bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Mechanical Strengths for Simulated High-Level Waste Forms
Authors: Igarashi Hiroshi , Takahashi Takeshi
Published: March 2011

Waste forms have been developed and characterized at PNC (Power Reactor and Nuclear Fuel Development Corporation)to immobilize high-level liquid waste generated from the reprocessing of nuclear spent fuel.

Mechanical strength tests were excecuted on simulated solidified highlevel waste forms which were borosilicate glass and diopside glass-ceramic. Commercial glass was tested for comparison. Measured strengths were three-point bending strength,uniaxial compressive strength,impact strength by falling weight method,and Vickers hardness. Fracture toughness and fracture surface energy were also measured by both notch-beam and indentation technique.

The results show that mechanical strengths of waste glass form are similar and that the glass ceramic form has the higher fracture toughness.
Oxidation of UO2 Fuel by Radicals Formed During Radiolysis of Water
Authors: Sunder S. , Shoesmith D.W. , Christensen H. , Miller N.H. , Bailey M.G.
Published: March 2011

The effects of radicals, formed during radiolysis of water, on the oxidation and dissolution of U02 were investigated as a function of dose rate and total dose. The U02 oxidation rate during radiolysis was monitored by recording the corrosion potential of a U02 electrode as a function of time. Changes in the surface of U02 were determined using cathodic stripping voltammetry (CSV) and X-ray photoelectron spectroscopy (XPS). Our studies suggest that the oxidation of U02, in irradiated de-oxygenated solutions consists of two stages. The first stage consists of the growth of a surface film of composition close to U02.33 and of thickness similar to that obtained (over longer exposure periods) in unirradiated oxygenated solutions. The rate of growth of this film appears to be proportional to the square root of the dose rate. The second stage consists of oxidative dissolution of this film (as U02+2). This step mainly occurs at higher doses. Relative rates of oxidation of U02 to U02.33, the first stage, were obtained in four different solutions favouring the formation of selected radicals.
Corrosion Product Identification and Relative Rates of Corrosion of Candidate Metals in an Irradiated Air-Steam Environment
Authors: Reed Donald T. , Swayambunathan V. , Tani B. S. , Van Konynenburg Richard A.
Published: March 2011

Previously reported work by others indicates that dicopper trihydroxide nitrate, Cu2NO3(OH)3, forms on copper and copper alloys subjected to irradiated moist air near room temperature. We have performed experiments over a range of temperature and humidity, and have found that this species is formed at temperatures up to at least 150° C if low to intermediate relative humidities are present. At 150°C and 100% relative humidity, only Cu2O and CuO were observed. The relative general corrosion rates of the copper materials tested in 1-month experiments at dose rates of 0.7 and 2.0 kGy/h were Cu > 70/30 Cu-Ni > Al-bronze. High-nickel alloy 825 showed no observable corrosion.
Corrosion Behavior of Zirconium Alloy Nuclear Fuel Cladding
Authors: Fraker Anna C. , Harris Jonice S.
Published: March 2011

Zircaloy−2 and −4 are used as nuclear fuel cladding. Both alloys are more than ninety-eight percent zirconium and are corrosion resistant to various media. Electrochemical measurements using polarization techniques have been made on these alloys in aqueous media with a pH of 8.5 and varying ionic concentration (1X and 10X) at temperatures of 22°C and 95°C. Results showed that under the test conditions of the study these alloys passivated and had negligible corrosion rates, but there were some variations in passivation due to surface preparation and some crevice corrosion was observed. Data are presented and discussed in terms of passivity, breakdown potential and susceptibility to localized corrosion.
Migration Behavior of Uranium Series Nuclides in Altered Quartz-Chlorite Schist
Authors: Ohnuki T. , Murakami T. , Sekine K. , Yanase N. , Isobe H. , Kobayashi Y.
Published: March 2011

The migration behavior of uranium series nuclides in an altered quartz-chlorite schist has been studied by utilizing data on the activity distributions of uranium series nuclides at Koongarra in the Northern Territory of Australia. The variation of 230Th/234U activity ratios (ARs) with distance along surface (2 m depth), intermediate (16 m) and deep (31 m) layers show different trends in the three layers parallel to the water flow. The relationship between the 234U/238U and 230Th/238U ARs reveals that the mobility of the uranium series nuclides is in order 238U, 234U and 230Th, and that the retardation factors oft 234U are greater than those of 238U by a factor of 1.1, 1.9 and 1.0 in the surface, intermediate and deep layers, respectively. X-ray diffraction patterns show different mineral assemblages, which are the alteration products of chlorite at the three layers. These results imply that the migration behavior of uranium series nuclides at each depth would be related to the alteration of chlorite.
Diffusion of Sodium and Copper in Compacted Sodium Bentonite at Room Temperature
Authors: Muurinen Arto , Olin Markus , Uusheimo Kari
Published: March 2011

Diffusion studies were carried out with sodium and copper in sodium bentonite. The experiments were performed at room temperature and densities of the samples varied from 0.8 to 1.8 g/cm3.

This paper describes the experimental methods used for the diffusion tests and gives the obtained measurement results. The evaluation of the diffusion mechanisms is at this stage preliminary, however.

