bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impedance Spectroscopy of Upper Mantle Earth Materials
Authors: Tyburczy J. A. , Roberts J. J. 
Published: April 2011

ABSTRACTEarth scientists study electrical properties of Earth materials to understand mechanisms of transport and deformation under conditions existing in the Earth's interior, and for comparison with direct determinations of the conductivity – depth structure of the Earth. We have performed impedance spectroscopic studies of natural and artificial (hot-pressed and sintered) rocks composed of (Mg9Fe1)2SiO4 olivine, a major constituent of the Earth's upper mantle between 40 and 400 km depth. The studies were performed over the frequency range 105 to 10−4 Hz at 1 bar total pressure and temperatures of 800 – 1400 °C under controlled oxygen atmospheres. Complex impedance plane analysis of the results shows depressed impedance arcs corresponding to grain interior and grain boundary transport in series, analogous to the behavior of zirconia and other materials. Distinct grain boundary phases that might cause the resistive grain boundary behavior are not observed. The exponent of the oxygen pressure dependence of the grain boundary conductivity ranges from 0.02 to −0.08, which is very different than the 1/5.5 to 1/7 dependence of the polaronic grain interior mechanism. However, lack of constraints on the composition of the intergranular material limit interpretation of these exponents in terms of mechanism. Key issues for application to the Earth's interior are determination of the mechanism and pressure dependence of the grain boundary transport.
Effect of Sol-gel Coating on Microstructure and Electrical Properties of Microwave Garnets
Authors: Cho Yong. S. , Brissette Leo , Amarakoon Vasantha. R. W. 
Published: April 2011

ABSTRACTMicrowave magnetic properties of Gd substituted yttrium iron garnets are known to depend on their microstructural characteristics such as porosity and grain size. Surface coating of the garnet powders through a gelation of Si and Mn organic solution was conducted to inhibit the grain boundary movement during sintering with considerable densification. High density and uniform microstructure were obtained after sintering at 1400°C in O2 atmosphere. Grain growth kinetics were studied with variation in sintering time as a function of grain size. An activation energy of 102.9 kcal/mol was obtained for grain growth of the sol-gel coated sample. Grain boundary region was investigated by using TEM and EDS. A very thin grain boundary layer was observed with Si segregation in the region. Electrical resistivity at 100 Hz was 1.46×109 Ωcm for the sol-gel coated sample sintered at 1400°C for 3hrs in O2. Above results were discussed and compared with those obtained by the conventional batch mixing of additives.
Scaling of Complex Conductivity for A Percolating Metal-Insulator Composite with Inter granular Tunneling Above and Below the Superconducting Transition
Authors: Mclachlan D. S. , Pakhomov A. B. , Oblachova I. I. , Brouers F. , Sarychev A. 
Published: April 2011

ABSTRACTThe complex conductivity was measured on 3d granular NbC-KCI composite samples at varying metal volume fraction p, frequency ω and temperature above and below the superconductivity critical Tc. The observed frequency dispersion is anomalous in that it is not in accord with the scaling theory of percolation transition. The results are compared with a recently developed scaling theory, which takes both intercluster tunneling and intercluster capacitance into account. The experimental estimates for the new critical exponents are in reasonable agreement with the theory. The very low value of the crossover frequency can also be understood. We also present the data showing the dispersion of the complex conductivity well below the superconducting transition Tc of NbC.
Impedance Spectroscopy of Ferromagnetic Materials
Authors: Valenzuela R. , Irvine J. T. S. 
Published: April 2011

ABSTRACTImpedance spectroscopy has been widely used to analyze polarization phenomena in dielectric, ferroelectric and solid electrolyte materials. In this paper, we review its extension to ferromagnetic materials, and discuss its application to the case of irreversible domain wall displacements which lead to ferromagnetic hysteresis phenomena.
Electrical Resistivity and Dielectric Properties of Hardened Cement Paste and Mortar
Authors: Buerchler D. , Elsener B. , Boehni H. 
Published: April 2011

ABSTRACTWater content, porosity, pore solution composition, resistivity and dielectric properties of hardened cement paste and mortar samples have been studied as a function of time and relative humidities. A model for the resistivity of cement based materials is presented and an interpretation of the dielectric properties is proposed.
Humidity Effects on Porous Silica Thin Films
Authors: Kokan J. R. , Gerhardt R. A. 
Published: April 2011

