bluuebunny/crossref_metadata_2025 huggingface dataset:
Calcium Phosphate Cement in a Rabbit Femoral Canal Model and a Canine Humeral Plug Model: A Pilot Investigation
Authors: Constantz B. R. , Young S. W. , Kienapfel H. , Dahlen B. L. , Sumner D. R. , Turner T. M. , Urban R. M. , Galante J. O. , Goodman S. B. , Gunasekaran S.
Published: March 2011

A new cementitious calcium phosphate biomaterial, SuperBone®, was implanted in both a rabbit femoral canal model and a canine humeral plug model. New Zealand White rabbits were implanted with cement through a novel surgical approach where cement was introduced by injection. In the canine model, a uniform gap of 3 mm around a fiber metal porous implant was filled by the cement. Undecalcified light and backscattered electron histological evaluations indicate the cement is highly biocompatible and is replaced by new bone in concert with cell-mediated resorption. Unlike the acrylic bone cement positive controls, no evidence of fibrous tissue was found around the cement.
Osteogenic Effect of Ashed Bone in Fixation of Hip Implants
Authors: Nash Alexis S.
Published: March 2011

The purpose of this work is to discuss the role of ashed bone reinforced Ultra-High Molecular Weight Polyethylene, UHMWPE, biocomposite in bringing about early biological fixation of hip implant by combining the high damping capacity of this composite with the osteogenic characteristic of ashed bone. This paper will present the damping results obtained for this composite containing 65 weight% ashed bone over a range of frequencies, 0.1–100 rad/s, using a forced vibration technique. Some of the data obtained for lower ash content compositions are compared. The structural characteristics of bone and ashed bone are illustrated using x-ray diffractometry, XRD, and scanning electron microscopy, SEM. The optimal ashing temperature and volume fraction of ashed bone are also significant parameters which will be discussed. The 65 weight % ashed bone composite was elected to simulate the bone mineral content and use as a bioactive agent for the enhancement of bone ingrowth in the early days post-implantation.
The Evaluation of Alpha Plaster of Paris as a Osteoconductive Material in the Adult Cat Calvarium
Authors: Knuckey N. W. , Saskin H. , Yanagasawa R. , Flanagan M.
Published: March 2011

Spontaneous new bone formation does not occur in the adult calvarium. In humans, cranial defects may require repair for brain protection, headaches or cosmetic. Over the years the search for the ideal cranioplasty material to repair such cranial defects has been extensive. We report an evaluation of alpha plaster of paris as an osteoconductive material in a cat craniectomy defect.

Adult cats of either sex were anesthetized with ketamine/halothane and a 15mm biparietal craniectomy defect created. The right side was filled with alpha plaster of paris and the left served as a control. There were 4 animals in each time cohort and animals were sacrificed at 6 weeks, 6 or 12 months. The cranium was removed, fixed, stained, histologically studied and analysised for the percentage of trabecular bone formation. At all durations the control defects were bridged by proliferative fibrous tissue membrane and less than 1% trabecular bone. At six weeks the plaster of paris filled defects were either totally or nearly totally replaced by new bone formation. The plaster was completely resorbed. At 6 wks there was 28% trabecular bone which increased to 93% at 52 wks. Our experiments demonstrate the oeteoconductive potential of alpha plaster of paris in the adult calvarium. This material needs to be evaluated in humans to ascertain its potential as a biocompatible cranioplasty material.
Relativistic Multiple Scattering Theory for Space Filling Potentials
Authors: Wang Xindong , Zhang X. -G. , Butler W. H. , Harmon B. N. , Stocks G. M.
Published: March 2011

We derive a relativistic full potential multiple scattering theory (MST) in direct analog to the non-relativistic full potential MST[1, 2]. The secular equation is derived fromi the Lippmann-Schwinger equation by expanding the wave function in terms of cell basis functions which are locally exact solutions of the Dirac equation. The relationship between this theory and currently widely used relativistic munffin-tin MST is also discussed.
Experiences with the Quadratic Korringa-Kohn-Rostoker Band Theory Method
Authors: Faulkner J. S.
Published: March 2011

The Quadratic Korringa-Kohn-Rostoker method is a fast band theory method in the sense that all eigenvalues for a given k are obtained from one matrix diagonalization, but it differs from other fast band theory methods in that it is derived entirely from multiple-scattering theory, without the introduction of a Rayleigh-Ritz variational step. In this theory, the atomic potentials are shifted by Δασ(r) with Δ equal to E-E0 and σ(r) equal to one when r is inside the Wigner-Seitz cell and zero otherwise, and it turns out that the matrix of coefficients is an entire function of Δ. This matrix can be terminated to give a linear KKR, quadratic KKR, cubic KKR, …, or not terminated at all to give the pivoted multiple-scattering equations. Full potentials are no harder to deal with than potentials with a shape approximation.
Transfer of Classical Multiple Scattering theory to Quantal Multiple Scattering Theory
Authors: Korringa J.
Published: March 2011

