bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Highly Active Waste Glasses Produced in a Hot Vitrification Pilot Plant
Authors: Cantale C. , Glatz J-P. , Toscano E.H. , Donato A. , Coquerelle M. , Fuger J.
Published: March 2011

Fully radioactive waste glasses produced in a hot vitrification pilot plant were characterized in the hot cells at the JRC-Karlsruhe. The work includes microstructural analysis before and after leaching by SOXHLET extractors (MCC-5S), as well as leachate and gel-layer chemical analysis. Partial devitrification, with phases enriched in metals and rare earths, was observed in one of the products. In the gel layers formed during the dissolution tests, enrichment in some elements (Fe,Ti,Gd,Nd,Ce) and depletion in glass constituents (Si,B,K,Ba,Ca,Na) as well as in Mo and Cs, were determined. This was in good qualitative agreement with the leachate chemical analysis.
Calculation of the Viscosity of Nuclear Waste Glass Systems
Authors: Shah R. , Behrman E.C. , Oksoy D.
Published: March 2011

Viscosity is one of the most important processing parameters and one of the most difficult to calculate theoretically, particularly for multicomponent systems like nuclear waste glasses. Here, we propose a semi-empirical approach based on the Fulcher equation, involving identification of key variables, for which coefficients are then determined by regression analysis. Results are presented for two glass systems, and compared to results of previous workers and to experiment. We also sketch a first-order statistical mechanical perturbation theory calculation for the effects on viscosity of a change in composition of the melt.
Identification of Secondary Phases Formed During Unsaturated Reaction of UO2 with EJ-13 Water
Authors: Bates J. K. , Tani B. S. , Veleckis E. , Wronklewicz O. J.
Published: March 2011

A set of experiments, wherein UO2 has been contacted by dripping water, has been conducted over a period of 182.5 weeks. The experiments are being conducted to develop procedures to study spent fuel reaction under unsaturated conditions that are expected to exist over the lifetime of the proposed Yucca Mountain repository site. One half of the experiments have been terminated, while one half are ongoing. Analyses of solutions that have dripped from the reacted UO2 have been performed for all experiments, while reacted UO2 surfaces have been examined for the terminated experiments. A pulse of uranium release from the UO2 solid, combined with the formation of schoepite on the surface of the UO2, was observed between 39 and 96 weeks of reaction. Thereafter, the uranium release decreased and a second set of secondary phases was observed. The latter phases incorporated cations from the EJ-13 water and include boltwoodite, uranophane, sklodowskite, compreignacite, and schoepite. The experiments are continuing to monitor whether additional changes in solution chemistry or secondary phase formation occurs.
Theoretical Modeling of Crevice and Pitting Corrosion Processes in Relation to Corrosion of Radioactive Waste Containers
Authors: Walton John C.
Published: March 2011

A mathematical and numerical model for evaluation of crevice and pitting corrosion in radioactive waste containers is presented. The model considers mass transport, mass transfer at the metal/solution interface, and chemical speciation in the corrosion cavity. The model is compared against experimental data obtained in artificial crevices. Excellent agreement is found between modeled and experimental values for the potential. The importance of full consideration of complex ion formation in the aqueous solution is emphasized and illustrated.
The Use of Additives for Reducing Hydrogen Yield in Mortar Containing Slag and Chloride Salts
Authors: Lewis Michele A. , Warren David W.
Published: March 2011

Cementitious waste forms are being considered for immobilizing nuclear waste before disposal. In earlier work, it was found that irradiation of a mortar formulation consisting of slag, portland cement, fly ash, water, and up to 10 wt % KCI-LiCl salt resulted in the generation of hydrogen. Yields were relatively high and the rates of generation were constant for the irradiation period investigated. The addition of small amounts of oxygenrich electron scavengers (NaN03, NaI04, KMn04, or Ag20) to the mortar was investigated as a means for reducing hydrogen yields. The addition of NaN03 reduced the hydrogen yield; changed the radiolytic products from hydrogen to a mixture of hydrogen, nitrogen, and N20; and reduced the pressurization rate after exposure to 400 Mrads. The addition of NaI04 and KMn04 reduced hydrogen yields slightly while the addition of Ag20 increased the yield. Moreover, the addition of FeS to a non-slag mortar changed the radiolysis mechanism but the addition of FeO did not. The results of these experiments provided an insight into the nature of the radiolytic reactions occurring in the mortar formulations and indicated that the radiolytic generation of gases might be controlled with the proper choice of additive.
Potentiodynamic Polarization Studies of Candidate Container Materials in Simulated Tuff Repository Environments
Authors: Beavers John A. , Thompson Neil G. , Harper William V.
Published: March 2011

Cortest Columbus is investigating the long-term performance of container materials used for high-level waste packages as part of the information needed by the Nuclear Regulatory Commission to assess the Department of Energy's application to construct a geologic repository for high-level radioactive waste. In one task of the program, a cyclic potentiodynamic polarization (CPP) technique was used to evaluate the corrosion behavior of the candidate container materials. In order to evaluate the expected range of environmental variables, a statistical experimental design approach was used. A Resolution IV experimental design for 15 variables was selected. The variables included temperature, pH, species present in the groundwater, and those generated by radiolysis. Complete matrices of CPP tests, which consist of tests in 33 environments, were performed on two candidate container materials; Type 304L Stainless Steel and Incoloy Alloy 825. In these tests, both alloys exhibited a wide range of behavior; including passive behavior, pitting and active corrosion. For each alloy, the environmental variables that affected corrosion behavior were identified.
Verfication of matrix diffusion by means of natural decay series disequilibria in a profile across a water-conducting fracture in granitic rock
Authors: Alexander W.R. , McKinley I.G. , MacKenzie A.B. , Scott R.D.
Published: March 2011

