bluuebunny/crossref_metadata_2025 huggingface dataset:
A New Generation of Ceramic Foams With Small Pore Size
Authors: Butcher Kenneth R. , Pickrell Gary R.
Published: April 2011

A new process, GPM, has been developed to produce low density ceramic articles in any ceramic composition. This new process can produce articles with densities as low as 5% of the theoretical density (95% void fraction). The modulus of rupture values for the GPM material are in general 3-4 times as strong as the same density and composition ceramic foam. Products made with this new process are finding wide applicability in the catalyst and catalyst support media, low mass kiln furniture, ceramic pre-forms for metal/polymer infiltration and insulation markets. The microstructure, pore size and interconnectivity, and the fluid absorption properties of the GPM material are discussed.
Generation of Monodisperse Protein Nanoparticles by Electrospray Drying
Authors: Gomez A. , Bingham D. , de Juan L. , Tang K.
Published: April 2011

The feasibility of producing relatively monodisperse and biologically active protein particles by electrospray drying is demonstrated. The process entails dissolving dry powder in an electrosprayable solution. The solution is then dispersed and, after solvent evaporation, dry residues can be collected on suitable deposition substrates. The process was demonstrated in the case of insulin. Particles were sized visually, using a scanning electron microscope (SEM), and aerodynamically, using an inertial impactor. When electrosprays of nearly saturated solutions were operated in the stable cone-jet mode, impactor data showed that the particle average aerodynamic diameter ranged from about 88 to 110 nm in diameter and the distributions were quasi-monodisperse with relative standard deviation estimated at approximately 10%. SEM observations for the same conditions showed average particle dimensions ranging from 98 to 117 nm, with predominantly doughnut shapes. Smaller particles can be generated by decreasing the insulin concentration and/or by spraying smaller liquid flow rates. The biological activity of the electrospray-processed insulin samples was confirmed by comparing binding properties on insulin receptors against a control sample. Although the maximum production rate for monodisperse insulin nanoparticles from a single cone-jet is low, at about 0.23 mg/hour, overall production can be increased by multiplexing the device with microfabrication techniques.
Novel three Dimensional Biodegradable Scaffolds for Bone Tissue Engineering
Authors: Marra Kacey G. , Campbell Phil G. , Dimilla Paul A. , Kumta Prashant N. , Mooney Mark P. , Szem Jeffrey W. , Weiss Lee E.
Published: April 2011

We have constructed osteogenic scaffolds using solid freeform fabrication techniques. Blends of biodegradable polymers, polycaprolactone and poly(D,L-lactic-co-glycolic acid), have been examined as scaffolds for applications in bone tissue engineering. Hydroxyapatite granules were incorporated into the blends and porous discs were prepared. Mechanical properties and degradation rates of the composites were determined. The discs were seeded with rabbit bone marrow or cultured bone marrow stromal cells and in vitro studies were conducted. Electron microscopy and histological analysis revealed an osteogenic composite that supports bone cell growth not only on the surface but throughout the 1 mm thick scaffold as well. Seeded and unseeded discs were mechanically assembled in layers and implanted in a rabbit rectus abdominis muscle. Bone growth was evident after eight weeks in vivo. Electron microscopy and histological analyses indicate vascularization and primitive bone formation throughout the seeded composite, and also a “fusion” of the layers to form a single, solid construct. Finally, we have begun to incorporate the growth factor IGF-I into the scaffold to enhance osteogenicity and/or as an alternative to cell seeding.
An Approach to Classify Degradable Polymers
Authors: Burkersroda F. v. , Goepferich A. M.
Published: April 2011

Despite tremendous progress towards a better understanding of polymer erosion, degradable polymers could so far not be classified according to their erosion behavior. It was the goal of this study to close this gap and to find those parameters that determine how a polymer erodes. Therefore, a dimensionless erosionnumber ε was defined, that can be calculated from the velocity of polymer degradation and water diffusion in the polymer bulk. s indicates whether erosion is a surface phenomenon (surface erosion) or whether it affects the complete polymer bulk bulk erosion). ε is characteristic for a polymer type and depends on the diffusivity of water inside polymer matrix, on the molecular weight of a polymer, and the dimensions of an eroding polymer matrix. The proposed erosion theory shows that ‘surface erosion’ and ‘bulk erosion’ are two potential erosion pathways that are open to any degradable polymer.
Cellular Adhesion and Spreading of Endothelial Cells Monitored in Real Time Using the Quartz Crystal Microbalance
Authors: Zhou Tiean , Braunhut Susan J. , Medeiros Diane , Marx Kenneth A.
Published: April 2011

We have applied the Quartz Crystal Microbalance (QCM) technique to continuously record the processes of endothelial cell (EC) adhesion, spreading and cellular mass distribution changes during initial cell to surface contact and homeostatic attachment. ECs (50,000) were layered onto a set volume of media in the QCM device and simultaneously in a mock cell used for photomicroscopy. As cells were observed in the mock cell device to contact and attach to the surface over 45-55 min, we measured in the QCM device a continuous decrease in frequency and continuous increase in resistance, achieving a maximum at about one hr (1400 Ω frequency change and 1400 Ω motional resistance change). These frequency and resistance values stabilized over the next 24 hrs and were unchanged out to 72 hr by QCM measurement (to ∼700 Hz, ∼700 Ω), as the cells were observed to spread in the mock device. Both bovine aortic (BAE) and bovine capillary (BCE) endothelial cells were studied and found to exhibit similar behavior. These studies demonstrate that QCM can be used to detect continuous changes in cell mass and viscoelastic behavior.
Artificial Protein Hydrogel Materials
Authors: Petka W. A. , Harden J. L. , Sakata J. K. , Tirrell D. A.
Published: April 2011