The transition firom classical to modern multiple scattering theory will be told in a very personal vein. The conjunction of a great teacher (Kronig). a classical problem (acoustical impedance of a porous plaster) the right reference (Kasterin's 1903 Moskau thesis) and my interest in the metallic state set the stage for a transfer from sound waves to Schroedinger waves. My 1947 Paper in Physica and Kohn and Rostoker's Physical Review paper of 1954 were shown to oe equivalent and constitute the basis of the KKR method, to the development of which Sam Faulkner has contributed more than anyone else. Details of these events will be presented.
Spin Polarised Relativistic Kkr
Authors: Staunton J.B. , Matsumoto M. , Strange P.
Published: March 2011

We review spin polarised multiple scattering theory and show how it can provide a description of magnetic anisotropic effects in metallic systems. An interpretation in terms of the leading relativistic corrections is given; namely the interaction between spin-orbit coupling and spin polarisation. It is pointed out that it is straightforward to vary the d-rection of spin polarisation within this formalism. As simple illustrations, the cases of two and three impurities in a non-interacting relativistic' electron gas are outlined and the origin of pseudo-dipolar and Dzyaloshinski-Moriya anisotropy highlighted. We go on to compare and contrast estimates of magneto-crystalline anisotropies of transition metals with those from alternative methods. Finally we discuss the paramagnetic spin susceptibility of metals within this framework and show that this work is complementary to magnetic anisotropy energy calculations. A generalised Stoner condition for the onset and direction of the magnetisation is given. Calculations for h.c.p. metals cobalt, scandium and yttrium are presented. We conclude by pointing out that this approach can be extended to set up a theory for the dynamical susceptibility with consequent implications for anisotropy of spin wave excitations.
A Multi-Atom, Self-Consistent, Relativistic Kkr Electronic Structure Program: Numerical Aspects and Applications
Authors: Guo G. Y. , Temmerman W. M.
Published: March 2011

A KKR program for self-consistent electronic structure and total energy calculations of complex solids has been developed. This program has been used to study structural, electronic and magnetic properties of a number of solids. In this paper, we give a description of several numerical techniques used in this KKR program which might be of use to other practitioners. We also present some results obtained using this program: c/a ratio of hexagonal Y, elastic constants of Mo, TiC and MgO, and static spin susceptibility of Pd.
Self-Consistent Electronic-Structure Calculations for Interface Geometries
Authors: Sowa Erik C. , MacLaren J. M. , Zhang X. -G. , Gonis A.
Published: March 2011

We describe a technique for computing self-consistent electronic structures and total energies of planar defects, such as interfaces, which are embedded in an otherwise perfectcrystal. As in the Layer Korringa-Kohn-Rostoker approach, the solid is treated as a set of coupled layers of atoms, using Bloch's theorem to take advantage of the two-dimensional periodicity of the individual layers. The layers are coupled using the techniques of the Real-Space Multiple-Scattering Theory, avoiding artificial slab or supercell boundary conditions. A total-energy calculation on a Cu crystal, which has been split apart at a (111) plane, is used to illustrate the method.
Multiple Scattering Calculations Applied to XAS: A Structure and Electronic Sensitive Tool
Authors: Sainctavit Philippe , Petiau J.
Published: March 2011

We present an application of multiple scattering theory with “muffin-tin” potentials to the calculation of X-ray absorption cross section. We have measured and calculated the K-edge spectra of atoms in compounds with zincblende structure : SiC, ZnS. We show that some spectral features can be precisely related to the local environnement around the absorbing atom.
Positron 2D-Acar Experiments and Electron-Positron Momentum Density in YBa2Cu307−x
Authors: Smedskjaer L.C. , Bansil A. , Welp U. , Fang Y. , Bailey K.G.
Published: March 2011

We discuss positron annihilation (2D-ACAR) measurements in the c-projection on an untwinned metallic single crystal of YBa2Cu3O7-x as a function of temperature, for five temperatures ranging from 30K to 300K. The measured 2D-ACAR intensities are interpreted in terms of the electron-positron momentum density obtained within the KKR-band theory framework. The temperature dependence of the 2D-ACAR spectra is used to extract a ‘background corrected’ experimental spectrum which is in remarkable accord with the corresponding band theory predictions, and displaysin particular clear signatures of the electron ridge Fermi surface.
Full Potential Electronic Structure Calculations and the Concept of Stress Fields and Energy Densities for Total Energy Calculations
Authors: Ziesche P.
Published: March 2011

With the availability of reliable full atomic cell orbitals the possibility arises to calculate pressure or stress, restoring or relaxation driving Hellmann -Feynman forces, and total energies (especially of defects) alternatively and directly via stress tensor fields and energy densities, two local quantities. Although quantum mechanical stress field and energy density can not be defined uniquely, there is a recent interest in these quantities, because integrals with physical meaning are gauge invariant.

