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Description: Progress is reported in the following studies: determination of the liquidus curve for U alloys having 0 to 4.8% C; the preparation and properties of the U - Cu, U -Sn, U-Bi, and U-Hg systems; the preparation of U by extraction of the hydride as amalgam; laboratory methods for the preparation of U and Th; the purification of Mg; determinations of B in lime; the effect of furnace temperafure and firing time on the yield of U; a comparison of the properties of Mg from various sources; and methods for casting U metal. (C.H.)
Date: October 31, 1958
Partner: UNT Libraries Government Documents Department

Nonequilibrium sulfur capture and retention in an air cooled slagging coal combustor

Description: Calcium oxide injected in a slagging combustor react with the sulfur from coal combustion to form sulfur bearing particles, which are deposited on the liquid slag layer on the combustor wall. Due to the low solubility of sulfur in slag, it must be drained from the combustor to limit sulfur gas re-evolution. Analysis indicated that slag mass flow rates in excess of 400 lb/hr should limit sulfur re- evolution. The objective of this 36 month project was to perform a series of 16 one day tests to determine the factors that control the retention of the sulfur in the slag. In the present quarterly reporting period, 3 days of combustor tests were performed, bringing the total number of tests performed to 19. Two of the test were a repeat of two tests performed in the previous quarter with a high, 37% ash, Indian coal. The high slag flow rate with that coal resulted in the highest observed sulfur retention to-date, namely 20% of the injected sulfur. In the present quarter, this test was repeated with the same coal feed rate but with 75% longer period of 2.4 hours. The total mineral matter injected was 635 lb/hr, compared to only 19.7 lb/hr of sulfur, of which 75% was from injected gypsum. However, despite excellent slag flow from the previous Indian coal tests, only 5.8% of the sulfur from the gypsum reported to the slag. Since substantial amounts slag remained on the combustor walls, it is concluded that still longer duration tests are required to establish equilibrium conditions. Current efforts are focused on finding a U.S. source of high ash coal to implement additional tests.
Date: August 13, 1997
Creator: Zauderer, B.
Partner: UNT Libraries Government Documents Department

Nonequilibrium Sulfur Capture and Retention in an Air cooled Slagging Coal Combustion.

Description: Calcium oxide sorbents injected in a slagging combustor react with the sulfur released during coal combustion to form sulfur bearing particles, some of which are deposited on the liquid slag layer on the combustor wall. Since the solubility of sulfur in liquid slag is low, the slag must be drained from the combustor to limit sulfur re-evolution into the gas phase. The objective of this 24 month project is to perform a series of 16 one day tests to determine the factors that control the retention of the sulfur in the slag that is drained from the combustor. The last of the 16 tests planned for this project was completed in the present reporting period. This was the first test in this project that validated one of the primary hypothesis of this project, namely to retain substantial quantities of sulfur in slag requires high slag mass flow rate. Previous attempts to achieve high sulfur retention with artificial slag met limited success. In this, the 16th test, a high, 37%, ash Indian coal was injected into Coal Tech`s 20 MMBtu/hr air cooled, slagging combustor with gypsum, CaSO{sub 4} (2H{sub 2}O). The slag analysis showed that 20% of the sulfur in the gypsum remained in the slag. This is double the highest sulfur concentration in slag measured in numerous test operations with this combustor. While the test results to date have met the objectives of this project, further high slag mass flow rate tests are planned with the Indian coal to optimize sulfur retention in slag.
Date: April 14, 1997
Creator: Zauderer, B.
Partner: UNT Libraries Government Documents Department

Time dependent effects and transport evidence for phase separation in La{sub 0.5}Ca{sub 0.5}MnO{sub 3}

Description: The ground state of La{sub 1{minus}x}Ca{sub x}MnO{sub 3} changes from a ferromagnetic metallic to an antiferromagnetic charge-ordered state as a function of Ca concentration at x {approximately} 0.50. The authors present evidence from transport measurements on a sample with x = 0.50 that the two phases can coexist, in agreement with other observations of phase separation in these materials. They also observe that, by applying and then removing a magnetic field to the mainly charge-ordered state at some temperatures, they can ``magnetically anneal'' the charge order, resulting in a higher zero-field resistivity. They also observe logarithmic time dependence in both resistivity and magnetization after a field sweep at low temperatures.
Date: February 17, 2000
Creator: Roy, M.; Mitchell, J. F. & Schiffer, P.
Partner: UNT Libraries Government Documents Department