Recombinant DNA methods were used to create a new class of artificial proteins that undergo reversible gelation in response to changes in pH or temperature. These proteins consist of terminal a-helical “leucine zipper” domains flanking a central, water-soluble polvelectrolyte segment. The formation of coiled-coil aggregates of the terminal domains in near-neutral pH solution triggers formation of a polymer hydrogel, with the central polyelectrolyte segment retaining solvent and preventing precipitation of the chains. Dissociation of the coiled-coil aggregates through elevation of pH or temperature causes dissolution of the gel and a return to the viscous behavior characteristic of a polymer solution. The pH and temperature range of the hydrogel state and its viscoelastic properties may be systematically varied through precise changes of the length, composition and charge density of the terminal and central blocks. Such control is of value in designing hydrogels with predetermined physical properties and makes these biosynthetic triblock copolymer systems attractive candidates for use in molecular and cellular encapsulation and in controlled reagent delivery.
Three Generations of Bile Acid Sequestrants
Authors: Mandeville W. Harry , Braunlin William , Dhal Pradeep , Guo Amy , Huval Chad , Miller Karen , Petersen John , Polomoscanik Steven , Rosenbaum David , Sacchiero Robert , Ward James , Holmes-Farley S. Randall
Published: April 2011

Cholestyramine, the first bile acid sequestrant to be marketed, has been in use for over 20 years. Despite its low potency, requiring 16-24 g of polymer to achieve 20% LDL cholesterol reduction in hypercholesterolemic individuals, only one other sequestrant, colestipol, has come to market in the ensuing period. GelTex Pharmaceuticals has been involved for over six years in the discovery and development of new, more potent polymeric sequestrants. Two binding mechanisms are presented — one that operates via an aggregate binding structure and one that is effective via a defined site binding structure. These two binding mechanisms are compared and contrasted through bile acid binding isotherms. The best of these new sequestrants bind bile acids through a combination of hydrophobicity and ion exchange. Optimization and balancing of each of these interactions led us to more potent materials. The first of these, colesevelam hydrochloride is expected to be three to four times more potent than cholestyramine. A third generation product is still in research at GelTex. With another twofold increase in potency possible, single tablet therapy may become a reality.
Resorbable Synthetic Bone Grafts Formed From a Silicon Stabilized Calcium Phosphate Bioceramic
Authors: Langstaff S. , Sayer M. , Smith T. , Pugh S.
Published: April 2011

Synthetic bone grafts resistant to random dissolution at physiological pH, yet capable of being gradually resorbed in vitro by osteoclasts have been created. Bulk ceramics and ceramic coatings formed from an additive stabilized colloidal sol possess two characteristic features: a phase mixture of calcium hydroxyapatite (HA) and a silicon stabilized tricalcium phosphate, and a microporous morphology based on inter-connected particles (0.2-1.0 μm). The characteristic phase composition arises during sintering through substitution reactions where silicon enters the calcium phosphate lattice under conditions of high chemical reactivity. Evidence for in vitro resorption lacunae on bulk ceramics is presented.
Plasma Surface Modification of Medical-Grade Ultra-High Molecular Weight Polyethylene for Improved Tribological Properties
Authors: Klapperich C.M. , Komvopoulos K. , Pruitt L.
Published: April 2011

Ultra-high molecular weight polyethylene (UHMWPE) is the principal material used to replace damaged cartilage in total joint replacement surgeries. This publication presents preliminary results from a new class of surface treatments to modify the surface chemistry and microstructure of UHMWPE under controlled processing conditions. Radio frequency plasmas were used to lightly crosslink the subsurface of UHMWPE and to modify the surface chemical state through the attachment of low-surface-energy fluorocarbon groups. A pin-on-disk apparatus was used to slide CoCrWNi pins with spherical tips on polished disks of plasma- treated and untreated UHMWPE immersed in a bath of preserved bovine serum. The wear resistance and surface chemical composition of tested specimens were characterized by surface profilometry and X-ray photoelectron spectroscopy (XPS), respectively. Changes in the surface hydrophobicity due to plasma treatment were evaluated using contact angle measurements. The prospect of surface plasma treatment in orthopedic applications is elucidated in the context of the obtained friction, wear, distilled water contact angle, and XPS results.
Interspecies Uptake of Polymeric Microspheres
Authors: Thanos Chris , Sandor Maryellen , Jong Yong , Jacob Jules , Yip Kay-Pong , Harper James , Morrell Craig , Scherer Jennifer
Published: April 2011

Particle uptake into intestinal tissue has seen increasing attention due to its implications in drug delivery. We attempted to observe a delivery system in vivo and examine uptake in different species. Microspheres were fabricated from polymers including polyanhydrides and delivered to an isolated loop of intestine in several species. The microspheres contained a dye either conjugated to a protein or incorporated freely and were used to qualitatively detect and locate the spheres in the villi of the length of the small intestine. Microspheres were dispersed, sized by a Coulter particle size analyzer, and characterized by confocal and cross-polarized light microscopy, FTIR and SEM. Coulter analysis revealed microspheres to be generally less than 5 microns in diameter. SEM typically showed homogeneous morphology among groups of microspheres. In vivo uptake experiments were performed in rodents, pigs, and ruminants using various microsphere formulations. Microspheres were delivered into the proximal end of the jejunum of anesthetized animals and allowed adequate transit time to be taken up. Animals were euthanized at various time points for explantation of tissue and sampling of blood. Excised samples were embedded inq polyvinyl alcohol, frozen, and cut into sections ranging between 7 and 14 μm in thickness. Our method of incorporating dyes allowed for simultaneous visualization by visible light microscopy and confocal laser scanning microscopy. Two-fluorochrome fluorescence of the microspheres and optical sectioning confirmed the presence of microspheres within intestinal tissue. The amount of uptake depended on the animal model, the duration of the experiment, and the composition of the microsphere. An assay for either the fluorescent dye, the protein attached to it, or the polymer encapsulating it may enable us to determine intracellular concentrations of mierospheres for the quantification of uptake.
Experimental Measurements of Nucleation Frequency and Crystal Growth Rate in Pd-Cu-Ni-P Metallic Glass
Authors: Nishiyama Nobuyuki , Inoue Akihisa
Published: April 2011