The mentioned fields can be defined (i) for the full many-body description with the exact one-particle density matrix and pair distribution function as well as (ii) for the Kohn-Sham one-particle description with LDA or beyond (gradient expansion approximation). If the local stress field for a special system once is constructed, then the global stress tensor and /or forces on nuclei can be calculated via the stress theorem and the force theorem by means of unit cell surface integrals. The energy density can be derived from the terms of the stress field by taking the trace and can be used to calculate defect energies without bothering about the thermodynamic limit.
An Updated Gas Source Focused Ion Beam Instrument for TEM Specimen Preparation
Authors: Alani Reza , Jones Joseph S. , Swann Peter R.
Published: March 2011

The construction and performance of an updated gas source precision ion milling system are described. The system is based on an existing focused ion beam machine which is able to image and mill selected areas of specimens that are too thick for TEM studies. The specimen image is formed using either secondary electrons or secondary ions, captured by a dual detector. The work chamber consists of three major components: the ion gun, the ion column and the specimen chamber. The ion gun is an electron impact ionization type with an optimized source size and allows the use of variety of gases. The updated system employs an objective lens with shorter focal length to enhance the resolution. The specimen chamber with an improved specimen eucentric stage, accepts side entry TEM specimen holders. This enables the specimen to move between the TEM and the instrument for further precision thinning as required without removal of the specimen from the holder and consequent risk of damage. The upgraded system resolves features <1μm in thickness. Its point milling rate for Ni is 1.4μm/min. The ability of the instrument for imaging and localized milling is demonstrated by a number of TEM images of semiconductors, metals, ceramics and composites.
Characterizing Hierarchical Structures of Natural Ivory
Authors: Zhang H. B. , Cui F. Z. , Wang S. , Li H. D.
Published: March 2011

This paper presents a detailed investigation of the hierarchical and structural organization of the collagen-based aggregates in ivory. Ivory from African elephants is selected as the prototype in this study. A sophisticated architecture composed of collagen fibers and hydroxyapatite-like particles is revealed by optical microscopy, scanning electron microscopy and transmission electron microscopy. X-ray diffraction and TEN with selected area diffraction are employed to analyze the structure. Electron spectroscopy for chemical analysis and infrared absorption spectroscopy give information about the composition and chemical environment of the atoms in ivory. It is found that the structure of ivory has a three-level hierarchical organization, which includes both organic and inorganic materials. In the structure the inorganic material exists inside an organic framework, located outside of the collagen fibrils in the extrafibrillar volume. This inorganic structure has a polycrystalline form. Both the chemical compositions and the chemical environment of the atoms in the hydroxyapatite-like particles in ivory are different from those in natural hydroxyapatite.
Cluster Assembly of Hierarchical Nanostructures
Authors: Siegel Richard W.
Published: March 2011

In the past few years, atom clusters with diameters in the range of 2–20 nm of a variety of materials, including both metals and ceramics, have been synthesized by evaporation and condensation in high-purity gases and subsequently consolidated in situ under ultrahigh vacuum conditions to create nanophase materials. These new ultrafine-grained materials have properties that are often significantly different and considerably improved relative to those of their coarser-grained counterparts owing to both their small grain-size scale and the large percentage of their atoms in grain boundary environments. Since their properties can be engineered during the synthesis and processing steps, cluster-assembled materials appear to have significant potential for the introduction of a hierarchy of both structure and properties. Some of the recent research on nanophase materials related to properties and scale are reviewed and some of the possibilities for synthesizing hierarchical nanostructures via cluster assembly are considered.
Biomimetic Sensors and Actuators
Authors: Markowski Kelley , Newnham Robert E.
Published: March 2011

Several types of biornimetic structures suitable for underseas systems are described. Composite sensors and actuators are modeled after coral, fish, sharks and bats.
Hierarchical Design Of Electrochromic Glasses
Authors: Demiryont Hulya
Published: March 2011

Layered electrochromic glass was investigated in order to test the feasibility of using hierarchical designs for new electrochromic devices. Matrix-type synthetic electrochromic structures were designed, and two types of matrix devices, polarization and plating, were produced and evaluated. The application and device requirements of electrochromic glasses are discussed.
Physics of Complex-Biological Membranes and Cell Interfaces
Authors: Evans Evan
Published: March 2011

Nature has developed exceptional designs for resilient “soft” materials and for interfacing “soft-hard” materials which show capabilities well-beyond our present day technology. Most of the properties of biological materials – and a great deal of biological function – emanate from chemical and physical characteristics of interfacial structures (membranes). Although material interfaces in biology are complicated, it appears that these structures have been invariably optimized (with respect to harsh-environmental requirements) by the slow “evolutionary-driven” engineering. Some “hierarchical” features and characteristic length scales for biological membranes are directly related to architecture; but others are more subtle and arise because conformations of much of the molecular structure are randomized by thermal fluctuations.
Disorder and Scaling in Regular and Hierarchical Composites
Authors: Duxbury P. M.
Published: March 2011

We first summarize the scaling behavior of breakdown strengths and transport and elastic moduli of random two phase composites. We then consider the effect of disorder on two hierarchical structures. The first, a tree-like structure illustrates the fact that disordered trees, such as occur in many natural circulatory systems, show large fluctuations in their conductance and current flow. The second, a continuous fiber composite (CFC), leads us to suggest that, due to its greater flaw tolerance, a hierarchical microstructural design may improve the longitudinal and transverse toughness of CFC's.
Structural Polysaccharides In Molecular Architecture of Plant Cell Wallsfrom Algae to Hardwoods
Authors: Atalla R. H. , Hackney J. M.
Published: March 2011

