bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Hydration Studies of Natural and Synthetic Glasses
Authors: Bates John K. , Abrajano Teofilo A. , Ebert William L. , Mazer James J. , Gerding Thomas J. 
Published: March 2011

ABSTRACTThe results of a series of hydration experiments on natural glasses (Hawaiian basalt, obsidian) and the nuclear waste glass WV-44 done to examine laboratory methods of accelerating reaction processes are summarized. The glasses were reacted in hydrothermal solution and in saturated vapor water. It was found that different reaction rates and processes were found using the differing conditions, and that laboratory efforts to accelerate and duplicate natural processes must account for the physical processes that occur naturally.
Obsidian Hydration Dating - Field, Laboratory, and Modeling Results
Authors: McGrail B. P. , Pederson L. R. , Strachan D. M. , Ewing R. C. , Cordell L. S. 
Published: March 2011

ABSTRACTHydration rind thicknesses found on obsidian artifacts provide one means of estimating the age of an archaeological site. The model used in the method usually assumes a diffusion-controlled reaction of the glass with water. However, results using this model are not always in agreement with other dating methods. Observations of secondary mineral formation on glasses in contact with water vapor suggests that other rate-controlling mechanisms may be operative. In this paper, we apply the glass dissolution code GLASSOL, coupled with the geochemical code PHREEQE to model the reaction of Glass Mountain obsidian in water. The results show the importance of accounting for the effects of solution chemistry on the time-dependence of the hydration reaction.
Oxidation and Protection of Fiberglass-Epoxy Composite Masts for Photovoltaic Arrays in the Low Earth Orbital Environment
Authors: Rutledge Sharon K. , Paulsen Phillip E. , Brady Joyce A. , Ciancone Michael L. 
Published: March 2011

ABSTRACTFiberglass-epoxy composites have been considered for use as structural members for the mast of the Space Station solar array panel. The low Earth orbital environment in which Space Station is to operate is composed mainly of atomic oxygen, which has been shown to cause erosion of many organic materials and some metals. Ground based testing in a plasma asher was performed in order to determine the extent of degradation of fiberglass-epoxy composites when exposed to a simulated atomic oxygen environment. During exposure, the epoxy at the surface of the composite was oxidized, exposing individual glass fibers which could easily be removed. Several methods of protecting the composite were evaluated in an atomic oxygen environment and with thermal cycling and flexing: The protection techniques evaluated to date include an aluminum braid covering, an indium-tin eutectic and a silicone based paint. The open aluminum braid offered little protection while the CV-1144 coating offered some initial protection against atomic oxygen. The In-Sn eutectic coating provided initial protection against atomic oxygen, but appears to develop cracks which accelerate degradation by atomic oxygen when flexed. Coatings such as the In-Sn eutectic may provide adequate protection by containing the glass fibers even though mass loss still occurs.
Potential for Diboride Reinforcement of Oxide Matrix Composites
Authors: Vedula K. , Abada A. , Williams W. S. 
Published: March 2011

ABSTRACTParticulate composites of TiB2 in ZrO2, Y2O3 and Al2O3 have been prepared by vacuum hot pressing. Specimens were tested in oxyacetylene flames at 1650 to 2050°C; in vacuum at 1600°C and by induction heating in air at 1400 to 1600°C in order to evaluate the chemical compatability between the diboride/oxide combinations, as well as the effectiveness of the oxides as diffusion barriers. Results indicate that the large vapor ressure of B2O3 formed at the diboride/oxide interfaces presents serious problems under all the conditions tested.
Selective Corrosion Resistance of Chromium Implanted Cu-37w%Zn Alloy
Authors: Hirvonen J-P. , Toivanen R.O. , Lindroos V.K. 
Published: March 2011

ABSTRACTSelective corrosion resistance of the chromium implanted brass as well as vacancy formation were investigated. Dealloying was observed to create excess vacancies. Chromium and boron and many other potentially beneficial alloying elements like C, N, Si, P, V, Co, Ni, Cu, Ge, As, Y, Nb, Pd, Ag, Sn, Sb, have a repulsive interaction with vacancies and they could increase the dezincification resistance in alpha brass but not in beta brass. Boron implanted brass was found to be more resistant to selective corrosion than the chromium implanted brass.
MBE Regrowth of AlGaAs on Ion Etched GaAs/AlGaAs Microstructures
Authors: Harbison J. P. , Scherer A. , Hwang D. M. , Nazar L. , Beebe E. D. 
Published: March 2011

