode) delivered a peak power density of 836mWcm- 2 at 550°C. These results establish GLAD sputtering as a promising strategy for engineering high-performance, nanoporous single-phase cathodes in LT-SOFC systems.

Electron emission with an ultrashort laser for single and double tipped carbon fiber field emitters is studied. Single-tip experiments demonstrate emission changes from multiphoton to single-photon assisted tunneling. Double-tip measurements do not evidence screening effects.

Biofuels derived from the mass cultivation of algae represent an emerging industry that aims to partially displace petroleum based fuels. Outdoor, open-pond, and raceway production facilities are attractive options for the mass culture of algae however, this mode of cultivation leaves the algae susceptible to epidemics from a variety of environmental challenges. Infestations can result in complete collapse of the algal populations and destruction of their valuable products making it paramount to understand the host-pathogen relationships of known algal pests in order to develop mitigation strategies. In the present work, we characterize the spatial-temporal response of photosynthetic pigments in Scenedesmus dimorphus to infection from Amoeboaphelidium protococcarum, a destructive endoparasite, with the goal of understanding the potential for early detection of infection via host pigment changes. We employed a hyperspectral confocal fluorescence microscope to quantify these changes in pigmentation with high spatial and spectral resolution during early parasite infection. Carotenoid abundance and autofluorescence increased within the first 24 h of infection while chlorophyll emission remained constant. Changes in host cell photosynthesis and bulk chlorophyll content were found to lag behind parasite replication. The results herein raise the possibility of using host-cell pigment changes as indicators of nascent parasite infection.

The confining walls in future fusion power plants will be subjected to an intense energetic bombardment from X-rays, ions, and neutrons. This is true for both direct-drive inertial fusion energy (IFE) and magnetic fusion energy (MFE) designs. We focus in this paper on the threat spectra presented by energetic ions. X-rays are predicted to present a less significant threat in direct-drive IFE, and neutron effects cannot be readily simulated in current experimental facilities. For the experimental results presented herein, the energetic ions are generated in the Repetitive High-Energy Pulsed Power 1 (RHEPP-1) facility at Sandia National Laboratories. Depending upon whether the ion pulses are of nitrogen (previous database) or helium (this paper), the pulse width varies from 100 ns to as much as 500 ns, respectively. While this is short compared to ˜500-μs transient events anticipated in MFE operation, data from both IFE and MFE experiments for tungsten exposure are shown to exhibit similar fluence thresholds when thermal diffusion is taken into account by use of the heat flux parameter H = Power density × t1/2, where t is the characteristic event time duration.Long-term exposure of tungsten to RHEPP-1 nitrogen pulses indicates that above a level of ˜1 J · cm−2 /pulse, polycrystalline tungsten roughens severely, the cause of which appears to be thermomechanical distress, with loosening of grains near the surface the primary result. This roughening is correlated with unacceptable mass loss. While this occurs below melting temperatures, allowing the surface to melt by raising the per-pulse fluence does not appear to be a viable approach to smoothing the surface. Oriented grain material such as ITER-specified tungsten performs significantly better than polycrystalline tungsten, but under helium exposure it appears to suffer additional surface deterioration that appears to be connected to helium pore and bubble formation at absorbed implantation levels of mid-1015 He/cm2. This level is below previously reported levels of concern for helium retention effects and well short of required survival duration. Experiments with three-dimensional "needle" geometries, designed to increase the effective surface area for heat absorption and reduce helium implantation in depth, show promising results that need further investigation to confirm long-term survival.

Laser-boosted lightsail experiments were carried out on 4-8 December 2000 with the 150 kW LHMEL II carbon dioxide CW laser at Wright Patterson Air Force Base - in their 2.74 m long, 2.13-, diameter vacuum chamber. All 5-cm diameter sail specimens were fabricated by ESLI. The prior Dec. '99 pendulum tests used ultralight carbon microtruss discs, sputter-coated with molybdenum on the front face to improve reflectivity at 10.6 um - and are the first known measurements of high power laser photonic thrust with real candidate lightsail materials. The Dec. '00 vertical wire- guided tests employed an improved moly-coated carbon-foil material with the same basic microtruss substructure. The performance of this new carbon foil sail was superior to the earlier specimens.

Abstract We have investigated the technique of evaporation and condensation of material in an inert gas (ECIIG) for the purpose of preparing ultrafine particles (of order 10 nm in diameter) with a narrow distribution of sizes. Gravity driven convection increases the rate of coalescence of the particles leading to larger sizes and a broader distribution. Here we report on analysis and experiments to investigate coalescence of particles. The possibility of reducing coalescence in micro-gravity is discussed. An experimental test in reduced gravity to be performed in a KC135 aircraft is described briefly.