The structural polysaccharides are a family of polymers of hexoses and pentoses that occur in all plant cell walls. The distinguishing characteristic of these polymers is a β-1,4-linked backbone. The most common among these is cellulose, which is the linear homopolymer of anhydroglucose. These polysaccharides are capable of aggregating into highly ordered structures that are the primary determinants of the mechanical and physical properties of cell walls. An overview of the variations in patterns. of structural-polysaccharide aggregation within cell walls is presented here. Among the majority of the algae cellulose is the dominant structural polysaccharide; thus the habit of aggregation is dominated by the patterns of cellulose. Among primitive plants, other structural polysaccharides represent a larger fraction of cell-wall mass and cellulose is less dominant. In woody tissues of higher plants, structural polysaccharides are the major components of the cell wall, and the patterns of aggregation are again dominated by the characteristic habits of cellulose. Within tile phylogenetic framework, higher levels of morphological development apparently involve greater complexity in the molecular architecture of the cell walls and a finer level of blending of the components of aggregates at the molecular level.
Self-Assembled α-Helical Polypeptide Films
Authors: Enriquez Erwin P. , Samulski Edward T.
Published: March 2011

Poly(γ-benzyl-L-glutamate) (PBLG) derivatized at its N-terminus with lipoic acid, a disulfide-containing moiety, self-assembles on gold from helicogenic solvents to give a thin film with the polypeptide α-helices orientation distribution different from the planar orientation in the unlabeled, physisorbed PBLG films (control) and Langmuir-Blodgett monolayers. The SA films were studied by angle-dependent XPS, reflection-absorption FTIR spectroscopy, and ellipsometry. The IR dichroic properties of the amide I and amide II bands were used to infer the orientational distribution of the helices in the self-assembled film and lead to two extreme pictures of the helix axis distribution function: (a) random (hemispherical distribution) and (b) perfect order with a tilt of 53° from the surface normal. Additional characterization is necessary to differentiate between these two distributions.
Design of Protein-Producing Bioreactors for Self-Assembling Systems.
Authors: Furlong Clement E. , Humbert Richard
Published: March 2011

Proteins, due to their complex structures, possess infinite possibilities for assembling themselves as well as other biological and nonbiological materials into complex, multicomponent structures. Many examples from nature demonstrate the high degree of flexibility, strength and “intelligence” offered by protein-organized, self-assembling systems. However, several problems must be overcome before self-assembling protein-based products can become commercially feasible. One problem is the high cost of protein production. A second problem involves the question of producing nonidentical protein subunits in the proper stoichiometry for self-assembly. A third problem involves the stability of the protein components of larger structures.

We have been developing protein-producing bioreactors to address the problems associated with the commercial production of proteins, both as individual products as well as components of self assembling systems. The approach that we have taken is to clone the gene or cDNA that encodes the desired protein(s) and tailor the expression of the protein so that it can be produced at high levels under conditions where cell division is blocked. This assures that supplied nutrients go into product and not biomass, and at the same time provides conditions where cells can be immobilized without fracturing the support matrix during division. The blocking of cell growth also allows for the adjustment of protein stoichiometry by setting the ratios of cells that produce different subunits of complex structures.

To simplify downstream processing and purification, we have designed a system where nearly pure protein is secreted directly into the medium. This approach allows for automated downstream processing and separation of product from cells before it is degraded. The model system that we are using for the development of the protein-producing bioreactors utilizes genetically modified strains ofEscherichia colithat secrete proteins which are usually found in the periplasmic space directly into the medium. The phosphatebinding protein serves as an ideal model protein for bioreactor development, since the regulatory elements that control its production are turned on by phosphate limitation, which also arrests cell division. We are presently determining if these regulatory and secretory elements can be used to direct the synthesis and secretion of heterologous proteins.
Structural and Morphological Features of Synthetic and Natural Polymers
Authors: Lotz Bernard
Published: March 2011

The crystal structures and crystalline morphologies of natural and synthetic polymers are briefly reviewed. Analogies and differences between these two systems are presented. Several examples of cross-fertilization of research in the two fields are presented, with emphasis, among natural polymers, on fibrous polypeptides and proteins.
Effects of Surface Treatment on Light Emission from Porous Silicon
Authors: Khan Babar A. , Pinker Ronald , Shahzad Khalid , Rossi Barbara
Published: March 2011

Visible light emission from porous silicon has recently been demonstrated by several groups. We have found that annealing of porous silicon samples in an inert atmosphere over 250C reduces the emission intensity, almost fully quenching it by 450C. We believe that this is due to the removal of passivating hydrogen, based on measurements of infrared absorption due to Si-H vibrational modes. We have also found that we can partially recover the emission intensity in these annealed porous silicon layers by passivation in a hydrogen plasma. We have therefore demonstrated that hydrogen passivation is necessary for the observation of visible emission from porous silicon. We have also shown that thermal oxidation of porous silicon over 200C reduces the PL emission. We propose that this reduction is also due to the loss of hydrogen passivation during the oxidation.
Optical Characterization of the Visible Photoluminescence from Porous Silicon
Authors: Fuchs H. D. , Brandt M. S. , Stutzmann M. , Weber J.
Published: March 2011

The visible photoluminescence of electrochemically etched silicon wafers is studied by cw- and pulsed-laser excitation. Raman data and infrared transmission measurements on the same samples prove the presence of oxygen and hydrogen in different bonding configurations in the luminescent layers. Identical optical properties are found for chemically synthesized siloxene (Si6O3H6) and its derivates. We present evidence that the origin of the strong room temperature luminescence in “porous” silicon can be traced to siloxene derivates present in the samples.
Characterization of Microporous Silicon Fabricated by Immersion Scanning
Authors: Bassous E. , Freeman M. , Halbout J.-M. , lyer S. S. , Kesan V. P. , Munguia P. , Pesarcik S. F. , Williams B. L.
Published: March 2011

