Hydrogen has been the source of intense research and diverse methodologies to store it are being investigated. Single and multi-walled carbon nanotubes (CNTs) show promise as good options to achieve high storage. Alth...
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ISBN:
(纸本)9781118029459
Hydrogen has been the source of intense research and diverse methodologies to store it are being investigated. Single and multi-walled carbon nanotubes (CNTs) show promise as good options to achieve high storage. Although the current hydrogen storage capacity of unsupported CNTs does not fulfill the DoE programmatic targets for on-board hydrogen storage systems, we are working on further research to modify the nanostructures to affect its properties. The main objective of this work is to evaluate mechanisms of functionalization and purification by chemical and irradiation techniques to create functional groups in the surface and add new gateways for atomic hydrogen intake into the nanotubes to enhance the hydrogen storage capacity. Functional groups serve as a medium to attach metal nanoparticles to carbon nanotubes. SEM, STEM and XPS were used for morphological chemical and structural characterization of the nanostructure. Nanoparticles were obtained in the range of 15 to 30nm with a better distribution for samples irradiated at 15kGy.
The nuclear Waste Management program at Lawrence Livermore National Laboratory is responsible for the development of the waste package design to meet the nuclear Regulatory Commission licensing requirements for the Ne...
The nuclear Waste Management program at Lawrence Livermore National Laboratory is responsible for the development of the waste package design to meet the nuclear Regulatory Commission licensing requirements for the Nevada nuclear Waste Storage Investigations (NNWSI) Project. The metallic container component of the waste package is required to assist in providing substantially complete containment of the waste for a period of up to 1000 years. Long term phase stability of the austenitic candidate materials (304L and 316L stainless steels and alloy 825) over this time period at moderate temperatures (100–250°C) can impact the mechanical and corrosion behavior of the metal barrier. A review of the technical literature with respect to phase stability of 304L, 316L and 825 is presented. The impact of martensitic transformations, carbide precipitation and intermediate (σ. χ, and η) phase formation on the mechanical properties and corrosion behavior of these alloys at repository relevant conditions is discussed. The effect of sensitization on intergranular stress corrosion cracking (IGSCC) of each alloy is also addressed. A summary of the impact of phase stability on the degradation of each alloy in the proposed repository environment is included.
In diagnostic radiology, the radiation interaction probability in matter is a strong function of the X-ray energy. The knowledge of the X-ray energy spectral distribution allows optimizing the radiographic imaging sys...
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Tungsten metal slugs were fabricated via Spark Plasma Sintering (SPS) of powdered metals at temperatures ranging from 1575 K to 1975 K and hold times of 5 minutes to 30 minutes, using powders with an average diameter ...
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ISBN:
(纸本)9781617828461
Tungsten metal slugs were fabricated via Spark Plasma Sintering (SPS) of powdered metals at temperatures ranging from 1575 K to 1975 K and hold times of 5 minutes to 30 minutes, using powders with an average diameter of 7.8 μm. Sintered tungsten specimens were found to have relative densities ranging from 83% to 94% of the theoretical density for tungsten. Consolidated specimens were also tested for their Vickers Hardness Number (VHN), which were plotted as a function of relative density. Concurrently, tungsten and rhenium powders with average respective diameters of 0.5 μm and 13.3 μm were pre-processed either by High-Energy-Ball-Milling (HEBM) or by homogeneous mixing to yield W-25at.%Re mixtures. The powder batches were sintered at temperatures of 1975 K and 2175 K for hold times up to 60 minutes yielding relative densities in the range 94% to 97%. The combination of HEBM and sintering showed a significant decrease in the intermetallic phases compared to that of the homogenous mixing and sintering.
This paper studies the feasibility of a 10 kWe radioisotope-powered closed Brayton cycle for pulsed power station keeping applications. The study evaluates the specific power of the proposed system compared to current...
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ISBN:
(纸本)9781617828461
This paper studies the feasibility of a 10 kWe radioisotope-powered closed Brayton cycle for pulsed power station keeping applications. The study evaluates the specific power of the proposed system compared to current solar-photovoltaic systems. To achieve a high power pulse from a continuous low power input, a boron thermal capacitor surrounds a tungsten cermet matrix containing a radioisotope heat source which gradually adds heat to the thermal capacitor. During a power pulse this heat is removed by a HeXe coolant which expands through a closed Brayton conversion cycle to produce electric power for the spacecraft's ion thrusters. Since real time heat rejection is not necessary for a pulsed power system, a lithium thermal capacitor absorbs waste heat for the duration of the pulse, and radiates that heat to space between pulses.
We predicted the ferroelectric–ferromagnetic multiferroic properties of EuTiO3 nanowires and generated the phase diagrams in coordinates of temperature and wire radii. The calculations were performed within the Landa...
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We predicted the ferroelectric–ferromagnetic multiferroic properties of EuTiO3 nanowires and generated the phase diagrams in coordinates of temperature and wire radii. The calculations were performed within the Landau-Ginzburg-Devonshire theory with phenomenological parameters extracted from tabulated experimental data and first-principles calculations. Since bulk EuTiO3 is antiferromagnetic at temperatures lower than 5.5 K and paraelectric at all temperatures, our goal was to investigate the possibility of inducing the ferroelectric and ferromagnetic properties of EuTiO3 by reducing the bulk to nanosystems. Our results indicate that ferroelectric spontaneous polarization of ∼0.1–0.5 C/m2 is induced in EuTiO3 nanowires due to the intrinsic surface stress, which is inversely proportional to the nanowire radius. Spontaneous polarization exists at temperatures lower than 300 K for wire diameter of ∼4 lattice constants with 10 N/m surface stress coefficient. Due to the strong biquadratic magnetoelectric coupling, the spontaneous polarization in turn induces the ferromagnetic phase at temperatures lower than 30 K for 2-nm nanowire and at temperatures lower than 10 K for 4-nm nanowire in EuTiO3. Thus, we predicted that the EuTiO3 nanowires can be the new ferroelectric–ferromagnetic multiferroic.
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