bluuebunny/crossref_metadata_2025 huggingface dataset:
Amorphous TiO2 and SiO2 Modified Alumina as Catalyst Support for Hydroprocessing of Maya Crude Oil Heavy Fractions
Authors: Lopez-Salinas E. , Itoh T. , Morales E. , Rivera S. , Medellin B. , Llanos M. E. , Beltran T. , Cortes M. T. , Zarate R. , Vazquez A. , Navarrete J.
Published: April 2011

A series of aluminas modified with 3-15 wt% S102 (AMASAs) and 2-9 wt% TiO2 (AMATAs) were prepared by a deposition and/or coprecipitation methods. The pore size distribution was varied by means of a pH-swing procedure where alternating pH acid-alkaline values generated 100-200 Å pores, particularly in the AMASAs case. However, the incorporation of TiO 2 in the AMATAs even after the pH-swing procedure results in a pore size and volume decrease- The degree of TiO 2 reduction is much higher in AMATAs obtained by deposition than those obtained by coprecipitation. The use of AMASAs as catalyst supports of 2.4 wt% Ni and 8.8 wt% Mo in the hydroconversion of a vacuum distillation residue brings about 1.5 times higher conversion to lighter fractions in comparison with a commercial alumina-based catalyst. AMATA-based catalyst shows similar activity and selectivity to the commercial catalyst. However, the presence of TiO2 (6 wt%) considerably increases the N and V removal, and decreases the formation of sediments.
Electrochemical Testing and Structural Characterisation of Nickel Based Catalytic Coatings Produced by Direct Spraying
Authors: Sillitto S.M.A. , Adkins N.J.E. , Hodgson D.R. , Paul E. , Ormerod R.M.
Published: April 2011

In this paper a novel processing technique has been used to produce a range of low overpotential nickel based electrocatalytic coatings for use in the Chlor-alkali industry. These coatings include pure nickel as well as Raney nickel alloys, with particular focus upon the beneficial effects of molybdenum additions to Raney nickel.

Structural characterisation of all coatings has been carried out using X-ray diffraction for quantitative phase identification, backed up by optical and electron microscopy for analysis of phase distribution. Measurement of the coatings' electrochemical properties has been performed in fully functioning micro-pilot scale electrolysis cells.
Synthesis of Transition-Metal-Oxides Meso-Structured Thin Films
Authors: Zhou H.S. , Honma I.
Published: April 2011

Highly ordered self-assembly organized silica meso-structured architectures have attracted increasing attention because these materials provide a rich source for scientific research and technological applications. This approach to meso-structured materials has been extended to non-silica oxides, especially transition-metal-oxides which might promise applications involving electron transfer or magnetic interactions. We report the syntheses of transition-metal-oxides meso-structured thin films (MSTF), such as TiO2, V2O5, Fe2O3 and Nb2O5, using a surfactant templating processing with spin coating method. X-ray diffraction patterns of the films showed that the films generally oriented in a lamellar structure. The phase transferring in V205 MSTF was also investigated.
Structure Effects of High Surface Area Molybdenum Nitride Powders, Macrocrystals and Nanoparticles as Catalysts for Thiophene Desulfurization
Authors: Roberts K. L. , Markel E. J.
Published: April 2011

Mo2N powder, macrocrystals and nanoparticles and porous Mo metal were synthesized using temperature programmed reduction of MoO3 powder and crystals with reactant feed gases consisting of NH3 N2/H2 mixtures and pure H2. The Mo-based catalysts were characterized using BET, XRD, TGA, SEM, and STM. The Mo-based catalysts were also analyzed for the hydrodesulfurization (HDS) of thiophene. The relatively lower surface area Mo2N macrocrystalline catalysts (SSA = 44 m2/g) have a greater area specific activity than that of the higher surface area Mo2N powder catalysts (SSA = 150 m2/g) for the HDS of thiophene. Mo metal catalysts have significantly lower activity for thiophene HDS than Mo 2N catalysts and the HDS selectivities of non-sulfided Mo metal catalysts are significantly different from those of Mo 2N catalysts.
Catalytic Combustion Technology Development for Gas Turbine Engine Applications
Authors: Carter Robert N. , Smith Lance L. , Karim Hasan , Castaldi Marco , Etemad Shah , Muench George , Boorse R. Samuel , Menacherry Paul , Pfefferle William C.
Published: April 2011

Catalytic combustion is one means of meeting increasingly strict emissions requirements for ground-based gas turbine engines for power generation. In conventional homogeneous combustion, high flame temperatures and incomplete combustion lead to emissions of oxides of nitrogen (NOx) and carbon monoxide (CO), and in lean premixed systems unburned hydrocarbons (UHC). However, catalyst-assisted reaction upstream of a lean premixed homogeneous combustion zone can increase the fuel/air mixture reactivity sufficiently to provide low CO/UHC emissions. Additionally, catalytic combustion extends the lean limit of combustion, thereby minimizing NOx formation by lowering the adiabatic flame temperature. An overview of this technology is presented including discussion of the many materials science and catalyst challenges that catalytic combustion poses ranging from the need for high temperature materials to catalyst performance and endurance. Results of ongoing development efforts at Precision Combustion, Inc. (PCI) are presented including modeling studies and experimental results from both bench-scale and combustor-scale studies.
Atomic force Microscopy to Quantify Local Mechanical Properties Of Tissue
Authors: Tsai S. , Rutherford Rib. , Clarkson B.H. , Kohn D.H.
Published: April 2011