A novel immersion scanning technique for making microporous silicon has been successfully applied to blank and lithographically patterned Si substrates. The advantages of the method lie in its simplicity, speed and adaptability to large and odd-size substrates. The photoluminescence (PL) spectra of microporous Si show a continuous decrease in intensity between 200K and 2K, but are fully reversible. Thermal desorption spectroscopy on microporous Si shows a classic hydrogen desorption spectrum which coincides with a quenching of the PL intensity. Under constant excitation, a degradation of PL Intensity occurs in oxygen and wet nitrogen but is only partially reversible in dry N2. Microporous Si PN junctions exhibiting normal I-V characteristics have been successfully fabricated with standard Si VLSI processes. Visible light emission under forward bias is detected which increases linearly In Intensity with Input current. This is the first observation of electroluminescence in the visible region from microporous SI PN junctions.
Pore Formation and Propagation Mechanism in Porus Silicon
Authors: Lehmann V. , Cerva H. , Gosele U.
Published: March 2011

This paper presents a model of the microporous silicon formation process which is based on hole depletion due to quantum confinement in the porous structure. This model is compared with the formation of larger porous structures (meso-, macroporous) where hole depletion is generated by a space charge region.
Photoluminescence Excitation Spectroscopy (PLE) of Porous Silicon
Authors: Wang Lei , Wilson M. T. , Goorsky M. S. , Haegel N. M.
Published: March 2011

PLE spectroscopy was performed on samples of porous Si at temperatures of 300 and 4.2 K. PLE provides information about the absorption coefficient in the limit of optically thin samples and is an alternative method for determining absorption data on porous Si without removal of the substrate. The spectra obtained correspond closely to the relative changes in absorption coefficient for bulk Si between 2.0 and 3.5 eV, with a strong increase above 3.0 eV which is due to the direct bandgap transition.
Effect of a Siliceous Additive in a Clay Engineered Barrier on Aqueous Corrosion of R7T7 Nuclear Waste Glass
Authors: Godon N. , Andriambololona Z. , Vernaz E.
Published: March 2011

Previous tests have shown that glass is highly corroded in the presence of smectite 4a, a clay under consideration for use as a repository engineered barrier material. Alteration experiments with French R7T7 glass were therefore conducted in moist clay media containing 5 wt% of a siliceous additive. Five siliceous materials were tested: silica gel, pozzolana, window glass, R7T7 glass frit and R7T7 glass, all in powder form. Following an initial 28-day preconditioning period during which the clay/additive/leachant system was allowed to reach equilibrium, a glass specimen was placed for 7 or 28 days in the moist clay medium. Glass alteration was characterized by the mass loss and by surface analysis. After 28 days in contact with the silica gel and with the three glass powders the mean glass corrosion rate calculated from the mass loss values was about 0.01 g.m−2d−1, versus 1.4 g·m−2d−1 with clay alone and 0.3 g·m−2d−1 with pozzolana. The use of a suitable additive can thus considerably attenuate the corrosive effects of moist smectite in contact with R7T7 glass.
Effects of Noble Metal Elements on Viscosity and Electrical Resistivity of Simulated Vitrified Products for High-Level Liquid Waste
Authors: Igarashi Hiroshi , Kawamura Kazuhiro , Takahashi Takeshi
Published: March 2011

The effects of noble metal elements such as ruthenium, rhodium and palladium on the viscosity and electrical resistivity of simulated nuclear waste glass were studied. The glass enriched with noble metals showed the viscosity of a non-Newtonian fluid. The viscosity of the waste glass with 10 wt% Ru0 2 was 3 to 7 times higher than that of glass without noble metals. The RuO2 was mainly responsible for the increase in viscosity for the glass enriched with noble metals. Electrical resistivity of the glass with 15 wt% RuO2 was one seventh to two orders of magnitude lower than that of glass without noble metals. The three noble metals contributed to the decrease in resistivity. The quantitative effects of noble metals on these properties were obtained.
The Platinum Metals in Hllw — Glass Products
Authors: Kelm Manfred , Oser Bernhard
Published: March 2011

The behaviour of the platinum metals in nuclear waste glass produced in a lab scale liquid fed ceramic melter was investigated. The platinum metals form two kinds of metallic conductive particles in the glass melt: RuO2 (preferentially needle shaped) and a Pd—Rh—Te alloy (tear—shaped). These phases decrease the electrical resistivity of the glass melt. Resistivities were measured at 950º and 1150 ºC. Powdered glass was used as starting material. For the same temperatures resistivities were calculated applying an equation derived for an embedment structure of highly conductive particles in a matrix of low conductivity. To match calculated and measuredresistivities one must assume needle—shaped particles. This gives evidence that mainly RuO2 contributes to the observed decrease in resistivity. If the measurements are started with glass blocks instead of glass powder, remarkably lower resistivities are measured in the melt. A comparison of both results indicates a partial destruction of particles or particle contacts by grinding. Thus, resistivities measured with ground samples are not representative of those effective in a melter.

