bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrical Characterization of the Structure and Other Phenomena in Superionic PbSnF4
Authors: Milova Galina , Denes Georges , Madamba M. Cecilia , Perfiliev M. 
Published: April 2011

ABSTRACTThe structure of PbSnF4 is derived from that of fluorite-type β-PbF2 The replacement of half the lead by tin results in a thousand-fold increase of the fluoride ion mobility, even though tin-fluorine bonds are strongly covalent. This is due to an increase of fluoride ion disorder on some sites. The structure of α-PbSnF4 can be interpreted as resulting from the insertion of two layers of [SnF]+ cations between each pair of layers of PbF8 cubes. This has profound bearings on the texture and properties of this material, since the tin(II) stereoactive lone pairs create very effective cleavage planes. In addition, the fluorine covalently bonded to tin occupy all vacant sites used to create Frenkel defects. However, superionicity is observed by complex impedance measurements. Transport number measurements show that fluoride ions are the charge carriers.
Resistivity as a Tool for Characterizing Point Defects in Nonstoichiometric Metallic Ceramics
Authors: Williams Wendell S. 
Published: April 2011

ABSTRACTCompounds of IVb and Vb transition metals and carbon are electronically conductive, hard materials that crystallize in the NaC1 structure but are very nonstoichiometric (carbon-poor), as in TiCx, where x is the carbon/metal ratio and is less than unity. Carbon atom vacancies are randomly located in the fcc carbon sublattice and act as scattering centers for conduction electrons. Data on the electrical resistivity as a function of the concentration of these point defects could be used in the opposite sense–i.e., to determine the defect concentration, (l-x), through a measurement of resistivity. The chemical composition (carbon/metal ratio) is then given directly by x. The random vacancies can be ordered by slow cooling from high temperatures, thereby eliminating the residual resistivity. The carbon/metal ratios of these ordered phases are either 3:4, 5:6 or 7:8 and thus can specify the chemical composition precisely.
Electrical and Optical Properties of Defects by Complementary Spectroscopies
Authors: Castaldini A. , Cavallini A. , Fernandez P. , Fraboni B. , Piqueras J. , Polenta L. 
Published: April 2011

ABSTRACTDeep levels in II-VI compounds were investigated by complementary junction and optical spectroscopy methods to assess the characteristics of the traps as well as the limits and the reliability of the techniques applied. The electrical properties have been investigated by current and capacitance transient spectroscopy, while the optical properties have been studied by cathodoluminescence. A critical and comparative analysis of the results obtained with the various methods allowed the determination of the parameters and the nature (majority or minority carrier trap) of most of the detected levels.
Composition Profiling of Graded Dielectric Function Materials by Spectroscopic Ellipsometry
Authors: Trolier-Mckinstry S. , Koh J. 
Published: April 2011

ABSTRACTSpectroscopic ellipsometry (SE) is a powerful optical tool for non-destructively depth-profiling the dielectric function of samples with a resolution in the Ångstrom range. In this work, the characterization of graded composition layers in transparent materials by SE is described. In modeling studies on the sensitivity limits of the technique, it has been shown that for known index profile shapes, the depth sensitivity can be quite high. For example, diffusion of Na2O into the surface of a vitreous silica sample can be detected for layers as thin as 100Å when the maximum refractive index contrast is only 0.005. The sensitivity of the technique increases as the diffusion depth and refractive index contrast increases. The accuracy of the thickness determination depends on the total thickness of the graded layer; for a given system, the accuracy of the composition measurements do not depend on the surface concentration.Leached alkali-aluminosilicate and modified lead silicate glasses were examined by SE to experimentally confirm the modeling predictions on the composition depth profiling. Extremely good correlation between the SE-determined depth profile and SIMS measurements on similar samples was obtained for the case of the modified lead silicate glass. For the aluminosilicate glass, simultaneous roughening of the glass surface during etching makes composition profiling more difficult.
Dielectric Properties Dependence on Residual Sodium and Potassium Content in Silica Xerogels
Authors: Meyers K. S. , Zhang G. , Gerhardt R. A. 
Published: April 2011