For regenerated tissue to be fully functional, it must exhibit the mechanical integrity of normal tissue. Because of the composite nature of tissues, regional variation in properties, and the fact that macroscopic mechanical testing is not always feasible with regenerated tissue, microscopic approaches are needed to better delineate structure-function relations. We have been utilizing an atomic force microscope (AFM) in conjunction with a picoindentation attachment to determine local, sub-micron level mechanical properties of normal and regenerated tissues. As representative data to establish the validity of this approach, regional hardness and stiffness values for dentin are presented. Repeated measures ANOVA indicated that moduli were site-specific. However, local variations at a given point (e.g. properties at < lpm spatial displacement) were less than site to site variations, validating the efficacy of the technique. Hardness and elasticity may be considered quantitative measures of degree of mineralization, enabling linkage between mechanical, structural, and biological measures of tissue regeneration.
Double Layered HA Coating, its Characterization and Preparation
Authors: Zhou P. , Asanami S. , Kawana H. , Hosonuma M. , Mitsui H. , Zhou H.
Published: April 2011

Hydroxyapatite (HA) has been universally used because of good biocompatibility. There are varieties of coating methods, however, they still have problems. The most significant problem is layer thickness. We introduced a new coating procedure to eliminate this difficulty.

The characterization of the coating was studied by X-ray diffractometry, infrared spectroscopy, SEM and chemical analysis. Said examination indicated that the double layer consisted of carbonate HA and CaTiO3 and the thickness of the layer was 2-4 μm. The coating was performed on the inner surfaces of 50-200 μm sized pores and was also consistent in the smallest of the pores even those of 50 μm. Our results indicated that the coating layer was homogeneous and thin. In addition, both layers consisted of Ca ions. The consistency of coating into even the smallest pore size suggested that our method promises to have widespread clinical applications in artificial implants because of increased surface contact area.
Fatigue-Crack Growth in the Superelastic Endovascular Stent Material Nitinol
Authors: Mckelvey A. L. , Ritchie R. O.
Published: April 2011

This paper describes a study of fatigue-crack propagation behavior in the superelastic alloy Nitinol. This work is motivated by biomedical applications, and the current interest to improve the design and performance of medical stents for implantation in the human body. Specifically, the objective of this work is to study the effect of environment on cyclic crack- growth resistance in a ∼50Ni-5OTi (at. %) alloy, and to provide the necessary data for the safe life predication of Nitinol endovascular stents. The material selected for this study has been heat treated such that it is superelastic at human body temperature. Characterization of fatigue-crack growth rates has been performed at 37°C on disc-shaped compact-tension samples, in environments of air, aerated deionized water, and aerated Hank's solution. Results indicate that, in fact, Nitinol has the lowest fatigue-crack growth resistance of metallic alloys currently used for implant-applications.
A Multilayer Approach to Fabricate Bioactive Glass Coatings on Ti Alloys
Authors: Gomez-Vega J.M. , Saiz E. , Tomsia A.P. , Marshall G.W. , Marshall S.J.
Published: April 2011

Glasses in the system Si-Ca-Na-Mg-P-K-O with thermal expansions coefficients close to that of Ti6AI4V were used to coat the titanium alloy by a simple enameling technique. Firings were done in air at temperatures between 800 and 840°C and times up to 1 minute. Graded compositions were obtained by firing multilayered glass coatings. Hydroxyapatite (HA) particles were mixed with the glass powder and the mixture was placed on the outer surface of the coatings to render them more bioactive. Coatings with excellent adhesion to the substrate and able to form apatite when immersed in a simulated body fluid (SBF) can be fabricated by this methodology.
Subcritical Crack Growth of Bioactive Glasses in Simulated Body Fluid
Authors: Bloyer D.R. , Mcnaney J.M. , Tomsia A.P.
Published: April 2011

A new series of bioactive glasses have been prepared with thermal expansion coefficients that more closely match that of Ti-based implant alloys. It is proposed that these glasses be used as coatings on biological implants that would provide improved fixation between the implant and tissue. As glasses are subject to environmentally assisted crack growth, it is important to develop an understanding of the stress corrosion crack growth (SCCG) behavior of this new family of glasses; furthermore, it is equally important to determine the effect of bioactivity on the SCCG properties of these glasses. This report will present the progress to date in the study of the SCCG properties of these new bioactive glasses
Evaluation of Cytokine Delivery Systems for Cancer Immunotherapy
Authors: Jong Y.S. , Egilmez N.K. , Chen F-A , Jacob J.S. , Smith L.P. , Mottl T.S. , Bankert R.B. , Mathiowitz E.
Published: April 2011

Cytokines are ideal candidates for controlled release systems; they typically have short half-livesin vivoand may be more effective with localized delivery. A novel microencapsulation technique, phase inversion nanoencapsulation (PIN), was used to encapsulate interleukin-2 or interleukin-12 in biodegradable polymer microspheres. Cytokine was quantified by ELISA and bioactivity analyzed using a murine cytotoxic Tcell line proliferation assay. The release rates of IL-2 was dependant on release buffer components; inclusion of 10% fetal calf serum resulted in significantly higher release rates compared to plain buffer. Encapsulated IL-2 remained stable at all timepoints assayed (up to 4 months) when stored at 4 °C. Results indicated that PIN can be used to encapsulate IL-2 and IL-12, which were released throughout the duration of the release study (up to one month). These microsphere formulations have shown tumor suppressive affectsin vivoand may provide a viable alternative to gene transfer for cancer immunotherapy.
Interactions Between Unimolecular Micelles and Liposomes
Authors: Guo J. , Farrell S. , Uhrich K. E.
Published: April 2011