The investigation of solid glass samples yielded the following results: Within a few hours, Pd—Rh—Te and RuO2 particles form fine sediments in the melter. The development of stable coarse sediments needs some 1000 h of melter operation. The Pd—Rh—Te alloy particles reach a mean diameter of 5 μm in the fine sediment and of 20 μm in the coarse one. With time, the alloy dissolves more Rhand Te. Finally, the alloy separates into two phases. RuO2 dissolves Cr and Rh.
Tellurium and Palladium Diffusion in the German Waste Glass Vg 98/12 Measured with the Rbs Method
Authors: Yamashita M. , Matzke Hj. , Linker G.
Published: March 2011

The diffusion of Te and Pd was measured in the German waste glass VG 98/012 usingion implantation to introduce these elements, and the Rutherford backscattering (RBS) method to measure their diffusion. Both elements tend to precipitate during manufacture ofnuclear waste glasses, and the Te-content of the precipitates depends on the annealing time. Diffusion of these elements is a basic property of the separation phenomenon. Diffusion of both elements was found to be very slow. Te-diffusion coefficients were in the range of 10-17 to 10-15 cm2s-1 between 540 and 590 αC. Surface evaporation of Te was observed at all heat treatments. Pd diffusion was not observed in this study, most likely due to limited solubility of Pd and formation of metal precipitates.
Microstructure, Partitioning and Dissolution Behaviour of Synroc Containing Acrinides
Authors: Blackford M.G. , Smith K.L. , Hart K.P.
Published: March 2011

Synroc formulations containing 10 wt% simulated PW-4b type HLW in combination with a single transuranic dopant (Np, Pu, Am or Cm) were fabricated and characterised using alpha-track methods, SEM, AEM and dissolution testing. The Pu, Am and Cm-doped samples were calcined in 3.5%H2/96.5%N2. One of the Np-doped Synrocs was calcined in an atmosphere of pure H2, whilst another Np-doped Synroc was calcined in a mixture of 3.5%H2/96.5%N2. All the different formulations displayed microstructures similar to those of Synroc containing actinide-free simulated HLW. AEM derived phase compositions and phase distributions are given. All the Synrocs showed good durability when exposed to leachants (including doubly deionised water, and pH- and Eh-buffered solutions with pHs between 2 to 10). There were no obvious differences between the two Np-doped samples. The improved appearance and behaviour of allthe Synrocs in this study compared with similar formulations described by other authors is attributed to improved mixing techniques during fabrication.
The Pyrochlore Line in the System CaO—ZrO2—TiO2: Implications on Synroc Phase Assemblages
Authors: Figueiredo M. Ondina , Santos António Correia dos , Cortina Carmen Parada , Basto M. Joao
Published: March 2011

Results of further studies on phase equilibria in system CaO—ZrO2—TiO2along the “pyrochlore” line ( Ca ZrxTi3-x07) are reported concerning the possible substitution of cerium for either calcium or zirconium in nominal “Ca Zr2 Ti 07”. The dominant tetragonal phase in this composition was identified as calzirtite. The structural role of zirconium and its tendency towards 7—coordination environments are discussed. Possible implications on high—level nuclear waste immobilizers like SYNROC are brieflyconsidered.
Solubility of Simulated Hlw Elements in Pyrochlore Structure
Authors: Hayakawa Issei , Kamizono Hiroshi
Published: March 2011

We have found that lanthanum zirconate (La2Zr2O7) with a pyrochlore structure can be used as a superior host phase for actinide and lantanide elements contained in high-level nuclear waste. The solubility of Ce, Nd and Sr in La2Zr2O7 is determined because Ce and Nd may simulate the segregation of actinide and lanthanide elements at the grain boundaries of polycrystalline La2Zr2O7. The results show that La2Zr2O7 is a promising material for confining actinide and lanthanide elements in its crystal structure.
Determination of Criteria for Selecting A UO2Fuel Dissolution Model for Nuclear Fuel Waste Management Concept Assessment
Authors: Sunder S. , Shoesmith D.W. , Miller N.H. , Wallace G.J.
Published: March 2011

Assessing the concept of direct disposal of used nuclear fuel in a geological vault requires a model to predict the dissolution rate of UO2in groundwater. A solubility-limited model can be used to calculate the dissolution rate of UO2fuel under non-oxidizing conditions. When the oxidative dissolution of UO2is an irreversible process, a kinetic model is more suitable to describe the dissolution of UO2under oxidizing conditions. Experimental studies were carried out using electrochemical techniques and X-ray photoelectron spectroscopy, XPS, to determine criteria for selecting the appropriate model for estimating used-fuel dissolution rates as a function of the redox conditions in the vault at the time of container failure. UO2electrodes were subjected to prolonged (>1000 min) potentiostatic oxidation, and the rate of oxidation and dissolution of UO2fuel was investigated as a function of the applied potential. UO2oxidation was also carried out by the products of water radiolysis and studied as a function of dose rate, total dose and solution chemistry.

