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Remediation of Cr(VI) by biogenic magnetic nanoparticles: An x-ray magnetic circular dichroism study

Description: Biologically synthesized magnetite (Fe{sub 3}O{sub 4}) nanoparticles are studied using x-ray absorption and x-ray magnetic circular dichroism following exposure to hexavalent Cr solution. By examining their magnetic state, Cr cations are shown to exist in trivalent form on octahedral sites within the magnetite spinel surface. The possibility of reducing toxic Cr(VI) into a stable, non-toxic form, such as a Cr{sup 3+}-spinel layer, makes biogenic magnetite nanoparticles an attractive candidate for Cr remediation.
Date: September 4, 2009
Creator: Telling, N. D.; Coker, V. S.; Cutting, R. S.; van der Laan, G.; Pearce, C. I.; Pattrick, R. A. D. et al.
Partner: UNT Libraries Government Documents Department

AEM investigation of tetrahedrally coordinated Ti{sup 4+} in nickel-titanate spinel

Description: Stoichiometry and site distribution of metastable nickel-titanate spinel was studied with AEM. Results of EDXS and EELS agree that the metastable spinel is nonstoichiometric and titanium-deficient relative to its hypothetical endmember composition, ``Ni{sub 2}TiO{sub 4}``. The titanium deficiency has been determined by EELS to be {Delta} = 0.025 {plus_minus} 0.005. Channeling-enhanced microanalysis and ELNES studies indicate that the Ti{sup 4+} and Ni{sup 2+} cations are in tetrahedral and octahedral coordination, respectively, so that the metastable spinel has the normal cation distribution: Ti{sub l-{Delta}}[Ni{sub 2(1+{Delta})}]O{sub 4}. This is consistent with neutron powder-diffraction studies and SiO{sub 2}-solubility measurements of similar equilibrated and quenched spinel-containing specimens. Metastable nickel-titanate spinel therefore contrasts with stable stoichiometric spinels which tend to the inverse cation distribution, Me[MeTi]O{sub 4}.
Date: December 31, 1994
Creator: Anderson, I.M.; Bentley, J. & Carter, C.B.
Partner: UNT Libraries Government Documents Department

Immiscibility in the Fe3O4-FeCr2O4 Spinel Binary

Description: A recent thermodynamic model of mixing in spinel binaries, based on changes in cation disordering (x) between tetrahedral and octahedral sites, is investigated for applicability to the Fe{sub 3}O{sub 4}-FeCr{sub 2}O{sub 4} system under conditions where incomplete mixing occurs. Poor agreement with measured consolute solution temperature and solvus is attributed to neglect of: (1) ordering of magnetic moments of cations in the tetrahedral sublattice antiparallel to the moments of those in the octahedral sublattice and (2) pair-wise electron hopping between octahedral site Fe{sup 3+} and Fe{sup 2+} ions. Disordering free energies ({Delta}G{sub D}), from which free energies of mixing are calculated, are modeled by {Delta}G{sub D} = {alpha}{chi} + {beta}{chi}{sup 2} - T(S{sub c} + {chi}{sigma}{sub el} + {gamma}{chi}{sigma}{sup mag}) where the previously-neglected effects are accommodated by: (1) adding a non-configurational entropy term to provide coupling between cation disordering and magnetic ordering and (2) revising the configurational entropy (S{sub c}) analysis. Applying the constraint {alpha} = -(2/3){beta} and regressing the existing database for Fe{sup 2+} ion disorder in Fe{sub 3}O{sub 4} gives: {beta} = -31,020 {+-} 1050 J mol{sup -1}, {sigma}{sub el}/R = -0.730 {+-} 0.081 and {gamma}, the coupling parameter between cation disordering and magnetic ordering, = -0.664 {+-} 0.075. The revised mixing model predicts a consolute solution temperature (T{sub cs}) = 600 C and a solvus at 500 C of n = 0.05 and 0.70 for the Fe(Fe{sub 1-n}Cr{sub n}){sub 2}O{sub 4} spinel binary.
Date: March 20, 2003
Creator: Ziemniak, S.E. & Castelli, R.A.
Partner: UNT Libraries Government Documents Department