Data from a rock drillcore, taken perpendicular to a water-bearing fracture in crystalline rock, clearly indicate water-rock interactions in and around the fracture. Although there is evidence of microfracturing at some distance from the main fracture, and therefore potential advective flow across the entire shear zone, simple calculations indicate that transport of Ra-226 in the vicinity of the main fracture can be described simply by matrix diffusion. This is a useful simplification for safety assessment studies and the consequences to the estimated radionuclide retardation in the vicinity of the fracture are discussed with respect to the probably over-conservative assumptions made in Nagra's safety assessment model base case.
The Solubility and Sorption of Uranium (VI) in a Cementitious Repository
Authors: Brownsword M , Buchan A B , Ewart F T , McCrohon R , Ormerod G J , Smith-Briggs J L , Thomason H P
Published: March 2011

The solubility behaviour of uranium(VI) has been studied in a number of waters representative of the pore waters to be expected in candidate repository backfill concretes and also in solutions of calcium and sodium hydroxides. The sorption of uranium has been studied on one of these candidates, a Portland cement with a slag filler. The same cement has been hydrothermally treated to simulate the temperature conditions in the repository and the product used for comparative studies.

The paper describes the experimental measurements and the results. The aqueous concentration of uranium over the uranates formed in the presence of sodium and calcium hydroxides was constant above pH 7 at 3 × 10−6 M. In the concrete pore waters the solubility of uranium was equal to or lower than this value. The distribution coefficient, Rd, for the sorption of uranium onto the slag cement was 2.5 × 104 ml g−1, and was increased by a factor two after hydrothermal treatment.
Modelling and Experimental Studies of Sorption in the Near Field of a Cementitious Repository
Authors: Brown P.L. , Haworth A. , McCrohon R. , Sharland S.M. , Tweed C.J.
Published: March 2011

A joint experimental and modelling programme is reported, which aims to improve our understanding of sorption processes of radionuclides onto repository materials. Diffusion/sorption experiments of sorption onto cement are described, although results are limited at this stage. The modelling studies use the coupled chemical equilibria and transport code CHEQMATE to simulate some of these experiments. The chemical part of the model is based on a simple mass-action model of sorption. More detailed comparisons will continue when the experiments are terminated, and the samples are sectioned.
Study on Relation Between Migration Behaviors and Chemical Forms of Cobalt
Authors: Ueta Shinzo , Katoh Naotake
Published: March 2011

Migration experiments focused on the relationship between sorption mechanism and chemical form of cobalt were carried out by means of column method. Adsorbents packed in the column were natural sand and artificial materials, for instance, charcoal. The experimental results were compared with three different migration models based on ion exchange, filtration, and adsorption, respectively.

Cobalt existed as cation in the low pH region, where the migration behavior of cobalt was described by the ion exchange model. Cationic and colloidal species of cobalt coexisted in the pH 8.5 solution. The migration behavior of cobalt in this solution was satisfactorily described by the coupled model of the ion exchange and the filtration. Chelated anionic cobalt was not retained on the sand but retained on the charcoal and the other artificial materials to considerable extent. Breakthrough curves of cobalt in the charcoal column were successfully described by the adsorption model. Chelated cobalt was retained on the charcoal better than cationic cobalt. Distribution coefficients of chelated cobalt and cationic one were 670 ml/g and 130 ml/g, respectively.
Thermal Behaviour of Backfill Material for a Nuclear Fuel Waste Disposal Vault
Authors: Yong R.N. , Mohamed A.M.O. , Cheung S.C.H.
Published: March 2011

The concept of disposing of used nuclear fuel in engineered rock formations is being studied in the Canadian Nuclear Fuel Waste Management Program. After the used fuel is emplaced in the vault, the vault would be backfilled. The backfill has to satisfy a number of engineering requirements. A reference backfill with satisfactory hydraulic, thermal and mechanical properties has already been selected.

As the used fuel in the waste containers decays, heat will be generated and this heat will raise the temperature of the backfill material. The performance of the reference backfill material was evaluated over the temperature range 20–100°C. This paper addresses the results of experiments on thermal response and pressure development in the backfill for the period shortly after vault closure.
Multifractal Phenomena in Porous Rocks
Authors: Muller J. , Hansen J.P. , Skjeltorp A.T. , Mccauley J.
Published: March 2011

The multifractal spectra of porespace of different types of porous sedimentary rocks are obtained using optical microscopy and a boxcounting technique. The computed f(α) functions were based on the canonical formalism, and can be used as a tool for rock characterization.
The Application of a Coupled Chemical Transport Model in a Trial Assessment of Deep Disposal of Low and Intermediate Level Radioactive Waste
Authors: Liew Steve K. , Economides Vea , Dawes Adrian , Read David
Published: March 2011