ABSTRACTImpedance Spectroscopy is being used to study the humidity sensitivity of porous silica thin films. The films are processed via a colloidal sol-gel method which leaves some remnant potassium and sodium. Previous work on bulk porous silica samples processed by the same method showed that the dielectric properties and ac conductivity were very sensitive to changes in humidity. The aim of this work was to determine if the same dependencies could be found in the thin films. The capacitance, dielectric loss, and ac conductivity of the films were measured in a controlled environment chamber from 20–80% RH for frequencies ranging from 10Hz–10MHz. In addition to characterizing films with varying amounts of residual alkali ions obtained through leaching, we have also measured films that were surface doped with controlled amounts of KCl, LiCl, or NaCl. Relative humidity dependencies in the films are not as dramatic as in the bulk samples. The reasons for this behavior are not yet clear, but may be associated with the porosity, thickness, and surface area of the films.
Redox Behavior of Palladium Ion in Oxide Glasses
Authors: Yamashita Masaru , Nishii Junji , Akai Tomoko , Yamanaka Hiroshi 
Published: April 2011

AbstractReduction and separation of Pd were investigated in soda-lime-alumino-borosilicate glass. The dependence on raw materials, melting atmosphere, concentration of Pd and melting temperature was examined by electrochemical oxygen activity measurement, optical absorbance, X-ray diffraction and microscopic observation. Pd ions were slowly reduced during melting and metal particles were formed. The separation was enhanced in a reducing atmosphere, at high temperature, for long melting periods and with high concentration of Pd. Pd metal particles of about 10 to 30 μm in diameter were observed by SEM and X-ray diffraction.
Vitrification of Simulated Intermediate-Level French and Russian Wastes in “Cold Crucible” Based Plant
Authors: Lifanov F. A. , Stefanovsky S. V. , Kobelev A. P. , Kornev V. I. , Savkin A. E. , Knyazev O. A. , Lashchenova T. N. , Merlin S. , Roux P. 
Published: April 2011

AbstractComparative tests on SGN and Radon simulated ILW vitrification with a cold crucible based experimental plant were performed. The batch was fed as paste with 20 wt.% moisture. An operation conditions, the ability of the cold crucible to maintain the differential pressure during the operation, process variables, product properties, off-gas and condensate compositions, the effect of melt agitation on melter capacity and cesium loss have been determined. Melt viscosity and resistivity have been measured. Material structures were studied using infra-red spectroscopy and electron microscopy. Leach rates of sodium and potassium cations as well as Cs-137 have been measured. The behavior of sulfate and chloride ions in the vitrification process as well as their solubility in SGN and “Radon” glasses have been investigated.
Secondary Phase Formation and the Microstructural Evolution of Surface Layers During Vapor Phase Alteration of the French Son68 Nuclear Waste Glass at 200 °C
Authors: Gong W. L. , Ewing R. C. , Wang L. M. , Vernaz E. , Bates J. K. , Ebert W. L. 
Published: April 2011

AbstractThe SON68 inactive “R7T7” composition is the French reference glass for the LWR nuclear waste glass. Vapor phase alteration was used to accelerate the reaction progress of glass corrosion and to develop the characteristic suite of secondary, alteration phases. Extensive solid-state characterization (AEM/SEM/HRTEM) was completed on six inactive R7T7 waste glasses which were altered in the presence of saturated water vapor (200 °C) for 91, 241, 908, 1000, 1013, and 1021 days. The AEM samples were examined in cross-section (lattice-fringe imaging, microdiffraction, and quantitative thin-film EDS analysis). The glass monoliths were invariably covered with a thin altered rind. The layer became thicker with time: 0.5μm for 22 days; 4 μm for 91 days; 6 μm for 241 days; 10 μm for 908 days; 26 μm for 1013 days; and <35μm for 1021 days. The composite alteration layer of the SON68 samples is at least four time less thick than that of the SRL 131 glass composition.Six distinctive zones, based on phase chemistry and microstructure, were distinguished within the well-developed surface layers. Numerous crystalline phases such as analcime, tobermorite, apatite, and weeksite were identified on the surfaces of the reacted glasses as precipitates. Two crystalline phases, Ag2TeO3 and (Ca,Sr)Mo3O9(OH)2, were found within the inner zones of surface layers, and they must have nucleated in situ, indicating that Ag, Te, Sr, and Mo can be retained within the surface layer. The majority of the surface layer volume is composed of two morphologically and chemically different structures: one consists of well-crystallized fibrous smectite aggregates occurring along with cavities, the A-domain; and the other consists of poorlycrystallized regions containing needle-like smectite (montmorillonite) crystallites, a silica-rich amorphous matrix, and possibly ZrO2 particles, the B-domain. The retention of rare-earths and Zr mostly occurred within B-domains and that of transition elements, such as Zn, Cr, Ni, and Mn, in A-domains. The recrystallization of poorly-crystallized B-domains into well-crystallized Adomains may influence the long-term behavior of rare-earths, Zr, and transition elements. The mechanism of surface layer formation during vapor phase alteration is discussed based on the cross-sectional AEM studies of surface layers of the SON68 waste glasses.
Long-Term Results from Unsaturated Durability Testing of Actinide-Doped DWPF and WVDP Waste Glasses
Authors: Fortner Jeffrey A. , Bates John K. 
Published: April 2011