Electrochemical cell for in-situ x-ray characterization

Description: An electrochemical cell suitable for in-situ XRD analysis is presented. Qualitative information such as phase formation and phase stability can be easily monitored using the in-situ cell design. Quantitative information such as lattice parameters and kinetic behavior is also straightforward. Analysis of the LiMn&sub2;O&sub4; spinel using this cell design shows that the lattice undergoes two major structural shrinkages at approx. 4.0 V and approx. 4.07 V during charging. These shrinkages correlate well with the two electrochemical waves observed and indicate the likelihood of two separate redox processes which charging and discharging.
Date: August 4, 1998
Creator: Doughty, D.H.; Ingersoll, D. & Rodriguez, M.A.
Partner: UNT Libraries Government Documents Department

Orbital Moment Determination in (MnxFe1-x)3O4 Nanoparticles

Description: Nanoparticles of (Mn{sub x}Fe{sub 1-x}){sub 3}O{sub 4} with a concentration ranging from x = 0 to 1 and a crystallite size of 14-15 nm were measured using X-ray absorption spectroscopy and X-ray magnetic circular dichroism to determine the ratio of the orbital moment to the spin moment for Mn and Fe. At low Mn concentrations, the Mn substitutes into the host Fe{sub 3}O{sub 4} spinel structure as Mn{sup 2+} in the tetrahedral A-site. The net Fe moment, as identified by the X-ray dichroism intensity, is found to increase at the lowest Mn concentrations then rapidly decrease until no dichroism is observed at 20% Mn. The average Fe orbit/spin moment ratio is determined to initially be negative and small for pure Fe{sub 3}O{sub 4} nanoparticles and quickly go to 0 by 5%-10% Mn addition. The average Mn moment is anti-aligned to the Fe moment with an orbit/spin moment ratio of 0.12 which gradually decreases with Mn concentration.
Date: October 22, 2010
Creator: Pool, V. L.; Jolley, C.; Douglas, T.; Arenholz, E. & Idzerda, Y. U.
Partner: UNT Libraries Government Documents Department

NOVEL REFRACTORY MATERIALS FOR HIGH ALKALI, HIGH TEMPERATURE ENVIRONMENTS

Description: Refractory materials can be limited in their application by many factors including chemical reactions between the service environment and the refractory material, mechanical degradation of the refractory material by the service environment, temperature limitations on the use of a particular refractory material, and the inability to install or repair the refractory material in a cost effective manner or while the vessel was in service. The objective of this project was to address the need for new innovative refractory compositions by developing a family of novel MgO-Al 2O3 spinel or other similar magnesia/alumina containing unshaped refractory composition (castables, gunnables, shotcretes, etc) utilizing new aggregate materials, bond systems, protective coatings, and phase formation techniques (in-situ phase formation, altered conversion temperatures, accelerated reactions, etc). This family of refractory compositions would then be tailored for use in high-temperature, high-alkaline industrial environments like those found in the aluminum, chemical, forest products, glass, and steel industries.
Date: September 1, 2011
Creator: Hemrick, James Gordon
Partner: UNT Libraries Government Documents Department

Immiscibility in the Nickel Ferrite-Zinc Ferrite Spinel Binary

Description: Immiscibility in the trevorite (NiFe{sub 2}O{sub 4}) - franklinite (ZnFe{sub 2}O{sub 4}) spinel binary is investigated by reacting 1:1:2 molar ratio mixtures of NiO, ZnO and Fe{sub 2}O{sub 3} in a molten salt solvent at temperatures in the range 400-1000 C. Single phase stability is demonstrated down to about 730 C (the estimated consolute solution temperature, T{sub cs}). A miscibility gap/solvus exists below Tcs. The solvus becomes increasingly asymmetric at lower temperatures and extrapolates to n - values = 0.15, 0.8 at 300 C. A thermodynamic analysis, which accounts for changes in configurational and magnetic ordering entropies during cation mixing, predicts solvus phase compositions at room temperature in reasonable agreement with those determined by extrapolation of experimental results. The delay between disappearance of magnetic ordering above T{sub C} = 590 C (for NiFe{sub 2}O{sub 4}) and disappearance of a miscibility gap at T{sub cs} is explained by the persistence of long-range ordering correlations in a quasi-paramagnetic region above T{sub C}.
Date: June 21, 2006
Creator: Ziemniak, SE; Gaddipati, AR; Sander, PC & Rice, SB
Partner: UNT Libraries Government Documents Department