Crystallization mechanism and kinetics of a Pd40Cu30Ni10P20 glass was investigated in a wide temperature range from 603 (near the glass transition temperature) to 764 K (near the equilibrium melting temperature) by using an isothermal annealing treatment for nucleation and growth. The nucleus density (nv) is about 5 × 1013 nuclei/m3 and is independent of annealing temperature. Therefore, it is assumed that the crystallization of the alloy was dominated by heterogeneous nucleation due to “quenched-in nuclei”. On the other hand, the crystal growth rate (Uc) increases from 1.07 × 10− to 5.68 × 10−5 m/s with rising annealing temperature from 603 to 764 K. These values of Uc are 2–3 orders of magnitude larger than the calculated Uc on the basis of Classical Nucleation and Growth Theory (CNT). Furthermore, the glass-forming ability of the alloy will be discussed in the framework of the present results.
Phase Equilibria in the Zr-Cu-Al System: Implications for Bulk Metallic Glass Formation
Authors: Syed S. A. , Swenson D.
Published: April 2011

Preliminary phase equilibrium relationships have been established in the Zr-Cu-Al system at 800 °C, using a combination of X-ray diffraction and electron probe microanalysis. These results are similar to previous investigations that have been reported in the literature. Several ternary phases are found to exist in this system, many of which lie within the gross compositional vicinity of interest to bulk amorphous alloy formation. The equilibrium phases present in the alloy Zr65Cu27.5A17.5, which exhibits a particularly high Tx-Tg in the amorphous state, are Zr2Cu and minor amounts of two additional phases: Zr3Al and what may be a ternary phase with a composition near Zr6CuAl3. When the 800 °C phase diagram isotherm is correlated with the known glass forming composition range of the Zr-Cu-Al system, it is found that the best glass forming behavior is confined to those regions of the diagram in which all equilibria include Zr-Cu constituent binary phases and Al-poor ternary phases. This may suggest that difficulties in the nucleation of these binary phases plays a role in the glass forming ability of Zr-Cu-Al and related higher order alloys.
Deformation Behavior of Bulk Amorphous Zr-Base Alloys
Authors: Leonhard A. , Heilmaier M. , Eckert J. , Schultz L.
Published: April 2011

Bulk Zr-Al-Cu-Ni alloys were produced by die casting into a copper mold under Aratmosphere. The microstructure of fully amorphous as well as partially crystalline samples was analyzed by X-ray diffraction (XRD), scanning (SEM) and transmission electron microscopy (TEM), and chemical analysis with special emphasis on the size and composition of the crystallites. The mechanical behavior of the different samples was investigated by constant compression rate tests. At room temperature the samples show inhomogeneous deformation and, independent of the chosen composition, relatively low Young's moduli of about 70 GPa, flow stresses around 2 GPa and elastic strains of up to 3 %. Fully amorphous samples show microplasticity of up to 2 % strain without significant work hardening while specimens with a fairly high volume fraction of crystalline phases are extremely brittle. In contrast, at high temperatures around the glass transition temperature T8 both amorphous and partially crystalline specimens exhibit at low strain rates homogeneous deformation with an initial stress overshoot followed by an extended region of plastic flow. As compared to room temperature, the peak stresses are much lower and are hardly influenced by the presence of small volume fractions of crystalline phases. The observed thermal stability against crystallization provides a promising possibility for easy shaping of complex parts at temperatures around Tg.
High-Strength Bulk Nanostructure Alloys Consisting of Compound and Amorphous Phases
Authors: Inoue Akihisa , Fan Cang
Published: April 2011

Bulk nanocrystalline alloys with good ductility and high tensile strength (σ f) in Zr-Al-Cu- Pd and Zr-Al-Cu-Ni-Ti systems were formed by partial crystallization of cast bulk amorphous alloys. The nanostructure alloys consist of Zr2(Cu, Pd) or (Zr, Ti)2Al surrounded by the remaining amorphous phase. The particle size and interparticle spacing of their compounds are less than 10 and 2 nm, respectively. The crystallization of a Zr60Al10Cu30 amorphous alloy occurs by the simultaneous precipitation of Zr2Al and Zr2Cu with a large particle size of 500 nm and hence the addition of Pd or Ti is effective for formation of the nanostructure. The Pd or Ti has much larger negative heats of mixing against Zr or Al, respectively, and the Zr-Pd or Ti-Al atomic pair seems to act as preferential nucleation sites leading to the primary precipitation of Zr2(Cu, Pd) or (Zr, Ti) 2Al. The nanostructure alloy cylinders of 2 to 3 mm in diameter keep good ductility in the volume fraction (Vf) range of the compounds below 40 %. The σ f and Young's modulus (E) increase from 1760 MPa and 81.5 GPa, respectively, at Vf=40 % to 1880 MPa and 89.5 Gpa, respectively, at Vf =40 % for the Zr60Al10Cu20Pd10 alloy and from 1830 MPa and 89.0 GPa, respectively, at Vf =0 % to 1940 MPa and 95.2 GPa, respectively, at Vf =28 % for the Zr53Al12Cu20Ni10Ti5 alloy. The formation of the bulk nanostructure alloys with high σ f is presumably due to the reentrance of free volumes into the remaining amorphous phase caused by quenching from the supercooled liquid region.
A Local Probe into the Atomic Structure of Metallic Glasses Using EELS
Authors: Alamgir F. M. , Ito Y. , Jain H. , Williams D. B. , Schwarz R. B.
Published: April 2011