ABSTRACTAs sodium and potassium are removed from silica xerogels through leaching, the dielectric properties of gels are significantly altered. Work has been done to relate the magnitude of the change in alkali ion content to the change in dielectric properties. Gels were prepared through a colloidal processing method and leached in ammonium nitrate, nitric acid, and water to reduce, to different degrees, the content of sodium and potassium ions. Atomic absorption (AA) was used to determine the actual sodium and potassium content of each gel after its capacitance and dielectric loss were measured as a function of frequency. All electrical measurements were carried out at room temperature and constant humidity. At least three samples for each leaching treatment were evaluated. Data obtained shows a definite relationship between the sodium and potassium content measured by AA and the dielectric constant.
Three Electrode Measurements on Solid Electrolytes
Authors: Pham A. Q. , Glass R. S. 
Published: April 2011

ABSTRACTAC impedance spectroscopy and chronopotentiometry have been used to study solid state ionic conductors. Results obtained using three electrodes are compared to those using a two electrode configuration. The uncompensated resistance was shown to depend strongly on the geometric placement of the electrodes. The optimal configuration is similar to the Luggin capillary arrangement in the liquid phase. The effect of non-negligible geometric capacitance on interpretation of results is discussed.
Spatially Resolving Impedance Spectroscopy
Authors: Jamnik J. , Fleig J. , Maier J. 
Published: April 2011

ABSTRACTTwo techniques for measurement of local electrical conductivity of inhomogeneous materials are described. I) A novel variant of the impedance technique for thin/thick film characterization was developed; due to the two-dimensionality of the cell set up, at different frequencies different parts of the material are probed. The technique was experimentally verified by measuring the position coordinate of a Ag strip artificially added to a AgCl film. Its application to the Ag/AgCl boundary is touched upon. II) Micro-electrodes were used to probe surface conductances and local subsurface conductivities. The technique was implemented by a home-made high impedance adapter and combined with AFM to measure the contact area. Several examples of application are shown, viz. measurements of a) the enhanced surface conductivity of mechanically polished AgCl crystals, b) the interdiffusion coefficient of Cd2+ in AgCl, and c) the grain conductivity of polycrystalline AgCl.
Ionic Conductivities of Doped CeO2 Thin Films as Related to Their Microstructure
Authors: Tian Chunyan , Chan Siu-Wai 
Published: April 2011

ABSTRACTThin films of 4% Y2O3 doped CeO2/Pd film/(001)LaA103 with a very low pinhole density were successfully prepared using electron-beam deposition technique. The microstructure of the films was characterized by x-ray diffraction and the electrical properties were studied as a function of temperature with AC impedance spectroscopy. A brick layer model was adopted to correlate the electrical properties to the microstructure of the films, which can be simplified as either a series or a parallel equivalent circuit associated with either a fine grain or a columnar grain structure, respectively. The conductivities of the films fell between the conductivities derived from the two circuit models, suggesting that the films are of a mixed fine grain and columnar grain structure. The measured dielectric constants of the films were found smaller than that of the bulk.
Structure and Electrical Properties of Conjugated Polymer Composites
Authors: Gong K. C. , Ma W. S. 
Published: April 2011

ABSTRACTThe microstructure and electrical property relationships in conjugated polymer composites( polyaniline (PAn) or polypyrrole(PPy)/thiokol rubber (TR)) have been characterized by 4-probe method , scanning electron microscope (SEM), x-ray energy dispersive spectrometer (EDS) and attenuated total reflection(ATR). The electrical conductivities of the two surfaces of the film, with film thicknesses from 0.01mm to 0.30mm, prepared by electropolymerization , were measured . The differences were related to the thickness of the film. As for a similar PPy/TR film, when trichloroacetic acid was regarded as the supporting electrolyte the film thickness was 0.05mm and the electrical conductivity of the surface on the solution side was reduced by about 21.3%. The studies of SEM, x-ray EDS , ATR for the chemical composition and microstructure of the two surfaces of the composite films showed that a reaction layer was present in the films. Moreover , the conductivity changes between two sides of a fold mark in the conducting composite film is discussed.
Current Density Effects on the Corrosion of Ceramic and Metallic Electrode Materials in Waste Glasses
Authors: Wang E. , Mohr R. K. , Buechele A. C. , Pegg I. L. 
Published: April 2011