The interactions between dipalmitoylphosphocholine (DPPC) vesicles and a hyperbranched polymer micelle, Core(hex)PEG5, were examined by visual observation, differential scanning calorimetry (DSC), fluorescence microscopy and dynamic light scattering (DLS). The results from the DSC experiments showed that introducing the polymer to DPPC small unilamellar vesicles completely transformed the vesicles into a large unilamellar structure within minutes, a process that normally takes 2 days at room temperature. The hyperbranched polymers transformed the liposomes to the thermodynamically stable state. Fluorescence microscopy experiments showed that the DPPC vesicles became larger after the polymers were added. In addition, the polymers prevented aggregation of the liposome vesicles yielding clear solutions for up to two weeks at room temperature. In contrast, DPPC vesicles without polymers aggregated to form precipitate within hours at room temperature. The average sizes of liposomes and liposome/polymer were determined by DLS measurement with diameters of 36.3 nm and 65.2 nm, respectively.
Production and Characterization of Large Porous Particles for Pulmonary Drug Delivery
Authors: Batycky Rick , Nice Jackie , Chen Donghao , Sung Jean , Lipp Mike , Mintzes Jeff , Dunbar Craig , Niven Ralph , Edwards David
Published: April 2011

Inhalation of dry powders comprised of large porous particles appears to promote long therapeutic action and increased systemic bioavailability (1-3). Relative to standard inhalation aerosols, dry powders possessing large porous particles clear relatively slowly from the lungs once inhaled (1) and show less aggregation prior to delivery. The diminished aggregation properties of large porous particles permits their use in a simple (and inexpensive) device without the need for carrier particles.
Bulk Metallic Glasses Produced by Detonation Gun Spraying
Authors: Shmyreva T. P.
Published: April 2011

Bulk metallic glasses in the form of amorphous coatings were produced by detonation gun spraying of eutectic alloy containing iron, chromium, phosphorus and carbon. The thickness of the resulting homogeneous amorphous deposit may be up to 2–3 millimeters. The heat capacity, the coefficient of thermal expansion, the corrosion resistance, the hardness and the short range order structure parameters were studied for the bulk metallic glasses and thin ribbon. The investigation revealed that time (for 3 year) and temperature (300–670K) related structural relaxation in amorphous alloys is a nonmonotonic wavelike process having an irreversible nature. The amorphous detonation sprayed coatings have been successfully employed for improving service properties of medical instruments.
Self-Diffusion in Bulk Metallic Glasses
Authors: Knorr K. , Macht M.-P. , Mehrer H.
Published: April 2011

We have studied self-diffusion in the bulk metallic glasses Zr46.75Ti8.25Cu7.5Ni10Be27.5 and Zr65Cu17.5Ni10A17.5 by means of the radiotracer method. Diffusion of 63Ni has been investigated as a function of temperature in both alloys and also as a function of hydrostatic pressure in Zr46.75Ti8.25Cu7.5Ni10Be27.5. With the isotope 95Zr diffusion studies of the major component Zr were performed in Zr46.75Ti8.25Cu7.5Ni10Be27.5. The diffusivity of 95Zr is much smaller than that of 63Ni. The temperature dependence of 63Ni self-diffusion into Zr46.75Ti8.25Cu7.5Ni10Be27.5 and into Zr65Cu17.5Ni10A17.5 cannot be described by a single set of Arrhenius parameters, breaks in the Arrhenius curves are observed. We attribute the non-linear Arrhenius behaviour to the transition from the glassy to the supercooled liquid state. For the first time activation volumes of diffusion in a supercooled melt have been determined. From the pressure dependence of 63Ni diffusion in Zr46.75Ti8.25Cu7.5 Ni10Be27.5 we get activation volumes around one mean atomic volume favouring a diffusion mechanism via vacancy-like defects.
Fracture and Fatigue in a Zr-Based Bulk Metallic Glass
Authors: Gilbert C. J. , Schroeder V. , Ritchie R. O.
Published: April 2011

The fracture and fatigue properties of the Zr41.2Ti13.8Cu12.5Ni10Be22.5 (at.%) bulk metallic glass alloy have been examined. The plane-strain fracture toughness of the fully amorphous alloy was found to exceed 50 MPa√m, although results were sensitive to strain rate, showed significant variability and were influenced by the presence of residual stresses following processing. Fracture surfaces exhibited a characteristic vein morphology, consistent with micromechanical models for meniscus instabilities. Local melting was evident, consistent with the emission of light during rupture and very high local temperatures (>1000 K) measured during fracture. Upon partial or complete crystallization, the alloy was severely embrittled, with toughnesses dropping to ∼1 MPa√m and the hardness increasing by ∼10%. Under cyclic loading, crack-propagation behavior in the amorphous structure was similar to that observed in polycrystalline metals; the crack-advance mechanism was associated with alternating crack-tip blunting and resharpening, as evidenced by presence of fatigue striations. Conversely, the (unnotched) stress-life (S/N) properties were markedly different. Crack initiation and subsequent growth occurred quite readily due to the lack of microstructural barriers that would normally provide local crack-arrest points. This resulted in a very low fatigue limit of∼4% the ultimate tensile strength.
Environmental and Stress State Effects on Fracture and Fatigue Crack-Growth in Zr-Ti-Ni-Cu-Be Bulk Amorphous Metals
Authors: Flores Katharine M. , Suh Daewoong , Dauskardt Reinhold H.
Published: April 2011