A series of trial assessments are being undertaken within the United Kingdom to rehearse procedures for post-closure radiological risk analysis of low and intermediate level radioactive waste disposal sites. These trial or “Dry Run” studies draw together workers from a variety of scientific disciplines allowing simultaneous rather than isolated development of assessment procedures. This paper illustrates the use of chemical codes and data within a probabilistic risk assessment framework through a demonstration exercise performed on a hypothetical repository located beneath Harwell, Oxfordshire. The implications for risk assessment practices reliant on the assumption of “conservative” parameters are highlighted by comparison with a more mechanistic approach which takes into account competitive effects.
PGSE-NMR & Sans from TPB Based Microemulsions
Authors: Lindemuth Paul M. , Hammouda Boualem , Duke Joseph R. , Blum Frank D. , Venable Raymond L.
Published: March 2011

Self-diffusion coefficients from pulsed-gradient spin-echo NMR are reported for four components of the tetradecylpyridinium bromide - 85% heptane/15% pentanol - water pseudoternary system. Measurements were taken throughout the inverted microemulsion region and also in a small isotropic region beyond the domain of lamellar liquid crystals. Observations of the self-diffusion coefficients for water relative to those of the surfactant, oil and alchohol show several distinct structural transitions within the water-in-oil region of the phase diagram. The smaller isotropic region exhibits a complete inversion of phase relative to the water-in-oil region. Conductivity measurements were used to further clarify the NMR data. Subsequent small angle neutron scattering (SANS) measurements on the same system show the transition from the single particle (heavy water + Stern layer droplet) scattering regime at low water concentration to the mixed single/interdroplet scattering regime when the intermicellar distance becomes comparable to the size of the micelles.
Curvature Elasticity of Block Copolymers and the Structure of Emulsified Polymer Blends
Authors: Wang Zhen-Gang , Safran S. A.
Published: March 2011

We consider the curvature elastic properties of a layer of block copolymer at the interface between two incompatible homopolymers. We focus on the relation between the relative lengths of the blocks and the elastic properties of the interfacial layer which determines the phase behavior. The curvature elastic moduli K and K, as well as the spontaneous curvature, c0, are obtained. The curvature free energy is used to predict the relative stability of spherical, cylindrical, lamellar, and ordered bicontinuous saddle-shaped structures as functions of concentration and polymer properties.
Nematic-Smectic a Phase-Transition Under Shear Flow
Authors: Bruinsma R. F. , Safinya C. R.
Published: March 2011

We discuss the effect of shear flow on the nematic to smectic A phase transition. The non-Newtonian flow properties (shear thinning and normal stress) ire correlated with the distortions of the structure-factor S(q). As a function of the Deborah number, we find first a deformation of S(q) and, beyond a critical Deborah number, highly distorted, one-dimensional fluctuations. The suppression of fluctuations by shear flow raises the critical temperature.
On Shear Thinning in Dilute Polymer Solutions
Authors: Rabin Yitzhak , Öttinger H. C. , Kawasaki K.
Published: March 2011

While recent remrmalization group studies predict shear thickening in the limit of large Weissenberg numbers, scaling theories predict shear thinning. The ocntroversy is related to the question whether the Weissenberg number or the shear rate should be kept fixed when taking the limit of infinitely long polymers.
Cooperative Effects in Strained Polymeric Networks
Authors: Deloche B , Sotta P , Herz J
Published: March 2011

The orientational order generated in a polymer network by an uniaxial stress is probed with NMR. The experiments are performed on an end-linked polydimethylsiloxane network. When a uniaxial force is applied a detailed analysis of the spectrum shows that the segmental motions become uniaxial around constraint direction. This experimental fact is explained by shortrange orientational interactions between chain segments.
Colloidal Particles of Noble Metals; A Route to Produce New Materials I
Authors: Hernández R. , Váquez A. , Díaz G. , Avalos M. , José-Yacamán M.
Published: March 2011

In the present paper we report the growth of monometallic and multimetallic particles from the reduction of metal sols. In particular the Au and Au–Pd alloys are reported on this work. A number of techniques are applied to the characterization of the particles. It is shown that particles from few nanometers to 100 pm can be prepared with a number of shapes and morphologies. Particularly conspicuous are the shapes with a five–fold symmetry axis.
Rheology of Phase Separated Block Copolymer Melts
Authors: Winter H. Henning , Morrison Faith A.
Published: March 2011

Flow can transfer the microphase separated morphology of block copolymers into a state of global order. For tri-block copolymers with cylindrical domains, this has been demonstrated by Folkes et al. (1973) and Hadziioannou et al. (1979). who established the existence of ‘single crystals’ of hexagonally ordered cylinders with uniform director throughout a sheared sample. The director is aligned with the shear direction. In this study, we investigate the flow induced ordering of cylindrical domain structure at increasing levels of shear.
Two-Component Grafted Polymer Layers
Authors: Witten T. A. , Milner S. T.
Published: March 2011

We report a theoretical study of the equilibrium statistical mechanics of polymer chains end-grafted in the dense liquid state to a surface. We consider the special features which arise when two immiscible polymer species are present. In constrast to ungrafted polymer blends, this system has two distinct scaling regimes of strong immiscibility: endsegregated and fully segregated. We discuss the mixing energy and bistability properties in each regime using approximations valid for large chain elongation.
Surface Hydrodynamic Modes on Concentrated Polymer Solutions and Gels
Authors: Harden J. L. , Pincus P. A. , Pleiner H.
Published: March 2011