ABSTRACTThe combination of an ion beam assisted etching (IBAE) system and a Molecular Beam Epitaxy (MBE) growth chamber integrally connected in the same set of ultrahigh vacuum (UHV) chambers has allowed us to etch patterns defined by a strontium fluoride mask down into the underlying semiconductor wafer, and regrow monocrystalline material around these patterned structures entirely in situ. Scanning electron microscopy (SEM) analysis of the regrown structures reveals very directional deposition of the overgrown material. Cross-sectional transmission electron microscopy (TEM) reveals a smooth interface and vertical sidewalls at the boundary between the etched surfaces and the overgrowth. Material deposited on the sidewalls is shown to be monocrystalline, while that deposited over the mask is polycrystalline. The SrF2 mask material, previously shown to be an excellent IBAE mask for extremely fine nanostructures, is also shown to be compatible with the high temperatures need for overgrowth, and regrowth around structures as small as ˜200 nm in size has been demonstrated.
The Influence of Arsenic Flux in the Defect Structure of MBE Deposited GaAs and Ga1−xAlxAs
Authors: Hatzopoulos Z. , Kiriakidis G. , Georgacilas A. , Roditis N. , Christou A. 
Published: March 2011

ABSTRACTThe dependence of the density of defects on the pressure ratio PAs/PGa and on the substrate temperature has been studied on a series of GaAs and GaAlAs samples prepared by MBE. Samples have also been desorbed prior to the MBE deposition by UV laser and the density of defects have been compared with the density of defects obtained in samples where thermal desorption occured. Optimum pressure ratios PAs/GPa and growth temperatures have been found for both GaAs and GaAlAs for minimum defect density. It is shown that insitu laser desorption, prior to MBE deposition is a feasible technique for attaining MBE structures with a low defect density, thus simplifying the substrate preparation process.
Anisotropic Ion Beam Assisted Etching of Optical Structures in GaAs and InP
Authors: Scherer A. , Gaag B. P. Van Der , Kash K. , Craighead H. G. , Grabbe P. 
Published: March 2011

ABSTRACTIon beam assisted etching (IBAE) was used to define submicron structures into GaAs/AlGaAs and InP/InGaAsP heterostructures. Etch rates in excess of I pm/minute were obtained after optimization of the etching process, allowing the fabrication of optoelectronic structures which require smooth, vertical sidewalls and depths of several microns. By altering the gas flow and the ion beam parameters, the same technique was used to pattern electron beam-written structures with lateral dimensions of less than 30 nm and aspect ratios in excess of 5:1 in GaAs.
Hydrogenation of GaAs and Application to Device processing
Authors: Pan N. , Feng M. S. , Jackson G. S. , Bose S. S. , Guido L. J. , Holonyak N. , Stillman G. E. 
Published: March 2011

ABSTRACTExposure of GaAs and AlGaAs to a hydrogen plasma has been shown to result in a significant change in the electrical and optical properties. The changes are related to the electrical deactivation of the deep and shallow impurities by hydrogenation. Spectroscopic and electrical measurements have shown that Si donors and C acceptors in high purity GaAs can be passivated by hydrogenation. Hydrogenation of p-type GaAs and AlGaAs has resulted in highly resistive material. SiO2 was found to be a suitable mask for the hydrogenation process. Single and multiple stripe geometry lasers have been fabricated by properly masking the laser structure. The lasers produced using the hydrogenation process have low threshold currents and are capable of cw room temperature operation.
A High Depth Resolution Backside Secondary Ion Mass Spectrometry Technique Used for Studying Metal/Gaas Contacts
Authors: Palmstrøm C. J. , Schwarz S. A. , Marshall E. D. , Yablonovitch E. , Harbison J. P. , Schwartz C. L. , Florez L. , Gmitter T. J. , Wang L. C. , Lau S. S. 
Published: March 2011