Our work has focused on the fracture and fatigue crack-growth mechanisms of a Zr41.25Ti13.75Ni10Cu12.5Be22.5 bulk metallic glass. These alloys exhibit failure strengths on the order of 2 GPa and toughnesses of 10–30 MPa√m with remarkably little plastic deformation. The effect of stress state on strength properties was studied in an effort to model fracture mechanisms. While fracture surfaces suggest significant plastic flow, failure strains are quite small and appear to be independent of stress state. Other methods of energy dissipation, including adiabatic heating, are discussed. Temperature increases of more than 20°C have been noted on the side face of the fracture sample at the crack tip during fracture. The micromechanics of fatigue crack growth are also considered and related to the batch chemistry, environment, and microstructure.
Superplastic Deformation and Viscous Flow in an Zr-Based Metallic Glass at 410°C
Authors: Nieh T. G. , Wang J. G. , Wadsworth J. , Mukai T. , Liu C. T.
Published: April 2011

The thermal properties of an amorphous alloy (composition in at.%: Zr-10Al-5Ti-17.9Cu-14.6Ni), and particularly the glass transition and crystallization temperature as a function of heating rate, were characterized using Differential Scanning Calorimetry (DSC). X-ray diffraction analyses and Transmission Electron Microscopy were also conducted on samples heat-treated at different temperatures for comparison with the DSC results. Superplasticity in the alloy was studied at 410°C, a temperature within the supercooled liquid region. Both single strain rate and strain rate cycling tests in tension were carried out to investigate the deformation behavior of the alloy in the supercooled liquid region. The experimental results indicated that the alloy did not behave like a Newtonian fluid.
Dynamic Failure Mechanisms in Beryllium-Bearing Bulk Metallic Glasses
Authors: Owen David M. , Rosakis Ares J. , Johnson William L.
Published: April 2011

The understanding of dynamic failure mechanisms in bulk metallic glasses is important for the application of this class of materials to a variety of engineering problems. This is true not only for design environments in which components are subject to high loading rates, but also when components are subjected to quasi-static loading conditions where observations have been made of damage propagation occurring in an unstable, highly dynamic manner. This paper presents preliminary results of a study of the phenomena of dynamic crack initiation and growth as well as the phenomenon of dynamic localization (shear band formation) in a beryllium-bearing bulk metallic glass, Zr41.25Ti13.75Ni10Cu12.75Be22.5. Pre-notched and prefatigued plate specimens were subjected to quasi-static and dynamic three-point bend loading to investigate crack initiation and propagation. Asymmetric impact loading with a gas gun was used to induce dynamic shear band growth. The mechanical fields in the vicinity of the dynamically loaded crack or notch tip were characterized using high-speed optical diagnostic techniques. The results demonstrated a dramatic increase in the crack initiation toughness with loading rate and subsequent crack tip speeds approaching 1000 m s−1. Dynamic crack tip branching was also observed under certain conditions. Shear bands formed readily under asymmetric impact loading. The shear bands traveled at speeds of approximately 1300 m s−1 and were accompanied by intense localized heating measured using high-speed full-field infrared imaging. The maximum temperatures recorded across the shear bands were in excess of 1500 K.
Viscosity Measurements for La-Al-Ni liquid Alloys by an Oscillating Crucible Method
Authors: Yamasaki Tohru , Tatibana Tomohiro , Ogino Yoshikiyo , Inoue Akihisa
Published: April 2011

The viscosity of liquid lanthanum-based and aluminum-based La-Al-Ni alloys has been measured by an oscillating crucible method of the inverse suspending type in the temperature range from melting temperature (Tm) up to about 1400 K. In the case of La55Al45-xNix (x = 10∼40 at. %) alloys, the viscosity increased with increasing Ni content up to about 20 at. % Ni and then decreased with increasing the Ni content, while the activation energy for viscous flow decreased to a minimum value at about 20 at. % Ni. This composition is well consistent with that of the La-Al-Ni alloy having largest glass-forming ability.
In-Situ Electron Diffraction Study of Structural Change in the Super-Cooled Liquid Region in Amorphous La-Al-Ni Alloy
Authors: Ohkubo T. , Hiroshima T. , Hirotsu Y. , Ochiai S. , Inoue A.
Published: April 2011

Atomic structures of an amorphous La55A125Ni20 alloy in the supercooled liquid state have been investigated by in-situ electron diffraction using a specimen-heating stage in TEM and the imaging-plate intensity recording. From the analysis of atomic pair distribution functions, changes in interatomic distances and coordination numbers were clearly observed at temperatures in the supercooled liquid state. From the reverse Monte Carlo simulations, structural units (icosahedral, Archimedean anti-prism and trigonal prism atomic clusters) typical of the metallic glass structure were found and increased in the supercooled liquid region. In addition, the deformation behavior was investigated using tensile test. The superplastic elongation was confirmed at optimum strain rates in the supercooled liquid region. From the TEM observation of tensile tested specimens with superplastic elongation, β-La (fcc) nano precipitates in the amorphous matrix were confirmed. The superplasticity in this alloy is thought to originate in viscous flow due to the glassy structure formation but is closely related to an additional flow mode with the microcrystalline precipitation from the amorphous state during the deformation.
Probing Slow Atomic Motions in Metallic Glasses using NMR
Authors: Tang X.-P. , Busch Ralf , Johnson William L. , Wu Yue
Published: April 2011

