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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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693 records · Page 39
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Enhancement under UV–visible and visible light of the ZnO photocatalytic activity for the antibiotic removal from aqueous media using Ce-doped Lu3Al5O12 nanoparticles

We report the first synthesis of Ce-doped Lu{sub 3}Al{sub 5}O{sub 12} Nanoparticles/ZnO Nanostructure (LuAG:Ce/ZnO NS) via a rapid hydrolysis/condensation of Zn(OAc){sub 2} on the surface of LuAG:Ce NPs. The structural, morphological and optical properties of LuAG:Ce/ZnO NS have been fully investigated using X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), High Resolution Transmission Electron Microscopy (HRTEM), Energy Dispersive X-ray Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR), diffuse reflectance UV–visible spectroscopy and N2 adsorption/desorption measurements. Results showed that ZnO Nanocrystals (ZnO NCs) of about 10 nm diameter are homogeneously grown on the surface of 100 nm LuAG:Ce NPs in a core/shell-like structure. The photocatalytic activity of the as-prepared nanostructure has been evaluated throught the photodegradation of sulfathiazole (STZ), a molecule widely used as antibiotic, under UV–vis and visible light irradiation. Results showed that STZ undergoes much higher photodegradation in the presence of LuAG:Ce/ZnO NS compared to the pure ZnO NCs under both UV–vis and visible light. This enhanced photocatalytic capability was found to result from higher specific surface area and visible light absorption in LuAG:Ce/ZnO NS, which allowed for more surface active sites and enhanced hydroxyl radicals (·OH) production from the nanostructured photocatalyst. The recyclability of LuAG:Ce/ZnO NS was also demonstrated.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Microstructural evolution and precipitation in γ-LiAlO 2 during ion irradiation

Polycrystalline γ-LiAlO 2 pellets were sequentially irradiated with 120 keV He + and 80 keV D 2 + ions to the fluences of 1 × 10 17 and 2 × 10 17 (He + + D + )/cm 2 at 573 K. Additional irradiation was performed to a fluence of 2 × 10 17 (He + + D + )/cm 2 at 773 K. The irradiated pellets were characterized using scanning transmission electron microscopy, time-of-flight secondary ion mass spectrometry, and grazing incidence x-ray diffraction. Lattice damage, amorphization, and fractures are observed with no evidence for the formation of secondary-phase precipitates in the pellets irradiated up to an ion fluence of 2 × 10 17 (He + + D + )/cm 2 at 573 K. In contrast, faceted precipitates with sizes larger than 100 nm formed in a pellet irradiated to 2 × 10 17 (He + + D + )/cm 2 at 773 K. Analyses of the diffraction and composition data suggest that the precipitates have a spinel-type structure, likely a non-stoichiometric LiAl 5 O 8 with Li depletion. This could be an intermediate phase with Li atoms at the octahedral and possibly tetrahedral sites as well. It is speculated that as the dose increases, Li loss will continue and the precipitates will approach a composition of alumina primarily in phases of α-Al 2 O 3 and amorphized Al 2 O 3 .

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2018

Effect of the Reaction Medium on the Mechanochemical Synthesis of LiAlO{sub 2}

An unactivated mixture of aluminum hydroxide (gibbsite) and lithium carbonate and a mixture mechanically activated in an AGO-2 planetary mill were heat-treated in air and under vacuum (0.05 Pa) at temperatures of up to 800–850°C, and the phase composition of the heat treatment products was determined by in situ X-ray diffraction. The results demonstrate that, in the case of the unactivated mixture or after mechanical activation for 1 min, heat treatments in air and under vacuum lead to the formation of α-LiAlO{sub 2} and γ-LiAlO{sub 2}, respectively. After mechanical activation for 5 or 10 min, heat treatment both in air and under vacuum leads to γ-LiAlO{sub 2} formation. A possible mechanism behind the effect of the reaction medium on the phase composition of LiAlO{sub 2} is analyzed.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Paramagnetic Ions in Distorted Perovskite YAlO{sub 3} Doped with Europium

In crystals of yttrium orthoaluminate doped with the {sup 151}Eu isotope, Eu{sup 2+}, Cr{sup 3+}, Gd{sup 3+}, and Мо{sup 3+} paramagnetic centers are detected. The fine structure parameters of the spin Hamiltonian are determined or refined for these centers. The orientation behavior of previously unobserved forbidden transitions is considered for the Cr{sup 3+} centers. It is shown that two Mo{sup 3+} signals that are detected in magnetic fields directed parallel to the crystallographic axes do not belong to different molybdenum centers, but are two intradoublet transitions of the same center.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Response of the Dielectric Parameters of (110)SrTiO{sub 3} Films to the Formation of Ferroelectric Domains in Their Volume

Three-layer SrRuO{sub 3}/SrTiO{sub 3}/SrRuO{sub 3} heterostructures were grown by laser evaporation on (110)LaAlO{sub 3} substrates. Photolithography and ion etching are used to form plane-parallel film capacitors, in which a layer of strontium titanate is placed between two film electrodes of strontium ruthenate. Data on the structure and orientation of the intermediate SrTiO{sub 3} layer in the grown heterostructures were obtained. The variation of the dielectric constant and dielectric loss of the SrTiO{sub 3} intermediate layer upon varying the temperature and intensity of an external electric field was studied.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Flash Sintering of Oxide Ceramics under Microwave Heating