Iodine Sequestration Using Delafossites and Layered Hydroxides

Description: The objective of this document is to report on early success for sequestering {sup 129}I. Sorption coefficients (K{sub d}) for I{sup -} and IO{sub 3}{sup -} onto delafossites, spinels and layered metal hydroxides were measured in order to compare their applicability for sequestering {sup 129}I. The studies were performed using a dilute fluid composition representative of groundwater indigenous to the Yucca mountain area. Delafossites generally exhibited relatively poor sorption coefficients (< 10{sup 1.7} mL/g). In contrast, the composition of the layered hydroxides significantly affects their ability to sorb I. Cu/Al and Cu/Cr layered hydroxide samples exhibit K{sub d}'s greater than 10{sup 3} mL/g for both I{sup -} and IO{sub 3}{sup -}.
Date: March 28, 2006
Creator: Pless, J.D.; Chwirka, J.B. & Krumhansl, J.L.
Partner: UNT Libraries Government Documents Department

Sapphire Fiber Optics Sensors for Engine Test Instrumentation

Description: This document is the final report for the Cooperative Research and Development Agreement (CRADA) between UT-Battelle and Prime Photonics, Inc. The purpose of this CRADA was to improve the properties of single crystal sapphire optical fibers for sensor applications. A reactive coating process was developed to form a magnesium aluminate spinel cladding on sapphire optical fibers. The resulting clad fiber had a numerical aperture, NA, of 0.09 as compared with 0.83 for the unclad fiber, dramatically enhancing its usefulness for sensor applications. Because the process allows one to control the diameter of the sapphire core within the fiber, it may be possible using this technology to develop waveguides that approach single-mode transmission character.
Date: September 19, 2003
Creator: Janney, MA
Partner: UNT Libraries Government Documents Department

Tuning magnetic frustration on the diamond lattice of the A-site magnetic spinels CoA12-xGax04: lattice expansion versus site disorder

Description: The spinels CoB{sub 2}O{sub 4} with magnetic Co{sup 2+} ions on the diamond lattice A site can be frustrated because of competing near-neighbor (J{sub 1}) and next-near neighbor (J{sub 2}) interactions. Here we describe attempts to tune the relative strengths of these interactions by substitution on the non-magnetic B-site. The system we employ is CoAl{sub 2-x}Ga{sub x}O{sub 4}, where Al is systematically replaced by the larger Ga, ostensibly on the B site. As expected, Ga substitution expands the lattice, resulting in Co atoms on the A-site being pushed further from one other and thereby weakening magnetic interactions. In addition, Ga distributes between the B and the A site in a concentration dependent manner displacing an increasing amount of Co from the A site with increasing x. This increased inversion, which is confirmed by neutron diffraction studies carried out at room temperature, affects magnetic ordering very significantly, and changes the nature of the ground state. Modeling of the magnetic coupling illustrates the complexity that arises from the cation site disorder.
Date: January 1, 2008
Creator: Proffen, Thomas E; Melot, Brent C; Page, Katharine; Seshadri, Ramzy; Stoudenmire, E M; Balents, Leon et al.
Partner: UNT Libraries Government Documents Department

OXYGEN ISOTOPIC COMPOSITIONS OF THE ALLENDE TYPE C CAIs: EVIDENCE FOR ISOTOPIC EXCHANGE DURING NEBULAR MELTING AND ASTEROIDAL THERMAL METAMORPHISM