We report a nuclear magnetic resonance (NMR) study of slow atomic motions in Zr-Ti-Cu- Ni-Be bulk metallic glasses. The employed 9Be spin alignment echo technique is able to probe Be motions with jump rate below 0.1 Hz. It was found that the Be motion is spatially homogeneous. The jump rate follows a perfect Arrhenius temperature dependence. The measured activation enthalpy of 1.2 eV is nearly identical to that obtained by Be diffusivity measurement using elastic backscattering (EBS); this indicates that energy barriers are the same for short and long range Be motions. The present work provides direct experimental evidences that exclude vacancy-assisted and interstitial diffusion mechanisms for Be motions in these systems. The result is interpreted in terms of the spread-out free volume fluctuation mechanism.
Improved Conformality of CVD Titanium Nitride Films
Authors: Liu Xinye , LU Yuan Z. , Gordon Roy G.
Published: April 2011

We demonstrate a novel approach to improving the step coverage of thin films made by chemical vapor deposition (CVD). Titanium nitride (TiN) films were deposited by atmospheric pressure CVD using tetrakis(diethylamido)titanium vapor (TDEAT) and ammonia gas (NH3) carried in nitrogen gas. Trimethylamine (NMe3) gas was added during some of the depositions. The substrates were patterned silicon wafers having holes with aspect ratio of 3.5 through a silicon dioxide layer. We discovered that the step coverage was significantly increased for TiN films made with NMe3. At 320 °C, the step coverage was increased from 70% to nearly 100%. Within the range of deposition temperatures used in our study, 320 °C to 370 °C, the amount of improvement increased as the deposition temperature decreased. The trimethylamine did not increase the resistivity or the impurity levels in the films, but it did reduce the growth rate slightly. We suggest that the trimethylamine adsorbs onto the surface, temporarily blocking some of the sites on which growth could take place. Thus the effective sticking coefficients for the precursors are decreased, and the step coverage is increased.
Characterization of Low-Temperature PECVD Silicon Dioxide Films
Authors: Deenapanray P. N. K. , Lengyel J. , Tan H. H. , Petravic M. , Durandet A. , Williams J. S. , Jagadish C.
Published: April 2011

Silicon dioxide (SiOx, x ≤ 2) films were plasma-deposited at a pressure of 1 Torr and low substrate temperature (≤ 300°C) by N20/lSiH4 flow. Deposition rates in the range 20–50 nm/min were achieved at 20 W rf source power. Deep level transient spectroscopy showed that no significant defect levels were introduced in the Si substrates at this low source power. The effects of flowrate ratio, R, of N2O/SiH4 and substrate temperature on film properties were determined using ex-situ spectroscopic ellipsometry, prism coupler, Rutherford backscattering spectroscopy (RBS), secondary ion mass spectrometry (SIMS), Fourier transform infrared spectroscopy (FTIR) and chemical etching (P-etch). Near-stoichiometric oxide layers were obtained for R ≥ 1, and a decrease in deposition rate with increasing R was observed. The increase in refractive index for R ≤ 1 has been correlated to compositional changes in the thin films. Complementary results were obtained from FFIR and P-etch measurements. Nitrogen was present in the films deposited using R = 4.4, for which the depostion rate showed an Arrhenius-like relationship to substrate temperature. No OH-related bands were observed in our films.
The characteristics of dc glow discharge and its effects on enhancement of diamond nucleation in HF-CVD system
Authors: Xu Z. , Narayan R. J. , Narayan J. , Sankar J.
Published: April 2011

We have investigated enhancement of diamond nucleation due to electrode biasing and compared these results with those obtained using substrate biasing. The electrode biasing results in near-surface dc glow discharge with characteristic negative glows and dark regions on both sides of the electrode (cathode). We have studied systematically diamond nucleation density as a function of substrate location with respect to the electrode and gas pressure. Using scanning electron microscopy and Raman spectroscopy, we have determined that a significant enhancement up to 109 cm-2 in diamond nucleation is achieved when the substrate is located in the negative glow region of the near-surface dc glow discharge. It is also found that gas pressure enhances nucleation site density but the quality of diamond decreases. The optimization of these parameters in obtaining high-quality diamond films is discussed.
The Thermochemical Surface Modification of the Iron-Carbon Alloys
Authors: Timofeeva Larissa A. , Dobrotvorskaya Maria V. , Stepanenko Victor M.
Published: April 2011

Iron and steel samples have been treated in overheated salt -water vapor environment (oxy-doping technique). SEM and optical microscope images of modified surface demonstrated that coating with three distinct layers was deposited. XPS, XRD and SEM + EDA studies were used for the composition evaluation, and non-uniform distribution of dopants was found. Tribological properties were determined, and it was found improvement of working characteristics in 2–10 times. Thermally enhanced difflusion model describing the coating formation was discussed.
Multilayer Coatings and Optical Materials for Tuned Infrared Emittance and Thermal Control
Authors: Martin P. M. , Johnston J. W. , Bennett W. D.
Published: April 2011

