Physics Commons^™

Corrosion Of Steel By Lead Bismuth Eutectic: Quarterly Report August September October 2002, John Farley

Transmutation Sciences Materials (TRP)

We continued with sputter depth profiling of 316 and 316L steel samples that have been exposed to LBE. We also calibrated the sputter depth profiling using a sample of SiO₂ on Si, and the SEM. This is a valuable independent determination of the thickness of oxide layers.

In the laboratory, progress continues using the XPS machine. Experiments have been performed on steel samples using Argon ions to mill away the surface of the sample, thereby making measurements as a function of depth. This "ion beam milling" proceeds slowly through the oxide layer that covers the steel sample. We are …

Dielectric Properties Of A Ferroelectric Copolymer Langmuir–Blodgett Film, Mahantappa S. Jogad, Stephen Ducharme

Stephen Ducharme Publications

We report measurements of the real (epsilon prime) and imaginary (epsilon double-prime) parts of the relative complex permittivity of a Langmuir–Blodgett film of ferroelectric copolymer of vinylidene fluoride (70%) with trifluoroethylene (30%). The measurements were made in the temperature range of 35 to 125° C, and frequency range of 19 Hz to 5 MHz. The results indicate low frequency loss due to conduction and dielectric loss peak near the ferroelectric–paraelectric phase transition.

Design And Analysis For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides: Quarterly Progress Report 5/16/02- 8/15/02, Yitung Chen, Randy Clarksean, Darrell Pepper

Fuels Campaign (TRP)

An important aspect of the Advanced Accelerator Applications (AAA) program is the development of a casting process by which volatile actinide element (i.e., americium) can be incorporated into metallic alloy fuel pins. The traditional metal fuel casting process uses an inductively heated crucible.

This process works well for the fabrication of metal fuel pins traditionally composed of alloys of uranium and plutonium, but does not work well when highly volatile actinides are included in the melt. The problem occurs both during the extended time period required to superheat the alloy melt as well as when the chamber must be evacuated. …

Corrosion Of Steel By Lead Bismuth Eutectic: Quarterly Report For May-June-July 2002, John Farley

Transmutation Sciences Materials (TRP)

The goal of this project is to understand the basic science of corrosion in the steel/LBE system.

We are taking more data, typically using the newly installed X-ray Photoelectron Spectrometry (XPS) apparatus, and analyzing our existing data. Undergraduate students Denise Parsons and Julia Manzerova have helped a great deal in the analysis of the data. We can obtain the elemental composition as a function of position within the sample. This gives clues to the migration of materials, the composition of the protective oxide layer, and the basic science of the corrosion process. We found dramatic differences between the exposed and …

Magnetic And Mössbauer Studies On Oxygen Deficient Perovskite, La₀.₆Sr₀.₄Feo3-Δ, Jinbo Yang, William B. Yelon, William Joseph James, X.-D. Zhou, Yixiang Xie, Harlan U. Anderson, Zili Chu

Physics Faculty Research & Creative Works

Samples of La_0.6Sr_0.4Fe_3-δ with varying oxygen vacancy contents were prepared by heating them in different gas flows. Magnetization measurement showed that samples with low oxygen vacancies have a magnetic ordering temperature in the range of 300-325 K while those with 9%-12% oxygen vacancies have a magnetic ordering temperature of 800 K and higher. Mössbauer spectra at 300 K exhibit paramagnetic or weak magnetic characteristics for the N₂, O₂, and air-quenched samples, whereas an average hyperfine field of 52 T is found for the CO/CO₂ reduced samples. The heat treatment in …

Humidity And Temperature Boundaries For Biofilm Formation In Yucca Mountain, Terry Ann Else, Penny S. Amy, James Jay, Amy J. Smiecinski

Publications (YM)