Diffusion of sodium seems to follow similar mechanisms as has been observed for cesium and strontium in several previous studies. The phenomena could be explained by some kind of diffusion of sorbed ions. The measured apparent diffusivities of sodium varied from 50×10−12 to 300×10−12 m2/s and the effective diffusivities from 80×10−12 to 1.6×10−9 m2/s depending on the density of bentonite and the salt concentration of water solution.

Low solubility of copper caused precipitation thus interfering the diffusion experiments. However, the part of copper which did diffuse into bentonite seemed to follow the same type of mechanism as sodium. The measured apparent diffusivities of copper varied from 5×10−12 m2/s.

The interaction between the cations in the circulating solutions and the sodium ion in bentonite were essential in this study.
Analytical and Numerical Models of Transport in Porous Cementitious Materials
Authors: Garboczi Edward J. , Bentz Dale P.
Published: March 2011

Fluid flow under applied pressure gradients and ionic diffusion under applied concentration gradients are important transport mechanisms that take place in the pore space of cementitious materials. This paper describes: 1) a new analytical percolation-theory-based equation for calculating the permeability of porous materials, 2) new computational methods for computing effective diffusivities of microstructural models or digitized images of actual porous materials, and 3) a new digitized-image mercury intrusion simulation technique.
Concrete Barrier Performance in Radioactive Waste Disposal in the Unsaturated Zone
Authors: Walton John C. , Otis Mark D.
Published: March 2011

Concrete barriers are an important component of many designs for disposal of radioactive waste in the unsaturated zone. In order to evaluate the effectiveness of the concrete barriers performance assessment models representing material degradation rates and transport properties must be developed. Models for evaluation of fluid flow and mass transport through partially failed concrete barriers located in the unsaturated zone are presented. Implications for the use of impermeable barriers in vault design are discussed. Concrete of highest quality may not always be desirable for use in all components of waste disposal vaults.
Mass Transfer in Water-Saturated Concretes
Authors: Atkinson Alan , Claisse Peter A. , Harris Andrew W. , Nickerson Allan K.
Published: March 2011

Cements and concretes are often considered as components of barriers for the containment of radioactive waste. The performance of such materials as mainly physical barriers to the transport of dissolved radionuclides depends on the mass transfer characteristics of the material. In particular the diffusion and sorption behaviour of the radionuclides and the water permeability are important. These parameters also influence how the chemistry of the concrete is imposed on the repository. In addition, the transport of gas through concrete controls the way in which gases escape from the repository.

Diffusion and gas transport have been measured in a variety of cementitious materials, covering both structural concretes and cementitious backfills; all possible repository construction materials. Measurements have been made using aqueous iodide, strontium and caesium ions and tritiated water as diffusants. The results show that the diffusion of tritiated water is more rapid than that of other species, whilst the transport of strontium and caesium is hindered by sorption; particularly in materials containing blast furnace slag. The transport of gas in these materials has been found to be very sensitive to the degree of water saturation and is extremely low in fully saturated structural concretes. Cementitious backfills have, nevertheless, been identified that have appreciable gas transport even when almost water saturated.

The consequences of the results for the performance of cementitious barriers are discussed.
Rheological and Kinetic Properties of Semi-Dilute Solutions of Elongated Micelles
Authors: Candau Sauveur J. , Waton G. , Merikhi F. , Zana R.
Published: March 2011

Measurements of the breaking time of cylindrical micelles of cetyltrimethylammonium bromide in aqueous solutions have been performed by means of T-Jump experiments with light scattering detection. The results provide an unambiguous test of a recent theoretical model for stress relaxation.
Nondiffusive Brownian Motion Studied by Diffusing-Wave Spectroscopy
Authors: Pine D. J. , Weitz D. A. , Durian D. J. , Pusey P. N. , Tough R. J. A.
Published: March 2011

On a short time scale, Brownian particles undergo a transition from initially ballistic trajectories to diffusive motion. Hydrodynamic interactions with the surrounding fluid lead to a complex time dependence of this transition. We directly probe this transition for colloidal particles by measuring the autocorrelation function of multiply scattered light and observe the effects of the slow power-law decay of the velocity autocorrelation function.
Microemulsion Performance Fluids
Authors: Bock J. , Robbins M. L. , Pace S. J.
Published: March 2011

Microemulsions are thermodynamically stable mixtures of two immiscible fluids, such as oil and water, and one or more surfactants or cosurfactants. These systems have a rich micro-structure and phase behavior which can take the form of a variety of multi-phase and single phase oil- or watercontinuous or bicontinuous fluids with unique and useful properties. The thermodynamic stability, ultra-low interfacial tension, clarity, high solubilization capacity and high interfacial area suggest uses “performance fluids.” The relationship between surfactant ussetsru cfotur reth eansde the phase behavior and properties of microemulsions is the key to their design. Through the proper selection of surfactants, microemulsion phase continuity can be tailored for a variety of applications. Two such applications, coal freeze conditioning and oil spill dispersion, are described in this paper.
Study of Curing Processes in PDMS at Various Stoichiometric Ratios by Longitudinal Ultrasonic Waves
Authors: Shefer A. , Gorodetsky G. , Gottlieb M.
Published: March 2011

Curing reactions of linear vinyl terminated poly(dimethylsiloxane) with a four functional hydride silane crosslinker at various stoichiometric ratios, were studied by wave propagation at ultrasonic frequencies. Longitudinal wave velocity was found to be sensitive to the covalent endlinking, and gel point in these systems.