AbstractResults from durability drip tests designed to simulate the unsaturated conditions in the proposed Yucca Mountain Repository are reported for two actinide-doped glasses used as model waste forms. These tests are being conducted with reference glass compositions doped with neptunium, plutonium, and americium from the Defense Waste Processing Facility (DWPF) and the West Valley Demonstration Project (WVDP), and have been ongoing for over 8 years. Solution compositions, including transuranics, have been periodically determined, and selected analyses of colloid formation and composition, glass corrosion layers, and solid alteration phases have been obtained by scanning and analytical transmission electron microscopies. The importance of integrated testing has been demonstrated, as complex interactions among the glass, the groundwater, and the sensitized stainless steel have been observed. The cumulative releases of both glassforming and dopant elements are presented along with identification of reaction phases and their partitioning between solution and solid phases. Alteration phases, including smectite clay, iron silicates, uranium silicates, and calcium thorium phosphate, have been observed forming on the glass and stainless steel and have occasionally been found suspended in solution as colloids. Actinides, except neptunium, concentrate into alteration phases or sorb onto the stainless steel. The subsequent transport of the actinides is then controlled by these phases.
Corrosion of Waste Glasses in Boom Clay: Studies of Element Concentrations by Sims
Authors: Lodding A. , Van Iseghem P. 
Published: April 2011

AbstractIn-situ corrosion tests on nuclear waste glasses in Boom clay provided direct contact glass-clay at 90°C, for periods of 2, 3.5 and 7.5 years. The corroded reference glasses (two R7T7 type glasses, four Pamela type glasses), were studied in terms of SIMS (secondary ion mass spectroscopy) and mass losses.The Al2O3 rich Pamela glasses appear to corrode in a selective-substitutional way, the other glasses dissolve almost congruently. Differences in the corrosion extent between the glasses are associated with compositional differences and secondary phase formation. SIMS analysis provides the reaction layer thickness and the relative element behaviour in this layer. Although relatively few, the data have provided a coherent picture of glass corrosion, in terms of corrosion mechanisms, time and glass composition dependence.
Investigation of Urtite as an Analog of Waste Slag from a Plasma Shaff Furnace
Authors: Dmitriev S. A. , Stefanovsky S. V. 
Published: April 2011

abstractMineralogical-geochemical investigation of a sample of nepheline syenite (urtite) as a natural analog of final radioactive waste form has been performed. The specimen of urtite consists of nepheline, alkali feldspar, pyroxene, sphene, apatite and minor magnetite and amphibole. As a first approximation, urtite simulates the mineral composition of waste slag produced in a plasma shaft furnace at SIA “Radon”. Determination of chemical compositions of the minerals by electron-probe microanalysis has shown that the main phases that hosted radionuclides and their geochemical analogs are as follows: nepheline (Rb and probably Cs), feldspar (Ba), sphene (Zr, Nb, REE, and actinides) and apatite (Sr, REE, and actinides).
Anomalous Diffusion in Radwaste Glasses
Authors: Ojovan M. I. , Karlina O. K , Kachalov M. B. 
Published: April 2011

AbstractFractal structure domains for inhomogeneities in radwaste glasses were determined. SEM and TEM photos were analyzed for this aim as well as the Cs-137 leaching process for glass specimens. Unusual character of leaching was observed provided by anomalous diffusion of radionuclides through fractal cluster made of inhomogeneous particles.
Performance Assessment of Zircon as a Waste Form for Excess Weapons Plutonium Under Deep Borehole Burial Conditions
Authors: Weber W. J. , Ewing R. C. , Lutze W. 
Published: April 2011