We present a coupled two-fluid model for hydrodynamic surface modes on concentrated polymer solutions and swollen polymer gels. This model is used to investigate such surface modes in the limit of strong coupling. We discuss the form of the modes as a function of polymer concentration and the effects of chain diffusion and surface tension on the nature of these modes.
“Aggregation in Block Copolymer Solutions”
Authors: de la Cruz M. Olvera
Published: March 2011

The ability to produce block copolymers has led to new materials with unique properties. The chemical connectivity of incompatible blocks forces segregation to occur at distances of the order of the block sizes. In block copolymer melts, the segregated domains form periodic ordered structures called microphases. Most block copolymers are strongly incompatible. In such cases, in order to ensure equilibrium microphase separated samples, the microphases are prepared from solution. Microphase separation in semidilute solutions of block copolymers in nonselective good solvent is analyzed. The solvent effects on the thermodynamics in the weak segregation limit are discussed. The concentration of block copolymer at the transition in good solvents, scales as φtN−.62and in ϑ solvents as N−.5. The transitions between microphase morphologies as a function of block copolymer concentration are studied.
Fluctuations in Phases of Membranes
Authors: Roux Didier
Published: March 2011

Surfactants in solution may associate into two dimensional aggregates (membranes) which self-organize either in liquid crystalline phases or in liquid isotropic phases made of connected bilayers. When specially designed surfactants or mixture of surfactants are used the elastic modulus of these membranes may be of the order kBT. In this case, thermal fluctuations are important and lead to interesting predictions among which the existence of undulation forces and logarithm corrections to thermodynamical properties, characteristic of fluctuations in two dimensional systems, have been observed experimentally.
Enhanced Adhesion From High Energy Ion Irradiation
Authors: Werner B. T. , Vreeland T. , Mendenhall M. H. , Qui Y. , Tombrello T. A.
Published: March 2011

We have found that irradiation of a variety of thin film–substrate combinations by heavy ion beams at energies of mega-electronvolts per atomic mass unit will produce a remarkable enhancement in the adherence of the film. For example, gold films can be firmly attached to soft materials such as Teflon using a 1 MeV beam of protons (1014 cm−2) or helium ions (1013 cm−2) and to harder materials such as silicon (1015 cm−2), quartz (2×1015 cm−2) and tungsten (2×1014 cm−2) with 0.5 MeV a.m.u.−1 beams of fluorine or chlorine ions. In the case of metal films on semiconductors a low resistance contact results. The mixed layer at the interface is observed to be quite thin (approximately 50 Å or less); for silver on silicon electron diffraction and imaging studies of the interface region reveal the presence of crystalline silver compounds.
Surface Morphology and Electronic Properties of ErSi2
Authors: Wu C. S. , Lau S. S. , Kuech T. F. , Liu B. X.
Published: March 2011

The surface of ErSi2, formed by the reaction of thin erbium layers with a singlecrystal silicon substrate, is typically dominated by deeply penetrating regularly shaped pits. These pits are shown to have detrimental effects on the electronic performance of Schottky barrier diodes. Surface pits may be reduced in density or eliminated entirely (i) by the use of silicon substrate surfaces prepared under ultrahigh vacuum conditions prior to metal deposition, (ii) by means of ion irradiation techniques or (iii) by reacting erbium with an amorphous silicon (a-Si) layer. In this investigation, planar ErSi2 layers (pit free) are made using the third approach with a sample structure of a-Si/Er/c-Si where c-Si denotes crystalline silicon. The fast reaction between a-Si and erbium leads to a planar sample structure of ErSi2/c-Si with little or no reaction between erbium and the c–Si substrate. The electronic performance of pit–free ErSi2 diodes made in this manner is shown to be much superior to that of diodes made by reacting erbium with silicon substrates.
Behavior and Influence of Oxygen in Chromium Silicide Formation
Authors: Lien C.-D. , WieluŃski L. S. , Nicolet M.-A. , Stika K. M.
Published: March 2011

We investigated the redistribution of oxygen after a thermally induced reaction of an evaporated chromium film deposited on an Si<100> substrate. To monitor the redistribution, 18O was implanted in the metal film or in the silicon substrate. Depth profiles were determined by the isotope-specific reaction 18O (p,α) 15N before and after thermal annealing. Silicide formation was monitored by 2 MeV 4He+ backscattering spectrometry.

It was found that oxygen in the chromium film remains stationary with respect to the chromium during silicide formation, but oxygen in the silicon substrate accumulates at the silicon-silicide interface. The phase formed is CrSi2, as for the unimplanted reference samples. The effect of oxygen on the rate of silicide formation is much more pronounced when the oxygen is in the silicon substrate rather than in the chromium film. This asymmetry is attributed to the fact that silicon is the dominant diffusing species during CrSi2 formation. These results are contrasted with those for nickel and platinum, where the metal moves in the silicide formed by these metals.
Schottky Contacts on Annealed GaAs
Authors: Miles R. E. , Tasker P. J. , Morgan D. V. , Howes M. J.
Published: March 2011