The observed changes in longitudinal wave velocity during the reaction are governed by changes in the bulk modulus of the system.
Polymers on a Random Liquid Surface
Authors: Duplantier Bertrand
Published: March 2011

We report a recent theoretical study of polymers moving on a random two-dimensional fluid surface. The metric of the liquid membrane is free to fluctuate and these new degrees of freedom couple to those of the polymers - as a result, the critical exponents describing the polymers are changed, but are nevertheless related to those in two dimensions. The relation to possible experimental studies on membranes with vanishing surface tension, which should search for new universal values of exponents u and 7, is discussed.
Domain Wall Fluctuations in Monomolecular Films
Authors: Seul M.
Published: March 2011

Domain wall fluctuations and instabilities in monomolecular amphiphilic films have been probed by fluorescence microscopy and spectral analysis based on techniques of digital image processing. Recent results address the analysis of the dynamics of domain wall motion.
Mechanical Properties of Crosslinked Semidilute Polymer Solutions Near and Far from the Gelation Threshold
Authors: Allain C. , Limat L. , Salome L.
Published: March 2011

Recently, many works have been devoted to the study of the critical properties of the sol-gel transition. Only a few of them have dealt with the description of the properties observed on the whole range of the values of the gelation control parameter. In the present paper, we discuss the steady-state rheological properties observed near and far from the gelation threshold and we show that the effective medium theory in conjunction with the percolation model allows to understand entirely the variations of the viscosity and of the elastic modulus.

In the first part, we present the gelling polymer system under study and the experimental methods with the help of which we measured the variations of the rheological quantities versus the concentration in crosslink points. In the second part, we discuss the critical behaviors observed near the gelation threshold. Finally, in the third part, we propose an effective medium theory applied to the description of the gelling polymer and we compare the variation of the viscosity measured outside of the critical domain to the results of these effective medium calculations.
Gravity Effect on Weakly Concentrated Gel Phases
Authors: Allain C. , Amiel C.
Published: March 2011

The influence of the gravity on fluids and mixtures near critical points or on heterogeneous materials are well known. In the present paper, we show that gravity also affects gelling systems. We report unexpected results on weakly concentrated gels which find their origin in the deformation under its own weight of the polymer network.
Epitaxial Growth of BaF2 on Semiconductor Substrates
Authors: Phillips J. M. , Feldman L. C. , Gibson J. M. , Mcdonald M. L.
Published: March 2011

We used Rutherford backscattering and channeling and transmission electron microscopy (TEM) to study the epitaxial growth of BaF2 vacuum deposited onto InP(100), InP(111), Ge(100) and Ge(111). We observed no epitaxy in BaF2 on Ge(100). The other three cases all show epitaxy, with quality ranging from poor for BaF2 on InP(111) through fair for BaF2 on InP(100) to excellent for BaF2 on Ge(111). Epitaxial quality depends strongly on substrate temperature for BaF2 on Ge(l11). TEM analysis indicates that there are neither misfit dislocations nor coherence at the BaF2–Ge(111) interface in spite of the 9.1% lattice mismatch.
Formation and Crystallization of Amorphous Silicides at the Interface Between Thin Metal and Amorphous Silicon Films
Authors: Herd S. R. , Ahn K. Y. , Tu K. N.
Published: March 2011

We investigated the interaction of extremely thin (less than 10 nm) crystalline gold and rhodium films with amorphous silicon by transmission electron microscope in situ annealing. In thin Au/Si bilayers an amorphous phase with a diffraction peak at d ≂ 0.226 nm is formed by thermal annealing between 150 and 200 °C. Depending on the thickness and composition, silicon sputtered onto thin gold films leads to the formation of a layer of amorphous silicon and a partially amorphous Au-Si layer during deposition. The silicon layer crystallizes by itself at temperatures as low as 150 °C, and at 300 °C the amorphous Au–Si layer crystallizes into a metastable gold silicide (for silicon-rich compositions). In Rh/Si bilayers an amorphous Rh–Si phase is formed by annealing to 300 °C and can be detected by electron diffraction for a rhodium thickness of less than 5 nm and compositions with more than 50% Si if completely reacted. Above 300 °C the amorphous Rh-Si crystallizes preferentially in the cubic form of RhSi for intermediate silicon compositions and in the orthorhombic form of RhSi for high silicon compositions. Excess amorphous silicon is not found to have a lowered crystallization temperature when in contact with the amorphous Rh-Si alloy, and crystalline silicon is only observed above 730 °C together with the cubic and/or orthorhombic RhSi. In Rh/Si bilayers with a thicker rhodium layer, no formation of an amorphous phase was observed on annealing; instead crystalline Rh2Si forms during annealing above 300 °C.
Lateral Diffusion of Platinum Through Pt2Si in Pt/Si Couples
Authors: Zheng L. R. , Hung L. S. , Mayer J. W.
Published: March 2011

Lateral diffusion couples formed by depositing platinum islands on silicon layers on Al2O3 were used in conjunction with scanning electron microprobe measurements to investigate the growth of platinum silicides in the temperature range 400–700 °C. The phase Pt2Si grows over a length of 4–30 μm with a rate proportional to the square root of time and an activation energy of approximately 1.3 eV. With samples containing 7 at.% Rh in the platinum, the growth rate of Pt2Si is reduced and the activation energy is increased to about 2.0 eV. In these Pt–7at.% Rh samples, electron-induced X-ray measurements indicate that rhodium remains in the original deposited region while both platinum and silicon diffuse in the formed Pt2Si region.
Influence of Nitrogen Impurities on Nickel and Platinum Silicide Formation
Authors: Ho K. T. , Nicolet M.-A. , WieluŃSki L.
Published: March 2011