AbstractZircon (ZrSiO4) is proposed as a waste form for excess weapons-grade plutonium. Zircon is an extremely durable ceramic that is often found as an accessory mineral in Precambrian terranes with ages up to 4 billion years. The chemical durability of zircon in groundwater far exceeds that of other waste forms, as modeled leach rates may be as low as 10-11g/m2d. At least 10 wt% Pu can substitute for Zr in zircon. Self-radiation damage from alpha decay leads to a crystalline-to-amorphous transformation that is modeled as a function of time and temperature for deep borehole conditions. Based on the results of this assessment, zircon could meet all necessary durability and criticality criteria required for a Pu waste form. The types of data used in this analysis are generally not available for other crystalline ceramics or glasses.
The Interaction Between Synroc-C and Pure Water or Boom Clay
Authors: Iseghem Pierre Van , Jiang Wei , Blanchaert Marc , Hart Kaye , Lodding Alexander 
Published: April 2011

AbstractWe investigated the interaction between Synroc-C and deionized water or Boom clay disposal media. We used powdered Synroc-C to achieve high SA/V (surface area to volume) conditions (100, 1000, 10000 m-1). The temperature was 90°C. Reaction progress up to 10+6 days/mi was reached. We conclude that dissolution in DW is mainly controlled by initial ion exchange, followed by matrix dissolution. In both Boom clay media (a 500 g/l and a 2000 g/l clay/claywater mixture) matrix dissolution is dominating. The depletion depth of the main Synroc constituent Ti is below 250 nm in the clay media, and below 2 nm in DW after 110 days corrosion at 100 m-1. The corrosion rates are very small, though we cannot present meaningful values. The effect of Boom clay is mainly to increase the solubility of Ti, Zr and the rare earths in solution.
Neptunium-Doped Synroc: Partitioning, Leach Data and Secondary Phase Development
Authors: Smith Katherine L. , Blackford Mark G. , Lumpkin Gregory R. , Hart Kaye P. , Robinson Brett J. 
Published: April 2011

AbstractNp-doped Synroc was subjected to modified MCC-1 leach tests in demineralised water at 70°C. Normalised total differential Np leach rates were about 10−4 g m−2 d−1 initially, decreased to about 10−5 g m−2 d−1 after 60 days and stayed approximately constant for periods totalling up to 2283 d. Scanning electron microscope (SEM) and analytical transmission electron microscope (AEM) examination of discs leached for periods totalling 56 d or longer showed that they were covered with crystalline anatase, brookite and ilmenite. The crystalline secondary phases initially nucleated in polishing scratches and on perovskite grains. However, after leaching for a total of 422 d most of the surface was covered. None of the secondary phases contained observable amounts of Np (< 0.2 wt%). These data are discussed in relation to previous work.
The CaO-TiO2-ZrO2 System at 1200 °C and the Solubilities of Hf and Gd in Zirconolite
Authors: Swenson D. , Nieh T. G. , Fournelle J. H. 
Published: April 2011

AbstractPhase equilibria are established in the CaO-TiO2-ZrO2 system at 1200 °C, using X-ray diffraction and electron probe microanalysis. The existence of two previously reported ternary phases, zirconolite (CaZrTi2O7) and calzirtite (Ca2Zr5Ti2O16), is confirmed. Each of these phases exhibits a significant range of homogeneity between TiO2 and ZrO2 while maintaining a nearly constant concentration of CaO. The ternary solubilities of the constituent binary phases are found to be negligible, with the exceptions of the perovskites, which display mutual solubility of at least 22 mol.% and may in fact form a series of continuous solid solutions. The solubilities of Hf and Gd in zirconolite are also investigated. While Hf-bearing samples did not reach thermodynamic equilibrium under the experimental conditions employed, the existence of a Hf analog to zirconolite, CaHfTi2O7, is conclusively demonstrated. The phase is stable at the stoichiometric composition, and its lattice parameters are very close to those reported in the literature for stoichiometric zirconolite. A Gd-bearing sample of the composition Ca0.88Zr0.88Gd0.24Ti2O7 is found to be essentially single phase zirconolite, in agreement with previous investigations at higher temperatures.
Description and Classification of Uranium Oxide Hydrate Sheet Topologies
Authors: Miller M. L. , Finch R. J. , Burns P. C. , Ewing R. C. 
Published: April 2011