Electron energy loss spectroscopy (EELS) is used to extract information on the topological arrangement of atoms around Pd in the bulk-glass-forming Pd60Ni20P20. It is found that the environment around Pd in the glass is only a slight modification of the Pd crystalline structure. However, the modification is enough to allow this alloy to form a glass in bulk. In examining the differences between the structure of crystalline Pd and glassy Pd60Ni20P20 it is concluded that incorporation of Ni and P into the structure frustrates the structure enough that glass formation becomes easy.
Oxide Formation on the Bulk Metallic Glass Zr46.75Ti8.25Cu7.5Ni10Be27.5
Authors: Kiene M. , Strunskus T. , Hasse G. , Faupel F.
Published: April 2011

In this investigation depth profiling by Ar+ ion sputtering in combination with x-ray photoelectron spectroscopy was used to determine the thickness and the chemical composition of the oxide layers formed on the bulk metallic glass Zr46.75Tig8.25Cu7.5Ni10Be27.5 (V4) under different preparation conditions. The thickness of the oxide layer was in the range between 4 nm and 30 nm for samples oxidized in air at room temperature and annealed in air at 573 K for 15 hours, respectively. The oxide layers showed an enrichment of Be at the outermost surface followed by a Be, Zr and Ti rich phase. Cu and Ni are depleted within the whole oxide layer. BeO, ZrO2 and various Ti oxides were detected in the oxide layer, whereas Cu and Ni occurred only in a non-oxidized zerovalent state. Our data indicate that the oxidation is controlled by the inward and outward diffusion of the metallic components.
Critical Cooling Rate Vs. Reduced Glass Transition: Scaling Factors and Master Curves
Authors: Clavaguera N. , Clavaguera-Mora M. T.
Published: April 2011

The aim of the present paper is to analyse the glass formation and stability of bulk metallic glasses. Attention is focused to metallic alloys as systems which may develop a large glassforming ability. Glass formation when quenching from the liquid state is discussed in terms of the thermodynamics and kinetics of the stable/metastable competing phases. Thermodynamics is required to relate glass transition temperature, Tg, to the energetics of the supercooled liquid. Kinetic destabilisation of equilibrium solidification and, consequently, glass forming ability are favoured by the high viscosity values achieved under continuous cooling. The relative thermal stability of the supercooled liquid depends on the thermodynamic driving force and interfacial energy between each competing nucleating phase and the molten alloy. It is shown that the quantities representative of the process, once scaled, have a temperature dependence that is mostly fixed by the reduced glass transition temperature, Tgr= Tg/Tm, Tm being the melting temperature. Based on the classical models of nucleation and crystal growth, the reduced critical cooling rate is shown to follow master curves when plotted against Tgr. Experimental trends for specific systems are compared to predicted values from these master curves.
Hydrogenation and Crystallization of Zr-Cu-Ni-Al Glasses
Authors: Köoster U. , Zander D. , Leptien H. , Eliaz N. , Eliezer D.
Published: April 2011

Zr-Cu-Ni-Al belongs to the best glass forming systems known. Hydrogen charging was performed electrochemically in a 2:1 glycerin-phosphoric acid electrolyte. In comparison to binary Zr-Ni glasses the absorption kinetics in amorphous Zr-Cu-Ni-Al were found to be slower, but the storage capacity is similar. Desorption is hindered by the formation of thin ZrO2 layers. Partial replacement of Ni by Pd in an amorphous Zr68 5Cu13Ni11Al7.5 alloy was found to change the absorption behavior to a faster kinetic and to improve the desorption. The influence of hydrogen on the thermal stability was studied by DSC as well as by xray diffraction and TEM. Hydrogen was observed to play an important role. With increasing H/M ratio amorphous Zr69.5Cu12Ni11Al7.5 was found to transform during annealing above the glass transition temperature into a quasicrystalline structure with decreasing grain size until a nanocrystalline microstructure is achieved. Above a hydrogen content of H/M = 0.05 instead of quasicrystals a tetragonal phase with lattice parameters close to those of Zr2Ni is formed. At very high hydrogen contents phase separation is assumed to take place followed by the formation of nanocrystalline ZrH2 and other phases with reduced Zr content.
Elastic and Dissipative Properties of Amorphous and Nanocrystalline Mg-Ni-Y Alloy
Authors: Soifer Y. M. , Kobelev N. P. , Brodova I. G. , Manukhin A. N. , Korin E. , Soifer L.
Published: April 2011