In the present study we investigate the influence of nitrogen on the silicide formation of thin nickel and platinum films. Nitrogen is introduced by implantation either in the metal films or in the silicon substrates. We use the rare stable isotope 15N for the implantation and the nuclear reaction 15N(p,α)12C for the detection and profiling of the impurity. For nitrogen in nickel, we find that at 350 °C nitrogen is mobile. It accumulates at the bottom nickel interface and, for a dose exceeding about 0.5 × 1016 N atoms cm−2, forms a barrier to silicide formation. When nitrogen is initially in the silicon substrate, the nitrogen profile is broadened in the same proportion as the dilution of the silicon sublattice when forming the silicide. Similar experiments with platinum films showed partially different behaviors. All results are explained in terms of a model based on the moving species during the silicide formation and the chemical affinity of nitrogen to the metal and to silicon.
Low Ohmicity Contacts to Mono- and Polycrystalline Silicon
Authors: Harrison H. B. , Williams J. S. , Reeves G. K.
Published: March 2011

With the continued rapid development of integrated circuits and the evolution towards higher chip component densities brought about by down–scaling of device dimensions, it is useful to assess the limits of performance of presently known device structures using current fabrication technology. The silicon gate field effect transistor is of obvious importance, since at the present limit of decreasing dimensions these devices are expected to give comparable speed and lower powerdelay products than their bipolar counterparts. The rapid developments in fabrication methods such as increases in wafer dimensions coupled with the reduction in device dimensions has led to a reduction in maximum processing temperatures. In particular, this downward trend is incompatible with the necessity to lower contact resistance given appropriate device down–scaling.

In this paper we present techniques using ion implantation and tailored impurity profiles that are compatible with low temperature ohmic contact formation. The application of these techniques to mono- and polycrystalline silicon are presented. Our results suggest that these techniques show considerable promise for semiconductor device applications. As a consequence, a production technology that optimizes the contact resistance to both gate-poly and drain and source regions is being investigated and current results will be presented.
Ion Implantation Technique For Simultaneous Formation of A Shallow Silicon p-n Junction and a Shallow Silicide-Silicon Ohmic Contact
Authors: Tsaur B.-Y. , Anderson C. H.
Published: March 2011

Electron beam evaporation is used to coat a p-type silicon substrate with a thin layer of tungsten and then with alternating layers of silicon and tungsten. Bombardment of the coated substrate with As+ ions causes intermixing of the metal and silicon layers, dispersion of contaminant atoms at the interface between the first metal layer and the substrate, and implantation of arsenic atoms in the substrate. Subsequent thermal annealing produces a shallow silicide–silicon ohmic contact and simultaneously activates the implanted arsenic donors to form a shallow p–n+ junction. This technique has been used for the fabrication of mesa diodes with good junction characteristics. A simplified version, in which only a single tungsten layer is deposited on the substrate, has been used as a self–aligned process in the fabrication of metal/oxide/semiconductor field effect transistors with a polycide gate. In the transistors the silicide contacts to the source and drain regions can be made very close to the gate, reducing both the series resistance of these regions and the overall device size.
Atomic Interdiffusion in Au/Amorphous Ni-Nb/Semiconductor Systems
Authors: Doyle B. L. , Peercy P. S. , Thomas R. E. , Perepezko J. H. , Wiley J. D.
Published: March 2011

Backscattering measurements were performed to assess the stability of amorphous Ni-Nb for contacts of high temperature electronics. The interdiffusion of amorphous Ni-Nb and three semiconductors—silicon, GaAs and GaP—was measured to study the stability for primary metallization applications. Diffusion of gold with amorphous Ni-Nb and the same three semiconductors was also investigated in order to address diffusion barrier applications of amorphous metals. The results indicate that the use of amorphous Ni-Nb as a contact or a diffusion barrier could extend the useful operation temperature range for GaP devices to above 550°C.
Evidence for Island Growth on Deposition of Silver Onto Si(111)7 × 7 at Room Temperature
Authors: Van Loenen E. J. , Iwami M. , Tromp R. M. , Van Der Veen J. F. , Saris F. W.
Published: March 2011

The growth process of silver deposited onto the Si(111) 7 × 7 surface at room temperature was studied with medium energy ion scattering in combination with channelling. Coverages studied were in the range 0−8 × 1015 Ag atoms cm−2. The measurements show that silver forms three-dimensional islands. Although incorporation of small amounts of silicon in the silver islands (less than 8 × 10−4 Si atoms cm−2) cannot be excluded, no evidence was found for mixing between silver and silicon or for silicide formation.
New Chemical Routes to Metal Nitrides
Authors: Gladfelter Wayne L. , Hwang Jen-Wei , Evans John F. , Hanson Scott A. , Jensen Klavs F. , Ho Kwok-Lun
Published: March 2011