Unimplanted n-type GaAs epitaxial layers have been annealed under the same conditions as those required to activate ion implants. If the duration of the anneal is sufficiently long (e.g. 10 min at 800°C) acceptor ions accumulate at the surface with a concentration of about 2×1022 m−3. Schottky contacts to annealed samples always show increased current densities up to six orders of magnitude greater than those in unannealed layers. This has the effect of lowering the Q values of varactor diodes made out of this material, up to frequencies of 1 GHz.
Energy-Dependent Photoemission in the Study of Silicon-d Metal Interfaces
Authors: Braicovich L.
Published: March 2011

New results are presented on the dependence on energy hv of the photoemission cross sections from d states of d atoms interacting with silicon (Si-Pd and Si-Ag). It is shown that the Cooper minimum is influenced by the atomic environment and that the Cooper effect is more pronounced when the interaction between the d atom and silicon becomes weaker. This approach together with an analysis of the shape of photoelectron spectra at the Cooper minimum is used in a discussion of the electron states in the reacted region of Si-Pd and Si-Mo interfaces.
Metallurgical Reactions in Au/(In–Ge) Ohmic Contacts to GaAs
Authors: Grovenor C. R. M.
Published: March 2011

The Au/(In–Ge) contact to GaAs was investigated to discover the metallurgical structure of the contact–GaAs interface. A variety of intermetallic phases in the form of precipitate particles or thin films were identified, and their presence was correlated with the temperature at which the contacts were fired. The possibility of predicting the structures of the fired contacts from simple metallurgical phase diagrams is discussed, and some evidence on the influence of the precipitating phases on the electrical character of the contacts is reviewed.
Surface Imaging of III–V Semiconductors by Reflection Electron Microscopy and Inner Potential Measurements
Authors: Yamamoto N. , Spence J. C. H.
Published: March 2011

Surfaces of two III–V semiconductor materials have been examined at 120 kV by reflection electron microscopy (REM) at high spatial resolution. Surface steps were found to give characteristic contrast due to several diffraction effects, one of which is interference between the Bragg (B) and Bragg–Laue (BL) reflected beam at a step edge. The electron diffraction pattern from a step showed split lines from B and BL reflections, which provides a method of accurately measuring the mean inner potential of these materials. Electron energy loss spectra showed large surface and bulk plasmon peaks which mainly limit the spatial resolution of REM. The penetration depth in REM is given.
Amorphous Thin Film Diffusion Barriers on GaAs and InP
Authors: Anderson W. T. , Christou A. , Davey J. E.
Published: March 2011

Thin film amorphous W-Si and TiW-Si diffusion barriers have been studied on GaAs and InP surfaces for the purpose of establishing their reliability for ohmic contacts and Schottky barriers, particularly under high temperature stress. The amorphous films were formed by a new method in which alternate layers of tungsten or TiW and silicon were sputter deposited to a total thickness of about 1300 Å and subsequently annealed near the glass transition temperature Tg(≈ 500 °C). Electron channeling and reflection electron diffraction were used to determine the amorphous nature of the films as deposited and after 4 h anneals near Tg. The as-deposited films had interfacial amorphous regions with compositions determined by interfacial reactions during the sputtering process. As-deposited W-Si films showed a weak channeling pattern which came from the unreacted polycrystalline tungsten layers. From Auger electron spectroscopy (AES) sputter profiles, it was concluded that the amorphous regions were at the W-Si interfaces which had the required tungsten-to-silicon composition ratio. After annealing at 500 °C for 4 h, the films were completely amorphous with no marked evidence of crystallization, indicating interfacial reactions extended completely into the tungsten layers. High magnification scanning electron microscopy (by a factor of 20 000) examination of the films after annealing revealed smooth and continuous surfaces with no evidence of grain boundaries. Diffusion along grain boundaries between gold and GaAs or InP in these amorphous thin films was thus almost completely eliminated. Interdiffusion of gold in layered structures (e.g. Au/(W–Si)/GaAs) was studied by AES sputter profiling techniques. No interdiffusion of gold or GaAs was observed after 16 h anneals at 400 °C. With Au/(W-Si)/InP structures, no interdiffusion was observed after 8 h anneals at 450 °C. These results are significant improvements over those for previous polycrystalline diffusion barriers (e.g. TiPt) which degrade after 1 h at 350 °C. Based on the AES sputter profiles, the diffusion coefficients in W-Si amorphous thin films were found to be less than 3 × 10−18 cm2 s−1 at 400 °C for gold, gallium and arsenic and less than 6 × 1018 cm2 s−1 at 450 °C for gold, indium and phosphorus.
ZrN Diffusion Barrier in Aluminum Metallization Schemes
Authors: Krusin-Elbaum L. , Wittmer M. , Ting C.-Y. , Cuomo J. J.
Published: March 2011

We have studied reactively sputtered ZrN, the most thermally stable of the refractory metal nitrides, for its diffusion barrier properties in aluminum metallization schemes with Rutherford backscattering spectroscopy and transmission electron microscopy (TEM). We find this compound to be very effective against aluminum diffusion up to 500 °C, independently of substrate temperature during sputtering. The useful temperature range can be extended by 50 °C with proper preannealing prior to aluminum deposition. The TEM study of the ZrN grain size as a function of annealing temperature revealed that the grain size does not change significantly upon annealing and that the grains are relatively small even at the highest annealing temperatures (about 300 Å at 900 °C). In addition, for annealing temperatures of and below 500 °C large portions of ZrN films were found to be of either amorphous or extremely fine–grain material, thus inhibiting the diffusion along grain boundaries. The presence of Zr3Al4Si5 ternary compound in samples annealed at 600 °C, as determined by X-ray analysis, may suggest that the ZrN barrier fails by decomposition of the film by aluminum.
Spectroscopic Characterization of a Pre-Ceramic Polymer For Sic/Tic System.
Authors: Babonneau Florence , Barre Patrice , Livage Jacques , Verdaguer Michel
Published: March 2011

