bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Processing on Fiber/Matrix Interfaces in Ni3Al/Sapphire Single Crystal Composites
Authors: Ringer D. , White C. L.
Published: April 2011

Composites consisting of Ni3Al modified with Zr, Fe, and B (IC-50) reinforced with continuous sapphire single crystal fibers have been prepared by vacuum hot pressing foil/fiber multilayers. Previous research detected formation of Zr-rich precipitates and sulfur segregation at fiber/matrix interfaces in these materials subsequent to fabrication. In this work, fiber bonding to the Ni3Al matrix has been characterized using fiber push-out tests. Segregation and precipitation at fiber/matrix interfaces has been examined using scanning Auger electron spectroscopy and scanning electron microscopy. For comparison, composites have also been prepared from Ni, Ni-Al, and Ni-Al-Zr solid solution matrices, to evaluate the effects of matrix strength and reactivity on processing and fiber/matrix reactions.
The Contribution of Matrix Plasticity to the “Frictional” Sliding of Debonded Fibers in Sapphire-Reinforced TiAl Matrix Composites
Authors: Galbraith J. M. , Koss D. A. , Hellmann J. R.
Published: April 2011

Large-scale fiber displacement behavior, usually characterized by a “frictional” sliding stress (τslide), has been studied in two sapphire-reinforced TiAl systems. Experimental results from fiber pushout and reverse push-back tests indicate that the large-scale sliding behavior of debonded fibers leads to an average τslide-value which progressively decreases during fiber displacements. Previous studies of SCS-6 (SiC) fiber-reinforced glass and metal matrix composites have attributed decreases in τslide to the fracture and wear of fiber asperities. However, given a matrix in which fiber asperities do not easily wear (e.g., a TiAl alloy), SEM examination of the fiber/matrix interface indicates that matrix plasticity plays a dominant role in the decrease of τslide with fiber displacement. Experimental evidence suggests that the observed decrease in τslide can be attributed to (1) a decrease in fiber roughness perceived by the matrix due to matrix grooving and (2) a relaxation of radial clamping as a result of material removal from the interface.
Additivity of Direct and Indirect Strengthening in TiB2-Reinforced Near-γ Titanium Aluminides
Authors: Kampe S. L. , Sadler P. , Christodoulou L. , Larsen D. E.
Published: April 2011

An experimentally-based description of strengthening in a series of TiB2-reinforced near-y titanium aluminides is presented. The analysis provides a means to examine the strengthening contributions which are individually attributable to compositional variants, to indirect sources which are present due to the influence of the particulate on the underlying microstructure, and to those directly evolving from the presence of the reinforcement and its interaction with dislocations. Once the indirect strengthening contributions are isolated and arithmetically removed from the magnitude of the experimentally determined composite strength, the resulting direct strengthening increments are found to obey a linear relationship with the inverse-squareroot of the edge-to-edge interparticle spacing. The description of the dependence on spacing is found to be compatible with other studies where similar relationships have been reported.
Ductile Phase Toughening of MoSi2: Effect of Reinforcement Morphology
Authors: Chen Long-Ching , Bahtishi Nedhal , Lederich Richard , Soboyejo Wolé
Published: April 2011

The effects of ductile reinforcement morphology on the mechanical behavior of MoSi2 reinforced with 20 vol.% Nb are presented. While all the composites exhibit improved fracture toughness relative to the monolithic MoSi2, the most significant improvement is obtained in the composite with laminate reinforcement, followed by coarse fiber, fine fiber and particulate reinforcements. Bend strength measurements indicate a ductile-brittle-transition-temperature of ∼1250°C, and highlight the attractive properties of laminate reinforced composite. Preliminary studies of room temperature fatigue crack growth in particulate reinforced composites show a stable fatigue crack growth, which is not achieved in monolithic MoSi2. Possible ways of achieving a better combination of mechanical properties are also discussed.
Thermal Fatigue of MoSi2 Particulate and Short Fiber Composites
Authors: Kush M. T. , Holmes J. W. , Gibala R.
Published: April 2011

Induction heating of disk shaped specimens was used to compare and contrast the thermal fatigue behavior of MoSi2 and MoSi2-based composites. Specimens were subjected to 5 s heating and cooling cycles between temperature limits of 700°C and 1200°C. The monolithic material and a MoSi2- 10 vol% TiC composite exhibited poor thermal shock resistance and could not be thermally cycled according to this temperature-time profile. A 30 vol% TiC composite exhibited much better thermal shock and thermal fatigue resistance as compared to the monolithic material, but exhibited undesirable oxidation. MoSi2-10 and 30 vol% SiC particulate composites exhibited excellent thermal shock and thermal fatigue resistance compared to that of the monolithic material. A MoSi2-10 vol% SiC whisker composite did not show improved thermal fatigue resistance due to the initial processing defects present in the material. The monolithic material and the 10 vol% TiC composite were also subjected to 30 s heating and cooling cycles between temperature limits of 700°C and 1200°C. Both of these materials exhibited better thermal fatigue resistance at this temperature-time profile, but the 10 vol% TiC composite also exhibited undesirable oxidation. The fatigue results are discussed with reference to the initial microstructure of the specimens and the stress-strain history of the specimens which was obtained by a thermoelastic finite element analysis.
Microstructure and Deformation of Ti-22Al-23Nb Orthorhombic-Based Monolithic and Composite Titanium Aluminides
Authors: dary François-charles , Woodard Shiela R. , Pollock Tresa M.
Published: April 2011