Description: Based on the mineralogy and petrography, coarse-grained, igneous, anorthite-rich (Type C) calcium-aluminum-rich inclusions (CAIs) in the CV3 carbonaceous chondrite Allende have been recently divided into three groups: (i) CAIs with melilite and Al,Ti-diopside of massive and lacy textures (coarse grains with numerous rounded inclusions of anorthite) in a fine-grained anorthite groundmass (6-1-72, 100, 160), (ii) CAI CG5 with massive melilite, Al,Ti-diopside and anorthite, and (iii) CAIs associated with chondrule material: either containing chondrule fragments in their peripheries (ABC, TS26) or surrounded by chondrule-like, igneous rims (93) (Krot et al., 2007a,b). Here, we report in situ oxygen isotopic measurements of primary (melilite, spinel, Al,Ti-diopside, anorthite) and secondary (grossular, monticellite, forsterite) minerals in these CAIs. Spinel ({Delta}{sup 17}O = -25{per_thousand} to -20{per_thousand}), massive and lacy Al,Ti-diopside ({Delta}{sup 17}O = -20{per_thousand} to -5{per_thousand}) and fine-grained anorthite ({Delta}{sup 17}O = -15{per_thousand} to -2{per_thousand}) in 100, 160 and 6-1-72 are {sup 16}O-enriched relative spinel and coarse-grained Al,Ti-diopside and anorthite in ABC, 93 and TS26 ({Delta}{sup 17}O ranges from -20{per_thousand} to -15{per_thousand}, from -15{per_thousand} to -5{per_thousand}, and from -5{per_thousand} to 0{per_thousand}, respectively). In 6-1-72, massive and lacy Al,Ti-diopside grains are {sup 16}O-depleted ({Delta}{sup 17}O {approx} -13{per_thousand}) relative to spinel ({Delta}{sup 17}O = -23{per_thousand}). Melilite is the most {sup 16}O-depleted mineral in all Allende Type C CAIs. In CAI 100, melilite and secondary grossular, monticellite and forsterite (minerals replacing melilite) are similarly {sup 16}O-depleted, whereas grossular in CAI 160 is {sup 16}O-enriched ({Delta}{sup 17}O = -10{per_thousand} to -6{per_thousand}) relative to melilite ({Delta}{sup 17}O = -5{per_thousand} to -3{per_thousand}). We infer that CAIs 100, 160 and CG5 experienced melting in an {sup 16}O-rich ({Delta}{sup 17}O < -20{per_thousand}) nebular gas in the CAI-forming region. The Type C and Type-B-like portions of CAI 6-1-72 experienced melting in an {sup 16}O-depleted ({Delta}{sup 17}O {ge} -13{per_thousand}) nebular gas. CAIs ABC, TS26 and 93 ...
Date: February 21, 2008
Creator: Krot, A N; Chaussidon, M; Yurimoto, H; Sakamoto, N; Nagashima, K; Hutcheon, I D et al.
Partner: UNT Libraries Government Documents Department

Growth and characterization of superconducting spinel oxide LiTi2O4 thin films

Description: Epitaxial films of LiTi{sub 2}O{sub 4} on single crystalline substrates of MgAl{sub 2}O{sub 4}, MgO, and SrTiO{sub 3} provide model systems to systematically explore the effects of lattice strain and microstructural disorder on the superconducting state. Lattice strain that affects bandwidth gives rise to variations in the superconducting and normal state properties. Microstructural disorder, such as antiphase boundaries that give rise to Ti network disorder, reduces the critical temperature, and Ti network disorder combined with Mg interdiffusion lead to a much more dramatic effect on the superconducting state. Surface sensitive X-ray absorption spectroscopy has identified Ti to retain site symmetry and average valence of the bulk material regardless of film thickness.
Date: March 10, 2009
Creator: Chopdekar, R.V.; Wong, F.; Takamura, Y.; Arenholz, E. & Suzuki, Y.
Partner: UNT Libraries Government Documents Department

Enhanced Magnetization of CuCr2O4 Thin Films by Substrate-Induced Strain

Description: We report the synthesis of epitaxial spinel CuCr{sub 2}O{sub 4} thin films that display enhanced magnetization in excess of 200% of the bulk values when grown on single-crystal (110) MgAl{sub 2}O{sub 4} substrates. Bulk CuCr{sub 2}O{sub 4} is a ferrimagnetic insulator with a net magnetic moment of 0.5 {micro}{sub B} due to its distorted tetragonal unit cell (c/a= 1.29) and frustrated triangular moment configuration. We show that through epitaxial growth and substrate-induced strain, it is possible to tune the magnetic functionality of our films by reducing the tetragonal distortion of the unit cell which effectively decreases the frustration of the magnetic moments allowing for an overall greater net moment.
Date: September 17, 2008
Creator: Iwata, Jodi M.; Chopdekar, Rajesh V.; Wong, Franklin; Nelson-Cheeseman, Brittany B.; Arenholz, Elke & Suzuki, Yuri
Partner: UNT Libraries Government Documents Department