To determine the long-term success of the recommended Yucca Mountain high-level nuclear waste repository, studies of bacterial colonization and biofilm development are needed. Bacteria involved in microbially-influenced corrosion and degradation are known to form biofilms with the potential to impact the integrity of repository packaging and structural materials. Temperature and humidity are environmental factors that can greatly affect biofilm formation. Therefore, it is necessary to determine the temperature and humidity conditions that affect biofilm formation. Microcosms, which simulated the repository environment of Yucca Mountain, were placed at temperatures ranging from 30° C to 70° C and in relative humidities ranging …

Design And Analysis Of A Process For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides, Yitung Chen, Darrell Pepper, Randy Clarksean

Fuels Campaign (TRP)

UNLV has developed and will continue to develop process models for the analysis of melt casting processes. This work will continue to be performed under the guidance of Argonne National Laboratory (ANL) engineers to ensure that their knowledge and experience benefits the project. The research to be conducted during the second year will center on performing detailed analyses on a conceptual design of an inductively heated skull-crucible casting furnace. Processing conditions will be analyzed, basic models utilized, and detailed heat and mass transfer models will be developed to analyze the most promising processes. The goal of this second year is …

Third Quarter Report, Covering January Through March 2002, John Farley

Transmutation Sciences Materials (TRP)

Progress from June 2001-November 2001 was presented at the winter meeting of the American Nuclear Society in Reno (November 12-15, 2001), and incorporated into a refereed conference proceeding. A copy of the refereed conference proceeding has been provided to Tony Hechanova. In brief, the paper described the new program to examine the corrosive effects of lead-bismuth eutectic (LBE) on steels. We employed various types of surface studies (Scanning Electron Microscope [SEM], and X-ray Photoelectron Spectrometry [XPS]) to examine steel samples that had been exposed to LBE for various lengths of time at various temperatures. The goal is to understand the …

Design And Analysis For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides: Quarterly Progress Report 11/16/01- 2/15/02, Yitung Chen, Randy Clarksean, Darrell Pepper

Fuels Campaign (TRP)

An important aspect of the Advanced Accelerator Applications (AAA) program is the development of a casting process by which volatile actinide element (i.e., americium) can be incorporated into metallic alloy fuel pins. The traditional metal fuel casting process uses an inductively heated crucible.

This process works well for the fabrication of metal fuel pins traditionally composed of alloys of uranium and plutonium, but does not work well when highly volatile actinides are included in the melt. The problem occurs both during the extended time period required to superheat the alloy melt as well as when the chamber must be evacuated. …

Thermoelectric Properties Of Bi2sr2co2o9 Whiskers Under Hydrostatic Pressure, F Chen, Kevin L. Stokes, Ryozi Funahashi

Physics Faculty Publications

We report the temperature dependence of thermopower (S) in the ab plane of Bi2Sr2Co2O9 {BC-222} single crystalline whiskers under high pressure up to 1.2 GPa. Special modifications were made to our high-pressure transport measurement system to improve the measurement accuracy of S for whiskers with high resistance. Pressure improved the contact resistance dramatically. We observed a slight decrease of S and four-wire electrical conductivity (sigma) under high pressure. As a result, the power factor (S2sigma) was decreased less than 20% by pressure. From the temperature dependence of sigma, the band gap of BC-222 whiskers increase very slightly …

Effect Of Ga Content On Defect States In Cuin1-XGaXSe2 Photovoltaic Devices, Jennifer T. Heath, J. David Cohen, William N. Shafarman, Dongxiang Liao, Angus Rockett

Faculty Publications

Defects in the band gap of CuIn_1-xGa_xSe₂ have been characterized using transient photocapacitance spectroscopy. The measured spectra clearly show response from a band of defects centered around 0.8 eV from the valence band edge as well as an exponential distribution of band tail states. Despite Ga contents ranging from Ga/(In+Ga)=0.0 to 0.8, the defect bandwidth and its position relative to the valence band remain constant. This defect band may act as an important recombination center, contributing to the decrease in device efficiency with increasing Ga content.