ABSTRACTUnderstanding metal/semiconductor contacts is important for the fabrication of device structures. To date most studies have been aimed at understanding the metallurgical or the electrical properties. Directly measuring the impurity concentrations immediately beneath a contact rather than inferring it from electrical measurements has up until now been difficult. This paper describes a backside SIMS technique which not only demonstrates the ability of measuring doping concentrations close to a metal/semiconductor contact but also is capable of measuring the consumption of semiconductor material during a metal/semiconductor reaction. The sample preparation technique can be used to enable backside profiling using other profiling techniques such as Auger and x-ray photoelectron spectroscopy depth profiling, Rutherford backscattering, and backside electrical evaluation. The Ge/Pd/GaAs solid phase ohmic contact is used to demonstrate the technique.
Silicon Induced Mixing of AlGaAs Superlattices – Behavior and Mechanisms
Authors: Schwarz S. A. , Venkatesan T. , Mei P. 
Published: March 2011

ABSTRACTMixing (or interdiffusion) of AlGaAs superlattice layers is greatly accelerated in the presence of Si doping. We have employed secondary ion mass spectrometry (SIMS) to monitor the depth dependence of the Al diffusion coefficient as well as the Si diffusion profile. Our results reveal unusually complex dependences on implantation and annealing conditions. To isolate the effects of chemistry and lattice damage, several structures were grown by molecular beam epitaxy (MBE) containing plateaus of Si concentration. The doping dependence and activation energy of Al diffusion were then evaluated in as-grown samples and in samples damaged by MeV Ga ion bombardment. To further elucidate the process, samples containing single or multiple implants of various dopants and impurities were examined. Microscopic and electrical characterizations were also performed. Al diffusion was found to be strongly inhibited by lattice damage and by very high Si doping levels. The Al diffusion coefficient has a high power law dependence on Si concentration while its activation energy is relatively unaffected by doping or lattice damage. A wide range of experimental and theoretical mixing studies are surveyed. Mixing models invoking Si pairs, divacancies, Fermi level arguments, and other mechanisms are critically assessed.
Te Induced AlAs/GaAs Superlattice Mixing
Authors: Mel P. , Schwarz S. A. , Venkatesan T. , Schwartz C. L. , Colas E. 
Published: March 2011

ABSTRACTTe enhanced mixing of AlAs/GaAs superlattice has been observed by secondary ion mass spectrometry. The superlattice sample was grown by organometallic chemical vapor deposition and doped with Te at concentrations of 2×1017 to 5×1018 cm−.3 In the temperature range from 700 to 1000 C, a single activation energy for the Al diffusion of 2.9 eV was observed. Furthermore, it has been found that the relationship between the Al diffusion coefficient and Te concentration is linear. Comparisons have been made between Si and Te induced superlattice mixing.
Corrosion of Radioactive, Crushed Waste Glass
Authors: Björner Inga-Kari , Christensen H. , Hermansson H. P. , Tsukamoto M , Werme L 
Published: March 2011

ABSTRACTThe corrosion experiments of crushed, radioactive waste glass at Studsvik within phase V of the JSS Project are described. The experiments were performed with high S/V ratios (1100 and 4000 m−1) which resulted in silica saturation already after the shortest reaction time studied (91 d).Thee long term leach rate of the soluble elements is about 10−3 g.m d−1, both in the presence and absence of bentonite. In the presence of bentonite + magnetite the leach rate is higher, about 0.007 g.m1.d−2. The release rate to the solution of Cs is one order of magnitude lower and that of Pu-238 + Am-241 three orders of magnitude lower than the release rate of the soluble elements Mo and B. Most of the Pu-238 and Am-241 fraction, found in the solution, is present as colloids.
Cooling and Cracking of Technical HLW Glass Products: Experimental and Numerical Studies
Authors: Kienzler Bernhard 
Published: March 2011

ABSTRACTVarious cooling procedures have been applied to canisters filled with inactive simulated HLW glass and the measured temperature distributions have been compared with numerically computed data. Stress computations of the cooling process were carried out with a finite element method. Only those volume elements having temperatures below the transformation temperature Tg were assumed to contribute thermoelastically to the developing stresses. Model calculations were extended to include real HLW glass canisters with inherent thermal power. The development of stress as a function of variations of heat flow conditions and of the radioactive decay was studied.
Investigation of the Redox Behavior of Technetium in Borosilicate Glass Melts by Voltammetry
Authors: Freude E. , Lutze W. , Rüssel C. , Schaeffer H. A. 
Published: March 2011