Interface Structure and Transport of Complex Oxide Junctions

Description: The interface structure and magnetism of hybrid magnetic tunnel junction-spin filter devices have been investigated and correlated with the transport behavior exhibited. Magnetic tunnel junctions made of theoretically predicted half-metallic electrodes (perovskite La0.7Sr0.3MnO3 and spinel Fe3O4) sandwiching a spinel NiMn2O4 tunnel barrier exhibit very high crystalline quality as observed by transmission electron microscopy. Structurally abrupt interfaces allow for the distinct magnetic switching of the electrodes as well as large junction magnetoresistance. The change in the magnetic anisotropy observed at the spinel-spinel interface supports the presence of limited interdiffusion and the creation of a magnetically soft interfacial layer, whose strong exchange coupling to the Fe3O4 electrode likely accounts for the low background magnetoresistance observed in these junctions, and the successful spin filtering when the barrier layer is ferrimagnetic.
Date: February 1, 2008
Creator: Nelson-Cheeseman, B. B.; Wong, F.; Chopdekar, R. V.; Chi, M.; Arenholz, E.; Browning, N. D. et al.
Partner: UNT Libraries Government Documents Department

Stabilization of insertion electrodes for lithium batteries.

Description: This paper discusses the techniques that are being employed to stabilize LiMn{sub 2}O{sub 4} spinel and composite Li{sub x}MnO{sub 2} positive electrodes. The critical role that spinel domains play in stabilizing these electrodes for operation at both 4 V and 3 V is highlighted. The concept of using an intermetallic electrode MM{prime} where M is an active alloying element and M{prime} is an inactive element (or elements) is proposed as an alternative negative electrode (to carbon) for lithium-ion cells. An analogy to metal oxide insertion electrodes, such as MnO{sub 2}, in which Mn is the electrochemically active ion and O is the inactive ion, is made. Performance data are given for the copper-tin electrode system, which includes the intermetallic phases eta-Cu{sub 6}Sn{sub 5} and Li{sub 2}CuSn.
Date: September 3, 1998
Creator: Thackeray, M. M.
Partner: UNT Libraries Government Documents Department

New Measurements of the Solubility of Metal Oxides at High Temperature

Description: The results of high temperature solubility studies at ORNL are presented in which mainly direct pH measurements were made of aqueous solutions in contact with the crystalline solid phases: Al(OH){sub 3}, AlOOH, Fe{sub 3}O{sub 4}, Mg(OH){sub 2}, Nd(OH){sub 3}, and ZnO. Examples are highlighted of specific phenomena such as: the kinetics of gibbsite and boehmite dissolution and precipitation; the appearance of metastable equilibria in the dissolution of Fe{sub 3}O{sub 4}; the extremely rapid precipitation of crystalline brucite, Mg(OH){sub 2}; and anomalies in the apparent solubility profiles of AlO(OH) and ZnO. General trends associated with the effects of temperature and ionic strength are mentioned. Some of the potentiometric investigations were augmented by conventional batch [AlO(OH) and ZnO], and flow-through column (ZnO) experiments. In the additional case of ZnCr{sub 2}O{sub 4}, the extremely low solubility of this spinel permitted application of only the latter technique and these results are discussed in terms of the measured chromium levels that resulted from incongruent dissolution.
Date: June 30, 2000
Creator: Palmer, G.A.; Benezeth, P.; Wesolowski, D.J.; Wood, S.A. & Xiao, C.
Partner: UNT Libraries Government Documents Department