Polytitanocarbosilane precursor for SiC/TiC ceramics was characterized by various spectroscopic techniques (29Si and 13C CP MAS NMR, Ti K-edge XANES and EXAFS) in order to follow how titanium ions are incorporated into the polycarbosilane-based polymer. This polymer has been fired in argon atmosphere, and the evolution of the local environments of Si and Ti atoms, during the pyrolysis process, have been followed using 29Si MAS-NMR and Ti K-edge X-ray absorption: this study reveals the formation of Si-O bonds above 500°C, while Ti-C bonds clearly appear around 800°C. Above 1000°C, Si-O bonds are consumed by reaction with excess carbon and the system finally crystallizes into SiC/TiC mixture above 1200°C.
Small-Angle Neutron Scattering and 27Al Nmr Studies on the Microstructure and Composition of Alumina Sol-Gels
Authors: Nazar L. F. , Napier D. G. , Lapham D. , Epperson E.
Published: March 2011

We have used small angle neutron scattering, static light scattering and 27Al NMR to examine the structure and composition of alumina sol-gels formed by the hydrolysis of aluminum alkoxides. For LT sols at low acid concentrations, and HT gels over a wide range of acid concentration, 27Al solution NMR suggests, by the dearth of spectral resonances, that high molecular weight species are being formed. Analysis of the small angle neutron scattering data in the Porod regime indicates these sol-gels exhibit a power-law dependence consistent with mass fractal dimensions ranging from 1.45 to 1.8. These fractal dimensions are consistent with models based on diffusion limited cluster aggregation. The fractal dimensions do not differ significantly between LT and HT sols at the same acid concentration. However, for both temperature regimes, the fractal dimension increases with increasing acid concentration, suggesting a progression to a more compact network. Static light scattering measurements indicate the Guiner radii of the cluster aggregates vary from 600 to 2000Å.
Precipitation of Uniform Particles: The Role of Aggregation
Authors: Zukoski C.F. , Chow M. K. , Bogush G.H. , Look J-L.
Published: March 2011

The conventional mechanism developed by LaMer (1) is often considered as the most relevant model for describing the precipitation of uniform particles. In this model, the concentration of a species is slowly increased above its equilibrium value until a critical concentration is reached and nucleation occurs. The resulting particles consume soluble species and the supersaturation level is reduced until there is a balance between particle growth and the generation of reactive species. At this point nucleation stops. Particle growth then continues by molecular addition of soluble species to the growing particles. Uniformity is achieved through a short nucleation time and a particle growth mechanism where the small particles grow more rapidly than the large particles.
Shear Indxuced order of Cncenirated Dispersions
Authors: Ackerson Eruce J. , Morris T .A.
Published: March 2011

The microstructure or interparticle ordering in concentrated dispersions of colloidal pmma (polymethylnethacrylate) particles in a mixture of tetralin and decalin have been monitored using light scattering techniques. These sterically stabilized, uniformly sized, nearly hard, colloidal spheres are observed to exhibit an equilibrium phase transition from a liquid-like ordering to a crystal-like ordering of suspended particles as the volume fraction of solids increases. The crystals have a close packed - random stacked structure. At the largest volume fractions a nonequilibrium glassy phase results.

Samples at different volume fractions are subjected to steady and oscillatory shear flow. Four basic structures are observed to exist: liquid or distorted liquid-like, string-like, sliding or randomly stacked layers, and face centered cubic (FCC) structures. Oscillatory shear studies will be reported here and are made as a function of strain amplitude and shear history, in addition to volume fraction. Generally, oscillatory shear is effective in ordering samples. For example, an unstable FCC ordering can be induced in an equilibrium liquid-like sample.
Consolidation of collodal suspensions
Authors: Shih Wei-Heng , Il Kim Seong , Shih Wan Y. , Schilling Christoeher H. , Aksay Ilha A.
Published: March 2011