A new class of intermetallic matrix composites (IMC's) based on orthorhombic titanium aluminides offer attractive properties for high-temperature structural components at temperatures up to 760°C. Results from an ongoing study on the microstructural stability and mechanical properties of the orthorhombic-based alloy Ti-22Al–23Nb (at%), in both monolithic and composite forms, are discussed. Oxygen acquired during processing or as a result of high-temperature exposure in air or vacuum has a pronounced influence on the microstructure of the monolithic and composite materials. Two-phase lath microstructures of ordered beta (βo) + orthorhombic (O) phases produced by processing low oxygen material above the beta transus are morphologically stable at 760°C. Conversely, in higher-oxygen three-phase microstructures containing O+βo+ α2(Ti3Al), lath coarsening and additional precipitation of α2 in oxygen-enriched sheet surface regions is observed. At 760°C/69MPa the two-phase lath microstructure has a higher creep resistance and lower tensile strength compared to the three-phase α2- containing microstructures of the higher oxygen material.
Processing and Properties of Nb5Si3/Nb Laminates
Authors: Short John , Kajuch Jan , Lewandowski John J.
Published: April 2011

Mechanical alloying(MA) and Reactive Sintering(RS) techniques were successfully used to produce Nb5Si3. Model laminates of mechanically alloyed Nb5Si3 and commercially pure niobium were prepared via vacuum hot pressing. Tensile properties for the as-received, vacuum heat treated and niobium with a solid solution of silicon were obtained at 298K and 77K. 298K bend tests were conducted in an in situ deformation stage in a SEM. 77K bend tests were also conducted. Toughness values are correlated to the ligament properties and effect of constraint.
Transformation Toughening Simulated at Different Length Scales
Authors: Clapp P. C. , Zhao Y. , Rifkin J. A.
Published: April 2011

The microscopic mechanism of “transformation toughening” is thought to be the stress reduction at a crack tip resulting from a displacive phase transformation induced by the stress field of a crack under external loading. Whether transformation toughening or “transformation embrittlement” is the result depends on many different characteristics of the displacive transformation, as well as the geometry of the stress field of the crack. Since both crack and displacive transformation dynamics are sufficiently rapid to be suitably simulated in a molecular dynamics scheme we have explored this approach with the ordered intermetallic NiAl, employing Embedded Atom Method (EAM) potentials. These potentials, in turn, have allowed the construction of a Ginzburg-Landau strain free energy functional (with all the material dependent parameters determined from molecular dynamics simulations) which may then be used to carry out Monte-Carlo simulations of the crack-transformation zone interaction on a substantially larger spatial scale. The simulations reported here show the complex microstructure involving self-accommodating martensite variants which result from the stress induced martensitic transformation near a crack tip in NiAl, and also measure the resulting reduction of stress intensity factor due to the transformation. It is concluded that current continuum mechanics models of transformation toughening need to be substantially revised if they are to adequately model the size, shape and microstructure of the transformation zone and produce accurate predictions of transformation toughening.
Combustion Synthesis of Niobium Aluminide Matrix Composites
Authors: Kachelmyer C. R. , Varma A.
Published: April 2011

Combustion synthesis of NbAl3-matrix composites with Al2O3 and B additions was studied using the thermal explosion mode. The addition of B to the reaction mixture resulted in the formation of NbB2, small amounts of NbB and unreacted Al. The Al2O3 addition did not affect the NbAl3-matrix reaction completion but the final product density increased with increasing Al2O3 loading. In both NbAl3-matrix composites, the reaction was initiated above the melting point of Al.
Polymer Derived, Stoichiometric SiC Fibers
Authors: Lipowitz J. , Rabe J. A. , Orr L. D. , Androl R. R
Published: April 2011

Polycrystalline, stoichiometric β- silicon carbide fiber tow suitable for ceramic or metallic matrix composite use has been prepared using a polymer precursor route to obtain textile grade, weavable fibers. Individual filaments have a diameter of 10 μm, an average tensile strength of up to 3.4 GPa (500 ksi), an elastic modulus up to 430 GPa (62 msi) and a density > 3.1 g/cm3. Crystallites average about 60 nm by x-ray line broadening. The SiC fiber shows improved mechanical and thermal stability properties, especially in an inert atmosphere, as compared to commercial polymer-derived SiC ceramic fibers. Thermochemical and mechanical properties, as well as fractography and microstructure will be presented.
Self Assembling Nanostructured Delivery Vehicles for Biochemically Reactive Pairs
Authors: Kossovsky Nir , Gelman A. , Hnatyszyn H.J. , Sponsler E. , Chow G.-M.
Published: April 2011

Intrigued by the deceptive simplicity and beauty of macromolecular self-assembly, our laboratory began studying models of self-assembly using solids, glasses, and colloidal substrates. These studies have defined a fundamental new colloidal material for supporting members of a biochemically reactive pair.

The technology, a molecular transportation assembly, is based on preformed carbon ceramic nanoparticles and self assembled calcium-phosphate dihydrate particles to which glassy carbohydrates are then applied as a nanometer thick surface coating. This carbohydrate coated core functions as a dehydroprotectant and stabilizes surface immobilized members of a biochemically reactive pair. The final product, therefore, consists of three layers. The core is comprised of the ceramic, the second layer is the dehydroprotectant carbohydrate adhesive, and the surface layer is the biochemically reactive molecule for which delivery is desired.