These studies show that significant oxidative dissolution of UO2appears possible for potentials more positive than -100 mV vs SCE in solutions with a pH close to that of the deep groundwaters, i.e., from 6 to 10. A kinetic model, which takes into account the mechanism of UO2oxidation, is more appropriate to estimate dissolution rates of UO2fuel for redox conditions more oxidizing than -100 mV vs SCE.
Gap and Grain-Boundary Inventories of Cs, Tc, and Sr in Spent LWR Fuel
Authors: Gray W. J. , Strachan D. M. , Wilson C. N.
Published: March 2011

Soluble radionuclides concentrated within the gap and grain-boundary regions of spent fuel could dissolve relatively rapidly were the waste container to fail and the fuel to be contacted by water in a geologic repository. To provide an estimate of the quantities of radionuclides that may be rapidly released, fractional inventories of Cs, Tc, and Sr concentrated within the fuel/cladding gap region have been measured for U.S. LWR spent fuels with fission gas release (FGR) values ranging from 0.25% to 18%. Separate measurements of the grain-boundary inventories of Cs, Tc, and Sr have been made for the same fuels. The Cs gap inventories were generally found to be about one fourth of the FGR values. The Cs grain-boundary inventories were generally less than 1% of the total Cs inventories and were not strongly correlated with FGR. Both the gap and grain-boundary inventories of Tc and Sr were near the detection limits of the methods used, less than 0.2% of the total inventories of these elements. However, some of the Tc may reside at the grain boundaries in the form of relatively insoluble metallic particles and not be detected by these experiments. Data obtained by comparing the dissolution behavior of fuel fragments with that of fuel grains were used to estimate the dissolution rate of Cs from the grain boundaries of one of the fuels. Surface-area normalized dissolution rates determined for fuel fragments in these same tests exceeded those determined for grains. A likely explanation is that the estimated fragment surface area did not take into account the “effective” grain-boundary surfaces.
Corrosion of Carbon-Steel Containers for Heat-Generating Nuclear Waste in Brine Environments Relevant for A Rock-Salt Repository
Authors: Smailos E. , Schwarzkopf W. , Kienzler B. , KÖster R.
Published: March 2011

In previous corrosion studies, carbon steels, especially the fine-grained steel TStE355, were identified as promising materials for heat-generating nuclear waste containers acting as a barrier in a rock-salt repository. In the present study detailed investigations have been performed on fine-grained steel to determine the influence of important parameters on its corrosion behaviour in disposal-relevant salt brines. These parameters are: brine composition (Mg Cl2-rich and NaCI-rich brines), temperature (90°C, 170°C), and salt impurities, such as H2S concentrations of 25 mg/I-200 mg/I salt brine.

Under the conditions of the tests used here, carbon steel was subjected to general corrosion. Pitting and crevice corrosion or stress-corrosion cracking were not observed. The increase in temperature from 90°C to 170°C strongly enhanced the corrosion rate of the steel. In the MgCl2-rich brines, considerably higher rates (37-70 μm/a at 90°C, 200-300 °m/a at 170°C) were observed than in the NaCI-rich brine (5 μm/a at 90°C, 46 μm/a at 170°C). H2S concentrations in the MgCl2-rich Qbrine of up to 200 mg/l did not influence significantly the corrosion rate of the steel. The corrosion rates determined imply corrosion allowances that are technically acceptable for thick-walled containers. In view of these results, fine-grained steel continues to be considered as a promising material for long-lived HLW containers.
In-Situ Corrosion Studies on Cast Steel High-Level Waste Containers Plated with Titanium/Nickel-Alloys
Authors: Schwarzkopf W. , Smailos E. , KÖster R.
Published: March 2011

Previous corrosion studies have shown that the passive alloys Ti 99.8-Pd and Hastelloy C4 are the most promising corrosion protection materials for long-term resistant carbon-steel containers for the disposal of heat-generating wastes in rock salt formations. Consequently, these materials are subject to more detailed investigations. The influence of selected container manufacturing characteristics (sealing technique, application mode of the corrosion protecting layer on the steel) on the corrosion behaviour of Ti 99.8-Pd and Hastelloy C4was studied using in-situ experiments. The corrosion resistance of the materials was examined both in NaCI brine and MgCl2-rich brine, which might enter into an HLW borehole under certain disposal conditions. Four electron-beam welded cast-steel tubes plated with corrosion protection layers made of Ti 99.8-Pd and Hastelloy C4, respectively, were stored for 18 months in 2-m deep heated boreholes in the Asse salt mine. The annular gap between the tubes and the borehole wall was filled with saturated NaCl-brine or Qbrine (MgCl2-rich). The vertical temperature profile in the boreholes ranged from 90°C to 200°C

In the cast-steel tube with a corrosion protection of Ti 99.8-Pd, no indication of corrosion was observed on the EB-welds or on the explosion plated material in both brines. The cast-steel tube with a corrosion protection of Hastelloy C4 also was found to be resistant to any kind of corrosion in the NaCl-brine. In the MgCl2-rich brine, however, small pitting corrosion of 15 pm was observed after 1.5 years on the passive surface layer that was formed.