After a brief introduction on how the differing properties of H2O and NH3may effect the strategies used to synthesize metal nitrides, an overview of our use of azides to produce aluminum nitride thin films will be presented. The effect of changing the nitrogen source to one which contains at least one N - C bond is to increase dramatically the carbon content of the films. Replacing the alkyl groups attached to the aluminum with hydride ligands removes the final carbon source and forms what appears to be a promising new class of precursors. This is demonstrated by the study of the reaction of Me3NGaH3with NH3to produce the novel trimer, [H2GaNH2]3. This fully characterized molecule converts at 150°C into gallium nitride. Surprisingly, it yields GaN having the sphalerite structure instead of the known wurtzite phase. A discussion of the reasons for this unusual route to a new crystalline phase of GaN is included.
Laser Densification of Sol-Gel Coatings
Authors: Taylor D.J. , Fabes B.D. , Steinthal M.G.
Published: March 2011

Alkoxide-derived silica coatings were deposited on fused silica by dip coating. The samples were covered with a metal film to absorb the infrared radiation from an Nd:YAG laser. Coupling the laser power to the coating produced localized surface heating on the samples. By scanning the sample across the beam's path, channels in the coating were formed. The channels varied from 150 μm to 600 μm wide and from 200Å to 1000Å deep depending on the laser power and the translation speed. The size and shape of the channels also depended on the composition of the sol-gel coating. Optical microscopy showed that there were no cracks in either the substrate or in the coating on the micron scale. SEM revealed cracks on the nanometer scale in the laser fired coatings and no cracks in the unfired coatings. Ellipsometry showed that the index of refraction increased with increasing depth of the channels.
Fractal Structure and Fractal Time in Silica Sol-Gels
Authors: Martin James E. , Wilcoxon Jess
Published: March 2011

Near the gel point, light scattering studies of silica sol-gels reveal fractal clusters whose size diverges as a power law, in accord with the predictions of percolation theory. More surprising is the appearance of a fractal time description of the dynamics of these clusters. This novel dynamics has recently been revealed by quasielastic light scattering from the density fluctuations that occur at the sol-gel transition. Since the relaxation of fluctuations in these branched polymer systems is self-similar, decay processes occur on all time scales (fractal time), and average decay times diverge. An interpretation of this observation will be presented that relies on a length-scale-dependent viscosity and the geometrical self-similarity of the sol-gel transition. The scattering theory is extended to the calculation of time- and frequency-dependent viscoelastic properties, as well as mechanical properties such as the shear modulus, steady state creep compliance, and viscosity. The viscoelastic predictions are found to be in good agreement with experimental data.
Low Wavenumber Raman Scattering in Silica and Silicophosphate Aerogels
Authors: Walden Barbara L. , Breval Else , White William B.
Published: March 2011

Raman spectra, measured on silica and silicophosphate aerogels in the range of 5 to 70 cm−1 , revealed a “particle band” that arises from the discrete particulate character of the gels at very small size scales. TEM measurements of the nanoscale structure in the gels correlate with the location of the particle band maximum.
The Influence of Cations on Growth Kinetics of Silica Aggregates
Authors: Beelen Theo P.M. , Wijnen Peter W.J.G. , Rummens Kees P.J. , Van Santen Rutger A.
Published: March 2011

Silica gels are prepared by acidification (pH = 2 − 4) of water glass. SAXS measurements show that the gel consists of fractal aggregates (D = 2.2). Although the fractal dimension is not influenced by addition of cations, Al3+ and Mg2+ retard the growth of the fractal aggregates, while TMA+ has a promoting effect.
Fractal Concepts And Aggregation Of Iron Oxides
Authors: Amal R. , Raper J.A. , Waite T.D.
Published: March 2011

The modelling of the aggregation kinetics of iron oxides has been succesful in predicting the increase in aggregate size as determined by dynamic light scattering measurements. The aggregates were found to exhibit fractal behaviour with fractal dimensions obtained from the scattering exponent in static light scattering studies dependent on the aggregation mechanism and ranging from 2.3 for rapid (diffusion limited) to 2.8 for slow (reaction limited) aggregation. Polydispersity and restructuring of aggregates were found not to affect the relationship between scattering exponent and aggregate fractal dimension. Excellent correspondence over a range of temperatures and ionic strengths has been obtained between results of sizing experiments using dynamic light scattering and sizes predicted using a modified Smoluchowski model incorporating fractal dimensions.
Positronium Decay in Silica Sol-Gels
Authors: Hopkins B. , Quarles C. A. , Zerda T. W.
Published: March 2011

Positronium lifetimes inside porous silica are measured and discussed in terms of surface interactions, oxygen and nitrogen induced quenching and pore sizes. Surface interactions are studied for silica gels having surfaces covered solely with hydroxyl or methoxy groups. A rapid decay of positronium inside the pores filled with gaseous or liquid oxygen is reported and explained in terms of quenching mechanisms. An increase in the measured lifetimes for pores filled with nitrogen is attributed to the change in the pore distribution function.
Titania/Silica Sol-Gel Films: Comparison of Techniques for Thin Film Thickness Measurement
Authors: Melpolder S. M. , West A. W. , Cunningham M. P. , Sharma R.
Published: March 2011

Two techniques for thin film measurement were compared: an optical method combining ellipsometry and reflectance spectroscopy, and cross-sectional transmission electron microscopy. These techniques were used to measure the absolute thicknesses of titania/silica sol-gel films in the size range 0.1 to 0.8 microns. The relative advantages and disadvantages of these methods will be described in this study.
Synthetic and Structural Studies Bismuth/Copper Alkoxides
Authors: Evans William J. , Hain John H.
Published: March 2011