We have characterized many of the physical properties of this system and have evaluated the utility of this delivery technology in vitro and in animal models. Physical characterization has included standard and high resolution transmission electron microscopy, electron and x-ray diffraction and ζ potential analysis. Functional assays of the ability of the system to act as a nanoscale dehydroprotecting delivery vehicle have been performed on viral antigens, hemoglobin, and insulin. By all measures at present, the favorable physical properties and biological behavior of the molecular transportation assembly point to an exciting new interdisciplinary area of technology development in materials science, chemistry and biology.
Electronic Structure Calculations of Pure and Oxidized Copper Clusters Using Jellium and MO - LCAO Models
Authors: Gronbeck Henrik , Andersson Mats , Rosen Arne
Published: April 2011

A self consistent jellium approach to the chemisorption of molecular oxygen on copper clusters is investigated and compared with local density MO - LCAO calculations. The jellium model is found to be well suited for chemisorption studies and the results explain the main trends in the measured chemisorption properties of O2 on copper clusters.
Nanostructural Investigation of Silica Aerogels
Authors: Wang Jue , Shen Jun , Wu Weidong , Zhou Bin
Published: April 2011

Silica aerogels are sol-gel derived nanostructured materials with high porosities up to 99.8%. The nanostructures of silica aerogels are investigated by BET, SEM, SAXS techniques. A typical fractal structure is found especially for base-catalyzed aerogels. That is the aerogels are made of particles of size a, these particles form the branching and interconnecting networks up to an average cluster size ξ, At length scales above ξ, the material is an homogeneous assembly of such clusters; between a and ξ, the structure is fractal. Meanwhile, the effects of catalysis and aging on the structures are investigated and discussed. The reasons why SCD technique should be used are also deeply discussed.
Studies on Nanostructured M50 Type Steel Using X-Ray Absorption Spectroscopy and NMR
Authors: Balasubramanian Mahalingam , Zhang Y.D. , Budnick J.I. , Gonsalves K.E. , Xiao T.D.
Published: April 2011

We have investigated the local structural and magnetic properties of Fe in nanostructured Fe-Cr-Mo-V-C M50 type steel. Experimental techniques which we used include XAFS and NMR. NMR results on as-synthesized M50 type steel shows that the material contains a small amount of bcc Fe plus some other highly disordered phase(s). XAFS measurements indicate that the near neighbor coordinations around Fe are not simply well ordered bcc or fcc Fe and that the sample doesn't have long range crystalline order. XAFS measurements on the consolidated sample show that Fe is predominantly in the form of bcc Fe with good long range order.
Chemical Synthesis and Characterization of Nanostructured Titanium Aluminide
Authors: Schwab S.T. , Paul P.P. , Pan Y-M.
Published: April 2011

Although plagued by a lack of ductility, titanium aluminides are among the most promising intermetallics under development. Significant improvements in ductility may be obtained from nanostructured intermetallics. Nanosize particles of TiAl3 have been prepared by heat-treatment of chemically synthesized precursor (compound 1). Nanosized TiAl3 has been characterized by chemical analysis, XRD, EDS, NMR, and HREM.
HRTEM Analysis and Magnetic Properties Study of Surface Oxidizing and Nitriding of Nanocrystalline Particles
Authors: Hsu Chi-Ming , Lin Hong-Ming , Tsai Kuen-Rong , Lee Pee-Yew
Published: April 2011

Nanocrystalline iron powders were produced by means of the gas condensation. Pure nitrogen, or oxygen, or air, was introduced into the as-made powders before they were taken from the chamber. Various atmospheres produced varied layer structures around the iron particles. A high resolution transmission electron microscope was used to analyze the crystal structure and vibrating-sample magnetometer was used to measure the magnetic properties of nanocrystalline iron particles. The results showed that a layer of amorphous or nanocrystalline structure was formed initially on the surface of iron particles. This thin amorphous layer crystallized into Fe304 after annealing under electron irradiation when the introduced atmosphere was pure oxygen or air. However, it formed a passivated layer of ζ-Fe2N when nitrogen was introduced. The exchange anisotropy between the iron core and the superficial iron oxide or nitride shell was observed as the sample was cooled in an applied field of 10 kOe from room temperature to 5 K. The shift of the hysteresis loop caused by exchange anisotropy was 16% for the nitride shell and 8% for the oxide shell.
Metal Cluster Oxidation: Sticking Probabilities and Ionization Potential Shiffs
Authors: Andersson Mats , Holmgren Lotta , Persson John L. , Åklint ThorbjÖrn , RosÉn Arne
Published: April 2011

This study deals with the initial oxidation of some 3d metal clusters in gas phase. In the experiments neutral metal clusters in a supersonic beam are made to collide with one or a few oxygen molecules in a reaction cell. The reaction products are detected with photoionization and mass spectrometry. By comparing the abundance of unreacted and reacted clusters, absolute sticking probabilities (S) can be determined. Transition metals with open d shells, e.g. Ni, have high, almost constant S for O2 on clusters containing more than 20 atoms. The size evolution of S for Cu, on the other hand, shows repeated minima and maxima. Cluster sizes which have high ionization potentials (IPs) and closed electronic shells, according to the spherical jellium model, are the ones with the lowest S. The IPs of CunO2 clusters have also been investigated. Compared with the IPs of the pure Cu clusters, the IPs of the oxidized clusters are generally higher and the large drops at the shell openings are less distinct.
The Preparation, Characterization and Application of Organosols of Early Transition Metals
Authors: Bonnemann Helmut , Brijoux Werner
Published: April 2011