The internal friction and Young's modulus of amorphous Mg84Ni12.5Y3.5 alloy obtained by the melt spinning technique have been measured by a vibrating reed method at frequency of 250 Hz at heating and cooling runs in the temperature range from 300K to 625K.. The crystallization kinetics of the alloy was studied by the calorimetric methods (DSC and DTA). The structure of the samples was determined by the x-ray diffraction technique. The Young modulus measurements have revealed the irreversible multi-step changes (up to 50%) accompanied by the irreversible internal friction peaks. These changes were observed in the same temperature intervals where the anomalies of thermal properties were found out. The results obtained are explained by the structural rearrangement from amorphous to nanocrystalline state during the annealing.
Deformation Behavior of FCC Crystalline Metallic Nanowires Under High Strain Rates
Authors: Qi Yue , Ikeda Hideyuki , Cagin Tahir , Samwer Konrad , Johnson William L. , Goddard William A.
Published: April 2011

We used molecular dynamics (MD) methods to study the deformation behavior of metallic alloy crystal nanowires of pure Cu, NiCu alloy and NiAu alloy, under high rates of uniaxial tensile strain, ranging from 5* 108/s to 5* 10/s. These nanowires are just about 2 nm thick and hence cannot sustain dislocations, instead we find that deformation proceeds through twinning and coherent slipping mechanisms. NiAu has a 13% size mismatch whereas NiCu only 2.5%. As a result the critical strain rate at which the “nanowire crystals” flow like a “liquid” is 100 times smaller for NiAu. We also calculated the elastic constants at each strain state for all strain rates to identify the relation between mechanical “shear” instability and deformation process.
Amorphous and Disordered Materials - the Basis of New Industries
Authors: Ovshinsky S. R.
Published: April 2011

As in the past, materials will shape the new century. Dramatic changes are taking place in the fields of energy and information based on new synthetic materials. In energy, the generation of electricity by amorphous silicon alloy thin film photovoltaics; the storage of electricity in nickel metal hydride batteries which are the batteries of choice for electric and hybrid vehicles. In the information field, phase change memories based on a reversible amorphous to crystalline transformation are widely used as optical memories and are the choice for the new rewritable CDs and DVDs. The scientific and technological bases for these three fields that have become the enabling technologies are amorphous and disordered materials. We will discuss how disordered, multielemental, multiphase materials can throw new light upon metallic conductivity in both bulk and thin film materials. We will demonstrate new types of amorphous devices that have the ability to learn and adapt, making possible new concepts for computers.
Heat Treatment of Molten Rapidly Quenched Precursor as a Method to Improve the Glass Forming Ability of Alloys
Authors: Manov V , Brook-Levinson E , Molokanov V. V. , Petrzhik M. I , Mikhailova T. N.
Published: April 2011

Improvement of glass forming ability (GFA) of two soft magnetic amorphous alloys (Fe75.5Ni1 3Si8.6B13.5 and Co69.6Fe1.3Mn4.5Si14.3B9 3Mo1) by heat treatment of melts prepared from different precursors (bulk ingot, rapidly quenched ribbons and granules) was studied. An assumption that the maximum undercooling ability corresponds to the maximum GFA was used to optimize the heat treatment mode. A temperature range was found by DTA for each alloy melt, favoring its undercooling (so called “undercoolable melt”). Usage of rapidly quenched precursor expands the range towards lower temperatures. GFA of the alloys was estimated by several melt quench techniques (casting, spinning and INROWASP). Fully amorphous samples with the thickness of 0.06–0.5 mm were prepared.
NMR Investigations of the Bulk Metallic Glass Zr55Cu30Al10Ni5
Authors: Hoffmann W. , Baenitz M. , Lüders K. , Gebert A. , Eckert J. , Schultz L.
Published: April 2011

Nuclear magnetic resonance (NMR) was applied for structural investigations of the bulk metallic glass system Zr55Cu30A110Ni5. The 63Cu as well as 27Al resonance was used. For both nuclei, two different spin-lattice relaxation rates were found which can be explained by different local environments of the nuclei.
Deposition of Epitaxial Carbide Films and Superlattices by Co-Evaporation of C60 and Transition Metals
Authors: Högberg H. , Norin L. , Lu J , Malm J. O. , Jansson U
Published: April 2011

Thin films of TiC, VC and NbC have been deposited on MgO(001) by co-evaporation of C 60 and the metal. The metal induced a decomposition of the C60 cage and a subsequent carbide formation at 100 °C. Epitaxial TiC films were easily obtained at 250 °C, while higher deposition temperatures were required for epitaxial growth of VC(400 °C) and NbC(500 °C). The films grew with the relation MeC(001)//MgO(00 1) and MeC[ 100]//MgO[ 100]. It was also possible to deposit TiC/NbC/MgO polycrystalline multilayers and TiC/VC/MgO superlattices structures by a sequential evaporation of the metals.
Properties of Catalytic CVD SiNx For Antireflection Coatings
Authors: Izumi A. , Matsumura H.
Published: April 2011

We propose a novel preparation of high quality silicon nitride (SiNx) films by catalytic chemical vapor deposition (Cat-CVD) method for the application of antireflection coatings. It is found that the refractive index (n) of the Cat-CVD SiNx films are controlled from 2.0 to 2.5 by varying the flow ratio of SiH4 and NH3. The properties of the SiNx (n = 2.0) are investigated, and it is found that, 1) the 16-BHF etching rate of the Cat-CVD SiNx film is only 23 A/min, and the film shows excellent moisture resistance, 2) the Cat-CVD SiNx film shows good insulating properties, and the breakdown electric field is higher than 9 MV/cm and the interface state density is 5.6x 1011 cm2eV-1, 3) the step coverage of the film is very conformal.
Growth and Stress Characterization of LPCVD SiC Films Deposited on Bare, Carbonized and Oxidized Si(001) Substrates
Authors: Hurtós E , Rodríguez-Viejo J , Zekentess K , Clavaguera-Mora M. T
Published: April 2011