A key step in the processing of ceramics is the consolidation of powders into engineered shapes. Colloidal processing uses solvents (usually water) and dispersants to break up powder agglomerates in suspension and thereby reduce the pore size in a consolidatd compact. However, agglomeration and particle rearrangement leading to pore enlargement can still occur during drying. Therefore, it is beneficial to consolidate the compact asdensely as possible during the suspension stage. The consolidation techniques of pressure filtration and centrifugation were studied and the results are reported in this paper. In particular, the steady-state pressure-density relationship was studied, and information was obtained regarding the consolidation process, the microstructure, and the average density profile of consolidated cakes. We found that the compaction processes in these two consolidation methods are quite different. In general, a consolidated cake is a particulate network made up of many structural units which are fractal objects formed during aggregation in the suspension. In pressure filtration, compaction is a process of breaking up the fractal structural units in the particulate network by applied pressure; the resulting partie rearrangement is produced by overcoming energetic barriers which are related to tee packing density of the compact. Recently, we performed Monte Carlo simulations on a cluster-cluster aggregation model with restructuring,1 and found the exponential relationship between pressure and density is indeed the result of the breaking up of the fractal structural units.2 On the other hand, in centrifugation, compaction involves the rearrangement of the fractal structural units without breaking them so that the self-similar nature of the aggregates is preserved. Furthermore, we calculated density profiles fom the bottom to the top of the cakes by solving the local static force balance equation n the continuum particulate network. In pressure filtration of alumina and boehmite, the cakes are predicted have uniform density. The results of γ-ray densitometry3 on a pressure-filtrated alumina cake confirmed this prediction. In contrast, in centrifugation, the density profiles are predicted to show significant variation for cakes on the order of one centimeter high. Moreover, the pressure-filtered boehmite cakes showed no cracking during drying. This indicated that pressure filtration is a good consolidation technique for nanometer-sized particles such as boehmite. The improved drying property is probably a result of a minimal shrinkage due to the formation of higher packing densities during filtration.
29Si Nmr Study of Silicon Alkoxides: from the Condensation Kinetics in Solution to the Determination of The Fractal Dimension in Aerogels
Authors: Devreux F. , Boilot J.P. , Chaput F. , Lecomte A.
Published: March 2011

The complete condensation kinetics of three silicon alkoxides have been studied by 29 Si NMR in the conditions of rapid hydrolysis (acidic medium, water in excess). The gelation of the tetravalent TEOS takes several weeks, whereas the trivalent MTEOS and VTEOS do not form gels. From a quantitative data analysis, we deduce that the first steps of the condensation proceed by progressive formation of small organized units. This accounts for the occurence of highly condensed agglomerates, the absence of gelation in trivalent systems and the very slow kinetics (logarithmic function of time). For the tetravalent TEOS, this is followed by an aggregation phase, which leads to gelation. After the gel time, the transformation of the sol fraction into gel has been followed by observing the broadening of the static NMR spectra. Moreover, the structures of the aerogels obtained by hypercritical drying and of the densified materials resulting from further sintering are characterized by MAS NMR. In particular, measurements of the nuclear relaxation in samples doped with paramagnetic impurities give directly the fractal dimension D of the silicate lattice. The measured value is in agreement with that obtained by the SAXS technique in aerogels (D≈2.2) and is close to D=3 for the densified materials.
Molecular Orbital Modeling of Water Adsorption on a Tetrasiloxane Ring
Authors: West J. K. , Wallace S.
Published: March 2011

A water molecule hydrogen bonded to a surface SiOH group produces an IR vibrational transmission peak (ν3) at 2.82 μm. Water was adsorbed into the pores of a metal alkoxide derived silica gel monolith, and the increase in the wavelength of the first vibrational overtone (2ν3) of this peak was measured as a function of the adsorbed water content W (g H2O/g SiO2). The peak shifted from 1.390 to 1.420 μm as W increased by 0.14 g/g. Intermediate Neglect of Differential Overlap (INDO) Molecular Orbital (MO) theory was used to model this process. The effect of a H2O molecule, hydrogen bonded to a hydroxylated tetrasiloxane ring, on the structure of the ring and the water molecule was investigated. The bond length of the O-H group H-bonded to the water molecule increased, as expected from the increase in wavelength of the 2ν3 IR peak.
Formation Of Spinel Iron Oxide In Solution
Authors: Jolivet Jean Pierre , Tronc Elisabeth , Belleville Philippe , Livage Jacques
Published: March 2011

The alkalizing of aqueous mixtures Fe111 + xFe11 has been investigated at pH ≈ 8 for 0≤x≤0.5. Three composition zones have been observed. At x0.25 the system, made of spinel particles, was homogeneous during all the evolution.
Characterization Of Ultralow-Density Silica Aerogels Made From A Condensed Silica Precursor
Authors: Hrubesah Lawrence W. , Tillotson Thomas M. , Poco John F.
Published: March 2011

Silica aerogels having densities in the range of 0.003 to 0.05 g/cm3, have been prepared from a condensed silica formulation involving a two-step hydrolysis/condensation process with tetramethoxysilane (TMOS). This work describes the preparation of these unique ultralow-density aerogels, and compares several of their properties with those of aerogels made by a single step, base catalysed process.
Microstructural Dependence Of Aerogel Mechanical Properties
Authors: Lemay J.D. , Tillotson T.M. , Hrubesh L.W. , Pekala R.W.
Published: March 2011

Aerogels are highly porous solids derived from the hypercritical drying of covalently crosslinked gels. SEM, TEM and scattering studies reveal that these materials have an open-cell morphology with a solid matrix composed of interconnected colloidal-like particles (30–200 A) Processing variables and synthetic conditions largely determine the microstructure and morphology. In this study, the structure-mechanical property relationships of silica, resorcinolformaldehyde, and carbon aerogels are examined.
The Effects of Hydrolysis Conditions, and Acid and Base Additions, on the Gel-To-Ceramic Conversion in Sol-gel Derived PbTio3
Authors: Schwartz Robert W. , Lakeman C. D. E. , Payne D. A.
Published: March 2011