On the basis of these results, Ti 99.8-Pd continues to be considered as a promising corrosion protection material for long-lived HLW containers.
Obsidians and Tektites: Natural Analogues for Water Diffusion in Nuclear Waste Glasses
Authors: Mazer James J. , Bates John K. , Stevenson Christopher M. , Bradley C. R.
Published: March 2011

Molecular water diffusion in natural obsidians and tektite was investigated in vapor hydration tests performed between 75 and 230°C for up to 400 days. Reaction progress was monitored using measurements of the birefringent hydration layer, an alteration feature associated with strain caused by molecular water diffusion in obsidians. The hydration rate constants and temperature dependence of the reaction are strongly correlated with the logarithm of the initial total water content of the glass. These values have been quantified for conditions relevant to the potential Yucca Mountain repository. The low initial total water concentrations of Savannah River Lab nuclear waste glasses produced at the bench-top scale help to minimze the effects of molecular water diffusion in waste glasses. The results of this study indicate that molecular water diffusion does not dominate waste glass reactions under conditions considered in this study. However, it is unknown whether molecular water diffusion will be important under other reaction conditions, especially longer time periods.
Experimental Determination of Parameters Governing Heat-Induced Moisture Movement in A Clay Buffer
Authors: Selvadurai A.P.S.
Published: March 2011

This paper discusses the experimental evaluation of the hygro-thermal parameters governing coupled heat and moisture movement within a moist clay buffer, which is developed as an engineered barrier for the isolation of heat emitting nuclear waste containers in either a borehole environment or in an in-room emplacement scheme.
Hydrothermal Field Experiment Simulating Steel Canister Embedded in Expansive Clay - Physical Behavior of the Clay
Authors: Pusch Roland , Karnland Ola , Lajudie Alain , Atabek Rosemarie
Published: March 2011

Field heat experiments with kaolinite/smectite clay surrounding heaters in boreholes were conducted for 0.7 and 4 years with temperatures up to 170-180°C. The short test gave a high degree of water saturation even in the hottest part (> 75 %) and almost no change in physical properties and mineral composition. The long test gave a dry inner zone of claystone, indicating gas formation, and rich precipitation of silica/aluminum compounds and sulphate minerals. Brittleness characterized the hot parts and stiffening occurred also in the colder parts due to precipitation of silica and aluminum.
Development of A Model for Handling the Movement of Redox Fronts and Other Sharp Reaction Fronts
Authors: C. Nyman , V. Ozolins , L. Moreno , I. Neretnieks
Published: March 2011

We have developed a coupled transport and reaction computer program which is adapted to handle sharp reaction fronts. Such fronts develop in the ground and typical examples are redox fronts and dissolution/precipitation fronts. The program is developed to describe the chemical evolution around radioactive waste repositories but it is applicable to other situations as well. To validate the program we compare our results with data from other geochemical equilibrium programs, such as EQ3/6 [1], PHREEQE [2] and transport programs such as CHEQMATE [3]. Natural analogues like the Osamu Utsumi mine at Poços de Caldas in Brazil and the uranium ore body at Cigar Lake in Saskatoon, Canada, are studied using the program.
Modelling the Chemical Environment Near A Waste Disposal Site in A Granitic Host-Rock Influence of Factors Controlling the Solubility of Radionuclides
Authors: Barbier Jean , Fabriol Robert , Ouzounian Gerald
Published: March 2011

Maximum aqueous concentrations of six radionuclides (Sr, Np, U, Th, Pu and Tc) near a disposal site with a quartz sand or clay engineered barrier in a granitic environment, were calculated in a previous study by computer modelling. A sensitivity study has been carried out in order to assess the importance of three factors in determining the maximum concentrations likely to be found in solution: the maximum temperature reached, water salinity, and the dissolution constants used. In the circulating fluid, final concentrations for Pu, Tc and Th depend mostly on the final temperature. The solubility of Sr is influenced by the fluid salinity. The final concentration of Np is affected by the temperature of the waste disposal site. Uncertainty in the dissolution constants causes the greatest relative variation in calculated U concentrations.
Numerical Simulations of Heterogeneous Chemical Reactions Coupled to Fluid Flow in Varying Thermal Fields
Authors: Carnahan C. L.
Published: March 2011

A numerical simulator of reactive chemical transport with coupling from precipitation-dissolution reactions to fluid flow, via changes of porosity and permeability, is applied to precipitation-dissolution of quartz and calcite in spatially and temporally variable fields of temperature. Significant effects on fluid flow are found in the quartz-silicic acid system in the presence of a persistent, strong gradient of temperature. Transient heat flow in the quartz-silicic acid system and in a calcite-calcium ion-carbonato species system produces vanishingly small effects on fluid flow.
Non-Linear Effects of Glass Composition on Chemical Durability: Physical Stability of Surface Layers
Authors: Muller I. S. , Buechele A. C. , Pegg I. L. , Macedo P. B.
Published: March 2011

Presented here are results relating to the possible causes for the very strong nonlinearity in the relationship between glass composition and glass durability, as determined by MCC 3 or Product Consistency (PCT) tests. We have previously found a rapid increase in leachate concentrations with small changes in composition (as little as 1 weight percent SiO2 or Al2O3) over some composition ranges near those of interest for nuclear waste disposal. This rapid rise occurs over a narrow transition region in composition space that provides a natural division between more durable and less durable glasses. Our new data on glasses of interest to the West Valley Demonstration Project (WVDP) suggest that this effect is not due to phase separation. Results from leach tests conducted with and without constant agitation are compared in an attempt to determine whether the physical integrity of alteration layers plays an essential role, as might be the case if formation-spallation cycles were important in this process. Microstructural data are also presented in order to compare the alteration layers on the more durable and less durable glasses leached with and without agitation.