The reaction of Bi[OC(CH3)3]3 with [Cu(μ-O2CCH3)2]2 has been investigated as a possible route to mixed-metal materials containing bismuth and copper. The product distribution obtained from this reaction depends not only upon the stoichiometry, but also upon the method of product isolation. Products containing bismuth and copper are obtainable as well as an unusual, soluble hexametallic copper(II) alkoxide acetate complex, Cu6[OC(CH3)3]6(O2CCH3)6. The mixed-metal products were examined by differential scanning calorimetry, and thermolyzed and hydrolyzed samples of these products were compared by scanning electron microscopy.
Heterometallic Alkoxides as Precursors to Multicomponent Oxides
Authors: Hubert-Pfalzgraf Liliane G. , Papiernik Renee , Massiani Marie-Cecile , Septe Bernard
Published: March 2011

Lead(II) oxides are involved in various advanced materials. Their high volatility as compared to that of other elements makes chemical routes to such materials especially attractive. Various synthetic routes to lead(II) alkoxides have therefore been estimated. They display a strong tendency to undergo spontaneous condensation reactions, giving oxoalkoxides Pb4O(OR)6 (R = tBu, iPr, Et). Reaction between Pb4O(OEt)6 and [Nb(OEt)5l2 does not proceed by simple addition of the alkoxides, but the lead tetranuclear oxoalkoxide is transformed to a hexanuclear one, Pb6O4 (OEt)4 , whose oxo ligands bear Nb(OEt)5 moieties, the overall formula being Pb6O4 (OEt)4 [Nb(OEt)5]4 1. The stoichiometry between the two metals corresponds to that of the PNM ceramic, and 207Pb NMR has been used as a tool to study the reactivity of 1 in the presence of various modifiers and magnesium ethoxide.
Stabilization, Characterization and Optical Applications of Niobium and Tantalum Oxide Sols Prepared Via Alkoxide Routes
Authors: Parraud Stephen , Hubert-Pfalzgraf Liliane G. , Floch Herve
Published: March 2011

Hydrolysis of niobium and tantalum pentaethoxides in ethanol and in the presence of basic (ammonia, tetramethylammonium hydroxide, di and triethylamine) or acidic (nitric or hydrochloric acids) additives was investigated. Triethylamine gives monodispersed, small particles of amorphous M2O5,nH2O (M = Nb, Ta). These colloidal suspensions were used to obtain thin films by spin-coating techniques. The coatings display a thickness of 100–300 nm and a refractive index around 1.7. Laser damage tests at 1064 nm wavelength with a pulse length of 3 ns were carried out on the single layer systems. The threshold values (one-onone) are in favor of the Ta2O5 coatings with an average of 14.5 ± 2.1 J/cm2 , by comparison with 8.3 ± 1.6 J/cm2 for the Nb2O5 films.
Particle Growth and Development During the In-Situ Precipitation of Silica in a Polymeric Matrix
Authors: Xu Ping , Wang Shuhong , Mark James E.
Published: March 2011

The hydrolysis of tetraethoxysilane much used in the sol-gel approach to ceramics can be studied in a matrix isolation technique in which the silica thus formed precipitates within a polymeric material. This technique was applied here in the in-situ precipitation of silica particles in an elastomeric matrix of poly(dimethylsiloxane). Transmission electron microscopy and mechanical property measurements were carried out as a function of time over a period of 60 days. The equilibrium amount of silica precipitated was obtained relatively quickly, after approximately one day, but reorganization of the particles continued for several days thereafter. This “aging” process resulted in particles that are better defined and more uniform in size, but their ability to reinforce the elastomeric materials was only marginally increased. Scattering techniques are also being used to obtain additional information on this interesting process.
The Formation of thin Films and Fibers of TiC from a Polymeric Titanate Precursor
Authors: Ting S-J. , Chu C-J. , Limatta E. , Mackenzie J. D. , Getman T. , Hawthorne M. F.
Published: March 2011

The synthesis and characterization of several polymeric titanates and their conversion to carbon deficient TiC is described. The physical properties of one of these titanates allows it to be drawn into fibers and applied to substrates as thin films. Pyrolysis of these fibers and films to carbon deficient TiC is described.
Characterization of Ceria Stabilized Zirconia Coatings on Metal Substrates
Authors: Maggio Rosa Di , Scardi Paolo , Tomasi Andrea
Published: March 2011

In this study ceria stabilized zirconia was used to obtain an uniform and adherent film on iron and 304 S.S.. Coatings were prepared by dipping in solutions of organometallic precursors of zirconium and cerium. Structure and morphology of samples were investigated using SEM and XRD techniques before and after thermal treatments. The oxidation behaviour in air of coated samples was followed through thermogravimetrical analysis in a range of temperature from 773 K to 1123 K. The preliminary results show, for the samples coated and pretreated in high vacuum at 923 K, a good decrease in oxidation rate.
Evolution of Surface area During the Controlled Growth of Silica Spheres
Authors: Bogush Gregory H. , Brinker C. J. , Majors P. D. , Smith D. M.
Published: March 2011