Many thermal control applications require thin film coatings that emit or absorb strongly at near infrared and infrared wavelengths. One of the primary applications for these coatings is thermal control for surfaces and structures of spacecraft, which are exposed to solar radiation during at least 60% of their orbit, causing wide temperature fluctuations. Another recent application for this type of coating is infrared emissive imaging employing a fiber optic infrared scene projector. While single layer coatings can provide high emissivity in a broad wavelength band, multilayer coatings can be used to obtain higher emissivities over a narrow wavelength band. This band can be tuned to a specific range of temperatures and wavelengths. Coatings developed for thermal control have a reflective base layer, either ZrN or a refractory metal boride or silicide. These materials have increased durability compared to metal layers. The multilayer coating deposited over the based layer consists of an A1203/SiO2 stack with high emittance at 300 K (9.8 μm), and solar reflectance near 0.6. Multilayer tuned infrared absorber/emitter coatings are applied to fiber optic infrared scene projectors. The coatings consists of a three layer Si3N4/Cr/Si3N4 absorber tuned at the 1.06 μtm laser wavelength, and a six layer Cr/dielectric/Cr/dielectric/Cr/dielectric coating which emits strongly in either the 3 - 5 jim or the 8 - 12 μm infrared wavelength bands. Absorption bands of the coatings are independently tunable. All coatings are deposited by reactive DC and RF magnetron sputtering onto 2.5-in fiber optic faceplates. Either Si3N4, Si, or ZnS thin film dielectric materials were used in the emitter coatings. With an input laser power of 15 W, the coatings emit at a black body temperature 529 K, which compared well with predicted performance.
Micro- And Nano-Mechanical Behavior of Diamondlike Carbon Containing Foreign Atoms Prepared by Pulsed Laser Deposition
Authors: Wei Q. , Narayan R. J. , Sharma A. K. , Sankar J. , Oktyabrsky S. , Narayan J.
Published: April 2011

We have prepared diamondlike carbon (DLC) films using KrF excimer pulsed laser (248 nm). The DLC films were deposited on Si (100) substrates and Cu and Ti were incorporated into the films through adopting a new target design. Visible Raman spectroscopy analysis of G-peak was correlated to internal stress changes in the DLC films due to incorporation of foreign atoms. Reduction of internal stresses in the presence of foreign atoms was established. This is consistent with adhesion studies that showed significant improvement in adhesion of DLC films containing dopants. Nanohardness and Young's modulus of DLC films containing Ti and Cu showed some decrease as compared to pure DLC. The experimental results are discussed in terms of the effect of dopants on the short range environment of the continuous random network (CRN) of DLC.
Nitrogen Implantation Effects on the Chemical Bonding and Hardness of Boron and Boron Nitride Coatings
Authors: Jankowski Alan , Felter Thomas , Patterson Robert , Hayes Jeffrey , Anders Simone , Stamler Thomas , Poker David
Published: April 2011

Boron nitride (BN) coatings are deposited by the reactive sputtering of fully dense, boron (B) targets utilizing an argon-nitrogen (Ar-N2) reactive gas mixture. Near-edge x-ray absorption fine structure analysis reveals features of chemical bonding in the B ls photoabsorption spectrum. Hardness is measured at the film surface using nanoindentation. The BN coatings prepared at low, sputter gas pressure with substrate heating are found to have bonding characteristic of a defected hexagonal phase. The coatings are subjected to post-deposition nitrogen (N+ and N2+) implantation at different energies and current densities. The changes in film hardness attributed to the implantation can be correlated to changes observed in the B ls NEXAFS spectra.
Laser Assisted Deposition of Carbon Nitride Coatings
Authors: Kumar Ashok , Alexandrescu R.
Published: April 2011

We have investigated the growth of carbon nitride (CNx) coatings on various substrates using laser assisted methods such as pulsed laser deposition (PLD) and laser chemical vapor deposition (LCVD). It has been shown that the both techniques produce good quality thin films of CNx. In PLD, a laser beam (λ= 248 nm) has been used to ablate the pyrolytic graphite target in nitrogen atmosphere, where as CO2 laser was used to irradiate carbon-nitrogen containing mixtures such as C2H2/N20/NH3 in LCVD method. A comparative analysis will be presented in terms of structural properties of CNx films prepared by both techniques.
Property and Processing Comparison of Optical Coatings Made by Ion Assisted Evaporation and Magnetron Sputtering
Authors: Pawlewicz W. T.
Published: April 2011

Ion Assisted Evaporation and Magnetron Sputtering are the two most important Physical Vapor Deposition processes used for optical coatings today. Each has advantages and limitations, and each is best for different coating applications. This paper provides a brief but comprehensive comparison of the two. Starting with introductory process descriptions, the paper compares Ion Assist and Sputtering feature-by-feature and ranks them in scorecard fashion. Features examined include: adatom energetics, reactivity, materials compatibility, thickness uniformity, deposition rate, substrate temperature, durability, environmental stability, refractive indices, absorption, scatter, mechanical stress control, and scalability (chamber and substrate size). The comparison is illustrated with examples from the author's twenty-four years of optical coating experience at three companies, with more than forty coating chambers (small, medium and very large), in research, development and production coating environments.
Preparation And Characterization Of Carbon Nitride Thin Films By Electron Cyclotron Resonance (Ecr) Sputtering Method
Authors: Aoi Yoshifumi , Tani Youji , Hisa Masaaki , Kamijo Eiji
Published: April 2011

Crystalline carbon nitride films were deposited by electron cyclotron resonance (ECR) plasma sputtering method using a carbon target and a nitrogen gas atmosphere. The deposited films were characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and X-ray diffraction (XRD). Nitrogen content of the deposited film was varied with substrate selfbias potential and substrate temperature. Bonding states of nitrogen and carbon in the deposited filns were different according to the substrate temperature, sp3 C-N bonds were observed for the film deposited at 600 °C. Crystallization of carbon nitride thin film was observed hen the deposition was carried out an elevated substrate temperature.
The Oxidation of Ni and Ni-20Cr Deposited with Chromia Thin Films VIA Combustion CVD
Authors: Alexiou A. E. , Hendrick M. R. , Hampikian J. M.
Published: April 2011