We report on the results of the analysis of the effect of flash sintering, which is observed upon heating compacted powder materials by high-intensity microwave radiation. Ceramic samples of Y{sub 2}O{sub 3}, MgAl{sub 2}O{sub 4}, and Yb: (LaO){sub 2}O{sub 3} were sintered to a density exceeding 98–99% of the theoretical value during 0.5–5 min without isothermal hold. The specific microwave power absorbed volumetrically in the samples was 20–400 W/cm{sup 3}. Based on the analysis of the experimental data (microwave radiation power and heating and cooling rates) and of the microstructure of the obtained materials, we propose a mechanism of flash sintering based on the evolution of the thermal instability and softening (melting) of the grain boundaries. The proposed mechanism also explains the flash sintering effect observed when a dc or a low-frequency ac voltage is applied to the samples. The microwave heating makes it possible to implement flash sintering without using electrodes for supplying energy to the articles being sintered.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Monitoring the Caustic Dissolution of Aluminum Alloy in a Radiochemical Hot Cell Using Raman Spectroscopy

Chemical processing of highly radioactive materials commonly takes place in heavily shielded hot cells. The remote, real-time monitoring of chemical processing streams via optical spectroscopic techniques in hot cells may be particularly useful. Here in this paper, we describe the implementation of Raman spectroscopy and chemometric analysis to monitor the dissolution of aluminum-clad targets containing irradiated aluminum–neptunium oxide cermet pellets in caustic solutions in a hot cell environment. Partial least squares regression analysis was used to generate calibration models to quantify the concentration of dissolved aluminum, nitrate, and hydroxide in solutions within the radiochemical hot cell. This work explored a systematic approach to optimize a matrix of calibration standards using a D-optimal experimental design. The Design of Experiments-based regression model, in comparison to more traditional analytical approaches, was found to be the more practical method for building calibration models, with fewer samples, to obtain informative analytical data from Raman spectra.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Calcium- Silicate-Cement Based Blends with Natural Zeolites - Self-Healing Performance under Conditions of High-Temperature Geothermal Wells

Geothermal cements are subjects to thermal and mechanical shocks, high temperatures and aggressive environments that can cause cement damage and compromise well integrity, contaminate underground waters and, if not repaired in time, lead to the well collapse. Repairs of the damaged areas are problematic for subterranean constructions. Self-repairing cements are especially attractive for such applications.

15 GEOTHERMAL ENERGY↗
DOE OSTI2018

Acoustic Monitor for Particle Size and Bed Friction in a Carbonate Fluidized Bed at High Temperature - 18014

Previous work has shown that acoustic spectra of fluidized bed pressure fluctuations show many useful bed properties [1-3]. This current work further explores the use of acoustic monitors for an 18' diameter, 66-74'' height fluidized bed at >640 deg. C. This process denitrates and agglomerates an injected sodium/aluminum nitrate aqueous simulant and produces at steady-state a denitrated product of 200-300 micron sodium carbonate/aluminate particles. The fluidized bed shows characteristic acoustic resonances around 1-2 Hz in the FFT (Fast Fourier Transform) of pressure fluctuations for each of three taps at fluidized bed heights of 12'', 39'', and 58''. The acoustic resonance spectra depend on a bed friction that once calibrated, monitors the HMPD (harmonic mass mean particle diameter or Sauter mean diameter) along with other important bed properties. This fluidized bed operates at high temperature with an evolving HMPD that can be steady state with an appropriate superficial spatial velocity (SSV). The acoustic FFT integrated power spectrum, IPS, of pressure fluctuations represents the bed-friction damped RMS (root mean square) pressure fluctuations at each tap. The transition from a static to fluidized bed at each bed height occurs when the damped bed RMS pressure fluctuations are greater than the static head (the FFT zero Hz designated zero Hz proportional to FFT zero Hz) at that bed height. A bed will de-fluidize and become static at a bed height when bed friction completely dampens the RMS pressure fluctuations, which occurs for decreasing particle size among other factors. The ratio IPS/zero Hz then provides a continuous monitor of bed friction damping as well as particle size as the HMPD. Since HMPD and bed friction damping are both very important parameters for fluidized particle beds, the acoustic HMPD and bed friction damping both provide very useful monitors for fluidized bed operation. Such acoustic monitors have shown that they are especially sensitive to the presence of very fine particles in the bed of less than 50 microns diameter. Acoustic monitors for particle size and bed friction damping will be very useful in any fluidized bed, especially fluidized beds where particle size changes. The fluidized bed friction damping depends on many other bed properties besides particle size such as bed height, density, SSV, void fraction, gas viscosity, and fluidization scheme and so acoustic bed friction should also be useful for monitoring other bed properties besides particle size. In fact, the change in the static bed friction slope with SSV upon fluidization follows the Ergun function and reveals a minimum fluidization velocity for each HMPD. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