ABSTRACTTechnetium is a potentially hazardous radionuclide in the waste vitrification process as its oxides are volatile. Electrochemical measurements, i.e. potentiometry and voltammetry are applied to investigate the redox reactions of Tc in the glass melt. Re is studied for comparison. Under normal oxidizing conditions Tc is in the -T-state, and substancial losses of Tc occur as a result of compound volatility. Reducing conditions lead to the formation of TcO2, which precipitates from the melt. Stronger reducing conditions lead to the formation of metallic Tc
Product Models for the Vitrification of West Valley High-Level Wastes
Authors: Pegg I. L. , Saad E. E. , Feng X. , Adiga R. B. , Freeborn W. P. , Macedo P. B. 
Published: March 2011

ABSTRACTProperty models have been developed for the major properties that need to be controlled in the production of borosilicate glasses for West Valley high-level nuclear waste immobilization. The chemical durability is the most important parameter for product performance, while melt viscosity is the most critical parameter in assuring the processability of the glass. Simple models for these properties are described that are based on data from numerous glasses which were prepared with compositions in the region around the West Valley reference glass. A scheme for optimization of the target glass and for predicting the acceptability of glasses resulting from natural process variations is illustrated. This involves integration of the product models with a process model that was described previously. This approach has guided the present placement of the West Valley reference glass.
Fabrication and Leach Testing of Synroc Containing Actinides and Fission Products
Authors: Reeve K. D. , Levins D. M. , Seatonberry B. W. , Ryan R. K. , Hart K. P. , Stevens G. T. 
Published: March 2011

ABSTRACTSynroc containing mixed fission products and four actinides (237Np, 239Pu, 241Am and 244Cm) was fabricated by hot pressing on a 75 g-scale in separate hot-cell and glove-box facilities. Samples were physically characterised by density, which ranged from 98.2 to 99.1% of theoretical, by scanning electron microscopy (SEM) and by the cc-track etch technique to determine the distribution of actinide elements.The chemical durability of specimens prepared from the hot-pressed Synroc was determined in 460 leach tests carried out under static conditions at 70°C. Release of 137Cs dominated the fission-product source term while 237Np was the most leachable actinide element. Short-term release is dominated by the initial spilce from Cs and other readily soluble species at grain boundaries and in non-equilibrium phases. Long-term release is probably controlled by matrix solubility. A phenomenological model is developed which accounts for both short- and long-term release.
Mechanism of Heavy Element Retention in Hydrated Layers Formed on Leached Silicate Glasses
Authors: Petit J.-C. , Dran J.-C. , Trotignon L. , Casabonne J.-M. , Paccagnella A. , Della Mea G. 
Published: March 2011

ABSTRACTWe have investigated the relationship between hydrated layer formation during aqueous corrosion of silicates and retention of heavy elements (Fe, REE, actinides). Our approach is based on the comparison of the dissolution behaviour of silicate glasses, silicate minerals implanted with increasing doses of lead ions (1×E+12 to 1×E+15 ions/cm2), sorption experiments on silica surfaces and direct precipitation of hydrosilicates. The characterization of reacted surfaces was performed by combining Rutherford backscattering spectrometry (RBS) for profiling heavy elements with Resonant Nuclear Reaction Analysis (RNRA) for hydrogen profilimetry. The accumulation of these elements does not necessarily imply a selective dissolution and can be explained by the “precipitation” of hydroxides or hydrosilicates.
Surface Analysis of UO2 Leached in Mineral Water Studied by X-Ray Photoelectron Spectroscopy
Authors: Lahalle M. P. , Krupa J. C. , Guillaumont R. , Genet M. , Allen G. C. , Holmes N. R. 
Published: March 2011

ABSTRACTX-rays photoelectron spectroscopy (XPS) analysis has been carried out on uranium dioxide single crystals placed in both deionised or mineral water at 60 °C and 90 °C for a few months. The surface layer on the sample immersed in mineral water at 90 °C was sufficiently thick to mask the presence of uranium in the recorded XPS spectrum. Depth profiling experiments showed that the deposit was ∼ 100 nm in thickness and revealed the formation of a mixed magnesium-uranium oxide region between the bulk UO2 and the outer magnesium- rich layer. Analysis of the aqueous medium following immersion of the UO2 samples showed that the concentration of uranium released to the mineral water was 10 to 100 times lower than that in deionised water.
Leaching of Cesium from a Cement Matrix
Authors: Torstenfelt B. , Hedin G. 
Published: March 2011