Colloidal early transition metals are of great interest in both powder technology and catalysis. We report a new process for preparing organosols of zerovalent Ti, Zr, V, Nb and Mn
Magnetic Properties of Nanosize Iron Clusters
Authors: Venturini E. L. , Wilcoxon J. P. , Newcomer P. P.
Published: April 2011

Isolated, monodisperse α-Fe clusters between 1.4 and 15 nm in diameter were prepared inside inverse micelles using an oil-continuous, nonaqueous system. The magnetic properties of these clusters were studied in a SQUID magnetometer as a function of cluster size, temperature and applied magnetic field. The blocking temperature, coercive field and remanent moment of 12.5 nm Fe clusters in inverse micelles are significantly lower than those reported for clusters of similar α-Fe core size but with a surface oxide. The novel synthesis technique may yield metallic clusters with essentially intrinsic magnetic properties.
Grain Boundaries in Nanophase Materials and Conventional Polycrystals – Are They Distinct?
Authors: Mehta S. C. , Smith D. A. , Erb U.
Published: April 2011

Nanograined materials, with grain sizes in the range of 1–20 nm, exhibit significant enhancement of grain boundary dependent properties such as yield strength, intergranular fracture toughness, grain boundary diffusivity, specific heat and thermal expansion coefficient. Measurements by indirect techniques suggest that the grain boundaries in nanophase materials are structurally different from the boundaries in their conventional polycrystal counterparts. Exploratory HRTEM observations, on the other hand, indicate that the grain boundary structure in nanophase materials is the same as that found in grain boundaries in conventional polycrystals. This paper reports an HRTEM investigation of the microstructure in electrodeposited nanocrystalline (nc) Ni1wt.%P alloy. These observations reveal the presence of about 8-10 vol. % porosity in the microstructure. There is also evidence for the presence of an amorphous phase at some grain boundaries and triple junctions. A comparison of grain boundary structures with boundaries in conventional materials suggests that grain boundaries in the nc Ni-P alloy are, for the most part, normal.
Characterization of Nanoscale Particles Produced by Laser Vaporization / Condensation in a Diffusion Cloud Chamber
Authors: El-Shall M. Samy , Slack W. , Hanley D. , Kane D.
Published: April 2011

Nanoscale metal oxide particles have been synthesized by using a novel method which combines laser vaporization of metal targets with controlled condensation in a diffusion cloud chamber. The following oxides have been synthesized: ZnO, SiO2, Fe2O3, Bi2O3, PdO, NiO, AgO, TeO, Sb2O3, TiO2, ZrO2, A12O3, CuO, In203, SnO2, V2O5 and MgO. With this method, the size of the particles can be conveniently controlled by careful control of the degree of supersaturation which is accomplished by adjusting the temperature gradient, total pressure, and partial pressure of the metal vapor generated by laser vaporization in a diffusion cloud chamber. The microscale structures of the SiO2 and A1203 particles exhibit interesting web-like matrices with a significant volume of vacancies. These materials may have special applications in catalysis and as reinforcing agents for liquid polymers.
Molecular Sieve Thin Films via Laser Ablation
Authors: Balkus Kenneth J. , Riley Scott J. , Gnade Bruce E.
Published: April 2011

Laser ablation has become widely recognized as an effective technique for the preparation of thin solid films. We have employed an excimer laser (KrF, 248 nm) to deposit well dispersed thin films of aluminum phosphate molecular sieves on a titanium nitride substrate. Results for the ablation of AIPO4-5, AIPO4-H3 and AIPO4-H1 molecular sieve targets are presented. The laser power and repetition rate as well as substrate distance and temperature affect the thin film formation. A subsequent hydrothermal post treatment of the ablated films was found to enhance the surface crystallinity. The molecular sieve thin films were characterized by XRD, SEM, XRF, and FT-IR spectroscopy.
Quantum Confinement in GaP Nanoclusters
Authors: Laurich Bernhard K. , Smith David C. , Healy Matthew D.
Published: April 2011

We have prepared GaP and GaAs nanoclusters from organometallic condensation reactions of E[Si(CH3)3]3 (E = P, As) and GaCl3. The size of the as synthesized clusters is 10 Å to 15 Å. Larger clusters of 20 Å to 30 Å size were obtained by thermal annealing of the as grown material. X-ray diffraction and transmission electron microscopy confirm the high crystalline quality. A lattice contraction of 6.7% could be seen for 10 Å sized GaAs clusters. The clusters are nearly spherical in shape. Optical absorption spectra show a distinct line which can be assigned to the fundamental transition of the quantum confined electronic state. The measured blue shift, with respect to the GaP bulk absorption edge is 0.53 eV. As the cluster is smaller than the exciton radius, we can calculate the cluster size from this blue shift and obtain 20.2 Å, consistent with the results from X-ray diffraction of 19.5 Å for the same sample.
Spontaneous Formation of Ag and Au Particles in Alcohols
Authors: Huang Z.-Y. , Quinn M. , Mills G. , Galef W.
Published: April 2011

Metal particles are generated via the spontaneous reduction of Ag+ and AuCl4− ions by solvent molecules that takes place in air-saturated alcoholic solutions containing hydroxide ions. Changes in the plasmon band of the Ag particles are observed when the metal particles are in contact with Ag20 particles. The optical changes are explained in terms of surface effects of the metal particles. Larger shifts of the Au plasmon band and light scattering were observed at the initial stages of the particle formation process. These effects are explained in terms of formation of networks consisting of small metal particles. It is proposed that generation of small Au particles occurs mainly on silica surfaces, and that particle-networks are formed when small particles desorb from the surfaces.
Sorption Behavior of Neptunium on Bentonite-Effect of Calcium Ion on the Sorption -
Authors: Kozai Naofumi , Ohnuki Toshihiko , Muraoka Susumu
Published: April 2011