Description: A new screening method for fuel contamination in soils was recently developed as American Society for Testing and Materials (ASTM) Method D-583 1-95, Standard Test Method for Screening Fuels in Soils. This method uses low-toxicity chemicals and can be used to screen organic-rich soils. In addition, it is fast, easy, and inexpensive to perform. The screening method calls for extracting a sample of soil with isopropyl alcohol following treatment with calcium oxide. The resulting extract is filtered, and the ultraviolet absorbance of the extract is measured at 254 nm. Depending on the available information concerning the contaminant fuel type and availability of the contaminant fuel for calibration, the method can be used to determine the approximate concentration of fuel contamination, an estimated value of fuel contamination, or an indication of the presence or absence of fuel contamination. Fuels containing aromatic compounds, such as diesel fuel and gasoline, as well as other aromatic-containing hydrocarbon materials, such as motor oil, crude oil, and coal oil, can be determined. The screening method for fuels in soils was evaluated by conducting a collaborative study on the method and by using the method to screen soil samples at an actual field site. In the collaborative study, a sand and an organic soil spiked with various concentrations of diesel fuel were tested. Data from the collaborative study were used to determine the reproducibility (between participants) and repeatability (within participant) precision of the method for screening the test materials. The collaborative study data also provide information on the performance of portable field equipment versus laboratory equipment for performing the screening method and a comparison of diesel concentration values determined using the screening method versus a laboratory method. Data generated using the method to screen soil samples in the field provide information on the performance of the method ...
Date: April 1, 1997
Creator: Sorini, Susan S. & Schabron, John F.
Partner: UNT Libraries Government Documents Department

Grain boundary structures in La{sub 2/3}Ca{sub 1/3}MnO{sub 3} thin films

Description: As with many other oxide-based compounds that exhibit electronic behavior, structural defects have a strong influence on the electronic properties of the CMR manganites. In this work, the authors have studied the effect of grain boundaries on the transport properties and on the local orientation of magnetization. Thin films of the perovskite-related La{sub 2/3}Ca{sub 1/3}MnO{sub 3} compound were deposited onto bicrystal substrates using pulsed laser deposition. Transport measurements showed some enhancement of magnetoresistance across the grain boundary. The structure of the boundary was evaluated by electron microscopy. In contrast with the highly meandering boundaries typically observed in bicrystals of high temperature superconductors, the boundaries in these films are relatively straight and well defined. However, magneto-optical imaging showed that the local magnetization was oriented out of the plane at the grain boundary while it was oriented within the plane in the grains on either side. This coordinated reorientation of local magnetization near the grain boundary leads to enhanced magnetoresistance across the boundary in low fields.
Date: October 26, 1999
Creator: Miller, D. J.; Lin, Y.-K.; Vlasko-Vlasov, V. & Welp, U.
Partner: UNT Libraries Government Documents Department

The temperature dependent anomalous Hall effect in La-Ca-Mn-O films

Description: The colossal magnetoresistance of La{sub 1{minus}x}Ca{sub x}MnO{sub 3} has been reported in many experiments. The authors present their study of the anomalous Hall effect in epitaxial La{sub 0.67}Ca{sub 0.33}MnO{sub 3} thin films. They have measured the temperature dependence of resistivity, magnetization and AHE coefficients between 300K and 5K for the samples grown on different substrates. From these studies, the relation between the resistivity and AHE coefficient as well as the temperature dependence of AHE coefficient are explored. The results show that the direction of AHE is reversed below approximately 100K. This sign reversal is discussed in term of the change of band structure and the co-existence of hole-like and electron-like conduction.
Date: October 27, 1999
Creator: Lin, Y.; Miller, D. J.; Jiang, J. S.; Pearson, J. & Bader, S. D.
Partner: UNT Libraries Government Documents Department

Measurement of the critical current and transient characteristics of a high-temperature superconductor tube using a pulsed current supply.