AbstractVitrification by joule-heating requires suitable electrode materials. Molybdenum electrodes are used often in high temperature (∼1500°C) joule-heated melters producing commercial glass while Inconel 690 has been the material of choice for lower temperature (∼1150°C) high-level nuclear waste vitrification. Vitrification of diverse waste streams at higher-temperatures places increasingly severe demands upon the electrode materials. Some commercially available ceramics possess sufficient conductivity at high temperatures to be used as electrodes. Many mixed- and low-level waste vitrification applications involve significant amounts of reducible species that accelerate the corrosion process for metallic electrodes. In addition, the corrosion rate of all electrode materials depends on the electrode current density. A special test rig was designed that measures the dependence of corrosion rate on both current density and temperature over extended periods of time. Molybdenum, Inconel 690, and three types of commercial ceramic coupons were tested over a range of conditions in simulated waste glasses containing key reducible species (e.g., PbO, CuO, ZnO, SO3). The corrosion rates show strong dependencies on the current density. Coupons were sectioned and the glass-coupon interface examined using Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS). Cu, Pb, Ni and Sn were found to be reduced to their metallic states at the molybdenum coupon surfaces and were active in the corrosion process.
The Release of Technetium from Defense Waste Processing Facility Glasses
Authors: Ebert W. L. , Wolf S. F. , Bates J. K. 
Published: April 2011

AbstractLaboratory tests are being conducted using two radionuclide-doped Defense Waste Processing Facility (DWPF) glasses (referred to as SRL 131A and SRL 202A) to characterize the effects of the glass surface area/solution volume (SN) ratio on the release and disposition of Tc and several actinide elements. Tests are being conducted at 90°C in a tuff ground water solution at S/V ratios of 10, 2000, and 20,000 m−1 and have been completed through 1822 days. The formation of certain alteration phases in tests at 2000 and 20,000 m−1 results in an increase in the dissolution rates of both glasses. The release of Tc parallels that of B and Na under most test conditions and its release increases when alteration phases form. However, in tests with SRL 202A glass at 20,000 m−1, the Tc concentration in solution decreases coincidentally with an increase in the nitrite/nitrate ratio that indicates a decrease in the solution Eh. This may have occurred due to radiolysis, glass dissolution, the formation of alteration phases, or vessel interactions. Technetium that was reduced from Tc(VII) to Tc(IV) may have precipitated, though the amount of Tc was too low to detect any Tc-bearing phases. These results show the importance of conducting long-term tests with radioactive glasses to characterize the behavior of radionuclides, rather than relying on the observed behavior of nonradioactive surrogates.
Schoepite and Dehydrated Schoepite
Authors: Hawthorne F. C. , Finch R. J. , Ewing R. C. 
Published: April 2011

AbstractSchoepite, [(UO2)8O2 (OH)12]·12H2O, dehydrates irreversibly to a defect structure-derivative of α-UO2 (OH)2 with composition UO3·0.75H2O (dehydrated schoepite) according to the reaction.[(UO2)8O2 (OH) 12]+12H2O ↠ 8[(UO2 )O0.25 (OH)1 5.] + 12H2O.Natural crystals change from translucent yellow schoepite to opaque yellow, polycrystalline dehydrated schoepite. The complete transformation occurs in three steps: (I) loss of interlayer H20 in schoepite causing collapse of the layers; (2) atomic rearrangement within the sheets from a schoepite-type arrangement to a configuration which may be similar to that of rnetaschoepite, UO3.2H2O; (3) a second rearrangement to the defect α-UO2 (OH)2-type sheet. Although dehydrated schoepite may transform to stoichiometric α-UO 2(OH)2 in water above approximately 290°C, it does not hydrate at any temperature. Schoepite transforms slowly in air at ambient temperature to metaschoepite, although this may take geologically long periods. The transformation of schoepite to dehydrated schoepite can occur rapidly at room temperature if crystals, which have only partially converted to metaschoepite. are subjected to external stress.
Thermodynamic Modelling of the Sorption of Radioelements onto Cementitious Materials
Authors: Heath T. G. , Ilett D. J. , Tweed C. J. 
Published: April 2011