The sorption behavior of neptunium on bentonite was studied with batch type sorption and desorption experiments over a pH range of 2 to 8. A series of parallel studies using Na-smectite, Ca-smectite and admixtures of Na-smectite and calcite quantified the capacity of Ca2+ (which occurs in bentonite as an exchangeable cation of smectite and as a component of calcite) to inhibit the sorption of neptunium. The distribution coefficient (Kd) of neptunium for bentonite was constant from pH 2 to 7, while for pure Na-smectite Kd increased below pH 5 due to “specific sorption” of neptunium on Na-smectite. Specific sorption was defined as occurring when neptunium could be desorbed by a strong acid (1 M HCl) but was stable in the presence of 1 M KCl. It was found that the quantity of neptunium sorbed on Na-smectite was inversely proportional to the concentration of Ca2+ in solution, an effect most pronounced at pH <5. These results show that Ca2+ limits the specific sorption capacity of Na-smectite for neptunium. Similarly, in the mixture of Na-smectite and calcite, sufficient Ca2+ was solubilized to depress neptunium sorption. This investigation demonstrates that Ca2+ contained in bentonite as exchangeable cation and released from calcite reduces the specific sorption of neptunium.
Adsorption Behavior of I– Ions on Minerals for Geologic Disposal of 129I Wastes
Authors: Sazarashi M. , Ikeda Y. , Seki R. , Yoshikawa H. , Takashima Y.
Published: April 2011

The I– adsorption on a modified mineral, which is prepared by impregnating Ag(l) nitrate complex with thiourea(tu) into montmorillonites, have been studied by batch method. The modified mineral was found to adsorb I– ions selectively even under the coexistence of Cl– ions. The distribution ratio(Kd) is 5000 ml/g under the conditions of initial [I–] = 1.0 × 10−5 M(M = mol/dm3), pH = 6.4, and solution/modified mineral = 100 ml/g. It was found that the [Ag(tu)]I precipitates are formed by mixing Nal solution with Ag(l)-tu complex solution, while any precipitates are not formed in addition of NaCl solution, and that anion exchange property of the modified mineral is low. Furthermore, it was confirmed that the [Ag(tu)]I complexes are present in the modified minerals after adsorbing I– ions. From these results, the I– selective adsorptivity of the modified mineral was considered to be due to the formation of [Ag(tu)]I precipitates within the interlayer region of montmorillonite.
Significance of Electrostatic Sorption in the Retardation of Radionuclides Released from a Repository
Authors: Meier H. , Zimmerhackl E. , Zeitler G. , Menge P.
Published: April 2011

Results of zeta potential measurements by electroosmosis with site-specific waters and sedimentary rocks from strata overlying the Gorleben salt dome are given and compared with sorption data of radionuclides obtained in batch experiments. It is shown that zeta potentials of sediment-groundwater systems in spite of being lower than the corresponding surface potentials are a sensitive indicator of interface reactions depending on the type of the sediment, ionic strength of waters, pH and temperature. Moreover, it is demonstrated that sorption data and, additionally, the influence of various parameters can often be understood by taking into account variable electrostatic forces between charged surfaces and nuclide species.
Thermodynamic Modeling of Neptunium(V) Solubility in Concentrated Na-CO3-HCO3-Cl-ClO4-H-OH-H2O Systems
Authors: Novak Craig F. , Roberts Kevin E.
Published: April 2011

Safety assessments of nuclear waste repositories often require estimation of actinide solubilities as they vary with groundwater composition. Although a considerable amount of research has been done on the solubility and speciation of actinides,1,2relatively little has been done to unify these data into a model applicable to concentrated brines. Numerous authors report data on the aqueous chemical properties of Np(V) in NaClO4, Na2CO3, and NaCl media, but a consistent thermodynamic model for predicting these properties is not available. To meet this need, a model was developed to describe the solubility of Np(V) in Na-Cl-ClO4-CO3aqueous systems, based on the Pitzer activity coefficient formalism for concentrated electrolytes. Hydrolysis and/or carbonate complexation are the dominant aqueous reactions with the neptunyl ion in these systems. Literature data for neptunyl ion extraction and solubility are used to parameterize an integrated model for Np(V) solubility in the Np(V)-Na-CO3-HCO3-Cl-ClO4-H-OH-H2O system. The resulting model is tested against additional solubility and extraction data, and compared with Np(V) solubility experiments in complex synthetic brines.
Humate Complexation of Neptunium(V) and its Modeling
Authors: Moriyama Hirotake , Nakata Yasuhiro , Higashi Kunio
Published: April 2011

The complexation behavior of Np(V) with humate was investigated by spectrophotometry in the pH range from 5.7 to 10 in 0.01–0.5M NaClO4. The absorption peaks of NpO2+and Np(V) humate were observed at 979.6nm and 989.9nm, respectively, and the apparent complexation constant of the Np(V) humate was found to be pH-dependent. A two-site complexation model was applied to the interpretation of the observed pH-dependence by considering the participation of the two functional groups of carboxylate and phenolate. The dissociation and complexation constants of both functional groups were determined.
The Geochemical Behaviour of Nickel in the Repository Environment
Authors: Savage David
Published: April 2011