A simple LPCVD reactor has been used to deposit 3C-SiC on oxidized, bare and MBE carbonized Si (001) wafers. The deposition experiments were conducted at different temperatures, times and gas flows pyrolizing tetramehylsilane (TMS). Voids at the interface and hillock formation were observed preferentially on the bare Si substrates due to Si outdiffusion. The best LPCVD films were obtained at temperatures around 1170°C on smooth single-crystalline carbonized substrates. The nucleation and growth of 3C-SiC on Si02/Si substrates proceeds at a slower rate with the formation of 3D island with a high aspect ratio.
The Chemical Vapor Deposition of Zirconium Carbide onto Ceramic Substrates
Authors: Glass John A. , Palmisiano Nick , Welsh R. Edward
Published: April 2011

Zirconium carbide is an attractive ceramic material due to its unique properties such as high melting point, good thermal conductivity, and chemical resistance. The controlled preparation of zirconium carbide films of superstoichiometric, stoichiometric, and substoichiometric compositions has been achieved utilizing zirconium tetrachloride and methane precursor gases in an atmospheric pressure high temperature chemical vapor deposition system. Laminar and equiaxial microcrystalline morphologies were obtained for superstoichiometric and substoichiometric zirconium carbide; respectively, allowing cursory metallographic identification of composition. Observed reductions in film density associated with zirconium carbide films that contain additional free carbon or excess zirconium are reported. These changes in film density were found to be consistent with compositional changes. An apparently linear relationship (correlation of 0.99) between methane flow in this chemical vapor deposition system and zirconium carbide stoichiometry in the substoichiometric range deposited above ZrC0.61 has been observed.
Chemical Vapor Deposition of Diamond from Alcohol Precursors at 1.0 Torr
Authors: Gilbert Donald R. , Singh Rajiv K. , Huang Ming
Published: April 2011

Typically, diamond chemical vapor deposition (CVD) is conducted at pressures of 10 to 100 Torr and temperatures of 700 - 1000 °C. Both thermally activated (hot-filament) and plasma enhanced (DC, microwave) systems are used to deposit diamond from mixtures of hydrogen and some carbon-containing monomer, most typically methane. These systems may produce films of high phase purity which typically exhibit tensile intrinsic (non-thermal) growth stresses. We have used an electron cyclotron resonance (ECR) enhanced plasma system to deposit diamond films at a pressure of 1 Torr over a temperature range of 550 - 700 °C using methyl alcohol as the carbon source. Optical emission spectroscopy (OES) was used to analyze the plasma discharge for the determination of active species present during diamond growth. Correlations of emission variations with film characteristics were made to evaluate their importance in the diamond formation process. Particular emphasis was placed on the nature of the intrinsic growth stresses developed in this process, which appeared to be consistently compressive in nature based on Raman analysis.
Gas Phase and Surface Kinetics of Diamond-Like Carbon Films Growth in Pecvd Reactors
Authors: Masi Maurizio , Cavallotti Carlo , Carrà Sergio
Published: April 2011

The surface and gas-phase kinetic of deposition of diamond-like carbon films (DLC) obtained in plasma reactors using methane as precursor was here investigated. Kinetic constants of electronic reactions were evaluated using experimental ionization and neutral dissociation cross sections and the Druyvestein electron distribution function. Kinetic constants for ionic and neutral reactions were found in the literature. Surface reactions were divided into processes involving the impingement of gas-phase radicals or ions from the plasma and desorption or recombination reactions of adsorbed surface species. The kinetic constants of the former processes were evaluated.from the ambipolar theory or from the kinetic theory of gases, while the other kinetic constants were determined from analogy with hydrocarbon chemistry. The exception is the desorption of adsorbed methyl radicals, whose kinetic constant was fitted over experimental data. The predictivity of the model was tested through the simulation of three reactors described in the literature widely differing for operating conditions.
Epitaxial Growth of Diamond on an Iridium (100) Substrate by Microwave Plasma-Assisted Chemical Vapor Deposition
Authors: Tsubota Toshiki , Tsuruga Shigenori , Saito Takeyasu , Kusakabe Katsuki , Morooka Shigeharu , Maeda Hideaki
Published: April 2011

Diamond films were grown heteroepitaxially on iridium (100) substrates by microwave plasma-assisted chemical vapor deposition (MPCVD) using methane gas as the carbon source. The iridium substrate, which was formed on a MgO (100) substrate by means of sputtering at 850 °C, was treated by imposing a negative bias between -150 and -200 V for 15 min. Methane concentration and substrate temperature were maintained at 3° and 650–740 °c, respectively. At a substrate temperature of 740 °C, diamond particles were formed at a population density of (0.15- 1.5)x108 cm-2, and most of them were oriented to MgO (100). After a further reaction for 1 h under conditions which were optimized for diamond growth, the oriented diamond particles were coalesced, and islands of (100) diamond were formed.
Growth and Erosive Wear Properties of MPCVD Diamond Coatings on Sintered Tungsten Carbide Substrates
Authors: Amirhaghi S. , Reehal H. S. , Wood R. J. K. , Wheeler D. W.
Published: April 2011