Description: The transient response of a melt-cast-processed BSCCO-2212 superconductor tube is investigated by using a pulsed current source. It was found that (1) the maximum induced current and the excitation current at field penetration increase with the maximum excitation current, and (2) there is a time delay between peak excitation current and peak magnetic field inside the superconductor. These observations can be explained by the concept of magnetic diffusion. The ac steady-state critical current of the superconductor was found to depend on the magnitude of the current increment. The critical current determined by using the pulsed current system agrees fairly well with the ac steady-state critical current determined by using relatively large current increment.
Date: August 27, 1998
Creator: Cha, Y. S.
Partner: UNT Libraries Government Documents Department

Energy and environmental (JSR) research emphasizing low-rank coal

Description: The products of plastic thermal depolymerization can be used for the manufacture of new plastics or various other hydrocarbon-based products. One thermal depolymerization development effort is ongoing at the Energy & Environmental Research Center (EERC) of the University of North Dakota, under joint sponsorship of the American Plastics Council, the 3M corporation, and the Department of Energy. Thermal depolymerization process development began at the EERC with a benchscale program that ran from 9/92 to 6/93 (1). Testing was conducted in a 1-4-lb/hr continuous fluid-bed reactor (CFBR) unit using individual virgin resins and resin blends and was intended to determine rough operating parameters and product yields and to identify product stream components. Process variables examined included temperature and bed material, with a lesser emphasis on gas fluidization velocity and feed material mix. The following work was performed: (1) a short program to determine the suitability of using CaO in a postreactor, fixed bed for chlorine remediation, (2) thermal depolymerization of postconsumer plastics, and (3) testing of industrial (3M) products and wastes to determine their suitability as feed to a thermal depolymerization process. The involvement of DOE in the development of the plastics thermal depolymerization process has helped to facilitate the transfer of coal conversion technology to a new and growing technology area -- waste conversion. These two technology areas are complementary. The application of known coal conversion technology has accelerated the development of plastics conversion technology, and findings from the plastics depolymerization process development, such as the development of chlorine remediation techniques and procedures for measurement of organically associated chlorine, can be applied to new generations of coal conversion processes.
Date: December 1, 1994
Creator: Sharp, L.L.
Partner: UNT Libraries Government Documents Department


Description: Recent instrumentation developments in photoemission are providing new insights into the physics of complex materials. With increased energy and momentum resolution, it has become possible to examine in detail different contributions to the self-energy or inverse lifetime of the photohole created in the photoexcitation process, Employing momentum distribution and energy distribution curves, a detailed study of the optimally doped cuprate, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub g+{delta}}, shows that the material behaves like a non-Fermi liquid with no evidence for the quasi-particles characteristic of a Fermi liquid.
Date: October 13, 1999
Creator: JOHNSON,P.D.
Partner: UNT Libraries Government Documents Department


Description: In reduction reactions of CeO/sub 2/, with calcium and a CaCl/sub 2/ flux, the use of vibrational energy was shown to have a marked effect on the yield of coalesced metal. Buttons of 40 to 50% theoretical yield were obtained from the vibrated reductions. As the flux concentration is decreased, the slag becomes more viscous containing undissolved CaO. The undissolved CaO present prevents the metal from completely coalescing, but the metal can be recovered from the slag and coalesced under CaCl/sub 2/ containing a small amount of calcium to reduce any oxide skin present. Cerium pellet yields of 50 to 60% metal were obtained by the procedure and were not difficult to handle in air. Cerium was used as a stand-in material for plutonium. (B.O.G.)
Date: February 13, 1956
Creator: Tolley, W. B.
Partner: UNT Libraries Government Documents Department

Anomalous Hall effect in Gd-doped La{sub 2/3}Ca{sub 1/3}MnO{sub 3}

Description: Ceramic samples of (La{sub 1-x}Gd{sub x}){sub 2/3}Ca{sub 1/3}MnO{sub 3} were prepared and used as targets to grow films onto LaAlO{sub 3} substrates by pulsed laser deposition. Electrical resistance and thermopower, measured vs temperature and applied magnetic fields indicate transport dominated by positive small polarons in the high temperature paramagnetic state. The Hall effect was measured in 0.5 {mu}m thick films of composition x=0 and x=0.25. No evidence for extraordinary hall effect was found in the paramagnetic regime. Instead, the magnitude of the Hall coefficient decreases exponentially with temperature. This behavior and its anomalous negative sign are interpreted to result from face-diagonal hopping of small polarons in the Mn sublattice.
Date: October 1, 1996
Creator: Jaime, M.; Hardner, H.; Salamon, M.B.; Rubinstein, M.; Dorsey, P. & Emin, D.
Partner: UNT Libraries Government Documents Department