Chromia thin films were deposited onto substrates of Ni and Ni-20Cr by gaseous fuel combustion chemical vapor deposition. The chemical precursor utilized to achieve chromia films was aqueous 0.27M chromium nitrate, and the depositions took place within the flame at temperatures between 200 and 550°C. Amorphous coatings were deposited between 200 and 375°C, whereas crystalline coatings of chromia (eskolaite) were deposited between 400 and 550°C. The eskolaite deposition rate was approximately five times faster than the amorphous chromia. Chromia coatings containing 2 wt% yttria were also formed. The deposition temperature necessary to form crystalline chromia/yttria coatings was slightly higher (∼50°C) than those containing chromia only. The ability of the various coatings to provide oxidation protection was characterized using thermogravimetric analysis (TGA). The eskolaite coatings that are at least 1 im thick reduce the oxidation mass gain/area of Ni-20Cr by nearly a factor of ten and the parabolic constant by an order of magnitude, whereas the amorphous chromia coatings that are 0.6 μm thick do not demonstrate such an improvement. Yttria-doped chromia coatings further reduce the parabolic constant by two orders of magnitude, consistent with expectation. Characterization of the coatings was accomplished using a variety of techniques, including SEM, TEM, EDS, and XRD.
Mullite Diffusion Barriers for SiC-C/C Composites Produced by Pulsed Laser Deposition
Authors: Fritze H. , Schnittker A. , Witke T. , Rüscher C. , Weber S. , Scherrer S. , Schultric B. , Borchardt G.
Published: April 2011

Pulsed Laser Deposition (PLD) allows the ablation of nonconductive and high melting point target materials and the preparation of films with complex composition. High energy impact leads to melting and evaporation of the target material in a single step. In case of mullite ablation, the flux of the metal components is stoichiometric. Under reduced pressure the oxygen content in the layers decreases. However, after a short oxidation treatment, the formation of mullite in the coating is completed, as confirmed by IR spectroscopy and XRD investigations. For a commercial Si-SiC precoated C/C material, the effectiveness of additional PLD mullite layers as outer oxidation protection is tested in the temperature range 773 K < T < 1873 K. Mullite coatings with a thickness of 2.5 pm improve the oxidation behaviour significantly. Because of SiO2 formation at the mullite-SiC interface, all samples exhibited a mass increase upon oxidation. For oxidation durations of three days, only amorphous SiO2 is formed at the mullite-SiC interface. The inward diffusion of oxygen across the outer mullite-containing layer controls the kinetics of the reaction, as was deduced from 18O diffusivity measurements in PLD mullite layers. At temperatures close to the eutectic temperature (1860 K), mullite can seal defects. The calculated oxidation rates resulting from the diffusion parameters in SiO2 and mullite are close to the thermogravimetric data.
Effects of Reactor Decontamination Complexing Agents on Soil Adsorption of Metals
Authors: Serne R. J. , Lindenmeier C. W. , Cantrell K. J. , Owen A. T.
Published: April 2011

The effects of picolinate, an organic ligand used to decontaminate nuclear reactor cooling systems, in leachates generated from shallow-land burial (SLB) of low-level nuclear wastes (LLW) on soil adsorption was determnined. Using batch adsorption tests and varying the concentration of picolinate, the adsorption tendencies of two metals [Ni(II) and U(VI)] and the ligand were measured as a function of solution pH. We found that when total metal concentrations were fixed at 10−5M, picolinate at ligand-to-metal [L:M] ratios ≥10 did significantly reduce adsorption of Ni but even at a L:M ratio of 100 there was no effect on U(VI) adsorption. These results are compared with data on other metals in the presence of picolinate and for metal adsorption in the presence of EDTA. We conclude that picolinic acid is less of a threat than EDTA in waste leachates to reduce metal adsorption (increase mobility) and that picolinate concentrations must reach or exceed 10−4M for the most impacted metals (i.e., those that form the very strongest complexes with picolinate). There are no leachate data on these decontamination agents for the common burial technique (disposal of de-watered resins in high integrity containers) that can be used to evaluate potential hazards of these organo-radionuclide complexes.
79Se: Geochemical and Crystallo-Chemical Retardation Mechanisms
Authors: Chen Fanrong , Burns Peter C. , Ewing Rodney C.
Published: April 2011

79Se is a long-lived (1.1×106 years) fission product which is chemically and radiologically toxic. Under Eh-pH conditions typical of oxidative alteration of spent nuclear fuel, selenite or selenate are the dominant aqueous species of selenium. Because of the high solubility of metalselenites and metal-selenates and the low adsorption of selenite and selenate aqueous species under alkaline conditions, selenium may be highly mobile. However, 79Se released from altered fuel may be immobilized by incorporation into secondary uranyl phases as low concentration impurities, and this may significantly reduce the mobility of selenium. Analysis and comparison of the known structures of uranyl phases indicate that (SeO3) may substitute for (SiO3OH) in structures with the uranophane anion-topology (α.-uranophane, sklodowskite, boltwoodite) which are expected to be the dominant alteration phases of UO2 in Si-rich groundwater. The structural similarity of guillemninite, Ba[(UO2)3 (SeO3)2O2](H2O) 3 to phurcalite, [(UO2)3(PO4)2O2](H2O)7, suggests that the substitution (SeO3)↔ (PO4) may occur in phurcalite. The close similarity between the sheets in the structures of rutherfordine and [(UO2)(SeO3)] implies that the substitution (SeO3) ↔ (CO3) can occur in rutherfordine. However, the substitutions: (SeO3) ↔ (SiO3OH) in soddyite and (SeO3) ↔ (PO4) in phosphuranylite may disrupt their structural connectivity and are unlikely to occur.
Fate of Neptunium in an Anaerobic, Ethanogenic Microcosm
Authors: Banaszak J. E. , Webb S. M. , Rittmann B. E. , Gaillard J.-F. , Reed D. T.
Published: April 2011