Several mechanisms have been proposed for the growth of silica spheres by the controlled hydrolysis of silicon alkoxides, the limiting cases of which are the conventional and aggregative growth models. The evolution of surface area predicted from the two models is substantially different at early times into the reaction. In order to probe the change in surface area during growth, 1H NMR measurements of the solvent were made during the growth process. It has been demonstrated that the spin-spin relaxation time.(T2) for an absorbed phase is less than that of the bulk solvent. Using this principal, the change in surface area can be followed in situ during the reaction. The experimental results were compared to the predictions of the conventional model and found not to be in agreement.
The Cracking of Sol-Gel Films During Drying
Authors: Garino Terry J.
Published: March 2011

The cracking behavior of acidic silica sol-gel films during drying and low temperature heat treatment was studied. Films that cracked during drying exhibited a variety of unusual crack morphologies including sinusoidal cracks and parallel crack pairs. The effects of the water content of the sol and temperature on the critical thickness above which cracking of the films occurred were determined. The critical thickness decreased with increasing water content, most likely because the surface tension of the liquid in the pores of the gel increases with water content and because sols with low water concentrations did not gel until the solvent had evaporated. To determine why the critical thickness decreased with temperature, thermal analysis and shrinkage measurements of both constrained and unconstrained films were performed. Thermogravimetric analysis indicated that rapid weight loss occurred in the temperature region where the rapid decrease in critical thickness occurred. A small amount of shrinkage of the films also occurred in this region. Finally, shrinkage measurements of films debonded from the substrate indicated that shrinkage was very anisotropic with nearly all of the shrinkage occurring in the plane of the film and very little in the thickness direction.
Effect of Inclusions on Shrinkage
Authors: Scherer George W.
Published: March 2011

The effects of inclusions on densification are discussed, including their influence on the development of stresses during drying, and on the kinetics of sintering. Special attention is given to the problem of crystallization during sintering.
Hybrid Gels Designed for Mullite Nucleation and Crystallization Control
Authors: Huling Jeffrey C. , Messing Gary L.
Published: March 2011

The controlled nucleation of phase transformations by seeding is an established technique for influencing transformation kinetics and sintered microstructures in ceramics. Previous studies have focused on seeding with ultrafine, solid particles having the requisite crystal characteristics for either homo- or heteroepitactic nucleation of the desired phase. Size separation of particulate seed crystals is not an efficient process and thus more recent efforts have concentrated on chemical approaches to nucleating solid phase transformations. Hybrid gels, in which two or more gels are combined to capitalize on the benefits of each, have been reported for the homoepitactic nucleation of mullite. In principle, the molecularly-mixed gel crystallizes to mullite at ∼1000°C and, in turn, acts to nucleate the colloidal gel component's transformation to mullite at higher temperatures. However, the transformation sequence and kinetics are profoundly affected by the interfacial reaction between the two gels comprising the hybrid. This paper discusses how the physical distribution and chemistry of the gel components can be manipulated for the control of mullite nucleation, crystallization and microstructure development.
Rheology for Better Sol-Gel Fiber and Film Formation
Authors: Macosko C. W. , Mecartney M. L. , Scriven L. E.
Published: March 2011

Flow behavior of a liquid or suspension depends on how stress varies with strain rate, strainrate rotation, and strain history, as well as the progress of evaporation, extent of reaction, and degree of aggregation in sol-gel systems. Rheological methods suitable for measuring flow behavior are summarized. Examples of measurements and microstructural observations by transmission electron microscopy made during gelation of four sol-gel systems are presented. The relation of rheological response to microstructure is discussed.
Densification and Crystallization Of Thin Transition Metal Oxide Coatings From Metal Alkoxides
Authors: Hirashima H. , Muratake R. , Yamashita T. , Chiba T.
Published: March 2011

Monolithic gels of V2O5, Ta2O5 , and Nb2O5 have been prepared from VO(C2H5O)3 , Ta(C2H5O)5 , and Nb(C2H5 O)5 througg hydrolysis in ethanol Solutions. The conditions for gel formation have been determined. Thin coatings of these gels, less than 100 nm in thickness, have been prepared by dip coating. Changes in the thickness, d, and refractive indices, n, have been measured by ellipsometry during drying. In the first stage of drying, d decreases and n increases rapidly. Densification of the coatings takes place due to evaporation of solvent. In the following stage, increase in d and decrease in n have been observed for thin V2O5 gel coatings, about 30 nm or less in thickness. These results suggest that coarsening of pores and/or increase in surface roughness take place due to release of the capillary pressure during drying. Both d and n have increased with increasing number of dipping. After heat treating, decrease in d and increase in n have been observed.
Biomimetic Ceramics
Authors: Calvert Paul
Published: March 2011

This paper discusses the possible advantages to be gained from a bio-mimetic approach to ceramics and reviews the work now in progress that will lead us to be able to mimic biological structures with synthetic materials.
Synthesis of Nanoceramic Particles by Intravesicular Precipitation
Authors: Bhandarkar Suhas , Yaacob Iskandar , Bose Arijit
Published: March 2011