AbstractThe uranyl oxide hydrates (UOH) are important corrosion products of uraninite and UO 2 in spent nuclear fuel under oxidizing conditions. However, the systematics of the crystal chemistry, thermodynamic parameters, and solubilities of this mineral group are poorly understood. With the exception of the synthetic UO2 (OH)2 polymorphs, all UOH crystal structures are based on sheets of edge-sharing 5- and 4-coordinated uranyl dipyramids. This structural similarity suggests that it is possible to develop a model by which to estimate the thermodynamic behavior of UOHs from data on structural endmember phases. Toward this end, a method of quantitatively describing all known UOH sheets has been developed. Only four structural unit chains are required to construct the uranyl oxide hydrate sheets (as well as the structurally similar U3O8 sheets). The H-chain is restricted to α-UO2 (OH)2 and is made up of hexagonally coordinated uranyl ions sharing opposing edges. The “arrowhead” chain composed of pentagonal dipyramids sharing edges and alternating with trigonal vacancies is present in all other UOH sheets. These arrowhead chains are directed and can occur in both an ↑ and ⇓ “sense” within a single sheet. The P-chain consists of edge-sharing pentagonal dipyramids forming a zigzag chain. The P-chain is flanked on both sides by arrowhead chains of the same “sense”. The remaining structural unit is a discontinuous “chain” of rhombic dipyramids. This “R-chain” is produced when nested adjacent ⇑ and ⇓arrowhead chains are translated by a diagonal shift. This “chain” occurs in sheets which contain only 4-coordinate uranyl ion and those containing both 4- and 5-coordinate uranyl ions.
Sulfur Polymer Cement as a Low-Level Waste Glass Matrix Encapsulant, Part I: Thermal Processing
Authors: Sliva Paul , Peng Y. Benjamin , Bunnell L. Roy , Peeler David K. , Feng Xiangdong , Martin Paul , Turner Paul J. 
Published: April 2011

AbstractSulfur polymer cement (SPC) is a candidate material to encapsulate low-level waste (LLW) glass. Molten SPC will be poured into a LLW glass cullet-filled canister, surrounding the glass to act as an additional barrier to groundwater intrusion. This paper covers the first part of a study performed at Pacific Northwest National Laboratory concerned with the fundamental aspects of embedding LLW glass in SPC. Part one is a study of the SPC itself. Variations in SPC properties are discussed, especially in relation to long-term stability and controlling crystallization in a cooling canister.
Vitrifiable Concrete for Disposal of Spent Nuclear Fuel Reprocessing Waste AT I.N.E.L.
Authors: Gougar M. L. D. , Siemer D. D. , Scheetz B. E. 
Published: April 2011

AbstractA cement capable of being Hot Isostatically Pressed (HIP 'ed) into a glass-ceramic has been proposed for use as the waste form for SNF reprocessing wastes at the Idaho National Engineering Laboratories. Such an “intermediate” cement, with a composition based on that of common glasses, has been designed and tested. The cement formulations included mixed I.N.E.L. wastes, blast furnace slag, reactive silica, alumina, and I.N.E.L. soil or vermiculite, which was activated with potassium or sodium hydroxide. Modified FUETAP processing was performed and the cement was subsequently characterized. Results of compressive strength testing ranged from 1452 psi to 4163 psi, exceeding the NRC-suggested standard of >500 psi. Total dissolved solids concentrations in waste form leachates were calculated from a static leach test in which leachate conductivity was measured. Effective diffusivities for radioisotopes Cs and Sr were calculated from leachate analysis data. Diffusivity values were on the order of 10-15 to 10-10 cm2/sec, which compare favorably with diffusivities in other materials.
Pore Solution Chemistry of Simulated Low Level Liquid Waste Incorporated Cement Grouts
Authors: Sahu Sadananda , Diamond Sidney 
Published: April 2011

AbstractExpressed pore solutions from simulated low level liquid waste cement grouts cured at room temperature, 50°C and 90°C for various duration were analyzed by standard chemical methods and ion chromatography. The solid portions of the grouts were formulated with portland cement, fly ash, slag, and attapulgite clay in the ratios of 3:3:3:1. Two different solutions simulating off-gas condensates expected from vitrification of Hanford low level tank wastes were made. One is highly alkaline and contains the species Na+, PO43-, NO2-, NO3- and OH-. The other is carbonated and contains the species Na+, PO43-, NO2- NO3- and CO32- In both cases phosphate rapidly disappeared from the pore solution, leaving behind sodium in the form of hydroxide. The carbonates were also removed from the pore solution to form calcium carbonate and possibly calcium monocarboaluminate. These reactions resulted in the increase of hydroxide ion concentration in the early period. Subsequently there was a significant reduction OH- and Na+ ion concentrations. In contrast high concentration of NO2- and NO3- were retained in the pore solution indefinitely.