AbstractA model has been developed for the sorption of radioelements onto cementitious materials based on the diffuse-layer modelling approach. The model assumes that silicon sites (>SiOH) and calcium sites (>CaOH) dominate the surface chemistry and the sorption of radioelements onto the cementitious materials. Both types of site may undergo surface protonation and deprotonation reactions. Cement-based systems vary greatly in their chemistry depending on their calcium-tosilicon molar ratio, and the corresponding variation in the surface chemistry has been incorporated by allowing sorption of calcium ions onto silicon sites. This process results in a change from a silica-type surface, at very low calcium-silicon ratios, to a calcium hydroxide-type surface for high-calcium cement-based materials. The predicted variation in the surface chemistry is consistent with literature data on measured zeta potentials of cements. The model has been applied successfully to describe the sorption of simple caesium and iodide ions at varying calciumsilicon ratios. In a Nirex repository for low and intermediate level wastes, a high-calcium cementitious backfill would be specified. This model has allowed a consistent interpretation of experimental data for sorption of key radioelements, including uranium and plutonium, onto the backfill, under saline and non-saline conditions.
A Computer Program to Facilitate Performance Assessment of Underground Low-Level Waste Concrete Vaults
Authors: Snyder K. A. , Clifton J. R. , Pommersheim J. 
Published: April 2011

AbstractA computer program (4SIGHT) to facilitate performance assessment of underground concrete vaults for low level waste (LLW) disposal facilities is being developed at the National Institute of Standards and Technology (NIST). Specifically, the program predicts the hydraulic conductivity and the service life of an underground concrete vault. The hydraulic conductivity estimate is based upon empirical relations. The service life is estimated from consideration of three major degradation processes: steel reinforcement corrosion, sulfate attack, and leaching. The performance prediction is based upon ion transport equations for both diffusion and advection. Most importantly, the computer program incorporates the synergistic degradation effects of all three processes, and their effect upon the transport coefficients.
Evaluation of Factors Affecting Diffusion in Compacted Bentonite
Authors: Lehikoinen J. , Carlsson T. , Muurinen A. , Olin M. , Salonen P. 
Published: April 2011

AbstractThe information available from the open literature and our studies on exclusion, sorption and diffusion mechanisms of ionic and neutral species in bentonite has been compiled and re-examined in relation to the microstructure of bentonite. The emphasis is placed on a more thorough understanding of the diffusion processes taking place in compacted bentonite. Despite the scarcity of experiments performed with neutral diffusants, these imply that virtually all the pores in compacted bentonite are accessible to neutral species. Anion exclusion, induced by the overlap of electrical double layers, may render the accessible porosity for anions considerably less than the porosity obtained from the water content of the clay. On the basis of the compiled data, it is highly probable that surface diffusion plays a significant role in the transport of cations in bentonite clays. Moreover, easily soluble compounds in bentonite can affect the ionic strength of porewater and, consequently, exclusion, equilibrium between cations, and surface diffusion.
A Capillary Network Model for Coupled Gas and Water Flow in Engineered Barriers
Authors: Impy M. D. , Grindrod P. , Clark K. J. , Takase H. 
Published: April 2011

AbstractA two-dimensional capillary network model for gas migration through a water-saturated medium is presented. The model is an extension of previously developed capillary bundle models, and provides a discrete alternative to classical continuum Darcy models. The need for such an alternative has become apparent from recent experimental results that suggest gas migrates through low permeability water-saturated media via a small number of preferential pathways.
Experimental Study on Groundwater Flow and Mass Transport in a Heterogeneous Porous Medium
Authors: Hatanaka Koichiro , Watari Shingo , Uchida Masahiro , Takase Hiroyasu , Impey Michael D. 
Published: April 2011

AbstractIn performance assessment of geological disposal systems the phenomenon of dispersion in geological media is one of the most important processes to be modeled and is dependent on the heterogeneity of the media. In order to understand the dispersion process in a well defined heterogeneous field, laboratory experimental apparatus, named MACRO, was constructed to study fluid flow and mass transport. A synthetic heterogeneous field was constructed in a flow-bed using six kinds of glass beads with diameters of 0.1, 0.15, 0.2, 0.4, 0.6 and 0.8 mm. Both dye (brilliant blue) and NaCI solution were used as tracers in the experiment. A particle tracking method, considering advection, was used in numerical simulations of the experiment, and the dispersion effect was assumed to be expressed by the variability of the local advective velocity in a high resolution numerical grid. The simulated results obtained by the particle tracking method agreed with the measurement, confirming the applicability of modelling approach used in this study.
Discrete-Fracture Modeling of Thermal-Hydrological Processes at Yucca Mountain and the Llnl G-Tunnel Heater Test
Authors: Nitao John J. , Buscheck Thomas A. 
Published: April 2011