59Ni may make significant contributions to calculated doses in performance assessment (PA) studies of geological repositories for radioactive waste, due principally to the adoption of relatively high near-field solubilities. Ni concentration values used in PA are typically 1–6 orders of magnitude greater than those measured in natural groundwaters. This difference is a result of the utilisation in PA of solubility data for pure nickeliferous solids, and in some instances, the selection of solids chemically incompatible with the disposal environment. The geochemical behaviour of Ni is reviewed. It is considered highly unlikely that Ni will form discrete pure solids in the repository near-field, so that partition as a trace element into solid solutions should be considered. Henry’s law behaviour of trace elements is discussed and geochemically-realistic Ni solubility values for HLW and L/ILW disposal scenarios calculated. It is concluded that Ni will behave according to the chemical conditions of the disposal environment, which should be reflected in the choice of solubility data for PA. The adoption of solid solution modelling for other elements of interest to PA should be considered.
Illite in the Oklo Natural Fission Reactors in Gabon: Considerations for Cs Containment
Authors: Szabó Gyula , Guczi Judit , Nagy Bartholomew , Janeczek Janusz , Ewing Rodney C.
Published: April 2011

The ∼2 Ga old Oklo, Okelobondo and Bangombé natural reactors in the Republic of Gabon contain solid graphitic bitumens and clay minerals, both of which have effected the containment, or partial containment, of 235U and several fission products. In laboratory experiments, sorption of 134Cs by illite, and illite coated with petroleum was measured in aqueous NaCl solutions to simulate subsurface (connate) waters in sedimentary rocks. Elevated temperatures and increasing salinity of the NaCl solutions facilitated the removal of sorbed cesium from illite.
Uranium Fixation During Uranium Migration Under an Oxidizing Condition
Authors: Murakami Takashi , Tsuzuki Katsuyuki , Sato Tsutomu , Isobe Hiroshi , Ohnuki Toshihiko
Published: April 2011

A rock specimen, collected downstream of the Koongarra uranium ore deposit, Australia, was examined mainly by high resolution transmission electron microscopy in order to understand the uranium fixation mechanism. Uranium was found to exist as saleeite (Mg(UO2)2(PO4)2.10H2O) microcrystals of 1 – 20 nm scattered between iron minerals (mainly goethite and hematite) of 2 – 50 nm. The microtextural relationship between saléeite and the iron minerals revealed that the iron minerals function as catalyst for the formation of saléeite. The intermediate metamict microstructures of the saléeite microcrystals are consistent with the estimated formation age of saléeite, 1 to 3 × 106 years. Uranium has been, thus, fixed as saléeite downstream as well as in the secondary ore deposit. Saléeite in the secondary ore deposit showed completely periodic to fully metamict microstructures, suggesting that saléeite, a major uranium mineral in the secondary ore deposit, probably began to form a few million years ago and continued to form for the next million years.
Temperature Dependence of Amorphization for Zirconolite and Perovskite Irradiated with 1 Mev Krypton Ions
Authors: White T. J. , Ewing R. C. , Wang L. M. , Forrester J. S. , Montross C.
Published: April 2011

A transmission electron microscope investigation was made of zirconolites and perovskites irradiated to amorphization with 1 MeV krypton ions using the HVEM-Tandem Facility at Argonne National Laboratory. Three specimens were examined - a prototype zirconolite CaZrTi2O7, a gadolinium doped zirconolite Ca0.75Gd0.50Zr0.75Ti2O7and a uranium doped zirconolite Ca0.75U0.50Zr0.75Ti2O7. The critical amorphization dose Dc was determined at several temperatures between 20K to 675K. Dc was inversely proportional with temperature. For example, pure zirconolite requiring 10x the dose for amorphization at 475K compared with gadolinium zirconolite. Using an Arrhenius plot, the activation energy Ea for annealing in these compounds was found to be 0.129 eV and 0.067 eV respectively. The greater ease of amorphization for the gadolinium sample is probably a reflection of this element’s large cross section for interaction with heavy ions. Uranium zirconolite was very susceptible to damage and amorphised under 4 keV argon ions during the preparation of microscope specimens. In each sample, zirconolite coexisted with minor perovskite, reduced rutile (Magneli phases) and zirconia. These phases were more resistant to ion irradiation than zirconolite. Even for high gadolinium loadings, perovskite (Ca0.8Gd0.2TiO3) was 3-4 times more stable to ion irradiation than the surrounding zirconolite crystals.
The Microbiology of The Maqarin Site, Jordan - A Natural Analogue for Cementitious Radioactive Waste Repositories
Authors: West Julia M , Coombs Patricia , Gardner Susan J , Rochelle Christopher A
Published: April 2011

The Maqarin site, Jordan is being studied as a natural analogue of a cementitious radioactive waste repository. The microbiology has been studied and diverse microbial populations capable of tolerating alkaline pH were detected at all sampling localities. Dissolved organic carbon was identified as the potentially most important reductant with sulphate identified as the main oxidant, both supplying energy for microbial life. Calculations on upper limits of microbial numbers were made with a microbiology code (MGSE) using existing information but the results are overestimates when compared with field observations. This indicates that the model is very conservative and that more information on, for example, carbon sources is required.
Formation of Actinide(III)-Humate and its Influence on Adsorption on Kaolinite
Authors: Takahashi Yoshio , Minai Yoshitaka , Kimura Takaumi , Meguro Yoshihiro , Tominaga Takeshi
Published: April 2011