Adherent diamond coatings up to ∼35 um thick have been grown by microwave plasma CVD (MPCVD) on sintered tungsten carbide (WC) substrates and their erosive wear properties investigated under high velocity air-sand erosion testing. Two different sintered tungsten carbide (WC) substrates have been investigated and compared, the binder being either 6%Co or 5%Ni by weight. Coating properties are sensitive functions of surface pre-treatment and deposition procedures. Adherent coatings offer significantly better erosion resistance compared to uncoated substrates, with the erosion rate being lower by up to a factor between ∼5 and 20 for particle test velocities of 148 ms-1 and 63 ms-1 respectively. Films with low residual stress appear to exhibit longer times to failure which tends to occur catastrophically along the coating-substrate interface.
Process Windows and Properties of Tungstenand Vanadium-Oxides Deposited by MSIP-PVD-Process
Authors: Knotek O. , Lugscheider E. , Bäarwulf S. , Barimani C.
Published: April 2011

The tungsten and vanadium oxides are well known to be usable as solid lubricants at elevated temperatures. Such metal-oxides are interesting for tribological insets at atmospheric conditions because of their “oxidation stability”. This paper reports about investigations made to find stable process windows for the deposition of tungsten and vanadium oxides in a reactive d.c. mode by the MSIP-PVD-process. One focus of the study is on the metal oxide-phases generated in the MSIP-process under various conditions and their mechanical and metallographic properties. Coatings were deposited, developed and analyzed by standard testing methods such as SEM, microhardness (nanoindentation), XRD and scratch testing to characterize the mechanical and structural properties. Stable process windows will be presented for the reactive mode as well as the influence of different process parameters to the microstructure and the material properties. It will be shown that it is possible to deposit vanadium-oxides despite contamination effects in wide ranges by adapting the gas-flow. Process failure was determined at 15 - 18 % oxygen partial pressure for reactively deposited tungsten oxides.
Hafnium Hydroxide Complexation and Solubility: the Impact of Hydrolysis Reactions on the Disposition of Weapons-Grade Plutonium
Authors: Cerefice G. , Draye M. , Noyes K. , Czerwinski K.
Published: April 2011

The stability constants for the complexation of hafnium by hydroxide ions is investigated by potentiometric titration over a range of ionic strengths (1m = 0.1 to 6.6 molal). The stability constants are determined from the titration data using the HYPERQUAD suite of programs. The stability constants at infinite dilution are determined using the Specific Ion Interaction Theory from the stability constants determined by titration. The results are shown with the error given as 2 standard deviations.

log β11 (Hf(OH)3+) = 13.84 ± 0.54
log β12 (Hf(OH)22+) = 25.71 ± 0.39
log β13 (Hf(OH)3+) = 36.24 ± 0.88
log β14 (Hf(OH)40) = 45.52 ± 0.80

The solubility product of Hf(OH)4 (s) is determined in 0.1 M NaC1O4 by measuring the total hafnium in solution that is in equilibrium with an excess of hafnium hydroxide solid under an argon atmosphere. The total Hf concentration is determined by ICP-AES. The solubility product is determined using the stability constants measured for the H f hydrolysis products in 0.1 M NaClO4. The precipitate examined is confirmed to be a hydroxide by IR spectroscopy. For Hf(OH)4 (s) in 0.1 M NaC1O4, the solubility product is log Ksp (Hf(OH)4 (s)) = −51.8 ± 0.5

The solubility and stability constants determined are used, along with literature values for plutonium solubility and complexation constants, to examine the behavior of hafnium and plutonium under the conditions expected at Yucca Mountain.
Preferential Association of Adsorbed Uranium with Mineral Surfaces: A Study Using Analytical Electron Microscopy
Authors: Lumpkin G. R. , Payne T. E. , Fenton B. R. , Waite T. D.
Published: April 2011

Analytical electron microscopy (AEM) has been employed to characterize the distribution of U(VI) on several mineral substrates, including standard kaolinite samples and weathered rock samples from Koongarra, Australia. Results of this study reveal that pre-existing impurity phases play a significant role in the uptake of U(VI) on standard kaolinite samples. Using a natural sample from the weathered zone of the Koongarra uranium deposit, we have also demonstrated that U(VI) sorption is controlled by iron oxyhydroxides (predominantly goethite) which constitute a small fraction of the sample. Limited sorption of U(VI) was observed on the clay minerals of this substrate. Uptake of U(VI) by goethite increases with total uranium content up to the point of uranium precipitation, after which it decreases dramatically. Uranium precipitation is indicated by the appearance of a uranyl oxyhydroxide phase.
Actinide Biocolloid Formation in Brine by Halophilic Bacteria
Authors: Gillow J. B. , Francis A. J. , Dodge C. J. , Harris R. , Beveridge T. J. , Brady P. V. , Papenguth H. W.
Published: April 2011

We examined the ability of a halophilic bacterium (WIPP 1A) isolated from the Waste Isolation Pilot Plant (WIPP) site to accumulate uranium in order to determine the potential for biocolloid facilitated actinide transport. The bacterial cell surface functional groups involved in the complexation of the actinide were determined by titration. Uranium, added as uranyl nitrate, was removed from solution at pH 5 by cells but at pH 7 and 9 very little uranium was removed due to its limited solubility. Although present as soluble species, uranyl citrate at pH 5, 7, and 9, and uranyl carbonate at pH 9 were not removed by the bacterium because they were not bioavailable due to their neutral or negative charge. Addition of uranyl EDTA to brine at pH 5, 7, and 9 resulted in the immediate precipitation of U. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) analysis revealed that uranium was not only associated with the cell surface but also accumulated intracellularly as uranium-enriched granules. Extended X-ray absorption fine structure (EXAFS) analysis of the bacterial cells indicated the bulk sample contained more than one uranium phase. Nevertheless these results show the potential for the formation of actinide bearing bacterial biocolloids that are strictly regulated by the speciation and bioavailability of the actinide.
Incorporation of radionuclides from the electrometallurgical treatment of spent fuel into a ceramic waste form
Authors: Pereira C. , Hash M. C. , Lewis M. A. , Richmann M. K. , Basco J.
Published: April 2011