AbstractAn in situ heater test was performed at G-Tunnel, Nevada Nuclear Test Site, to investigate the thermal-hydrological response of unsaturated, fractured volcanic tuff under conditions similar to those at Yucca Mountain. The NUFT flow and transport code was used to model the test using discrete-fracture and equivalent-continuum approaches. Nonequilibrium fracture flow and thermal buoyant gas-phase convection were found to be the likely causes for observed lack of condensate imbibition into the matrix. The potential repository at Yucca Mountain was also modeled. Disequilibrium fracture flow is predicted to occur for less than a hundred years after emplacement followed by a period of fracture-matrix equilibrium, during which the equivalent-continuum and discrete-fracture models give almost identical results.
Alteration History Studies in the Exploratory Studies Facility, Yucca Mountain, Nevada, USA
Authors: Levy S. S. , Norman D. I. , Chipera S. J. 
Published: April 2011

AbstractBy mid-1995, the Exploratory Studies Facility (ESF) extended about 1.1 km from Exile Hill westward toward Yucca Mountain, mostly within densely welded, devitrified Tiva Canyon Tuff. Secondary mineral occurrences in this unit include breccia cements of mordenite, a fibrous zeolite, and vapor-phase deposits of silica, alkali feldspar, apatite, hollandite, amphibole, and zircon. Calcite is also a common secondary mineral in faults and fractures. Studies of water and gas contents in fluid inclusions in calcites from a fault in nonwelded tuff and a fracture in densely welded tuff suggest mineral deposition under transient locally saturated conditions. Calcite in the nonwelded tuff incorporated air from the unsaturated tuff adjacent to the fault.A highly altered interval within pre-Pah Canyon tuffs just above the top of the Topopah Spring Tuff may be a fossil fumarole or other hydrothermal feature associated with cooling pyroclastic deposits, overprinted by later zeolitic alteration. The observed quartz, cristobalite, opal-CT, and fluorite have been widely identified as products of syngenetic devitrification and vapor-phase alteration in and above the Topopah Spring Tuff. Smectite, also an abundant secondary mineral at the ESF site, has been observed elsewhere at this stratigraphic level.Zeolitic alteration of nonwelded tuffs above the Topopah Spring Tuff, as seen in the ESF, has also been noted in drill core and outcrop at northeastern Yucca Mountain. The hydrologic and geochemical conditions that favored zeolitization only in certain areas of this stratigraphic interval have yet to be determined.
Simfuel Leaching Studies in Granitic Groundwater Under Oxidizing Conditions
Authors: Garcia-Serrano J. , Serrano J. A. , Diaz-Arocas P. P. , Quiñones J. , Almazan J. L. R. 
Published: April 2011

AbstractSimulated high-bumup nuclear fuel (SIMFUEL) has been leached in synthetic groundwater under oxic conditions. SIMFUEL pellets were ground and sieved to two particle sizes (50–100 and 100–315 μm). An extensive solid characterization of the fragments was carried out by various techniques. Elemental analysis has also been performed prior to the leaching tests.The release of U and the minor components (Mo, Ba and Sr) was monitored during the long term dissolution experiments (350 days). These minor components exhibit a trend similar to uranium, high release at the beginning followed by a plateau. The M/U calculated ratios show different behavior although after a period of time, depending on the particle sizes, constant ratios were observed.SIMHUEL powder was used in order to simulate the physical effect of bum-up on the fuel structure. This fact seems to play an important role on the uranium release. A comparison with the results given in the literature for SIMFUEL pellet leaching tests shows good agreement with the values reported.
Characterization of the Altered Zone Around a Fracture in Palmottu Natural Analogue
Authors: Hartikainen K. , Pietarila H. , Rasilainen K. , Nordman H. , Ruskeeniemi T. , Höltiä P. , Siitari-Kauppi M. , Timonen J. 
Published: April 2011

AbstractA drill core sample penetrating at a natural fracture has been analysed by helium gas techniques and by α-autoradiography. Porosity and diffusivity profiles away from the fracture have been determined and compared with structural profiles. Model calculations are used to determine the effects of sample size on the measured porosities and diffusivities.