Apparent stability constants of Eu(III)- and Am(III)-humates determined at various pH (4.8 to 8) and supporting electrolyte concentration (0.02 to 1 mol/1), indicate that the humate complexes may be dominant species in the aquifer. Distribution coefficients of Eu(III) and Am(III) between kaolinite and solution phase were affected strongly by the presence of humic acid in the solution. Adsorption of humic acid may be an important factor controlling fixation of actinides(III) on mineral surfaces.
Effects of Smectite Illitization on Transport of Actinides Through Engineered Barriers of HLW Repositories
Authors: Ahn Joonhong , Nagasaki S. , Tanaka S. , Suzuki A.
Published: April 2011

Effect of smectite illitization on mass release rate from the bentonite-filled buffer of the engineered barriers is analyzed based on experimental results of sorption of americium and neptunium onto illite-smectite mixtures, and on mathematical models for smectite illitization by K+diffusion, water flow through the engineered barriers, waste glass dissolution, and transport of americium and neptunium including solubility sharing with two major americium isotopes and moving boundary effect of the neptunium precipitation region. Numerical results for mass release rates of americium and neptunium as well as time-dependent pore velocity and glass dissolution rate are shown. Illitization effect is negligible with parameter values assumed here.
Experimental Study of Cation Diffusivities in Homoionized Montmorillonite by Electrical Conductance Method
Authors: Okamoto Masahide , Takase Toshio , Higashi Kunio
Published: April 2011

Montmorillonite purified from bentonite was homoionized by leaching with a chloride solution of sodium, potassium, cobalt or strontium, and then leaching with ethanol until the leachate contained only a negligible amount of the cation.

The electrical conductances of thus obtained Na-, K-, Co- and Sr- homoionized montmorillonite were measured. Applying the Nernst- Einstein equation to the electrical conductance, the diffusion coefficient for cations attached to the solid phase (montmorillonite) Ds, and that for cations in the bulk water phase Dw, were evaluated independently. As predicted, Ds was almost independent of the solid/liquid ratio, while Dw increased rapidly with the decrease of the ratio towards the diffusion coefficient in free water.
Hydraulic and Diffusive Properties of Clay-Based Backfill Material for a Low-and Intermediate-Level Waste Repository
Authors: Cho W.J. , Lee J.O. , Hahn P.S. , Park H.H.
Published: April 2011

The results of experimental studies performed to determine the radionuclide diffusion coefficients in a compacted clay and the hydraulic conductivities of clay/crushed granite mixtures with various clay contents are presented. Clay used in the experiments is a natural clay from the southeastern part of Korea, and it contains mainly calcium bentonite. The hydraulic conductivities of clay/crushed granite mixtures decreased with increasing clay content. In case of clay content of 50 wt.%, they maintain the considerably lower values even at the dry density of 1.5 Mg/m3. The diffusion coefficients for 90Sr, 137Cs, 60Co and 125I in water saturated clay at a dry density of 1.4 Mg/m3 were measured at room temperature. The average apparent diffusion coefficients obtained are 4.5 × 10−12 m2/s, 9.0 ×10−13 m2/s, 3.4 × 10−13 m2/s and 6.7 × 10−11 m2/s for 90Sr, 137Cs, 60Co, and 125I, respectively.
The Role and Objectives of the Peaceful Use of Nuclear Energy
Authors: Hayashi Masayoshi
Published: April 2011

It is a great pleasure for me to deliver the keynote address this morning, opening the 18th International Symposium on the Scientific Basis for Nuclear Waste Management. On behalf of the Atomic Energy Commission of Japan, I would like to welcome all of you, particularly those who have travelled across the ocean to attend this symposium.
Mechanical Properties of Bentonite-Sand Mixtures Under Triaxial Stress Condition
Authors: Umedera M. , Fujiwara A. , Yasufuku N. , Hyodo M. , Murata H.
Published: April 2011

A series of triaxial compression tests is being conducted under the drained condition on bentonite and sand mixtures, known as buffer, in saturated and optimum water content states to clarify the mechanical properties of the buffer.

It was found that the mechanical properties of bentonite and sand mixtures are strongly influenced by water and bentonite contents: shear strength in a saturated state is less than that in an optimum water content state; shear strength decreases rapidly with increasing bentonite content. Strength properties are much dependent on confining pressure.
Experimental Studies on the Interaction of Groundwater with Bentonite
Authors: Sasaki Y. , Shibata M. , Yui M. , Ishikawa H.
Published: April 2011

Interactions of sodium bentonite with distilled water and two types of synthetic groundwater were studied by batch experiments. In the experiments, clay and pure minerals were reacted at room temperature under aerobic and anaerobic condition as a function of time and liquid/solid ratio. The clay and pure minerals used in the experiments were Kunigel-VI (crude Na-bentonite), Kunipia F(purified Na-bentonite), purified Na-smectite(purified from Kunipia F), calcite and pyrite as accessory minerals. The chemical composition in the liquid phase was analyzed through centrifugation and ultra filtration. Alteration of the distribution of exchangeable cation in the bentonite was analyzed by NH4Ac and XRD. The results indicated that the interaction between bentonite(Kunigel-Vl) and groundwater under aerobic condition was described by ion exchange reaction of smectite, dissolution of calcite and oxidation of pyrite.