Neptunium is found predominantly as Np(IV) in reducing environments, but as Np(V) in aerobic environments. Currently, it is not known how the interplay between biotic and abiotic processes affects Np redox speciation in the environment. To evaluate the effect of anaerobic microbial activity on the fate of Np in natural systems, Np(V) was added to a microcosm inoculated with anaerobic sediments from a metal-contaminated freshwater lake. The consortium included metal-reducing, sulfate-reducing, and methanogenic microorganisms, and acetate was supplied as the only exogenous substrate. Addition of more than 10−5M Np did not inhibit methane production. Total Np solubility in the active microcosm, as well as in sterilized control samples, decreased by nearly two orders of magnitude. A combination of analytical techniques, including VIS-NIR absorption spectroscopy and XANES, identified Np(IV) as the oxidation state associated with the sediments. The similar results from the active microcosm and the abiotic controls suggest that microbially produced Mn(II/III) and Fe(II) may serve as electron donors for Np reduction.
Investigation of Bacterial Transport in the Large-Block test, A Thermally Perturbed Block of Topopah Spring Tuff
Authors: Chen C.-I , Meike A. , Chuu Y.-J. , Sawvel A. , Lin W.
Published: April 2011

Transport of bacteria is investigated as part of the Large-Block Test (LBT), a thermally perturbed block of Topopah Spring tuff. Two bacterial species,Bacillus subtilisandArthrobacter oxydans, were isolated from the Yucca Mountain tuff. Natural mutants that can grow under the simultaneous presence of the two antibiotics, streptomycin and rifampicin, were selected from these species by laboratory procedures, cultured, and injected into the five heater boreholes of the large block hours before heating was initiated. The temperature, as measured 5 cm above one of the heater boreholes, rose slowly over a matter of months to a maximum of 142°C and to 60°C at the top and the bottom of the block. Samples were collected from boreholes located approximately 5 ft below the injection points. Double-drug-resistant bacteria were found in the collection boreholes nine months after injection. Biochemical tests support the identification ofB. subtilisin the collection boreholes. Double-drug-resistant microbes also appeared in the heater boreholes where the temperature had been sustainably high throughout the test. The number of double-drugresistant bacteria that were identified in the collection boreholes increased with time until the heater was deactivated. Negative indications in the collection holes after the heater was deactivated support the supposition that these bacteria were the species that were injected. An apparent homogeneous distribution among the collection boreholes suggests no pattern to the migration of bacteria through the block. The relationship between bacterial migration and the movement of water is not yet understood. These observations indicate the possibility of rapid bacterial transport in a thermally perturbed geologic setting. The implications for colloid transport need to be reviewed.
Murataite-based ceramics for actinide waste immobilization
Authors: Stefanovsky S. V. , Yudintse S. V. , Nikonov B. S. , Omelianenko B. I. , Ptashkin A. G.
Published: April 2011

Studying the Synroc, doped with a simulated HLW, we have found, along with conventional Synroc phases (zirconolite, perovskite, hollandite), an extra phase with a stoichiornetry (Ca, Mn, U, TR)4(U, TR, Zr, Ti) 2(AI, Ti)7O22. XRD and TEM study has shown this phase is related to a very rare mineral murataite. In the present work a ceramic based on murataite is studied. The ceramic samples in the system: Ca-Mn-Ti-Zr-U-Ce-AI-Fe-O were produced and examined in details using XRD, SEM/EDS, TEM, and optical microscopy. Total amount of actinide (U) and rare earth (Ce, Gd) elements in the murataite exceeds 20 wt%. Isomorphic substitution schemes in the structures of synthetic and natural murataites are discussed. High isomorphic capacity of the murataite structure towards actinides and REEs, flexibility of its composition, feasibility of synthesis by melting, including a cold crucible melting, and very high chemical durability under hydrothermal conditions make the murataite-based ceramics very promising for actinides and excess weapon Pu fixation.
Corrosion of K-3 Glass-contact refractory in sodium-rich aluminosilicate melts
Authors: Lu X. D. , Gan H. , Buechele A. C. , Pegg I. L.
Published: April 2011

The corrosion of the glass-contact refractory Monofrax K-3 in two sodium-rich aluminosilicate melts has been studied at 1208 and 1283°C using a modified ASTM procedure with constant agitation of the melt by air bubbling. The results for the monolithic refractory indicate a fast initial stage involving phase dissolution and transformation and a later “passivated” stage in which the surface of the refractory has been substantially modified. The composition of the stable spinel phase in the altered layer on monolithic coupons of K-3 is almost identical to the equilibrium composition bracketed by the dissolution of powdered K-3 into under-saturated melts on the one hand, and by crystallization of spinels from supersaturated melts on the other. The temperature and melt shear viscosity were found to have significant effects on the rates of K-3 dissolution and transformation.