ABSTRACTThe leaching rate of cesium has been studied in cement. The solidification matrix was a standard Portland cement with increased sulphate resisting properties mixed with 300 kg/m3 or 350 kg/m3 powdered ion exchange resins, and with or without 5 weight-% zeolite added to the grout. The leaching rates from an ordinary cement matrix and a cement matrix mixed with zeolite were measured to be (1.3 to 2.6)×10–7 kg/m2s and (1.6 to 2.1)×10−8 kg/m2s, respectively. From the leaching data the apparent diffusivity of cesium in an ordinary cement matrix with a waste load of 300–350 kg/m3 powdered ion exchange resins was measured to be (0.6 to 1.3)×10−10 m2/s, and in a cement matrix mixed with 5 weight-% zeolite and the same waste load, the diffusivity was measured to be (0.8 to 1.0)×10−12m2/s.
Non Destructive Waste form and Package Characterization by Computerized Tomography
Authors: Illerhaus B. , Goebbels J. , Kettschau A. , Reimers P. 
Published: March 2011

ABSTRACTTransmission computerized tomography (TCT) was used for nondestructive characterization of nuclear waste packages (HLW, ILW). Ready conditioned waste packages may be tested to reveal density fluctuations, cracks, fluids etc. Emission computerized tomography (ECT) combined with TCT gives the activity distribution corrected for density variations within the waste packages.
Package Characterization by Laboratory Leaching and Diffusion Experiments using Radionuclides
Authors: Das H. A. 
Published: March 2011

ABSTRACTThe leaching of solid inorganic waste from loaded concrete or cement by Incoming water can be described in terms of a “steady-state” outward diffusion of the saturated solution, formed inside the pores. The derived equations permit the prediction of long-term leaching behaviour. Radiotracer experiments enahle the determination of the parameters involved.
Characterization of Bituminous, Intermediate-Level Waste Products
Authors: Kopajtic Z. , Laske D. , Linder H. P. , Mohos M. , Nellen M. , Zwicky H. U. 
Published: March 2011

ABSTRACTThe influence of γ-irradiation on the properties of two types of bituminous reprocessing waste has been studied. Standard test methods were adapted for use with radioactive samples. Measurements of penetration, gas generation, thermal stability and leaching of irradiated and non-irradiated samples have been compared.
Safety Analysis and Comparison of Toxicities for the Disposal of Radioactive Waste of Negligible Heat Generation Including Transuranic Elements
Authors: Berg H. P. , Ehrlich D. , Thomauske B. 
Published: March 2011

ABSTRACTRequirements on radioactive waste of negligible heat generation with respect to transuranic elements, derived from the safety analysis of the operational phase of the Konrad repository, are described and resulting activity limitations are discussed. For assessing the long term safety, the calculation of individual doses in connection with the very slow water movements and, additionally, toxicity comparisons to other waste and to the natural toxicity at the site are discussed. Some information is given on the procedure of taking into account the activity limitations in an optimal way when planning emplacement campaigns.
Performance Assessment with Realistic Data for a Hypothetical High-Level Waste Repository in A Salt Dome
Authors: Hirsekorn R.-P. , Storck R. 
Published: March 2011

ABSTRACTIn the frame of the European R&D program on “Management and Storage of Radioactive Waste” assessments for HLW repositories in different geological formations have been performed with realistic data. Part of this action was the discussion of altered evolution scenarios for a repository in a salt dome.For the considered HLW repository a combined altered evolution scenario with brine intrusion via the main anhydrite vein and brine intrusion from undetected brine pockets has been considered. For this scenario limited intrusions of brine at very early times are assumed, which inundate boreholes and parts of the repository. Radionuclides are leached out of the waste forms and contaminate the brine. At later times brine intrusion via the main anhydrite is assumed to take place. Under certain conditions contact between both amounts of brine is possible, and contaminated brine reaches the overburden. Here, the radionuclides are swept away with the groundwater flow.Decisive for the transport of radionuclides from the repository to the geosphere are several interacting effects (e.g. convergence, permeability, pressure) which determine the movement of brine through the drifts and seal-ings. For the parameters involved in the modelling of physical and chemical effects as realistic data as available (best estimate) were used. Local sensitivity studies show that with the best estimate values for some parameters the combined intrusion scenario is just at the transition point between release and no release.Results are obtained showing time histories for the decrease of the voids in the repository, release rates for relevant nuclides injected into the overburden, and for dose rates. Dependences on the model parameters are discussed and most relevant parameters are identified.