From these experimental studies, the model of the interaction of groundwater with bentonite proposed by Wanner was modified. The comparison between calculation and experimental results showed good agreement and indicated that this model could be adopted to predict porewater chemistry of bentonite for performance assessment of geological isolation system of high level waste.
The Importance of Thermal Loading Conditions to Waste Package Performance at Yucca Mountain
Authors: Buscheck Thomas A. , Nitao John J.
Published: April 2011

Temperature and relative humidity are primary environmental factors affecting waste package corrosion rates for the potential repository in the unsaturated zone at Yucca Mountain, Nevada. Under ambient conditions, the repository environment is quite humid. If relative humidity is low enough (<70%), corrosion will be minimal. Under humid conditions, corrosion is reduced if the temperature is low (<60°C). Using the V-TOUGH code, we model thermo-hydrological flow to investigate the effect of repository heat on temperature and relative humidity in the repository for a wide range of thermal loads. These calculations indicate that repository heat may substantially reduce relative humidity on the waste package, over hundreds of years for low thermal loads and over tens of thousands of years for high thermal loads. Temperatures associated with a given relative humidity decrease with increasing thermal load. Thermal load distributions can be optimized to yield a more uniform reduction in relative humidity during the boiling period.
Contributions of Thermodynamic and Mass Transport Modeling to Evaluation of Groundwater Flow and Groundwater Travel Time at Yucca Mountain, Nevada
Authors: Murphy William M
Published: April 2011

Constraints on groundwater flow and groundwater travel time (GWTT) at the proposed HLW repository site at Yucca Mountain, Nevada, U.S.A., can be provided through thermodynamic modeling of relations between gas, liquid, and solid phases, and mass transport modeling. In the unsaturated zone at Yucca Mountain the observed distribution of 14C can be reasonably represented by a mass transport and mass transfer model representing diffusion of 14C02 in the gas phase from the ground surface and equilibrium between aqueous and gas phases, in the absence of net advective flow. This mechanism could also account for aqueous phase 14C activities in the unsaturated zone. Thermodynamic interpretations indicate that groundwaters extracted from boreholes in the water saturated tuffaceous aquifer at Yucca Mountain are undersaturated with respect to calcite, providing evidence that groundwater flow bypasses zones of rock containing calcite and therefore must be channelized. This conclusion is supported by published isotopic data for calcites and groundwaters.
The Nagra/Pnc Grimsel test site Radionuclide Migration Experiment: Rigorous Field Testing of Transport Models
Authors: Umeki H. , Hatanaka K. , Alexander W.R. , Mckinley I.G. , Frick U.
Published: April 2011

The long-term programme of in-situ radionuclide migration experiments in the underground test site at Grimsel (GTS) involves the development and testing of radionuclide transport models with their associated databases. The field experiments are carried out in a water-bearing shear zone in crystalline rock utilising a suite of tracers of differing geochemical behaviour. A rigorous model testing procedure has been developed for the GTS radionuclide migration experiment. This paper describes application of this testing procedure to a solute transport code developed by PNC.
Diffusion Measurements on Crystalline Rock Matrix
Authors: Hartikainen Kari , HautojÄrvi A. , Pietarila H. , Timonen J.
Published: April 2011

A new gas flow technique is introduced such that experiments on very long samples are possible. This new technique together with increased accuracy of the measurements, allows the observation of power law tails in the break-through curves. Dispersion in these experiments can be controlled in great detail, and therefore the power law tails can be used to determine very accurately the parameters relevant in matrix diffusion. Results for rock and metal samples are shown, and they are fitted with model calculations which include both dispersion and matrix diffusion. The introduced technique, which is designed for ordinary drill cores, is suitable for scanning a large number of samples in a very short time.
U Series Concentration Distributions Around Rock Fractures—Qualitative Indication of Matrix Diffusion
Authors: Suksi Juhani , Saarinen Leena , Ruskeeniemi Timo , Rasilainen Kari , Siitari-Kauppi Marja
Published: April 2011

Concentrations of U series nuclides (238U, 234U, 230Th, 226Ra and 231Pa) across secondary U accumulations in rock matrix around water-carrying fractures were examined to find records of radionuclide movement. The accumulations, loaded in rock pores, were separated without dissolving the host rock. The concentration profiles observed, form patterns which point to both “old” and “young” U accumulations and, moreover, post accumulation movement of certain radionuclides. In the case of the young U accumulation, shown to have occurred between 10,000 and 33,000 years ago, the apparent diffusivity of Da=6.10-15 m2/s for U could be calculated.
Conditioning Stochastic Groundwater Flow Models on Head Data
Authors: Jackson K. Andrew
Published: April 2011

We present a new method for conditioning realizations of the logarithm Y of transmissivity on head data. Each realization is conditioned by subtracting a linear combination of certain basis functions, each corresponding to a measurement, obtained by a process based on co-kriging. The required cross covariance between head and Y can be numerically computed very efficiently using the adjoint method. The coefficients in the linear combination are chosen to try to rninimise the differences between computed and measured heads. The most efficient methods for such non-linear optimisation problems are those that exploit information about the second derivatives of the function being minimised. We show how these second derivatives can be computed very efficiendy using the adjoint method for certain classes of finite-element schemes. We illustrate our method by application to the WIPP-2 test case of the international INTRAVAL project. We show that the match between computed and measured heads is greatly improved. We compare our method with approaches that use pilot points. Our method is exact if the variability of the Y field and the deviations of the measured heads from the values computed for the mean of the Y field are both small, whereas pilot-point methods are only approximate. However, our method may be more expensive computationally. Finally, we discuss the extension of our method to conditioning on transient head data and to dealing with boundary conditions.