An electrometallurgical process is being developed at Argonne National Laboratory to treat spent metallic nuclear fuel. In this process, the spent nuclear fuel is electrorefined in a molten salt to separate uranium from the other constituents of the fuel. The treatment process generates a contaminated chloride salt that is incorporated into a ceramic waste form. The ceramic waste form, a composite of sodalite and glass, contains the fission products (rare earths, alkalis, alkaline earth metals, and halides) and transuranic radionuclides that accumulated in the electrorefiner salt. These radionuclides are incorporated into zeolite A, which can fully accommodate the salt in its crystal structure. The radionuclides are incorporated into the zeolite by hightemperature blending or by ion exchange. In the blending process the salt and zeolite are simply tumbled together at >450°C (723 K), but in the ion exchange process, which yields a product more highly concentrated in fission products, the molten salt is passed through a bed of the zeolite. In either case, the salt-loaded zeolite A is mixed with glass frit and hot isostatically pressed to produce a monolithic leach resistant waste form.Zeolite is converted to sodalite during hot pressing. This paper presents experimental results on the experimental results on the fission product uptake of the zeolite as a function of time and salt composition.
Erosion of Magnesium Potassium Phosphate Ceramic Waste Forms
Authors: Goretta K. C. , Singh D. , Tlustochowicz M. , Cuber M. M. , Burdt M. L. , Jeong S. Y. , Smith T. L. , Wagh A. S. , Routbort J. L.
Published: April 2011

Phosphate-based chemically bonded ceramics were formed from magnesium potassium phosphate (MKP) binder and either industrial fly ash or steel slag. The resulting ceramics were subjected to solid-particle erosion by a stream of either angular Al2O3 particles or rounded SiO2 sand. Particle impact angles were 30 or 90° and the impact velocity was 50 m/s. Steady-state erosion rates, measured as mass lost from a specimen per mass of impacting particle, were dependent on impact angle and on erodent particle size and shape. Material was lost by a combination of fracture mechanisms. Evolution of H2O from the MKP phase appeared to contribute significantly to the material loss.
Surface features and alteration products of natural zirconolite leached in silica-saturated solutions
Authors: Helean K. B. , Lutze W. , Ewing R. C.
Published: April 2011

Zirconolite, CaZrTi2O7, has been proposed as an immobilization phase for the disposition of excess weapons Pu and other actinides (e.g., 235U). Due to actinide incorporation, zirconolite is expected to sustain α-decay event damage and become aperiodic (=metamict) over time. The leaching behavior of metamict zirconolite is, therefore, of interest. Because groundwater in a variety of geologic settings contains up to saturation concentrations of silicic acid, H4SiO4, silica-saturated solutions were used. Natural, metamict (> 1026 α-decay events per mn3) zirconolite grains, nominally (Ca, Th)ZrTi2O7 (U.S. National Museum sample #B20392, Walawada, Sri Lanka) were leached in two separate silica-saturated solutions at 150 °C for 60 days. Surface features and alteration products were examined using scanning electron microscopy (SEM) and quantitative energy dispersive X-ray spectroscopy (EDS). Secondary electron (SEI) images of the surfaces of the leached grains from both experiments revealed pores, probably due to the accumulation of He-bubbles from α-decay events, of approximately 4% as estimated by contrast enhanced gray-scale analysis of digital images. SEI of the zirconolite surface before leaching showed a smooth surface. The pores not only increase the surface area of the metamict zirconolite, but also act as nucleation sites for alteration phase growth. One experiment was conducted in a silica-saturated solution containing approximately 100 ppm P as measured by atomic absorption spectroscopy (AAS). The main alteration phase was euhedral, monoclinic cheralite, (Th, Ca, Ce)(P, Si)O4 (monazite group). The second experiment was conducted in the absence of P. The main alteration phase was subhedral cubic thorianite, ThO2.
A study of alteration phases on glass-bonded zeolite and sodaiate using the vapor hydration test
Authors: Sun Donglin , Wronkiewicz D. J. , Simpson L. J.
Published: April 2011

This paper focuses on the reaction of glass-bonded zeolite and sodalite ceramic waste forms, naturally occurring sodalite, and their respective alteration phases that formed after reaction in a Vapor Hydration Test (VHT). Scanning electron microscope (SEM) analysis of the glass-bonded zeolite and sodalite samples indicate that NaCI is the major alteration phase present, along with KCI, Na-Al-Si, and Na-K-Ca-Al-Si phases. The order of precipitation of salt crystals from ceramic waste form occurred in the sequence NaCl ⇒ KC1 ⇒ CaCl2 and MgCl2. We also found aluminum silicate phases containing Ca, Mg, K-Na-Ca, K-Mg, Na-K-Mg, K-Ca-Na-Mg, as well as CaCO3, SiO2. The ratio of Si/Al in the alteration phases was noted to increase from approximately 1.5 to 5 during the progressive alteration of the samples. This trend indicates a relative increase in the contribution of silicon from the relatively Si-rich glass regions of the samples over time. Phases enriched in Cs, Ba and rare earth elements (RE) were also observed on the altered samples. Alteration phases initially appeared along the micro-fractures during the early stages of alteration. The number of micro-fractures, density of alteration phase cover, and grain size of alteration phases increased with reaction time and temperature.