Microstructure of Swift Heavy Ion Irradiated MgAl(Sub 2)O(Sub 4) Spinel

Description: Plan view and cross-section transmission electron microscopy was used to investigate the microstructure of magnesium aluminate spinel (MgAl{sub 2}O{sub 4}) following room temperature irradiation with either 430 MeV Kr, 614 MeV Xe, or 72 MeV I ions. The fluences ranged from 1 x 10{sup 16}/m{sup 2} (single track regime) to 1 x 10{sup 20}/m{sup 2}. Destruction of the ordered spinel crystal structure on both the anion and cation sublattices was observed in the ion tracks at low fluences. At intermediate fluences, the overlapping ion tracks induced the formation of a new metastable crystalline phase. Amorphization with a volumetric expansion of {approximately}35% was observed in spinel irradiated with swift heavy ions (electronic stopping powers >7 keV/nm) at fluences above 1 x 10{sup 19}/m{sup 2}. These results demonstrate that swift heavy ion radiation can induce microstructural changes not achievable with conventional elastic collision irradiation at comparable temperatures.
Date: November 30, 1998
Creator: Matzke, H.; Skuratov, V. A. & Zinkle, S. J.
Partner: UNT Libraries Government Documents Department

EFFECTS OF XE ION IRRADIATION AND SUBSEQUENT ANNEALING ON THE PROPERTIES OF MAGNESIUM-ALUMINATE SPINEL

Description: Single crystals of magnesium-aluminate spinel MgAl{sub 2}O{sub 4} were irradiated with 340 keV Xe{sup 2} ions at {minus}173 C ({approximately} 100 K). A fluence of 1 x 10{sup 20} Xe/m{sup 2} created an amorphous layer at the surface of the samples. The samples were annealed for 1 h at different temperatures ranging from 130 C to 880 C. Recrystallization took place in the temperature interval between 610 C and 855 C. Transmission electron microscopy (TEM) images show two distinct layers near the surface: (1) a polycrystalline layer with columnar grain structure; and (2) a buried damaged layer epitaxial with the substrate. After annealing at 1100 C for 52 days, the profile of implanted Xe ions did not change, which means that Xe ions are not mobile in the spinel structure up to 1100 C. The thickness of the buried damaged layer decreased significantly in the 1100 C annealed sample comparing to the sample annealed for 1 h at 855 C.
Date: April 1, 2000
Creator: AFANASYEV, I. & AL, ET
Partner: UNT Libraries Government Documents Department

Spinel electrodes for rechargeable lithium batteries.

Description: This paper gives a historical account of the development of spinel electrodes for rechargeable lithium batteries. Research in the late 1970's and early 1980's on high-temperature . Li/Fe{sub 3}O{sub 4} cells led to the evaluation of lithium spinels Li[B{sub 2}]X{sub 4} at room temperature (B = metal cation). This work highlighted the importance of the [B{sub 2}]X{sub 4}spinel framework as a host electrode structure and the ability to tailor the cell voltage by selection of different B cations. Examples of lithium-ion cells that operate with spinel anode/spinel cathode couples are provided. Particular attention is paid to spinels within the solid solution system Li{sub 1+x}Mn{sub 2-x}O{sub 4} (0 {le} x {le} 0.33).
Date: November 10, 1999
Creator: Thackeray, M. M.
Partner: UNT Libraries Government Documents Department

Application of Electron Backscattered Diffraction (EBSD) and Atomic Force Microscopy (AFM) to Determine Texture, Microtexture, and Grain Boundary Energies in Ceramics

Description: Crystallographic orientations in alumina (Al<sub>2</sub>0<sub>3</sub>) and magnesium aluminate spinel (MgAl<sub>2</sub>0<sub>4</sub>) were obtained using electron backscattered diffraction (EBSD) patterns. The texture and mesotexture (grain boundary misorientations) were random and no special boundaries were observed. The relative grain boundary energies were determined by thermal groove geometries using atomic force microscopy (AFM) to identify relationships between the grain boundary energies and misorientations.
Date: May 19, 1999
Creator: Glass, S.J.; Rohrer, G.S.; Saylor, D.M. & Vedula, V.R.
Partner: UNT Libraries Government Documents Department

Ionic modeling of lithium manganese spinel materials for use in rechargeable batteries