{open_quotes}Local texture, current flow, and superconductive transport properties of Tl1223 deposits on practical substrates{close_quotes}

Description: Quantitative investigations of the crystal grain orientations and electrical transport properties of high temperature superconducting (HTS)TiBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+x} (Tl1223) deposits on polycrystalline substrates show that current flow comprises percolative networks of strongly-coupled material. Superconductive transport properties on different samples, on the same samples at different widths, and on samples with artificially-induced strong flux pinning defects confirm the nature of current flow, and suggest that these materials may be useful as a new class of HTS conductors.
Date: May 1, 1996
Creator: Christen, D.K.; Specht, E.D. & Goyal, A.
Partner: UNT Libraries Government Documents Department

High T{sub c} superconductors: New insights from angle-resolved photoemission

Description: Recent angle-resolved photoemission (ARPES) studies of the high T{sub c} superconductors by the Argonne group are briefly reviewed. First we discuss sum rules to establish a spectral function interpretation of the data, and the use of ARPES to obtain the momentum distribution. We then apply these ideas to the normal and superconducting state spectra for Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8}. Among the topics discussed are the Fermi surface, polarization selection rules, bilayer splitting and the superconducting gap.
Date: November 1, 1995
Creator: Randeria, M.
Partner: UNT Libraries Government Documents Department

Trilayer Josephson junctions produced by atomic layer-by-layer FORCE (Flexible Oxide Reaction Controlled Epitaxy). Final report

Description: Lawrence Livermore National Laboratory is working with Varian Associates to lay the groundwork for the routine, reproducible fabrication of high-temperature superconducting trilayer structures. The objectives of this program are: To identify high temperature, superconducting materials, metallic and insulating barrier materials and associated substrate and electrode materials for engineered trilayer structures that can provide Josephson Junction devices with desired characteristics for sensor or electronic circuit use. To identify and test potentially useful analysis techniques and to provide data appropriate for the validation and analysis of the input materials, trilayer structures and completed JJ devices. To integrate the analysis results with the existing Varian data base to optimize the growth and fabrication process to obtain more reproducible devices across each chip and from chip to chip. These objectives were defined by a detailed set of milestones for both Lawrence Livermore National Laboratory and Varian Associates all of which have been meet. The timing of the milestones was revised midway through the CRADA term to allow a longer time to pursue the objectives at no additional cost to either partner.
Date: September 30, 1995
Partner: UNT Libraries Government Documents Department

From double exchange to superexchange in charge ordering perovskite manganites

Description: The authors found dynamic ferromagnetic correlations at the room temperature in perovskite manganites which have an antiferromagnetic insulating ground state. They are replaced by antiferromagnetic correlations when the electrons order. The results indicate that the double exchange mechanism is turned off by electron localization at low temperatures.
Date: August 17, 1998
Creator: Bao, W.; Axe, J.D.; Chen, C.H.; Cheong, S.W.; Schiffer, P. & Roy, M.
Partner: UNT Libraries Government Documents Department

Science and technology of reduced-dimensional magnetic materials

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). This work involved the synthesis of single crystal and thin film samples of magnetoresistive manganites (LaMnO{sub 3} doped with Ca and Sr) and the characterization of their electronic transport properties to understand the underlying physical mechanisms responsible for the colossal magnetoresistance (CMR) of these materials. The experimental program was supplemented by a modeling effort that sought to develop microscopic mathematical models of the observed phenomena. The authors succeeded in finding an important relation between the magnetization and resistivity in these materials, which helps to explain the importance of lattice distortions accompanied by clusters of ferromagnetic spins (called spin-lattice polarons) in the CMR phenomena. In addition, they developed rudimentary tunnel junctions of CMR-insulator-CMR multilayers that will lead to possible applications of these materials as magnetic sensors.
Date: December 31, 1998
Creator: Heffner, R.H.; Bishop, A.R.; Hundley, M.F.; Jia, Q.; Neumeier, J.J.; Trugman, S.A. et al.
Partner: UNT Libraries Government Documents Department