Nanometer sized magnetic particles have been fabricated by aqueous phase coprecipitation inside single compartment vesicles. These vesicles were generated by sonicating egg yolk phosphatidylcholine molecules in an appropriate ionic solution containing the reactant cations. Using cobalt and ferric nitrate as the starting solution, the reaction product was the desired cobalt ferrite; direct formation of the oxide is potentially a very important step. For the barium and ferric nitrate systems, the reaction product could not be identified easily. However, we have not been able to produce barium ferrite directly. In an attempt to compare the effect of drastic changes in the microenvironment, we have also completed aqueous phase precipitation in multilamellar vesicles. For the aluminum nitrate system, precipitation takes place only in the outermost “annular” space. Multiple particles are formed, and the resultant diffraction pattern shows a close match with an aluminum hydroxide chloride complex. This differs significantly from the product in single compartment vesicles, where β-Al2O3 was formed, and in free precipitation which resulted in Al(OH)3.
Wet Chemical Derived Films For Electrical Applications
Authors: Uhlmann D.R. , Teowee G. , Boulton J.M. , Zelinski B.J.J.
Published: March 2011

Wet chemical methods have been used with success to synthesize films for a variety of electrical applications. After first reviewing the important microstructural features of films, the present paper focuses attention on ferroelectric (FE) films. The present state of and critical issues facing wet chemically derived FE films are considered. The needs for more extensive microstructural characterization and for more systematic exploration of electrical behavior are emphasized.
Evolution Of Molecular Structure In Alkoxide-Derived Lithium Niobate
Authors: Eichorst Dennis J. , Payne D. A.
Published: March 2011

Structural rearrangements during the sol-gel processing of lithium niobate were investigated by FTlR and Raman spectroscopic methods. The reaction of lithium ethoxide with niobium ethoxide resulted in the formation of a bimetallic alkoxide, LiNb(OEt)6 , which could be crystallized from solution. Single crystals were comprised of helical polymeric units consisting of niobium octahedra linked by lithium in tetrahedral (distorted) coordination. Successive crystallizations from solution allowed for the enhanced purification of the alkoxide precursor. Hydrolysis of the bimetallic alkoxide resulted in the formation of an amorphous network structure, which contained niobium-oxygen octahedral units modified by lithium. Heat-treatment facilitated structural rearrangements for the niobium environment, which allowed for the formation of the lithium niobate crystal structure. Further heat-treatment above 700°C resulted in structural changes associated with lithium oxide volatility.
Preparation Of Copper And Copper-Barium-Yttrium Sols From Metal 2-(2-Ethoxyethoxy)Ethoxides and Conversion Of Copper-Barium-Yttrium Alkoxide Precursors to Ba2YCu3O7−δ.
Authors: Scozzafava Mary Rose , Rhine Wendell E. , Cima Michael J.
Published: March 2011

The hydrolysis of copper 2–(2-ethoxyethoxy)ethoxide solutions and barium-yttrium copper 2–(2-ethoxyethoxy)ethoxide solutions were investigated. Copper sols with particle sizesof 3–10 nm have been prepared from THF solutions. Sols from barium-yttrium-copper alkoxides were also prepared in THF with particle sizes of 4–10 nm as determined by transmission electron microscopy (TEM) and 50–80 nm as determined by photon correlation. Compositional analysis showed that the sols had a similar composition to the parent solution. Choice of atmosphere and solvent system played an important role in the progress of the hydrolysis reaction. Powders obtained from barium-yttrium-copper solutions can be converted to Ba2YCu3O7−δ.
Chemical Synthesis of Aluminum Nitride Powders
Authors: Coffman Phillip R. , Petuskey William T. , Dey Sandwip K.
Published: March 2011

An organoaluminum precursor was synthesized by a low temperature reaction and characterized by NMR, FTIR and mass spectrometry. This compound was pyrolyzed under several experimental conditions to obtain aluminum nitride powders. The pyrolyzed products were subsequently characterized by XRD and SEM. The mechanisms of precursor development and subsequent pyrolysis are discussed.
Incorporation of Polyaniline Into a Silica Gel Via the Sol-Gel Technique
Authors: Nishida F. , Dunn B. , Knobbe E.T. , Fuqua P.D. , Kaner R.B. , Mattes B.R.
Published: March 2011

The sol-gel process has been used to incorporate a conjugated polymer, polyaniline, in silica gel. The emeraldine base form of the polymer is partially solubility in aprotic polar solvents which are compatible with the sol. The effect of sol environment on the emeraldine base form of polyaniline was investigated. The soluble emeraldine base form is maintained at pH ≥ 2.4 enabling good optical quality gels to be synthesized. The type of alkoxysilane and the water ratio used in preparing the sol influence the solubility of the emeraldine base.
Vanadium Pentoxide Gels: Structural Development and Rheological Properties
Authors: Bailey J.K. , Nagase T. , Pozarnsky G.A. , Mecartney M.L.
Published: March 2011

Cryogenic transmission electron Microscopy (cryo-TEM) and rheological characterization were conducted in order to understand structural development of vanadium pentoxide gels during processing. Sols were prepared by ion exchange from sodium metavanadate solutions. Cryo-TEM revealed that fine threads about 1.5nm wide initially form and grow into ribbons approximately 25nm wide and at least 1000nm long. The threads appear to self assemble into the ribbons. During this structural development, the dynamic viscosity increased. Upon steady shearing of the sols, the system exhibited thixotropy, i.e. the viscosity decreased with time under constant shear stress and subsequently rheopexy, the viscosity increased with time. Comparison of the structure before and after shearing indicated that during the rheological experiments aggregation of small particles or fragments was occurring.