Description: In order to understand and evaluate materials for use in Li ion rechargeable battery electrodes, we have modeled the crystal structures of various Mn oxide and Li Mn oxide compounds. We have modeled the MnO{sub 2} polymorphs and several spinels with intermediate compositions based on the amount of Li inserted into the tetrahedral site. 3-D representations of the structures provide a basis for identifying site occupancies, coordinations, Mn valence, order-disorder, and potentially new dopants for enhanced cathode behavior. XRD simulations of the crystal structures provide good agreement with observed patterns for synthesized samples. Ionic modeling of these materials consists of an energy minimization approach using Coulombic, repulsive, and van der Waals interactions. Modeling using electronic polarizabilities (shell model) allows a systematic analysis of changes in lattice energy, cell volume, and the relative stability of doped structures using ions such as Al, Ti, Ni, and Co.
Date: December 31, 1995
Creator: Cygan, R.T.; Westrich, H.R. & Doughty, D.H.
Partner: UNT Libraries Government Documents Department

Composite electrodes for lithium batteries.

Description: The stability of composite positive and negative electrodes for rechargeable lithium batteries is discussed. Positive electrodes with spinel-type structures that are derived from orthorhombic-LiMnO{sub 2} and layered-MnO{sub 2} are significantly more stable than standard spinel Li[Mn{sub 2}]O{sub 4} electrodes when cycled electrochemically over both the 4-V and 3-V plateaus in lithium cells. Transmission electron microscope data of cycled electrodes have indicated that a composite domain structure accounts for this greater electrochemical stability. The performance of composite Cu{sub x}Sn materials as alternative negative electrodes to amorphous SnO{sub x} electrodes for lithium-ion batteries is discussed in terms of the importance of the concentration of the electrochemically inactive copper component in the electrode.
Date: February 3, 1999
Creator: Hackney, S. A.; Johnson, C. S.; Kahaian, A. J.; Kepler, K. D.; Shao-Horn, Y.; Thackeray, M. M. et al.
Partner: UNT Libraries Government Documents Department

Microstructural and Mechanical Characterization of Actively Brazed Alumina Specimens

Description: Alumina (94 and 99.8% grade compositions) was brazed directly to itself with gold-based active brazing alloys (ABA's) containing vanadium additions of 1,2 and 3 weight percent. The effects of brazing conditions on the joint properties were investigated. Wetting behavior, interfacial reactions, microstructure, hermeticity and tensile strength were determined. Wetting was fair to good for the ABA and base material combinations. Microanalysis identified a discontinuous Al-V-O spinel reaction product at the alumina-braze interface. Tensile strength results for 94% alumina were uniformly good and generally not sensitive to the vanadium concentration, with tensile values of 85-105 MPa. There was more variability in the 99.8% alumina strength results, with values ranging from 25-95 MPa. The highest vanadium concentration (3 wt. %) yielded the highest joint strength for the brazed 99.8% alumina. Failures in the 99.8% alumina samples occurred at the braze-alumina interface, while the 94% alumina specimens exhibited fracture of the ceramic substrate.
Date: August 26, 1999
Creator: Hosking, F.M.; Cadden, C.H.; Stephens, J.J.; Glass, S.J.; Yang, N.Y.C.; Vianco, P.V. et al.
Partner: UNT Libraries Government Documents Department

Modeling of Spinel Settling in Waste Glass Melter

Description: Our objective is to determine the fraction and size of spinel crystals in molten HLW glass that are compatible with low-risk melter operation. To this end, we are investigating spinel behavior in HLW glass and obtaining data to be used in a mathematical model for spinel settling in a HLW glass melter. We will modify the current glass-furnace model to incorporate spinel concentration distribution and to predict the rate of spinel settling. Also, we will determine the nucleation agents that control the number density and size of spinel crystals in HLW glass.
Date: June 1, 2000
Creator: Hrma, Pavel; Schill, Petr; Nemec, Lubomir; Klouzek, Jaroslav, Mika, Martin & Brada, Jiri Glass Service, Ltd., Vsetin, Czech Republic
Partner: UNT Libraries Government Documents Department