Corrosion Of Steel By Lead Bismuth Eutectic: Year 1 Annual Report, John Farley

Transmutation Sciences Materials (TRP)

The goal is to investigate the corrosion of stainless steel by lead-bismuth eutectic (LBE), which has been proposed for use as a blanket coolant and a spallation target in the transmuter.

Corrosion Of Steel By Lead Bismuth Eutectic, John Farley, Dale L. Perry, Allen L. Johnson

Transmutation Sciences Materials (TRP)

This research program will analyze various steel samples that have been exposed to LBE as part of the national program to develop LBE and transmutation technologies. This information will be paramount in developing engineering efforts to control, avoid, and/or minimize the effect of corrosion of steels by LBE in transmuter and LBE systems. Additionally, this program provides UNLV researchers with hands-on experience that will be crucial in developing the UNLV LBE program, supporting the University’s mission with the ISTC target complex, and the future development of additional facilities to examine LBE systems.

The research group plans to test the hypothesis …

Effect Of Oxygen Vacancies On The Magnetic Structure Of The La₀.₆Sr₀.₄Feo3-Δ Perovskite: A Neutron Diffraction Study, Zili Chu, William B. Yelon, Jinbo Yang, William Joseph James, Harlan U. Anderson, Yixiang Xie, Satish K. Malik

Physics Faculty Research & Creative Works

Magnetic interactions in perovskite compounds of the type La_1-xSr_xMO_3-δ (M=3d transition such as Mn and Fe) are presumed to arise through a super exchange between 3d electrons of the magnetic ions via oxygen orbitals. The magnetic structure of La_0.6Sr_0.4FeO_3-δ has been studied with neutron diffraction. Oxygen vacancies were created by annealing samples under various gases including N₂, air and mixtures of CO/CO₂. All La_0.6Sr_0.4FeO_3-δ compounds maintain the rhombohedral structure (space group R3̄c). The air- or oxygen-annealed samples have almost no oxygen …

Atomic Hydrogen Cleaning Of Inp(100): Electron Yield And Surface Morphology Of Negative Electron Affinity Activated Surfaces, M. A. Hafez, H. E. Elsayed-Ali

Electrical & Computer Engineering Faculty Publications

Atomic hydrogen cleaning of the InP(100) surface has been investigated using quantitative reflection high-energy electron diffraction. The quantum efficiency of the surface when activated to negative electron affinity was correlated with surface morphology. The electron diffraction patterns showed that hydrogen cleaning is effective in removing surface contaminants, leaving a clean, ordered, and (2×4)-reconstructed surface. After activation to negative electron affinity, a quantum efficiency of ∼6% was produced in response to photoactivation at 632 nm. Secondary electron emission from the hydrogen-cleaned InP(100)-(2×4) surface was measured and correlated to the quantum efficiency. The morphology of the vicinal InP(100) surface was investigated using …

High-Efficiency Solar Cells Based On Cu(Inal)Se[Sub 2] Thin Films, S. Marsillac, P. D. Paulson, M. W. Haimbodi, R. W. Birkmire, W. N. Shafarman

Electrical & Computer Engineering Faculty Publications

A Cu(InAl)Se₂solar cell with 16.9% efficiency is demonstrated using a Cu(InAl)Se₂thin film deposited by four-source elemental evaporation and a device structure of glass/Mo/Cu(InAl)Se₂/CdS/ZnO/indium tin oxide/(Ni/Algrid)/MgF₂. A key to high efficiency is improved adhesion between the Cu(InAl)Se₂ and the Mo back contact layer, provided by a 5-nm-thick Ga interlayer, which enabled the Cu(InAl)Se₂ to be deposited at a 530 °C substrate temperature. Film and device properties are compared to Cu(InGa)Se₂ with the same band gap of 1.16 eV. The solar cells have similar behavior, with performance limited by recombination through …