Lead titanate was prepared by the sol-gel processing of metal alkoxide solutions. The effects of hydrolysis level (i.e., moles H2O/mole PbTiO3) and acid and base additions (HNO3 or NH4OH) on the properties of desiccated gels, and the gel-to-ceramic conversion, were studied. Microstructural, structural, and physical properties were characterized at three stages of the processing cycle: (i) the desiccated gel state; (ii) the amorphous state, following organic pyrolysis; and (iii) the crystalline state. Differences in the physical and structural properties for the desiccated gels, which were induced through manipulation of the hydrolysis conditions, persisted in the amorphous state after organic pyrolysis. Minor differences remained after crystallization. Variations in material properties, with low temperature processing (e.g., the gel-to-glass transformation), were considered from the standpoint of hydrolysis and additive effects on the gel network structure and consolidation behavior. Data are reported for the densification and crystallization behavior for the gels. Through proper control of hydrolysis conditions, relatively dense ceramics were obtained at temperatures as low as 700°C.
Properties of Films Prepared from Low Surface Area/Density Alumina-Silica
Authors: Hietala S.L. , Smith D.M. , Hietala V.M. , Frye G.C. , Hurd A.J. , Brinker C.J.
Published: March 2011

A sol-gel method was used to prepare bulk, closed pore, amorphous alumina-silica. Films
prepared from this 47wt% A12O3-SiO2 composition were examined by SAW, ellipsometry and electrical measurements. The films were found to have a surface area of 1.1 cm2/cm2, a refractive index of 1.44 at 633 nm, and a relative permittivity of 6.2 at 200 KHz. These properties indicate potential applications as hermetic seals, barrier coatings, dielectric layers for capacitors and passivation coatings for electronic circuits.
Molecular Structure Of Metal Alkoxide Precursors
Authors: Sanchez C. , Toledano P. , Ribot F.
Published: March 2011

Oxo-alkoxides and allied derivatives are the organic counter part of polyanions and polycations. Most of them do not lead to further polymerization and are therefore dead endswhich are grnerally not directly involved in the formation of macromolecular oxide networks. However their well defined structure make them good models for the basic understanding of the first steps of hydrolysis- condensation reactions. The structural characterization of a new metal oxo species Ce6(μ3-O)4(μ3-OH)4(acac)12 obtained via the hydrolysis of acetylacetone modified cerium isopropoxide is presented. Possible mechanisms of formation of this compound as well as for some other titanium Ti6(μ2-O)2(μ3-O)2(μ2-OAc)4(μ2-OPri)6(OPri)6 and niobium Nb8O10(OEt)20 based oxo-alkoxides will be discussed.
Molecularly Modified Alkoxide Precursors for Synthesis of Dielectric Ceramics.
Authors: Phule Pradeep P. , Khairulla Farida
Published: March 2011

Chemical synthesis of titanate and zirconate based multicomponent electronic ceramics using molecularly modified alkoxide precursors is discussed. Controlled chemical polymerization of the modified alkoxides was conducted to prepare multicomponent gels which on calcination at moderate temperatures (700 – 1000°C) formed high purity, ultrafine powders (e.g. BaTiO3, ZrTiO4, LiTaO3). In the sol-precipitation technique modified precursors were used to prepare ultrafine (< 100 nm) and crystalline powders of such ceramics as BaTiO3 and BaZrO3 at low temperatures (< 100°C), under highly alkaline (pH > 13) conditions.
Crystallization of In-Situ SiC-Mullite Composites from Multicomponent Alumina-Silica Gels
Authors: Jagota S. , Parvizi-Majidi A.
Published: March 2011

Silica and alumina gels were mixed to make a hybrid of a mullite precursor gel and a silicon carbide precursor gel. The crystallization of these above 1400 °C, to form in-situ composites of silicon carbide whiskers in a matrix of mullite, cristobalite and a glassy phase, was studied for different processing conditions.
Sol-Gel Coatings on Acoustic Wave Devices: Thin Film Characterization and Chemical Sensor Development
Authors: Frye Gregory C. , Jeffrey Brinker C. , Ricco Antonio J. , Martin Stephen J. , Hilliard Janice , Doughty Daniel H.
Published: March 2011

We have investigated the use of porous oxide coatings, formed using sol-gel chemistry routes, as the discriminating elements of acoustic wave (AW) chemical sensors. These coatings provide several unique advantages: durability, high adsorption capacity based on large surface areas, and chemical selectivity based on both controlled pore size and acid/base, ion exchange or chelation chemistry. The porosity of these coatings is determined by performing nitrogen adsorption isotherms using the AW device response to mass changes to monitor the uptake of nitrogen at 77 K. These studies demonstrate how sol-gel chemistry and film deposition can be combined to tailor the microstructure of thin oxide coatings. The chemical sensitivity and selectivity obtained with this class of coatings will be demonstrated using several examples: hydrous titanate ion exchange coatings, zeolite/silicate microcomposite coatings, and surface-modified silicate films.
Crystallization Kinetics Of Metallo-Organics Derived Pzt Thin Film
Authors: Chen K.C. , Mackenzie J. D.
Published: March 2011

PZT films on fused silica substrates were prepared by a multiple dipping-firing process from a stable solution of titanium isopropoxide, zirconium n-propoxide and lead 2- ethylhexanoate. The crystallization kinetics of the amorphous PZT films was studied by quantitative X-ray analysis. The crystallization of the amorphous film to perovskite phase
involved a transitional pyrochlore structure phase. The entire crystallization was described by a consecutive phase transformation process in which nucleation dominated.